Postnatal Development of Responses to Airflow Obstruction

Abstract

1. Obstruction of the upper airway could be an initiating factor in the Sudden Infant Death Syndrome (SIDS). Responses to upper airway obstruction include augmentation of respiratory efforts, active dilation of the upper airway and electrocortical arousal. Vulnerable individuals may fail to mount these responses effectively. 2. Respiratory and arousal responses to obstruction of the upper airway have been investigated in newborn lambs. In conscious lambs, nasal obstruction causes a profound augmentation of inspiratory efforts, mild asphyxiation and eventual formation of an oral airway. The ability to establish an oral airway involves both chemoreception and mechanoreception and improves with age. 3. In sleeping lambs, obstruction of tidal airflow leads to progressive hypoxaemia, augmentation of inspiratory efforts, bradycardia and arousal. Arousal occurs earlier and with less hypoxaemia and bradycardia in non-REM sleep than in REM sleep. Arousal occurs after inspiratory efforts have increased to the same extent during both sleep states, suggesting that mechanoreception, or a sense of inspiratory effort, is important in initiating arousal. 4. Obstruction of nasal tubes tends to cause arousal from sleep earlier, and with less hypoxaemia and less augmentation of inspiratory effort, than when a more compliant face mask is obstructed. This supports the suggestion that mechanoreception, which may be involved in the perception of inspiratory effort, is a determinant of arousal. 5. With increasing postnatal age, lambs become less arousable in response to airflow obstruction when in REM sleep. This suggests that lambs may become progressively more vulnerable to the effects of airway obstruction during the immediate newborn period.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Prior Hypoxia Exposure, Endotoxin and Sleep State on Arousal Ability to Airway Obstruction in Piglets: Implications for Sudden Infant Death Syndrome

“…However, during the pre-endotoxin period, respiratory responsiveness was reduced in REM sleep, consistent with studies in dogs [19,35] , lambs [20] and piglets [21] exposed to arousal stimuli. These fi ndings differ from human infants, where NREM sleep is consistently associated with an elevation in arousal threshold [22,36,37] .…”

“…The impairment to autonomic function implied by these fi ndings may be refl ected in dysfunction of airway mechanoreceptors [16,17] . Mechanoreceptor activation is important for the initiation of protective responses during upper airway obstruction [18][19][20] and was probably the common stimulus mediating the response to airway obstruction in the present animals (given the consistently small reduction in arterial SaO 2 observed during obstruction tests). However, we found no evidence of impaired responsiveness to airway obstruction during the thermo- genic phase of a fever.…”

“…Findings from our laboratory on neonatal piglets have shown that experimentally induced endotoxin-generated thermogenesis is associated with a reduction in heart rate variability and barorefl ex sensitivity [15] . The impairment to autonomic function implied by these fi ndings may be refl ected in dysfunction of airway mechanoreceptors [16,17] , which are important for the initiation of protective responses during upper airway obstruction [18][19][20] .…”

“…We examined the individual and combined effect of each of these on arousability to complete and subtotal airway obstruction. Because arousal mechanisms are affected by sleep state in animal models [19][20][21] and neonatal human infants [22] , we also compared responses to airway obstruction between non-rapid eye movement (NREM) and rapid eye movement (REM) sleep states.…”

It Takes a Mouth to Eat and a Nose to Breathe: Abnormal Oral Respiration Affects Neonates' Oral Competence and Systemic Adaptation

“…Thus, any disruption of the normal nasal breathing route through (uni- or bilateral) nasal obstruction may affect not only the respiratory function but also all interdependent sensorimotor nasal, oral, and laryngeal functions. Nasal obstruction can result from either congenital or postnatal causes and may amplify resistance to air-flow and impair sucking-swallowing responses, with increased risks of aspiration or of more severe and threatening respiratory distress conditions [15]. In addition, nasal obstruction alters the “trophic” flow of sensory information towards the olfactory brain.…”