ANALYSES TO PERFORM 1. Choose a duration of the simulation to be - PDF document

Lesson 6 University of Bergamo Engineering and Management for Health FOR CHRONIC DISEASES MEDICAL SUPPORT SYSTEMS LESSON 6 Lumped parameter models of the cardiovascular system: practical lesson. Ettore Lanzarone March 25, 2020 Practical lesson ANALYSES TO PERFORM 1. Choose a duration of the simulation to be sure that the initial transient time is over 2. Compare the two models. Which is the most accurate one and why? 3. Evaluate the pressure in the aortic segments 2 – 7 in the complete model. What do you observe? Is it in agreement with the medical literature?

Lesson 6 Practical lesson ANALYSES TO PERFORM 4. Study a pathological case: old patient with rigid vessels. All compliances reduced by a fixed percentage. What do you observe? Did you expect that? 5. Study a surgical case: insertion of an aortic prosthesis. Resistances are increased and compliances are decreased in segments 3 – 7 Practical lesson Feedbacks from the students…

Lesson 6 Practical lesson • Transient time model 1 Pressure P Transient is expired when two consecutive cardiac cycles are equal. Any analysis (e.g., average pressure) should be performed after removing the initial cycles. Practical lesson • Transient time model 2 Pressure P 3 To change average pressures vary peripheral resistances Same consideration. Even starting with an initialization the system is not yet at the steady state. By changing initialization the transient is reduced but it is impossible to know a priori the pressures at the beginning of the cycle.

Lesson 6 Practical lesson • Waveform model 1 Pressure P Shape not fully accurated but main characteristics are respected. Practical lesson • Waveform model 2 Dicrotic notch Pressure P 3 Accurate shape that respects physiological measurements

Lesson 6 Practical lesson • Waveform model 2 Pressures P 3 – P 4 – P 5 – P 6 Increased and delayed systolic peak (in agreement with the literature) is kept. If you «export» and compute average values, they decrease along with the network Practical lesson • Rigid vessels model 2 Generally increased pressures. • Prosthesis model 2 Pressure increasing in the segments above and with the prosthesis. If you impose a flow and vary the properties of a segment, all segments below are not affected (unless the modifications change the flow: heart reacts as it is not a perfect volumetric pump, or different distribution of flows above the variation).