Pathophysiology of Cardiovascular Disease

Question 1

What is the equation for cardiac output?

Answer 1

CO= HR (heart rate) x SV (stroke volume)

Question 2

Define heart failure…

Answer 2

A complex syndrome initiated by an inability of the heart to maintain a normal cardiac output at normal filling pressures

Question 3

In what ways can heart failure be classified?

Answer 3

According to cause
Underperfusion vs congestion
Right-sided or left-sided heart failure

Question 4

In what ways can function of the cardiovascular system be impaired sufficiently to bring about heart failure?

Answer 4

1) Pump failure
2) Volume overload
3) Pressure overload
4) Arrhythmias
5) Diastolic failure

Question 5

Define pump failure and give an example of a condition which causes pump failure…

Answer 5

Intrinsic failure of contraction of the heart muscle e.g. dilated cardiomyopathy

Question 6

Define volume overload of the heart and give examples of diseases that may cause this…

Answer 6

Chronic increase in the amount of blood that must be pumped by a given cardiac chamber e.g. shunts (VSD/PDA), regurgitations (mitral value insufficiency), anemia or increase metabolic demands of tissues as in hyperthyroidism

Question 7

Define pressure overload of the heart and give examples…

Answer 7

Systemic or pulmonary hypertension or an outflow obstruction such as aortic or pulmonic stenosis, which results in increased resistance to emptying of a chamber

Question 8

How to arrhythmias lead to heart failure?

Answer 8

Compromised cardiac output because of increased or decreased heart rate. Tachycardia - shorten diastole and impaired filling thus reducing the stroke volume. Bradycardia - limits cardiac output by limiting heart rate.

Question 9

How does diastolic failure lead to heart failure and given example diseases…

Answer 9

Impaired ventricular filling with normal systolic function such as in pericardial tamponade or hypertrophic cardiomyopathy

Question 10

What is the final common pathway of heart failure/

Answer 10

Under-filling of the arterial circulation which causes congestive heart failure. This initiates a cascade of several nervous and endocrine adaptations and eventually a change in the structure and function of the heart.

Question 11

What are the autonomic effects in heart failure?

Answer 11

Parasympathetic dominance to a sympathetic dominance. Drop in arterial blood pressure is sensed by baroreceptors. Increased adrenergic cardiac effects and vascular alpha effects ensure to increase HR and contractility and increase vascular resistance in efforts to store blood pressure

Question 12

Explain the renin-angiotensin-aldosterone system…

Answer 12

Various stimuli (renal underperfusion, sympathetic stimulation and decreased chloride delivery to parts of the renal tubule) induce renin release from the kidney. Renin leads to cleaving of angiotensin I from angiotensinogen. Angiotensin converting enzyme (ACE) then catalysts the production of angiotensin II from angiotensin I. Angiotensin II is a potent vasoconstrictor and acts as a stimulus for aldosterone release from the zone glomerulosa of the adrenal cortex which in turn leads to sodium and water retention from the renal tubules.

Question 13

Explain the role of ADH in endocrine effects on the cardiovascular system…

Answer 13

Marked drop in blood pressure leads to a non-osmotic release of ADH which brings about free water retention leading to increased circulating fluid volume. This is at the expense of poor osmoregulation; an a dilational hyponatraemia ensures. ADH also brings about vasoconstriction and increase in vascular resistance.

Question 14

Where is the main site of manufacture, storage and release of natriuretic peptides of the heart?

Answer 14

The myocardium

Question 15

What are ANP and BNP?

Answer 15

Atrial natriuretic peptide (ANP)

Brain natriuretic peptide (BNP)

Question 16

Explain the release of NPs and their subsequent effect…

Answer 16

In disease states BNP is manufactured predominantly in the ventricular myocardium. Both peptides are released in response to cardiac chamber wall stress and therefore tend to increase as filling pressures increase. Levels are elevated in patients with heart disease and are therefore used as a bio marker for the presence to disease. They counteract hormone systems to cause vasorelaxation and increase sodium loss. In congestive heart failure they are usually overwhelmed bu other vasoconstrictive and sodium retaining mechanisms.

Question 17

What is hypertrophy?

Answer 17

Increase in cell size (vs. Hyperplasia, which is cell number)

Question 18

What factors contribute to hypertrophy of the heart?

Answer 18

Falling cardiac output
Adrenergic stimulation
Angiotensin II
Increased intracellular calcium

Question 19

What are the two types of cardiac hypertrophy?

Answer 19

Eccentric (Increased diameter)

Concentric (Decreased diameter)

Question 20

Why might ischemia and regional hypoxia develop in a hypertrophic heart?

Answer 20

Increase in myocardial mass means an increase in myocardial oxygen demand. This demand outstrips the ability of the coronary circulation to provide leading to ischaemia and hypoxia.

Question 21

What is the normal function of the vasculature?

Answer 21

To distribute substrates of cellular metabolism through the body and removed waste products created as a consequence

Question 22

Give examples of substrates of metabolism transported by vasculature…

Answer 22

Oxygen
Glucose
Amino acids
Ketone bodies
Triglycerides

Question 23

Give examples of waste products created by cellular metabolism..

Answer 23

Carbon dioxide

Lactate

Question 24

What is the Starling hypothesis?

Answer 24

Equilibrium of fluid exchange across capillary walls is determined in hydrostatic pressure and oncotic pressure that excises across the capillary wall.

Question 25

In normal vasculature where is the gain and loss of fluid?

Answer 25

Normally, net loss of fluid from the capillary at the arteriolar end and a net gain at the venous end

Question 26

Why does excess fluid (oedema) form?

Answer 26

1. Increase vascular hydrostatic pressure (right-sided heart failure or venous occlusion)
2. Increased vascular permeability (e.g. vasculitis)
3. Decreased plasma oncotic pressures (e.g. hypoproteinaemia)
4. Decreased lymphatic drainage (e.g. lymphoedema)

Question 27

What forms of vascular disease are there?

Answer 27

1. Thrombosis and embolism
2. Vasculitis
3. Degeneration vascular disease
4. Malformation of vasculature
5. Hypertension

Question 28

Give examples of a degenerative vascular disease..

Answer 28

Arteriosclerosis and atherosclerosis

Question 29

Give example of a malformation of vasculature…

Answer 29

PDA

PSS

Question 30

Hypertension can be classified as either…

Answer 30

Systemic (most common in elderly cats)

Pulmonary