Comparative physiology of respiratory mechanisms: a study of the effect of carbon dioxide inhalation on the decerebrate duck

Abstract

The respiratory response to CO₂ inhalation was investigated on decerebrate Aylesbury ducks. CO₂ was administered via a low resistance, low dead space perspex valve and tracheotomy tube. The ducks remained in good condition with normal postural and righting reflexes for several days. On inhaling a new CO₂-air mixture it took about 10 minutes to achieve a new steady state of ventilation.

The ventilatory minute volume rose proportionately with the inspired CO₂ concentration and the percentage increase ventilation was comparable with decerebrate hens and with man. Inspired CO₂ concentration above 6% caused depression of respiration. CO₂ inhalation had little effect on respiratory frequency; ventilation was increased mainly by increased tidal volume; the relation between ventilation and tidal volume was linear up to four times the resting ventilation.

The R.Q. change on CO₂ inhalation found in the duck was different from that seen in man, but similar to that of hens. The quantity of CO₂ eliminated in the duck was similar to that found in most studies in mammals but the quantity of CO₂ taken up was about ten times larger.

The basic pattern of the effect of CO₂ inhalation in stimulating respiration seems similar in ducks (diving birds), hen (non-diving birds) and man. But in the ducks much larger quantities of CO₂ were lost from the inspired CO₂ - air mixtures than observed in most studies on the mammals.