Pulmonary development in growing guinea pigs exposed to chronic hypercapnia.

The role of lung stretch in causing pulmonary hyperplasia was studied in weanling male guinea pigs breathing air or 5% CO2 (in 22% O2, 73% N2) for 4 weeks. By the end of the exposure, oxygen consumptions were similar for both groups, but tidal volume and minute ventilation doubled in the hypercapnic group compared to controls. Arterial and venous blood gases reflected compensatory increases in plasma bicarbonate in animals breathing 5% CO2. The two groups did not differ in growth rate, lung volume or weight, alveolar surface area, anatomically estimated pulmonary diffusing capacity, or lung cellularity and protein content. Despite a chronic doubling of tidal volume during a peak growth period, hyperventilation did not stimulate pulmonary development, at least in normoxia and when oxygen consumption remained constant.