Left ventricular ejection and the Heather Index measured by non-invasive methods during postural changes in man

Area of Science:

• Cardiovascular Physiology
• Biomedical Engineering
• Diagnostic Techniques

Background:

• Accurate measurement of left ventricular ejection time (LVET) is crucial for assessing cardiac function.
• Thoracic impedance cardiography (dZ/dt) offers a non-invasive method for monitoring hemodynamic parameters.
• Comparing LVET derived from different methods is essential for validating new techniques.

Purpose of the Study:

• To compare left ventricular ejection time (LVET) measurements obtained from external carotid pulse tracings and thoracic impedance (dZ/dt) waveforms.
• To evaluate the correlation of the Heather Index, derived from ECG and dZ/dt, with other cardiac performance indicators.
• To assess physiological responses during head-up and head-down tilting using these methods.

Main Methods:

• Measurement of LVET using external carotid pulse tracing and dZ/dt waveform analysis.
• Utilizing the second heart sound or the X-point of the dZ/dt tracing as end-points for LVET.
• Calculation of the Heather Index from ECG and dZ/dt tracings.
• Monitoring physiological variables during head-up and head-down tilting maneuvers.

Main Results:

• Differences between LVET measured by carotid pulse and dZ/dt were consistently small, typically 1% or less.
• The Heather Index demonstrated a correlation with established indices of cardiac performance.
• Physiological changes during head-up and head-down tilting aligned with expected cardiovascular responses.

Conclusions:

• Thoracic impedance (dZ/dt) provides a reliable, non-invasive method for measuring left ventricular ejection time with high agreement with carotid pulse methods.
• The Heather Index shows potential as a useful indicator of cardiac performance.
• The study validates the use of dZ/dt and associated indices in assessing cardiovascular adjustments to postural changes.