Abstract
Breathing frequency (f) in lambs falls with increasing postnatal age. They rely on powerful airway reflexes to maintain lung volume and an effective respiratory rhythm during sleep between 2-6 weeks of age. Small changes in ambient temperature (Ta) were observed to modulate f by effecting expiratory time (Te) and thus the dependancy on intra-airway vagal reflexes. Irreversible respiratory failure could thus occur.
The age relationship of Ta on f during sleep was therefore studied in detail in 9 chronically instrumented self-reared lambs at three Tas 10° , 15° , 20°C (in some 5°, 25° and 30°) at 2, 6, 12 and 28 days of age.
f decreased significantly with postnatal age (39.7 (3D) to 27.5 (28D) p > .001) regardless of Ta (10-20°C). No change in f occurred between 10 and 20°C at 2 or 6 days of age but a significant fall in f occurred between 20 and 10°C at 12 days (p < .001) and 28 days (p < .01). Shivering was observed in lambs < 6 days at 10°C and f increased markedly between 25 and 30°C.
Thus, f is sustained for the first 2 weeks by metabolic demands and then, as thermal efficiency improves, by vagal airway reflexes modulated by Ta before the chemical drive to breathing fully matures. A postneonatal vulnerability to sleep related respiratory failure perhaps analogues to SIDS is suggested by these results.
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Andrews, D., Wollner, J., Fedorko, L. et al. RESPIRATORY FAILURE AND THE MATURATION OF THE AMBIENT THERMAL STIMULUS TO BREATHING DURING SLEEP IN LAMBS. Pediatr Res 18, 796 (1984). https://doi.org/10.1203/00006450-198408000-00031
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DOI: https://doi.org/10.1203/00006450-198408000-00031