In vitro evaluation of an extended pulse pressure method for the estimation of total arterial compliance

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The Pulse Pressure Method (PPM) is a reliable iterative technique to estimate total (and segmental) arterial compliance. However, due to the necessity of simultaneous aorta pressure and flow wave measurements, the application of the method is restricted to animal studies or specific clinical conditions that allow aorta flow measurements. The authors therefore propose an extended Pulse Pressure Method (EPPM) where the flow wave is restricted by a triangular wave reconstructed from cardiac output. Both the PPM and EPPM are validated on an in vitro model of the arterial tree. The model is a 1:1 scale representation of the aorta including the major branches to the head, upper and lower limbs, and abdominal organs. It contains 37 elastic tapering tubes, made of natural latex rubber (1 MPa). The model is connected to a pulse duplicator system of the human left heart to provide the model of normal (or pathological) pulsatile inflow. Downstream 28 vascular beds are the interface to the venous side, with individually adjustable resistances and compliances. This allows the simulation of physiological and pathological conditions. The EPPM and PPM are tested on a normal configuration (total compliance C=1.40 ml/mmHg, total resistance R=0.73 mmHg/ml/s, mean arterial pressure MAP=65 mmHg, cardiac output CO=5.1 l/min) and a pathological configuration (C=0.29 ml/mmHg, R=2.34 ml/mmHg, MAP=75 mmHg. CO=1.9 l/min). Heart rate is 60 beats per minute in all cases. For both conditions the PPM is found to be accurate and reproducible (0.29/spl plusmn/0.02 ml/mmHg for the stiff and 1.42/spl plusmn/0.04 ml/mmHg for the compliant model). The EPPM slightly underestimates total arterial compliance (0.27/spl plusmn/0.03 ml/mmHg and 1.37/spl plusmn/0.06 ml/mmHg for the pathological resp. normal case). The EPPM thus weakens the tight restrictions of the PPM and renders the method less invasive. It is also illustrated that the in vitro model is a useful tool for haemodynamic studies, and suitable to validate invasive and non-invasive clinical research protocols.