Five awake previously tracheotomized mongrel dogs were challenged with inspiratory resistive breathing (IRB). The mean peak tracheal pressure = -35.4 +/- 1.1 cmH2O, ETCO2 = 39.8 +/- 1.5 mmHg was sustained for 2 h/d over 4 consecutive d. On the fourth day, following IRB, the dogs were placed under general anaesthesia, and the diaphragm was perfused via the internal mammary artery with a low molecular weight fluorescent tracer (Procion orange, FW = 631), to which normal muscle fibers are impermeable. Muscle fiber membrane damage was identified on tissue sections by using fluorescent microscopy showing the presence of the tracer in the cytoplasm. Four dogs undergoing the same protocol (except 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 predominantly 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 muscle training programs induces muscle membrane and sarcomere injury.

A Ac ct ti iv vi it ty y o of f l la at ti is ss si im mu us s d do or rs si i m mu us sc cl le e d du ur ri in ng g i in ns sp pi ir ra at to or ry y t th hr re es sh ho ol ld d l lo oa ad ds s M. Orozco-Levi, J. Gea, J. Monells, X. Aran, M.C. Aguar, J.M. BroquetasActivity of latissimus dorsi muscle during inspiratory threshold loads. M. Orozco-Levi, J. Gea, J. Monells, X. Aran, M.C. Aguar, J.M. Broquetas. ©ERS Journals Ltd, 1995. ABSTRACT: The ability of the latissimus dorsi muscle (LD) to participate as an accessory inspiratory muscle has been the subject of controversy. Electromyographic (EGM) activity of LD was evaluated in 11 healthy subjects (aged 30±2 yrs; forced expiratory volume in one second (FEV 1 ) 106±5% predicted; maximal inspiratory pressure (PImax), 120±6 cmH 2 O) under different breathing conditions. The ipsilateral biceps brachii was chosen as the control muscle. The EMG was recorded from surface electrodes, but needle electrodes were also used for LD evaluation in a subset of three subjects. The EMG signal from both muscles was recorded simultaneously, rectified and integrated, with subtraction of the electrocardiographic signal. Situations evaluated were: 1) maximal voluntary contraction (MVC); 2) apnoea; and 3) breathing under progressive inspiratory threshold loads (20-100% PImax, at 20% intervals). A close relationship was evident between LD recordings from surface and needle electrodes (r=0.975). Activity of LD at baseline was 1.8±0.4% MVC, and showed a phasic increase during inspiration under loads. This change had a linear tendency and was significant for loads corresponding to 40, 60, 80 and 100% of PImax when compared to the control muscle. At this latter level, LD activity was equivalent to 32±5% MVC (range 11-61%), whereas mean activity of the control muscle was less than 7.5% MVC.These results demonstrate that LD is progressively recruited in healthy subjects during inspiratory loading, and suggest that LD could participate as an accessory muscle for the breathing effort under specific conditions. For these reasons, LD does not appear to be an appropriate control for studies of the respiratory muscles. Eur Respir J., 1995, 8, 441-445 Inspiratory loading induces an increase in the activity of the main inspiratory muscles, such as the diaphragm and parasternal intercostals [1][2][3], and may induce muscle fatigue. Activity of other muscles from the chest wall, or even the trunk, can also increase under these circumstances [4,5]. Nevertheless, both the specificity and physiological significance of this recruitment remain controversial. Latissimus dorsi (LD) is a trunk muscle. It's origins are in the dorsal and lumbar vertebrae, the sacrae midline, the posterior iliac crest and the lower ribs. All of its fibres converge together to insert into the humerus by a common tendon. The LD participates in different functions, such as maintaining body posture and collaborating in the adduction and internal rotation of the arm [6,7]. Although some anatomists and physiologists have argued that ...

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