Dynamic Elastance in Cardiovascular Physiology
Dynamic elastance is a functional parameter of arterial load that measures the ratio between arterial pulse pressure variation and stroke volume variation during respiration, serving as an index of ventriculo-arterial coupling that predicts arterial pressure responses to hemodynamic interventions. 1
Definition and Physiological Basis
Dynamic arterial elastance (Eadyn) is calculated as the ratio between arterial pulse pressure variation (PPV) and stroke volume variation (SVV) during respiratory cycles, representing the dynamic relationship between pressure and volume changes in the arterial system 1, 2
Unlike static measures of arterial stiffness, dynamic elastance captures the instantaneous pressure-volume relationship during the cardiac cycle, providing information about the functional state of the cardiovascular system 1
Eadyn is mathematically expressed as PPV/SVV and serves as a functional assessment of arterial tone that can be measured at the bedside using various monitoring techniques 3
Relationship to Ventriculo-Arterial Coupling
Dynamic elastance is inversely related to ventriculo-arterial coupling (defined as the ratio of effective arterial elastance to end-systolic elastance) and directly related to left ventricular efficiency 1
Higher Eadyn values indicate better left ventricular efficiency and lower ventriculo-arterial coupling ratios, suggesting optimal interaction between the heart and arterial system 1
Unlike effective arterial elastance (Ea), which is primarily determined by heart rate and systemic vascular resistance, Eadyn reflects the dynamic interaction between the left ventricle and arterial system during respiratory variations 4
Clinical Applications
Eadyn has demonstrated good predictive performance for arterial pressure responses to fluid administration in mechanically ventilated hypotensive patients, with an area under the receiver operating characteristic curve of 0.92 2
Cut-off values for predicting fluid responsiveness typically range from 0.65 to 0.89, with most values centered between 0.7 and 0.8 2
Eadyn can predict arterial pressure responses to vasopressor adjustments, making it useful for guiding norepinephrine titration in patients with vasoplegic syndrome 3, 5
Implementation of Eadyn-based algorithms has been shown to decrease the duration of norepinephrine treatment and ICU length of stay in patients with vasoplegic syndrome after cardiac surgery 5
Measurement Techniques
Eadyn can be measured using various techniques including uncalibrated pulse contour analysis, which makes it accessible in clinical settings 3
Modern monitoring systems can calculate Eadyn automatically by tracking the relationship between pulse pressure and stroke volume variations during mechanical ventilation 1, 2
For accurate measurement, patients should be mechanically ventilated with adequate tidal volumes to induce sufficient cardiopulmonary interactions 2
Distinction from Other Elastance Concepts
Dynamic elastance differs from passive elastance (Ep) and active elastance (Ea) of the left ventricle, which together explain left ventricular pressure dynamics throughout the cardiac cycle 6
While passive elastance represents the resistance to filling and active elastance characterizes contractile state, dynamic arterial elastance specifically reflects the arterial system's response to volume and pressure changes 6
Dynamic elastance should not be confused with effective arterial elastance (Ea), which is computed as the ratio of end-systolic pressure to stroke volume and does not reflect pulsatile left ventricular afterload or arterial stiffness 4
Clinical Implications and Limitations
Eadyn appears to have better predictive performance in ICU patients compared to surgical patients in the operating room, suggesting context-specific utility 2
The measurement requires mechanical ventilation and sufficient cardiopulmonary interaction, limiting its application in spontaneously breathing patients 2
While Eadyn provides valuable information about ventriculo-arterial coupling, it should be interpreted alongside other hemodynamic parameters for comprehensive cardiovascular assessment 1, 5