Ventilatory chemosensitivity in the chick embryo

In the externally pipped chicken embryo, oxygen consumption through the chorioallantoic membrane ((V overdot)(O2) CAM) ranged between 2 and 55% (mean similar to 24%) of that through the lungs ((V overdot) (O2) lung). Hypercapnia (5'-10' of 2, 5, or 8% wCO(2)) or mild hypoxia (15% O-2) had minor effects on (V overdot)(O2), whereas moderate or severe hypoxia (10-5% O-2) caused large drops of (V overdot)(O2). Hypoxia or hypercapnia delivered through the lungs increased pulmonary ventilation (E), largely through increases in tidal volume (V-T). Exposures of the whole embryo provoked (V overdot)(E) responses either similar, or significantly higher, than with exposures of the lungs alone, because of greater increases in V-T. The larger the (V overdot)(O2) CAM, the smaller were the (V overdot)(E) and V-T responses when hypoxia or hypercapnia were delivered through the lungs. Hypoxic or hypercapnic exposures for longer periods of time (30'-40') gave qualitatively similar results. We conclude that in the externally pipped chick embryo (1) the increase in V-T is the primary means of expressing the hypoxic or hypercapnic (V overdot)(E) chemosensitivity, (2) hypometabolism contributes to the hypoxic hyperventilation, and (3) CAM gas exchange lowers the ventilatory effects of lung hypoxia or hypercapnia. (C) 2003 Elsevier Science B.V. All rights reserved.