Hypoxic arousal is thought to be mediated through activation of peripheral chemoreceptors. Decreased ability to arouse in response to hypoxemia and maternal smoking are two factors believed to play a significant role in SIDS. The aim of this study was to determine if nicotine affects the arousal response to acute hypoxemia and whether this effect is associated with an altered cardiorespiratory response to decreased oxygen saturation.

Subjects & Methods: Five chronically instrumented, unanesthetized lambs (mean age 4±1 days) were studied during a 5 min hypoxic challenge (0.1 FiO2) during quiet sleep (QS) and active sleep(AS). Each lamb was studied during a saline infusion and during a 0.5μg/kg/min nicotine infusion on two consecutive days. Ventilation(V1), heart rate (HR), blood pressure (BP) and transcutaneous oxygen saturation (SaO2) were recorded. Sleep states and arousal were defined by electrophysiologic and clinical criteria. Time from start of hypoxia to arousal from sleep, SaO2 at arousal, peak V1 at 2 min of hypoxia and HR and BP at peak V1 were calculated.

Results: No consistent pattern of arousal with regard to nicotine infusion was identified in AS. In QS, however, the mean time from start of hypoxia to arousal increased from 1.0±0.8 min during control to 2.8±1.6 min during nicotine infusion (p<0.05). The mean SaO2 at arousal was 77±12% during control, and 59±13% during nicotine infusion (p=0.02). In 4 of the 5 animals during nitcotine infusion, the hypoxia-induced increases in V1 and HR were lower than during control, 30±12% and 63±31 bpm, respectively, although these differences did not attain statistical significance. No increase in BP was observed during nicotine infusion.

Conclusion: The finding of delayed arousal at a lower SaO2 and also a lower hypoxic ventilatory response in most animals suggest that nicotine impairs oxygen sensitivity which is believed to be deficient in SIDS victims. (Supported by HD 28916 and HL 14214)

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Hafström, O., Milerad, J., Asokan, N. et al. NICOTINE DELAYS AROUSAL DURING HYPOXEMIA IN SLEEPING LAMBS. † 2302. Pediatr Res 39, 386 (1996).

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