Sources of error in noninvasive pulmonary blood flow measurements by Partial rebreathing: A computer model study

• Published in: Anesthesiology (Philadelphia) Vol. 98; no. 4; pp. 881 - 887
• Main Authors: YEM, Johnny S, YONGQUAN TANG, TURNER, Martin J, BAKER, A. Barry
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD Lippincott 01.04.2003
• Subjects: Adult; Air Pressure; Biological and medical sciences; Carbon Dioxide - analysis; Carbon Dioxide - metabolism; Cardiovascular system; Computer Simulation; Humans; Investigative techniques of hemodynamics; Investigative techniques, diagnostic techniques (general aspects); Male; Medical sciences; Models, Anatomic; Models, Statistical; Pulmonary Alveoli - physiology; Pulmonary Circulation - physiology; Reproducibility of Results; Respiration, Artificial; Respiratory Mechanics; Human; Lung; Male; Respiratory system; Rebreathing; Blood flow; Partial; Non invasive method; Adult; Hemodynamics; Measurement method; Mathematical model; Measurement error
• DOI: 10.1097/00000542-200304000-00014
• ISSN: 0003-3022

Partial rebreathing is a noninvasive method for measuring pulmonary blood flow (PBF). This study examines the systematic errors produced by the partial rebreathing technique utilizing a comprehensive mathematical model of the cardiorespiratory system of a healthy, 70-kg adult male. The model simulates tidal breathing through a branched respiratory tree and incorporates the effects on carbon dioxide dynamics of lung tissue mass, vascular transport delays, multiple body compartments, and realistic blood-gas dissociation curves. Four studies were performed: (1) errors produced under standard conditions, (2) effects of recirculation, (3) effects of alveolar-proximal airway partial pressure of carbon dioxide (Pco(2)) differences, and (4) effects of rebreathing time. Systematic errors are less than 10% when the simulated PBF is between 3 and 6 l/min. At 2 l/min, PBF is overestimated by approximately 35%. At 14 l/min, PBF is underestimated by approximately 40%. At PBF of greater than 6 l/min, recirculation causes approximately 60% of the systematic error, alveolar-proximal airway differences cause approximately 20%, and alveolar-arterial differences cause approximately 20%. The standard rebreathing time of 50 s is shown to be excessive for PBF of greater than 6 l/min. At PBF of less than 3 l/min, errors are caused by inadequate rebreathing time and alveolar-arterial gradients. Systematic errors in partial rebreathing cardiac output measurements have multiple causes. Our simulations suggest that errors can be reduced by using a variable rebreathing time, which should be increased at low PBF so that quasi-equilibrium in the alveoli can be achieved and decreased at high PBF to reduce the effects of recirculation.