Volume-Pressure Analysis of Reflex Changes

Mental arithmetic stress is known to cause forearm arterial dilation, but the venous responses, including possible changes in the volume-pressure relation, have not been defined. Hence, 10 apparently normal subjects, eight men and two women, mean age 46±9 years, were studied before and during mental arithmetic stress. Changes in forearm venous volume were estimated with 99mTc blood pool scintigraphy. Group variability of this measurement technique was 1.8+2.3%. A brachial blood pressure cuf was used to obtain venous occluding pressures of 0, 10, 20, and 30 mm Hg. Mental arithmetic stress increased group systolic and diastolic blood pressure from 126±12 to 152+±20 mm Hg and from 83±8 to 93+±-15 mm Hg, respectively (p<0.001). Heart rate increased from a mean of 75+15 to 85± 17 beats/min (p<0.01). There was no evidence of interaction between or nonlinearity of the volume-pressure plots. Linear regression then yielded the equations V=99.8+0.96P before and V=86.3+0.96P during mental arithmetic stress, which represents a 13.5±1.6% decrease in forearm vascular volume (p<0.001). We conclude that 1) a linear relation exists between forearm venous volume and pressure at physiologic pressures before and during mental arithmetic stress; 2) mental arithmetic stress causes forearm venoconstriction; and 3) such venoconstriction takes place by