Jan-Willem Lankhaar
VU University Medical Center
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Featured researches published by Jan-Willem Lankhaar.
Medical & Biological Engineering & Computing | 2009
Nico Westerhof; Jan-Willem Lankhaar; Berend E. Westerhof
Frank’s Windkessel model described the hemodynamics of the arterial system in terms of resistance and compliance. It explained aortic pressure decay in diastole, but fell short in systole. Therefore characteristic impedance was introduced as a third element of the Windkessel model. Characteristic impedance links the lumped Windkessel to transmission phenomena (e.g., wave travel). Windkessels are used as hydraulic load for isolated hearts and in studies of the entire circulation. Furthermore, they are used to estimate total arterial compliance from pressure and flow; several of these methods are reviewed. Windkessels describe the general features of the input impedance, with physiologically interpretable parameters. Since it is a lumped model it is not suitable for the assessment of spatially distributed phenomena and aspects of wave travel, but it is a simple and fairly accurate approximation of ventricular afterload.
European Heart Journal | 2008
Jan-Willem Lankhaar; Nico Westerhof; Theo J.C. Faes; C. Tji-Joong Gan; Koen M. Marques; Anco Boonstra; Fred G. van den Berg; Pieter E. Postmus; Anton Vonk-Noordegraaf
AIMS Pulmonary arterial compliance (C) is increasingly being recognized as an important contributor to right ventricular afterload, but for monitoring of treatment of pulmonary hypertension (PH) most often still only pulmonary vascular resistance (R) is used. We aimed at testing the hypothesis that R and C are coupled during treatment of PH and that substantial changes in both R and C would result in more haemodynamic improvement than changes in R alone. METHODS AND RESULTS Data were analysed of two right-heart catheterizations of 52 patients with pulmonary arterial hypertension and 10 with chronic-thromboembolic PH. The product of R and C (= stroke volume over pulse pressure) did not change during therapy (P = 0.320), implying an inverse relationship. Changes in cardiac index correlated significantly (P < 0.001) with changes in R (R(2) = 0.37), better with changes in C (R(2) = 0.66), and best with changes in both (R(2) = 0.74). CONCLUSION During therapy for PH, R and C remain inversely related. Therefore, changes in both R and C better explain changes in cardiac index than either of them alone. Not only resistance but also compliance plays a prominent role in PH especially in an early stage of the disease.
Journal of Magnetic Resonance Imaging | 2005
Jan-Willem Lankhaar; Mark B.M. Hofman; J. Tim Marcus; Jaco J.M. Zwanenburg; Theo J.C. Faes; Anton Vonk-Noordegraaf
To investigate whether an existing method for correction of phase offset errors in phase‐contrast velocity quantification is applicable for assessment of main pulmonary artery flow with an MR scanner equipped with a high‐power gradient system.
Hypertension | 2007
Nico Westerhof; Jan-Willem Lankhaar; Berend E. Westerhof
To the Editor: Recent hypertension research has shown that large artery compliance is an important determinant of systolic pressure, pulse pressure, and cardiovascular disease. Many methods exist to determine compliance or its inverse, arterial stiffness; the time constant of the aortic pressure decay in diastole, the ratio of stroke volume over pulse pressure, and pulse wave velocity are among the most used. These methods require either invasive measurements or 2 simultaneous measurements and are not practical to use in epidemiological studies or in night–day variations. Dolan et al1 recently suggested the use of the Ambulatory Arterial Stiffness Index (AASI), defined as 1 minus the slope of the (linear) relation between diastolic and systolic pressure, as a measure of arterial stiffness. The AASI is easy to …
Annals of Biomedical Engineering | 2009
Jan-Willem Lankhaar; Fleur A. Rövekamp; Paul Steendijk; Theo J.C. Faes; Berend E. Westerhof; Taco Kind; Anton Vonk-Noordegraaf; Nico Westerhof
Simulations are useful to study the heart’s ability to generate flow and the interaction between contractility and loading conditions. The left ventricular pressure–volume (PV) relation has been shown to be nonlinear, but it is unknown whether a linear model is accurate enough for simulations. Six models were fitted to the PV-data measured in five sheep and the estimated parameters were used to simulate PV-loops. Simulated and measured PV-loops were compared with the Akaike information criterion (AIC) and the Hamming distance, a measure for geometric shape similarity. The compared models were: a time-varying elastance model with fixed volume intercept (LinFix); a time-varying elastance model with varying volume intercept (LinFree); a Langewouter’s pressure-dependent elasticity model (Langew); a sigmoidal model (Sigm); a time-varying elastance model with a systolic flow-dependent resistance (Shroff) and a model with a linear systolic and an exponential diastolic relation (Burkh). Overall, the best model is LinFree (lowest AIC), closely followed by Langew. The remaining models rank: Sigm, Shroff, LinFix and Burkh. If only the shape of the PV-loops is important, all models perform nearly identically (Hamming distance between 20 and 23%). For realistic simulation of the instantaneous PV-relation a linear model suffices.
American Journal of Physiology-heart and Circulatory Physiology | 2009
Taco Kind; Nico Westerhof; Theo J.C. Faes; Jan-Willem Lankhaar; Paul Steendijk; Anton Vonk-Noordegraaf
The time-varying elastance concept provides a comprehensive description of the intrinsic mechanical properties of the left ventricle that are assumed to be load independent. Based on pressure-volume measurements obtained with combined pressure conductance catheterization in six open-chest anesthetized sheep, we show that the time to reach end systole (defined as maximal elastance) is progressively prolonged for increasing ventricle pressures, which challenges the original (load-independent) time-varying elastance concept. Therefore, we developed a method that takes into account load dependency by normalization of time course of the four cardiac phases (isovolumic contraction, ejection, isovolumic relaxation, filling) individually. With this normalization, isophase lines are obtained that connect points in pressure-volume loops of different beats at the same relative time in each of the four cardiac phases, instead of isochrones that share points at the same time in a cardiac cycle. The results demonstrate that pressure curves can be predicted with higher accuracy, if elastance curves are estimated using isophase lines instead of using isochrones [root-mean-square error (RMSE): 3.8 +/- 1.0 vs. 14.0 +/- 7.4 mmHg (P < 0.001), and variance accounted for (VAF): 94.8 +/- 1.3 vs. 78.6 +/- 14.8% (P < 0.001)]. Similar results were found when the intercept volume was assumed to be time varying [RMSE: 1.7 +/- 0.3 vs. 13.4 +/- 7.4 mmHg (P < 0.001), and VAF: 97.4 +/- 0.5 vs. 81.8 +/- 15.5% (P < 0.001)]. In conclusion, phase-dependent time normalization reduces cardiac load dependency of timing and increases accuracy in estimating time-varying elastance.
Chest | 2007
C. Tji-Joong Gan; Jan-Willem Lankhaar; Nico Westerhof; J. Tim Marcus; Annemarie Becker; Jos W. R. Twisk; Anco Boonstra; Pieter E. Postmus; Anton Vonk-Noordegraaf
American Journal of Physiology-heart and Circulatory Physiology | 2006
Jan-Willem Lankhaar; Nico Westerhof; Theo J.C. Faes; Koen M. Marques; J. Tim Marcus; Piet E. Postmus; Anton Vonk-Noordegraaf
American Journal of Physiology-heart and Circulatory Physiology | 2006
C. Tji-Joong Gan; Jan-Willem Lankhaar; J. Tim Marcus; Nico Westerhof; Koen M. Marques; Jean G.F. Bronzwaer; Anco Boonstra; Pieter E. Postmus; Anton Vonk-Noordegraaf
European Heart Journal | 2007
Anton Vonk-Noordegraaf; Jan-Willem Lankhaar; Marco J.W. Götte; J. Tim Marcus; Pieter E. Postmus; Nico Westerhof