title: Measurement uncertainty in pulmonary vascular input impedance and characteristic impedance estimated from pulsed-wave Doppler ultrasound and pressure: clinical studies on 57 pediatric patients.
abstract: Pulmonary vascular input impedance better characterizes right ventricular (RV) afterload and disease outcomes in pulmonary hypertension compared to the standard clinical diagnostic, pulmonary vascular resistance (PVR). Early efforts to measure impedance were not routine, involving open-chest measurement. Recently, the use of pulsed-wave (PW) Doppler-measured velocity to non-invasively estimate instantaneous flow has made impedance measurement more practical. One critical concern remains with clinical use: the measurement uncertainty, especially since previous studies only incorporated random error. This study utilized data from a large pediatric patient population to comprehensively examine the systematic and random error contributions to the total impedance uncertainty and determined the least error prone methodology to compute impedance from among four different methods. We found that the systematic error contributes greatly to the total uncertainty and that one of the four methods had significantly smaller propagated uncertainty; however, even when this best method is used, the uncertainty can be large for input impedance at high harmonics and for the characteristic impedance modulus. Finally, we found that uncertainty in impedance between normotensive and hypertensive patient groups displays no significant difference. It is concluded that clinical impedance measurement would be most improved by advancements in instrumentation, and the best computation method is proposed for future clinical use of the input impedance.
authors.affiliation: Department of Mechanical Engineering, University of Colorado at Boulder, Boulder, CO 80309, USA.
authors.forename: Lian
authors.initials: L
authors.lastname: Tian
authors.forename: Kendall S
authors.initials: KS
authors.lastname: Hunter
authors.forename: K Scott
authors.initials: KS
authors.lastname: Kirby
authors.forename: D Dunbar
authors.initials: DD
authors.lastname: Ivy
authors.forename: Robin
authors.initials: R
authors.lastname: Shandas
mesh_terms: D000293:Adolescent; D001794:Blood Pressure; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D006976:Hypertension, Pulmonary / Q000000981:diagnostic imaging / Q000503:physiopathology; D007223:Infant; D008168:Lung / Q000098:blood supply* / Q000000981:diagnostic imaging* / Q000502:physiology / Q000503:physiopathology; D008297:Male; D011651:Pulmonary Artery / Q000000981:diagnostic imaging* / Q000502:physiology / Q000503:physiopathology; D012107:Research Design; D012189:Retrospective Studies; D018617:Ultrasonography, Doppler, Pulsed / Q000379:methods*; D035501:Uncertainty
references.citation: Am Heart J. 2008 Jan;155(1):166-74
references.pmid: 18082509
references.citation: IEEE Trans Biomed Eng. 1988 Jan;35(1):62-8
references.pmid: 3338813
references.citation: Circulation. 2004 Oct 26;110(17):2609-17
references.pmid: 15492299
references.citation: Circ Res. 1965 May;16:401-15
references.pmid: 14289149
references.citation: Fed Proc. 1980 Feb;39(2):196-201
references.pmid: 7353677
references.citation: Hypertension. 2007 Jun;49(6):1248-55
references.pmid: 17404183
references.citation: Eur Respir J. 1996 Nov;9(11):2196-9
references.pmid: 8947059
references.citation: J Appl Physiol. 1963 Jan;18:134-40
references.pmid: 13941792
references.citation: Circ Res. 1977 May;40(5):451-8
references.pmid: 856482
references.citation: Circulation. 1978 Sep;58(3 Pt 1):460-5
references.pmid: 679436
references.citation: Biofeedback Self Regul. 1996 Jun;21(2):105-19
references.pmid: 8805961
references.citation: J Physiol. 1955 Mar 28;127(3):553-63
references.pmid: 14368548
references.citation: Circ Res. 1969 Dec;25(6):637-49
references.pmid: 5364641
references.citation: Hypertension. 1988 Oct;12(4):380-7
references.pmid: 3169948
references.citation: Circ Res. 1975 May;36(5):565-70
references.pmid: 1122568