CARDIOVASCULAR CHANGES DURING ACUTE EPISODIC REPETITIVE HYPOXIC AND HYPERCAPNIC BREATHING IN RATS

It has been shown that chronic repetitive ambient hypoxia, simulating pulmonary gas disturbances observed in apnoea, leads to systemic hyper tension in rats, However, the relative roles of hypoxia (HO), hypercap nia (HC), gas stress and vigilance on the cardiovascular changes have not yet been demonstrated, The aim of this study was to investigate th e acute haemodynamic changes observed during the repetitive inhalation of various gas mixtures in rats for HO alone and HO + HC, and to anal yse the effects of vigilance and of the stress of gas administration, We studied 6 unanaesthetized Wister rats chronically instrumented with an aortic catheter. Nitrogen, nitrogen + CO2 mixtures and compressed air were randomly hypoxemia administered in a Plexiglass chamber for 1 0 s and then flushed by compressed air for 20 s, Two cycles were repea ted every min for 10 to 12 min, The inhaled gas fractions (FI,O-2, FI, CO2) were monitored by O-2 and CO2 analysers, Blood pressure (BP) was measured by a P23XL transducer. The blood gases were analysed by a 130 6 IL meter, In control experiments, with compressed air alone, there w ere no significant acute changes in heart rate (HR) and BP. During HO there were no changes in HR or BP at FI,O-2 values from 0.05-0.14, whi lst at FI,O-2 values from 0-0,05 systolic blood pressure (SEP) rose si gnificantly (+25.3+/-25.7 (so) mmHg) and HR decreased (-93,8+/-124,1 b pm), During HOHC, SEP rose (+35.1+/-26.4 mmHg) and HR decreased (-139. 3+/-75.7 bpm), significantly more than in HO alone, SEP was linearly c orrelated with Pao, during HO (r=0,53) and also during HOHC (r=0,44) a nd was not directly related to Pa,CO2 which has, nevertheless, an addi tive effect to HO, SEP rose with each challenge significantly more whe n the rats were awake than when asleep (behavioural sleep), We conclud e that in this acute repetitive inhalation model, the rise in SEP is n ot related to gas stress or to Pa,CO2 but to a decrease in Pa,O-2 and is enhanced by wakefulness.