Potential Benefit from an H1-Receptor Antagonist on Postexercise Syncope in the Heat

MCCORD, J. L., T. K. PELLINGER, B. M. LYNN, and J. R. HALLIWILL. Potential Benefit from an H-1-Receptor Antagonist on Postexercise Syncope in the Heat. Med. Sci. Sports Exerc., Vol. 40, No. 11, pp. 1953-1961, 2008. Purpose: HI-receptors mediate the early portion (i.e., first 30 min after exercise) of postexercise hypotension. Immediately after exercise, syncope call occur due to an exaggerated form of postexercise hypotension. Therefore, we hypothesized that orthostatic hypotension occurring immediately after exercise would be attenuated with all H-1-receptor antagonist. Methods: We studied 15 endurance exercise-trained men and women in an environmental chamber set at 35 degrees C and 30.0% humidity. Subjects were studied in the Supine position before a 45-min bout of treadmill running at 50% of (V) over dotO(2max). Immediately after exercise, measurements were taken in the Supine position before the subjects were moved from a supine to a 60 degrees head-Lip tilt. Measurements included arterial pressure, heart rate, and brachial and cutaneous blood flow oil a control and all H-1-receptor antagonist (blockade) day. Results: Mean arterial pressure was reduced I min into the tilt compared with preexercise values on the control day (76.2 +/- 0.5 vs 74.2 +/- 0.5 min Hg; P < 0.05). This reduction was not seen oil the blockade day (75.2 +/- 0.3 vs 75.0 +/- 0.5 min Hg; P > 0.41). There were no differences in brachial vascular conductance (calculated as flow/pressure) in response to the head-Lip tilt between the Study days (P > 0.23). The length of the head-up tilt was compared between study days for each subject. When contrasting this difference, the blockade lengthened the mean tilt time by 94 s (P = 0.098). Conclusion: These data suggest that an Hi-receptor antagonist Could potentially benefit postexercise syncope in a hot environment.