Fig. 1.
Data analysis of the efferent phrenic nerve activity. The digitalized raw signals (top) were rectified and the integrated by constructing the integrated phrenic neurogram (∫Phr) with a 100-ms time constant (middle). The phrenic spike frequency curve was constructed by averaging discharge frequency per 100-ms period (bottom). Inspiratory duration (TI) was defined as the duration of burst activity on the phrenic spike frequency curve, and expiratory duration (TE) was defined as the period between the end of inspiration and the onset of the subsequent burst. Therefore, the duration of each respiratory cycle was determined by calculating the sum of TI and TE. The following parameters were measured: spike frequency area-under-the-curve (AUC), ∫Phr AUC, central respiratory rate (respiratory cycles/minute), and inspiratory-to-expiratory duration ratio (TI:TE).