Abstract 2106

We examined the various ventilatory morphologies of periodic breathing during quiet sleep in four groups of subjects: Groups 1 (n=10, gestational age 30±1 wk, postconceptional age 32±1 wk), Group 2 (n=10, GA 31±1 wk, PCA 36±1 wk), Group 3 (n=10, GA 38±1 wk, PCA 42±1 wk, ), and Group 4 (n=10, weight 111±9 kg, age 50±4 yr). Respiratory pattern and ventilation were measured using a flow-through system, and sleep state was monitored. The breathing morphologies were defined according to the respiratory flow as crescendo-decrescendo, flat, and decrescendo. We found 1) a predominant crescendo-decrescendo type of breathing in preterm infants (Groups 1 and 2, >50%) and this changed to a predominant decrescendo breathing in adults (Group 4, 50%); 2) the duration of the total cycle, breathing and apneic phases did not change significantly among the neonatal groups within the same breathing morphology, but they almost doubled in adult subjects; however, the number of breaths per breathing interval remained the same (crescendo-decrescendo) or less (flat and decrescendo) in adults as compared to preterm infants; 3) the duty cycle (breathing interval/cycle duration) was higher in adults only in the crescendo-decrescendo group; 4) ventilation was highest in the middle of the breathing interval in the crescendo-decrescendo type, in the beginning of the interval in the decrescendo type, and more uniform in the flat type of breathing interval; and 5) at the beginning of each breathing interval, alveolar PACO2 was highest and alveolar PAO2 and O2 saturation lowest. The findings suggest a change in the strategy of the respiratory control system during periodic breathing between the infant and the adult, with a switch from a predominately crescendo-decrescendo to a predominately decrescendo pattern. We speculate that this change is related to the very low lung volume in preterm infants due to poor chest wall recoil, which predisposes to collapse at the end of apnea; this prevents the chemical drive of inducing large tidal volumes at the beginning of the next breathing interval, a fact that does not apply to adult subjects.

(Supported by The Children's Hospital Foundation of Manitoba Inc.)