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Potential effects of 6 vs 12-weeks of physical training on cardiac autonomic function and exercise capacity in COPD


To contrast the potential effects of a physical training program (PTP), for 6 versus 12 weeks duration, on cardiac autonomic modulation by linear and nonlinear heart rate variability (HRV) indices and exercise capacity in moderate-to-severe COPD patients. Twenty COPD patients were assigned randomly to either a training group (n=10) or a control group (n=10). HRV at rest and during submaximal test was determined by linear (rMSSD and SDNN) and nonlinear indices [SD1, SD2 and sample entropy (SE)]. In addition, key responses were obtained during cardiopulmonary exercise testing (CPX), the walking distance (WD) during the six minute walking test and submaximal constant speed testing (CST). PTP consisted of 30 minutes of aerobic exercise training on a treadmill, 3 times per week at 70% of CPX peak speed rate. Patients were evaluated on baseline, 6 and 12 weeks. Significant improvements in HRV indices, WD, as well as, other physiological responses were observed after 6 weeks of the PTP and maintained until 12 weeks (P<0.05). However, after 12 weeks, the SD1 index demonstrated an additional improvement compared with 6 weeks (P<0.05). Peak oxygen uptake and dioxide carbon production improved only after 12 weeks (p<0.05). Interestingly, the 6th week-baseline delta (6th week-baseline) of WD, SDNN and SE were significantly higher than 12th week-6th week delta (P<0.05). These results indicate that beneficial changes on cardiac autonomic modulation in conjunction with improvement in submaximal functional capacity occur in the first 6 weeks of PTP in moderate to severe COPD. (AU)

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