HEART-RATE VARIABILITY IN WOMEN DURING 40-HOUR PROLONGED WAKEFULNESS

Abstract

Heart-rate variability patterns of 18 women during a 40-h constant routine of prolonged wakefulness under controlled laboratory conditions were analyzed. The authors tested the circadian timing of the autonomic nervous system and the relationship between the sympathetic and vagal branches in women with both a functional disorder of vascular regulation (main symptom: cold hands and feet) and prolonged sleep onset and controls without these symptoms. Spectral analysis of R-R intervals during paced breathing episodes revealed significantly lower power values in the high-frequency band (HF; 0.15–0.4 Hz) but not in the low-frequency band (LF; 0.04–0.15 Hz), leading to a significantly elevated LF/HF ratio in the former group. A significant circadian rhythm in LF power and heart rate occurred in both groups, and a significant correlation was found between sleepiness and sympathovagal balance (r = .53, p < .05). These findings indicate not only an autonomic imbalance in the first group compared with controls, but also two strategies of the autonomic nervous system to fight against fatigue in women. One implies circadian control and the other homeostatic control, and both are reflected by the LF/HF ratio. (Author correspondence: [email protected])

Keywords:

• Autonomic nervous system
• Blood pressure
• Circadian rhythms
• Constant routine
• Heart rate variability
• Paced breathing
• Vascular dysregulation

ACKNOWLEDGMENTS

We are very grateful to Prof. Anna Wirz-Justice for helpful comments to the manuscript, Doreen Hartwich for discussion, and Sarah Chellappa and Jakub Späti for corrections. We thank also Claudia Renz, Marie-France Dattler, and Giovanni Balestrieri for their help in data acquisition and the volunteers for participating. This work was supported by the Swiss National Science Foundation grants 3100A0-102182/1 and 3200B0-116504/1 (to K.K.), the Gottlieb Daimler and Karl Benz Foundation, and the Schwickert-Stiftung.

Declaration of Interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.