Submitted on August 5, 2008
Revised on September 18, 2008
Accepted on September 30, 2008
Individualization of transfer function in estimation of central aortic pressure from the peripheral pulse is not required in patients at rest
Berend E. Westerhof1*, Ilja Guelen2, Wim J. Stok3, Han AJ Lasance4, Carl APL Ascoop5, Karel H. Wesseling2, Nico Westerhof6, Willem Jan W Bos5, Nikos Stergiopulos7, and Jos AE Spaan3
1 BEMEYE
2 BMEYE
3 Academic Medical Center, University of Amsterdam
4 AEGON
5 St. Antonius Ziekenhuis
6 VU University Medical Center
7 EPFL
* To whom correspondence should be addressed. E-mail: berend.westerhof{at}bmeye.com.
Central aortic pressure gives better insight into ventriculo-arterial coupling and better prognosis of cardiovascular complications than peripheral pressures. Therefore transfer functions (TF), reconstructing aortic pressure from non-invasively measured peripheral pressures, are of great interest. Generalized TFs (GTF) give useful results, especially in larger study populations, but detailed information on aortic pressure might be improved by individualization of the TF. We found earlier that the time delay, representing the travel time of the pressure wave between measurement site and aorta is the main determinant of the TF. Therefore, we hypothesized that the TF might be individualized (ITF) using this time delay. In a group of 50 patients at rest, aged 28-66 years (43 men) undergoing diagnostic angiography, ascending aortic pressure was 119±20/70±9 mmHg (systolic/diastolic). Brachial pressure, almost simultaneously measured using catheter pullback, was 131±18/67±9 mmHg. We obtained brachial-to-aorta ITFs using time delays optimized for the individual and a GTF using averaged delay. Using ITFs, reconstructed aortic pressure was 121±19/69±9 mmHg and the Root Mean Square Error, RMSE, as measure of difference in wave shape was 4.1±2.0 mmHg. Using the GTF, reconstructed pressure was 122±19/69±9 mmHg and RMSE 4.4±2.0 mmHg. The augmentation index (AI) of the measured pressure was 26±13%, with ITF and GTF the AIs were 28±12% and 30±11%, respectively. Details of the wave shape were reproduced slightly better with ITF but not significantly, thus individualization of pressure transfer is not effective in resting patients.
