Assessment of the central chemosensitivity in man under transient or progressive hypercapnia

AbstractIn healthy man, the central chemosensitivity to CO2 was studied after depression of the arterial chemoreflex drive by inhalation of pure oxygen. The effectiveness of the functional decrease of arterial chemoreceptor function was assessed by the delayed hyperventilation which followed transient inhalation of hypercapnic gas mixtures for 3 or 5 breaths in hyperoxic conditions. In such a case, the first significant increase in tidal volume (VT) occurred 13.9 ± 3.2 (SE) sec later than the early change in this variable measured in normoxic conditions. The stimulus strength was estimated by the change in CO2 partial pressure in end-tidal alveolar gas (δPETCO2). The central chemosensitivity (sCO2), defined as the ratio between change in ventilation (δV) and δPETCO2, was assessed either by transient inhalation of gas mixtures containing 5 to 8 % CO2 in pure O2 (“varying transients”) or by progressive hypercapnia (rebreathing in pure O2).(1) In both cases, the first significant change in ventilation was du...