The effect of oxygen on the fibrinolytic enzyme systemin vivo

Abstract

SUMMARY Arterial hypoxia has been accepted as a potent stimulus to increased fibrinolytic activity in vivo. This study has shown that significant levels of arterial hypoxaemia induced in healthy volunteers by breathing a hypoxic gas mixture have failed to induce changes in the fibrinolytic enzyme system. Hypoxia has been widely accepted as a potent stimulus to increased plasma fibrinolytic activity in vivo (Kwaan and McFadzean, 1956;Clarke, Orandi and Cliffton, 1960;Cliffton, Clarke, and Murphy, 1961); in view of the physiological importance of this suggested relationship, the present study was set up to investigate the effect on plasma fibrinolytic activity ofhealthy volunteers ofvariations in inspired oxygen content. Materials and MethodsTen normal healthy volunteers aged 22-40 years, having given their full informed consent, were included in the study. Over a 30-minute period each was exposed to a 15-minute period breathing oxygen at an inspired concentration of 11-5% and a 15-minute peroid breathing oxygen at an inspired concentration of 21 %.The subjects were paired and the second in each pair breathed the gases in the opposite sequence to the first. The order in which the gases were breathed was randomly allocated to the five pairs. This technique was used to ensure that equal numbers breathed the gases in each order. The subjects were not informed of the sequence in which the gas mixtures were used. Two gas cylinders of air mixtures of 11-5 % and 21 % were prepared and joined by a Y-connector and tubing via a 4-litre anaesthetic bag to a one-way valve box and mouthpiece. Seated comfortably at rest, with a nose clip in position, each subject breathed air from one cylinder via the anaesthetic bag and the expired air was exhausted to atmosphere. After 15 minutes to allow adequate time for equilibration of gases in the body and for Received for publication 8 March 1971. changes in plasma fibrinolytic activity to occur, a sample of venous blood was obtained. The air supply was changed to the other gas cylinder and the subject breathed the new gas mixture with a different oxygen concentration for a further 15 minutes. In three subjects small samples of air from the end of each expiration were collected in a bag over the last five minutes of each 15-minute period using an automatic end-tidal sampler (Mills, 1971); the total volume was then analysed for its oxygen concentration. An estimate of the concentration of oxygen in the alveolar gas was, therefore, obtained and this afforded confirmation that the partial pressures of oxygen in the arterial blood were within the range predicted for each level of oxygen presented to the subject in the inspired air.The procedure was then repeated with the same volunteers using gas mixtures with oxygen concentration of 21 % and 43-5 %. End-tidal sampling was used in nine subjects to confirm that the partial pressure of oxygen in the arterial blood was within predicted levels.Whole blood was obtained at rest, and again immediately after each mixture was breathed, by clea...

Studies on the Blood Fibrinolytic System in Congestive Cardiac Failure

“…Hypoxaemia of mixed venous blood, which reflects decrease in cardiac output (Muir, Kirby, King & Miller, 1970), might affect the release of plasminogen activator from venous endothelium. However, it has been shown that acute hypoxaemia in healthy subjects does not induce changes in the fibrinolytic enzyme system (Cunningham, Boyd, Windebank, Moran & McNicol, 1971), and in subjects with congenital heart disease fibrinolytic activity does not correlate with oxygen saturation (Menon, 1969). Indeed, in some cases of cyanotic heart disease fibrinolysis is accelerated (Goldschmidt, 1969;Johnson, Abildgaard & Schulman, 1968); this was noted in the four patients with congenital heart disease of the present study.…”