The oxygen consumption of new‐born and adult mammals. Its dependence on the oxygen tension in the inspired air and on the environmental temperature

Abstract

Infants during birth and shortly afterwards are particularly liable to suffer from hypoxia, and much research has been directed to elucidating the effects of oxygen lack in the new-born. Evidence that moderate hypoxia (15% oxygen) causes a significant reduction in oxygen consumption in human infants was first produced by Cross, Tizard & Trythall (1955; it was later reported that lambs (Acheson, Dawes & Mott, 1957), and puppies and kittens (Moore, 1956a, b), respond in a similar fashion. It thus appeared that the new-born respond differently from adults, since it was generally accepted that the oxygen consumption of an adult mammal does not fall until death due to hypoxia is imminent (in the region of 6 % oxygen). Then, in a review of the physiology of the new-born, McCance & Widdowson (1957) pointed out that adult small mammals behave in the same way as new-born animals, and not in the 'adult' manner. The situation was now confusing, since it was not clear whether it was size or maturity that determined the response to hypoxia. The present experiments were undertaken in order to make a direct comparison between new-born and adult animals of roughly the same size, and to obtain more information about the various types of response to hypoxia. A brief preliminary report of this work has been published (Hill, 1958). METHODSIn order to investigate the effect on metabolism of hypoxia, immaturity, body size and environmental temperature, an apparatus had to be devised which would measure the oxygen consumption of a single unanaesthetized small mammal, breathing gas of any chosen composition between 21 % and 5 % oxygen in nitrogen, at various environmental temperatures. Good time resolution was essential, so apparatus that would give a continuous direct record was desirable.Oxygen lies in the fact that any gas other than air must be supplied from a reservoir. Closedcircuit methods are more readily adapted to the problem in hand, since they permit much better time resolution, and easily lend themselves to graphic recording. In a closed circuit, if the C02 produced by the animal is absorbed, then the animal's oxygen consumption is indicated continuously by the amount of gas that must be added to keep the volume of the circuit constant. A closed-circuit apparatus was adopted; its essential features are: (1) The oxygen content of the circuit gas is readily and predictably varied, as required, by removing and replacing oxygen, i.e. by altering the total volume of the circuit. (2) Once the chosen oxygen level has been attained an automatic device is then used to feed oxygen into the circuit at exactly the same rate as the animal consumes it. The volume of the circuit is held constant, and thus the composition of the circuit gas is kept constant while oxygen consumption measurements are made. (3) The amount of oxygen allowed into the circuit during each minute or half minute is recorded on a kymograph, measuring the animal's rate of oxygen consumption, A02/At. (4) The need for a temperaturecontrolled room has been obviated by ...

The effects of hypoxia in the new‐born lamb before and after denervation of the carotid chemoreceptors*

“…As has been mentioned previously, some evidence is available (Reeves & Leathers, 1964) which suggests that the oxygen uptake is dependent on and limited by pulmonary artery flow in the new-born calf and it is possible that the observed fall in oxygen uptake in the new-born of a number of species Adamsons, 1959;Cross et al 1959;Hill, 1959) may be explained in these terms. It may also be pertinent that the greatest fall in oxygen uptake observed by Cross et al (1959) was in those new-born lambs whose resting oxygen uptake was highest.…”

Oxygen Consumption in the New‐born Rat and the Effects of Maternally Administered Analgesics

“…Hill (1959) found that for kittens maintained at the neutral temperature, the oxygen concentration of inspired air could be reduced to 10% before oxygen consumption was affected. However, more relevant is the report of Taylor (1960) …”

Glutamatergic neurotransmission modulates hypoxia-induced hyperventilation but not anapyrexia

“…Hypoxia reduces Tb and metabolism in newborns and adults of many species (27,28), including humans (29). Hypoxia also leads animals to select ambient temperatures that favor Tb below those seen in normoxia, suggesting the occurrence of a drop in the thermoregulatory set point (30,31).…”