Effects of anemia and growth retardation on respiratory activity in the piglet.

Respiratory activity (RA) was assessed in a piglet model by giving chloralose (Ch), 6 mg/kg i.v. every 2 min, until the appearance of apnea. The total cumulative dose of Ch (mg/kg) which produced permanent apnea (lethal dose, LD) was determined. The slope of the dose-respiratory frequency curve (R = ae-lambda Ch) was also computed. The LD of Ch increased progressively with age, while respiratory frequency (lambda) decreased. However, in piglets with severe spontaneous anemia (hematocrit less than 10%), the LD of Ch was less than half that expected for the age groups, and the rate of reduction of gamma was much greater. The enhanced sensitivity to inhibition of RA may relate in part to anemia with reduced O2-carrying capacity to the CNS, and in part to growth retardation with delayed respiratory center maturation.