Respiratory modulation and baroreflex control of heart rate in space

Paper number

IAC-08.A1.2.2

Author

Dr. Bart Verheyden, Belgium

Coauthor

Mr. Kurt Couckuyt, K.U. Leuven, Belgium

Coauthor

Mr. Jiexin Liu, K.U. Leuven, Belgium

Coauthor

Prof. André Aubert, University Hospital Gasthuisberg, Belgium

Year

2008

Abstract

Purpose: During everyday life, baroreflex-mediated cardiovascular adjustments are essential in maintaining blood pressure control on a beat-to-beat basis. In astronauts in space, gravitational pressure gradients do not arise in the circulation so that baroreflex function remains chronically unchallenged. This is likely to affect the neural control of heart rate and blood pressure; however the way in which this occurs is incompletely understood. We tested the hypothesis that neural cardiovascular control in space will be in between preflight standing and supine control.

Methods: We studied nine male cosmonauts who each took part in seven different space missions aboard the ISS (age 40 – 52 yrs, height 1.69 – 1.85 m, weight 67 – 90 kg). Data collection was performed between 30 and 45 days before launch in the standing and supine positions, and after 8 days into spaceflight. Cosmonauts were carefully trained to perform in-flight data collection by themselves. They were instructed to pace their breathing to a fixed rate of 12 breaths per minute (0.2 Hz) for a total duration of 3 minutes. The electrocardiogram and beat-by-beat finger arterial blood pressure were recorded at 1-kHz sample rate. Respiratory rate was evaluated using an abdominal pressure sensor. We used power spectral analysis to calculate respiratory sinus arrhythmia (RSA) as well as the low-frequency (0.04 - 0.15 Hz) powers of spontaneous oscillations in heart rate and systolic blood pressure. Baroreflex sensitivity (BRS) was estimated in the time domain using cross-correlation analysis. 

Results: We found that mean blood pressure as well as heart rate were highest in the standing position before spaceflight and returned to the pre-flight supine values after eight days into space. Accordingly, respiratory sinus arrhythmia and the spontaneous baroreflex sensitivity of heart rate were lowest in baseline standing position. The low-frequency oscillations in RR-interval did not differ across conditions, while those in systolic blood pressure were highest in the standing position before flight. All hemodynamic and spectral data from in-flight measurements were similar to the pre-flight supine condition. 

Conclusions: Our data show that both heart rate and blood pressure in space correspond to pre-flight supine values. In-flight cardiovascular control is further characterized by chronically increased vagal-cardiac modulation and suppressed sympathetic vasomotor activity, compared with the upright posture on Earth. We therefore have to reject our hypothesis that cardiovascular control after a week into spaceflight is shifted in between standing and supine control.

Abstract document

IAC-08.A1.2.2.pdf

Manuscript document

IAC-08.A1.2.2.pdf (🔒 authorized access only).

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