Title: A closed-circuit heart-lung preparation.—Effect of alterations in the peripheral resistance and the capacity of the circulation
Abstract: Investigations of “resistance” and “capacity” effects in relation to the control which they exert upon the vascular system have been carried out by many physiologists, notably by Weber (1), Volkmann (2), Donders (3), de Jager (4), Bayliss and Starling (5), and L. Hill (6, 7). According to Weber, the rise in arterial blood pressure due to arteriole vaso-constriction is caused by an increase in peripheral resistance and by a diminution in the capacity of the circulation. Bayliss and Starling (5) brought forward evidence in favour of this view and pointed out that the venous pressure was in part determined by a balance between these two factors. In opposition to Weber’s view, L. Hill and Barnard (6) hold that capacity changes have no effect on the venous pressure since the vascular system is not filled to distension. In a later paper L. Hill (7) states that reduction in the capacity of the splanchnic area is of importance in so far as it increases the diastolic filling, and so the output of the heart, but that the mean hydrostatic pressure cannot be considered to contribute to this result. The part played by constriction of the veins in altering the venous and arterial pressure is discussed in a paper by Connet (8) in which a full bibliography is given. In a paper published in the ‘ Journal of Physiology ’ (9) I described a modification of Starling’s heart-lung preparation, in which the blood circuit was converted to a closed system, so as to imitate more closely the conditions ruling in the animal body, while maintaining the various factors fully under control of the experimenter. The arrangement is shown in fig. 1. The blood from the aorta flows through a cannula placed in the brachio-cephalic artery (A), the velocity of flow being recorded by a Pitot tube (B) or by a Henderson’s cardiometer. The peripheral resistance is regulated by a compressible fingerstall (D), a second resistance (D') being inserted for studying the effects of shunt circuits. The blood then passes to the venous reservoir (K) which consists of a rubber bag of approximately 250 c.c. capacity. The distal end of the venous reservoir is connected to the superior vena cava. A finger-stall (C) joined by a side tube to the arterial system represents the elasticity of the arterial sytem ; this finger-stall and the venous reservoir K when enclosed in plethysmographs enable the experimeter to study alterations in the volume of the systemic circulation.