Occupational noise exposure, noise-induced hearing loss, and the epidemiology of high blood pressure

The role of noise exposure in the etiology of high blood pressure is unclear. A cross-sectional study of occupational noise exposure and high blood pressure was conducted in March 1981-August 1982 in a group of blue-collar workers from a noisy (greater than or equal to 89 dBA) and a less noisy plant (less than 81 dBA). There were 197 randomly sampled men from the noisier plant and 169 from the comparison factory. Clinical examinations, audiograms and a psychologic inventory were conducted. Body mass index, alcohol intake, and family history of hypertension were comparable for the two groups. There was no difference in mean systolic or diastolic blood pressure between workers in the two plants. There was, however, a strong relationship between severe noise-induced hearing loss (greater than or equal to 65 dBA loss at 3, 4, or 6 k Hz) and high blood pressure (greater than or equal to 90 mmHg diastolic or taking blood pressure medication) in the 56+ age group in both plants after adjusting for risk factors (p less than 0.02). Multiple regression analysis revealed that in the noisier plant, body mass index, severe noise-induced hearing loss, and noisy hobbies explained a significant amount of the variation in diastolic pressure (p less than 0.05) R2 = 0.19. This suggests that there may be a population at increased risk for hearing loss and high blood pressure.

Osmotic opening of the blood-brain barrier in the rhesus monkey without measurable brain edema

The blood-brain barrier in the rhesus monkey was opened to intravascular Evans blue-albumin, without causing brain edema or altering brain electrolytes, by perfusing 2.5 molal recrystallized D,L-lactamide into the internal carotid artery for 20--30 sec. Gross neurological and behavioral sequelae were absent in 7 of 8 animals with barrier opening, and 2 days after perfusion no statistically significant changes were observed in sodium, potassium or water contents of perfused as compared to unperfused gray and white matters of brains of the 7 normal animals. Brain endema may not have developed because parenchymal albumin was excreted or metabolized by 2 days. It is suggested also that closure of the barrier after several hours prevents salt from accompanying plasma fluid into the brain. Entry of fluid without salt would reduce, before measurable edema developed, any transcapillary osmotic gradient established by prior entry of plasma albumin.