Effects of Atropine and Isoproterenol on Cardiac Output, Central Venous Pressure, and Mean Transit Time of Indicators Placed at Three Different Sites in the Venous System

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Abstract
Two milligrams of atropine given intravenously increased the cardiac output, the mean arterial pressure, and the heart rate and lowered the central venous pressure, stroke output, and peripheral resistance. Tsoproterenol given intravenously at the rate of 1 µg. per minute increased the cardiac output with only an average increase in pulse rate of nine beats per minute. The stroke volume was increased. The central venous pressure and the peripheral resistance were decreased. These observations on the circulation were made in the steady state. They demonstrate that the minute output of the heart can be increased by either a rise in rate or an increase in stroke volume in the presence of a fall in central venous pressure. They do not define the order of events leading to the steady state. When the indicator was placed in the superior vena cava, neither atropine nor isoproterenol changed the volume in which the indicator was diluted during its first circulation. Both atropine and isoproterenol decreased the volumes in which the indicators were diluted when they were injected into the antecubital or femoral veins.