[Systolic time intervals by intratracheal pneumocardiogram and the effects of inhalation anesthetics on cardiac...

Intratracheal pressure change due to cardiogenic oscillation was obtained by a high gain pressure transducer attached to the endotracheal tube while the patient was apneic during the operation. Such pressure change has been called as intratracheal pneumocardiogram (ITCG), which consists of wide waves and some spikes. Systolic time interval (STI) was obtained by measuring the intervals between certain spikes. The STIs measured by ITCG were compared with those by echocardiogram and by the conventional method. Also the effects of halothane, enflurane and isoflurane on cardiac performance were evaluated using the STI by ITCG. The STI measured by ITCG correlated well with that by echocardiogram, which indicated that the STI by ITCG was a useful noninvasive method to monitor the cardiac performance during general anesthesia. The STI by ITCG showed that the left ventricular ejection time (LVET) decreased in halothane and enflurane anesthesia. The pre-ejection period (PEP) and the PEP/LVET ratio increased in all three types of anesthesia. Especially the PEPs during halothane and enflurane at 1.8 MAC (minimum alveolar concentration) were greater than that of isoflurane. The results suggest that isoflurane has less cardiac depressive action than halothane and enflurane.