L42 - Cardiac output 2 - mechanical events and stroke volume Flashcards
What can the cardiac cycle be divided into? (2)
- systole - ventricular contraction, blood ejection
- diastole - ventricular relaxation, blood filling
What are the systole and diastole main values? (2)
- systolic, diastolic LV to body - 80, 120
- systolic, diastolic RV to lungs - 8, 28
What is the cardiac cycle driven by?
changes in pressure within ventricles
What are the valves like during isovolumetric ventricular contraction? (2)
- AV valve - closed, P ventricles > atria
- aortic, pulmonary valves - closed, P ventricles < arteries
What are the valves like during ventricular ejection? (2)
- AV valve - closed, P ventricles > atria
- aortic, pulmonary valves - open, P ventricles > arteries
What are the valves like during isovolumetric ventricular relaxation? (2)
- AV valve - closed, P ventricles > atria
- aortic, pulmonary valves - closed, P ventricles < arteries
What are the valves like during ventricular filling, -ve P in ventricles? (2)
- AV valve - open, P ventricles < atria
- aortic, pulmonary valves - closed, P ventricles < arteries
What are the valves like during ventricular filling, atrial contraction? (2)
- AV valve - OPEN
- aortic, pulmonary valves - CLOSED
What is the aortic pressure like during the cardiac cycle? (2)
- systole - aortic valve open, absorbed pressure
- diastole - aortic valve closes, pressure decreases linearly, squeezes blood out
What is ventricular pressure like during the cardiac cycle? (2)
- systole - pressure inc = AV valve closes, pressure increases and decreases (peak)
- diastole - AV valve opens, P is lower in atrium
What is left ventricular volume like during the cardiac cycle? (2)
- end diastolic volume - contraction - volume decreases
- end systolic volume - relaxation - volume slowly builds up
What is the ECG like during the cardiac cycle? (3)
- P wave - contraction of atria
- QRS wave - ventricle contraction
- T wave - ventricle relaxation
What is stroke volume? (2)
- amount of blood pumped out of the heart during each cardiac cycle
- equivalent to EDV - ESV
What are the heart sounds? (4)
- caused by closure of heart valves
- 1st sound - closure of AV, “lub” - onset of systole contraction
- 2nd sound - closure of pulmonary, aortic valves, “dub” - onset of diastole relaxation
How do you listen to heart sounds?
using a stethoscope
What are the cardiac defects that can be detected using a stethoscope? (3)
- murmurs - change from laminar to turbulent flow
- damaged valve - stenosis, noisey change in flow
- ventricular fibrillation - heart attack
What factors affect stroke volume? (3)
- filling pressure - amount of blood that comes back to heart
- contractility (effects of SNS) - sympathetic nerves, circulating agents
- arterial pressure opposing ejection
What factors affect central venous pressure (CVP)? (4)
- contraction of central/peripheral veins - inc
- respiratory pump - in = inc, out = dec
- blood vol - dec blood vol = dec CVP
- skeletal muscle pump - inc muscle activity
How does CVP affect stroke volume? (3)
- the more blood that comes back the more needs to be pumped out
- measured as EDV
- inc stroke volume
What is the frank starling mechanism determined by? (2)
- length tension relationship
- the greater stretch, the more tensioned developed in cardiac muscle
How does the Frank-Starling mechanism work? (6)
- if inc venous returns to RV = inc contraction
- more blood to lungs
- inc venous return to LV = inc contraction
- inc stroke vol
- blood doesn’t accumulate in lungs
- ensure blood in matches blood out
How does contractility regulate stroke volume? (3)
- sympathetic regulates
- increases heartbeat
- regulates force/stroke volume
How does sympathetic nerves work to regulate stroke volume? (3)
- releases noradrenaline that act upon B1 adrenergic receptors
- inc force and speed of cardiac muscle contraction
- inc ventricular contraction - shifts F-S upwards - inc stroke vol for same EDV
What is congestive heart failure? (4)
- characterised by dec cardiac output
- tiredness, shortness of breath
- fluid retention - pulmonary edema
- swelling ankles and legs
