The respiratory response of the new‐born lamb to inhaled CO₂ with and without accompanying hypoxia*

Abstract

and values for both were reduced with the acid-base disturbances seen in the first 10 days after birth. Evidence was given which suggested that the response of the new-born lamb to inhaled C02 was similar to that of man acclimatized to a P-02 of 70-75 mm Hg.5. In the lightly anaesthetized lamb, bilateral section of the sinus nerves caused a small reduction in the sensitivity to inhaled 5 % C02 in air, an increase in the respiratory lag and a reduction in the rate at which v increased.6. It was concluded that, in the new-born lamb, the carotid chemo-* Supported in part by USPHS grant HE 06285.

The effects of hypoxia on the ventilatory response to sudden changes in CO2 in newborn piglets.

“…In preterm human infants and preterm primates the total CO2 slope decreased when the inspiratory 02 concentration was lowered Guthrie et al 1985) despite the positive C02-02 interaction at the peripheral chemoreceptor level that was found in preterm infants (Albersheim et al 1976). Purves (1966) showed that in the term newborn lamb the total CO2 slope increased as Pa 2 fell, as in our piglets. and Guthrie et al (1985) speculated that the negative interaction between 02 and CO2 in infants may be related to different changes in medullary blood flow induced by hypoxia and hypercapnia in the newborn compared to adults (Hernandez, Brennan, Vannucci & Bowman, 1978;Rosenberg, Jones, Traystman, Simmons & Molteni, 1982;Koehler, Jones & Traystman, 1982).…”

“…The secondary depression, however, was found to be central of origin (Lawson & Long, 1983;Darnall et al 1991). Purves (1966) observed in one lamb an appreciable depression of the C02 slope during severe hypoxia (Pa, o2 = 2 8 kPa). He considered this as an example of a probably central depression of respiration.…”

“…The question arises whether the depression of the CO2 sensitivity by hypoxia is a common feature in young mammals. Purves (1966) .showed that in the newborn lamb the CO2 slope varied inversely with Pa°2 as in the adult. Only severe hypoxia in one lamb caused a marked depression of the slope.…”

The reproducibility of the response of the human newborn to CO2 measured by rebreathing and steady‐state methods.

“…Using three-point measurements to define 1i-PET co2 slopes, we found alinearities, or points of inflexion, in six of eight response lines. Alinearities of this sort have been described (Dejours et al 1965;Purves, 1966), and may arise because the alveolar PCO2 is underestimated when the Vt is small. Under such circumstances, measurements made in air should be ignored; the slope is best measured between the two hypercapnic points (Dejours et al 1965;Purves, 1966).…”

“…Alinearities of this sort have been described (Dejours et al 1965;Purves, 1966), and may arise because the alveolar PCO2 is underestimated when the Vt is small. Under such circumstances, measurements made in air should be ignored; the slope is best measured between the two hypercapnic points (Dejours et al 1965;Purves, 1966). This observation has practical importance: our results indicate that twopoint measurements of slope (using air and 4 % C02) would have significantly underestimated the ventilatory response in most tests, calling into question the reliability of results obtained in this manner.…”