Figure 6-16 Representative record from one subject while awake and during halothane anesthesia. The three upper tracings are electromyograms. Lower tracings represent ribcage and abdominal dimensions measured by respiratory impedance plethysmography. Open and solid circles denote the beginning and end of inspiration, respectively. Notice that the amplitudes of ribcage and abdominal excursions diminish during halothane but that the relationship between their amplitudes is preserved. (From Warner DO, Warner MA, Ritman EL: Human chest wall function while awake and during halothane anesthesia. I. Quiet breathing. Anesthesiology 82:6, 1995.)