What is the AHI (Apnea Hypopnea Index)

Dear Winston

It is inspiring to learn of your interest in sleep apnea.  I will be happy to do my best to simplify, clarify and muddy your understanding of the AHI.  AHI stands for Apnea Hypopnea Index. It is the standard for defining the presence of significant sleep disordered breathing and the condition of Obstructive Sleep Apnea.  

It started long ago in the history of sleep medicine. In actual time, it was just 40-50 years ago.  Physicians noted breathing problems during sleep.  Over a decade or so it was clear from investigations that the problem was one of blockage of the airway in the throat during sleep.  The blockage resulted in less air getting in and out of the lungs.  The blood oxygen levels would drop, while the carbon dioxide level would increase.  The sleeper responded with increased breathing efforts, which opened the airway.  By the 1980’s, testing for these variables had evolved from investigative to the clinical practice level.

The AHI is the fundamental measurement for obstructive and central types  of sleep disordered breathing.  The A stands for apnea, or absence of breath.  The H stands for hypopnea, or a critical reduction of airflow causing the same physiologic changes that the apnea produces. The I stands for index but actually represents a measurement of rate, the number of apneas and hypopneas per hour of sleep.  The apnea as used in AHI represents the absences of air movement at the nose and mouth.  Respiratory efforts by the diaphragm and chest may or may not be present. These are the simple definitions.  

Clinicians and physiologists have much more specific definitions.  Our definitions include the magnitude and duration of physiologic changes, as well as the types of equipment used for the measurements and the frequency of the changes.  It should not surprise you that significant debate continues about the details of those changes. Opinions differ. Unfortunately, the efficient computerized testing systems we utilize, ease the burden of testing large numbers of people, but limit the ability to look at multiple variations of potential changes in definitions.

In this country, current technical definitions and the threshold for diagnosing the medical condition of apnea are cemented in place by the regulatory bodies; Medicare and commercial insurance companies set the standards.  While the definitions set are supported by reported evidence, the standards are far from perfect and will not change soon.

The AHI is the gold standard for the definition of obstructive and central sleep apnea.  Five events, apneas and or hypopneas, per hour of sleep meet  diagnostic level for apnea.  The level of 5 events was arrived at arbitrarily, based on early work in the field.   Although accepted by those regulating groups, the actual minimal AHI needed to establish the diagnosis is not really known. 

It is known that the higher the AHI the greater the risk for long-term medical problems.  When a sleep study is complete and the AHI criteria for apnea is met, it is described as mild (5-15 events}, moderate (15-30 events) or severe (>30 events) apnea. The adjectives (mild, moderate and severe) represent the long-term risk for medical complications, not how a person feels. These separations into different severities of apnea, represent more tradition than science. In fact, the AHI is only a good predictor of severity for long-term complications at high levels (more complications) and very low levels (less complications). In the decades since these definitions for the onset and the severity of the disease were adopted, much research has been done. It appears that further definitions of these obstructive events would improve the accuracy of our diagnoses and the predictability of the future for the patient.

 The current definitions have served time well. As a clinical tool, the AHI has proven to be extremely useful. It is accepted worldwide. Tremendous improvement in diagnosis and therapy for sleep apnea has occurred utilizing these measurements. There are limitations, however. This is specifically true when scientific studies of the condition are performed.

 The role of low oxygen levels has been investigated more than any other factor. You will recall oxygen is measured on testing by the noninvasive transcutaneous method that reports oxygen saturations. Our technical definitions include a certain drop in oxygen saturation that is caused by the interruption to the airflow during the breathing events. The roles of the duration, severity and timing of the drop of oxygen in the sleep pattern as well as the total time spent at certain levels of oxygen desaturation are not known. Studies reviewing low oxygen levels during apnea suggest that the time spent with saturations of less than 90% together with the AHI is more accurate in predicting long-term medical complications than the AHI alone.

Another major factor not addressed with current testing is the use of a rate measurement for diagnostic purposes. A rate does not measure total exposure to apnea events. That is dependent on actual sleep time. An easy example is the difference of someone sleeping six hours versus another person who sleeps nine hours. They both can have the same AHI, but the person sleeping nine hours will be exposed to 50% more apnea events than the person who only sleeps six. The importance of exposure has not been studied at all.

The events we measure, apneas and hypopneas, do not occur uniformly throughout a night of sleep.  The event frequency can change based upon body position.  They can occur more while sleeping on the back verses the stomach.  The events can occur more in REM sleep than in slow wave or Non-REM sleep.  Research into the effects of these variables as predictors of long-term outcomes is limited.

Well, I believe it is time to close. The AHI is an immensely useful tool in the diagnosis and treatment of sleep apnea.  It is the gold standard measurement for the diagnosis of sleep apnea.  It needs to be improved upon and will be. As you will learn throughout your career, medicine changes slowly. Opinions are more rigid in medicine and in science than most believe. So, keep an open mind.  This, like all things medical, will change with time.

RGH 7 April 2023 (28960)

Hypoglossal Nerve Stimulator


Yes, I am aware of the national TV ads for the hypoglossal nerve stimulator for Obstructive Sleep Apnea. Earlier this year I prepared an information sheet on the subject. I will add it to this letter.

It is a second line therapy and works for a limited sub group of patients with Obstructive Sleep Apnea.  CPAP is far more successful in controlling sleep apnea.

It primarily indicated for those who have failed CPAP. Unfortunately, there is no accepted definition what constitutes failing CPAP therapy. Reasons for stopping CPAP are many and sometimes complex.  I have been intrigued by the issues that cause a patient to discontinue or be unable to use it and will add more on the subject on another occasion.

RGH 29.112

Sept 2023



“Inspire” is a device that senses an obstructive apneas and then sends a signal to the hypoglossal nerve through a wire. It activates the nerve, which causes the base of the tongue to move forward.  The device, wires that sense the apnea and the wire from the device to the nerve are implanted under the skin. It is remotely controlled.

CANDIDATES/INDICATIONS (Varies from FDA, Insurance and Medical societies)

Its primary indication for use is failure to be able to use CPAP. Problems with insomnia, restless legs or other sleep disorders must be controlled before being considered for Inspire. The obstructive apnea rating (apnea hypopnea index or AHI) on diagnostic testing should be between 15 and 65.  Weight should be a BMI of under 32.  BMI varies by height. For a 5’11” person a BMI of 32 is 225 lbs.  Some insurances will allow a slightly higher BMIs. You must be older than 18 years of age. It is indicated when apnea obstruction occurs at the base of the tongue.


A rough estimate of the cost of the device, its implantation, testing and physician visits will be between forty and fifty thousand dollars.


“Inspire” is a second line therapy and insurance companies only approve those who have failed other forms of treatment.


If you meet the criteria for the device, you will be evaluated to see if the device will correct your apnea. The evaluation steps include a facility based sleep study, a sedated endoscopy of your upper airway and provider visits. Many will not fit the type of obstruction that the device will correct and will not be candidates.

    If you are a candidate, then implantation, physician review and repeat testing to insure appropriate function will be required.  These steps include surgery, a post activation facility based sleep study and provider visits.

    The overall time from initial consideration to successful activation is about 5 to 6 months.  Medical follow up currently is recommended every 6 to 12 months.


The goals of treating obstructive apnea are to reduce the AHI to less than 5 and to improve the quality of sleep. CPAP will achieve AHIs < 5 a very high percentage of the time. The Inspire device will reduce the AHI to less than 5 in approximately 50% of recipients.  The rest will have a reduction in their AHIs but not to normal levels.  Standard therapies such as CPAP may still be needed.  


“Inspire” is a man made product with batteries.  Wires can break.  Wires cannot easily be removed. Batteries or new wires may be required in the future.  There are a limited number of experienced physicians available to deal with the device. Other devices may still be needed and recommended to control your apnea condition.

Wuhan Virus

Winston July 3, 2020

Thank you for sharing your friend’s newspaper opinion piece on the current epidemic with me.  Congratulations to her on her writing success.

She is very emotional in her response, which is not unexpected for a non-medical person.  Unfortunately she mixes politics with the natural history of infectious disease.

Her thinking is complicated by not having the training to have a full grasp of the numbers being reported about the epidemic.  The numbers of epidemiology are complicated, confusing and often incomplete or not timely.  As a professional, I have been having a difficulty sorting through what information is being reported.  All of which is complicated by the frequent news headlines and incomplete data being presented on television, radio, newspapers and Internet.  

Most people are emotional about the subject and that certainly includes those in the news business, government officials and surprisingly, some medical professionals.  Many are not objective. Many have secondary interest. All know what is wrong, but they are short on fixes.

This infection will go on just like the flu does.  The infection, despite all measures will spread though the population.  It will not be stopped by social distancing, mask, hand sanitizers, or other non-treatment or non-immunization techniques.  Those things may help you to avoid being one of the infected ones, but people will be people and the virus will spread.  It will be stopped when enough people have been infected so that it becomes difficult for it to be spread, since most have developed immunity from prior infection (herd immunity).  Or, it will be stopped when a good treatment is identified or an immunization developed.  

Us old timers are at higher risk, as are those who have underlying conditions, most likely including untreated Obstructive Sleep Apnea.  So Winston, use your CPAP!!! Your youth is a good, but not perfect, fortress and defense against this bug.  It is best not to get it.  Do what you can to protect yourself. 

As the number of test performed increases, the number of cases of infection will increase.  What you should watch is the number of patients with the virus hospitalized, the number of cases per capita, and the percent of tested patients who are positive for the virus.  I would not follow the percentage of hospital beds used or beds available since hospital administrators, public health administrators, press and politicians can manipulate the percentages for secondary gain.

I differ in my opinion from your friend.  This country’s response to the virus has been the best in the world with a few notable exceptions mostly in New York.  A few of the major reasons would include:

More testing            

Less dying

More secondary support – supplies, test, ventilators, vaccine work, emergency hospital beds, etc

More openness in data reporting

As a physician, there is no country in the world that I would rather be in during this, or for that matter, any pandemic.  Mistakes have been made and more will be made, but those mistakes do not change my opinion of the country’s response.

The Wuhan virus is a mean respiratory bug that has the potential for serious illness and death.  It is meaner than the flu, but only a little more so.  Most people infected with the virus do not need hospitalization and many, if not the majority, do not even know that they were infected.

So Master Winston, keep a safe distance, wear you mask around others, and wash those hand.  As they might say in the military, keep you head down and move fast.   And of course, use your CPAP.  This will pass.


A Right to Healthcare – Its not that Simple

Winston  Oct 29, 2022

Yes, I will try to answer your question. I understand your training has led you to believe that healthcare is a right. Why, you ask, did I pause before saying,  “It’s not that simple. But if it were, the answer would have to be no.”

Consider first what is meant by the term, healthcare. Like most words, it is likely interpreted differently by almost everyone. The views will run from having clean water, a family doctor available for medical problems to those that would include anything to do with a person’s health.  These are widely divergent categories of products and services based on different delivery systems and business models.  It is almost impossible to discuss a ‘right to healthcare’ without understanding everything that is included in the discussion – the components of healthcare. 

It is not the only term that needs to be defined. What do the promoters mean by the word, right? Maybe it is best to consider its meaning first.  

When right is used as a noun, as it is in a ‘right to healthcare,’ common definitions according to Merriam-Webster include:  qualities of moral correctness or moral propriety; something to which someone has a just claim; something to which someone may claim as their due; and, a cause of truth or justness.  The proponents of a ‘right to healthcare’ usually mean the second or third of these definitions, a just claim or their due.

Healthcare has only one definition listed. Merriam-Webster defines it as ‘efforts to maintain or restore physical, mental or emotional well-being especially by trained or licensed professionals.’  Practically speaking, this definition would essentially cover all aspects of personal and public health. It would include the fields of preventive medicine, public health and personal medical care along with institutional medical care. Each of these fields is unique in how it is currently organized and delivered while sharing some common features. The shared features include the need for physical plants of operation, equipment to provide the services, support staff to carry out the services and a professional staff. These factors are needed in varying quantities and of different types for each of these fields of endeavors.

For clearer understanding we need to look more specifically at the services included in healthcare. These would include public health services, preventive medicine services (public or individual), individual’s urgent and chronic medical care, and institutional care (hospitalization and similar). We need to consider all the services that might be determined to be healthcare.

Public health is widely practiced throughout most local communities in our country.   Public health services maintain and ensure clean water and adequate sewers, track communicable diseases and advise the population about those diseases. Their services, physical plant, equipment, staff and professionals are paid for and employed by government units. They are paid for by taxes and by fees for water and sewer services. For the majority of urban areas in this country, these health services are for all practical purposes already a right provided by the government. Certainly, there are exceptions for rural and smaller communities, but most citizens already enjoy public health as a government service.  Paid for by their taxes.

Preventive medical services are currently provided by both government operations and individual medical providers. Examples of government services include monitoring of new and current medications for problems, providing recommendations for vaccinations, and monitoring of medical devices. Again, the facilities, staff, equipment and professionals are supplied and paid for by the government taxes and fees usually paid by the businesses for the service.

At a more personal level, physicians, providers, healthcare businesses and employers  (insurance companies, medical practices, clinics, hospitals and businesses) may provide guidance and assistance on preventive medical measures that an individual needs. These businesses provide the physical plant, staff, equipment and professional organization needed. The expense for these services is recouped through fees, insurance payment, employers and other methods. The healthcare provided at this level is the first at which an individual may be responsible for all or part of the cost of the services.

The next component leads further into individual responsibility, providing an individual’s urgent and ongoing medical care. This is the form of healthcare we are familiar with and what is most often thought of when discussing ‘a right to healthcare’. In our country’s history, these services have been provided by individual professionals who own and operate their own businesses. Recent change in economics, economic policy and legal structures of medical businesses has led to more large organizations (hospitals and insurance companies) owning more of these types of businesses. In these operations in any form, the expenses – from cotton swabs to physician income – are paid for by individuals, either directly or through surrogates (employers, insurances or others).

An individual’s surrogates are the primary payees for the institutional care portion of our healthcare delivery system. This portion of healthcare, hospitalization primarily, is where the largest cost (facilities, equipment, staff and professionals) occurs. Again, most of the cost is paid for by individuals or their surrogates.  

In these areas of healthcare where the individual is mostly responsible for the cost of the service, there is one major group of individuals that is not responsible directly. Those are individuals on government insurance such as Medicare.  In Medicare and other government plans, a person may have a markedly reduced or no exposure to the direct cost of the services.  Those who argue for a ‘right to healthcare” would like all services for all citizens to be paid for by the government.

My comments have gone on long enough so I will save my additional thoughts for a future letter. I would add in closing what I think summarizes the whole question.

A ‘right to healthcare’ should mean everyone has access to and freedom to decide how to obtain their healthcare.  At present, I would argue that it is already the case, but it is disappearing rapidly.  In reality, the discussion is not about freedom to get healthcare, but getting healthcare for free.



Open Letter to Winston


Yes, I received your note.  I apologize for my delay in setting this up.  Your idea to post these so you can keep track of them was a good one.  I will select a few of my past notes and post them here for you.  

I found the first of my letters. We will start with it.

RGH August 1, 2022


It will seem strange to receive this from me, as we have not talk seriously except on rare occasions. I have been a family friend beginning decades before your birth.  Now, you are away from home with a new wife, pursuing a medical education.  A calling I have followed for more decades than I have known your family.  It is a difficult master with challenging hurtles and responsibilities that each of us experience differently.    

Our interactions are few and infrequent, intermingled with talk from family and friends on special occasions and holidays. Meaningful thoughts don’t seem to reach across the table or room.  Medical or should I say professional conversations often by there nature are inappropriate in those situations.  So, I have returned to the written word to communicate my beliefs, attitudes and some would say prejudices developed over my 50 years in medicine as first a doctor and now as a physician.

Do not be surprised by the letters or the subjects.  You may respond with your questions and thoughts, but do not feel obliged.  They represent an attempt to pass to you some little perspective on your chosen profession.


Rat Journals, Sturgeon’s Law and the Hawkins’ Corollary

Dear Winston

Ref: Rat Journals, Sturgeon’s Law and the Hawkins’ Corollary

Yes, I know I have mentioned Hawkins’ Law to you many times. And yes, you need to know what I mean.  I will answer that for you with a little background.  Have you heard of Sturgeon’s Law?

Sturgeon’s Law   “Ninety percent of everything is crap”

            Corollary 1:  “The existence of immense quantities of trash in science fiction is admitted and it is regrettable: but it is no more unnatural than the existence of trash anywhere.”

            Corollary 2:  “The best science fiction is as good as the best fiction in any field.”

Sturgeon was, early in his career, a science fiction writer and an editor of a science fiction magazine.  He received intense criticism for the quality of writing in science fiction and his response was what was to become known as Sturgeon’s Law.  References point out that others have had similar insights.

Voltaire in a short story,  “… but in all times, in all countries, and in all genres, the bad abounds, and the good is rare.”

Rudyard Kipling in the ‘The Light that Failed’,  “Four-fifths of everybody’s work must be bad. But the remnant is worth the trouble for its own sake.”

George Orwell in ‘Confessions of a book reviewer’,  ‘In much more than nine cases out of ten, the only objectively truthful criticism would be “ This book is worthless”.’

I initially encountered Joseph Hawkins, M.D, when I was first year resident in internal medicine at the University of Oklahoma.  At that time, Joe was the Consultant to the Army Surgeon General who oversaw assignments of duty stations for doctors going on active duty.  I was a recent draftee about to enter the US Army. 

Someone I knew in the Army had given me his name and the number of his office in Washington. I called him about my potential assignment on entering the Army, hoping not to go to Vietnam.  When I advised him that I would be a partially trained internal medicine specialist when I went on active duty and suggested I might be valuable at a major hospital, he laughed.  Joe gave me some sage advice.  He said I should consider entering an Army medical residency program to complete my training.  Probably the best advice I have ever been offered in my entire medical career.

Over a decade later, Joe and I found ourselves in Phoenix, in adjacent hospitals, in the same specialty – Pulmonary and Critical Care Medicine.  He was the director of fellowship training for our specialty at a regional teaching hospital and I was the director of the Pulmonary, Sleep and Critical Care services, at a hospital that helped with their training programs.  We shared training fellows and clinical experiences till his retirement.  

At our monthly journal club meetings, Joe would frequently ask. “What does the Rat journal have in it this month?”  One of our leading specialty journals had become focused on basic science research, departing from its decades long tradition of clinical based reporting.  For a time it frequently involved rats.  The journal became known to our group as the Rat Journal.  Practically all of its publications had little to do with the practice of medicine and most had little to do with significant advancements in sciences.

I believe the growing volume of medical literature is, and possible always has been, of little practical or insight value.  I would call it Hawkins’ Law or the Hawkins’ corollary to Sturgeon’s Law:  Ninety percent of medical research is crap.

As physicians, it is our burden and task to sort the information overload and find the 10%.  A firm foundation is needed in what is generally accepted knowledge, (knowing the current basic understanding of the medical disease, issue or problem) to judge how a new piece of information alters, changes or discounts our basic understanding.  Remember that the understanding of all human diseases will be further defined, changed, or altered during your medical career.  



Apr 23, 2022

The Causes of Obstructive Sleep Apnea – The How and Why

There are complex airway dynamics resulting in blockage of the upper airway producing Obstructive Sleep Apnea.  Although complex, the process can be viewed in a general non-technical manner to help one understand the causes of obstructive sleep apnea.

In such an overview, we find two components to the events producing blockage of the airway during sleep: airway muscle relaxation and airway size.  How does each of these contribute to the development of obstructive apnea?  

The basic event of sleep apnea is the relaxation of the upper airway (the throat above the Adam’s apple to the nose and mouth) narrowing it critically or totally, resulting in a blockage limiting the amount of air traveling into or out of the lungs. This causes a drop in the blood oxygen and an increase in the blood carbon dioxide.  These are changes, which the brain notices immediately.  The very next breathing effort by the diaphragm is stronger.  These efforts keep increasing until two or three breaths later, on average about 15 to 20 seconds, the effort is strong enough that the throat opens and air moves in and out again.  Commonly, but certainly not always, this is accompanied by a loud snore or snort.  These events are what produce Obstructive Sleep Apnea.

While these events alone may not be medically important, they produce problems when they occur repeatedly.  A measurement of five events per hour while sleeping is considered diagnostic of Obstructive Sleep Apnea in the United States.  Problems are thought to develop at this point.

Relaxation of the tongue and pharyngeal muscles play a role in developing these events.  As we age, muscle tone decreases.  Strength reduces.  Tissue tone becomes slack, to say the least.  We have all seen the effects of age in our family, friends and maybe even ourselves.  The same changes take place in our tongue, pharyngeal muscles and supporting tissues.  The prevalence data for obstructive sleep apnea show a steady increase with age.  Those greater than 70 years of age are reported to have an 80% frequency of occurrence.

Muscle relaxation and muscle changes with age are major components of the causation of obstructive apnea.   

What role does airway size play in causing obstructive apnea?  The size of the airway determines how much muscle relaxation is needed for the critical narrowing to occur.  Smaller airways will close more easily than larger ones

 It is best to look at the airway size as two issues – weight and genetics.  

In the 1960s, doctors discovered and described the obstructive apnea problem in obese patients.  For the first 20 years after its description, many strongly believed that obstructive apnea was just a complication of obesity, not an independent problem.  When a person gains weight, the fat tissue is added over the muscles below the skin in most areas of the body, including under the skin in the throat.  The accumulation in the throat makes the size of the airway smaller.  With a smaller airway, less relaxation is required to cause the critical narrowing resulting in an obstructive apnea event.  

It is now well known that at certain weights almost everyone will have apnea.  The medical community uses a measurement that is a calculation based on height and weight.  This is called the Body Mass Index or BMI.  A normal BMI is 20 to 25.  When a person’s BMI reaches 40, ninety percent of those individuals will have sleep apnea.

Obesity can cause sleep apnea.  What is its contribution to all those individuals with the condition?  No one agrees and there has been ongoing debate since the 1970s.  

Like most medical controversies, variation in the reported studies makes the issue more difficult to understand.  

Early attempts to understand the effects of weight loss on apnea used an improvement in symptoms as the mark of correcting the problem.  When obese patients with apnea lose a significant amount of weight, they feel and sleep better.   The authors of those reports concluded that obstructive sleep apnea was cured by weight loss.  But, did it really cure the apnea?

As more studies were done, the investigators began testing for apnea after weight loss.  To assess the effect of weight loss on correcting apnea, the reports used changes in patients’ sleep test measurements.  Typically, they would use a percentage drop in the number of apnea events or select a set level of events at 15 or 5 per hour.  The level of 5 is the diagnostic level accepted for the diagnosis of the condition.  These studies report a high level of symptomatic improvement with weight loss.  Unfortunately, only 10-15% of obese patients will drop their levels below 5 after weight loss.  Most will reduce the number of events limiting the severity, but few can be considered as cured.  For an individual, weight loss can have significant beneficial effects on treatment, need for treatment and symptoms.  However, when viewed as a cause, few can be considered to have obstructive apnea caused by obesity.

My experience reported a few years ago at a community sleep center gives an insight.  For every one hundred cases of newly diagnosed obstructive sleep apnea, 60 will have BMIs in the obese range, meaning that 60% were obese. After weight loss, we know only 10 to 15% of individuals will have their apnea event drop below 5 per hour.  In the one hundred newly diagnosed individuals with apnea, weight loss will correct the apnea in only 6-10 of the 60 who had weight issues.  The other 50- 54 previously obese now are of normal weight and still have apnea.  They will feel better after weight loss, but they will still have apnea.  There are now a total of approximately 90 who still have apnea.  Why?  

There is the problem of muscle relaxation of course, but there is the other component of airway size – Genetics.

Sleep doctors look at throats when evaluating their patients.  As a practitioner for many years, I have looked at the throats of thousands of patients with obstructive apnea.  How many abnormal throats have I observed?  Not many.   I have seen one throat malignancy in my last two thousand exams.  By including enlarged tonsils and changes due to prior surgeries, the total would still be very low.  Very few patients with apnea have abnormal throats.  However, all throats ARE DIFFERENT.  

As someone who looks at throats for a living, I can tell you that throats are like faces.  They are all similar, but they are all different. Some have large tongues, some small jaws, some low palates, some high palates, some narrow throats, some wide, but all are different.

Our throats are part of our physical anatomy given to us by our parents.  It is our genetic gift for life.   There are an infinite number of combinations that might be expected. The easiest way to describe the effects of our anatomy and genetics on our throats is simply by the throat’s size.  Some throats are large and some are small.  Smaller throats have less room for the relaxation that occurs during sleep and as a result, obstructive apnea may occur at a younger age.  A large throat may result in one never having the condition.

Over the past fifty years there are a variety of diseases and conditions that have been recognized as producing Obstructive Sleep Apnea.  Severe hypothyroidism and acromegaly are examples.  These are rare causes.  They affect muscle relaxation and airway size in a variety of ways.  Some ethnic groups have been shown to have a higher incidence of Obstructive Sleep Apnea – predominately those of Southeast Asian and black heritage.  These increases are proposed to be secondary to the bony structure of the face and cranium reducing airway size in those populations.

So these are the factors that lead to obstructive apnea: age, muscle relaxation, weight and genetics.  By the time we are in our 70s, most of us will suffer from the condition.  It could almost be considered a part of the aging condition.  Add in the genetic component and the weight factor, obstructive apnea can appear at a younger age.      


Three Predominate Components To

The Development Of Obstructive Sleep Apnea

Muscle relaxation – Increases with Age

Airway size – Genetics

Airway size – Weight

The combination of the above factors in some proportion leads to the development of obstructive sleep apnea for the majority of affected individuals.

It is best to think of Obstructive Sleep Apnea as a potential companion you will share for life.   Like grey hair and glasses for most, hearing aids for some, obstructive sleep apnea is in your future.  Once accepted and treated, it becomes just another of life’s companions and not a dreaded disease.  

RGH  June 6, 2022

Causes of Obstructive Sleep Apnea – The Who (Prevalence)

When we have medical problems, we all want to understand the ‘who’, ‘how’ and ‘why’ of the condition.  Knowing may lead to changes or corrections that might fix and potentially remove the problem.  Many professionals have invested their careers studying obstructive sleep apnea (OSA), trying to understand the ‘hows’ and ‘whys’ of OSA.  It remains a subject that few professionals agree upon. Perhaps it’s best to review the broad landscape of OSA before we look at the details; reviewing the forest before the trees.  Let’s look at the ‘who’ of OSA.

OSA is a common condition.  How many people have it and what are their characteristics?  We have a general outline for the answers to these questions and it is best to start with an understanding of those facts.  First, how common is it?

Investigators have studied and reported answers to our questions, but the answers seem to change with each report.   There are real reasons for the differing answers.  Depending upon the how the information was obtained, the answers will vary.  The source of the estimates can be from formal research designed to uncover the answer, population studies of many types, questionnaire reviews, insurance data reviews, or combinations of these and other techniques.  The frequencies reported range from highs of 50% from Germany and 37% from Switzerland, to lows of 3% in Australia.  When reviewing these reports, one is struck by the differences in how people were selected for inclusion in the studies; the variations in the definitions used to label someone as having OSA and by the increasing level of its reported occurrence as the years passed and the condition became more commonly known. 

The differences in these reports are not hard to understand.  Each has a specific method to gather potential individuals into the report.  Enrollment into the study varies.  In many reports, the individuals have to volunteer to provide private medical information.  Even the report from closed medical populations in countries with government run medical systems cannot identify cases if the individuals do not participate.  The wise blind man can only grasp what he can feel and the wise investigator can only see what he has chosen to look at.

Another factor to take into account is how the report defines ‘having OSA’.  Are test results required?  If so, what kind of test and what parameters are necessary to establish the diagnosis?  What level of OSA does the study accept?  Does it include what is generally considered to be mild OSA (5-15 apnea event per hour)?  Does it require the higher level of moderate OSA (greater than 15 event per hour) or does it include both and how are they reported? Each report varies.

Many details chosen by investigators will determine the population they report and thus, the prevalence of the condition.  Reviewing for this presentation, I went to the National Library of Medicine website to look for appropriate information.  My search identified 10,388 articles with information about the prevalence of obstructive sleep apnea.

Prevalence is the frequency of occurrence of something (in this case obstructive sleep apnea) in a selected defined population. 

The important fact is that this condition is very common.   How common is it?  No consensus exists.  The table below is constructed from several studies over the last 30 years and gives you an idea of reported values and how they have increased over the years.

I believe it is safe to say that at least 20 to 25% of adults in the United States have mild or greater apnea.  Why the increase in prevalence with passing years?  It is unclear, but most likely it represents the increase in awareness of the problem. 

But, we need to be aware of still more details about who experiences OSA 

Age is an important factor when measuring the prevalence of OSA.   Few reports have elderly individuals participating.  However, the report from Germany on 4,420 individuals from 20-81 years provides some answers.  Half of the population had at least mild OSA and 20% had moderate or severe OSA.  When broken down by age, 80% of men 70 y/o and older had some degree of OSA.  The Swiss study also demonstrated a significant increase with age.  Older studies do not show such a high prevalence in the elderly, but the majority of them did not include elderly individuals in the populations studied.  Time will tell, but obstructive sleep apnea is very common in the elderly.

There is evidence that some ethnic groups may have more Obstructive Sleep Apnea than others. Particularly individuals of Southeast Asian or Black heritage. It is proposed that the cranial and facial boney structure in those groups leads to smaller upper airways.

What about occurrences during our youth and young adulthood? OSA is known to occur in infancy, childhood and during the teenage years.  The prevalence for those ages is considered to be between 1 and 5%.  As for early adulthood, there is substantial information from multiple reports to indicate it occurs in 5% to 8% of 18-30 year olds.

In the summary above I have used numbers that include both sexes.  There is a significant difference in the occurrence of OSA between the sexes.   In the report from Switzerland, 50% of men and 24% of women in the report had OSA.  For most reports a significant difference between men and women is noted during the premenopausal years.  With aging and menopause, the occurrence of OSA in women increases.  

Summary – The Prevalence of Obstructive Sleep Apnea

The frequency increases with age in both sexes.  After the age of 70, the occurrence rate is dramatic reaching up to 80% of adults in one study.   

It is more common in men than women.  After menopause the occurrence in females increases significantly


Prevalence and association analysis of obstructive sleep apnea with gender and age differences.   Fietze et al.  J Sleep Res  2019 Oct; 28(5):e12770

Estimation of the global prevalence and burden of obstructive sleep apnea: a literature-based analysis.  Benjafield et al.  Lancet Respir Med. 2019Aug; 7(8):687-698

Prevalence of sleep-disordered breathing in the general population: the HypnoLaus study.  R Henzer et al.  Lancet Respir Med. 2015 Apr; 3(4): 310-318

Screening for Obstructive Sleep Apnea in Adults US Preventive Services Task Force Recommendation Statement.  JAMA January 24/31 2017; 317(4) 407-414

Diagnosis and management of childhood obstructive sleep apnea syndrome. Marcus CL, Brooks LJ, Draper KA, Gozal D, Halbower AC, Jones J, Schechter MS, Ward SD, Sheldon SH, Shiffman RN, Lehmann C, Spruyt K, American Academy of Pediatrics. Pediatrics. 2012;130(3):e714. 



Apnea – A Word with Many Uses

Obstructive Sleep Apnea is a very common malady. It is familiar to many and is frequently a subject of both social and medical conversations. Individuals not engaged in frequent work with Apnea conditions may be confused by its usage and rightly so. Discussions and writings about the subject can use the term with different meanings.  When used by professionals, it can also be used in various ways. It has a physiologic technical meaning; it is used as a proper name of medical conditions; and, it has a common usage that is less specific.

The word – apnea – comes from the Latin and Greek languages. The Latin ‘a + pnea’ means without breath and the Greek ‘apnoia’ means without pain. The Webster dictionary defines apnea as ”Transient cessation of respiration”. Webster’s definition fits well with the current technical use of the word, but fails to show the scope of the word’s use that has increased over the past half-century with the recognition of the associated clinical conditions.

Webster’s definition fits well with the current technical use of the word, but fails to show the scope of the word’s use…

The word is used technically to label a cessation of breathing. Sleep testing, in facilities or at home, and physiologic monitoring of hospital patients can identify periods when no air is going in or out of the nose or mouth. No breaths can be measured. These events are called Apneas.  

The word is used technically to label a cessation of breathing.

The addition of chest movement measurements during these apnea events further defines these periods of apnea.  If the breathing efforts are persistent during an apnea episode, the event is labeled an Obstructive Apnea. If no breathing efforts are being made by the chest, the pump that moves air in and out, the apnea is caused by the lack of chest effort and is called a Central Apnea.  It is called central because breathing effort by the chest is controlled, started and adjusted, by the Central Nervous System.  If the breathing problem is associated with both partially reduced chest movement and total cessation of movement, it is labeled a Mixed Apnea.   As we can see, the technical apnea breathing events are further defined as obstructive, central or mixed.

‘Apnea’ is used as part of the proper name of medical conditions

‘Apnea’ is used as part of the proper name of medical conditions. These conditions were described and first recognized approximately a half-century ago, but probably have been affecting mankind for our entire history. Obstructive Sleep Apnea is the first of these. When breathing is blocked or partially blocked for 10 seconds at least five times per hour, a diagnosis of the clinical syndrome of Obstructive Sleep Apnea is established.

Central Sleep Apnea is the clinical condition where the primary form of apneas measured is central.  It is established when a certain percentage of the physiologic apneas recorded on testing are the central type.  Central Sleep Apnea can be the result of multiple medical issues that range from cardiovascular problems to neurologic conditions.  It can be rarely seen on its own and not associated with other medical problems.  

A third commonly accepted diagnostic term is Complex Sleep Apnea.  This diagnostic group represents individuals with obstructive sleep apnea treated with CPAP whose breathing events do not resolve when they are treated. Their Apnea Hypopnea Index remains high. However, on repeated testing with CPAP, the breathing events are now predominantly Central Apneas. The CPAP treatment caused a change from Obstructive Apnea events to Central Apnea events. This type of medical condition is called Complex Sleep Apnea.

The term Apnea Hypopnea Index (AHI) may be new to some, but it is very important that it is understood. The ‘Apnea’ referred to is the physiologic measured Apneas. ‘Hypopnea’ is a partial obstructive breathing event measured on testing.  They have the same secondary effects as apnea events but without the total cessation of airflow. The AHI is a calculated number representing the total events (Apnea and Hypopneas) per hour. 

The AHI is the measurement on a diagnostic sleep test that determines if an apnea condition of some type is present.  With a patient on therapy, it is the number that is followed by the physician to determine how well the therapy is working.  It is measured on most CPAP machines and can be reviewed by the patient on a day-by-day basis.  The AHI on a diagnostic test is and has been the measurement to determine the severity of sleep apnea conditions for many years. The AHI is an example of the technical use of the word apnea.

…the common use of the term Apnea is far less specific…

Finally, the common use of the term Apnea is far less specific than the uses we have reviewed. Often, the word is used to encompass a broad range of the field. In writings and conversations, it will be used by an author as a single word to cover all, or one, of the apnea medical conditions – obstructive sleep apnea, central sleep apnea and complex sleep apnea. When discussing Obstructive Sleep Apnea conversationally, most will speak about apnea, meaning obstructive sleep apnea.  The most simple descriptive of its common use is as a substitute for the clinical conditions associated with breathing problems during sleep.

What we have covered.

1. Apnea is technically an absence of breaths (no airflow at the nose and mouth). 

2. Apnea, used technically, during sleep is further defined by its features to be obstructive, central or mixed.

*Obstructive apnea

*Central apnea

*Mixed apnea

3. Apnea is used in the formal name of medical conditions including:

*Obstructive Sleep Apnea

*Central Sleep Apnea

*Complex Sleep Apnea

4. Apnea, used in its technical manner, is a component of the Apnea Hypopnea Index measurement used to judge the severity of the problem.

5. Apnea’s common use is as a general term covering one or all of the clinical conditions 

RGH June 29, 2020

The Goals of Obstructive Sleep Apnea Treatment

“Why am I using that this thing?” they asked me.  This ‘thing’ they were referring to is also known as CPAP.

Many people find themselves having had a sleep test and they are not sure why. They have a CPAP machine (Constant Positive Airway Pressure machine). Yet, they tell me, “I don’t know why.” Yes, they’ve been told they have apnea (Obstructive Sleep Apnea or OSA), but why do they need to do this? It is a question that they should be able to answer. Why do we use CPAP?  Why do we treat OSA?

Why do we treat OSA?

 When a sleep evaluation or sleep testing was considered for you, your physician felt it might explain some of your sleep related symptoms or medical problems.  It might have been for snoring that you were not even aware had been occurring. Maybe you were sleepier than you wanted to be or more sleepy than your family or friends thought you should be. It could have been for another non-related issue.  Your doctor was concerned that your problem with glaucoma, asthma or hypertension may have been made worse by or possibly even caused by a sleep condition. The test was ordered.  Obstructive Sleep Apnea was found and now you have a CPAP machine.

Obstructive Sleep Apnea may cause symptoms. Excessive sleepiness, poor quality nocturnal sleep and waking up with headaches are just a few of these symptoms. Your snoring could be waking your spouse.  Certainly, you would prefer not to have the symptoms.  You want to sleep better and to feel better during the day. 

One of the major goals of therapy for OSA, including CPAP, is to improve or eliminate symptoms.  When the obstructive apnea is corrected, many of its symptoms resolve or improve, sometimes dramatically.  If you had symptoms when your apnea was diagnosed, one goal of therapy is to improve or correct those symptoms.   

Most symptoms of OSA are not specific.

Most symptoms of OSA are not specific.  A wide range of medical conditions, some common and others not so common, can cause these symptoms.  It is unfortunate, but our sleepiness or headaches do not come with labels telling us what is causing them to occur.  Often, sleep apnea treated with CPAP will totally correct the obstructive events, but the symptoms that led to the evaluation and testing do not go away.  

Many patients at the time they are diagnosed with significant obstructive apnea will have few or no symptoms.  These individuals have varying degrees of OSA severity on their sleep testing.  Surprisingly, significant OSA can be seen with minimal symptoms or even no symptoms.  While the number of obstructive events per hour will generally be related to the severity of the symptoms, is it not unusual to see patients with both moderate and severe apnea with few symptoms.  Even without symptoms, our current knowledge strongly supports the need for their treatment.

Many patients at the time they are diagnosed with significant obstructive apnea will have few or no symptom.

Understanding the reason for treating individuals with few or no symptoms requires a little more information. Obstructive Sleep Apnea is the repeated interruption of someone’s breathing while asleep. The obstructions result in a blood oxygen drop and an arousal to light sleep or brief awaking. These arousals are not usually associated with full awakenings.  Most individuals are not aware that the obstructions have occurred.  

There are two types of obstructions. The first is a total blockage of the airway with a drop in blood oxygen level while breathing efforts from the chest continues.  The technical term for complete obstruction is Apnea. The second is a partial blockage of the airway while the breathing continues.  These partial blockages cause the same problems as seen with an apnea. The technical term for the partial obstruction is Hypopnea. The two types of obstruction are measured during a night or portion of a night of sleep testing. The numbers of each are added together. When divided by the duration of the sleep where the measurements were made, the results represent the number during an average hour of sleep.  The resulting number is the Apnea-Hypopnea Index or AHI.   The AHI is the average number of apneas and hypopneas in one hour of sleep.

The AHI is considered a measurement of the severity of Obstructive Sleep Apnea. Other factors enter into the measurement of severity. The most common would be the degree of oxygen drop that occurs with these obstructive events.  It is generally accepted that an AHI of less than 5 is not considered to be diagnostic of OSA.  An AHI of 5 to 15 events per hour is considered mild OSA.  An AHI of 15 to 30 is moderate and above 30 is severe Obstructive Sleep Apnea.

The AHI is considered a measurement of the severity of Obstructive Sleep Apnea.

In the past 40 years, thousands of research studies on Obstructive Sleep Apnea have been performed. The vast majority utilize the severity scale noted above. Those studies strongly support the current concept of the role of apnea in causing and aggravating other medical conditions.

The higher a person’s AHI on their diagnostic sleep test, the more likely they will die from a stroke or heart attack.  The risk is far higher than those who have no obstructive sleep apnea.  And, they die younger. When the AHI is greater than 15 per hour the risk is significant. An increased risk is measurable at an AHI of five but it is relatively small.  It is very small at an AHI of less than five.  It is generally accepted the long-term treatment of patients with an AHI greater than 15 at the time of diagnosis will improve secondary medical conditions and prolong life.

The second goal of therapy is obvious. It is to reduce or eliminate as many apnea and hypopnea events as possible. A person with OSA cannot know what their AHI is on any given day, night, week or month.  As noted above, the symptoms do not always reflect the success of OSA treatments.  However, with modern CPAP machines, technology can measure those events (AHIs) while you use the machine. Reports are now available on most machines, on most machine manufacturer’s websites, or through your physician.  You and your physician can know how well your therapy is controlling your AHI.

What have we covered.

1. Obstructive Sleep Apnea can occur with minimal or no symptoms.

2. Obstructive Sleep Apnea is treated for two reasons

3. Obstructive Sleep Apnea treatment may only improve one of the reasons it is being treated.

4. The Apnea Hypopnea Index (AHI) is the number of obstruction events per hour of sleep.The AHI while on therapy demonstrate how well the therapy is controlling the Obstructive Sleep Apnea.

Three questions follow naturally from this brief review. These topics will be addressed in future post.

1. Why do I still have symptoms on treatment for OSA?

2. If I have mild OSA when diagnosed, do I need treatment?

3. What is the definition of apnea?  

Why is OSA treated?  The two reasons are: to improve symptoms and control the obstructive events.  When we treat OSA, the treatment may be successful treating both, or just one of the two.  One or both may be the reason CPAP, or another treatment, was recommended for you. 

Goals of treatment for Obstructive Sleep Apnea

1.Control symptoms 

2. Control the obstructive events

RGH 6-23-2020