Parental tobacco smoking is associated with lower airway function and an increased incidence of wheezy respiratory illnesses in infants. We evaluated in 76 healthy infants whether exposure to parental tobacco smoking was associated with airway hyperreactivity, which could contribute to lower airway function and the increased wheezy illnesses. Airway function was measured using the raised-volume rapid thoracic compression technique, and airway reactivity was assessed by methacholine challenge (0.015-10 mg/ml), which was stopped for a more than 30% decrease in forced expiratory flow (FEF)(75) or the final dose with a less than 30% decrease. Parental tobacco smoking was associated with lower baseline airway function (FEF(50), 600 vs. 676 ml/second, p < 0.04; FEF(25-75), 531 vs. 597 ml/second, p < 0.05). Infants exposed to tobacco smoking were approximately half as likely to develop a more than 30% decline in FEF(75) at any given methacholine dose (hazard ratio = 0.4, p = 0.001). In addition, a history of asthma in an extended family member increased the likelihood that an infant would develop a more than 30% decline in FEF(75) (hazard ratio = 1.7, p = 0.04). We conclude that exposure to parental smoking is associated with lower airway function but not increased airway reactivity; however, family history of asthma is associated with heightened airway reactivity.
We describe a method for measuring carbon monoxide diffusing capacity (DL(CO)) and alveolar volume (V(A)) in sleeping infants, using a single 4-sec breath-hold technique. The breath-hold maneuver is obtained by inducing a respiratory pause of the respiratory system. Several inflations of the respiratory system with room air to a lung volume with an airway pressure of 30 cmH2O (V30) inhibit inspiratory effort. The respiratory system is then inflated with a test gas containing helium and a stable isotope of carbon monoxide (C18O), and a respiratory pause is maintained for 4 sec and followed by passive expiration to functional residual capacity. Concentrations of helium and C18O are continuously measured with a mass spectrometer. Twelve healthy infants between 6-22 months of age were evaluated. For 9 of 12 subjects, duplicate measurements of alveolar volume at 30 cmH2O (V(A30)) and DL(CO) were within 10%, which are the recommendations for older children and adults. Among these 9 subjects, values of V(A30) and DL(CO) increased with increasing body length (r2 = 0.82 and 0.79, respectively). The remaining 3 subjects had two values within 10-15%. Measurement of V(A) and DL(CO) with the single breath-hold technique at an elevated lung volume offers the potential to assess growth and development of the lung parenchyma early in life.
Respiratory system compliance (Crs) in infants with cystic fibrosis (CF) has been reported as decreased or not different compared with healthy control subjects; however, the reported measurements of Crs were "quasi-static" or by the single-breath occlusion technique, with all measurements limited to tidal lung volume, as well as using inspiratory rather than expiratory pressures. We compared the passive elastic properties of the respiratory system of sleeping infants with CF (n = 10) and healthy control subjects (n = 34) by measuring static deflation pressure--volume (PV) curves from a lung volume at 30 cm H(2)O (V(30)) to FRC. There was no significant difference between the groups for Crs, which was measured as the slope between airway relaxation pressures of 5 and 15 cm H(2)O, the linear portion of the deflation PV curve. In addition, when PV curves were normalized to V(30), there were no differences between the infants with CF and healthy control subjects in the fractional volumes at any airway pressure. The infants with CF had significantly lower forced expiratory flows; however, lower flows did not correlate with fractional volumes measured from the PV curve. Our findings indicate that infants with CF have normal elastic properties of the respiratory system.
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