The impact of obstructive sleep apnea on exercise capacity in a cardiac rehabilitation program.

PURPOSE: Cardiac rehabilitation (CR) improves clinical outcomes in patients with cardiovascular disease (CDV). Patients with CVD often have multiple comorbidities, including obstructive sleep apnea (OSA), potentially affecting their ability to participate and achieve functional improvement during CR. We aimed to test the hypothesis that OSA reduces peak exercise capacity (EC) in patients undergoing CR and to explore if OSA treatment modifies this relationship. METHODS: Data from a retrospective cohort of CR patients was analyzed. OSA was defined as a respiratory event index > 5/h or physician diagnosis. Patients with OSA were considered "treated" if using continuous positive airway pressure regularly during the CR period. Change in METs was the primary study outcome. RESULTS: Among 312 CR patients, median age of 67 years, 103 (33%) had known OSA (30 treated, 73 untreated). Patients with OSA vs. those with no OSA were more likely to be obese and male; otherwise, groups were similar. Compared with the no OSA group, patients with OSA had lower pre-CR METs (3.3 [2.9-4.5] vs. 3.9 [3.1-5], P = .01) and lower post-CR METs (5.3 [4-7] vs. 6 [4.6-7.6], P = .04), but achieved a similar increase in METs post-CR (1.8 [0.6-2.6] vs. 2.0 [0.9-3], P = .22). Furthermore, compared to no OSA, pre-CR and post-CR METs tended to be similar in patients with treated OSA, but lower in untreated patients, with similar increases in METs across all groups, even when adjusting for covariates via multivariable regression. CONCLUSION: OSA is prevalent in patients with CVD undergoing CR. CR substantially improves exercise capacity independent of OSA status, but screening for-and treatment of-OSA may improve the absolute exercise capacity achieved through CR.

Taurine depresses cardiac contractility and enhances systemic heart glucose utilization in the cuttlefish, Sepia officinalis.

Taurine is the most abundant amino acid in the blood of the cuttlefish, Sepia officinalis, where levels can exceed 200 mmol L(-1). In mammals, intracellular taurine modulates cardiac Ca(2+) handling and carbohydrate metabolism at much lower concentrations but it is not clear if it exerts similar actions in cephalopods. Blood Ca(2+) levels are high in cephalopods and we hypothesized that taurine would depress cardiac Ca(2+) flux and modulate contractility in systemic and branchial hearts of cuttlefish. Heart performance was assessed with an in situ perfused systemic heart preparation and contractility was evaluated using isometrically contracting systemic and branchial heart muscle rings. Stroke volume, cardiac output, and Ca(2+) sensitivity were significantly lower in systemic hearts perfused with supplemental taurine (100 mmol L(-1)) than in controls. In muscle ring preparations, taurine impaired relaxation at high contraction frequencies, an effect abolished by supra-physiological Ca(2+) levels. Taurine did not affect oxygen consumption in non-contracting systemic heart muscle, but extracellular glucose utilization was twice that of control preparations. Collectively, our results suggest that extracellular taurine depresses cardiac Ca(2+) flux and potentiates glucose utilization in cuttlefish. Variations in taurine levels may represent an important mechanism for regulating cardiovascular function and metabolism in cephalopods.