H. W. Fritts

THE EFFICIENCY OF VENTILATION DURING VOLUNTARY HYPERPNEA: STUDIES IN NORMAL SUBJECTS AND IN DYSPNEIC PATIENTS WITH EITHER CHRONIC PULMONARY EMPHYSEMA OR OBESITY

The ventilatory apparatus is analogous to a mechanical system composed of an engine coupled to a pump. The engine comprises the chest wall and the diaphragm, while the pump embraces the airways and the lungs. Although the two units operate as a single assembly, their functions are distinct. The engine converts metabolic energy into mechanical work; the pump translates this work into a rhythmic exchange of air. According to this schema, the useful work of the chest wall and diaphragm is that performed on the surfaces of the lungs. Hence, the efficiency with which this work is accomplished is defined by the formula written below.

BLOOD FLOW THROUGH EACH LUNG IN MAN DURING UNILATERAL HYPOXIA

It is well established that pulmonary hypertension may be elicited in man by reducing the oxygen content of the inspired air. The mechanisms involved in this response to acute hypoxia, and the role of the individual segments of the pulmonary vascular tree in effecting this rise in pulmonary arterial pressure, are currently under investigation. In order to further analyze this phenomenon, a method has been developed for the separate measurement of blood flow through each lung in man. This method consists of a combination of (a) bronchospirometry, with each lung breathing a specifically selected oxygen mixture, (b) cardiac catheterization, and (c) arterial cannulation; this makes possible the application of the Fick principle, not only for the measurement of total blood flow, but also of blood flow through each lung. Previous attempts to partition pulmonary blood flow in man have been indirect, and have involved many assumptions (1). It is the purpose of this paper to 1) describe a method based on more direct data, and 2) present the results of studies concerning the effects of unilateral hypoxia upon the pulmonary circulation in man.

Estimation of Flow Through Bronchial-Pulmonary Vascular Anastomoses with Use of T-1824 Dye

A dye-dilution method devised to estimate the individual outputs of the ventricles has been used to assess the magnitude of the flow through bronchial-pulmonary anastomoses in patients with chronic lung disease. In 10 normal subjects the output of the left ventricle was, on the average, 0.9 per cent larger than the output of the right. In six patients with advanced pulmonary tuberculosis, the average value was 2.9 per cent, and in 11 patients with bronchiectasis 9.3 per cent. One patient, who had had her left main pulmonary artery ligated, exhibited an anastomotic flow of 20 per cent. In all groups the flow calculated from the Fick equation agreed within 20 per cent with that from the right ventricle. In the normal subjects and the patients with tuberculosis, the same general agreement between the Fick and the left ventricular output was observed. But in the patients with bronchiectasis and the woman with the ligated pulmonary artery, the Fick calculation underestimated the left ventricular output. This underestimation suggests that the blood traversing the bronchial-pulmonary anastomoses had an oxygen content approximating that in the systemic arterial blood.

Oxygen Consumption of Tissues in the Human Lung

A method for estimating the metabolic rate of the human pulmonary tissues is described. Six patients with far advanced pulmonary tuberculosis showed an average rate of 12 percent of the total oxygen consumption. A method for measuring the right ventricular output with an inert gas is also outlined, and the use of this approach to minimize errors in the estimation of the tissue metabolic rate is described.

Some Circulatory Effects of 5-Hydroxytryptamine in Man

Continuous infusions of small quantities of 5-hydroxytryptamine (5-HT) were made into the pulmonary artery in 7 human subjects. In only 1 instance was there an unequivocal rise in pressure in the pulmonary artery and this was accompanied by a rise in brachial arterial pressure. The most consistent effect of the drug was to raise the heart rate. There was no effect on the cardiac output. Single rapid injections of 5-HT were made into the right atrium in 3 other subjects. In 1 of these subjects the injection of 4 &mgr;g. per Kg. caused transient ventricular arrest and systemic hypotension followed by a sustained rise in pressure in the pulmonary and brachial arteries. The results of this study were thought to indicate the presence of a Bezold-like reflex. The rapid injection of 5-HT was therefore thought to be dangerous and the investigation was discontinued.

Effects of Acute Hypoxia on the Volume of Blood in the Thorax

Two different methods were used to study the effect of acute hypoxia on the volume of blood in the thorax. The first method entailed estimating the central blood volume by the Stewart-Hamilton dye-dilution technic; the second involved the use of a teeter-board. The 2 methods gave comparable results. Both indicated that the volume of blood in the thorax is not appreciably altered by hypoxia.

Influence of acetylcholine on human pulmonary circulation under normal and hypoxic conditions.

Summary Acetylcholine infused into the main pulmonary artery caused a slight fall in pulmonary arterial pressure when the subject breathed ambient air, but a greater fall in pressure after pulmonary hypertension had been produced by hypoxia. The fall in pressure was associated with either a constant or an increased cardiac output. The evidence suggests that acetylcholine causes vasodilata-tion in the lungs and that this action is largely dependent on the pre-existing tone of the pulmonary vessels.

Effect of elevating the wrist on the radial pulse in aortic regurgitation: Corrigan revisited

Five patients with severe aortic regurgitation had their intraarterial radial pulse recorded simultaneously with the external radial artery deflection of the other wrist. Recordings were made with the arms horizontal and repeated after elevation of the wrists, until the arms were vertical. Elevating the arm of a patient with aortic regurgitation increased the pulsation recorded over the radial artery, lowered mean intraarterial pressure, and reduced the pulse pressure. The results suggest that elevation increases the compliance of the arterial wall, primarily by moving the artery to a lower position on its pressure-volume curve. The same changes occurred in 5 normal subjects but were less pronounced.