Active Voice: Exercise Test to Screen for Obstructive Sleep Apnea?
By Trent A. Hargens, Ph.D.
Active Voice is a column by experts in science, medicine and allied health. The viewpoints expressed do not necessarily reflect positions or policies of ACSM.
Trent A. Hargens, Ph.D., is an ACSM member and Assistant Professor of Exercise Science with the Human Performance Laboratory at Ball State University in Muncie, Indiana. He is the Associate Coordinator of the Clinical Exercise Physiology Graduate Program. His research focuses on the cardiovascular and autonomic adaptations that result from obstructive sleep apnea and obesity and how exercise can impact those adaptations.
Sleep disorders, of which obstructive sleep apnea (OSA) is the most common, pose a significant personal and public health risk. Not only does OSA increase risks of hypertension, diabetes, congestive heart failure and cardiovascular disease, but it also accounts for a five-fold increase in the risk of motor vehicle accidents. As a result, OSA is a health problem that should concern all of us.
Recent estimates suggest that as many as one in four American adults are at risk for and should be evaluated for OSA. As age and obesity are prime risk factors for this disorder, we should expect the prevalence to increase as our population ages and becomes more obese. Unfortunately, the majority of at-risk individuals goes undiagnosed for OSA, probably due to the high cost of testing and treatment, inconvenience, and long wait time for full-night polysomnography (PSG) testing, which remains the gold standard test for diagnosis. Simpler and more cost-effective screening tools are clearly needed to improve the risk stratification and clinical decision-making that lead to patient selection for diagnostic PSG testing. If we can optimize screening and selection for PSG testing, we can conserve costs and allow the patients to be tested who most need assessment.
The graded exercise test (GXT) has long been a safe and effective screening tool for identifying individuals at high risk for cardiovascular disease. In addition, hemodynamic responses to exercise and recovery have shown to be prognostic for hypertension, cardiovascular disease and mortality. Several recent studies have identified unique responses to exercise testing that help distinguish patients with OSA. These include blunted heart rate and exaggerated ventilatory response during the GXT and blunted heart rate recovery during the early post-exercise minutes. The latter response has been shown to normalize after several weeks of OSA treatment with continuous positive airway pressure (CPAP), the most widely used treatment. This suggests that OSA has a primary role in causing the delayed heart rate recovery and is a significant sign of impaired autonomic function. Autonomic dysfunction in OSA is well known under resting conditions and normal daily activity, but has only recently been identified in exercise test responses.
Unfortunately, when it comes to questions of whether OSA reduces physical fitness or makes a person less inclined to regularly engage in healthful physical activity, research has not yet provided clear answers. The effects of confounders, such as obesity, have clouded this determination so far. More research is needed.
Regardless, the GXT shows promise as a screening tool to identify individuals at risk for OSA. Large-scale studies are needed to associate these OSA-related response profiles with PSG findings before the power of the test as a screen for sleep apnea can be established. A risk prediction model that includes simple measures such as body mass index, neck girth, snoring history, resting blood pressure (or medication for same) and daytime sleepiness, along with some of the readily available GXT responses may turn out to perform very well.
Sleep apnea is a disorder that often goes unnoticed or is dismissed as innocuous, like a snoring problem that keeps your spouse awake at night. In reality, OSA is a serious disorder by which people may be subjected to exaggerated risk for cardiovascular and metabolic diseases. It is one more factor that can place people at greater risk for early mortality, through a disease process or the increased risk for motor vehicle accidents due to profound sleepiness behind the wheel.