A COMPARISON OF THE EFFECTS OF ANOXEMIA AND CARBON‐DIOXIDE SATURATION ON COSTAL AND ABDOMINAL BREATHING

The effects of lowered alveolar oxygen and of increased alveolar carbon dioxide on costal and abdominal breathing were recorded with six encircling bands. Lowered alveolar oxygen most commonly increased the circumference of the chest and abdomen at the end of expiration and decreased the intra‐thoracic pressure. This expansion of the chest and abdomen was tentatively attributed to an increased tension of the diaphragm and of the inspiratory muscles of the chest. Sometimes anoxemia increased the expiratory circumference of the abdomen and decreased that of the chest. This differential effect was tentatively attributed to a greater development of tension in the diaphragm which, through the lungs, exerted an inward traction on the chest. During recovery from anoxemia costal respiratory movements were inhibited more than abdominal respiratory movements. The upper costal segments were inhibited more than the lower costal segments. Upper costal apnea and abdominal hyperpnea were not uncommon. In one experiment upper costal apnea was accompanied by abdominal hyperpnea greater than the hyperpnea of the immediately preceding anoxemia. As abdominal respiratory movements diminished during recovery the costal movements increased. This unusual co‐ordination (?) of costal and abdominal breathing led to a smooth return to normal ventilation. The effects of carbon dioxide differed importantly from those of anoxemia. In most experiments there was a decrease in circumference of the chest and abdomen at the end of expiration and a corresponding rise in the intra‐thoracic pressures. It was tentatively suggested that carbon dioxide decreases the tonus of the inspiratory muscles by inhibiting prevailing reflexes which tend to increase lung volume, and that anoxemia increases the tonus of the inspiratory muscles by augmenting these same prevailing reflexes.