Other Flashcards
Normal blood flow velocity
200cm/s
Normal myocardial velocity
20cm/s
TDI specificities
use low frequency + high amplitude of myocardial motion
o Velocity of tissue < blood flow
Record lower range of velocities → 20-150cm/s
o Amplitude in tissue > blood flow
Adjust filters to exclude lower reflective objects
Waves on TDI
S’: systolic contraction = positive frequency shift
Diastolic motion has 2 phases
* E’: early diastolic motion
* A’: late diastolic motion 2nd to atrial contraction
Between: IVCT and IVRT
PVR on echo
Poiseuille’s law
- Applies to steady laminar flow of homogenous fluid in rigid tube
- Resistance:
o Sensitive to changes in radius tube - Vascular impedance: instantaneous ratio of pulsatile pressure/flow
Flow (Q) = (pi (P1 – P2) r^4)/8nl
P-p = inflow pressure
R radius of tube
L is length of tube
N is viscosity of fluid
Resistance = 8nl/(pir^4 )
Factors that incr PVR
hypoxia, hypercapnia, ↑∑ tone, polycythemia, local serotonin, PTE (mechanical obst.), precapillary pulmonary edema, lung compression (pleural effusion)
Factors that decr PVR
oxygen, adenosine, isoproterenol, NO, prostacyclins, nitroprusside, Ca2+ blockers
Determinants of PVR
o Arteriolar tone
o Venous pressure: mLAP
Mean pulmonary capillary wedge pressure used to approximate LAP
PVR units and how to determine on echo
o Woods unit
PVR → directly related pressure gradient and inversely related to pulmonary flow
* Help distinguish: ↑PAP from ↑pulmonary flow or ↑ PVR
TR/RVOTVTI ratio
* Cutoff of 0.2 predictive for <2 Woods unit
* >2 considered ↑PVR
PVR = 10+0.16((TR velocity)/〖RVOT〗_VTI )
o Arbitrary resistance units (hybrid resistance unit): mmHg/L/min
mPAP: from early PI jet velocity
PVR = (mPAP-mLAP)/CO
mLAP = E/E’ + 4
o Metric resistance units: dynes-sec-cm-5
PVR =change P/Qp x 80
Total PVR from echo measure
- Resistance to flow from PA to LV in diastole
o Neglect LV diastolic pressure
o When mLAP cannot be measured
Total PVR =mPAP/Qp
Congenital shunts determination w/ PVR
- Ratio of PVR/SVR: used in Hu to determine if sx correction of defect is indicated
o Normal <0.25
o Moderate pulmonary vascular disease = 0.25-0.5
o Severe pulmonary vascular disease > 0.75
o Ratio >1: sx correction CI because of severity of pulmonary vascular disease - Studies in dogs:
o PVR doubled when Ht ↑ from 43 to 64%
o Resolution of cyanosis with ↓HT may lead to ↓PVR
How can one calculate LV dp/dt by Echo-Doppler?
- Dp/dt = rate of LV pressure change during IVCT
o Index of LV contractility - Assessment: from MR flow velocity jet on CW
o Slope of MR during interval between 1 and 3m/s
o Bernoulli: should = 32mmHg
Dp/dt = 32mmHg/time (s)
What is the value of the end-systolic volume index
Fractional shortening
* Measure of myocardial function in dogs with CVD
o CHF is 2nd to severe MR + volume overload
Not myocardial failure
* Large breed dogs tend to develop myocardial failure with CVD
Normal contractility = normal LV systolic chamber size even if LV dilation
* Dependent on preload, afterload and contractility
Causes of incr end-systolic volume index
↑preload, ↓afterload, ↑contractility
Value of systolic index and equation
- Can help differentiate abnormal myocardial function
o Independent of preload
o Hearts with normal contractility will shorten to normal LV systolic dimensions even if dilated
Systolic index = (End systolic volume)/BSA
Ref values systolic index
o Normal myocardial function <30ml/m2
o Mild myocardial failure 34-70 ml/m2
o Moderate myocardial failure 70-100 ml/m2
o Severe myocardial failure >100 ml/m2
- Expected end systolic dimension: allometric ratios
o ESDe = 0.95 x BW0.315
o ESD/ESDe ratio: may be more accurate when comparing small vs large breed dogs
Large breed dogs: myocardial failure → ratio > 1.13 ± 0.15
Small breed dogs: myocardial failure → ratio > 0.89 ± 0.21
What is the value of allometric scaling
- Most echocardiographic variables correlate to body mass index
- Eliminates need to use multiple breed specific variables
o Resolve difficulties of curves based on BW and BSA
Cardiac volumes: linearly related to BW (which is a volume)
CSA areas: linearly related to BSA - BW2/3
Linear dimensions: linearly related to body length - BW1/3
- M-mode measurements: allometric scaling can be used to predict normal values
Z scores: how different vs allometric scaling
- Deviation of anatomic physical measurement from size or age specific population
o Can be applied to echo measures
o Describes how many SD a given measure lies > or < a specific population mean
Z score interpretation
o Positive value: > population mean
o Negative value: < population mean
o ↑ (- or +) the value → ↑ deviation from population mean
Normal range considered 2xSD → Z = -2 to 2
Z = (x-u) p
* X = observed measurement
* U = expected measurement (population mean)
* P = standard deviation
Allometric scaling equation
Y = aBWb
Y: measurement
A/B: constants
- Proportionality constant
- Scaling exponant
Allometric scaling limitations
o Breed specific differences in some parameters
Ie. ↓ FS% in Greyhounds
Ref values only exist for limited # of breeds
Breed could affect normal values
o Reference values based on body size is only appropriate for mixed breeds
o Other factors can affect normal values: age, sex, obesity, activity level
Males usually have higher BW
High activity level → thicker LV walls and ↑ chamber dimensions
Fat free mass better predictor of measurements in Hu
HR: ↑HR → ↓ chamber dimensions
Puppies/young animals: greater normalized dimensions
o Effect of BW vs body type vs BSA
