Measurement of single breath‐hold carbon monoxide diffusing capacity in healthy infants and toddlers

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 cmH 2 O (V 30 ) inhibit inspiratory effort. The respiratory system is then inflated with a test gas containing helium and a stable isotope of carbon monoxide (C 18 O), and a respiratory pause is maintained for 4 sec and followed by passive expiration to functional residual capacity. Concentrations of helium and C 18 O 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 cmH 2 O (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 (r 2  = 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. Pediatr Pulmonol. © 2006 Wiley‐Liss, Inc.