Effects of Vasoactive Drugs on the Systemic and Splanchnic Circulation

This chapter reviews the methodology for circulatory studies and then focus on the hemodynamic effects of pharmacological agonists and antagonists of the a- and ß-adrenergic and serotonergic systems as well as the effects of nitrates. Patients with liver disease are known to have alterations in sympathetic nervous system activity, so it is surprising that much clinical and experimental research has focused on the hemodynamic effects of sympathomimetic and sympatholytic agents and other vasoactive drugs. In humans, the systemic circulation is accessible to study by many methods. Cardiac output is measured readily by the Fick principle, using either thermodilution with a pulmonary artery catheter, or dye dilution with simultaneous arterial and venous catheterization. Hepatic blood flow can also be measured by hepatic dye clearance techniques. In patients with abnormal liver architecture, accurate measurement of hepatic extraction is essential; otherwise estimates of flow based on plasma clearance alone lead to large errors.