Respiratory mechanical advantage of the canine external and internal intercostal muscles

Abstract

8916I have left the reference in this summary and that of MS 8917. Agreed with Lynn.

Spatial distribution of external and internal intercostal activity in dogs

“…Since it was also demonstrated that the expiratory discharges previously recorded from these areas in the cat (Le Bars & Duron, 1984) were exclusively the result of cross-contamination (Figs 1 and 2), the conclusion must therefore be drawn that the external intercostals have a definite inspiratory action on the lung during breathing. On the other hand, expiratory activity among the internal interosseous intercostals consistently predominated in the dorsal portion of the caudal segments, that is in the areas where the muscles have the greatest expiratory mechanical advantage (De Troyer et al 1999). As for the expiratory mechanical advantage, internal intercostal expiratory activity then decreased progressively in the cranial and ventral directions, such that no expiratory activity was detected in the middle and ventral portions of the most rostral segments where the muscles have an inspiratory mechanical advantage.…”

“…In the preceding paper, however, we have shown that in supine dogs, these muscles show marked topographic differences in mechanical advantage (De Troyer et al 1999). Specifically, the external intercostals in the dorsal third of the rostral interspaces were found to have a large inspiratory mechanical advantage (i.e.…”

“…The entire procedure was repeated in the ventral third of the sixth intercostal space in three animals and in the ventral third of the tenth intercostal space in two animals. For the six animals studied, a total of eleven areas where the external intercostals have a clear-cut expiratory mechanical advantage (De Troyer et al 1999) was thus investigated. In each animal, the two pairs of recording electrodes were then transferred to the external and internal intercostal muscles in the middle or the ventral third of the second interspace, that is in an area where the internal intercostals have an inspiratory, rather than expiratory, mechanical advantage (De Troyer et al 1999).…”

“…For the six animals studied, a total of eleven areas where the external intercostals have a clear-cut expiratory mechanical advantage (De Troyer et al 1999) was thus investigated. In each animal, the two pairs of recording electrodes were then transferred to the external and internal intercostal muscles in the middle or the ventral third of the second interspace, that is in an area where the internal intercostals have an inspiratory, rather than expiratory, mechanical advantage (De Troyer et al 1999). As in the caudal segments, the internal intercostal electrode was placed •1 cm ventral to the external intercostal electrode, midway between the two ribs making up the interspace.…”

“…However, we have previously emphasized (De Troyer et al 1999) that the maximal ÄPao values for the internal intercostals, in particular in the most caudal segments, are likely to pertain to elevated lung volumes. Consequently, estimates of the contributions of the different muscle areas to breathing can be made only during hyperinflation, as during breathing against elevated positive end-expiratory pressures (Fig.…”