Dec 26, 2009

Heart Disease

Hardening of arteries
   Tunica intima thickens with deposits of Cholesterol, Fibrous (scar) tissue, Dead muscle cells, Blood platelets        
      Arteries become less elastic and partially narrowed
        ↑BP which in turn accelerates atherosclerosis
         Leads to endothelium damage and weak walls

   Excess cholesterol leaks from lipoproteins (LDLs)
   Deposited on arterial walls
   Macrophages (white blood cells) are trapped within cholesterol
   Release free radicals which damage the arterial wall
   Activates blood platelets which stick to damaged areas releasing clotting factors (thromboxanes)
   Forms a plaque which may rupture to produce a thrombus
   Circulating thrombus is called an embolus
   Embolus may lodge elsewhere in the circulation (brain, heart arteries)
   NB: healthy arteries produce anti-clotting factors (prostaglandins) → don't form clots

Factors that aggravate atheroma formation / atherosclerosis:
   Hypertension (↑BP)
   Smoking (release of free radicals)
   High LDL and low HDL
   NB: they all cause endothelial damage

   Weak arterial walls may burst leading to severe loss of blood (haemorrhaging)
   Brain aneurysm is called a stroke

Deep Vein Thrombosis
   Clots are formed by
   Endothelial damage (see atherosclerosis)
   Altered blood components (dehydration, too many platelets)
   Altered blood flow (stasis of veins) → this is what causes DVT
      Prolonged immobility
      Such as paralysis, long-distance flights, lying down for weeks after surgery
   Thrombus often originates in calf veins
   Inflammation of vein walls → destroys vein valves
   Causes leg pain, swelling, and redness
   Elastic support stockings required for life
   Prevented by taking aspirin or warfarin which inhibit blood clotting

Coronary Heart Disease
   Atherosclerosis causes arteries to become narrowed
      More force required to move blood through narrowed vessels
      Blood pressure increases
   Stable angina
      ↑exercise leads to ↑oxygen requirements by heart
      Narrowed arteries prevent more blood to pass through
      Shortage of blood to heart muscle causes chest pain
      Cells do not die as some blood can still pass through
      Pain only occurs during activity but not at rest

Myocardial infarction (MI)
   Coronary artery is totally blocked by a thrombus/embolus
   No blood supply to heart muscle and cells die
   Irreversible if not treated within 90min

Heart failure
   Prolonged blockage of artery causes damage to heart muscle
   ↓contractions / ↓cardiac output / ↓pressure generated / less blood leaves heart
   More blood is stored:
       on the right side of the heart → enlarged heart
       in veins → swollen legs and enlarged liver

  Needed for
     Vitamin D production in skin
     Sex hormone production in gonads and adrenal glands
     Making cell membranes
     Produce bile acid (salts)
  Has properties similar to fats → soft, waxy, and insoluble (difficult to remove if deposits form)
  Transported in blood from liver to tissues
  Safe transport is needed due to its insolubility
  Achieved by lipoproteins, which are soluble fatty proteins
  These are wrapped around cholesterol
  Normally, only small amounts of free cholesterol escape

   Low density lipoproteins
  Carries cholesterol from liver to tissues
  Normally, some cholesterol 'leaks' from the lipoprotein and is absorbed to build cell membranes
   Excess LDL/cholesterol → too much cholesterol leaks out and causes atherosclerosis

   High density lipoprotein
   Picks up cholesterol from arterial walls and carries it away from tissues
   Travels to liver where cholesterol is removed with bile

↓antitoxidants (vitamins), more damage due to release of free radicals by phagocytes
Nicotine constricts arteries causing platelets to stick together → vasoconstriction → heart must work harder to force blood through → increases BP
↑BP causes damage to blood vessel lining / endothelium / collagen
Leads to rise on blood platelets and makes them more sticky / form a plug / adhere to collagen fibres
Release of thromboplastin/thrombokinase
Fibrinogen converted to insoluble fibrin
Platelet plug trapped by fibrin mesh
Raises conc. of fibrinogen (in blood) → increased risk of clotting
↑LDL causes more cholesterol to leak out in blood
Carbon monoxide reduces the efficiency of the blood in terms of carrying oxygen
Haemoglobin combines with CO more readily than with oxygen → forms carboxyheamoglobin
Associated with plaque formation
Principle CHD = heart muscle receives inadequate amount of blood or oxygen/(coronary) blood supply reduced

Beta blockers reduce heart rate and reduce oxygen required by heart
Aspirin prevents blood clotting and thrombosis formation
ACE inhibitors stabilize plaques → prevent thrombus to break off
Statins reduce LDL and increase HDL
Deflated balloon-like device is passed up to the heart via the aorta
Guided into damaged coronary artery and inflated to stretch the artery
Heart by-pass graft
Leg veins and arteries from chest are used to by-pass the blocked region of the coronary artery
Involves open heart surgery
Reperfusion therapy after a myocardial infarction
Angioplasty done within 90 minutes of onset of chest pain
May prevent irreversible damage to the heart muscle

1. Screen population for
   High BP
   High cholesterol
   Uncontrolled diabetes
   Smoking? Unhealthy diet? No exercises?
   Men over 55 and women over 65 are at highest risk
2. Monitor the behaviour of the heart during exercise
   Difficult but encouraging the population to adopt a more healthy lifestyle from an early age is important
   Often leads to changes in diet and weight management
3. Giving up smoking and reducing alcohol intake
    Reduces blood pressure
    Coronary heart disease is a long-term degenerative disease, starts at birth