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 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.