Venous return and the physical connection between distribution of segmental pressures and volumes.

More than sixty years ago, Guyton and coworkers related their observations of venous return to a mathematical model. Showing steady-state flow (F) as proportional to the difference between mean systemic pressure (Pms) and right atrial pressure (Pra), the model fit their data. The parameter defined by the ratio (Pms - Pra)/F, first called an "impedance," came to be called the "resistance to venous return.

Open-loop (feed-forward) and feedback control of coronary blood flow during exercise, cardiac pacing, and pressure changes.

A control system model was developed to analyze data on in vivo coronary blood flow regulation and to probe how different mechanisms work together to control coronary flow from rest to exercise, and under a variety of experimental conditions, including cardiac pacing and with changes in coronary arterial pressure (autoregulation). In the model coronary flow is determined by the combined action of a feedback pathway signal that is determined by the level of plasma ATP in coronary venous blood, an adrenergic open-loop (feed-forward) signal that increases with exercise, and a contribution of pressure-mediated myogenic control. The model was identified based on data from exercise experiments where myocardial oxygen extraction, coronary flow, cardiac interstitial norepinephrine concentration, and arterial and coronary venous plasma ATP concentrations were measured during control and during adrenergic and purinergic receptor blockade conditions.

A critical analysis of the view that right atrial pressure determines venous return.

A. C. Guyton pioneered major advances in understanding cardiovascular equilibrium.