Comprehensive Study of Heart Rate Recovery and Altered Ventilatory Response to Exercise in Patients with Obstructive Sleep Apnea

Background Obstructive sleep apnea (OSA) is a chronic disorder that results in many cardiovascular disorders including hypertension, arrhythmias and congestive heart failure (CHF). Polysomnography is the gold standard for diagnosis of OSA, even though up to 93% of women and 82% of men with moderate to severe OSA still remain undiagnosed. Cardiopulmonary exercise testing (CPXT) has been conventionally used for evaluation of coronary artery diseases and rehabilitation of cardiac patients. Modern systems allow for the analysis of gas exchange at rest, during exercise, and during recovery and also yield measures of oxygen uptake (V O2), carbon dioxide output (V CO2), and minute ventilation (V E) together with heart rate, blood pressure, electrocardiography findings, and symptoms. This may have clinical utility if added to the available screening tools used to identify OSA. Aim of study To assess altered ventilatory response and heart rate recovery in response to exercise in patients with obstructive sleep apnea and their relation to its severity. Methods and Results Case control study was enrolled including 30 patients with obstructive sleep apnea (OSA) divided according to severity (5 mild, 8 moderate and 17 severe) and 15 control healthy overweight with sedentary lifestyle individuals. The two groups underwent cardiopulmonary exercise testing and different pulmonary and cardiac parameters were calculated. Greater VE, VE/VCO2, VE/VO2 ratios and VE/VCO2 slope were statistically significant regarding the patients group (P < 0.001, F = 69.053, 104.381, 140.806 and 68.010 respectively according to ANOVA test). OSA patients had a reduced maximal exercise capacity expressed as lower VO2 peak, decreased breathing reserve (BR) and VO2 at anaerobic threshold compared to control group (P < 0.001, F = 22.597, 68.773 and 82.90 respectively). Delayed heart rate recovery (HRR) and weaker chronotropic response (CR) in patients with OSA than in controls with negative relationship to severity of OSA were proved (p < 0.001, F = 119.493 and 91.271 respectively). The study revealed elevated maximal systolic BP (max SBP), diastolic BP (max DBP) and recovery SBP in the following 2 minutes after exercise in patients with OSA relative to their healthy controls with positive relationship to the severity of OSA (P < 0.001, F = 37.129, 169.275 and 244.609 respectively). Conclusion Patients with OSA demonstrated exaggerated ventilatory response to exercise and autonomic dysfunction reflected by measurement of heart rate variability and reduced maximal exercise capacity than healthy controls. Abbreviations OSA, CHF, CPXT, VO2, VCO2, VE, VE/VCO2, VE/VO2, VE/VCO2, BR, CR, HRR, max SBP and max DBP.