A direct determination of the threshold level of the respiratory center under conditions of anesthesia has been made, apparently for the first time, by use of the integrated diaphragmatic electromyogram (EMG). The disappearance of electrical activity of the diaphragm was used to determine the apneic carbon dioxide pressure (pCO2) in anesthetized man. Controlled increases and decreases of ventilation in 11 anesthetized patients were correlated with the end-tidal carbon dioxide pressures. The onset of apnea occurred at an average pCO2 of 38 mm. Hg, 10 mm. Hg below the mean level of unassisted respiration. Recovery from apnea occurred at an average pCO2 that was 5 mm. Hg higher than at the onset. The discrepancy probably results from the slow equilibration of carbon dioxide between the blood and nerve cells of the respiratory center.
Fink BR, Hanks EC, Holaday DA, Ngai SH. MONITORING OF VENTILATION BY INTEGRATED DIAPHRAGMATIC ELECTROMYOGRAMDETERMINATION OF CARBON DIOXIDE (CO2) THRESHOLD IN ANESTHETIZED MAN. JAMA. 1960;172(13):1367–1371. doi:10.1001/jama.1960.03020130025007
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