ELSEVIER Respiration Physiology 96 (1994) 99-110 RESPIRATION PHYSIOLOGY Tidal volume perception in normal subjects: the effect of altered arterial Pco2 Harold L. Manning *'a, Scott Slogic b and J.C. Leiter c Departments of aMedicine, b Respiratory Care and ~ Physiology, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, USA Accepted 11 October 1993 Abstract We examined the relationship between tidal volume (VT) perception and level of CO2. Ten normal subjects were connected to a volume-cycled ventilator set in control mode, and VT and respiratory rate were adjusted until subjects were comfortable. At 2 levels of CO 2 which differed by 6-8 mmHg, subjects rated ten different ventilator tidal volumes which ranged from 40-200% of the VT that made them comfortable at the lower CO 2. Despite large differences in inspira- tory muscle activity, there was no significant difference between the two levels of CO2 for either the exponent [1.39 + 0.35 vs 1.36 + 0.49 (low CO 2 vs high CO2, mean + SD), P> 0.5] or constant (-0.09 + 0.12 vs -0.14 _+ 0.17, P> 0.1) for VT perception. For the group, there was no correla- tion between the hypercapnic ventilatory response (HCVR) measured by rebreathing and the exponent for VT perception. We conclude that: (1) the level of CO2 does not influence magni- tude estimation of VT; (2)respiratory muscle activity is not essential to VT perception; and (3) there is no correlation between the HCVR and magnitude estimation of VT. Key words: Carbon dioxide; Mammals, human; Perception, tidal volume; Sensation, respiratory, CO2; Ventilation I. Introduction Tidal volume (VT) is one of several respiratory sensations that can be quantified. For many sensory modalities, the relationship between stimulus magnitude (q~) and the magnitude of the resulting sensation (0) can be expressed by Stevens' law, 0= kq~ n, where the exponent n is an index of the sensitivity of the subject to that particular stimulus. A number of factors influence VT perception, including chest wall vibration (Stubbing et al., 1981), the mechanism of VT production (active vs passive) (Stubbing * Corresponding author. Tel.: (603)650-5533; Fax: (603)650-4437. 0034-5687/94/$7.00 © 1994 Elsevier Science B.V. All rights reserved SSD1 0034-5687(93)E0092-Y