The impact of 6 months of exercise-based cardiac rehabilitation on sympathetic neural recruitment during apneic stress

Abstract

The current study evaluated the hypothesis that six months of exercise-based cardiac rehabilitation (CR) would improve sympathetic neural recruitment in patients with ischemic heart disease (IHD). Microneurography was used to evaluate action potential (AP) discharge patterns within bursts of muscle sympathetic nerve activity (MSNA), in eleven patients with IHD (1 female; 61±9 years) pre- (Pre-CR) and post- six months of aerobic and resistance training-based CR (Post-CR). Measures were made at baseline and during maximal voluntary end-inspiratory (EI-APN) and end-expiratory apneas (EE-APN). Data were analyzed during 1-minute of baseline and the second half of apneas. At baseline, overall sympathetic activity was less Post-CR (all P<0.01). During EI-APN, AP recruitment was not observed Pre-CR (all P>0.05) but increases in both within-burst AP firing frequency (∆Pre-CR: 2±3 AP spikes/burst vs. ∆Post-CR: 4±3 AP spikes/burst; P=0.02) and AP cluster recruitment (∆Pre-CR: -1±2 vs. ∆Post-CR: 2±2; P<0.01) were observed in Post-CR tests. In contrast, during EE-APN, AP firing frequency was not different Post-CR compared to Pre-CR tests (∆Pre-CR: 269±202 spikes/min vs. ∆Post-CR: 232±225 spikes/min; P=0.54), and CR did not modify the recruitment of new AP clusters (∆Pre-CR: -1±3 vs. ∆Post-CR: 0±1; P=0.39), or within-burst firing frequency (∆Pre-CR: 3±3 AP spikes/burst vs. ∆Post-CR: 2±2 AP spikes/burst; P=0.21). These data indicate that CR improves some of the sympathetic nervous system dysregulation associated with cardiovascular disease, primarily via a reduction in resting sympathetic activation. However, the benefits of CR on sympathetic neural recruitment may depend upon the magnitude of initial impairment.