The Basics of Obstructive Sleep Apnea
Introduction to Obstructive Sleep Apnea
Snoring has long been known to disrupt and fragment the sleep of the snorer and the bed partner. However, only since the 1970s has it become clear that snoring can be a sign of a serious disorder, Obstructive Sleep Apnea (OSA). A relation to the cardiovascular disorders which are associated with chronic OSA was not clearly explained until the 1990s. Now we know that 10% of women and 25% of men are affected by OSA and many of these suffer from systemic hypertension, CAD, heart failure, atrial fibrillation, stroke, and pulmonary hypertension. With the growing epidemic of obesity around the world, the prevalence of OSA is rising rapidly. Cardiovascular specialists have a great opportunity to recognize and treat their patients with both disorders.
According to a survey of 100 clinical cardiologists, referral rates to a sleep center average seven or fewer per month, or almost 2% of the patients with both cardiovascular disease and OSA. Two-thirds have incorporated an assessment of sleep-disordered breathing (SDB) during a patient visit. They agree that diabetes mellitus is the most critical medical disorder they see, and that heart failure and atrial fibrillation predict OSA about 21-40% of the time. Two-thirds of cardiologists would refer patients to a sleep center and only one-third of respondents know that home sleep testing was approved by Medicare and insurers in 2008, which could increase referrals to a sleep specialist by 42%. One-third of doctors believe a cardiologist's role in identification and treatment of OSA should be referrals.
The most common reason reported for not referring patients to a sleep lab, was "cost of the sleep study for the patient," and having time to discuss sleep issues during a patient visit. Another survey reported the reason cited by cardiologists for failing to refer the OSA patient was "lack of confidence in current therapies (positive airway pressure)."
Two large studies have been published on OSA and heart disease, the Wisconsin Sleep Cohort and the Sleep Heart Health Study. These documented the impressive association of OSA and multiple cardiovascular conditions, particularly hypertension, coronary artery disease, and stroke.
In 2008, the American College of Cardiology and the American Heart Association, supported a Consensus Statement on Sleep apnea and Cardiovascular Disease" reported in JACC. It served as an initial "guideline" to the CV specialist for understanding the relationship of OSA and cardiovascular disease, as well as encouraged physicians to assure that their patients be identified and managed with available sleep medicine resources. Since that time, much research has been published and more is needed. Unfortunately, there are only a few dozen cardiovascular specialists in the US who are certified in Sleep Medicine, which may limit original cardiovascular research on OSA patients.
Pearl: Heart failure affects more than 5 million Americans.
Obstructive Sleep Apnea is the repetitive and partial collapse of the upper airway during sleep.
An apnea is confirmed when the airway completely obstructs for a minimum of 10 seconds.
A hypopnea occurs when the airway partially obstructs, with an associated 4% or more drop in oxygen saturation by oximetry – or, concurrent with an arousal from sleep. More than 5 – 10 apneas or hypopneas per hour (AHI) are abnormal and consistent with OSA. Excessive daytime sleepiness or fatigue and an AHI of greater than five per hour is considered Obstructive Sleep Apnea (5 – 15 is mild, 15 – 25 is moderate, and more than 30 is severe).
Central Sleep Apnea (CSA) is defined as a disorder of the central nervous system (CNS) drive to ventilation, and an exaggerated ventilatory response to chemical stimuli.
Both OSA and CSA can coexist. Central Apnea is commonly associated with advanced degrees of heart failure, recent cerebrovascular accident, narcotic drugs, and high altitude exposure.
RERA is a sequence of breaths characterized by increasing respiratory effort, leading to arousal from sleep, but not meeting the criteria for apnea or hypopnea. Patients with numerous RERAs are considered to have Upper Airway Resistance Syndrome, which fragments sleep and leads to excessive daytime sleepiness.
Symptoms of OSA
- Loud or disruptive snoring: more people snore than have OSA, so snoring alone is not diagnostic.
- Witnessed Apnea: carries the highest predictive significance of any "symptom," usually reported by a bed partner. Taking a history from a patient in the presence of a "sleep witness" cannot be overemphasized. Gasping awake may be a symptom volunteered by a patient without a witness, which may carry similar significance to witnessed events.
- Non-restorative Sleep: an un-refreshed feeling after a good opportunity for rest is complete.
- Excessive daytime sleepiness: since there is currently no objective biomarker for sleepiness, most of the assessments of their symptoms are subjective:
- The Epworth Sleepiness Score Scale
- The Stanford Sleepiness Survey
Pearl: heart failure and coronary patients rarely offer sleepiness as one initial complaint.
Pearl: smoking and alcohol drinking increase the risk and severity of OSA.
Signs and Physical Findings in OSA
- Obesity – the most predictive finding in OSA is central obesity. In patients who suffer from OSA, the typical BMI is between 25 and 30. Neck size correlates well with both obesity and OSA: Women will have a greater than 16" neck and men will have a greater than 17" neck. Not all obese patients will be found to have OSA.
- Craniofacial abnormalities – such as deviated nasal septum, retrognathia, and narrow posterior oropharynx. Anesthesiologists use the so-called "Mallampati Score" to assess the oral airway and predict difficult operative intubations, since it correlates well with tongue size. The cardiovascular specialist who sees Marfans patients, should note palatal abnormalities often correlating to OSA symptoms.
Pearl: many obese patients have diabetes, OSA, and cardiovascular disease. Hospitalized patients are often monitored with ECG and oximetry; unexplained transient hypoxemia is frequently a sign of OSA, and can lead to a wide variety of arrhythmias.
Evaluating a Patient for Obstructive Sleep Apnea
- Questionnaires to assess sleepiness, as mentioned previously, are the Epworth and Stanford, usually required by payors, to justify diagnostic testing. They generally assess the likelihood of falling asleep in inappropriate situations.
- Polysomnography (PSG)
- Attended studies – the gold standard for assessment of patients for OSA is the attended polysomnogram, performed in an accredited sleep center. Monitoring and recording of airflow, oxygen saturation, ventilatory effort, EMG, ECG, EMG, and body position. Night-to-night variability of 10% can be seen in the same person. In patients with severe enough OSA to be recognized and documented early in the test (usually before 2 am) a split study can be performed; this first half of the night is diagnostic, and the second half is therapeutic, with titration of CPAP (continuous positive airway pressure) to efficiency and tolerance after two AM.
Key to the detection of OSA is oxygen desaturation during sleep. Patients with the disorder are likely have wide swings in their oxygen saturations compared to normal sleepers. Young thin patients without lung disease may have false negative oximetry. COPD patients, in contrast, may have hypoxemia in the absence of OSA! Thus, oximetry alone is not considered an adequate diagnostic or screening tool for assessing patients for OSA.
Pearl: some have suggested a prediction formula for predicting OSA before sleep testing. One sensitive but not specific "formula" includes the presence of witnessed apneas, male gender, high BMI and neck circumference. Asians, women, and the elderly patient may not fit the formula, however. In the cardiology clinic, where hypertension is a common associated finding, including it in the formula may add power to the prediction capacity.
- Weight loss – in patients with elevated BMI and OSA, a 10% – 30% loss in body weight, can have a significant impact on snoring and apnea. Unfortunately weight loss rates among the obese are variable, and may require years before ideal weights are achieved. In the meantime, cardiovascular disease and health consequences.
- Positive Airway Devices – nasal CPAP has become the standard of care over the last 2 decades. This pneumatic splint prevents collapse of the upper airway. Between 90 – 100% of patients with OSA are candidates for CPAP. Compliance however is inconsistent, with only 46 – 89% of patients continuing CPAP after initiating therapy. It is intuitive that the more nightly hours of use, the greater the reduction in cardiovascular complications, but this cannot be defended with data, yet.
More To Come
Positive Airway Pressure Devices BiPAP, VPAP, APAP, oral appliances for mandibular advancement, and ENT surgery will be the subjects of an extensive review in the upcoming Cardiosource Clinical Communities Reviews in "The Basics of Sleep Apnea."
Key Learning Points
- Sleep Apnea is a common and potentially serious disorder. Its health associations span multiple organ systems, most dramatically the cardiovascular system: associated disorders include hypertension, heart failure, atrial gibrillation, stroke, pulmonary hypertension and coronary atherosclerosis. Chronic recurrent hypoxemia and wide swings in sympathetic nervous system activation appear to be the common related mechanisms.
- Sleep apnea is easily detected and responds effectively to therapy in compliant patients. Treatment options include: Weight loss, Continuous Positive Airway Pressure, Mandibular Advancement devices, or surgical intervention.
- More research is necessary to fully uncover the cause and effect relationships of OSA to vascular disease, and to improve therapies that impact morbidity and mortality from these two overlapping disease states.
- Kapa S, Shahrokh J, Somers VK. Obstructive sleep apnea and arrhythimias. Sleep Med Clin 2007; 2:575-81.
- Collop, NA, Obstructive sleep apnea: what does the cardiovascular physician need to know? Am J Cardiovasc Drugs 2005;5:71-81.
- Phillips B, Naughton MT. Obstructive Sleep Apnea. Fast Facts 2004, Health Press Limited, Oxford. Last Accessed Nov. 26, 2012. http://www.fastfacts.com/_files/samplefiles/FF_ObstSleeApne_sample.pdf
- Kryger, M H., Roth, T, Dement, WC. Principles and Practice of Sleep Medicine. 2011, Elsevier Health Sciences, Inc., Philadelphia, PA.
- Somers VK, White DP, Amin R, et al. Sleep apnea and cardiovascular disease: an American Heart Association/American College of Cardiology Foundation Scientific Statement from the American Heart Association Council for High Blood Pressure Research Professional Education Committee, Council on Clinical Cardiology, Stroke Council, and Council on Cardiovascular Nursing. J Am Coll Cardiol 2008. 19;52:686-717.
- Young, T. Rationale, design and findings from the Wisconsin Sleep Cohort Study: Toward understanding the total societal burden of sleep disordered breathing. Sleep Medicine Clin 2009;4:37-46.
- Hla KM, Young T, Finn L, Peppard PE, Szklo-Coxe M, Stubbs M. Longitudinal Association of Sleep Disordered Breathing and Nondipping of Nocturnal Blood Pressure in the Wisconsin Sleep Cohort Study. Sleep 2008 31:795-800.
Keywords: Atrial Fibrillation, Cardiovascular Diseases, Heart Failure, Hypertension, Hypertension, Pulmonary, Obesity, Sleep Apnea, Obstructive, Snoring, Stroke
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