Ventilatory response to increased dead spaces in the first week of life

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Abstract
We have developed a method for quantitatively assessing respiratory control in a group of 10 full‐term healthy babies, mean age at test 5 days, by measuring their ventilatory response to added external dead spaces. The dead spaces were equal to 0.5, 1, 2, and 3 anatomic dead spaces (2.2 ml/kg body weight), respectively. Tidal volumes were measured by a nasal mask and a 200‐I rigid container. End‐tidal CO2 was monitored via a tube in the nostril by a mass spectrometer. Baseline measurements were made during a 10‐minute period, after which similar recordings were obtained with each of the dead space tubes. The system was calibrated against a 20‐ml syringe. The mean baseline ventilation was 602 ml/minute. On the addition of 0.5, 1, 2, and 3 dead spaces, minute ventilations were increased by 37.5, 74.7, 150.7, and 273.6%, respectively. These increases were due to rises in tidal volume rather than respiratory rate. End‐tidal CO2 rose by 1.8 and 4 mmHg on the addition of 2 and 3 dead spaces. When the results were compared with expected minute ventilations—based on the baseline recordings and corrected for the added dead spaces and for changes in anatomic dead space ventilation due to alterations in respiratory rate—the results were within 10% of expected values.