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C Ca ar rd di io ov va as sc cu ul la ar r c ch ha an ng ge es s d du ur ri in ng g a ac cu ut te e e ep pi is so od di ic c r re ep pe et ti it ti iv ve e h hy yp po ox xi ic c a an nd d h hy yp pe er rc ca ap pn ni ic c b br re ea at th hi in ng g i in n r ra at ts s The aim of this study was to investigate the acute haemodynamic changes observed during the repetitive inhalation of various gas mixtures in rats for HO alone and HO + HC, and to analyse the effects of vigilance and of the stress of gas administration.We studied 6 unanaesthetized Wistar rats chronically instrumented with an aortic catheter. Nitrogen, nitrogen + CO 2 mixtures and compressed air were randomly administered in a Plexiglass chamber for 10 s and then flushed by compressed air for 20 s. Two cycles were repeated every min for 10 to 12 min. The inhaled gas fractions (FI,O 2 , FI,CO 2 ) were monitored by O 2 and CO 2 analysers. Blood pressure (BP) was measured by a P23XL transducer. The blood gases were analysed by a 1306 IL meter.In control experiments, with compressed air alone, there were 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, whilst at FI,O 2 values from 0-0.05 systolic blood pressure (SBP) rose significantly (+25.3±25.7 (SD) mmHg) and HR decreased (-93.8±124.1 bpm). During HOHC, SBP rose (+35.1±26.4 mmHg) and HR decreased (-139.3±75.7 bpm), significantly more than in HO alone. SBP was linearly correlated with Pa,O 2 during HO (r=0.53) and also during HOHC (r=0.44) and was not directly related to Pa,CO 2 which has, nevertheless, an additive effect to HO. SBP rose with each challenge significantly more when the rats were awake than when asleep (behavioural sleep).We conclude that in this acute repetitive inhalation model, the rise in SBP is not related to gas stress or to Pa,CO 2 but to a decrease in Pa,O 2 and is enhanced by wakefulness.

This article describes an experimental attempt to condition breathing pattern in rats. In this experiment, a freely moving rat was first rewarded by an electrical stimulation of the medial forebrain bundle whenever inspiratory duration (TI) exceeded 300 ms. A bidirectional control was then used: TIs longer than 400 ms were rewarded, and then TIs shorter than 300 ms were rewarded. The frequency of TIs longer than 300 ms increased when this event was rewarded, further increased when TIs above 400 ms were rewarded, and decreased during reversal conditioning (TI < 300 ms). At the beginning of the experiment, stimulation caused increased arousal and motor activity, but after prolonged conditioning, the brain stimulation was associated with quiet wakefulness. Although the general procedure appears to be well-suited to the experimental study of voluntary breathing, some possible improvements are suggested for further, more extensive investigations.

An experimental study was conducted in rats to evaluate the sensitivity of the liver to infrared hyperthermia. A 15-min hyperthermia session treating only the liver was done in rats with a normal hepatic parenchyma and in rats with hepatocarcinoma induced by chronic 3’-diethylaminoazobenzene intoxication, at various ranges of intrahepatic temperature. In normal rats, 40–42 °C hyperthermia was well tolerated, but the mortality rate increased when the intrahepatic temperature exceeded 42 °C. In rats with tumors, a 40–42 °C hyperthermia session was well tolerated in case of small tumors, but resulted in a high mortality rate in case of large tumors. In all cases, death occurred as a consequence of liver injury. This study using a simple method of hyperthermia defines the thermosensitivity of the neoplastic or normal rat liver and provides a basis for further investigations on the effect of hyperthermia on experimental liver tumors.