Quiet standing after carbohydrate ingestion induces sympathoexcitatory and pressor responses in young healthy males

Objective: To investigate the role of the sympathetic nervous system in the cardiovascular response to quiet standing in the postprandial state.

Method: Following a 30min pre-ingestion phase, 14 healthy young male subjects consumed a 600kcal carbohydrate-rich meal. Arterial blood pressure (BP) and heart rate (HR) were recorded for a further 120min. Measurements were obtained (Finometer) in both the supine (5min) and standing (5min) condition every 30min. Power spectral analysis of RR-interval and BP variability was calculated, and heart rate responses to the baroreceptor reflex were calculated to estimate spontaneous baroreflex sensitivity (sBRS). Derived stroke volume (SV) was measured to track changes to postural stress postprandially.

Results: Quiet standing increased RR-interval low frequency power, ratio of RR-interval low frequency power/high frequency power (ratio of RR LF/HF), and systolic BP low frequency power (SBP LF power), and decreased RR HF power and sBRS before, and after eating. After meal ingestion, SBP LF power increased and sBRS decreased in lying and standing conditions. During quiet standing postprandially, DBP and the mean arterial pressure increased (P<0.01). The increased BP is associated with increased SV (P<0.05) early postprandially, and increased SBP LF power (P<0.01) in the later postprandial phase. SBP LF power is inversely correlated with SV postprandially (P<0.001, R(2)=0.96).

Conclusion: The findings suggest a sympathetic activation mediated by baroreflex resetting. Quiet standing in the postprandial state enhances sympathetic outflow to the vasculature, increasing BP. SV may be a compensatory factor stabilising BP during quiet standing early postprandially.