To contrast the potential effects of physical exercise training program (PTP) of a 6 versus 12 weeks on cardiac autonomic modulation by linear and non-linear heart rate variability (HRV) indices and functional capacity in moderate-to-severe COPD patients.

This is a prospective randomized controled trial. A total of fifty two patients were recruited, however, only 32 patients met all inclusion criteria. Patients that were included presented: 1) a diagnosis of COPD according to criteria set forth by the Global Initiative for Chronic Obstructive Lung Disease (19), 2) compliance with medical management, 3) no change in medical management and no decompensation episodes for at least one month prior to study initiation, and 4) no participation in a regular physical exercise program for at least six months prior to study initiation. Exclusion criteria consisted of the presence of orthopedic or neurological conditions that would preclude participation in a physical exercise program, a history of cardiac arrhythmias, a past history consistent with heart disease, diabetes mellitus, arterial hypertension and failure to comply with the research protocol.

Patients were randomly assigned to physical exercise training program PTG, (n=17) or to a control group (CG, n=15) without aerobic exercise training by drawing of shuffled, opaque, coded envelopes that were opened immediately before starting each case. However, after the randomization process, five patients refused to continue and seven interested patients were excluded.

Finally the groups were composed of PTG (n=10) and control group (CG, n=10). Heart rate variability (HRV) on rest and during submaximal test was determined by linear analysis (rMSSD and SDNN) and nonlinear indices SD1, SD2 and sample entropy (SE). In addition, the physiological responses were obtained during cardiopulmonary exercise testing (CPX), the walking distance (WD) on 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.

All patients received regular treatment consisting of inhaled bronchodilators and steroids and the dosage did not changed during the study. The study protocol was approved by the Institutional Ethics Committee and all patients signed a written consent form prior to study initiation (109/2006). The target number of patients was calculated to be 10 patients in each group, based on a 5% type I error, a 2-sided test, and an 80% power to detect a change between the groups in 5 to SD2 at rest. Considering a drop out of 20%, 12 patients in each group were calculated. Due to the Gaussian distribution and/or homogeneity of variance in variable values, parametric tests were selected for statistical analysis.

Inclusion Criteria:

1. a diagnosis of COPD according to criteria set forth by the Global Initiative for Chronic Obstructive Lung Disease (19),
2. compliance with medical management,
3. no change in medical management and no decompensation episodes for at least one month prior to study initiation, and
4. no participation in a regular physical exercise program for at least six months prior to study initiation.

Exclusion Criteria:

1. presence of orthopedic or neurological conditions that would preclude participation in a physical exercise program,
2. a history of cardiac arrhythmias,
3. a past history consistent with heart disease, diabetes mellitus, arterial hypertension and failure to comply with the research protocol.