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

Abstract

SUMMARY1. The ventilatory response to square-wave challenges in end-tidal partial pressure of CO2 (Pc02) was investigated at three levels of arterial Po0 (Pa°2) in nineteen anaesthetized 2-to 11-day-old piglets.2. The ventilatory responses, measured on a breath-to-breath basis, were separated into a peripheral and a central component using a two-compartment model. Both components were described by a CO2 sensitivity, a time constant, a time delay and a single offset.3. Fifty-six responses were analysed against a background ofnormoxaemia (Pa°2 = 12 70 +0O72 kPa, mean + S.D.), fifty-three against a background of moderate hypoxaemia (Pao = 8-63 +034 kPa) and fifty-one against a background of severe hypoxaemia (Pa,02 = 4-98 +030 kPa).4. The sensitivity of the peripheral chemoreceptors in mediating the response to C02 increased from 38-3 + 17-0 ml min-kPa-1 kg-1 during normoxaemia to 48-8 + 15-3 ml min-kPa-1 kg-' during moderate hypoxaemia and to 72-9 + 24-0 ml min-1 kPa-1 kg-1 at severe hypoxaemia.5. As compared with the central CO2 sensitivity during moderate hypoxaemia and normoxaemia (1040± 39-0 and 1008 + 41 6 ml min' kPa-1 kg-', respectively) it decreased to 85 9 + 54-1 ml min-' kPa-1 kg-1 at severe hypoxaemia. 6. We conclude that in newborn piglets there is a positive interaction between hypoxia and hypercapnia at the level of the peripheral chemoreceptors while severe hypoxaemia reduced the C02 sensitivity centrally.

Blunted ventilatory response to hypoxia/hypercapnia in mice with cigarette smoke-induced emphysema

“…This positive interaction has been confirmed in recent studies carried out on goats, lambs, piglets, cats, rats, and mice (Daristotle et al 1987;Wolsink et al 1992;Carroll et al 1993;Tankersley et al 1994Tankersley et al , 2004Pepper et al 1995;Calder et al 1997), although some early studies showed a negative interaction in cats (Ou et al 1976). We compared the ventilatory response to hypoxic hypercapnia between CS-and FA-exposed mice.…”

A Comparison of the Ventilatory Response of Sleeping Newborn Lambs to Step and Progressive Hypoxaemia

“…The fact that the newborn appears to exhibit relatively greater depression than the adult to a similar stimulus has naturally suggested that it may be due to immaturity in the integration of central and peripheral responses to hypoxaemia (Johnston & Gluckman, 1993). A reduction in the PCOµ of the central chemoreceptor tissue may also play a significant role in determining the onset and extent of the decline in ventilation (Carroll, Canet & Bureau, 1987;Rigatto, Kwiatowski, Hasan & Cates, 1991;Wolsink, Berkenbosch, DeGoede & Olievier, 1991). This may occur as a result of the initial hyperpnoea blowing-off COµ, causing a fall in Pa,COµ, or as a result of hypoxaemia-induced cerebral vasodilatation (Neubauer, Santiago, Posner & Edelman, 1985).…”

Neonatal maturation of the hypercapnic ventilatory response and central neural CO2 chemosensitivity

“…The situation is a bit confusing in piglets. Anesthetized piglets (P2-P11) appear to have a more adult response pattern in which the ventilatory response to CO 2 is just as vigorous on P2 as it is in adults (Wolsink et al, 1992). However, the ventilatory response to CO 2 in intact piglets may reach its lowest point around P15 (Nattie, unpublished observations), and studies that are curtailed before 2 weeks of age may miss the developmental progression of ventilatory responses to CO 2 in piglets.…”