Polysomnography and OSA Diagnosis: Methods and Accuracy

Introduction to Obstructive Sleep Apnea

The National Commission on Sleep Disorders Research reports that approximately 12 to 18 million middle-aged Americans have obstructive sleep apnea (OSA), a prevalence comparable to that of asthma or diabetes. OSA is also a likely cause of approximately 38,000 cardiovascular deaths annually. Those afflicted with OSA are at greater risk for metabolic and cardiovascular disorders such as diabetes, hypertension, arrhythmias, and coronary artery disease. Despite being a common disorder, OSA remains overlooked by many primary care providers. Polysomnography is the definitive diagnostic test, providing objective documentation of apnea and hypopnea.

As cited in Brogan, Files, and Zeigler (2010), mild forms of OSA affect one in five American adults, and moderate to severe forms affect one in fifteen — not including elderly individuals or children. Of those affected, as many as 90% are currently undiagnosed. Recently, due to the common comorbidity with cardiovascular disease, the healthcare community has placed greater emphasis on OSA; yet many physicians still do not recognize the importance of sleep for general well-being and are insufficiently knowledgeable about the biochemical conditions or risk factors of interrupted sleeping patterns. Patients are not routinely asked about the quantity or quality of their sleep. Conducting a thorough examination and obtaining a detailed history of sleeping habits help form a basic clinical impression of a person's possible OSA, but polysomnography in a clinic or laboratory is required to confirm the diagnosis.

What Polysomnography Measures

The term polysomnography is derived from the Greek roots poly (many), somno (sleep), and graphy (to write), and refers to a number of overnight tests performed on patients to evaluate sleep disorders. It normally consists of analyzing a person's oral and nasal airflow, blood pressure and oxygen level, electrocardiographic activity, brain wave patterns, and movement of the eyes, respiratory muscles, and limbs. Overnight polysomnography is the only diagnostic modality recommended by the American Academy of Sleep Medicine. Overnight pulse oximetry and home sleep studies are helpful in ruling out OSA but are not recommended as standalone diagnostic tools.

Sleep Disorders Diagnosed by Polysomnography

Polysomnography helps diagnose and evaluate sleep apnea, a common disorder in middle-aged and elderly obese men in which the muscles of the soft palate at the back of the throat relax and close the airway during sleep. This may cause loud snoring and gasping for air at night, as well as excessive daytime sleepiness. Results are expressed using the apnea-hypopnea index (AHI) — the number of apneic and hypopneic episodes a patient experiences per sleeping hour. Apnea is defined as airflow cessation lasting ten or more seconds.

The definition of hypopnea has varied over time. The Clinical Practice Review Committee of the American Academy of Sleep Medicine and the Centers for Medicare & Medicaid Services define hypopnea as a reduction in airflow of at least 30% lasting at least ten seconds and resulting in 4% or more oxygen desaturation. Some laboratories also require an associated arousal (Mendez & Olson, 2006).

Conclusion

The field of polysomnography continues to grow, with more colleges and universities adding the program to their curricula. There were three accredited labs in 1977 and over 1,800 American Academy of Sleep Medicine accredited labs and centers in the U.S. by 2008. As research into night-to-night AHI variability and the limitations of single-night testing continues to accumulate, the clinical standards surrounding OSA diagnosis are likely to evolve — underscoring the ongoing importance of polysomnography in identifying and managing one of America's most prevalent yet underdiagnosed disorders.