[The ventilatory response to isocapnic hypoxia during head-down tilt].
The ventilatory response to isocapnic hypoxia was studied using rebreathing techniques in anesthetized and tracheostomized rats both in supine and in head-down tilt position (HDT-30 degrees). Hypoxic responses were calculated by the slope of ventilation against end tidal P(A)O2. The end-tidal P(A)CO2 was kept constant by varying expired gas flow through a CO2-absorbing bypass. The rebreathing was continued until P(A)O2 had fallen to between 70 +/- 3 and 50 +/- 2 mm Hg. The obtained results demonstrated that the maximal minute lung ventilation was 269 +/- 30 % during rebreathing test in supine position and 117 +/- 21% in the head-down tilt. It was also shown that the slopes of the relationship between minute ventilation and the decrease of end tidal P(A)O2 was 3-fold greater in supine than in HDT. The body position seems to affect the ventilatory response to isocapnic progressive hypoxia. In general, it may be a result of hemodynamic conditions alteration which increased respiratory resistive loads, changed the functional condition of carotid hemoreceptors and baroreceptor activity that modulate ventilatory response to chemoreceptor stimulation.
Aleksandrova
N P
NP
Donina
Zh A
ZhA
Danilova
G A
GA
Tikhonov
M A
MA
Baranov
V M
VM
D000818:Animals; D018475:Head-Down Tilt; D000860:Hypoxia / Q000378:metabolism / Q000503:physiopathology*; D010100:Oxygen / Q000378:metabolism; D012123:Pulmonary Ventilation; D051381:Rats; D017208:Rats, Wistar; D012119:Respiration
D010100:Oxygen