HORMONAL RESPONSES IN ELDERS EXPERIENCING PRE-SYNCOPAL SYMPTOMS DURING HEAD-UP TILT BEFORE AND AFTER EXERCISE TRAINING

Background. Hormonal responses of elderly individuals experiencing pre-syncopal symptoms during head-up tilt testing (HUT) were compared with responses of nonsymptomatic subjects both before (TI) and after (T2) 6 months of endurance training. Methods. Based on responses to HUT at T1, 35 men and women (ages 61-79 years) were placed into symptomatic and nonsymptomatic groups for analysis. Symptomatic subjects(n = 5) experienced lightheadedness, nausea, sweating, or syncope during T1 HUT but completed 15 minutes of HUT at T2. Training consisted of treadmill walking or stairclimbing 3 x/wk. 30-45 min/day, at 75-85% of maximal heart rate reserve. Adrenocorticotropic hormone (ACTH), vasopressin, aldosterone, norepinephrine, epinephrine, hemoglobin, and hematocrit were measured during supine rest prior to HUT, and either at the end of the 15-minute HUT or at symptom onset, Plasma volume (PV) was measured at supine rest; tilt-induced changes in PV were calculated from changes in hemoglobin and hematocrit. Results. During T1 HUT, symptomatic subjects had greater increases in vasopressin and a greater rate of PV loss (p<.05). Increases in ACTH and aldosterone were greater in symptomatic subjects at T1 and T2, while increases in norepinephrine were greater at T2 (p<.05). Reductions in tilt-induced vasopressin concentration and a decreased rate of PV loss were seen at T2 in symptomatic subjects. Conclusions. T1 results from symptomatic subjects are consistent with greater stimulation of volume-sensitive receptors induced by a greater rate of fall in PV. Exercise training resulted in increased tilt tolerance for symptomatic subjects associated with reductions in vasopressin concentration and rate of PV loss during tilt.