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Table 1 Parameters assessed in impedance cardiography

From: Systolic time ratio measured by impedance cardiography accurately screens left ventricular diastolic dysfunction in patients with arterial hypertension

Parameter

Definition

Formula

Heart rate

Number of heart beats per minute (bpm)

RR interval measurement on the ECG and extrapolation for bpm

Mean blood pressure (MAP)

Average pressure exerted by the blood on the arterial walls

Automatic (oscillometric method) = MAP is measured directly and SBP and DBP are derived

Cardiac output (CO)

Amount of blood ejected from the left ventricle / minute

CO = Stroke volume x Heart rate

Cardiac index (CI)

Standard CO for the body surface area (BSA)

CI = CO / BSA

Stroke volume (SV)

Amount of blood ejected from the left ventricle / heart beat

SV = VEPT x LVET x VI

(Z MARC Algorithm)

Stroke volume index (SVI)

Standard SV for the BSA

SVI = SV / BSA

Vascular systemic resistance (VSR)

Resistance to circulating blood in the arterial system

VSR = 80 x ((MAP-CVP)/CO)

Vascular systemic resistance index (VSRI)

Standard resistance to circulating blood in the arterial system for the BSA

VSRI = 80 x ((MAP-CVP)/CI)

Acceleration index (AI)

Initial acceleration of blood in the aorta that occurs within the first 10–20 milliseconds after opening of the aortic valve

AI = (d2Z/dt2 Max)/TFI

Velocity index (VI)

Aorta blood velocity peak

VI = (dZ/dtMax)/TFI

Thoracic fluid (TF)

Electrical conductivity of the thoracic cavity (determined by intravascular, interalveolar and interstitial fluids)

TF = 1/TFI

Left heart work (LHW)

Indicator of the amount of work the left ventricle exerts to pump blood every minute

LHW = (MAP – PAOP) x CO

Left heart work index (LHWI)

Standard LHW for the BSA

LHW = (MAP – PAOP) x CI

Systolic time ratio (STR)

Ratio of electrical and mechanical systole

STR = PEP / LVET

Pre-ejection period (PEP)

Time interval from the beginning of the electrical stimulation of the ventricles to the beginning of the opening of the aortic valve (electric systole)

Time interval between the start of wave Q on the ECG and point B on wave dZ / dt (opening of the aortic valve)

Left ventricular ejection time (LVET)

Time interval from opening to closing of the aortic valve (mechanical systole)

Time interval from point B to point X on wave dZ / dt

  1. CVP Central venous pressure (pressure in the thoracic and right atrial vein - 6 mmHg is considered by default), dZ / dt Max Maximum of the first derivative of ΔZ, d 2 Z / dt 2 Max Maximum of the second derivative of ΔZ, PAOP Pulmonary artery occlusion pressure (considered by default as 10 mmHg), TFI Thoracic fluid index (baseline thoracic impedance, Z0), VEPT Volume of electrically participating tissue (conductive volume for chest size affected by weight, height and sex)
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Clinical Hypertension

ISSN: 2056-5909

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