Cardiovascular Physiology Flashcards
Describe the important aspects of Cardiac function
Transport Oxygen CO2 Wastes Nutrients Hormones Heat Immunity
Determinates and regulation of cardiac output
- Heart rate: Nerves and hormones
- Contractililty: Stroke volume
- Preload
- afterload
Neural control
- PNS via vagus: Ach on muscarinic receptors affects only HR
- SNS - T1-4: Noradrenaline -> B1 receptors. Affects HR and Contractility (preload and afterload)
Hormonal : direct via adrenaline and indirectly
Determines of SVR
Neural
- SNS: - noradrenergic (Vasoconstrictor (α1) – eg. gut, skin. β1 inotropy. Vasodilator (β2) – eg. airways, muscle. β3 Heat production)
- PNS: Cholinergic – vasodilator eg M3 eg gut, M2 negative- chrontropy
Hormonal
- Systemic factors: Catecholamines, ADH, Angiotensin II, Aldosterone, ANP
- Endothelial factors: NO, Prostaglandins, thromboxane A2, Leukotrienes, Histamine, bradykinin, serotonin (5-HT)
Local
- Reactive hyperaemia: Adenosine, CO2, PO2, pH, K+, Temp
Myogenic
Describe the processes that facilitate venous return
Intravascular volume Venomotor tone Valves Pumps - MSK, Thoracic and abdominal pumps Suction by the heart
Describe the central control mechanisms of the CVS
Centro-lateral medulla Input - High pressure - baroreceptors — Carotid sinus - Low pressure - Volumereceptor - Chemoreceptors in the kidney - higher centres - Pain and stress
Cardiovascular physiology in aviation
G tolerance: Maintaining arterial blood pressure and cerebral perfusion
Hypoxia: Maintaining tissue oxygenating
Cardiovascular stresses of flight: Thermal, exertional, accident survival
CV disease causing incapacitation
General principles of Haemodynamimcs
Pascal’s principle: pressure at a point in a fluid is the same in all directions
Hydrostatic pressure: Ph=pgh
No flow means pressure anywhere at the same horizontal level is the same
Flow occurs from height to low pressure.
Moving fluid has momentum
Dynamic of flow - laminar vs turbulent.
Hydrostatic effects on blood pressure
Heart level 100mmHg Lower above heart Higher pressure below heart 22mmHg pressure drop heart to brain in the upright human at +1G Effects are multiples with G
Pressure in Vein
Low pressure 0-15mmHg
Effect of the environment on CVS disorders
Hypoxia of all types sustained G G countermeasures stress physical activity/workload
Effect of CVS disorders on aviation operations
Distracting symptoms - pain and palpitations Suddenly incapacitation, haemodynamic compromise - hypotension - syncope - silent disease - sudden death - thromboembolism
medication side effect
questions to ask referring specialist
What is the diagnosis
what is the % risk of incapacitation per year
what is the prognosis and risk of recurrence
what treatment, and what side effects?
what follow-up or monitoring is required?
cardiac investigations
Resting ECG: very poor sensitivity
Exercise stress ECG: easy, non-invasive, 1st line for CAD
Holter Monitoring: for rhythm and conduction disturbances, syncope and pre-syncope, post-ablation success.
MPS - assesses functional ischaemia even in the absence of anatomical lesions
Echocardiography: useful for ix for murmurs, suspicion of structural heart disease, pressure gradients/velocities, pericardial conditions, cardiomyopathy, EF estimation.
Stress ECHOcardiography: more sensitivity than exercise stress ECG, assesses functional ischaemia. useful if ECG uninterpretable eg LBBB
Coronary angiography: gold standard test for IHD
Calcium score:independent risk factor but expensive. stress echo is a better predictor of events
considerations for treatment of HTN
lifestyle changes first
don’t need to TMUFF if <160/100mmHg and overall CVD risk score acceptable
If failure to improve after maximum 6 months trial of conservative Mx then TMUFF and commence on pharmacological therapy
TMUFF 14 days initial
- 7 days with subsequent change
UMECR required
pharmacological tx of HTN
ACEi/ARB 1st line agents
Thiazide diuretics
Ca channel blockers - unfit for high-performance flying duties.
Beta - blockers: unfit for high - performance flying duties
alpha blockers NOT permitted for flying duties
some combination therapies may be unfit high performance or multi crew.
Consideration for lipid lowering agents
conservative therapy
- no TMUFF or MECR needed if overall CVD risk score is acceptable
- eg lifestyle changes and fish oil
Pharmacology
- statin first line medication option
- TMUFF 7 days
- 7 days with which subsequent change
- UMECR required
- can add ezetimibe, bile acid sequestrates, fibrate
Nictotinic acid not permitted for flying duties
Considerations for antirrhythmics
Underlying condition is likely disqualifying for military aviation In clivilian aviation, case by case - AF increasely common -rate control vs prophylaxis of AF - Sotalol and other B-blockers
Consideration for anticoagulation
Military
- aspirin acceptable
- clopidogrel disqualifying
- warfarin disqualifying
- Factor Xa inhibitors (NOACs)
Civilian
- warfarin requires evidence of stable INR control
- Class 1 multi crew only
Consideration for CABG
1st year 10% rate with venous grafts
2rd year onwards - 1-3% per annum
at least 6-12 months recovery
waiver consideration
- cardiology R/V annually
- EF >50%
- MPS
- demonstrates risk factor control
Angioplasty +/- stenting considerations
Risk of early re-stenosis, easing over times
6-12 months recovery
waiver consideration
- cardiology R/V annually
- EF 50%
- MPS
- Demonstrates RF control
- no combination anti-PLT therapy
Ground for 6 months post CABG and Angioplasty with stent if what consideration occur
Incomplete revascularisation
postoperative graft or stent failure
low output syndrome
post operative arrhythmias: AF 15-40%, most settle within 8 weeks, VT/VF mainly preoperatively with within 1 week.
adverse neurological outcomes
- major events 21% mortality
- minor event - 10% mortality
Consideration for pacemakers
disqualifying for military flying due to potential for EMR interaction with Device
Civilian
- restricted certification
- dual chambered, bipolar leads, annual checks.
Consideration for radio-frequency and cryoablation for AF
relatively high recurrence rate
Ground for 12months
Need to exclude arrhythmias provide to clear for fly
risk for pulmonary vein stenosis
what are the baseline need for CASA
LVEF >50%
absence f jeopardise myocardium - no reversible ischaemia
Acceptable incapacitation risk
