Effect of immersion on urinary lead excretion.

Abstract

The physiological effects of water immersion in man were studied by Epstein' in the 1970s in conjunction with the United States National Aeronautics and Space Administration's research into weightlessness. This showed that immersion up to the neck in water at 35°C produced a profound diuresis, naturesis, and an increased urinary excretion of calcium. These pronounced alterations in renal function brought about by immersion probably occur because the hydrostatic pressure of the water produces a redistribution of extracellular fluid in the body. There is a shift of about 700 ml of blood from the limbs to the thoracicocardiac compartment. This increase in the effective extracellular fluid volume is thought to mediate the renal changes by hormonal mechanisms. A recently discovered hormone, atrial naturetic peptide,2 has been found to have a role in regulating these changes but is unlikely to be the only factor concerned.One study of the treatment of lead poisoning by Bath Spa therapy during the eighteenth century3 has shown that a cure rate of about 49% was achieved in patients who had paralysis due to lead poisoning whereas in hemiplegias or paralyses of unknown aetiology the cure rate was only about 1 % and about 6% when the condition was secondary to spinal deformity.Admission to the Bath Hospital was conditional on the charity patients complying with the prescribed treatments and they were not discharged until a committee of the attending physicians considered that they had obtained the maximum benefit from the spa treatment and had agreed on both diagnosis and outcome. The doctors were to keep good records, an analysis of which was published annually. It was stated that many of the patients had been discharged as incurable from other hospitals before their admission to Bath. Between 1751 and 1758, 15 of the 31 patients with occupational exposure to lead had been referred from London hospitals as incurable; when they were discharged after a stay at the Bath Hospital, seven were cured and eight were much improved.Spa therapy was multifactorial necessitating removal from exposure, a change in diet (probably for Accepted 24 March 1986 the better), increased exercise, and a regimen that required the patient to drink the mineral water daily and to be immersed in the bath three times a week. Knowing that immersion affects the urinary excretion of calcium and that the metabolism of lead and calcium are closely related, we decided to investigate the effects of immersion on the rate of urinary lead excretion to see if this might have contributed to the successful treatment at Bath. MethodsThree lead workers with moderately raised blood lead concentrations volunteered to be immersed and were compared with seven control subjects.4 A 24 hour urine specimen was collected the day before immersion. No food or water was taken after 2230 on the day before the experiment. At 0730 on the day of the immersion a water load of 400 ml was taken but no food. At 0830 the subjects emptied their bladders and drank a further 200 ml of w...