EXPIRATORY DURATION AND ABDOMINAL MUSCLE RESPONSES TO ELASTIC AND RESISTIVE LOADING

To examine the nature of the central processing of pulmonary afferent information during expiration, expiratory duration (TE) and the immediate response of abdominal muscle expiratory activity (AbEMG) were measured during elastic and resistive loading which produced smooth increases in the expiratory time-volume profiles. Various size loads were presented for single expirations on anesthetized, tracheostomized cats. Increases in peak AbEMG and TE were found to be graded to the increase in end-expiratory lung volume (ΔV). However, resistive loading produced a greater TE and greater volume profile history than elastic loading for the same ΔV. The latency of AbEMG decreased with loading, implying that the increased peak AbEMG was due to increased motor drive as well as to the longer TE. Volume retention was less effective in decreasing the latency in early expiration. These data demonstrate the importance of the volume profile history in setting TE. The AbEMG response to lung inflation is primarily a time-dependent process in early expiration and an increasingly volume-dependent process later in expiration.