Influence of an acute fast on ambulatory blood pressure and autonomic cardiovascular control

Evidence suggests that intermittent fasting improves cardiovascular health by reducing arterial blood pressure, but contributing mechanisms are unclear. The purpose of this study was to determine the influence of an acute fast on hemodynamics, muscle sympathetic nerve activity (MSNA), and autonomic control at rest and during an arterial pressure challenge. Twenty-five young normotensive volunteers were tested twice, in the fed and fasted (24 h) states (randomized). Twenty-four hour ambulatory blood pressure was measured before an autonomic function test, which consisted of a 10-min period of controlled breathing (CB) at 0.25 Hz followed by 3, 15-s Valsalva maneuvers (VMs). We recorded the ECG, beat-to-beat arterial pressure, and MSNA throughout the autonomic test. Vagal-cardiac modulation via heart rate variability (HRV) was assessed in both time and frequency domains, cardiovagal baroreflex sensitivity (cvBRS) was assessed with linear regression, and stroke volume was estimated from pulse contour. All fed versus fasted comparisons presented are different at P < 0.05. Fasting reduced ambulatory mean arterial pressure (81 +/- 1 vs. 78 +/- 1 mmHg) and heart rate (69 +/- 2 vs. 65 +/- 2 beats/min). CB revealed enhanced HRV through increased RR intervals (992 +/- 30 vs. 1,059 +/- 37 ms) and normalized high frequency (HFnu) R-R interval spectral power (55 +/- 3 vs. 62 +/- 3%). Estimated stroke volume was higher after fasting (by 13%) as was cvBRS (20 +/- 2 vs. 26 +/- 5 ms/mmHg) and cvBRS during phase IV of the VM (9 +/- 1 vs. 12 +/- 1 ms/mmHg). MSNA (n = 12) did not change (16 +/- 11 vs. 15 +/- 8 bursts/min; P = 0.18). Our results show that acute fasting is consistent with improved cardiovascular health: such improvements are driven by reduced ambulatory arterial pressure and enhanced vagal-cardiac modulation.