Ventilatory and cardiovascular responses to hypercapnia after 20 days of head-down bed rest.
BACKGROUND
Few studies have attempted to investigate the influence of prolonged head-down bed rest (HDBR) on hypercapnic ventilatory chemosensitivity, and there are no data available regarding associated changes in arterial BP and heart rate (HR). The aim of this study was to clarify the influence of prolonged HDBR on ventilatory and cardiovascular responses to hypercapnia.


METHODS
There were five healthy men who participated in this study. Resting ventilatory and cardiovascular responses to hypercapnia were measured by means of Read's CO2 rebreathing method 4 d before and on the 19th day of HDBR. Measured variables included systolic and diastolic BP (SBP and DBP, respectively), inspired minute ventilation (VI), and end-tidal partial pressure of CO2 (PETCO2).


RESULTS
Ventilatory response to hyperoxic hypercapnia (deltaVI/ deltaPETCO2) decreased significantly on the 19th day of HDBR (1.42 +/- 0.65 to 0.90 +/- 0.41 L x min(-1) x torr(-1), p < 0.05). On the other hand, SBP, DBP, and HR responses (deltaSBP/deltaPETCO2, deltaDBP/deltaPETCO2, and deltaHR/deltaPETCO2) were unchanged.


CONCLUSIONS
The results from this study suggest that prolonged HDBR leads to diminished central hypercapnic ventilatory chemosensitivity.
Katayama
Keisho
K
Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, Japan. katayama@htc.nagoya-u.ac.jp
Sato
Kohei
K
Akima
Hiroshi
H
Ishida
Koji
K
Yanagiya
Toshio
T
Kanehisa
Hiroaki
H
Fukuoka
Hideoki
H
Fukunaga
Tetsuo
T
Miyamura
Miharu
M
D000328:Adult; D001510:Bed Rest; D002319:Cardiovascular System / Q000503:physiopathology*; D006801:Humans; D006935:Hypercapnia / Q000150:complications* / Q000503:physiopathology; D008297:Male; D016684:Prone Position / Q000502:physiology*; D012137:Respiratory System / Q000503:physiopathology*