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Pharyngeal dilator muscle contractile and endurance properties in neonatal piglets
1Department of Medicine (Pulmonary), Case Western Reserve University, University Hospitals of Cleveland, Ohio 44106.
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Neonatal piglets
Area of Science:
- Physiology
- Neonatal development
- Respiratory mechanics
Background:
- Pharyngeal dilator muscles are crucial for maintaining upper airway patency in newborns.
- Understanding their contractile properties is vital for neonatal respiratory health.
Purpose of the Study:
- To investigate the in vitro contractile properties of the sternohyoid muscle in neonatal piglets.
- To assess age-related changes in sternohyoid muscle function during early development.
Main Methods:
- Isometric contraction and relaxation times were measured in sternohyoid muscles from piglets aged 1-7 days and 14-20 days.
- Muscle fatigue was evaluated using prolonged repetitive stimulation and a standard fatigue test.
- Twitch potentiation and post-tetanic potentiation were observed.
Main Results:
- Neonatal piglet sternohyoid muscle exhibits moderate-to-fast contraction with good endurance.
- Force potentiation was observed during repetitive and tetanic stimulation.
- Older piglets (14-20 days) showed decreased muscle endurance compared to younger piglets (1-7 days).
Conclusions:
- The sternohyoid muscle in newborn piglets has physiological properties suitable for maintaining airway patency.
- While contractile kinetics remain consistent, muscle endurance declines with age in early postnatal life.
Abstract:
Pharyngeal dilator muscles are critical for maintaining upper airway patency in the neonatal period. The present study examined in vitro the contractile properties of a pharyngeal dilator muscle, the sternohyoid, in 1-7-day-old piglets (n = 24). Isometric contraction and half-relaxation times were 36.7 +/- 1.1 and 30.9 +/- 1.2 msec, respectively. Twitch potentiation ('staircase phenomenon') and post-tetanic potentiation were noted following repetitive stimulation. During prolonged repetitive stimulation with a standard (40 Hz) fatigue test, muscle force declined gradually over time, with loss of half of the initial force occurring over 138 +/- 11 sec, and a 2-min fatigue index (ratio of force at 2 min to initial force) of 0.52 +/- 0.03. An additional 10 piglets were studied at ages of 14-20 days. Muscle from older piglets had comparable isometric twitch kinetics as that of younger animals. However, sternohyoid muscle from the older piglets had worse endurance than muscle from the younger animals, as indicated by a shorter time required for force to decrease by half (86 +/- 10 sec, P < 0.01) and a lower 2-min fatigue index (0.36 +/- 0.03, P < 0.01). These data indicate that for the sternohyoid muscle of the newborn piglet (a) physiological properties are consistent with moderate to fast contraction with good endurance, (b) force potentiates during repetitive twitch stimulation and following a brief period of tetanic stimulation, and (c) there is worsening of endurance but no change in isometric twitch kinetics with increasing age during the first weeks of life.