DIAPHRAGM MUSCLE-FIBER INJURY AFTER INSPIRATORY RESISTIVE BREATHING

Five awake previously tracheotomized mongrel dogs were challenged with inspiratory resistive breathing (IRB). The mean peak tracheal pressur e = -35.4 +/- 1.1 cmH(2)O, ETCO(2) = 39.8 +/- 1.5 mmHg was sustained f or 2 h/d over 4 consecutive d. On the fourth day, following IRB, the d ogs were placed under general anaesthesia, and the diaphragm was perfu sed via the internal mammary artery with a low molecular weight fluore scent tracer (Procion orange, FW = 631), to which normal muscle fibers are impermeable. Muscle fiber membrane damage was identified on tissu e sections by using fluorescent microscopy showing the presence of the tracer in the cytoplasm. Four dogs undergoing the same protocol (exce pt IRB) served as control. The dye was seen in 7.6 +/- 2.6% and in 0.3 +/- 0.1% of fibers in the IRB and control groups, respectively (p < 0 .05). Via ATPase staining, it was found that fibers of type I were pre dominantly affected as compared to type II (p < 0.05). In addition, an increased area fraction of fibers demonstrating sarcomere disruption was found after IRB (2.4 +/- 0.5%) compared to pre-IRB (0.4 +/- 0.1%; p < 0.05). We conclude that resistive breathing of a magnitude similar to that seen in some respiratory diseases, or used in respiratory mus cle training programs induces muscle membrane and sarcomere injury.