A Tandem Forearm Plethysmograph for Study of Acute Responses of the Peripheral Veins of Man: The Effect of Environmental and Local Temperature Change, and the Effect of Pooling Blood in the Extremities1

The primary mechanism of action of the smooth muscle of the veins upon their contained blood is one of imparting pressure to the blood by a sur- rounding force. This mode of action is to be distinguished from that of the smooth muscle of the arterioles, which is one of maintenance of arterial pressure through resistance to the outflow of blood. The function of the arterioles as re- sistive elements in the circulation is evaluated by the relationship between the volume of the flow of blood through the arterioles per unit period of time and the change in pressure across the arterioles. The function of the veins as containers of the blood volume is best evaluated by the relationship between a change of the volume of the veins and the associated change of the pressure of the veins.