Decongestant effects on hemodynamics at rest, exercise, and recovery from exercise during--6 degrees of head down tilt.

HYPOTHESIS: Ten males were studied to examine the effects of a decongestant, pseudoephedrine hydrochloride, on rest, exercise, and recovery from exercise during -6 degrees of head down tilt (HDT). METHODS: Subjects were positioned in the HDT for a total of 6 hr: 2 hr 45 min rest, 30 min exercise, and 2 hr 45 min recovery. Sessions were identical except for the ingestion of a drug or placebo. Variables evaluated during rest, exercise, and recovery conditions were: systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), stroke volume (SV), cardiac output (Q), pulse pressure (PP), mean arterial pressure (MAP), total peripheral resistance (TPR), and forearm blood flow (FBF). RESULTS: During rest PP at 120 min was less than resting baseline, and MAP increased throughout rest. There was a treatment effect for SBP which increased up to 90 min from resting baseline for the placebo treatment only. Normal changes were found with exercise, with all variables increasing above baseline except for TPR which decreased. DBP showed no change during exercise. During the recovery condition for the drug treatment HR decreased, while SBP increased from 30 min. In addition, DBP and MAP were higher for the placebo at 30 min and higher for the drug at 90 min. CONCLUSION: The results show that ingestion of the sympathomimetic agent pseudoephedrine hydrochloride has no significant effects on the cardiovascular system during simulated microgravity.

Thermogenesis during rest and exercise in cold air.

Nine non-cold-acclimated subjects (5 female, 4 male, mean age 22.5 years) were studied to determine whether nonshivering thermogenesis contributes to cold-induced metabolic heat production during rest (50 min standing) and exercise (40 min treadmill walking) in 5 degrees C. Propranolol was administered orally (females, 60 mg, 1.12 mg.kg-1; males, 80 mg, 0.96 mg.kg-1) to block nonshivering thermogenesis. Measurements were taken at both 25 degrees C, 13.1 Torr (water vapor pressure; 1 Torr = 133.3 Pa) and 5 degrees C, 3.6 Torr, with sessions randomly assigned to be drug-neutral (DN), drug-cold (DC), placebo-neutral (PN), and placebo-cold (PC). Body core temperature was not different between any of the experimental conditions. Mean body temperature (5 degrees C, 32.2 +/- 0.20 degrees C (+/- SEM); 25 degrees C, 35.3 +/- 0.20 degrees C) and mean skin temperature (5 degrees C, 22.4 +/- 0.70 degrees C; 25 degrees C, 31.4 +/- 0.60 degrees C) were lower (p < 0.05) in the 5 degrees C than 25 degrees C environment (rest, exercise, drug (D), placebo (P), combined); while shivering (EMG) was higher (16.5 +/- 3.9% above baseline) at 5 degrees C than 25 degrees C (15 +/- 2.1% below baseline) (p < 0.05). The greater VO2 in 5 degrees C compared with 25 degrees C for the same condition is the thermoregulatory VO2 (TVO2). TVO2 (mL.min-1) was lower (p < 0.05) on the D (mean = 189.5 +/- 17.7) than on the P (mean = 238.1 +/- 20.2) during rest and during exercise (D, 206.1 +/- 63.7; P, 338.4 +/- 46.7). The EMG was 21% above baseline in the DC, and 12% above baseline for PC (p > 0.05). These results suggest a nonshivering component to heat production during acute cold exposure, which can be blocked with propranolol.