Acute Effects of Water- Versus Land-Based Exercise on Heart Rate Variability in Heart Transplant Recipients

Abstract

BACKGROUND AND PURPOSE: Heart transplant (HT) results in complete cardiac denervation, promoting autonomic nervous system (ANS) imbalance follows transplantation surgery, despite signs of partial cardiac reinnervation. Land-based exercise (LEx) is a well-established intervention for HT recipients, and the regular practice improves heart rate variability (HRV). On the other hand, water-based exercise (HEx) promotes important muscular and cardiovascular benefits in several diseases. However, its acute effect on ANS activity of HT recipients is unknown. Our purpose was to analyze the acute effects of HEx versus LEx on HRV in HT recipients. METHODS: Eighteen (6 female) clinically stable HT recipients (age: 46±10years; body mass index: 26±5; time of HT: 5±3 years) performed 30 min of HEx (heated swimming pool), LEx (treadmill walking) and no-exercise control sessions in a random order (2-5 days between each sessions). HEx and LEx aerobic exercise intensity was set between “relatively easy and slightly tiring” (11-13 in Borg scale). Instantaneous HR and RR interval were acquired before, immediately after and in the recovery (30 minutes after) of each session. HRV was analyzed by frequency domain methods and power spectral density was expressed as normalized units (nu) at low (LF) and high (HF) frequencies, and as LF/HF. RESULTS: Baseline and post-exercise HRV were not different between interventions. However, increased LFnu and decreased HFnu (P=0.01) were observed post 30 minutes of HEx (LFnu: 34.7±36; HFnu: 65.3±36), but not after LEx (LFnu: 27±30.1; HFnu: 72.2±29.8), when compared with control session (LFnu: 23.1±20.3; HFnu: 73.7±23.8). CONCLUSIONS: Increased LFnu and decreased HFnu were observed only after HEx. These results suggest that HEx may have a potential as a new therapeutic approach to attenuate ANS imbalance after heart transplantation.