Formulas Flashcards
Laplace
Wall Stress: Pressure x Radius/ 2x Wall thickness
Cardiac Output
SV x HR
Stroke Volume
LVEDV-LVESV
LV Stroke Index
SV/BSA
LV Cardiac Index
CO/BSA
FS
(LVd-LVs / LVd) x 100
EF
SV/EDV x 100
RV systolic pressure from VSD
Systolic BP- 4V2
V is max VSD velocity
(Systolic BP is LVSP in the absence of obstruction)
PA diastolic pressure
RA pressure plus 4V2 (V equals PR max at end diastole)
LV systolic pressure
Systolic pressure plus 4V2 (V equals AoV max)
LV EDP
Diastolic cuff pressure -4V2 (V equals AR max at end diastole)
LA systolic pressure
Systolic pressure -4V2 (V equals MR max)
PISA
(2 pi r 2) x Val / V max x VTI
Val- aliasing velocity
V max
Peak velocity of stenosis jet
R is PISA radius
Instantaneous flow rate by PISA
2 pi r2 X Val X 6
Pressure half time
Deceleration time x 0.29
FICK
02 consumption (ml/min) / (CaO2 - CvO2) x 10 (for liters per minute)
Or
O2 consumption/
A-VO2 1.36Hgb*10, where A-VO2 is arterial venous saturation difference
O2 content arterial blood
CaO2=(1.36 x Hb x SaO2) +0.003 x PaO2
O2 content venous blood
CvO2=(1.36 x Hb x SvO2) +0.003 x PvO2
thermodilution CO
(Temp Diff) x C /
Area under TDCO curve
Systemic Vascular resistance
- Measures LV afterload
(Ao mean - RA mean)*80/Qs
(Units are dynes/sec/cm-5)
Qs = systemic cardiac output
MAP
(2 x diastolic BP) + Systolic BP/ 3
Hakki valve area calculation
CO/
sq rt of peak to peak gradient
Gorlin for aortic valve area
- Measures valve area
CO (in cc’s) /
(SEP *HR)/44.3 *sq rt mean gradient
SEP- another Flashcard!
SEP (systolic ejection pd)
Time semilunar valves open to time they close
Measure @ 100mm/s paper speed
1 sm box 4mm, boxes x HR / paper speed
Peak to Peak
P1-P2- gradient
P1 is max LV systolic
P2 is max Ao systolic
Flamm
SvO2= 3 (SVC) plus 1(IVC) / 4
Qp
VO2 / (CpvO2-CpaO2) x 10
VO2 is O2 consumption
Qs
VO2/ (CaO2-CmvO2) x 10
Absolute Shunt
Qp-Qs
Pulmonic blood flow-Systemic blood flow
% shunt
(Qp-Qs) / Qp
No shunt
PBF = SBF = EBF
What is tau?
Time constant of isovolumetric relaxation (preload independent)
Highly dependent on accuracy of ventricular pressure measurements
Bainbridge reflex
Increased HR due to increased CVP
- increased venous return increases stretch on atria
- stretch receptors increase B fiber firing
- modulates autonomics to SA node –>increased HR
Poiseuilles law
The principle that the volume of homogeneous fluid passing per unit time through a capillary tube is directly proportional to the pressure difference btwn its ends and to the 4th power of its internal radius, and inversely proportional to its length and to the viscosity of fluid
Reynolds number
Dimensionless quality in fluid mechanics- used to determine the transition from laminar to turbulent flow.
Laminar flow occurs at low Reynolds numbers, where viscous forces are dominant
Turbulent flow is produced at high reynolds numbers, and dominated by inertial forces, chaotic flow instabilities
Left to right shunt
Qp-Qs
Flow ratios- what they mean
<1 indicates R–>L shunt
1 indicates no shunt
<1.5 indicates small shunt
>2.0 large shunt–> needs surgical intervention
Flow ratio equation (Qp:Qs)
Qp/ = (SA O2 - MV O2)/
Qs (PV O2 - PA O2)
MV is mixed venous
Anachrotic notch
Early notch on arterial pressure wave corresponding to the presystolic rise in pressure (isovolumetric contraction).
-notch occurs earlier and lower down on upstroke with severe SAS-
Slow build up of pressure and long interval btwn flow through narrowed orifice and aortic pressure peak
Venturi effect may contribute
-not
Bisferiens pulse
Presence of notch in middle of waveform suggests mild stenosis, but depth of notch suggestive of high flow velocity.
May see in diseases with increased volume - PDA, AR, mild AS
- presence is contraindication for valvulotomy in people- by already have significant regurg
Dichrotic notch
Corresponds to reflected waves from aortic valve closure.
Pulses alternans
Beat to beat alteration in pulse size and intensity. Left heart failure,poor contractility, tachycardia
Pulses paradoxus
Exaggerated decline in BP during inspiration (increased neg intrathoracic pressure). Tamponade, constrictive pericarditis, severe lung disease.
Decremental conduction
Functional block; attenuation of action potential amplitude as it progresses through the AV node and a reduction in its efficacy to excite adjoining cells.
AV nodal cells have slow recovery period and it becomes slower as HR increases.
Prolonged refractory pd also characteristic of nodal cells.
Pulmonary vascular resistance
(Mean PA pressure) - (PAW) x 80/CI
P
L–>R shunt formula
PBF-SBF
Or Qp-Qs
Bidirectional shunt formula
PBF-EBF
Where ebf is effective blood flow, the fraction of mixed venous return to lungs without shunt contamination
R–>L shunt formula
SBF-EBF
Tei index
IMP = (IVRT+IVCT) / ET
ET is ejection time
Continuity equation
Flow across LVOT equals flow across aortic valve
SV/ TVI (of AoV)
Mitral valve area from PHT
MVA = 220/PHT
Acoustic impedance
Resistance to flow of sound through medium (density X speed)
Bone shadow is high acoustic impedance
Reflection
Sound turned back at the boundary of a medium
Refraction
Change in direction of sound from one medium to another
Scatter
Structures that are small and irregular scatter sound in all directions- offered info about tissue character
Attenuation
Loss of energy from traveling through medium
(high freq more than low freq)
Large degree of attenuation = less transmission
Tissue harmonic imaging
U/S transmitted at one frequency and returned at higher frequency
Good for poor acoustic windows
Pulse repetition frequency
Number of pulses per seconds
Should be 2X sample depth
Nyquist the limit is 1/2 PRF
Nyquist limit
1/2 PRF.
Signal ambiguity of limit exceeded
Aliasing= signal ambiguity
SV
LVOT area x LVOT TVI
Regurgitant volume (from PISA)
EROA (from PISA) x MR TVI
Dp/dt
32mmHg/time (sec)
Qp:Qs
(Ao sat-MV sat) / (PV sat-PA sat)
Cardiac output
(Edv-esv)*hr
