Red blood cell count (RCC) and volume (MCV) of three subjects in a hypobaric chamber

Measurements of red blood cell count (RCC) and mean corpuscular volume (MCV) were made on three subjects during a 42-h continuous exposure to low barometric pressure. RCC varied insignificantly in two subjects, but increased steadily with time in the third. MCV decreased appreciably (12-14%) in all three subjects 5 h after exposure to the low pressure but returned close to baseline values after 40 h. It is concluded that 1) short exposures to low barometric pressures result in a reduction in red cell size; 2) increased red cell production in response to low oxygen levels shows individual variations.