Two weeks of remote ischaemic preconditioning alters sympathovagal balance in healthy humans

New Findings What is the central question of this study?Delayed cardiovascular responses occur following a single bout of remote ischaemic preconditioning (RIPC). Is heart rate variability (HRV), a surrogate marker of cardiac vagal control, able to detect a delayed effect after a single bout of RIPC? Do repeated bouts of RIPC further alter HRV? What is the main finding and its importance?Indices of HRV indicated a shift in sympathovagal balance toward greater parasympathetic activity following 2 weeks of RIPC but not after a single bout of RIPC. Thus, repeated bouts of RIPC were necessary to elicit changes in autonomic function. Remote ischaemic preconditioning (RIPC), induced by brief periods of ischaemia followed by reperfusion, protects against ischaemia-reperfusion injury and improves microvascular function. However, the effect of RIPC on autonomic function remains unclear. We hypothesized that RIPC, administered as a single bout or repeated over a 2-week period, will increase markers of cardiac vagal control measured by heart rate variability (HRV). Thirty-two young adults performed a single bout (n = 13), repeated bouts (n = 11), or served as a time control (n = 8). RIPC sessions consisted of four repetitions of 5 min unilateral brachial artery occlusion interspersed by 5 min of reperfusion. For the single bout protocol, resting lead II electrocardiogram (ECG) was collected before and 24, 48, 72 and 168 h post-RIPC. The repeated bout protocol consisted of three 4-day periods of RIPC training, each interspersed by a 1-day break. Similar to time controls, ECG was collected before and 24 h after the last RIPC bout. HRV was analysed by power spectral density and symbolic dynamics using 350-beat ECG segments. After a single bout of RIPC, no changes in HRV were observed at any time point (P > 0.05). After 2 weeks of repeated RIPC, the percentage of zero-variation fragments (baseline = 13.1 +/- 1.9%, post-RIPC = 6.9 +/- 1.5%,P < 0.05) and the LF/HF ratio decreased (baseline = 1.1 +/- 0.2, post-RIPC = 0.7 +/- 0.1,P < 0.01), whereas the percentage of two-variation fragments increased (baseline = 42.9 +/- 3.6%, post-RIPC = 52.5 +/- 3.0%,P < 0.01). These data indicate that repeated RIPC is necessary to elicit changes in sympathovagal balance, specifically resulting in increased vagal and decreased sympathetic activity.