title: The effect of head up tilting on bioreactance cardiac output and stroke volume readings using suprasternal transcutaneous Doppler as a control in healthy young adults.
abstract: To compare the performance of a bioreactance cardiac output (CO) monitor (NICOM) and transcutaneous Doppler (USCOM) during head up tilting (HUT). Healthy young adult subjects, age 22 ± 1 years, 7 male and 7 female, were tilted over 3-5 s from supine to 70° HUT, 30° HUT and back to supine. Positions were held for 3 min. Simultaneous readings of NICOM and USCOM were performed 30 s into each new position. Mean blood pressure (MBP), heart rate (HR), CO and stroke volume (SV), and thoracic fluid content (TFC) were recorded. Bland-Altman, percentage changes and analysis of variance for repeated measures were used for statistical analysis. Pre-tilt NICOM CO and SV readings (6.1 ± 1.0 L/min and 113 ± 25 ml) were higher than those from USCOM (4.1 ± 0.6 L/min and 77 ± 9 ml) (P < 0.001). Bland-Altman limits of agreement for CO were wide with a percentage error of 38 %. HUT increased MBP and HR (P < 0.001). CO and SV readings decreased with HUT. However, the percentage changes in USCOM and NICOM readings did not concur (P < 0.001). Whereas USCOM provided gravitational effect proportional changes in SV readings of 23 ± 15 % (30° half tilt) and 44 ± 11 % (70° near full tilt), NICOM changes did not being 28 ± 10 and 33 ± 11 %. TFC decreased linearly with HUT. The NICOM does not provide linear changes in SV as predicted by physiology when patients are tilted. Furthermore there is a lack of agreement with USCOM measurements at baseline and during tilting.
authors.affiliation: Department of Anesthesiology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China. joannyzh@gmail.com.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Anesthesia and Intensive Care, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong, SAR.
authors.forename: Lester A H
authors.initials: LA
authors.lastname: Critchley
authors.affiliation: Department of Sports Science and Physical Education, Faculty of Education, The Chinese University of Hong Kong, Shatin, Hong Kong, SAR.
authors.forename: Daniel C W
authors.initials: DC
authors.lastname: Lee
authors.affiliation: Department of Anesthesia and Intensive Care, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong, SAR.
authors.forename: Kim S
authors.initials: KS
authors.lastname: Khaw
authors.affiliation: Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Kowloon, Hong Kong, SAR.
authors.forename: Shara W Y
authors.initials: SW
authors.lastname: Lee
mesh_terms: D002302:Cardiac Output / Q000502:physiology*; D002404:Catheterization; D015150:Echocardiography, Doppler / Q000379:methods*; D005260:Female; D064368:Healthy Volunteers; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics; D006801:Humans; D016014:Linear Models; D008297:Male; D008991:Monitoring, Physiologic; D056888:Patient Positioning; D011651:Pulmonary Artery / Q000473:pathology; D013318:Stroke Volume / Q000502:physiology*; D013815:Thermodilution / Q000379:methods*; D055815:Young Adult
keywords: Bioreactance; Cardiac output; Doppler; Head up tilting