Does Respiratory Sinus Arrhythmia Increase Nocturnal Blood Pressure?

Abstract

By ambulatory blood pressure monitoring (ABPM), nocturnal blood pressure (BP) may increase before heart rate (HR), but the details are unknown.Among 102 participants who underwent ABPM, > 90% on hypertension treatment, the averaged BP (HR) data were examined for the time at which the BP (HR) increased significantly above the mean midnight BP (HR) between 3:00 AM - 9:00 AM in all patients and in subgroups divided by clinical variables. Participants were also divided according to the respiratory sinus arrhythmia (RSA) index, which is the ratio of the longest and shortest RR intervals obtained under normal breathing, and the effects of RSA on the nocturnal hemodynamics were examined.The average age of the patients was 70 ± 11 years, and there were 47 (46.1%) males. After midnight, the BP increased and was significantly greater than the midnight BP at 5:00 AM. The time of significant increase in BP was affected by clinical variables and the RSA index; an RSA index < 5% (> 10%) was associated with the earliest (latest) time of BP increase. However, the HR remained unchanged until 7:00 AM or later. According to the ABPM data, a discordant time course between BP and HR and the effect of RSA were evident during the nocturnal period.BP increased earlier than HR toward dawn, and this phenomenon was affected by clinical variables. A low RSA index facilitated the onset of BP increase. The underlying mechanisms and clinical significance of the role of RSA in circulatory regulation remain to be investigated.