COLD PRESSOR STIMULUS TEMPERATURE AND RESTING MASSETER MUSCLE HEMODYNAMICS IN NORMAL HUMANS

Cold presser stimulation reportedly increases sympathetic nerve activi ty in human skeletal muscles. This study examined the effect of cord p resser stimulation on the resting haemodynamics of the right masseter muscle in normal individuals, using near-infrared spectroscopy. Nine h ealthy non-smoking males with no history of chronic muscle pain or vas cular headaches participated. Their right hand was immersed in a water bath (4, 10, 15 degrees C) for exactly 1 min. Each trial lasted 7 min (1 min before, I min during, 5 min after stimulation) and a strictly random order was utilized for the three test temperatures and the mock trial. Masseter muscle haemoglobin concentration and oxygen saturatio n, as well as heart rate and blood pressure, were continuously recorde d in each trial. After completing the four trials, each participant pr oduced and sustained a 30-s maximum voluntary clench in the intercuspa l position. Data across the four trials were baseline-corrected and th en magnitude-normalized to the individual's highest absolute haemoglob in and oxygen signal during the 30-s maximal clenching effort. Haemogl obin and oxygen saturation increased progressively during cold presser stimulation as the water temperature decreased (Hb, p < 0.0001; O-2, p = 0.0327); very little effect was seen during the mock trial. Heart rate and blood pressure also increased progressively during the stimul ation as the temperature decreased (heart rate, p = 0.0013; systolic b lood pressure, p = 0.0042; diastolic blood pressure, p = 0.0156). Thes e data suggest that cold presser stimulation induces a strong increase in intramuscular blood volume which appears to be due to both a local vasodilative response and increased cardiac output. (C) 1998 Elsevier Science Ltd. All rights reserved.