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Input impedance of the systemic circulation in man

W W Nichols, C R Conti, W E Walker

    Circulation Research
    |May 1, 1977
    PubMed
    Summary
    This summary is machine-generated.

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    Systemic input impedance was measured in 16 subjects. Those with coronary artery disease and hypertension had higher aortic input impedance, suggesting they better met increased energy demands.

    Area of Science:

    • Cardiovascular Physiology
    • Biomedical Engineering
    • Hemodynamics

    Background:

    • Systemic input impedance is a critical hemodynamic parameter reflecting the heart's interaction with the arterial system.
    • Understanding aortic input impedance in humans is essential for diagnosing and managing cardiovascular diseases.
    • Previous studies have characterized aortic input impedance in canines, but human data, especially in disease states, is less defined.

    Purpose of the Study:

    • To determine the systemic input impedance in human subjects undergoing cardiac catheterization.
    • To compare aortic input impedance between healthy individuals and those with coronary artery disease (CAD), with and without hypertension.
    • To establish normal limits for aortic input impedance in humans.

    Main Methods:

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  • Pulsatile pressure and flow were measured in the ascending aorta of 16 human subjects using a catheter-tip electromagnetic velocity meter and an external transducer.
  • Subjects were categorized into three groups: Group A (no cardiovascular disease), Group B (CAD, mean aortic pressure < 100 mm Hg), and Group C (CAD, mean aortic pressure > 100 mm Hg).
  • Frequency spectra of impedance were analyzed, and characteristic impedance was calculated.

    • Main Results:

    • Frequency spectra of impedance were qualitatively similar across all groups.
    • Characteristic impedance was significantly lower in normal subjects (Group A, 53 dyn sec cm⁻⁵) compared to subjects with CAD (Groups B & C, 129 dyn sec cm⁻⁵).
    • In subjects with CAD, characteristic impedance was higher in hypertensive individuals (Group C, 202 dyn sec cm⁻⁵) than in those with lower mean pressures (Group B, 95 dyn sec cm⁻⁵).
    • External left ventricular work (hydraulic power) was highest in Group C (2372 mW), suggesting they met increased energy demands.
    • Normal limits for aortic input impedance in humans were tentatively defined as 26-80 dyn sec cm⁻⁵.

    Conclusions:

    • Aortic input impedance is elevated in human subjects with coronary artery disease, particularly when hypertension is present.
    • Individuals with higher aortic input impedance (Group C) demonstrated greater left ventricular hydraulic power, indicating an ability to meet increased energetic demands.
    • Further research is required to elucidate the factors contributing to elevated impedance in CAD, beyond age and transmural pressure.