1. Dr .Lakshmi Gopalakrishnan Southern Railway Hospital
Cathlab hemodynamics – 1 pressures, waveforms ,cardiac output and resistance
Dr .Lakshmi Gopalakrishnan
Southern Railway Hospital

2. HEMODYNAMICS IN CARDIAC CATHETERIZATION
PRESSURE MEASUREMENTS
MEASUREMENT OF FLOW
VASCULAR RESISTANCE
Principle of Ohm’s Law : Q = ∆ P / R

3. Pressure recording system
Consists of catheter , transducer, amplifier and recorder
Must meet :
amplitude linearity
adequate frequency response
phase linearity
calibration of transducer over range of amplitudes,and a plot gives linear relationship
optimal damping

4. Frequency response and optimal damping

5. Pressure Measurement systems
Fluid filled catheters
Micromanometer catheters

6. Transducers –
to be calibrated against a known pressure, “ zeroed” placing at mid chest level and balanced ( zero all the transducers being used simultaneously) immediately prior to obtaining simultaneous recordings

7. Fluid filled system - contd
Sources of error
Distortion of the output signal due to frequency response and damping charecteristics
optimal damping achieved by short, wide-bore , non compliant catheter directly connected to transducer with no air bubbles in the liquid .This achieves frequency response close to output –to-input ratio of 1.
catheter whip artifact, end-pressure artifact, catheter impact artifact, catheter tip obstruction

8. Pressure measurement – micromanometer system
Advantages include higher natural frequencies, optimal damping characteristics, no whip artifacts
Less distorsion of waveforms, lack the msec delay
Commercially available ones have both end hole and side holes for over the wire use and angiography and ones with two tip transducers for pressure gradients
Disadvantages - expense, fragility, added procedure time
Used for research work only.

9. Fluid filled catheter vs micromanometer catheter

10. Normal pressure waveforms
Atrial waveforms
Right atrium a wave highest
Pre – a wave pressure
a wave
x descent
x’ descent
v wave
y descent
Left atrium v wave highest , pressure higher
Pulmonary capillary wedge, similar to LA waveform, damped, delayed

13. Respiratory variation
During spontaneous respiration intrathoracic pressure falls in end expiration by 3-4 mmhg and end-inspiration by 7-8 mmhg
This reduces the RA, LA, Aortic pressures and hence underestimates
All recordings in end expiration since it closely resembles the atmospheric pressure

17. Atrial waveforms- important points
Shows two positive waves ‘a’ atrial and ‘v’ ventricular and negative waves x’ and y descents
‘a’ wave is prominent with abnormalities of reduced RV,LV compliance
‘v’ wave is prominent in AV valve regurgitation
X’ and y descents are diminished in pericardial tamponade
X’ and y descents are accentuated in constriction and restrictive diseases

18. Ventricular pressure waveform
Consists of
Small rapid-filling wave
slow filling wave
‘a’ wave co-incident with atrial systole
Ventricular systolic pressure wave
Pressures reported are
early diastolic pressure
End- diastolic pressure
peak systolic pressure

19. Ventricular pressure waveform -- diastole

20. Ventricular pressure waveform - systole

21. Arterial pressure waveforms
Rapidly rising systolic pulse wave
‘ incisura’
End diastolic pressure
Measured central aortic pressure wave is a conjugate of both forward and reflected waves
factors that augment pressure wave reflections
vasoconstriction
heart failure
hypertension
ilio femoral obstruction
valsalva – after release

22. Aortic pressure waveform

23. Central aortic pressure waveform a conjugate of forward & reflected waves

24. Aortic pressure waveforms as a function of distance from the Aortic valve

25. from augmentation of reflected waves
Aortic pressure waveform before & after occlusion of femoral –major increase
from augmentation of reflected waves

26. Pulmonary artery pressure waveform

27. Cardiac output
Quantity of blood supplied to systemic circulation per unit time in L / min
Determined by preload, heart rate and myocardial contractility
Cardiac index = CO in L / min / m2 BSA
Other variables like age, posture, temperature considered while interpreting CO

28. Determination of CO - Technique
Fick’s oxygen method
Thermodilution method
Fick’s principle- states that the total uptake or release of any substance by an organ is the product of blood flow to the organ and the art- venous concentration difference of the substance
CO = O2 consumption / AV Oxygen difference
CO = x BSA
(Sa O2 – Sv O2) x Hb x 1.36 x 10
Error in this method -10%
Most accurate in low output states and conditions with irregular HR like AF and V bigeminy

29. Thermodilution method
Injection of 10ml of cold saline in the Right atrium
Measure the temp change in the PA and a transient drop in temp occurs
Curve plotted of the temp of PA vs time
Has a smooth up slope and a more gentle decline
Area under the curve is inversely proportional to the CO
CO = CC x (Tb – Ti).
Where cc is the computation constant, Tb the blood temperature and Ti the injectate temperature
Severe TR is a contraindication to use of the method
Error with this method 5- 20%
Most accurate in high output states and less accurate in low output states

30. Thermodilution curves – PA temperature vs time

31. Vascular resistance
In clinical practice Ohm’s law : Q = ∆ P / R is used to calculate resistance
Systemic vascular resistance = AO mean - RA mean
Q S
Pulmonary vascular resistance = PA mean - LA mean QP
pressures are in mmhg , flow in litres per min and resistance in Hybrid resistance unit or Wood’s unit expressed as mmhg / litre/ min
Wood units can be converted to metric units by conversion factor 80
expressed as dynes.sec.cm -5
Vascular resistance is normalized for BSA giving a Resistance Index.
SVRI = Ao(mean) – RA(mean) 80
______________________ CI
Where CI is Cardiac Index Thus SVRI = SVR x BSA

32. NORMAL VALUES FOR VASCULAR RESISTANCE
Systemic vascular resistance dynes – sec – cm -5
Systemic vascular resistance index dynes – sec – cm-5 m2
Pulmonary vascular resistance dynes – sec – cm-5
Pulmonary vascular resistance index dynes – sec – cm-5 m2

33. Thank you for your kind attention !