The goal of these studies was to determine whether the hypertension caused by excessive salt loading results from sodium-induced expansion of the extracellular fluid volume or whether the salt increases the pressure in some other way, such as by causing vascular constriction. In one group of sheep, a combination of total nephrectomy and hemodialysis was used to produce and maintain step increases in extracellular fluid volume for 1 wk without a significant change in sodium ion concentration. In a 2nd group, unilateral nephrectomy, dialysis, and DOCA administration were used to cause step increases in sodium ion concentration while the extracellular fluid volume was held as close to normal as possible. The results showed a 41% increase in arterial pressure in the high-volume sheep and only a 4% increase in pressure in the high-sodium sheep. In both instances the total exchangeable sodium increased almost equally--a 21% increase in the high-sodium sheep. The data support the concept that sodium retention causes hypertension almost entirely because of sodium-induced expansion of the extracellular fluid volume.

As a means of partially distinguishing age effects and other risk factors in presbyacusis, hearing thresholds for 56– to 65–year-old participants screened for exclusion of selected risk factors were compared with thresholds for 48– to 55–year-old participants without the same risk factors. Hearing thresholds for both age groups were also compared with age-appropriate International Standards Organization (ISO) norms. Even after screening participants for exclusion of selected risk factors, differences in hearing sensitivity remained across age groups. Across the male and female groups, thresholds were generally better (lower) for 48 to 55 year olds than for 56 to 65 year olds. ISO norms generally underestimated the degree of hearing loss for participants of comparable age in the present study. The underestimation was small at lower test frequencies, was generally greater for men, and was largest at test frequencies above 2000 Hz. Abbreviations: ANSI = American National Standards Institute, EHLS = Epidemiology of Hearing Loss Study, ISO = International Standards Organization