CR: PBL 2 (Heart and Exercise) Flashcards
Define pulse pressure
Systolic BP - Diastolic BP (difference)
Define mean arterial pressure
Arithmetic mean of arterial blood pressure (CO x TPR)
Define pre-load
Pressure of blood in the ventricle before contraction
What is central venous pressure?
Pressure of blood in the great veins as they enter the right atrium
Define venous return
The volume of blood returning to the right atrium in one minute
Define total peripheral resistance
Resistance to the flow of blood in the whole system (MAP/CO)
Define systemic vascular resistance
Resistance to blood flow offered by all of the systemic vasculature (not pulmonary) - (MAP - RA pressure)/CO
Define ‘ejection fraction’
Proportion of EDV which is ejected by contraction
What is meant by ‘central command’
The anticipatory response of the autonomic nervous system to exercise which causes CO and arteriole adjustment
How does the cardiovascular system respond to exercise immediately?
Local chemicals cause arteriole dilation (lactic acid, nitric oxide and increased CO2, H+ and K+ levels)
How does the autonomic nervous system respond to exercise?
Sympathetic fight or flight response initiated:
a1 receptor –> causes blood shunting from digestion
B1 receptor –> increases HR and contraction force (SV)
B2 –> bronchodilation
Why does heart rate change after exercise?
Increased sympathetic stimulation to SAN
Why does systolic blood pressure change after exercise?
Greater volume of blood in ventricles due to increased venous return –> exerts greater pressure on arterial walls in systole
Why does diastolic blood pressure change after exercise?
Decreases due to vasodilation to the actively respiring muscles/tissues
Why does stroke volume change after exercise?
Starling’s law - greater distension of ventricular sarcomere with increased preload –> greater contraction –> greater volume of blood ejected in one beat
How do you calculate mean arterial blood pressure?
1/3(pulse pressure) + diastolic BP
OR CO x TPR
How may mean arterial pressure values be indicative of ischaemia?
MAP is considered to represent perfusion pressure, so less than 65mmHg may be indicative of ischaemia
What are normal BP values?
Systolic: Below 120mmHg
Diastolic: Below 80mmHg
What are normal HR values?
60-100bpm
What are normal stroke volume values?
70ml
What are normal cardiac output values?
4.9-5.6 L/min
What are normal pulse pressure values?
40mmHg
What are normal mean arterial pressure values?
65-110mmHg
Why doesn’t MAP change after exercise?
Despite increased cardiac output, there is vasodilation of muscles which counteracts increased pressure
Why does pulse pressure increase after exercise?
Due to increased difference in blood pressures (systolic up, diastolic down)
What factors affect heart rate?
autonomic innervation, hormones, fitness and age
What factors affect stroke volume?
Heart size, fitness, gender, contractility, duration of contraction, preload and afterload
How do you calculate stroke volume?
EDV - ESV
How does preload affect SV and CO?
Increased preload increases SV and CO
How does afterload affect SV and CO?
Increased afterload (resistance) decreases SV and CO
Outline the Frank-Starling mechanism
Increased venous return –> increased EDV (ventricular filling) –> increased preload –> increased myocyte stretch or sarcomere –> greater recoil –> greater ejection –> greater SV and CO
What is a baroreceptor?
Stretch receptor
Where are baroreceptors found?
Aorta, carotid arteries, vena cava and atria
How do baroreceptors respond to an increase in stretch?
Parasympathetic stimulation increased –> decreased HR and SV –> decreased BP
How do baroreceptors respond to a decrease in stretch
Parasympathetic stimulation suppressed –> increase HR and SV –> increased flow and BP
What are chemoreceptors?
Receptors that respond to changes in chemicals such as pO2, pCO2, H+ and lactic acid
Where are chemoreceptors found?
CNS and by baroreceptors
How do chemoreceptors respond to an increase level of chemicals?
Sympathetic stimulation suppressed –> decreased HR and SV
How do chemoreceptors respond to a decreased level of chemicals?
Sympathetic stimulation increased –> increased HR and SV
What would exercise-induced hypotension indicate?
Coronary artery disease if drop of more than 10mmHg systolic BP during exercise
What would exercise-induced angina indicate?
Angina is severe chest pain that radiates to shoulder/arm and is due to inadequate cardiac blood supply –> coronary artery disease
Name the two main mechanisms blood flow to tissues can be increased during exercise
Greater stroke volume –> greater CO
Vasodilation
