heart failure and oedema

Question 1

how is the blood volume distributed through veins, arteries etc.

Answer 1

• veins = 64%
• Arteries/arterioles = 15%
• capillaries = 5%
• heart = 7%
• lungs = 9%

Question 2

how is blood resistance distributed trhough veins, arteries etc.

Answer 2

• arteries/arterioles = 66%
• capillaries = 27%
• veins = 7%

Question 3

what happens in the capillary beds

Answer 3

• transfer of nutrient and waste products
• under smooth muscle control for constriction/relaxation
• precapillary sphincter controls regional flow
• gaps between endothelial cells allow diffusion

Question 4

describe the distribution of water within the body

Answer 4

• intracellular fluid compartment = 2/3 of total body water within cells
• extracellular fluid compartment = 1/3 total body water. 80% intersitial fluid, 20% blood plasma

Question 5

describe how extracellular fluid is balanced

Answer 5

plasma and interstitial fluid are in dynamic equilibrium. 2 things determine direction of equilibrium:
- hydrostatic pressure (force exerted against inner capillary wall promoting formation of tissue fluid (net filtration pressure OUT)
- colloid osmotic pressure (exerted by plasma proteins promoting fluid reabsorption INTO circulatory system

Question 6

how does hydrostatic pressure aid in the exchange of fluid in tissues

Answer 6

hydrostatic pressure is higher in the arterial end than the venous end.
- pressure must push fluid OUT at arteriole end to force nutrients into tissues
- pressure must allow fluid to re enter the circulatory system at the venous end to allow waste products to be removed from tissues

Question 7

describe this graph

Answer 7

at the start of the capillary beds (arteriole end) hhydrostatic pressure is greater than osmotic pressure (which stays the same throughout) to push fluid out into the tissues. this is beneficial because it forces fluid carrying nutrients and oxygen into the tissues.
at the end, (the venous end) hydrostatic pressure falls below osmotic pressure, allowing waste products to reenter the capillary beds.
remember: hydrostatic is pressure OUT of vessels and osmotic is pressure IN

Question 8

describe how starlings forces determine whether fluids are going in or out of vessels

Answer 8

starling force = (hydrostatic pressure in the capillary + colloid osmotic pressure of the intersitial fluid) - (hydrostatic pressure in the interstitial fluid + colloid pressure of the blood plasma)

Question 9

what are the functions of the lymphatic system

Answer 9

• Assists in circulation of body fluid between cells and bloodstream (returns tissue fluid to circulation)
• protects body against foreign materials (carries to lymph nodes)
• transports dietary fats

Question 10

what is oedema

Answer 10

• an excessive accumulation of intersitial fluid (may be free fluid in cavities)
• can be localised or general
• starlings forces are out of balance (increased outward filtration pressure, decreased inward absorption pressure = leaky vessels)

Question 11

what causes increased outward filtration pressure?
decreased inward pressure?

Answer 11

increase outward:
- increased arterial pressure (dont see this clinically b/c of pressure decrease in venous and capillary end)
- increased venouc pressure (by either obstruction of the vessels locally or generalised increase in venous pressure

decreased inward:
- Fall in plasma COP
- protein loss
- reduced protein synthesis

Question 12

what causes oedema

Answer 12

• vasogenic (leaky vessels) caused by local inflammation or generalised vasculitis
• lymphatic disease
• hyperaemic/hydrostatic caused by localised obstruction, high venous pressures (heart failure)
• osmotic caused by low plasma COP

Question 13

what are the clinical findings of oedema

Answer 13

• can be localised or generalised
• fluid in skin (pitting oedema)
• fluid within tissue in a body system (lungs if L sided heart failure, brain if vascular disease)
• free fluid in body cavities (pleural fluid in cats = heart failure, free fluid in abdomin in dogs (ascites) = right sided heart failure)

Question 14

what are the 2 words used to describe heart failure

Answer 14

• congenital
• acquired

Question 15

desccribe the development of acquired heart disease

Answer 15

• develops later in life
• > 95% of all heart diseases (very common)
• require medical therapy

Question 16

what are the primary causes of acquired heart failure

Answer 16

• degenerative valvular disease (aortic or mitral)
• heart muscle disease (cardiomyopathy)
• valve/endocardial infection
• pericardial disease
• rate/rhythm abnormalities

Question 17

describe degenerative valvular disease

Answer 17

• develops later in life
• cause unknown
• may/may not develop into heart failure
• regurgitation into atrium during systole (compare atrial and aortic/pulmonic pulses
• picked up as murmur
• causes jet lesions caused by abnrormal flow of pressure

Question 18

describe heart muscle diseases

Answer 18

• cardiomyopathy (especially in large breed dogs like dobermans)
• develops later in life
• cause unknown
• usually develops into heart failure
• in the cat rarely dilated
• usually restrictive (stiff heart)
• or hypertrophic (heart is thick walled)

Question 19

describe dilated cardiomyopathy

Answer 19

• in the dog usually dilated if have cardiomyopathy
• disease of the heart muscle
• muscle function becomes poor
• heart does not pump effectively

Question 20

compare eccentric hypertrophy and concentric hypertrophy

Answer 20

• eccentric occurs with volume loading (valve incompetence/ dilated CMO)
• concentric occurs with pressure load (hypertension or aortic/pulmonic stenosis)

Question 21

compare acute vs chronic heart failure

Answer 21

acute:
- rare
- vascular disease and acute myocardial infarction (heart attack)

chronic:
- most common
- usually degenerative conditions

Question 22

explain pathophysiology of heart failure

Answer 22

whatever the cause, cardiac output falls and is detected as a drop in blood pressure
-degenerative valve disease (regurgitation means less forward flow into the aorta)
dilated cardiomyopathy (forward flow falls due to poor contractility
restrictive/hypertrophic cardiomyopathy (forward flow falls because heart cannot fill)

Question 23

what mechanisms are activates to restore blood pressure in heart failure

Answer 23

1. SNS activation
2. RAAS (renin angiotensin aldosterone system)
3. cardiac enlargement (later)

Question 24

what are the effects of the compensatory mechanisms of heart failure and how can they cause adverse effects long term

Answer 24

• HR increases
• contractility increased
• vasoconstriction
• salt and water retention
• cardiac enlargement

all of these are ideal in the short term, but long terms can worsen heart function or cause lean on effects to other organs
- HR and contractility increase = sick heart works harder = increased O2 demand but O2 availibility is decreased
- vasoconstriction = increased afterload = CO falls more = valves leak more
- salt and water retention = volume of blood returned to heart increases, volume of fluid in vessels increases, pressure in capillaries increases = oedema develops
- cardiac enlargement = AV valves leak more sue to stretch, O2 demand increases, O2 supply decreases = cells die and if not replaced scar tissue forms = contractility falls more