Changes in central respiratory patterns and activity following acute lung injury in the in situ rat preparation

Abstract

We have quantified changes in the variability of the respiratory patterns after acute lung injury (ALI) and reported increased respiratory rate and increased measures of linear and nonlinear variability by using Mutual Information (MI) and Nonlinear Complexity Index (NLCI). These changes are associated with lung and brainstem inflammatory responses. We hypothesize that changes in respiratory pattern after ALI are, in part, mediated centrally. To test our hypothesis we administered either bleomycin (0.5U in 50 μL of saline, n=9) or saline (50 μL, n=9) intratracheally to rats (Sprague‐Dawley, Harlan, P21–22). After 7d, central respiratory patterns were measured by recording the left phrenic, hypoglossal and vagal nerve activities using a perfused in situ preparation. Comparing in situ preparations from bleomycin to saline‐treated rats, bleomycin‐treated rats exhibited: 1) higher burst frequency (26 ± 4 vs. 20 ± 4 bpm, p=0.01), 2) lower coefficient of variation (p=0.01) integrated vagal nerve activity had 3) greater MI (p=0.01) and NLCI (p=0.01) and 4) phrenic and vagal nerve activities displayed increased early inspiratory activity. Fundamental changes in the respiratory patterns evoked by ALI persisted in the absence of vagal feedback from lung or blood chemistry indicating that central mechanisms are involved in generating the respiratory pattern after 7d of ALI. Supported by HL 087377, VA Research Service