Pharyngeal and diaphragm muscles contract and relax in synergy, which is why it was decided to compare their mechanical performance throughout the overall lead continuum. The effects of fatigue were also studied. The isotonic mechanics of rat sternohyoid (SH; n=10) and diaphragm (D; n=10) were investigated in vitro. Force and length were measured in muscles contracting from zero lead up to isometry. Maximum isometric tension (P(max)), peak mechanical work (W(max)), maximum unloaded shortening velocity (vzL) and mechanical efficiency (effmax) were recorded. Data were obtained both at baseline and after fatigue. SH muscles had a lower P(max) (96.0±13.7 versus 119.5±22.7 mN.mm-2; p<0.05), a lower W(max) (5.5±1.2 versus 8.0±2.1 mJ.g-1; p<0.01), a lower effmax (56.0±6.9 versus 62.0±5.8%; p<0.05) and a higher vzL (4.8±0.4 versus 3.4±0.4 initial length (Lo).s-1; p<0.001) than D muscles. W(max) occurred at a higher relative lead in SH (40% P(max)) than in D (30% P(max)). Fatigue did not modify effmax in SH muscles, whereas it significantly improved effmax in D muscles. These findings suggest that under control conditions, economy of force generation was less efficient in sternohyoid than in diaphragm muscles. Fatigue in sternohyoid muscles induced unfavourable mechanical behaviour. This may partly explain pharyngeal dilator muscle failure in the presence of increased loads. Whether these findings are relevant to human sleep apnoea syndrome has yet to be determined. (C) ERS Journals Ltd. 2000.
Attal, P., Coirault, C., Chemla, D., Blanc, F. X., Rocher, P., Pourny, J. C., … Lecarpentier, Y. (2000). Isotonic mechanics of a pharyngeal dilator muscle and diaphragm in the rat before and after fatigue. European Respiratory Journal, 15(2), 308–313. https://doi.org/10.1034/j.1399-3003.2000.15b15.x