Hemodynamic Calculations

Question 1

Stroke Volume and Cardiac Output

Answer 1

Volume = Area x Distance
SV = CSA x VTI
•measure VTI at identical location where radius is measured
•accuracy depends on : parallel alignment of u/s beam to blood flow and accurate determinations of CSA

CO = SV x HR

Question 2

Qp / Qs

Answer 2

CO through right / CO through left
Qp / Qs = SV pa / SV lvot
SV pa = A pa x VTI pa
SV lvot = A lvot x VTI lvot

Qp / Qs = (A pa x VTI pa) / (A lvot x VTI lvot)

Question 3

Regurgitant Volume

Answer 3

Volume of blood that goes backwards… what goes in must come out — forward through outflow tract or backwards through atrioventricular valve

Diastolic LV inflow = Systolic LV outflow = SV forward + R vol
SV mv = SV lvot + Rvol mv …
Rvol mv = SV mv - SV lvot …
Rvol mv = (A mv x VTI mv) - (A lvot x VTI lvot)
A mv by PHT, DT, PISA, or continuity equation

Question 4

Regurgitant Fraction

Answer 4

The fraction that goes backwards

RF = backwards flow / total flow
RF = Rvol / Inflow
RF = Rvol / SV mv

Question 5

Regurgitant orifice area (ROA)

Answer 5

Area of the hole…
Volume = Area x Distance
Rvol = ROA x VTI mr
ROA = Rvol / VTI mr

Question 6

Intracardiac pressures

Answer 6

Simplified Bernoulli equation
•delta P = 4v^2
(P1 - P2) = 4v^2

Flow goes from higher pressure P1 down its gradient to the lower pressure P2
V is the peak instantaneous velocity

•RVDP = RAP unless TV stenosis (rare)
•RVSP calculated from TR jet and = PASP unless PV stenosis (subtract gradient across PV)
•PAMP calculated from PI early velocity:
PAMP - RVDP = 4 x PI early^2 ...
PAMP = 4*PI early^2 + RAP
•PADP calculated from PI late velocity:
PADP - RVDP = 4 x PI late^2 ...
PADP = 4*PI late^2 + RAP
•LAP estimate from MR jet and LVSP = SBP unless AV pathology:
LVSP - LAP = 4*Vmr^2
LAP = SBP - 4*Vmr^2
•LVSP calculated from LAP obtained from catheter:
LVSP - LAP = 4*Vmr^2
LVSP = 4*Vmr^2 + LAP
•RVSP calculated from flow across VSD:
LVSP - RVSP = 4*Vvsd^2
RVSP = LVSP - 4*Vvsd^2

Question 7

Dp / Dt

Isovolumetric rate of LV pressure rise during isovolumetric contraction of the LV

Answer 7

Calculated as the slope of the LV pressure rise from 4-36 mmHg (Vmr = 1 to V mr = 3 m/s)
•independent of afterload
•dependent on preload
•assumes LAP doesn’t change much
•steeper the slope the faster the pressure increases and better the systolic function

Dp / Dt … 32 / Dt (Normal > 1200 mmHg/s)