Lecture 24 : Cardiovascular Integration

Question 1

What is the equation for mean arterial blood pressure?

Answer 1

MABP = CO x TPR

Question 2

What value is the resting arterial blood pressure?

Answer 2

~90 mmHG

Question 3

What is the function of arterial blood pressure?

Answer 3

Provides sufficient pressure to overcome resistance of the vessel while flowing at the desired rate
- Needed to maintain adequate perfusion (fainting)

Question 4

What are 4 reflex mechanisms maintaining normal arterial pressure?

Answer 4

1. Arterial Baroreceptors
2. Carotid and aortic chemoreceptors
3. Cardiopulmonary Baroreceptors - “low pressure receptors”
4. Central chemoreceptors - in medulla

Question 5

What are the sensors of arterial baroreceptor reflex?

Answer 5

Aortic and carotid sinus baroreceptors

Question 6

Where are the afferent fibres of the arterial baroreceptor sensors?

Answer 6

Travel in vagus and glossopharyngeal nerves to CVS centres in brainstem - nucleus tractus solitarius in the medulla

Question 7

What type of activity is in the afferent and efferent nerves for barorecptors?

Answer 7

Tonic activity

Question 8

What is the purpose of tonic activity?

Answer 8

It means that the system can respond readily to either a fall or an increase in arterial pressure

Question 9

What happens to parasympathetic and sympathetic activity if arterial pressure increases?

Answer 9

• Increase activity in baroreceptor afferent fibres
• Parasympathetic activity to the heart increases
• Sympathetic activity to the heart and blood vessels decreases

Question 10

What occurs to the variables of the heart when arterial pressure increases?

Answer 10

Heart rate, cardiac contractility and total peripheral resistance will fall, and vasodilation will occur
* Effects on the heart will reduce its pump function as CO = HR X SV
* Dilation of the veins reduces venous return and the filling pressure of the heart - reduces preload and thus CO further
* MABP = CO x TPR, the combined drop in CO and TPR due to vasodilation will reduce arterial pressure

Question 11

How do frequency distribution curves of a normal vs. denervated baroreceptor differ?

Answer 11

• Intact baroreceptors have narrow operating range in pressure
• Denervated baroreceptor nerves have a wide pressure distribution

Question 12

What is the key role of baroreceptors?

Answer 12

Controlling minute-minute pressure changes at normal physiological state

Question 13

How does posture affect central venous pressure?

Answer 13

• When lying down most vessels are close to the heart so pressure above and below the heart is the same
• CVP at heart = 3mmHg
• When standing up veins below the heart distend and transmural pressure increases
• CVP at heart = 0mmHg

Question 14

Describe the sequence of orthostatic hypotension:

Answer 14

1. Decrease CVP
2. Decrease right stroke volume (starling law)
3. Decrease left ventricular filling pressure
4. Decrease left stroke volume (starling law)
5. Decrease arterial pressure
6. Decrease cerebral blood flow - lack of O2
7. Dizziness, visual fade

Question 15

How does baroreflex preserve cerebral perfusion?

Answer 15

Decrease in arterial blood pressure
1. Decrease input from low pressure receptors
2. Decrease input from high pressure receptors
3. Increase sympathetic drive to; SA node, myocardium, resistance, and capacitance vessels

Question 16

What is the result of the baroreflex at the cardiovascular level when going from supine to tilt?

Answer 16

HR increases
SV decreases - reduced preload
CO decreases a little bit
TPR increases
MABP maintained

Question 17

What is the skeletal muscle pump in the legs?

Answer 17

When muscles contract it compresses veins and prevents accumulation of blood in legs

Question 18

What occurs to cardiac output during exercise?

Answer 18

Can increase from 5L/min to 35L/min

Question 19

Where does most of cardiac output go during exercise?

Answer 19

Exercising muscles

Question 20

Where does vasoconstriction occur during exercise?

Answer 20

Abdominal organs, kidneys and other non-exercising muscles

Question 21

Describe the hemodynamic changes during exercise?

Answer 21

Increase:
* HR, SV, thus CO
* Skeletal muscle blood flow
* Systolic BP and MABP
Decrease:
* TPR
Same:
* Diastolic BP

Question 22

How do different levels of blood loss affect the body?

Answer 22

• 10% - no significant threat
• 20-30% - clinical shock, CO and BP falls
• > 40% - severe, cerebral and coronary perfusion

Question 23

What occurs during a haemorrhage?

Answer 23

1. Haemorrhage
2. Hypovolaemia
3. Decrease central blood volume
4. Decrease ventricular end diastolic volume
5. Decrease ventricular SV (Frank-starling mechanism)
6. Haemorrhagic shock
   Flow diagram on one note

Question 24

What 3 steps occur in the bodies response to blood loss?

Answer 24

1. Rapid - within seconds, baroreceptor
2. Intermediate - within minutes, fluid reabsorption
3. Long term - days, kidneys

Question 25

How is blood volume restored after blood loss?

Answer 25

* Cells not replaced for several week * Circulating volume rapidly restored from ISF * Slower replacement of lost volume - salt and water

Question 26

For CVS function is volume or composition more important?

Answer 26

Volume - appropriate fullness of the vessels

Question 27

What is autotransfusion?

Answer 27

Transfusion of water from around the body into the blood stream 1. Haemorrhage 2. Decrease blood volume 3. Decrease capillary hydrostatic pressure 4. Absorption from ISF

Question 28

What 2 factors cause capillary pressure to decrease?

Answer 28

1. Blood loss 2. Reflex vasoconstriction of small arteries and arterioles

Question 29

Describe the process of the long-term response of fluid replacement:

Answer 29

1. Decreased renal perfusion triggers renin/angiotensin II 2. Angiotensin II: - vasoconstrictor - reduces renal perfusion; less urine (+ ADH) - reduces renal Na loss - stimulates aldosterone - stimulates thirst 3. Increase body water and salt

Question 30

How are components replaced in the blood and how long does this take?

Answer 30

Replacement of: - Red blood cells by bone marrow - Albumin by liver Takes around 6 weeks