Observations on the Pulmonary Arterial Blood Pressure in the Cat

Summary. The pulmonary arterial blood pressure was recorded in anaesthetized cats by means of a special cannula, according to MELLIN's technique. In most experiments the thorax was closed and the animal was breathing spontaneously. The pulmonary arterial pressure in 9 experiments averaged 23 cm water, or approximately 17 mm Hg, at an average systemic pressure of 132 mm Hg. The average ratio thus was about 1: 8, with the limits 1: 5 and 1: 14. Pressure variations of 1–2 cm blood synchronous with the breathing were regularly recorded. In one case, slow large waves of 1–2 minutes duration and about 5 cm amplitude were observed. Even great variations in the systemic blood pressure, elicited from the pressoregulating reflex mechanisms, were hardly accompanied by variations in the pulmonary arterial pressure. During muscular work a moderate rise in pulmonary blood pressure generally occurred, greater when air was breathed than when oxygen alone was administered. Clamping the pulmonary artery to one lung did not cause any change in systemic pressure (confirming LICHTHEIM and TIGERSTEDT) but caused a moderate rise in pulmonary arterial pressure. Breathing of pure oxygen lowered the pulmonary arterial pressure and oxygen‐lack raised it. Carbon dioxide 6.5–20.5 per cent in oxygen raised the pressure sligthly, but constantly. These effects were not influenced by vagotomy. The effect of injections of adrenaline, nor‐adrenaline, acetylcholine and histamine and of stimulation of pulmonary nerves were studied in some cases. The experiments seem to warrant the conclusion, that the regulation of the pulmonary blood flow is mainly mediated by a local action of the blood and alveolar gases leading to an adequate distribution of the blood through the various parts of the lungs according to the effeciency of aeration.