Heart Rate Recovery Following Aerobic Exercise Training in Patients with Interstitial Lung Disease

Abstract

Interstitial lung disease (ILD) is characterized by a progressive decline in alveolar diffusion capacity and pulmonary function, often abetted by capillary destruction and hypoxic vasoconstriction. These abnormalities manifest themselves symptomatically by a severe reduction of exercise capacity and excessive fatigue. Heart rate recovery (HRR) reflects the capability of the autonomic nervous system to adapt and cope with the training load and can predict the accumulation of fatigue. Therefore, HRR can be a physiological measure of the endurance capacity and the ability to resist fatigue-induced changes. PURPOSE: To examine the influence of changes in resting heart rate (HR) following an aerobic exercise training (AET) program on recovery HR in patients with ILD. METHODS: 13 ILD patients (57±9 years) underwent a 10-week treadmill walking program at 70-80% of HR reserve for 30-45 minutes thrice a week. The six minute walk test (6MWT) was performed on an 80-meter oval track prior to and at the end of the AET program in accordance with the American Thoracic Society guidelines. Resting HR was measured by pulse oximetry after 10 minutes of seated rest before starting the 6MWT. Recovery HR was measured after 2 minutes of seated rest following the end of the 6MWT. RESULTS: Paired t-test comparisons of pre- and post-AET resting and recovery HRs revealed two HR change patterns which divided the patients into two cohorts. Subset 1 (n=7) displayed a statistically significant decrease in resting HR (104±11 vs. 88±10, p=0.002) and recovery HR (120±12 vs. 104±10, p=0.001) after the 10-week AET. Subset 2 (n=6) displayed a statistically significant increase in resting HR (86±12 vs. 97±12, p=0.034) and no significant improvements in recovery HR. There was a near identical increase in post-training six minute walk distance in subset 1 and 2 of 49 (p=0.045) and 50 meters (p=0.043) respectively. CONCLUSIONS: Our findings show that a decrease in resting HR following AET may be associated with a faster recovery, perhaps permitting patients to more readily engage in subsequent physical activities. The variations in training adaptations in resting and recovery HR suggest a variable cardiac autonomic modulation to exercise training in patients with ILD, implications of which are yet to be explored. NIH/IRP 1 Z01 CL06006802; http://ClinicalTrials.gov; NCT00678821