Measurement of cardiac output during exercise by open-circuit acetylene uptake

• Published in: Journal of applied physiology (1985) 1999-10, Vol.87 (4), p.1506-1512
• Main Authors: Barker, Rebecca C, Hopkins, Susan R, Kellogg, Nancy, Olfert, I. Mark, Brutsaert, Tom D, Gavin, Timothy P, Entin, Pauline L, Rice, Anthony J, Wagner, Peter D
• Format: Article
• Language: English
• Subjects: Acetylene - pharmacokinetics; Adult; Anatomy & physiology; Biological and medical sciences; Cardiac Output - physiology; Cardiology - methods; Exercise; Exercise - physiology; Female; Fundamental and applied biological sciences. Psychology; Gases; Heart; Humans; Male; Oxygen Consumption - physiology; Solubility; Space life sciences; Vertebrates: cardiovascular system
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.1999.87.4.1506

1  Department of Medicine, University of California, San Diego, La Jolla, California 92093; and 2  Department of Thoracic Medicine, Royal Adelaide Hospital, Adelaide, South Australia, Australia Noninvasive measurement of cardiac output ( T ) is problematic during heavy exercise. We report a new approach that avoids unpleasant rebreathing and resultant changes in alveolar P O 2 or P CO 2 by measuring short-term acetylene (C 2 H 2 ) uptake by an open-circuit technique, with application of mass balance for the calculation of T . The method assumes that alveolar and arterial C 2 H 2 pressures are the same, and we account for C 2 H 2 recirculation by extrapolating end-tidal C 2 H 2 back to breath 1   of the maneuver. We correct for incomplete gas mixing by using He in the inspired mixture. The maneuver involves switching the subject to air containing trace amounts of C 2 H 2 and He; ventilation and pressures of He, C 2 H 2 , and CO 2 are measured continuously (the latter by mass spectrometer) for 20-25 breaths. Data from three subjects for whom multiple Fick O 2 measurements of T were available showed that measurement of T by the Fick method and by the C 2 H 2 technique was statistically similar from rest to 90% of maximal O 2 consumption ( O 2 max ). Data from 12 active women and 12 elite male athletes at rest and 90% of O 2 max fell on a single linear relationship, with O 2 consumption ( O 2 ) predicting T values of 9.13, 15.9, 22.6, and 29.4 l/min at O 2 of 1, 2, 3, and 4   l/min. Mixed venous P O 2 predicted from C 2 H 2 -determined T , measured O 2 , and arterial O 2 concentration was ~20-25 Torr at 90% of O 2 max during air breathing and 10-15 Torr during 13% O 2 breathing. This modification of previous gas uptake methods, to avoid rebreathing, produces reasonable data from rest to heavy exercise in normal subjects. maximal exercise; new methodology; inert gas