The effect of changes in inspiratory time on neonatal triggered ventilation

Nine preterm infants with hyaline membrane disease were studied using a ventilator triggered from abdominal movement. It was possible to alter respiratory rate over a short space of time by adjustments of the inspiratory time setting. There was a marked inverse relationship between inspiratory time and both ventilator and baby's respiratory rate-mean baby respiratory rate was 62 breaths/min at an inspiratory time of 0.2 s and 45 breaths/min at 0.8 s. This drop was statistically significant (P<0.005). Mean tidal volume changed little over this range. This interaction meant that mean minute ventilation was optimal at inspiratory times of 0.2 to 0.4 s, being 269 and 258 ml/kg per minute, respectively, but at 0.8 s fell to 213 ml/kg per minute (P<0.05).