Hemodynamics

 

Bernoulli's principle

Simplified formula for converting velocity difference obtained by spectral Doppler to instantaneous pressure gradient. This clinical equation has been derived from the more complex Bernoulli equation by assuming that viscous losses and acceleration effects are negligible and by using an approximation for the constant that relates to the mass density of blood, a conversion factor for measurement units. In addition, the simplified Bernoulli equation assumes that the proximal velocity can be ignored, a reasonable assumption when velocity is ‹1 m/s because squaring a number ‹1 makes it even smaller. When the proximal velocity (V1) is over ›1.5 m/s or the aortic velocity (V2) is ‹3.0 m/s, the proximal velocity should be included in the Bernoulli equation.

 

ΔP=P2−P1=4(V2²−V1²)

 

Continuity equation

Aortic valve area can be calculated by using the principle of conservation of mass — "What comes in must go out". Aortic valve area indexed to body surface area should be considered for the large and small extremes of body surface area. For patients with prosthetic aortic valves, patient-prosthesis mismatch is suspected when effective orifice area (EOA) indexed to body surface area ‹0.85 to 0.9 cm2/m2. Patient-prosthesis mismatch is considered severe when EOA index ‹0.65.

 

A1xV1 = A2xV2

 

A = Area (∏r²) cm², V = velocity cm/s

 

Aorta valve area (AVA) = (D LVOT / 2)² x 3.14 x Vmax LVOT / Vmax peak of AoS jet (D LVOT = diameter LVOT in cm)

 

 

Myocard performance index

Also known as the Tei index. It is an index that incorporates both systolic and diastolic time intervals in expressing global systolic and diastolic ventricular function. Systolic dysfunction prolongs prejection (isovolumic contraction time, IVCT) and a shortening of the ejection time (ET). Both systolic and diastolic dysfunction result in abnormality in myocardial relaxation which prolongs the relaxation period (isovolumic relaxation time, IVRT).

 

LV MPI=IVCT+IVRT/LVET = MCOT−LVET/LVET

 

Proximal isovelocity surface area

Quantification of mitral regurgitation using the principle of conservation of mass by analyzing the Proximal Isovelocity hemispheric Surface Area of the flow convergence on the ventricular side. This method is more accurate for central regurgitant jets than eccentric jets, and for a circular orifice than a non-circular orifice.

 

VFR=2•π•r2•Vr

 

ERO=VFR/VMaxR

 

Vol=ERO•VTI

 

 

Flow patterns

Pressure Half Time.

MVarea = 220/PHT

 

Hepatic vein flow

 

 

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