Airway thermal volume in humans and its relation to body size

Vladimir B. Serikov 1 , E. Heidi Jerome 2 , Neal W. Fleming 1 , Peter G. Moore 1 , Frederick A. Stawitcke 4 , and Norman C. Staub 3 1 Department of Anesthesiology, University of California, Davis 95616; 2 Department of Anesthesiology and 3 Cardiovascular Research Institute, University of California, San Francisco 94143; and 4 Hewlett-Packard Laboratories, Palo Alto, California 94303 Received 4 December 1996; accepted in final form 10 April 1997. Serikov, Vladimir B., E. Heidi Jerome, Neal W. Fleming, Peter G. Moore, Frederick A. Stawitcke, and Norman C. Staub. Airway thermal volume in humans and its relation to body size. J. Appl. Physiol. 83(2): 668-676, 1997. The objective of this study was to investigate the influence of volume ventilation ( E ) and cardiac output ( ) on the temperature of the expired gas at the distal end of the endotracheal tube in anesthetized humans. In 63 mechanically ventilated adults, we used a step decrease in the humidity of inspired gas to cool the lungs. After change from humid to dry gas ventilation, the temperature of the expired gas decreased. We evaluated the relationship between the inverse monoexponential time constant of the temperature fall (1/ ) and either E or . When E was increased from 5.67 ± 1.28 to 7.14 ± 1.60 (SD) l/min ( P = 0.02), 1/ did not change significantly [from 1.25 ± 0.38 to 1.21 ± 0.51 min 1 , P = 0.81]. In the 11 patients in whom changed during the study period (from 5.07 ± 1.81 to 7.38 ± 2.45 l/min, P = 0.02), 1/ increased correspondingly from 0.89 ± 0.22 to 1.52 ± 0.44 min 1 ( P = 0.003). We calculated the airway thermal volume (ATV) as the ratio of the measured values to 1/ and related it to the body height (BH): ATV (liters) = 0.086 BH (cm) 9.55 ( r = 0.90). cardiac output; ventilation; temperature; lungs; lung mass; lung capacity; heat exchange; conductivity; noninvasive measurement 0161-7567/97 $5.00 Copyright © 1997 the American Physiological Society