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Cathlab hemodynamics – 1 pressures, waveforms ,cardiac output and resistance

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## Cathlab hemodynamics – 1 pressures, waveforms ,cardiac output and resistance

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**Cathlab hemodynamics – 1pressures, waveforms ,cardiac**output and resistance Dr .Lakshmi Gopalakrishnan Southern Railway Hospital**HEMODYNAMICS IN CARDIAC CATHETERIZATION**• PRESSURE MEASUREMENTS • MEASUREMENT OF FLOW • VASCULAR RESISTANCE • Principle of Ohm’s Law : Q = ∆ P / R**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**Pressure Measurement systems**• Fluid filled catheters • Micromanometer catheters**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**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**Pressure measurement – micromanometer system**• Advantages include higher natural frequencies, optimal damping characteristics, no whip artifacts • Less distorsion of waveforms, lack the 30- 40 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.**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**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**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**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**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**Central aortic pressure waveform a conjugate of forward &**reflected waves**Aortic pressure waveforms as a function of distance from the**Aortic valve**Aortic pressure waveform before & after occlusion of femoral**–major increase from augmentation of reflected waves**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**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 = 130 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**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**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**NORMAL VALUES FOR VASCULAR RESISTANCE**Systemic vascular resistance 1170 + 270 dynes – sec – cm -5 Systemic vascular resistance index 2130 + 450 dynes – sec – cm-5 m2 Pulmonary vascular resistance 67 + 30 dynes – sec – cm-5 Pulmonary vascular resistance index 123 + 54 dynes – sec – cm-5 m2