Twenty-Four Hour Rhythms in Cardiovascular Physiology

Many physiological parameters, such as heart rate and blood pressure, display pronounced daily rhythms, with significant differences between day and night levels. The ability to anticipate the 24 h cycle of ambient light confers an adaptive advantage, allowing organisms to prepare for periods of activity and rest. Considering chronophysiology is essential when designing, conducting, and interpreting laboratory experiments because of the often considerable amplitude of the rhythms. This review introduces a straightforward mathematical tool to detect 24 h rhythms in physiological datasets. Next, the review examines 24-h diurnal rhythms in heart rate, QT interval, and blood pressure, based on telemetry recordings from conscious, freely moving mice. These examples illustrate how long-term, continuous monitoring of physiological parameters enables precise characterization of daily cycles when present. Furthermore, the large datasets obtained through methods such as telemetry make it possible to determine whether the observed rhythms are dependent on heart rate. Circadian and diurnal rhythms play an essential role in cardiovascular physiology, influencing key parameters such as heart rate and blood pressure. Considering chronophysiology is therefore essential when designing, conducting, and interpreting physiological studies.