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The Cardiovascular System
Dr Suzannah Phillips
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Summary
Overview of structure and function
Common disorders of the CVS
– Cardiac Markers
– Clinical application of cardiac markers
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Structure and Function
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The cardiovasular system
Consists of the heart and blood vessels.
Function
– Transport mechanism:
oxygen
nutrients - glucose, electrolytes
antibodies / white blood cells to sites of infection
hormones
waste products of metabolism
heat
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The Cardiac cycle
BP 120/80
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The Circulatory System
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The Capillary Bed
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Arterial Structure
Venous Structure
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Cardiovascular disorders
1. Cardiovascular disease
2. Coronary heart disease
3. Heart Failure
4. Hypertension
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1. Cardiovascular Disease (CVD)
Atherosclerosis which effects arteries in the heart, brain and peripheral tissues.
Atherosclerosis – deposition of lipid and matrix protein in the
arterial wall (medium to large arteries)
– narrowing of the vessel lumen
– reduced blood supply
– Heart – causes coronary heart disease
– Brain – causes stroke
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Atherosclerotic plaques
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Steps by which smooth muscle cells (SMC) colonize the atherosclerotic plaque.
Hofnagel O , Robenek H Cardiovasc Res 2009;81:242-243
Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2008. For permissions please email: [email protected]
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Risk factors for CVD
Age Gender Race Family History Smoking Cholesterol Hypertension Obesity Diabetes Mellitus Low physical activity
Biochemical – Homocysteine
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2. Coronary Heart Disease (CHD)
Failure of the coronary circulation to meet the demands of the heart (increased
demand/decreased supply)
Caused by:
– cardiovascular disease (coronary arterial disease, CAD)
– Vasospasm, anaemia, arrhythmias
Lack of oxygen - Ischaemia
Also called ischaemic heart disease (IHD)
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Myocardial Infarction (MI)
End result of CHD
Prolonged ischaemia – cell death (necrosis)
May also get collagen scarring
Most commonly a result of CAD
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CAD
Atherosclerosis in coronary arteries causing inadequate oxygen supply to the heart.
This leads to
1. Stable angina
2. Acute coronary syndrome (ACS)
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Stable angina
– partial occlusion of cardiac artery
– unable to supply oxygen if increased demand (excerise, stress)
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Acute coronary syndrome
Due to plaque rupture.
Causing:
1. Unstable angina
2. Myocardial infacrtion
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Diagnosis of ACS and MI
1. ECG changes
2. Biochemical Cardiac Markers of CVD
Cardiac enzymes Myoglobin Troponins
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Cardiac enzymes
1. ALT (alanine aminotransferase) liver, skeletal and cardiac muscle, kidney.
Cytoplasm of cells
Increased in plasma following circulatory failure, MI.
X10 URL
2. AST (aspartate aminotransferase) liver, skeletal and cardiac muscle, kidney.
Cytoplasm of cells
Increased in plasma following circulatory failure, MI.
X10 URL
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Cardiac enzymes 3. LDH (Lactate dehydrogenase)
Wide tissue distribution.
Five isoforms LDH1 – LDH5. LDH1 – significant in MI
Measure total LDH
X10 URL
4. CK (Creatine Kinase) Skeletal and cardiac muscle, brain.
Dimer of two subunits M or B.
3 isoforms: MM (skeletal and cardiac), MB (35% of cardiac activity, 5% skeletal), BB (brain)
Measure CK and CK-MB (both raised in muscle damage)
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Myoglobin
Present in all muscle
Haem protein – oxygen transport.
Found in cytoplasm
Troponins (Tn)
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Three proteins: Troponin T – binds to tropomyosin Troponin I – inhibitor of ATPase Troponin C – binds calcium
Troponin T and I used as markers for cardiac damage (cardiac specific isoforms).
Troponin I more specific, skeletal troponin T isoforms cross react in cardiac Troponin T assay.
High sensitive assays (hsTnT / hsTnI) – lower detection limits
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Detection time depends on:
Size Cellular location Plasma clearance
myoglobin
Cardiac marker
Starts to rise (hrs)
Time to peak value (hrs)
Duration of rise (days)
myoglobin 2-4 8-10 1
AST 6-8 24-48 3-4
LDH 12-24 48-72 7-12
CK-MB 2-6 18 1-2
Troponin 4-6 12-24 7-10 / 3-10
Cardiac Marker Detection in Serum
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Use in the diagnosis of MI
1950 1960 1970 1980 1990 2000
AST in
AMI
Optimized
CK Assay
CK-MB
Monoclonal
Antibody cTnI in
AMI
Electrophoresis
for CK and LDH
LDH in
AMI
CK in
AMI
POC
Testing
CK-MB
Mass
Assay cTnI for Risk
Stratification
First
CK-MB
Assays
RIA for
Myoglobin
cTnT
in AMI
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WHO definition of MI
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Other causes of a raised troponin
Trauma Congestive heart failure–acute and chronic Hypertension Hypotension, often with arrhythmias Renal failure Critically ill patients, esp with diabetes Hypothyroidism Myocarditis Pulmonary embolism Sepsis Burns, esp if TBSA > 30% Amyloidosis Acute neurological disease, including CVA Rhabdomyolysis with cardiac injury Vital Exhaustion Polymyositis
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3. Heart failure (HF / CHF)
Failure of heart output to meet demand.
Symptoms:
– SOB, fatigue, oedema
Causes:
– Cardiomyopathy
– Inflammation
– Valvular heart disease
– Ischaemic heart disease
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Diagnosis of HF
Echocardiogram – gold standard
Markers of Heart Failure:
Brain natriuretic peptide (BNP)
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BNP
• Natriuretic peptide secreted primarily from ventricules as a prohormone (proBNP).
• Immunoassays available for BNP and NT-proBNP
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BNP
Increased in
– cardiac failure
– ventricular hypertrophy
Useful ‘rule-out’ test – echo referral
Negative result excludes heart failure.
Prognostic indicator in heart failure
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4. Hypertension
BP >140/90 mmHg Risk factor CVD – CHD or stroke Essential hypertension – unknown cause Endocrine hypertension - Conn’s, Cushings,
phaeochromocytoma.
Biochemical markers: ― No specific biochemical markers for hypertension ― Diagnosing endocrine causes ― Management/monitoring treatment
― renal function ― electrolytes
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The Respiratory System
Dr Suzannah Phillips
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Summary
Overview of structure and function
Common disorders
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Basic Structure
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Function:
1. Gas exchange: CO2 exchanged for O2 (ventilation)
2. Acid-base regulation
Regulation of respiration: • Respiratory centre in medulla – controls rate and depth of breathing.
• Driven by CO2 concentration (PCO2). Maintained within tight limits.
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Arterial blood gases (ABG)
Blood gases: PCO2 and PO2 – gas exchange
Acid base: pH, PCO2, HCO3 – acid base balance
Monitoring lung function
PCO2 levels:
Determined by ventilation in the aveolar
Areas of good ventilation in the lung are able to compensate for any aveoli with poor ventilation by hyperventilation
PO2 levels:
Determined by Ventilation in the aveolar Concentration of O2 in the inspired air Perfusion of the lung
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Hypercapnia ↑PCO2 Hypocapnia ↓PCO2
Disorders of Respiration
Hypoxaemia – ↓O2 in the blood
TYPE 1
• adequate ventilation • defective oxygenation • hypoxaemia
TYPE 2 • inadequate ventilation • hypercapnia and hypoxaemia
Hyperventilation • hypocapnia
PO2 PCO2
Type 1 ↓ N
Type 2 ↓ ↑
Hyperventilation N ↓
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Common Causes
Type 1:
– Pneumonia, PE, COPD, ARDS
Type 2:
– COPD, exhaustion, opiates
Hyperventilation
– Anxiety, salicylate, hypoxaemia
Chronic Obstructive Pulmonary Disease • emphysema • bronchitis
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Other respiratory disorders:
1. Cystic fibrosis
Part of the UK Newborn Screening programme
Immuno-Reactive Trypsin (IRT)
2. A1AT deficiency
No inhibition of neutrophil elastase - emphysema
A1AT
3. Carbon monoxide poisoning
CO has higher affinity for Hb than O2 - hypoaemia
Carboxyhaemoglobin (COHb)
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Learning points!
Basic understanding of CVD and know common risk factors
Understand CHD and its consequences e.g. ACS Know the role of cardiac markers in CHD and
their limitations Know the role of cardiac markers in HF Understand the basic physiology of the lung Understand the role of ABG in monitoring lung
function. Know the common causes of respiratory
dysfunction