Eur J Appl Physiol (1982) 48:415-422 European Journal of Applied Physiology' and Occupational Physiology 9 Springer-Verlag 1982 Arterial Carbon Dioxide Estimates During Upper Body Exercise* Michael N. Sawka, Daniel S. Miles, Jerrold S. Petrofsky, and Roger M. Glaser Dept. of Physiology, School of Medicine, Wright State University, Dayton, OH 45435, USA Veterans Administration Medical Center, Dayton, OH 45428, USA Summary. The purpose of this investigation was to develop a regression equation to predict arterial carbon dioxide tensions (PaCO2) from end-tidal carbon dioxide tensions (PETCO2) during upper body exercise. A secondary purpose was to examine the ability of an existing regression equation developed for lower body exercise (Jones et al. 1979) to predict PaCO2 during upper body exercise. Nine male subjects completed a progressive intensity, discontinuous test on an arm crank ergometer with submaximal power output (PO) levels of 25, 74, and 98 W. During each submaxirnal PO level, steady state oxygen uptake was achieved and appropriate physiological responses were measured. PETCO2 was found to be significantly (p < 0.05) higher than PaCO2 at both the 74 and 98 W levels. In addition, when PETCO2's were regressed against their corresponding PaCO2 tensions a correlation coefficient of r = 0.66 was found. Based upon our subjects' PETCO2 and tidal volume (VT) responses, a multiple regression equation was constructed to predict their PaCO2 (SPaCO2), this being SPaCO2 = 24.7 + 0.43 PETCO2 - 3.3 Vx. When SPaCO2 was regressed against the corresponding PaCO2 tension, a correlation coefficient of r = 0,84 was found. When the equation of Jones et al. (1979) was used to predict PaCO2 a correlation coefficient of r = 0.77 was found. No significant differences were found between tensions predicted by either equation and the actual PaCO 2 at any PO level. These results indicate that either prediction equation can be satisfactorily used to estimate PaCO2 tensions during upper body exer- cise. Key words: Alveolar-arterial CO 2 differences - Arm crank exercise - Arterial PCO2 estimates - End-tidal CO2 - Upper body exercise * Supported by the Medical Research Services of the Veterans Administration, NIH Grant No. 7RO1NS16003-01 and by Air Force Contract No. F33615-78-0501 Offprint requests: Dr. Michael N. Sawka, US Army Research Institute of Environmental Medicine, Kansas Street, Natick, MA 01760, USA 0301-5548/82/0048/0415/$ 01.60