Partition of the venous return to the heart

Abstract

The experiments described in this paper were undertaken to supplement knowledge about the relative rates of blood flow in the superior and inferior venae cavae. During the investigations some of the factors which modified the rates of flow in the venae cavae were examined and the rates of flow in some other veins were measured. METHODSExperiments were performed on dogs (9-21 kg) anaesthetized with chloralose (041 g/kg intravenously). Briefly, the principle of the method was to feed blood into the right atrium at a controlled and measured rate, and to measure the venous return flow in the superior vena cava (SVC), inferior vena cava (IVC) or other veins. The arrangement of the apparatus and preparation is shown in Fig. 1.Blood was drained from the veins by right-angled glass cannulae connected to outflow tubes which led to the flow recorders. The openings of these outflow tubes were set at the level of entry of the SVC into the right atrium.The flow recorders (Fig. 2) were a modification of the type described by Stephenson (1949). In the original form described by Stephenson, there was a back pressure into the vein as the flow increased and there was also a tendency for the calibration of the recorder, to be upset because of a gradual gas exchange between the venous blood and the air in the flow recorder. These two faults were eliminated by introducing an air break between the outflow tube and the recorder and by arranging a by-pass arm so that at any time the uninterrupted venous flow could be diverted from the recorder while the zero position was being re-set. By using tubes of various diameters at the bottom of the recorder the same recorder could be used for different ranges of flow. The ranges usually employed for different veins were: IVC, 250-1300 ml./min; SVC, 150-800 ml./min; femoral and jugular veins, 10-120 ml./min.After passing through the flow recorders the blood was collected into a Perspex trough and returned to the main reservoir. This reservoir was fitted with a level gauge connected to a volume recorder so that alterations in the distribution of blood between the reservoir and the animal could be measured.Blood was pumped from the reservoir through a flow recorder to an input reservoir from which the heart was fed. The height of the blood in the input reservoir was kept constant by an overflow tube, and the input to the heart was regulated by a screw clip on the tube leading to the right atrium. The blood pump was a double Dale-Schuster pump with a valve chamber modified so that an output of up to 2-3 1./min could be obtained (Coleridge & Hemingway, 1953).

The effect of haemorrhage on venous return and regional blood flow in the anaesthetized cat

“…This confirms the findings of Coleridge & Hemingway (1958) and Howarth (1962). Howarth showed that this response was attributable, at least in part, to cerebral vasodilation.…”

Caval long‐circuit in the dog

“…Though our two series of perfusions differed in many respects, the superior vena cava carried a similar proportion of the total caval flow (30 and 27 %) and these figures are in close agreement with the determinations of Coleridge & Hemingway (1958), who found that the superior 37 38 C. V. GREEN WAY AND F. HO WARTH vena cava accounted for 30 % of the combined caval flows. It should be noted that in the second of these three groups of experiments the azygos vein was intact, while in the other two it was tied.…”

“…In intact dogs the mean cardiac outputs after 3-4 hr of pentobarbitone anaesthesia were 1300 ml./min by a dye-dilution method, 1700 ml./min by a pulse-contour method and 1400 ml./min by a Fick procedure (Nash et al 1956;, while in our preparations the mean total venous return which omits azygos, coronary and bronchial flows was 963 ml./min. We found, as did Coleridge & Hemingway (1958), that the size of the total caval flow appeared to be determined, to some extent, by the skill and experience gained in making the preparations, and in our last 6 experiments the mean total caval flow was 1100 ml./min. The difference between this value and those ofNash et al and Howell & Horvath may not be significant.…”

“…W6gria et al (1943) and Coleridge & Hemingway (1958) commented that the total caval flows in their preparations were lower than the cardiac output usually attributed to anaesthetized dogs. It has been shown that the cardiac output of both cats (Baxter, Cunningham & Pearce, 1952; Grundy & Howarth, 1957) and dogs (Nash, Davis & Woodbury, 1956; declines during the course of prolonged pentobarbitone anaesthesia and many of our dogs had been anaesthetized for 3-4 hr before total caval long-circuit was established.…”

The PRESENCE OF Β‐ADRENERGIC RECEPTORS IN THE HEPATIC VASCULATURE

“…By accommodating one-quarter of the total cardiac output per minute (Bender & Horvath, 1963, and by holding 25-30% of the total blood volume, the liver is the principal determinant of the venous return to the heart (Coleridge & Hemingway, 1958;Knisely, Harding & Debacker, 1957).…”