PMID: 19198187Feb 10, 2009

The ventilatory response to isocapnic hypoxia during head-down tilt

Rossiĭskii fiziologicheskiĭ zhurnal imeni I.M. Sechenova
N P AleksandrovaV M Baranov

Abstract

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.

Related Concepts

Anoxemia
Dioxygen
Respiration
Expiratory Airflow
Rats, Wistar
Trendelenburg Position (Finding)
Carbon Dioxide
Carotid Arteries
Drug Resistance
Head

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