HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:
Guest Access | Sign In via User Name/Password

This Article Full Text Free Full Text (PDF) Free Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Add to My Personal Article Archive Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (10) Citing Articles via Google Scholar Google Scholar Articles by Sun, X.-G. Articles by Wasserman, K. Search for Related Content PubMed PubMed Citation Articles by Sun, X.-G. Articles by Wasserman, K.

Comparison of Exercise Cardiac Output by the Fick Principle Using Oxygen and Carbon Dioxide*

Correspondence to: Karlman Wasserman, MD, PhD, FCCP, Division of Respiratory and Critical Care Physiology and Medicine, Department of Medicine, Harbor-UCLA Medical Center, PO Box 405, St. John’s Cardiovascular Research Center, 1000 W Carson St, Torrance, CA 90509-2910; e-mail: kwasserm{at}ucla.edu

Background and study objective: Theoretically, cardiac output (CO) calculated by the Fick principle should be the same using O₂ (CO[O₂]) or CO₂ (CO[CO₂]) as the test gas. However, agreement depends on the accuracy of gas exchange and blood gas measurements and the validity of the equations to convert measured variables into blood gas contents. Considering the widespread use of indirect estimates of pulmonary artery blood PCO₂ and CO₂ content to measure Fick principle CO during exercise, we wished to determine whether CO[O₂] and CO[CO₂] were equal during exercise and whether CO[CO₂] could be accurately and precisely determined using direct measures of pulmonary artery blood.

Preparation and methods: Five healthy young nonsmoking volunteer men performed incremental exercise from rest to peak exercise on two separate occasions with intervening rest. Catheters were placed in brachial and pulmonary arteries to allow repeated blood sampling every minute during concurrent breath-by-breath gas exchange measurements from rest to peak exercise. CO[O₂] was compared with CO[CO₂] at multiple levels of exercise. Using standard equations, arterial and mixed venous O₂ contents were calculated from hemoglobin concentration (Hb), oxyhemoglobin saturation (SO₂), and PO₂, whereas CO₂ contents were calculated from PCO₂, pH, Hb, and SO₂. Blood gas analyzers were used for measurement of pH, PCO₂, and PO₂, and a co-oximeter was used for measurement of Hb and SO₂. Initial calculations suggested that exercise CO[CO₂] was 14% higher than CO[O₂] and helped disclose small systematic measurement errors in PCO₂ for values > 45 mm Hg detected by proficiency testing surveys and documented with blood tonometry in the blood gas analyzer.

Results: After correcting PCO₂ for the small systematic measurement error found, the measures and equations used to calculate arterial and mixed venous O₂ and CO₂ contents were adequate to provide mean CO values that are reasonably similar. However CO[CO₂] values were more than twice as variable as CO[O₂].

Conclusions: The increased variability of Fick principle CO[CO₂] compared with CO[O₂] is attributable to the much lower extraction ratio for CO₂ and the greater complexity in calculation of blood CO₂ than O₂ contents. These results raise concerns about the accuracy and precision of estimating CO and stroke volume using CO₂ as a test gas, even with direct measurement of blood CO₂ contents in normal subjects.

Key Words: blood CO₂ content • cardiac output • exercise • Fick principle • PCO₂ • proficiency testing • tonometered blood

This article has been cited by other articles:

				A. Crisafulli, C. Carta, F. Melis, F. Tocco, F. Frongia, U. M Santoboni, P. Pagliaro, and A. Concu Haemodynamic responses following intermittent supramaximal exercise in athletes Exp Physiol, November 1, 2004; 89(6): 665 - 674. [Abstract] [Full Text] [PDF]

				A. Crisafulli, F. Melis, F. Tocco, U. M. Santoboni, C. Lai, G. Angioy, L. Lorrai, G. Pittau, A. Concu, and P. Pagliaro Exercise-induced and nitroglycerin-induced myocardial preconditioning improves hemodynamics in patients with angina Am J Physiol Heart Circ Physiol, July 1, 2004; 287(1): H235 - H242. [Abstract] [Full Text] [PDF]

				G. Laszlo Respiratory measurements of cardiac output: from elegant idea to useful test J Appl Physiol, February 1, 2004; 96(2): 428 - 437. [Abstract] [Full Text] [PDF]

				X.-G. Sun, J. E. Hansen, N. Garatachea, T. W. Storer, and K. Wasserman Ventilatory Efficiency during Exercise in Healthy Subjects Am. J. Respir. Crit. Care Med., December 1, 2002; 166(11): 1443 - 1448. [Abstract] [Full Text] [PDF]

				R. Uda, M. Onaka, T. Okuno, H. Mori, X.-G. Sun, and C. Lee The Second Gas Effect is Not Statistically Valid * Response Anesth. Analg., March 1, 2002; 94(3): 765 - 766. [Full Text] [PDF]

				S. Godfrey, H. Kazemi, D. Systrom, K. Wasserman, X.-G. Sun, J. E. Hansen, H. Ting, and W. W. Stringer Carbon Dioxide Pressure-Concentration Relationship in Arterial and Mixed Venous Blood J Appl Physiol, November 1, 2001; 91(5): 2412 - 2414. [Full Text] [PDF]

				X.-G. Sun, J. E. Hansen, R. J. Oudiz, and K. Wasserman Exercise Pathophysiology in Patients With Primary Pulmonary Hypertension Circulation, July 24, 2001; 104(4): 429 - 435. [Abstract] [Full Text] [PDF]

				X.-G. Sun, J. E. Hansen, W. W. Stringer, H. Ting, and K. Wasserman Carbon dioxide pressure-concentration relationship in arterial and mixed venous blood during exercise J Appl Physiol, May 1, 2001; 90(5): 1798 - 1810. [Abstract] [Full Text] [PDF]