Because we believe that the use of a face mask in the measurement of tidal volume in infants may be associated with alterations in tidal volume and breathing pattern, we devised and validated a headbox with attached pneumotachometer that allows infants to lie in a quiet undisturbed state while measurements are made. We bench-tested the headbox system, then applied it and a conventional face mask-pneumotachograph system, in random order, to 20 preterm infants to measure tidal volume, minute volume, and number of apneic episodes. Control was provided by application of an inductive plethysmograph to all subjects for documentation of respiratory rate and nonquantitated tidal volume amplitude. Measurements completed on 16 of the 20 infants show that tidal volume and breathing frequency are decreased and number of apneas increased using the headbox and suggest that measurement of tidal volume and apneic episodes by headbox more accurately reflects the physiologic baseline condition of the resting preterm infant.
Courtney et al. (Sat,) studied this question.