title: Transmission of calibration errors (input) by generalized transfer functions to the aortic pressures (output) at different hemodynamic states.
abstract: BACKGROUND
  Aortic pressure waveforms are calculated non-invasively by applying generalized transfer functions (GTF) to tonometric radial pressure waveforms. Input errors mainly during acquisition and calibration of tonometric pressures are "transferred" to aortic pressure calculation. The present study aimed to quantify the proportion of specific input errors which is "transferred" by the GTFs in a wide range of hemodynamic conditions and for different error combinations in brachial systolic (SBP) and diastolic (DBP) blood pressure measurements.
  
  
  METHODS
  Aortic pulse wave analysis was performed in 103 subjects (52 normotensive and 51 untreated hypertensive) by the SphygmoCor System. Each pressure waveform was initially calibrated by sphygmomanometrical brachial pressures. Isolated, parallel and reverse errors in brachial SBP/DBP from -10 to +10 mmHg were simulated, by recalibration of the recorded radial pressure waveforms, inducing specific "errors" of GTF-input values. For every recalculated aortic SBP and DBP, the difference from the initial estimated value was considered to represent the "transferred error" to the aortic pressure estimation.
  
  
  RESULTS
  Parallel errors by +/-5 mmHg in both SBP and DBP resulted to an identical change in GTF-derived aortic pressures, as expected. When an overestimation in SBP by 5 mmHg and an underestimation in DBP by -5 mmHg occurred (reverse errors), almost 56% of this error (approximately 2.8 mmHg) was transferred. An isolated error in brachial SBP by +/-5 mmHg was transmitted by 76% ( approximately 3.8 mmHg) to GTF-derived aortic SBP. In subjects with mean blood pressure>117 mmHg or with heart rates<74 bpm, a greater percent of the calibration error was transferred to GTF-derived blood pressures.
  
  
  CONCLUSIONS
  Input errors in brachial pressure values result in a quantifiable effect on transfer function output (aortic pressures). The percent of the "error transfer" by the GTFs depends on heart rate and BP levels, which should be taken into account when applying GTFs at populations with different hemodynamic conditions.
authors.affiliation: Unit of Biomedical Engineering, First Department of Cardiology, Hippokration Hospital, and Vascular Laboratory, Department of Clinical Therapeutics, Alexandra Hospital, Medical School, National University of Athens, Greece. theopap@mail.ntua.gr
authors.forename: Theodore G
authors.initials: TG
authors.lastname: Papaioannou
authors.forename: John P
authors.initials: JP
authors.lastname: Lekakis
authors.forename: Emmanouil N
authors.initials: EN
authors.lastname: Karatzis
authors.forename: Christos M
authors.initials: CM
authors.lastname: Papamichael
authors.forename: Kimon S
authors.initials: KS
authors.lastname: Stamatelopoulos
authors.forename: Athanassios D
authors.initials: AD
authors.lastname: Protogerou
authors.forename: Myron
authors.initials: M
authors.lastname: Mavrikakis
authors.forename: Christodoulos
authors.initials: C
authors.lastname: Stefanadis
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001011:Aorta / Q000503:physiopathology*; D001794:Blood Pressure / Q000502:physiology; D001795:Blood Pressure Determination / Q000379:methods*; D001916:Brachial Artery / Q000503:physiopathology; D002138:Calibration; D005260:Female; D006339:Heart Rate; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D017534:Radial Artery / Q000503:physiopathology