Associations between morning heart rate variability and ambulatory blood pressure characteristics in young adults.

We aimed to quantify associations between resting heart rate variability (HRV) and ambulatory blood pressure (BP) characteristics in young adults. Thirty-two apparently healthy young adults (50% male) were included in the study. Short-term HRV was obtained via electrocardiography in the laboratory following an overnight fast to determine the mean RR interval, standard deviation of normal RR intervals (SDNN), and root-mean square of successive differences (RMSSD). Participants left the laboratory wearing an ambulatory BP monitor for 24 h to determine awake, asleep, and overall systolic and diastolic BP, and asleep BP dipping ratios. In males, higher SDNN and RMSSD were associated with lower asleep systolic and diastolic BP, and greater systolic BP dipping, with SDNN also associated with diastolic BP dipping (Ps <0.05). In females, higher mean RR, RMSSD, and SDNN were associated with lower awake diastolic BP, and RMSSD with lower overall diastolic BP (Ps <0.05). Our findings indicate potential sex differences in how cardiac-autonomic function associates with BP regulation throughout the day. In males, HRV showed stronger associations with nocturnal BP characteristics, whereas in females, HRV associations were more pronounced with daytime BP.