EFFECTS OF SEDATION PRODUCED BY THIOPENTONE ON RESPONSES TO NASAL OCCLUSION IN FEMALE-ADULTS

To test the hypothesis that full wakefulness is a important factor in the control of the route of breathing in adult humans, we have studied th responses to nasal occlusion before and during sedation with thiop entone in 14 female subjects. A tightly fitting partitioned face mask separated the nasal and oral breathing routes. Nasal and ora breathing were identified from changes in carbon dioxide concentration and airw ay pressure in the different compartments of the face mask. Arteria ox ygen saturation (Sp(O2)) was monitored simultaneously. Eleven of 14 su bjects breathed only through the nose (nasal breathers) both before an d during sedation. In these subjects, the time required to initiate or al breathing in response to nasal occlusion during sedation was signif icantly longer than that before sedation (mean 37.7 (SD 15.5) s vs 3.2 (1.3) s (P < 0.01)). Also, there was a significant difference (P < 0. 01) in the smallest values of Sp(O2) attained during nasal occlusion b efore (98.0 (0.8) %) and after (89.3 (4.3) %) sedation. In adult human s the ability to maintain adequate ventilation by switching from the n asal to the oral route in response to nasal occlusion is greatly impai red during sedation, probably because of the impairment of conscious i nfluence on the control of the palatal muscles.