PHRENICOTOMY IN THE RAT - ACUTE CHANGES IN BLOOD-GASES, PH AND BODY-TEMPERATURE

Adult male rats were used to compare blood gases, pH and body temperature (Tb) before and after acute bilateral phrenicotomy. Under anaesthesia a femoral artery was catheterised and ties were placed round the phrenic nerves of seven rats (PNX group), while in five rats the ties were placed in the vicinity of the phrenic nerves (SHAM group). Twenty-four hours after surgery arterial blood samples were collected during quiet wakefulness (QW) and grooming (G), before and 1 h after the ties were pulled, and analysed for P(O2) P(CO2) and pH. No changes were detected in the SHAM samples taken before and after the ties were pulled. In the PNX group a significant decrease in Th occurred (QW, 0.6-degrees-C; G, 1.5-degrees-C). Following PNX Pa(O2) decreased by 11.2 mmHg (QW) and 10.0 mmHg (G); Pa(CO2) increased by 2.6 mmHg (QW) and 2.4 mmHg (G) and pH fell by 0.04 (QW) and 0.03 (G). All changes except in Pa(CO2) (QW) were significant. It is concluded that the changes in Th, blood gases and pH which follow phrenicotomy in the rat are due to an increase in dead space ventilation (VD) and a small reduction in alveolar ventilation (VA) associated with a faster, shallower pattern of breathing.