The Effect of Respiratory Muscle Training on Heart Rate Variability in Healthy Young Adults

Abstract

Changes in intra-thoracic pressure with loaded breathing may elicit changes in heart rate variability by repeatedly stimulating stretch and pressure receptors that can modulate cardiac regulation including the balance between sympathetic and parasympathetic tone. An increase in heart rate variability is believed to reflect this balance in autonomic control of the heart and has been used in previous studies as a way to assess changes in cardiac regulation. Therefore, we hypothesized that training of the respiratory muscles, similar to whole body endurance training, would supply significant stimuli to augment heart rate variability. PURPOSE: To determine if inspiratory muscle training improves measures of heart rate variability in healthy young adults. METHODS: Pulmonary function testing, maximal inspiratory pressure (PImax), and resting heart rate (HR) was obtained prior to and following a 5 wk inspiratory training program (IMT) in fourteen (6 females; 8 males) healthy young (25 ± 5 yrs; ± SE) adults. Subjects rested in the supine position for 15 min prior to obtaining electrocardiography (EKG) recordings (2 × 20 min periods) for the analysis of heart rate variability (HRV). Subjects underwent 5 wks of inspiratory muscle training (3 d/wk, 30 min/d) with the initial resistance set at 70% PI. Resistance was gradually increased throughout the 5 wks as each subject adapted to the resistance. All tests were repeated post-training for comparison. Ectopic beats were removed from the EKG recordings. HRV was analyzed in the frequency domain and included low frequency (LF, 0.04–0.15 Hz) and high frequency (HF, 0.15–0.4 Hz) components. RESULTS: Subjects showed normal pulmonary function (FEV1.0 /FVC >78%). Both FEV10 (Pre, 91 ± 2; Post, 97 ± 3% predicted, p<0.05) and MVV (Pre, 109 ± 4; Post, 126 ± 7% predicted, p<0.05) were improved with 5 wks of IMT. IMT resulted in a decrease (p<0.05) in PImax (Pre, −148 ± 9 mmHg; Post, −179 ± 10 mmHg). In spite of significant changes in respiratory muscle function, IMT did not affect resting HR (Pre, 64 ± 2 bpm; Post, 65 ± 1 bpm), the LF (Pre, 43.3 ± 7 nu; Post, 50.1 ± 4.3 nu) or HF (Pre, 46.5 ± 6.1 nu; Post, 43.7 ± 3.8 nu) components. CONCLUSIONS: Although 5 weeks of IMT significantly enhanced inspiratory muscle strength, there was no appreciable change in resting HRV. It may be that IMT training is of little benefit to healthy young individuals that already exhibit considerable HRV but may be of benefit to those with lower HRV such as cardiac patients and/or older adults. Supported by deArce Memorial Endowment Fund, The University of Toledo