Attenuation of hypoxic ventilation by hyperbaric O2: effects of pressure and exposure time.
Hyperoxia affects O2 chemoreception in the highly perfused carotid bodies and causes a reduction of the ventilatory hypoxic drive (HD) as was shown for anesthetized cats and awake rats. We looked for a quantitative description of such an effect on HD as a function of both O2 pressure and exposure duration. Ventilation of rats was measured using the barometric method before and after hyperbaric O2 (HBO) exposure, at either air, 80% O2, or 4% O2. We used three exposure durations: 180, 550 and 900 min. The O2 pressure ranged between 1.2 and 3.0 ATA. At each time duration we used four to five groups of rats at a range of O2 pressures that yielded the full scale of effect on HD but avoided obvious lasting difficulties in breathing. HBO caused a reduction of breathing frequency and elevation of tidal volume in both air and 80% O2 but almost no change in minute ventilation. Hypoxic minute ventilation (4% O2) decreased after HBO, mainly through reduced frequency. HD was described by a power function of O2 pressure for each HBO duration. HD did not decline below 20% of the full control response. Ventilatory HD diminution is pictured as a function of both O2 pressure and HBO duration. The dependency of HD on exposure time and on pressure is similar to other known toxic effects of HBO.
Liberzon
I
I
Israel Naval Hyperbaric Institute, Haifa.
Arieli
R
R
Kerem
D
D
D000818:Animals; D001274:Atmospheric Pressure; D002344:Carotid Body / Q000503:physiopathology; D002628:Chemoreceptor Cells / Q000503:physiopathology; D006931:Hyperbaric Oxygenation; D000860:Hypoxia / Q000503:physiopathology / Q000628:therapy*; D008297:Male; D051381:Rats; D012119:Respiration; D013997:Time Factors