cardiodynamics Flashcards
definition of cardiodynamics
cardiodynamics is the study of blood flow i.e the cardiac output
blood flow is required for the flow of organ perfusion and for the delivery of oxygen and removal of co2 from tissues
flow equation
change in pressure/resistance
how do you calculate change in pressure
mean arterial pressure- right arterial pressure
cardiac output definition
stroke volume xheart rate
blood pressure equation
blood pressure= cardiac outputx total peripheral resistance
if the pressure stays the same what does decreasing resistance do to the flow
increase the flow
if sepsis causes vasodilation how does this reduce blood flow instead of improving it
reduces afterload
reduced venous return
reduced preload-dilation of venules
hypovolaemia- vasodilation causes permeable leaky capillaries
causes myocardial depression- affects contractility
how is cardiac output controlled intrinsically
determined by the degree of stretch in myocardial fibres
how is cardiac output controlled extrinsically
determined by the activity of autonomic nervous system and circulating hormones
what three factors can affect cardiac output by affecting heart rate and stroke volume
preload
afterload
contractility
what is preload
stretch of the heart muscle at the end of diastole determined by end diastolic volume and venous return
what is afterload
resistance heart must overcome to eject blood during systole its determined by systemic vascular resistance and aortic pressure
what is meant by contractility
strength of myocardial contractions independent of afterload and preload
how does increasing preload increase cardiac output
frank starling law increasing preload enhances stroke volume because a greater volume of blood stretches the ventricular walls, optimising overlap of actin and myosin filaments in the heart muscle for a more forceful contraction
increased preload increases stroke volume which increases cardiac output
how does enhances contractility increase cardiac output
increases ejection fraction (volume of blood pumped out of left ventricle with each beat) which boosts stroke volume
sympathetic nervous system activation adrenaline and noreadrenaline
positive ionotrophic agents digoxin dobutamine
increased contractility increases stroke volume so increased cardiac output
how does reducing afterload increase cardiac output
reduces workload on the heart as less resistance that ventricle pumping needs to overcome making it easier for the ventricles to eject blood
lower afterload leads to increased stroke volume increasing cardiac output
ace inhibitors and nitrates can reduce afterload
heart rate will increase cardiac output up until a certain point why
very high heart rate will reduce ventricular filling because diastole is shortened as very high heart rate reduces stroke volume
what happens during exercise to the cardiac output
during exercise the cardiac output increases and is mostly contributed to by an increase in heart rate there is a slight increase in stroke volume of the heart this is due to vasodilation of the peripheral circulation and therefore a decrease in resistance to the cardiac contractions therefore a slightly higher pulse pressure. there is also an increase in stroke volume related to the the increased venous return and starlings force. increased muscle activity drives increased venous return. increased respiratory effort therefore pumping more return to the left side. increased sympathetic activity will increase contractility
if the heart rate is too fast how do we slow it down
drugs
dc cardiovert shock with electricity
parasympathetic stimuli
