Cardiovascular responses to head-up tilt after an endurance exercise program.

The cardiovascular responses to 10 min of orthostasis were assessed before and after an aerobic exercise program. Five men and five women (18-25 years old) exercised for 7 weeks, four times per week, for 50 min per session at 70% of maximal heart rate (HR). Before and after the exercise program, maximal aerobic power (VO2max) was determined, and HR, systolic (SBP), diastolic (DBP), and pulse (PP) blood pressures were measured each minute during 5 min of supine rest, 10 min of foot-supported 70 degree head-up tilt (HUT), and 5 min of supine rest. Orthostatic tolerance was not determined. Calf compliance was measured in five of the subjects before and after the program as the change in leg volume at occluding pressures of 20, 40, 60, 80, and 100 mm Hg. Following the program, VO2max increased by 8.7% (p = 0.012), while decreases were noted in resting HR (9.4%, p = 0.041), SBP (5.0%, p less than 0.0005), and DBP (14.2%, p less than 0.0005). Despite a greater HR increase during HUT (7.1 beat.min-1, p = 0.034), SBP decreased by 3.4 mm Hg during HUT after the exercise program (p = 0.008). No differences were noted in the changes in DBP, MAP, or PP upon tilting (p greater than 0.05). After the program, the amount of fluid pooled in the calf at high occluding pressures (80 and 100 mm Hg) increased by 0.96 +/- 0.24 and 1.10 +/- 0.33 ml.100 ml tissue-1 (X +/- S.E.M., p = 0.017 and p = 0.028, respectively). We suggest that control of blood pressure during 10 min of orthostasis may be altered by endurance exercise training.