Respiratory, cardiovascular, and metabolic adjustments to hypoxemia duringsleep in piglets

The influence of sleep on ventilation, metabolic rate, cardiovascular funct ion, and regional distribution of blood flow during hypoxemia (Pao(2) of 45 -50 mmHg (1 mmHg = 133.3 Pa)) was studied in piglets at 6 +/- 1 and 34 +/- 5 days (mean +/- SD). Measurement of ventilation and metabolic rate was don e in a metabolic chamber, and blood flow was measured using the microsphere technique. A subgroup of animals was instrumented for cardiac output measu rement (dye-dilution technique) and continuous monitoring of the hemoglobin saturation in oxygen (Sao(2)). We found that although sleep did not influe nce the metabolic and cardiac output response to hypoxemia, it affected the ventilatory response as well as the brain and the respiratory muscle blood flows. During active sleep in the older animals, the ventilatory response to hypoxemia was smaller than in the other two states; marked drops in Sao( 2) occurred with changes in the breathing pattern; and that state was assoc iated with the highest rate of brain blood flow. As well, age affected the ventilatory and metabolic response, but not the cardiovascular response to hypoxemia. The age dependent ventilatory changes with hypoxemia (smaller ve ntilatory response in the young than in the older animals) were related to the different levels of oxygen consumption. In summary, active sleep was re sponsible for all the sleep-dependent changes in the response to a moderate degree of hypoxemia.