Dissociation between CO2/H+ ventilatory chemosensitivity and room air pulmonary ventilation

The purpose herein is to report several examples in awake mammals of a dissociation between CO 2 ‐H + ventilatory chemosensitivity and room air V I . We found in piglets that eupneic PaCO 2 increased gradually from 26.5 ± 0.5 to 34.4 ± 1.2 between postnatal days (PN) 3–4 and PN 19–21 but CO 2 sensitivity (expressed as V I 5% CO 2 / V I room air) was unchanged between PN 3–4 and PN 19–21. In Sprague Dawley rats, we found that CO 2 sensitivity was minimal between PN 0 and PN 14, but then it increased dramatically between PN 14 and PN 21, whereas room air V I /body weight decreased gradually from PN 0 to PN21. Finally, we found that in adult goats, neurotoxic lesioning of the rostral ventrolateral medulla, medullary raphe, and cerebellar fastigial nucleus (CFN) decreased CO 2 sensitivity, but only increased eupneic PaCO 2 by 2.0 ± 1.1, 0.2 ± 0.8, and 2.9 ± 0.3% respectively. Moreover, the CFN lesions doubled the day‐to‐day variability in CO 2 sensitivity but did not alter variability of eupneic PaCO 2 . We conclude that under the conditions listed above, CO 2 ‐H + ventilatory chemosensitivity is not a critical determinant of eupneic V I . (Supported by NIH HL‐25739 and Department of Veterans Affairs.)