Ventilatory compensation for continuous inspiratory resistive and elastic loads during halothane anesthesia in humans.
Inspiratory mechanical loads were applied to the airway continuously for 5 min in healthy young adult volunteers maintained in a near steady-state of halothane anesthesia 1.1 MAC. The loads, both flow resistive and elastic in nature, had been selected to reduce the first loaded tidal volume approximately 10, 30 or 50%--these being designated "small," "medium," and "large" loads, respectively. The actual magnitudes of resistive load were 8 +/- 1, 21 +/- 3, and 48 +/- 6 cmH2O X l-1 X s, and of elastic load 6 +/- 1, 18 +/- 1, and 41 +/- 5 cmH2O X l-1 (mean +/- SEM). All loads caused an immediate reduction of ventilation proportional to the size of the load. This was followed by a gradual recovery of ventilation toward control values over approximately 2 min and then nearly stable ventilation for the rest of the loading period. Respiratory frequency was unchanged throughout. At 5 min of loading, ventilation and PaCO2 had been nearly steady for 3 min and O2 uptake and CO2 output at the airway were unchanged from control, suggesting the establishment of a near steady respiratory state. With the small and medium loads of both types, ventilation and PaCO2 in this near steady-state were not detectably different from control. With the large loads, however, ventilation was significantly reduced and PaCO2 slightly increased. The end-expiratory position of the chest wall and the relative contributions of the rib cage and abdomen-diaphragm to ventilation, as estimated by anteroposterior chest wall magnetometers, were not consistently altered by any load.(ABSTRACT TRUNCATED AT 250 WORDS)
D000009:Abdominal Muscles / Q000502:physiology; D000328:Adult; D000770:Anesthesia, Endotracheal; D002245:Carbon Dioxide / Q000032:analysis / Q000097:blood; D003964:Diaphragm / Q000502:physiology; D005260:Female; D005652:Functional Residual Capacity; D006221:Halothane; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic; D010092:Oximetry; D010100:Oxygen / Q000097:blood; D011659:Pulmonary Gas Exchange; D012123:Pulmonary Ventilation; D012119:Respiration; D012121:Respiration, Artificial; D012126:Respiratory Dead Space; D013909:Thorax / Q000502:physiology; D013990:Tidal Volume
D002245:Carbon Dioxide; D010100:Oxygen; D006221:Halothane