Analysis of cardiorespiratory phase coupling and cardiovascular autonomic responses during food ingestion.

The present study analyzed whether the phase coherency (λ) of respiratory sinus arrhythmia (RSA) is altered by food ingestion in healthy young subjects. After 5min of resting control, 13 healthy volunteers were asked to eat a solid meal with access to water at their own pace, followed by 5min of the postprandial state. The R-R interval (RRI), beat-to-beat blood pressure (BP), and respiratory activity were recorded using electrocardiography, a Finapres device, and inductance plethysmography, respectively. The stroke volume was calculated by the pulse-contour method from continuous BP measurement, and the cardiac output (CO) was obtained by multiplying the stroke volume by the heart rate. From the oscillatory signals of RSA and respiration, λ was computed; additionally, frequency domain indexes of the heart rate variability (HRV) were calculated using a short-time Fourier transform. A steady-state 3-min resting period (R), food ingestion period (FOOD), and the first 2-min and the last 3-min of the post prandial period were analyzed separately. We also compared the responses to gum chewing (GUM) and water intake (WATER) using the same protocol on separate days. A shortening of RRI and increases in BP and CO were observed in FOOD compared to R, suggesting a shift of sympathovagal balance toward sympathetic activation. Similar responses but smaller magnitudes were observed in the GUM condition, whereas only transient shortening of RRI was observed in the WATER condition. The HRV indexes did not show any significant changes in response to GUM and WATER but sympathovagal balance was shifted in favor of sympathetic dominance in FOOD. λ decreased during all of the conditions. There was a significant negative correlation between λ and the indirect measure of sympathovagal balance. These results suggest that ingestion of food induces enhanced cardiac sympathetic activity and that a phase coherence of RSA could provide a sensitive measure for evaluating the cardiac autonomic profile.