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Measurements in CVS

Organisation of the Body

QuestionAnswer
Measuring arterial blood pressure Place a fluid filled catheter in an artery - measure pressure wave Gives continuous measurement of each heart beat - used in the ICU Hard to do as the catheter needs to go into an artery - deep inside the body
Right and left heart cardiac catherterisation Feed catheter through arterial or venous systems to access one side of the heart Measure pressure at any point e.g. inside ventricles Can inject dye to see narrowing of coronary arteries
Typical measured pressures Right atrium - 2-6 mmHg Right ventricle - 25/4 mmHg Pulmonary artery - 25/20 mmHg Left atrium - 4-12 mmHg Left ventricle - 120/9 mmHg Aorta - 120/80 mmHg
Non-invasive arterial blood pressure Cuff inflated to block blood flow to arm = done here as pressure change is very little from aorta As cuff deflates appearance of 1st Krokoff sounds indicates systolic pressure Loss of these sounds indicates diastolic pressure
Measuring peripheral blood flow 2 pressure cuffs At write - 200 mmHg - no blood flow to hand At arm - 40 mmHg - above venous but below diastolic Blood enters arm but cannot leave - arm swells - rate of swelling is converted to blood volume
2D Doppler ultrasound Used on carotid artery Measures velocity/time Converted to blood volume/time
Fick's Principle Rate of O2 uptake = Blood flow (Arterio-venous conc difference) You know O2 added/removed at tissue bed- give an idea of flow Hard to do
Measuring cardiac function using imaging Cineangiography - similar to catheter Echocardiography - ultrasound to throat Nuclear cardiology - radioisotope tracer taken up into myocardium Cardiac magnetic resonance imaging
Stroke volume EDV = end diastolic volume ESV = end systolic volume SV = stroke volume SV = EDV-ESV
Ejection fraction EF = SV/EDV Tells you the proportion of diastolic volume ejected in systole Normally 55-65%
Why measure ejection fraction A good predictor of prognosis - severely reduced indicated cardiac failure with survival of 50% over 5 years Normal = >55% Mildly reduced = 45-54% Moderately reduced = 35-44% Severely reduced = <35%
LV cineangiography Inject dye into the heart to see how it contracts
Transthoracic echocardiography 5th intercostal space-cuts from apex of the heart - gives 4 chamber view Where ultrasound cuts through chest wall determines the picture Anterior posterior image - right ventricle closer to the front - shows valves e.g. aortic valve and descending aorta
Doppler flow measurements Allows velocity to be measures Sees increase in velocity to a peak Cardiac output = stroke volume x heart rate
Nuclear cardiology Inject a radioactive substance - taken up into myocytes Patient in gamma camera - pictures of how the ventricular wall moves Can see areas not taking up stains - may show old myocardial infarction
Cardiac magnetic resonance imaging Very accurate Edge detection is very good Easy to measure size of chambers - accurate calculations
Measuring coronary perfusion Echocardiography Nuclear cardiology Cardiac magnetic resonance imaging Cardiac CT Contract angiography
Myocardial perfusion imaging Do at both rest and after exercise Areas stained at rest but not during exercise show partial blocking of coronary arteries - high heart rate leads to these areas not receiving blood flow
Cardiac MRI with contrast Looks at how wall take up contrast agents When areas remain stained for long periods - old myocardial infarctions - cannot contract
Cardiac CT Look at arteries themselves Visualise all structures Convert back into a 3D image
Cardiac Catheterisation Angiogram - inject dye via a catheter - can see narrowing Can be fixed there and the by placing a wire down the artery A balloon is inflated in the artery placing a stent to keep the artery open
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