Cardiac phase-dependent time normalization reduces load dependence of time-varying elastance.

Area of Science:

• Cardiovascular Physiology
• Biomedical Engineering
• Cardiac Mechanics

Background:

• The time-varying elastance concept describes intrinsic left ventricular properties, assumed to be load-independent.
• Previous studies suggest end-systole timing is prolonged with increased ventricular pressures, challenging this load-independence assumption.

Purpose of the Study:

• To develop and validate a method accounting for cardiac load dependency in time-varying elastance estimation.
• To improve the accuracy of predicting left ventricular pressure curves.

Main Methods:

• Utilized pressure-volume measurements from combined pressure conductance catheterization in anesthetized sheep.
• Developed a novel normalization method using isophase lines, connecting points at the same relative time within cardiac phases, instead of isochrones.
• Assessed accuracy using root-mean-square error (RMSE) and variance accounted for (VAF).

Main Results:

• The isophase line method significantly improved pressure curve prediction accuracy (RMSE: 3.8 +/- 1.0 vs. 14.0 +/- 7.4 mmHg; VAF: 94.8 +/- 1.3 vs. 78.6 +/- 14.8%).
• Similar improvements were observed when assuming time-varying intercept volume.
• Phase-dependent normalization reduced cardiac load dependency of timing.

Conclusions:

• Phase-dependent time normalization effectively reduces cardiac load dependency in timing.
• This approach enhances the accuracy of time-varying elastance estimation and pressure curve prediction.