Speed and Profile of the Arterial Peripheral Chemoreceptors as Measured by Ventilatory Changes in Preterm Infants

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Abstract
To measure the response time of the peripheral chemoreceptors, we studied 13 preterm infants [birth weight 1602 ± 230 g (mean ± SEM); gestational age 31 ± 1 wk; postnatal age 15 ± 1 d] during inhalation of 21% O2 (15 ± 5 s) followed by 100% O2 (1 min). We used a flow-through system to measure ventilation and gas analyzers to measure alveolar gases. Hypoventilation was observed at 3.6 ± 0.6 s and was maximal at 6.8 ± 1 s after O2 began. This maximal response was always associated with an apnea (>3 s). Alveolar Po2 increased from 13.5 ± 0.1 kPa (101 ± 0.8 torr) (control) to 28.0 1.2 kPa (210 ± 9 torr) (1st O2 breath), to 42.0 ± 2.4 kPa (315 ± 18 torr) (1st hypoventilation), to 45.9 ± 4.1 kPa (344 ± 31 torr) (breath preceding maximal response), and to 53.6 ± 4.1 kPa (402 ± 31 torr) (at maximal response). Minute ventilation was 0.192 ± 0.011 (control), 0.188 ± 0.011 (1st O2 breath), 0.088 ± 0.016 (1st hypoventilation; p < 0.0001), 0.122 ± 0.016 (breath preceding maximal response; p < 0.0002), and 0.044 ± 0.011 L/min/kg at maximal response (p < 0.0001). This decrease in ventilation was due to a decrease in frequency with no appreciable change in tidal volume. The initial period of hypoventilation (19 ± 4 s) was followed by a breathing interval (10 ± 2 s) and a second period of hypoventilation (14 ± 3 s) before continuous breathing resumed. These findings suggest that the peripheral chemoreceptors in these infants have a high baseline activity and a fast response time.

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