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Diaphragm muscle fatigue resistance during postnatal development
G C Sieck1, M Fournier, C E Blanco
1Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota 55905.
Insights
Postnatal development of cat diaphragm muscle shows faster contractions and reduced fatigue resistance with age. Changes in muscle fiber types do not fully explain these functional shifts.
Area of Science:
- Physiology
- Developmental Biology
- Muscle Biology
Background:
- The diaphragm is crucial for respiration, and its development is vital for survival.
- Understanding postnatal changes in diaphragm function is essential for pediatric respiratory health.
Purpose of the Study:
- To investigate the developmental changes in contractile and fatigue properties of the cat diaphragm muscle during the first 6 weeks of postnatal life.
- To correlate these functional changes with alterations in muscle fiber type composition and size.
Main Methods:
- Assessment of diaphragm muscle contractile properties (twitch contraction time, half-relaxation time, force-frequency relationship) at various postnatal ages.
- Evaluation of diaphragm fatigue resistance.
- Histochemical analysis (myofibrillar adenosinetriphosphatase staining) to classify muscle fiber types (Type I and Type II) and determine their proportions and cross-sectional areas.
Main Results:
- Twitch contraction time and half-relaxation time decreased with age, indicating faster muscle response.
- The force-frequency relationship shifted leftward with development.
- Diaphragm fatigue resistance was highest at birth and declined progressively.
- The proportion of Type I fibers increased, while Type II fibers decreased, with age.
- Type II fibers showed a greater increase in cross-sectional area compared to Type I fibers.
Conclusions:
- Postnatal development leads to faster contractile speeds and reduced fatigue resistance in the cat diaphragm.
- Observed changes in diaphragm contractile and fatigue properties are not solely explained by shifts in the relative proportions or sizes of histochemically defined Type I and Type II fibers.
- Further investigation into contractile protein composition is warranted to explain these developmental adaptations.
Abstract:
Changes in the contractile and fatigue properties of the cat diaphragm muscle were examined during the first 6 wk of postnatal development. Both twitch contraction time and half-relaxation time decreased progressively with age. Correspondingly, the force-frequency curve was shifted to the left early in development compared with adults. The ratio of peak twitch force to maximum tetanic force decreased with age. Fatigue resistance of the diaphragm was highest at birth and then progressively decreased with age. At birth, most diaphragm muscle fibers stained darkly for myofibrillar adenosinetriphosphatase after alkaline preincubation and thus would be classified histochemically as type II. During subsequent postnatal development, the proportion of type I fibers (lightly stained for adenosinetriphosphatase) increased while the number of type II fibers declined. At birth, type I fibers were larger than type II fibers. The size of both fiber types increased with age, but the increase in cross-sectional area was greater for type II fibers. On the basis of fiber type proportions and mean cross-sectional areas, type I fibers contributed 15% of total muscle mass at birth and 25% in adults. Thus postnatal changes in diaphragm contractile and fatigue properties cannot be attributed to changes in the relative contribution of histochemically classified type I and II fibers. However, the possibility that these developmental changes in diaphragm contractile and fatigue properties correlated with the varying contractile protein composition of muscle fibers was discussed.