6. Quantitative Doppler And Hemodynamics

Question 1

Volumetric Flow Equation

Answer 1

Vol. flow (cm^3/s) = velocity (cm/s) x cross-sectional area (cm^2)

Question 2

Stroke Volume Equation (VTI)

Cardiac Output Equation

Answer 2

SV = VTI (cm) x cross-sectional area (cm^2)

VTI = stroke distance = distance red cells have travelled in a systolic ejection phase

CO = SV x HR

Question 3

Best location to determine CO and SV with Doppler?

Answer 3

LVOT

1. Blood flow is laminar and has a blunt/flat front profile
   * blood flow at any point in the LVOT reflects the mean flow velocity through the cross section of the vessel
   * vs parabolic profile (in ascending aorta) or turbulent profile (aortic root after stenotic aortic valve)
2. LVOT is the most circular section and doesn’t change significantly with cardiac cycle
3. Entire ejected stroke volume crosses the LVOT

Question 4

Calculating RV stroke volume

Answer 4

Two locations

1. Main PA
   - RVOT VTI x RVOT cross sectional area
   * flawed because RVOT changes shape with cardiac cycle
2. Mitral valve
   - Using pulsed wave at level of mitral annulus, determine VTI at that point
   - MV VTI x mitral valve area (using mitral annulus diameter)
   * flawed because mitral valve is not circular and changes shape during cardiac cycle (more than RVOT)

Question 5

Regurgitant Volume

Answer 5

• In a regurgitation valve,
  SV = regurgitant volume + forward flowing SV
• Regurgitant volume determined by:
  = SV regurgitant valve - SV normal valve
• can use normal AV to assess MR
• can use normal MV to assess AI

Question 6

Intracardiac Shunts (Qp/Qs)

Answer 6

Qp/Qs = ratio of pulmonic to systemic SV

• helps to provide assessment of congenital lesions and PFO as well as their repair

Question 7

Continuity Equation

Answer 7

• based in conservation of mass
• used to solve for aortic valve area, for example

VTI1 x CSA1 = VTI2 x CSA2

Question 8

Bernoulli Equation

Answer 8

• describes the relationship between flow velocity and pressure gradient

Pressure gradient = 0.5p(v2^2-v1^2) + p(dv/dt) + R(v)
Convection Flow Viscous
acceleration acceleration friction

p: density of blood (1.06x 10^3 kg/m^3)
v2: peak velocity proximal to area of interest
v1: peak velocity in area of interest

Question 9

Simplified Bernoulli Equation

Answer 9

Pressure gradient = 4v^2

Original equation:
Pressure gradient = 0.5p(v2^2-v1^2) + p(dv/dt) + R(v)
Convection Flow Viscous
acceleration acceleration friction

1. At peak flow, flow acceleration non-existent
2. Viscous friction contributed significantly only with orifice area&raquo_space;»»>v1 so v1 can essentially be eliminated

Question 10

Bernoulli Equations, intracavitary pressures

Answer 10

RVSP/PASP = RAP + 4(V tr jet ^2)
PA mean = RAP + 4(V pi jet early ^2)
PA diastolic = RAP + 4(V pi jet late ^2)
Left atrial pressure = SBP - 4(V mr jet ^2)
LV end diastolic pressure/wedge = DBP - 4(V ai jet end^2)

Question 11

Systemic Vascular Resistance, normal range

Answer 11

10 - 14 Wood units

Question 12

Calculate SVR using Doppler techniques

Answer 12

= Velocity MR jet/ VTI lvot

If > 0.27 then SVR >14 WU (high)
If < 0.20 then SVR <10 WU (low)

Question 13

Calculate PVR using Doppler techniques

Answer 13

PVR = (velocity TRjet/VTI rvot) x 10 + 0.16

                    OR

PVR = 0.156 + (1.54 x [(PEP/AcT)/TT]
Using RVOT Doppler profile:
PEP= pre-ejection period
AcT= acceleration time
TT= total systolic time

       OR

RVPEP/VTI rvot

If < 3 WU
If 0.4-0.6, then PVR 3-7.5 WU
If >0.6, then PVR >7.5 WU

    OR

Propagation velocity of RVOT

If Prop velocity rvot > 20 cm/s, then PVR < 2 WU

Question 14

Normal Resistances

Answer 14

-PVR-
0.25-1.6 WU
20-130 dynes*s/cm^5

-SVR-
9-20 WU
800-1600 dynes*s/cm^5

dynes*s/cm^5 = woods x 8

Question 15

PISA

Answer 15

• proximal isovelocity surface area

Valve Area = 2pi(r^2) x angle/180 x Vn/Vm

r = radius of shell
angle = angle shell makes with respect to leaflet
Vn = nyquist velocity
Vm = max velocity across valve