Abstract
Using an isolated lung the effects of halothane on hypoxic pulmonary vasoconstriction (HPV) were studied in the presence of cyclooxygenase blockade. The pulmonary vasculature can be divided into arterial, middle and venous segment resistances. Analysis of the vascular pressure-flow relationship further separates resistance into a flow dependant resistance (1/slope) and a zero-flow pressure intercept (Pcrit). We ventilated six lobes with control (35 per cent O2) and hypoxic (three per cent O2) gas mixtures with the addition of either 0, 0.5, 1.0, or 2.0 per cent halothane. We found that after addition of indomethacin (5 mg · kg− 1), ventilation with three per cent O2 increased total resistance by 87 per cent over baseline with the increase primarily in the middle vascular segment. During normoxic ventilationPcrit was 7.9 cm H2O and this increased significantly with hypoxia to 11.5 cm H2O). Only 2.0 per cent halothane blocked the increases in middle segment resistance and inPcrit. We conclude that following cyclooxygenase blockade, halothane inhibits HPV by acting on middle segment vessels.
Résumé
Nous avons étudié, sur poumon isolé, les effets de l’halothane sur la vasoconstriction pulmonaire hypoxique (HPV) en présence d’inhibiteur de la cyclooxygénase. Les secteurs artériel, médian et veineux contribuent successivement à la résistance vasculaire pulmonaire. En analysant les courbes pressiondébit, on peut calculer la résistance (1/pente) et la pression d’ouverture (PCRIT). NOUS ventilions six lobes pulmonaires avec de I’oxygène à 35 pour cent (contrôle) ou à trois pour cent (hypoxie) en y ajoutant 0, 0,5, 1,0 ou 2,0 pour cent d’halothane. Après l’injection de 5 mg · kg− 1 d’indométhacine et avec trois pour cent d’O2, la résistance totale augmentait de 87 pour cent par rapport au contrôle, surtout en secteur médian. LaPcrit était significativement moins élévee en condition normoxique, passant de 7,9 à 11,5 cmH2O en condition hypoxique. Il fallait deux pour cent d’halothane pour bloquer cette augmentation de resistance et de pression d’ouverture. Done, malgré une inhibition de la cyclooxygénase, l’halothane renverse l’HPV du secteur vasculaire médian.
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Supported by the ICI Pharma Canadian Research Award in Anaesthesia. Also supported by a grant from the Saskatchewan Heart Foundation.
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Johnson, D., Mayers, I. & Hurst, T. Halothane inhibits hypoxic pulmonary vasoconstriction in the presence of cyclooxygenase blockade. Can J Anaesth 37, 287–295 (1990). https://doi.org/10.1007/BF03005577
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DOI: https://doi.org/10.1007/BF03005577