THERMOREGULATORY VASOCONSTRICTION INCREASES THE DIFFERENCE BETWEEN FEMORAL AND RADIAL ARTERIAL PRESSURES

Objective. Thermoregulatory vasoconstriction locally increases arteria l wall tension and arteriolar resistance thereby altering physical pro perties of the arteries. The arterial pressure waveform is an oscillat ory phenomenon related to those physical characteristics; accordingly, we studied the effects of thermoregulatory vasomotion on central and distal arterial pressures, using three hydraulic coupling systems havi ng different dynamic responses. Methods. We studied 7 healthy voluntee rs. Central arterial pressure was measured from the femoral artery and distal pressure was measured from the radial artery, using 10.8-cm lo ng, 20-gauge catheters. Three hydraulic coupling systems were used: (1 ) a 10-cm-long, 2-mm internal diameter connector; (2) a 150-cm-long, 1 -mm internal diameter connector (Combidyn 520-5689, B. Braun, Melsunge n, Germany); (3) a 180-cm long, 2-mm internal diameter connector(Medex MX564 and MX562, Medex Inc., Hillard, OH). Brachial artery pressure w as measured oscillometrically. Core temperature was measured at the ty mpanic membrane. The vasomotor index, defined as finger temperature mi nus room temperature, divided by core temperature minus room temperatu re, was used to estimate the degree of vasoconstriction. Constriction was considered near maximal when the index was less than 0. 1, and min imal when it exceeded 0.75. Measurements were taken every 3 min. Basel ine readings were obtained when subjects were warm. They then were coo led by exposure to 20-degrees-C to 22-degrees-C room air and a circula ting-water mattress set at 4-degrees-C until index was less than 0.1. They then were rewarmed by increasing water temperature to 42-degrees- C and adding a forced-air warmer until the vasomotor index exceeded 0. 75. Data were analyzed by ANOVA and linear regression. Results. Thermo regulatory vasoconstriction was associated with marked arterial pressu re waveform changes. Radial pressure showed, in lieu of a dicrotic not ch, large oscillations of decreasing amplitude. Femoral pressure showe d a single diastolic oscillation of smaller amplitude. The waveforms a ppeared different, depending on the hydraulic coupling system used, ar tifact being more marked with the longer connectors. On the average, r adial systolic pressure exceeded femoral systolic pressure during vaso constriction; however, during vasodilatation, femoral systolic pressur e exceeded radial systolic pressure (p < 0.05). Oscillometric measurem ents underestimated systolic pressure, and did so more markedly during vasoconstriction. There were no differences in the values of mean and diastolic pressures. Conclusion. Thermoregulatory vasoconstriction al ters radial arterial pressure waveform, artifactually increasing its p eak systolic pressure compared with the femoral artery. Poor dynamic r esponses of recording systems further distort the waveforms. Consequen tly, radial artery pressure may be misleading in vasoconstricted patie nts.