VASCULAR: REGULATION OF MAP II

Question 1

Compare arterial and venous pressure in the head vs feet

Answer 1

Arterial pressure is lower in the head (60 mmHg) than compared to the feet (185 mmHg)
Venous pressure is lower in the head (-10 mmHg) compared to feet (95 mmHg)

Question 2

Define: syncope

Answer 2

fainting; due to insufficient cerebral perfusion

Question 3

Describe how hypotension causes fainting

Answer 3

Gravity (standing straight) → Increase hydrostatic pressure → venous pooling → increase capillary filtration of plasma → more fluid entering interstitial space → decreased effective circulatory volume → decreased venous return and cardiac output → decreased cerebral blood flow

Question 4

Describe vasovagal syncope

Answer 4

Caused by sudden withdrawal of sympathetic nervous system and increased parasympathetic nervous system activity (vagal) → vasodilation (decrease total peripheral resistance and cardiac output) and decreased heart rate
Perhaps due to cerebral circulation causing a sudden withdrawal of SNS

Most common cause of fainting

Triggers:
Emotional - sight of blood, emotional distress
Postural - prolonged standing

Question 5

Describe why those with Parkinson’s disease may faint often

Answer 5

Orthostatic hypotension due to autonomic failure

Drop in blood pressure upon standing up

Impaired baroreflex response to standing

Question 6

List the various reasons that cause fainting

Answer 6

Vasovagal syncope (emotional/postural)

Orthostatic hypotension e.g. autonomic failure

Supine hypotension e.g. spinal cord injury (damage to sympathetic fibres), pregnancy

Shock (e.g. hemorrhagic)

Post-exercise hypotension (venous pooling of blood)

Question 7

Treatment for orthostatic hypotension and syncope

Answer 7

Lifestyle adjustments
- Tilt training
- Salt
- Exercise training: increase plasma volume and baroreflex sensitivity
- Water drinking

Salt loading
- water retention and plasma volume expansion

Head up sleeping
- increased plasma volume
- decreased atrial filling –> decreased ANP –> sodium retension
- nocturnal baroreflex stimulation

Adjustment of medication

Fludrocortisone

midrodrine

pacemaker

Question 8

How does fludrocortisone treat fainting?

Answer 8

synthetic corticosteroid (mineralocorticoid)
mimics aldosterone
promotes renal sodium reabsorption
increases plasma volume

Question 9

How does midodrine treat fainting?

Answer 9

Short acting a1 agonist
Vasoconstriction

Question 10

How does a pacemaker treat fainting?

Answer 10

very effective in syncope due to arrhythmia

ineffective in syncope due to hypotension

• Pacemakers prevent the fall in heart rate that occurs with a faint but not the fall in blood pressure; thus doesn’t prevent fainting!

Question 11

What is a normal BP?

Answer 11

<120/<80

Question 12

What is the etiology of hypertension

Answer 12

10% renal hypertension
Caused by a problem with renal artery
Block in renal artery → renal artery thinks that systemic artery is low → increases systemic arterial pressure

90% idiopathic (unknown origin)

Question 13

What do those with hypertension have in common?

Answer 13

Higher total peripheral resistance

Suggests that arteriole radius is key in the process of hypertension development

High levels of vasoconstrictors

Contributing factors (genetics, lifestyle, diet (salt intake))

Question 14

Name 2 hypertension pharmacological treatments

Answer 14

1. Diuretics (e.g. furosemide)
   limit Na+ reabsorption (inhibits Na-K-2Cl symporter) → decreased plasma vol → decreased MAP
2. ACE inhibitors (e.g. captopril)
   reduce angiotensin II
   decreased vasoconstriction
   decreased aldosterone secretion → decreased Na+ reabsorption → decreased plasma volume → decreased MAP
   decreased cardiac hypertrophy
3. Angiotensin II receptors blockers (e.g. losartan): reduces action of angiotensin II
4. Ca2+ channel antagonists e.g. nifedipine, verapamil
   Block Cav1.2
   preferential effect to act on Cav1.2 in VSM vs. cardiac muscle → decreased Ca2+ current → vasodilation and reduced contractility
5. β-adrenergic antagonists (β blockers) e.g. propranolol: decrease CO and MAP - not suitable for asthmatics

Question 15

Describe the lifestyle treatments for hypertension

Answer 15

Dietary -”DASH” diet (Dietary Approaches to Stop Hypertension)
- Reduce Na+ intake
- Reduce caffeine intake (positive inotrope)
- Reduce fat intake
- Achieve and maintain healthy dietary balance

Lifestyle
- Increase activity levels
- Smoking cessation
- Achieve and maintain a healthy body weight
- Decrease alcohol intake
- Decrease stress