Journal of applied physiology
-
The volume-pressure relationship of the vasculature of the body as a whole, its vascular capacitance, requires a measurement of the mean circulatory filling pressure (Pmcf). A change in vascular capacitance induced by reflexes, hormones, or drugs has physiological consequences similar to a rapid change in blood volume and thus strongly influences cardiac output. The Pmcf is defined as the mean vascular pressure that exists after a stop in cardiac output and redistribution of blood, so that all pressures are the same throughout the system. ⋯ A change in Pmcf provides a uniquely useful index of a change in overall venous smooth muscle tone if the blood volume is not concomitantly changed. The Pmcf also provides an estimate of the distending pressure in the small veins and venules, which contain most of the blood in the body and comprise most of the vascular compliance. Thus the Pmcf, which is normally independent of the magnitude of the cardiac output, provides an estimate of the upstream pressure that determines the rate of flow returning to the heart.
-
Quantitative relationships in CO2 transport and exchange processes were combined for use as the basic components of an original mathematical model for the calculation of venoarterial blood CO2 concentration difference (v-aDCO2). This is calculated as the sum of the increment in CO2 concentration (CCO2) related to the increase in CO2 tension (delta P) from arterial to venous value at constant O2 saturation (delta CCO2/delta P) and of the increment in CO2 concentration related to the decrease in O2 saturation (delta S) from arterial to venous value at constant CO2 tension (delta CCO2/delta S). ⋯ The results provided by the model compared remarkably well with the results of previously published measurements (r2 = 0.96-0.99). This new model allows one to overcome some of the limitations implicit in previously available methods and provides a useful tool for the assessment and monitoring of hemodynamic, metabolic, and O2-CO2 exchange patterns in whole body and regional vascular beds.