Research project PX/7/LP/11 (Research action PX)
This proposal was based on previous experiments performed in microgravity (µg): Euromir-95 and Neurolab STS-90, respectively 6 months and 15 days in µg. Our results have shown that heart rate (HR) decreases in µg, shows an adaptation during the flight, increases on return to normal gravity and remains high up to 15 days after return. In addition, it was demonstrated that the analysis of the heart rate variability (HRV), specially its respiratory component, the respiratory sinus arrhythmia (RSA), can bring new understanding to the adaptation of the autonomic control of HR and the cardio-pulmonary system to µg. Our observations, and previous studies, show that an adaptation of the autonomic control of HR occurs in µg and that this adaptation is, at least partially, responsible of the orthostatic intolerance that astronauts endure after exposure to µg. As severity of orthostatic intolerance increases with exposure to µg, this could be a potential hazard for longer spaceflight, especially for the accomplishment of a human mission to Mars. Respiratory movements, electrocardiogram, continuous blood pressure (BP) and thoracic electrical impedance were non-invasively measured during 5 controlled tidal breathing (CTB) protocols. These protocols were chosen because of their simplicity to perform and because they allow the analysis of how the autonomic nervous system regulates HR. Indeed, the spectral analysis of HRV as well as the amplitude and phase of the RSA are studied as non-invasive markers of the sympathetic-parasympathetic balance of the autonomic control of HR. The amplitude of RSA increases with the breathing period. The proposed protocol, imposing multiple controlled breathing frequencies, allows studying this relationship between breathing period and amplitude of RSA which is a window on the autonomic control of HR. Previous studies (Neurolab study) have shown that 15 days after return to normal gravity, cardiac parameters had not yet reached preflight values. This proposal, with measurements during week 3 and 4 after landing, should shed light on the duration of the readaptation process to normal gravity for the cardio-respiratory interactions. In addition to HRV analysis, the measurement of thoracic electrical impedance allows the determination of pulse transit time (PTT) and systolic time intervals (Pre Ejection Period and Left Ventricular Ejection Time), before and after the flight. Experiments performed during the 29th ESA parabolic flight campaign demonstrated the strong gravity and posture dependence of these parameters. In addition, these parameters are also influenced by autonomic regulation. Therefore, they are independent measurements and should be helpful in the interpretation of alterations of the different autonomic components and in the study of the process of readaptation to normal gravity.
Satellite(s) or flight opportunity(ies):
- International Space Station (Odissea Mission)
Field of research:
Life Science: Human Physiology
