Cardio-respiratory variability of healthy young subjects.

Young men have high cardio-respiratory variability reflecting the balance between robustness and adaptability to environmental and internal changes that characterize health. However, there are few biomarkers of this variability, thus it is important to determine the ranges for healthy men. Moreover, the health condition of women has considerable correlations with their menstrual cycle. Nevertheless, there is no complete characterization of how this cycle affects the overall physiological state, in particular the cardio-vascular and respiratory variability. To quantify these changes, cardio-respiratory time-series of young subjects are recorded daily during one month to determine the respiratory and heart-rate variability. As an initial proof of concept, four males (control group) and four females performed three maneuvers (clinostatism, rhythmic breathing at 0.1 Hz, and orthostatism) on a 5-minute interval. We also collected data on the circadian rhythm through physical activity and skin temperature. Females' menstrual cycle phase is determined from a clinical interrogation, physiological indicators of the cycle (cervical mucus fluidity and temperature elevation) and hormone determination by blood and urinary samples. Physiological time series of heart rate and breathing dynamics are less variable in women than in men, maybe due to the protective function of hormones, but to have conclusive remarks requires a study on a larger population. [ABSTRACT FROM AUTHOR]