Abstract
Summary: The relationships between tidal volume (V1), ventilation (V1), inspiratory duration (Ti), and total breath duration (Ttol) during hyperventilation induced by 4% CO2 exposure were studied in five term and four preterm lambs to evaluate the effect of continuous positive airway pressure (CPAP) on control of breathing. At barometric pressure VF was 308 ± 44 ml/kg and V1 was 41.5 ± 10.3 ml (mean ± SD) in term lambs; in preterm animals, VF was 511 ± 133 ml/kg and V1 was 32.6 ± 0.6 ml. Application of CPAP (+ 5 cm H2O) produced an increase in thoracic gas volume of 9.6 ± 3.4 ml/kg in term lambs and 9.6 ± 3.5 ml/kg in preterm lambs. VF, V1 and the slope of the V1-V1 relationship were not significantly affected by CPAP. At barometric pressure, all animals showed inverse curvilinear relationships between V1 and Ti and between Vi, and Ttoi. When CPAP was applied, Ti and the relationship of Vi to Ttod did not change; the curvilinear relationship between Vi and Ttod was unchanged in shape, but was shifted to the right due to a significant increase in expiratory time (Te) in response to the increase in end expiratory lung volume. The increase in Te was 0.10 ± 0.05 sec in term lambs (mean ± SD. P < 0.01) and 0.11 ± 0.04 sec in preterm lambs (P < 0.01). Vagotomy abolished the curvilinear relationship between Vi and Ttod and decreased the slope of the Vi-Vi, relationship. The data indicate that vagal feedback control of breathing is similar in term and preterm lambs. The mechanism responsible for breath-to-breath regulation of Ti and Ttod is unchanged when CPAP is applied and is dependent on phasic lung volume changes above end expiratory volume.
Speculation: Recent studies in human infants have shown that application of continuous positive airway pressure results in the prolongation of inspiratory time and the slowing of respiratory rate implicating either a vagal response (20) or the generation of intercostal afferent impulses related to a stahilization of the rib cage (10). Although our data in lambs cannot he extrapolated to the human infant, our results suggest that the beneficial effect of continuous positive airway pressure on apnea of prematurity is probably independent of the vagal control mechanism, and that the reflex phenomenon is prohably derived from the intercostal afferent impulses.
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Monin, P., Cashore, W., Hakanson, D. et al. Lack of Effects of Continuous Positive Airway Pressure on Vagal Control of Breathing in Term and Preterm Newborn Lambs. Pediatr Res 11, 967–971 (1977). https://doi.org/10.1203/00006450-197709000-00007
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DOI: https://doi.org/10.1203/00006450-197709000-00007