Short-term Control of Blood Pressure

Question 1

What are the three causes of changes in blood flow that occur during normal day to day life? (3)

Answer 1

1. Tidal breathing
2. Changes in body position
3. Valsalva maneuver

Question 2

What are some of the normal physiological mechanisms that maintain blood flow in response to day to day changes? (4)

Answer 2

1. Vascular auto-regulation
2. Baro-receptor mediated effects
3. Central nervous system ischemic response effects
4. Renal baro-receptor mediated effects

Question 3

What are some of the abnormal responses that can be seen in the short term control of BP? (4)

Answer 3

1. Abnormal auto-regulatory effects
2. Autonomic dysfunction
3. Drop in BP too large
4. Pulsus parodoxus (and tidal breathing)

Question 4

What happens if the body senses alterations in flow and BP?

Answer 4

Triggers compensatory mechanisms to maintain flow and BP.

Question 5

How does changing body posture affect BP?

Answer 5

Effects of gravity on venous return

Question 6

How does the valsalva maneuver affect BP?

Answer 6

Increases intrathoracic pressure = decreases venous return

Question 7

What is vascular autoregulation?

Answer 7

Local blood flow maintained relatively constant despite an increased BP.

Question 8

What is the response of vascular autoregulation when BP is increased?

Answer 8

Increased BP - stretch of arteriolar muscles - vasoconstriction - decreased flow

Question 9

What is the response of vascular autoregulation when BP is decreased?

Answer 9

Decreased BP - increased vasodilator metabolites - increased flow

Question 10

Where are the baro-receptors found?

Answer 10

Carotid, aortic, renal baro-receptors

Question 11

What effect do the baro-receptors have on BP?

Answer 11

Baroreceptors pick up decreased blood pressure
= activate SNS
- vasoconstriction, increased heart rate, increased cardiac contractility
= increased cardiac output and increased BP

Question 12

The baroreceptors work in synergy with what other response?

Answer 12

CNS ischemic response

Question 13

What does the cerebral ischemic response protect against?

Answer 13

The cerebral ischemic response safeguards cerebral perfusion

Question 14

What does VMC stand for?

Answer 14

Vasomotor center

Question 15

What is effect of the cerebral ischemic response?

Answer 15

Massive decrease in BP = Greatly decreased cerebral blood flow = Increased PCO2, Increased H+ = Activation of VMC = Increased sympathetic response = (intense vasoconstriction) Increased HR, Increased TPR = RESTORES BP

Question 16

What are the renal BR mediated RAAS effects?

Answer 16

Decreased blood pressure:

1. Renin release
2. Aldosterone release

Question 17

What is the effect of renin on BP?

Answer 17

Renin converts Angiotensinogen to Angiotensin I = converted by ACE (in lungs) to Angiotensin II = VASOCONSTRICTION = increased TPR

Question 18

What is the effect of aldosterone on BP?

Answer 18

Aldosterone causes increased Na+ re-absorption in kidney (Na+ and H2O resorption) = increased plasma volume = increased venous return = Frank-Starling effect = Increased stroke volume = Increased CO

Question 19

What are the two causes of abnormal responses to changes in BP?

Answer 19

1. Autonomic dysfunction

2. Drop in flow or BP too large for ANS to cope

Question 20

What are the consequences of abnormal responses to changes in BP?

Answer 20

Dizziness, fainting and syncope

Question 21

What are the signs and symptoms of compensatory changes following acute drops in blood flow and BP?

Answer 21

Pallor, sweating, tachycardia, nausea

all due to sympathetic activation

Question 22

What are the two types of autonomic dysfunction abnormal responses?

Answer 22

1. Neurological

2. Emotional (vasovagal)

Question 23

What are some causes of neurological autonomic dysfunction?

Answer 23

1. Neuropathies (DM, strokes)

2. Blood clots in the VMC

Question 24

Explain vasovagal syncope:

Answer 24

Activation of hypothalamus - activation of PSNS - increased vagal firing - decreased HR - venodilation (venous pooling) - decreased venous return - decreased stroke volume - decreased BP (vasodilation also = decreased BP)

Question 25

What causes vasovagal syncope?

Answer 25

Severe anxiety, pain, fear (emotional stress)

Question 26

What are the three causes of a drop in BP that is too large?

Answer 26

1. Circulatory
2. Arrhythmias
3. Neurological
   OR any other cause of shock (hypovolemic, cardiogenic shock etc.)

Question 27

What can cause a drop too large: circulatory reasons?

Answer 27

Decreased SV (MI, Heart Failure)

Question 28

What can cause a drop too large: arrhythmic reasons?

Answer 28

1. Decreased heart rate = decreased CO

2. Increased heart rate = decreased filling time = decreased SV

Question 29

What can cause a drop too large: neurological reasons?

Answer 29

Pharmacological agents:

1. Venodilators = decreased venous return
2. Vasodilators = decreased BP

Question 30

What is pulsus paradoxus defined as?

Answer 30

BP >10mmHg lower during inspiration than during expiration

Question 31

What are some examples of causes of pulsus paradoxus?

Answer 31

1. Asthma (very negative ITP)

2. Cardiac tamponade (pericardial restraint)

Question 32

What is the effect of inspiration on BP?

Answer 32

1. Negative intrathoracic pressure = pressure gradient between venous reservoir (extrathoracic) and R heart (intrathoracic) = increased filling of R heart = expansion of RV = bulging of septum into LV
2. Relative pooling of blood in lungs (both lungs and L heart are intrathoracic therefore no pressure gradient) = decreased filling of L heart
   Decreased filling of L heart plus bulging of septum into LV = decreased SV from LV = decreased BP
3. Negative intrathoracic pressure = decreased external pressure on aorta = decreased BP

Question 33

What is the overall effect of tidal breathing on BP?

Answer 33

BP lower during inspiration than during expiration (normally <10 mmHg)