Exercise and Heat Stress in Cystic Fibrosis Patients

Abstract

Summary ICystic fibrosis (CF) is characterized by high sweat sodium and chloride concentrations. CF patients have long been assumed to be at risk for heat illness, but there has been no quantitative documentation that CF patients actually have a greater loss of sodium and chloride than normals when under environmental stress. We compared thermoregulatory responses of eight CF patients with five normal controls during 90-min exposures to exercise and heat stress. Both groups reached similar peak rectal temperatures and peak heart rates; they had similar sweat volumes and rates. CF patients showed the normal rise in renin and aldosterone and the normal fall in urine sodium excretion; however, CF patients lost significantly more sodium (48.8 + 23.4 mEq/liter/ m2 versus 20.2 + 11.2 mEq/liter/m2) and chloride (46.6 + 21.6

Aldosterone Metabolism and Transepithelial Potential Difference in Normal and Cystic Fibrosis Subjects

“…The normal values for aldosterone excretion rates are also congruent with previous experience in CF patients who do not have far-advanced disease (14)(15)(16). Although some CF patients are presumed to have hyperaldosteronism secondary to cardiopulmonary, renal, or hepatic disease and the loss of salt via the kidney or sweat ducts (1 7-1 9), our patients demonstrate several characteristics which are associated with the maintenance of normal aldosterone metabolism: 1) "mild" clinical disease with no evidence of cardiac or hepatic insufficiency, 2) high ad libitum Na+ intake, and 3) normal renal function.…”

Sodium supplementation is not required to maintain serum sodium concentrations during an Ironman triathlon

“…Four separate studies show that subjects with cystic fibrosis maintain their serum [Na + ] within the normal range during exercise. [33][34][35][36] These studies clearly establish that even patients with cystic fibrosis, who excrete a ''salty sweat'' during exercise, do not need to replace their excessive Na + losses during exercise to maintain their serum [Na + ] within the normal range.…”

Travelling with cystic fibrosis: Recommendations for patients and care team members

“…A low tolerance of CF patients to climatic heat stress has been described [47][48][49]. Because they have up to three times higher concentrations of sodium and chloride in their sweat, serum osmolality becomes lower compared to healthy controls when exercising in hot conditions and drinking pure water [50]. This relative hypoosmolality deprives the patients of a trigger from thirst, leading to an underestimation of their fluid needs and "voluntary dehydration" [51].…”