Hypothermia-induced Haemostatic and Biochemical Phenomena. An Experimental Model.

Hypothermia (24°C) was induced in 7 healthy male dogs. Hematological, hemostatic and biochemical parameters were evaluated before the onset and after 3 h of hypothermia. Following hypothermia, there was a significant increase in red cell count, hematocrit and haemoglobin concentration. The white cell and platelet counts were decreased significantly and the mean platelet volume increased significantly. The activated partial thromboplastin time was significantly prolonged whereas the prothrombin time was unchanged. Associated with these changes there was a significant increase in serum glucose and a small increase in aspartate transaminase activity probably due to muscle leakage. No change occurred in the more liver-specific alanine transaminase. The arterial pH decreased and the changes in gasses observed as a result of hypothermia were compatible with a mixed respiratory-metabolic acidosis. The mean aortic blood pressure also dropped markedly. The hematological and hemostatic changes suggest that widespread tissue 'injury' occurs even in short term hypothermia with platelet activation and accumulation in the liver and spleen. This model of hypothermia may be of use in the study of the thrombotic diathesis observed in this condition and serve as a test bed for drugs of potential use in conditions such as Raynaud's syndrome and hypothermic surgery (e.g. coronary artery bypass).

[Primary effect of carotid body stimulation on left ventricular inotropism in swine]. / Efeito primário da estimulação do corpo carotideo sobre o inotropismo ventricular esquerdo no porco.

The cardiovascular response to carotid body stimulation has been a interesting and simultaneously controversial subject. In fact, several authors described different responses depending on the animal species used (cat, dog, rabbit, monkey), time of stimulation (short-term v. long-term) and experimental conditions and procedures. According to our experience, the response to carotid body stimulation with cyanide, in normal breathing dogs, consists in hyperpnoea, bradycardia with arterial blood pressure fall (by means of longer diastolic periods), followed by a marked rise in arterial blood pressure and heart rate, after curarization. Concerning the inotropic response to carotid chemoreceptors stimulation, there exists some controversial and even antagonic opinions. In fact, some authors describe a positive inotropic effect, others a negative inotropic effect, and others still defend no inotropic response at all. In the present work, the authors try to contribute to the solution of this problem, studying a group of animals (pig) anaesthetised with chloralose, in which the major modulators of the inotropic response to carotid body stimulation (ventilation; heart rate; and ventricular load conditions) were controlled. To the evaluation of cardiac contractile state, indexes derived from the systolic isovolumic phase were used (maximum left ventricular pressure, dP/dtmax; dP/dtmin) in all the animals. In some animals, other indexes were also used (Vmax, Vpm, (dP/dt)/DP40, Tau and PB). The authors concluded that, in the present experimental conditions, the primary response to carotid body stimulation, in the pig, includes a positive inotropic effect.

[Effects induced hypothermia on hepatic portal circulation]. / Effets de l'hypothermie provoquée sur la circulation portale hépatique.

Studies of the liver circulation in dogs during hypothermia, showed that portal blood flow is reduced with no significant changes of blood pressure and with important vascular resistance. These effects are probably due to the contraction of pre-capillaries sphincters.

[Effect of induced hypothermia on the systemic circulation]. / Effet de l'hypothermie provoquée dans la circulation systémique.

Studies of the systemic circulation in dogs (n = 5) during hypothermia showed that cardiac output, mean arterial pressure, total peripheral resistance, pulse rate, work L. V. is reduced and the stroke volume is increased. The authors think that these effects are probably due to metabolic alterations during hypothermia.

[Effect of induced hypothermia on the capillary circulation of the liver]. / L'effet de l'hypothermie provoquée dans la circulation capillaire du foie.

Micro-angiographic studies of the liver, in dogs under established hypothermy, showed that the contrast injected in the portal vein does not perfuse the sinusoidal structures. This fact is, probably, due to the contraction of pre- and post-capillaries sphincters. On the contrary, in dogs under normal temperature the injected contrast largely perfused the capillaries and all supra-heptic vascular system.