Lecture 24 : Cardiovascular Integration Flashcards
(30 cards)
What is the equation for mean arterial blood pressure?
MABP = CO x TPR
What value is the resting arterial blood pressure?
~90 mmHG
What is the function of arterial blood pressure?
Provides sufficient pressure to overcome resistance of the vessel while flowing at the desired rate
- Needed to maintain adequate perfusion (fainting)
What are 4 reflex mechanisms maintaining normal arterial pressure?
- Arterial Baroreceptors
- Carotid and aortic chemoreceptors
- Cardiopulmonary Baroreceptors - “low pressure receptors”
- Central chemoreceptors - in medulla
What are the sensors of arterial baroreceptor reflex?
Aortic and carotid sinus baroreceptors
Where are the afferent fibres of the arterial baroreceptor sensors?
Travel in vagus and glossopharyngeal nerves to CVS centres in brainstem - nucleus tractus solitarius in the medulla
What type of activity is in the afferent and efferent nerves for barorecptors?
Tonic activity
What is the purpose of tonic activity?
It means that the system can respond readily to either a fall or an increase in arterial pressure
What happens to parasympathetic and sympathetic activity if arterial pressure increases?
- Increase activity in baroreceptor afferent fibres
- Parasympathetic activity to the heart increases
- Sympathetic activity to the heart and blood vessels decreases
What occurs to the variables of the heart when arterial pressure increases?
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
How do frequency distribution curves of a normal vs. denervated baroreceptor differ?
- Intact baroreceptors have narrow operating range in pressure
- Denervated baroreceptor nerves have a wide pressure distribution
What is the key role of baroreceptors?
Controlling minute-minute pressure changes at normal physiological state
How does posture affect central venous pressure?
- 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
Describe the sequence of orthostatic hypotension:
- Decrease CVP
- Decrease right stroke volume (starling law)
- Decrease left ventricular filling pressure
- Decrease left stroke volume (starling law)
- Decrease arterial pressure
- Decrease cerebral blood flow - lack of O2
- Dizziness, visual fade
How does baroreflex preserve cerebral perfusion?
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
What is the result of the baroreflex at the cardiovascular level when going from supine to tilt?
HR increases
SV decreases - reduced preload
CO decreases a little bit
TPR increases
MABP maintained
What is the skeletal muscle pump in the legs?
When muscles contract it compresses veins and prevents accumulation of blood in legs
What occurs to cardiac output during exercise?
Can increase from 5L/min to 35L/min
Where does most of cardiac output go during exercise?
Exercising muscles
Where does vasoconstriction occur during exercise?
Abdominal organs, kidneys and other non-exercising muscles
Describe the hemodynamic changes during exercise?
Increase:
* HR, SV, thus CO
* Skeletal muscle blood flow
* Systolic BP and MABP
Decrease:
* TPR
Same:
* Diastolic BP
How do different levels of blood loss affect the body?
- 10% - no significant threat
- 20-30% - clinical shock, CO and BP falls
- > 40% - severe, cerebral and coronary perfusion
What occurs during a haemorrhage?
- Haemorrhage
- Hypovolaemia
- Decrease central blood volume
- Decrease ventricular end diastolic volume
- Decrease ventricular SV (Frank-starling mechanism)
- Haemorrhagic shock
Flow diagram on one note
What 3 steps occur in the bodies response to blood loss?
- Rapid - within seconds, baroreceptor
- Intermediate - within minutes, fluid reabsorption
- Long term - days, kidneys
