Blood mobilization from the liver of the anaesthetized dog

Abstract

SUMMARYThe abdominal circulation contains a high proportion of the total blood volume and this can change either passively in response to changes in vascular distending pressure or actively (termed a capacitance response) to changes in sympathetic nervous activity. The liver is the largest abdominal organ and this study was designed to evaluate its potential contribution to overall vascular capacitance and compliance. In chloralose anaesthetized dogs, the liver was vascularly isolated, perfused through the portal vein and hepatic artery at either constant pressures or constant flows and drained from the hepatic veins at constant pressure. Changes in vascular resistance were assessed from changes in inflow pressures or flows and hepatic blood volume was determined by differences between net inflow and outflow. During constant flow perfusion the change in hepatic volume (capacitance change) in response to supramaximal stimulation of sympathetic nerves at 16 Hz was (mean + S.E.M.) -2-40 + 0-61 ml (kg body weight)-'. This response was not significantly different during constant pressure perfusion. The changes in portal venous and hepatic arterial pressures during stimulation at constant flow perfusion were +0-67 + 0.13 and +4-92 + 0-67 kPa, respectively. The compliance of the liver, assessed as the change in volume to a change in hepatic venous pressure, was +544 + 0-18 ml kg-' kPa-. These results indicate that the liver has a major capacitance role, comparable to that of the canine spleen and, in addition, is highly compliant. No evidence was found to suggest that a sphincter on the hepatic outflow exists. Assuming similar responses occur in humans, who do not possess a large contractile spleen, the liver would be the most important controllable blood reservoir in the body.

Reflex control of splanchnic blood volume in anaesthetized dogs

“…This revealed that, although the splanchnic circulation did make a small contribution, the major part of the active response was from the liver, approximately 2 ml (kg body weight)¢. This value is only a little less than that which we previously measured from the isolated liver in response to direct sympathetic stimulation at 16 Hz (2·4 ml (kg body weight)¢; Noble et al 1998). Interestingly, in confirmation of our recent findings of the effects of direct sympathetic stimulation, there was no apparent passive response of the liver.…”

“…Because of this species variability, in all experiments in the present report we excluded responses from the spleen by firmly tying the splenic pedicle. The other major blood-containing organ in the abdomen is the liver, and we have recently examined its capacitance role in response to electrical stimulation of the splanchnic nerves, with portal venous and hepatic flows controlled (Noble et al 1998). These experiments showed that stimulation caused a reduction in hepatic capacitance of a magnitude similar to that seen in the canine spleen.…”

“…1982; Noble et al 1998). However, the splanchnic circulation (the gastrointestinal circulation and associated viscera which drain through the portal vein) is also likely to make a contribution.…”

Potential Effects of Aggressive Decongestion During the Treatment of Decompensated Heart Failure on Renal Function and Survival

“…This great compliance facilitates a relative pressure-volume disconnect allowing large changes in blood volume to be associated with small changes in pressure. In line with this physiology, filling pressures such as central venous pressure and pulmonary capillary wedge pressure have repeatedly demonstrated little to no correlation with measures of volume status such as circulating blood volume and hemodynamic response to fluid challenge (17,19-27). In addition to the inherently compliant nature of these vessels, their capacity can be greatly altered by changes in sympathetic tone with increased tone leading to a significantly altered pressure-volume relationship (9,18,27-29).…”

Fatigue and autonomic dysfunction in non-alcoholic fatty liver disease

“…3 Correlation between fatigue severity and change in average blood pressure from baseline (measured over 10 min) and on standing (first 10 min) in NAFLD patients a systolic blood pressure, b mean arterial pressure of advanced liver disease. In animal studies the normal liver and spleen have been demonstrated to function as major capacitance vessels which act as reservoirs of blood immediately available to respond to hypotensive stress [27,29,30]. Increased organ rigidity associated with the development of cirrhosis and portal hypertension could reduce the capacitance function of the liver and spleen, respectively, giving rise to blood pressure lability (although whether this is the case or, indeed, whether the liver and spleen even have the same capacitance function in humans remains to be determined).…”