Lecture 6 - cardiovascular response to stress Flashcards
What external factors affect CO?
ANS noradrenaline / adrenaline drugs electrolytes excercise
How is CO measured?
HR x SV
What is SV?
EDV - ESV
typical values for SV/EDV/ESV
SV = 70
EDV=140
ESV=70
What factors affect HR?
- autonomic innervation
- hormones
- fitness levels
- age
What factors affect SV?
- heart size
- fitness levels
- gender
- contractility
- duration of contraction
- Preload
- afterload
How is heart rate maintained?
SAN intrinsic rate of 110bpm
PNS lowers the rate to 60-80
what are factors that change the HR?
chronotropic agents?
What are positive chronotrophic factors?
- SNS
- excercise
- increased body temperature
- hypercalaemia
- hypokalaemia
- hyponatraemia
- chemorceptors –> acidotic
- atropine/caffeine
What factors are negative chronotrophic?
- PNS–> AcH
- hypocalaemia
- hyperkalaemia
- hypernataemia
- alkali state
How does HR increase during excercise?
exercise stimulate proprioceptors in vessels and increases body temperature
What is HR max
The maximum rate the heart can reach without affecting the filling of the ventricles
why is there a limit to rapid filling time?
excessive increase in HR affects CO
what is preload
Volume of blood entering the ventricles
-Preload= the degree of stretch on myocardium when filled with blood at end of diastole (EDV)
What is afterload
resistance the ventricles have to overcome to pump blood out the ventricles
What is contractility ?
contraction of the myocardium
What is the preload increased in?
hypervolaemia
regurg of cardiac valves
heart failure
What is afterload increased in?
HTN
vasoconstriction
What happens when afterload increases?
CO increases
What does a higher preload mean
Higher EDV
What factors reduce preload
myocardium damage –> reduced stretch
Increased HR –> reduced filling time
What factors ensure blood returns to the heart
- gravity when standing -ve
- skeletal muscle pump +ve
- A-T pump when breathing +ve
Impact of IV fluids on blood volume?
Bainbridge reflex
- receptors in the right atrium detect distension
- sympathetic activity stimulate through SAN
- HR increases
impact of IV fluids on BP in atrium?
Baroreceptor reflex
- pressure increase detected by baroreceptors in atria#
- signals to decrease HR
- increased urine output –> decreased vasopressin and increased ANP
What does the overall effect of the baroreceptor and bainbridge reflex depend on?
the previous HR
Explain how ANP works?
- secreted by the heart
- in response to atrial stretch
- causes glomerular arteriolar dilation
- diuresis
explain how RAAS works?
- regulates pressure + volume
- decrease in GFR –> kidney releases renin
- renin cleaves AT-1 into AT-2
- AT-2 is a potent vasoconstrictor –> increases BP
What does an increase in afterload do to SV?
decreases SV
what factors increase afterload?
- HTN
- cartoid artery stenosis
- atherosclerosis
- carotid valve stenosis
- pulmonary hypertension
What does an increased afterload lead to?
LVH
What is SCD?
- inherited heart condition
- heart muscle thickens and becomes stiff
- most common genetic heart condition 1 in 500 affected
- AD
How is contractility affected in pathology?
Acidoisis (poorly: diabetes, heart attack, sepsis) – reduced contractility
H+ is the strongest –ve ionotrope
Ionotropes for cardiogenic shock
+ve: Digoxin, Ad, NorAd, Dopamine, Dobutamine
-ve: β blockers, Diltiazem
What is the frank-starling law?
The Frank–Starling law of the heart represents the relationship between stroke volume and end diastolic pressure. The law states that the stroke volume of the heart increases in response to an increase in the volume of blood in the ventricles, before contraction, when all other factors remain constant
What does the frank-starling graph represent
relationship between cardiac output and EDV
What does a steep curve on a frank-starling graph represent?
increased contractility
-
What does a less steep frank-starling curve show?
reduced contractility
