Fowler, Ward S.

Measurements were made of O2 uptake, CO2 output and CO2 tension of arterial and mixed venous blood and expired alveolar gas in 28 anesthetized and paralyzed dogs ventilated with air at a constant rate. Retention of CO2 was not observed in the lateral decubitus position with either closed or open thorax. Induction of open pneumothorax resulted in an unexplained metabolic alteration characterized by an increase in O2 uptake and CO2 elimination and a decrease in plasma buffer base. Small amounts of CO2 were eliminated from exposed pleura. The left pulmonary artery was occluded (after left thoracotomy) and 1 hour later the left bronchus also was occluded—or the order was reversed. CO2 retention of major degree was observed after initial occlusion of the artery and retention of minor degree after occlusion of the bronchus. During the 2nd hour (after additional occlusion) the previously retained CO2 was eliminated. The results suggest that the ventilatory requirements are not influenced specifically by effects of lateral position, open pneumothorax, or small right-to-left shunts, but rather are determined to a large degree by the metabolic production of CO2 and the degree to which ventilation is distributed to perfused alveoli. Submitted on December 3, 1958

The distribution of tidal air and nonshunted blood flow to each lung, the elimination of CO2 from each lung, and Paco2 were measured in ten anesthetized and paralyzed dogs during intermittent positive-pressure breathing in the supine position and before and after thoracotomy in the lateral decubitus position. Ventilation via a divided tracheal airway (Wright-Lategola) at a constant rate and a constant volume (±5%) with 65% oxygen in nitrogen was provided by a Bird ventilator. Reduction of total CO2 elimination and increase of ratio of total physiologic dead space to tidal volume were observed after thoracotomy. Mean percentages of total ventilation and blood flow to, and CO2 elimination from, the right lung were about 58% in the supine position. When the right or left lung became dependent in the lateral decubitus position, its proportional ventilation and CO2 elimination decreased. After thoracotomy was made on the superior nondependent side, further reductions were noted and blood flow to the dependent lung also decreased. Proportional CO2 elimination was more dependent on alveolar ventilation than on the ratio of ventilation to perfusion.

Action potentials of single vagal afferent nerve fibers from slowly adapting pulmonary stretch receptors, transpulmonary pressure and rate of air flow were recorded in anesthetized cats with open thoraxes during varied volumes and rates of inflation and deflation of the lungs. Both discharge frequency and total transpulmonary pressure varied with lung volume and also with its rate and sign of change. Effects of acceleration of volume on discharge frequency were not observed. The receptors provide signals related to the work of breathing.