Lack of positive interaction between CO2 and hypoxic stimulation for P-CO2-VAS response slope in humans

To compare the effect of hypoxia on ventilatory responses and respiratory s ensation to carbon dioxide. 29 young adults were examined using a modified Read's rebreathing method with four experimental conditions. We used varyin g gas mixtures and kept PETO2 constant at > 300. 100, 80 and 60 mmHg for ea ch four rebreathing tests. Respiratory sensation was measured br visual ana log scale (VAS). Thr slope of the CO2-ventilation response curve increased significantly with hypoxia. confirming a positive ventilatory interaction b etween hypoxia and hypercapnia. However, the slope of the CO2-VAS response curve remained unchanged. The VE-VAS relation slope tended to become depres sed with advancing hypoxia. i.e. the magnitude of VAS elicited by a given v entilation decreased with hypoxia, signifying that dyspneic sensation was e ffectively mitigated during hypoxic hyperventilation. We suggest that this relief of dyspneic sensation might be due to the inhibitory respiratory eff ect from augmented pulmonary stretch receptor (PSR) activity. (C) 2001 Else vier Science B.V. All rights reserved.