by Robert Hooper | General, Letters to Winston, Sleep Apnea, Sleep Disorders, Sleep Disorders
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)
by Robert Hooper | General, Letters to Winston, Professional
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.
RGH
28,775
by Robert Hooper | Letters to Winston
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
Winston
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.
RGH
by Robert Hooper | Letters to Winston
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.
RGH
BGC/JG/24601
Apr 23, 2022
by Robert Hooper | Professional, Sleep Apnea, Sleep Disorders, Sleep Disorders
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.
SUMMARY:
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
