Other

Question 1

Normal blood flow velocity

Answer 1

200cm/s

Question 2

Normal myocardial velocity

Answer 2

20cm/s

Question 3

TDI specificities

Answer 3

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

Question 4

Waves on TDI

Answer 4

 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

Question 5

PVR on echo

Question 6

Poiseuille’s law

Answer 6

• 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 )

Question 7

Factors that incr PVR

Answer 7

hypoxia, hypercapnia, ↑∑ tone, polycythemia, local serotonin, PTE (mechanical obst.), precapillary pulmonary edema, lung compression (pleural effusion)

Question 8

Factors that decr PVR

Answer 8

oxygen, adenosine, isoproterenol, NO, prostacyclins, nitroprusside, Ca2+ blockers

Question 9

Determinants of PVR

Answer 9

o Arteriolar tone
o Venous pressure: mLAP
 Mean pulmonary capillary wedge pressure used to approximate LAP

Question 10

PVR units and how to determine on echo

Answer 10

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

Question 11

Total PVR from echo measure

Answer 11

• Resistance to flow from PA to LV in diastole
  o Neglect LV diastolic pressure
  o When mLAP cannot be measured

Total PVR =mPAP/Qp

Question 12

Congenital shunts determination w/ PVR

Answer 12

• 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

Question 13

How can one calculate LV dp/dt by Echo-Doppler?

Answer 13

• 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)

Question 14

What is the value of the end-systolic volume index

Answer 14

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

Question 15

Causes of incr end-systolic volume index

Answer 15

↑preload, ↓afterload, ↑contractility

Question 16

Value of systolic index and equation

Answer 16

• 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

Question 17

Ref values systolic index

Answer 17

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

Question 18

What is the value of allometric scaling

Answer 18

• 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

Question 19

Z scores: how different vs allometric scaling

Answer 19

• 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

Question 20

Z score interpretation

Answer 20

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

Question 21

Allometric scaling equation

Answer 21

Y = aBWb
Y: measurement
A/B: constants
- Proportionality constant
- Scaling exponant

Question 22

Allometric scaling limitations

Answer 22

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