Nocturnal peak in cardiac baroreflex effectiveness aligns with nocturnal trough in systolic blood pressure in young healthy adults: Possible circadian effects

Figures

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  FIGURE 1. Forced desynchrony protocol. Participants completed a 30‐h protocol, blinded to the time. After 2 h of admission period, all participants underwent five consecutive 6‐h days (i.e., 4 h wake period and 2 h of sleep opportunity). White bars represent room lighting at 150 lux; black bars, sleep opportunities in total darkness (<1 lux); and gray bars, dim light wake periods below 8 lux. Blue drops represent salivary sampling, black upside‐down arrows represent measurements (EKG, beat‐to‐beat blood pressure, and vascular ultrasound), and brown bars represent isocaloric meals.

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  FIGURE 2. Circadian variation on resting absolute systolic blood pressure (BP) (a) and diastolic BP (b), cardio‐vagal baroreflex effectiveness index (BEI) (c), brachial artery vascular conductance (VC) (d), cardio‐vagal baroreflex sensitivity (BRS) (e), vascular endothelial function (VEF) (f), low‐frequency of absolute systolic BP variability (g), and brachial artery positive hyperemic shear rate (h). Models plotted with continuous lines are significant (p < 0.05), while dashed lines are not statistically significant (p > 0.05). The dashed red vertical line in all graphs indicates the trough of systolic BP based on the model. Individual data are shown plotted in 90° circadian bins and aligned with 0° representing the dim light melatonin onset, and habitual sleep represents the average clock time for the self‐selected sleep period at home (bottom X axis). Top X axis has clock time.

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  FIGURE 3. Circadian variation on up‐up and down‐down sequences of cardio‐vagal baroreflex effectiveness index (BEI) (a, b). Data were plotted for each participant into three 8‐h circadian phase bins representing circadian morning, afternoon, and night. To calculate the 8‐h bin, we defined circadian night based on each participant's dim‐light melatonin onset time. Bars represent mean values, and error bars represent standard deviation. Brackets indicate p‐value from multiple pairwise comparisons after a significant interaction in the one‐way ANOVA for repeated measures.

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  FIGURE 4. Average of the total number of systolic BP sequences (a) and average number of all validated baroreflex sequences (b) during each wake period across the forced desynchrony protocol. Data were plotted for each participant into the 5 wake periods. Bars represent mean values, and error bars represent standard deviation.