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The accuracy of inferring left ventricular volume from dimension depends on the frequency of information needed to
Insights
Estimating left ventricular volume from cardiac dimensions is common but not always accurate. This method is reliable for slow changes but may lead to significant errors when assessing rapid volume changes.
Area of Science:
- Cardiovascular Physiology
- Biomedical Engineering
- Medical Imaging
Background:
- Left ventricular volume is crucial for cardiovascular assessment.
- Direct measurement of left ventricular volume is not feasible.
- Estimating volume from cardiac dimensions is a widely used practice lacking rigorous justification.
Purpose of the Study:
- To critically evaluate the assumptions and limitations of estimating left ventricular volume from cardiac dimensions.
- To investigate the impact of hemodynamic states and signal frequency on the accuracy of dimension-based volume estimation.
- To provide a framework for understanding the validity of this estimation method across different physiological conditions.
Main Methods:
- Analysis of the relationship between left ventricular dimensions and volume under varying hemodynamic conditions.
- Consideration of the frequency content of cardiac volume and dimension signals.
- Theoretical evaluation of the assumptions underlying dimension-to-volume conversion.
Main Results:
- The underlying assumptions for estimating left ventricular volume from dimensions are strictly false.
- Errors in volume estimation are negligible for slow changes (below heart rate) if all dimensions are measured.
- Significant inaccuracies can occur when assessing rapid volume changes (above heart rate).
Conclusions:
- Estimating beat-to-beat left ventricular volume changes from dimensions is generally valid at frequencies up to the heart rate.
- Accurate assessment of rapid left ventricular volume dynamics (above heart rate) using dimensions is likely not possible.
- The frequency content of the signal is critical for determining the reliability of dimension-based volume estimations.
Abstract:
Left ventricular volume is an important variable in cardiovascular physiology. Because volume cannot be transduced directly, by necessity people measure one or more cardiac dimensions, then implicitly or explicitly estimate volume. Despite its common use, this practice has never been adequately justified. Previous validations of the use of left ventricular dimensions to infer volume have ignored the complexity of the relation between dimensions and volume, particularly over a broad range of hemodynamic states, and have not considered the frequency content of the volume signal needed to answer a given physiological question. We show that, strictly speaking, the assumptions underlying this practice are false. The resulting errors are of little practical consequence under many circumstances, whereas they can be quite important under other circumstances. We consider the frequency content of the volume signal to organize our examples and findings. In this general framework, we find that, for most assessments of volume change from dimension change at or below a frequency of about the heart rate (e.g., beat-to-beat end-diastolic volume), there is no limitation, provided all relevant dimensions are measured. However, for information at frequencies above the heart rate (i.e., rapid changes in volume or dimension), it is probably not possible to draw accurate conclusions about left ventricular volume from dimension data.