Individualizing the aorto-radial pressure transfer function: feasibility of a model-based approach

Area of Science:

• Cardiovascular Physiology
• Biomedical Engineering
• Vascular Mechanics

Background:

• Noninvasive assessment of central aortic pressure from radial artery pressure is crucial for cardiovascular risk evaluation.
• Arterial pressure waveforms are influenced by wave reflections, which can be altered in conditions like coronary artery disease.
• Transmission line models offer a framework to understand pressure wave propagation and reflection in the arterial system.

Purpose of the Study:

• To apply a three-segment transmission line model to characterize the radial-carotid/aorta pressure transfer function (TFF) in patients with coronary artery disease (CAD) and controls.
• To evaluate the impact of different TFFs on the reconstruction of carotid pressure waveforms and derived hemodynamic indices.
• To determine if TFF parameters or derived indices can differentiate between CAD patients and healthy individuals.

Main Methods:

• A three-segment transmission line model was fitted using noninvasively measured radial and carotid artery pressures in 31 controls and 30 CAD patients.
• Model parameters, including reflection coefficients, were analyzed.
• Different TFFs (averaged, upper, and lower enveloping) were assessed to reconstruct carotid pressure (P(car,r)) from radial pressure.
• Pulse pressure (PP) and augmentation index (AIx) were calculated from original and reconstructed P(car).

Main Results:

• The distal reflection coefficient was significantly higher in CAD patients (0.85 ± 0.21) compared to controls (0.71 ± 0.25; P < 0.05).
• Model parameters were otherwise similar between groups and unrelated to blood pressure, age, or heart rate.
• Averaged TFF (TFF(avg)) showed the closest morphological agreement between original and reconstructed P(car) (RMS error 4.3 ± 2.3 mmHg).
• TFF(avg) best predicted measured PP and AIx, though PP and AIx were higher in CAD patients regardless of the TFF used.

Conclusions:

• Averaged TFFs can introduce discrepancies between reconstructed and measured pressure waveforms, affecting derived augmentation index.
• Despite potential reconstruction errors, different TFFs appear to retain information that effectively distinguishes between coronary artery disease patients and controls.
• The elevated distal reflection coefficient in CAD patients warrants further investigation regarding its clinical significance.