1169 EXERCISE IN THE HEAT IN CYSTIC FIBROSIS PATIENTS

Abstract

Cystic fibrosis (CF) is characterized by high sweat sodium (Na) and chloride (Cl), yet little is known about CF patients' response to exercise in the heat. We examined the responses of 5 CF patients with mild lung disease and 3 non-CF controls (N) to single sessions of cycle exercise in the heat. Subjects had free access to water, and pedalled at 50% peak VO2 for 60-90 minutes in a heat chamber at 37-38°C (DB), 24-29°C(WB). Urine and serum osmolality and electrolytes were measured before and after exercise, as were serum renin and aldosterone. Sweat volume, rate, and electrolytes were measured. Rectal temperatures (Tr) and ECG were monitored continuously. N and CF had similar Tr (101. 1 ± 1.3, 101.0 ±.08, p>.5), peak HR (175 ± 16, 165 ±12, p>.25), sweat rates (5.8 ±2.0, 8.1 ±2.1 ml·m-2.min-1, p>.1). CF had the expected higher sweat Na (76 ±24 mEq.L-1) and Cl (70±21mEq.L-1) than control (44 ± 5 and 37 ± 7 mEq.L-1, p <.05). CF showed a normal rise in renin (6.8 before, 21.4 ng.ml-1.hr−1 after, p<.05) and aldosterone (13.6 before, 45.4 ng·dl-1 after, p<.05) with exercise. CF urine Na fell with exercise (172.2 to 119.8 mEq.L-1, p<.05). Despite this evidence of renal salt conservation, CF serum Cl fell (102.4 to 98.8 mEq.L-1, p <.05) while control serum Cl did not change (104 mEq.L-1) and CF serum osmolality fell (272.2 to 263.8 mosm.L-1, p<.05). Even though CF patients can mount hormonal responses to exercise/heat stress and can conserve salt through renal mechanisms they lose more salt than normal people. Prolonged or repeated exercise in the heat may be dangerous for CF patients.