TOTAL ARTERIAL COMPLIANCE IN DOGS: THE PULSE PRESSURE METHOD VERSUS THE AREA METHOD

P. Segers’, P. Verdonck’, Y. Deryck2, S. Brimiouiie3, R. Naeije’, N. Stergiopuios4

‘H$drauiics Laboratory, IBlTECH, University of Gent, Belgium; Cardiac Anesthesia, University Hospital of Cent, Belgium;

‘Laboratory of Cardiovascular and Respiratory Physiology, Free University of Brussels, Belgium; 4Biomedical Engineering Laboratory,

Laussnne. Switzerland.

INTRODUCTION: The pulse pressure method (PPM) has been reported (I) as an accurate technique to estimate total arterial compliance (C). In this study, we applied PPM on (i) biological dog data and (ii) mathematical model (TL model) simulations of different hemodynamic conditions with known C. METHODS: (i) Dog daru. Ascending aorta pressure and flow were measured on 8 mongrel dogs weighing 12-38 kg (2). Cardiac output was altered by inflation of an intravenous balloon, and measurements were done at baseline, intermediate and low flow conditions. (ii) TL-model data Ascending aorta pressure and flow have been calculated using a linear transmission line model representing the human arterial circulation. Three hemodynamic states were simulated, with C varying from 0.69 (low C) over 1.38 (control) to 2.07 mVmmHg (high C). Simulations arc done for 60. 90 and 120 beats/minute. (iii) Total arterial compliance C is calculated with PPM and the area method of Liu et al. (3) using the last 2J3’& of diastoie. RESULTS AND DISCUSSION: (i) Dog dam. The correlation between the area method and PPM is relatively poor (1=0.65; P<O.OOl), with the arca method overestimating PPM. Bland-Aitman analysis shows that up to 0.7 ml/mmHg, there is no systematic difference between PPM and the area method; for higher values, the area method yields estimates higher than PPM. (ii) TL-model. The area method yields acceptable results (estimates within 25%) for low C at 60 and 90 beats min-i, for control conditions at 60 beats min-1, and high C at 120 beats/tin. With the exception of low C at 120 beatslmin. PPM estimates compliance within 25%.

0.0 0.5 1.0 1.5 2.0 2.5 3.0

(area + PPM)/2 (ml/mmHg) Fig. 1 The area method versus PPM CONCLUSIONS: We found a good agreement between the PPM and the area method for low and normal values of total compliance (0.5 ml/mmHg in dogs; 1.6 ml/mmHg in humans). For higher C, the area method tends to overestimate compliance. We therefore recommend the use of PPM to estimate total compliance when ascending aorta pressure and flow measurements are available. REFERENCES: 1. Stergiopuios N, J J Meister, N Westerhof. Ann Biomed Eng 22: 392- 397, 1994. 2. Deryck Y , S Brimiouiie, M Maggiorini, D de Canniere, R Naeije. Anesth Analg 83:958-964,1996. 3. Liu Z, K Brin, F Yin. Am J Physioi 251:H588-H600,1986 CORRESPONDENCE: Patrick Segers, Hydraulics Laboratory, BlTECH, University Gent, St- Pietersnieuwstraat 41.9000 Gent, Belgium. patrick.segers@rug.ac.be

CAVAL FILTERS BRANCHES DESIGN INFLUENCE ON FLOW IN A CYLINDRICAL TUBE : NUMF,RlCAL AND

EXPERIMENTAL 3D APPROACH ‘P. Fourgeau, ‘R. Perrauit, ‘J. Doffin, ‘G. Morin, ‘B. Bach-tijour

‘LEA-UMR 6609 du CNRS, Universiti de Poitiers ‘Ecole Nationale V&&&&e de Names

INTRODUClTON: in order to stop the migration of thromhi from lower limbs towards the lungs, filters are placed in the inferior vena cava. Most of previous works were studies on capture efficiency as well as stresses in the metallic branches of the filters. But, the filters are by themselves able to produce embolism, so studies are begun in this way, to prevent thrombosis and disease recurrence [l-3]. In the present work, we study the influence of filter branches shapes on induced blood flow disturbances. METHODS: An experimental bench is used to visualize the flow in different diametral laser planes. Several filters are placed in a cylindrical tube of 19 mm diameter [2,3]. A steady flow of about 820 mllmin. of a newtonian fluid (4 CP viscosity) supply the filter. Three different filter designs are studied. Two of them are made of cylindrical branches and one is ma& of lameila shape struts. In order to correlate the studies, Fluent software was used to develop a model with a cylindrical obstacle disturbing the flow as the filter ring. RESULTS AND DISCUSSION: The experimental study and the numerical simulation give interesting informations on the flow as well as discrepancies between different filter shapes. The flow is shifted towards the walls by the ring which gives rise to a wake, more important in the experimental study. Furthermore, the velocity decrease through the filter is greater when the filter has numerous capture and stabiiisation branches. Wail shear stress is high along the ring and low along branches extrados. In different diametral planes, with cylindrical branches, downstream velocity profiles are similar, unlike flat struts one. In this last case, the flow is more deviated towards the tube wall with boundary layer around the branches. As a result, the pressure drop through the flat struts filter is higher. filter setting in a flow, whatever its geometry and branches shape are. induces hydrodynamic disturbances more or less strong. inside the noticeable wake, there are low shear rate values, and higher ones inside the jets and at the interfaces. These phenomena are enhanced for lameliae filters. CONCLUSION: Because of blood flow and rheology complexities due to filter branches designs, fibrinoiytic and platelets aggregation may occur and possibly lead to thrombi genesis and filter fibrinoiytic covering. REFERENCES: 1. A.A. Katsamouris & al, Radiology, 166.2.361-366, 1988 2. R. Penauit & al, Journal des Maladies Vasculaires, 19,199-205.1994 3. P. Fourgeau & al, Actes 13& Con&s Fran@ de Mbcanique, 1, 141- 144,1997 ACKNOWLEDGEMENTS: Supported by the “R&ion Poitou-Charentes” CORRESPONDENCE: Fourgeau Patrice, LEA-Universitk de Poitiers, Bat de Physique, F-86022 Poitiers Cedex, Phone : 05.49.45.36.18, Fax : 05.49.45.34.03, Robert.Perrauit@campus.univ-poitiers.fr

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