Clinical Pathophysiological Studies on the Effect of Induced Hypoxemia on the pulmonary Circulation : A Consideration on the Pathogenetic Mechanism of Shock Induced by Hypoxemia.

Abstract

While there are many reports as to the elevation of the pulmonary artery blood pressure during an induced hypoxemia, quantitative relationships between the change in respiration and that in the pulmonary circulation is not yet fully clarified in cases with different diseases. Many studies have been done in this department since 1954 by using the method of induced hypoxemia combined with the cardiac and venous catheterization on the blood circulation through various organs, such as the heart, brain, liver and kidneys, and the response to the induced hypoxemia has been studied in a variety of conditions. This paper aims to describe the author's study on the effect of induced hypoxemia on the pulmonary circulation and also his consideration on the relation between the pulmonary and the systemic circulation in normal subjects, patients with pulmonary tuberculosis and cardiac patients.Methods and Subjects Each subject was examined by the cardiac and venous catheterization method under the resting and fasting condition; with the catheter tip in a main pulmonary artery, the subject was made to breathe from a sourve of 10% O2 gas with half mask and Douglas bag for a period of 20 minutes.The pulmonary artery pressure was recorded by an electro-manometer at intervals of 5 minutes; the blood gas was measured on the mixed venous blood and arterial blood at the same time. The subjects examined 23 cases in total, including 5 normal subjects (Group A), 12 patients with pulmonary tuberculosis (Group B), 6 cases with cardiac diseases (Group C) consisting of 5 cases with mitral stenosis and one case of ventricular septal defect.Results(1) Respiration and O2 consumption : The rate of respiration and minute ventilation volume were increased in all groups, i.e., hyperventilation, and there was no significant difference among the groups. The rate of O2 consumption (per minute) was decreased in all groups; it was decreased more markedly in pulmonary and cardiac patients than in normal subjects, the difference being statistically significant.(2) Blood gas : The O2 contents were markedly reduced in the arterial blood and mixed venous blood. The recorded arterial blood O2 saturations were; normal subjects (62.8%), pulmonary tuberculosis (63.0%) and cardiac disease (59.8%). The mixed venous blood O2 saturations were : normal sebjects (42.6%), pulmonary tuberculosis (43.5%) and cardiac disease (42.5%). There was no significant difference among the groups. The CO2 contents of the arterial blood and mixed venous blood were slightly reduced in all groups, the decrease being more marked in the group of pulmonary tuberculosis than in other groups.(3) Systemic circulation : The mean brachial artery blood pressure was lowered in all cases, but relatively more markedly in pulmonary (10%) and cardiac patients (18.7%) than in normal subjects (4.4%).(4) Pulmonary Circulation : The mean pulmonary artery pressure was elevated in all groups; the degree of such elevation was obviously different from group to group and in ascending order as follows : normal subjects, pulmonary patients, cardiac patients. The elevation of the mean pulmonary artery pressure value per 10% decrease in oxygen saturation of the systemic arterial blood amounted to 1.3, 1.9, 3.3 mmHg respectively. The pulmonary "capillary" pressure was not altered in all groups.While the pulmonary blood flow was reduced in all groups, and it was then reduced more markedly in pulmonary (30.1%) and cardiac patients (29.8%) than in normal subjects (10%). The pulmonary vascular resistance was therefore increased in all groups and it was increased more markedly in pulmonary and cardiac cases than in normal subjects.The pressure work of the right ventricle was increased markedly (22 %) in normal subjects, but slightly (13%) in cardiac patients. [the rest omitted]