Heart rate response to transient chemoreceptor stimulation in term infantsis modified by exposure to maternal smoking

Modulation of heart rate (HR) during transient hyperoxia, hypoxia, and hype rcapnia was studied in 46 healthy term infants on 103 occasions (postnatal d 2 to 82). Twenty-three infants had smoking mothers (median, 11 cigarettes /d). Transient chemoreceptor stimuli (100% O-2, 15% O-2, or 3% CO2) were pr esented repeatedly during quiet sleep. Beat-by-beat IIR and breath-by-breat h ventilation were recorded continuously. The coherently averaged HR and ve ntilation responses to each stimulus were calculated for each infant at eac h age. Outcome variables (HR change from baseline to end of stimulation, ma ximum HR change, and time to half-maximum) were analyzed by ANOVA. Overall, HR declined during hyperoxia (median change, 4.2 beats/min) and rose durin g hypoxia (median change, 4.2 beats/min) and hypercapnia (median change, 4. 6 beats/min). The percentage change in HR was positively correlated with th e percentage change in ventilation (p < 0.001). Increasing number of cigare ttes smoked by the mother was correlated with deeper HR declines and smalle r HR rises (p = 0.02). For the population as a whole, the HR response lagge d 3.8 s behind the ventilatory response during hyperoxia and hypoxia (p < 0 .001), whereas during hypercapnia there was no significant lag. The lag in HR response in the smoke-exposed group was 3.5 s greater than that in the c ontrol group for all three stimuli (p = 0.001), and the difference increase d with the number of cigarettes smoked by the mother (p < 0.01). Both pulmo nary reflexes and the type of the chemoreceptor stimulus seemed to influenc e HR. Maternal smoking affected the magnitude and time-course of the HR res ponse in a dose-dependent manner.