Cardio Flashcards
How may cardiac output be regulated without requiring nervous/ hormonal input?
Frank-Starling relationship Increasing venous return Dilates ventricles more Increases cardiac stretch Increases contractile force of muscle Increases stroke volume
Describe the relationship between velocity and cross-sectional area
Linear velocity is inversely proportional to cross-sectional area
(rapids in centre parks is slower when river is wide and faster when narrow)
Velocity equation (including flow and area)
Velocity (v) = Flow (Q) / Cross sectional area (A)
volume flow remains constant
What’s the relationship between flow and pressure difference at the inlet and outlet (ΔP) for a rigid tube?
Flow is directly proportional to change in pressure
What’s the relationship between flow and length?
Flow is inversely proportional to length
What’s the relationship between flow and viscosity?
Flow is inversely proportional to viscosity
What’s the relationship between flow and radius?
Flow is directly proportional to the radius to the power 4
What is the term that describes ability to stretch and expand?
Compliance
What is the term that describes ability to recoil?
Elasticity
Equation for mean arterial pressure
Mean arterial pressure = diastolic pressure + 1/3 pulse pressure
What is mean arterial pressure?
It drives blood through the vasculature from the arteries to arterioles, capillaries, venules, veins, and back to the heart
Is carefully regulated by short-term and long-term regulatory and compensatory mechanisms
Is a time-weighted average of pressure values in large systemic arteries during the cardiac cycle
Why is a simple average of the systolic and diastolic pressure values is not an adequate estimate of the mean arterial pressure?
The ventricles do not spent equal lengths of time in systole and diastole
Approximately:
1/3 time is spent in systole
2/3 in diastole
What is the mean arterial pressure a function of?
1) Rate at which the heart pumps blood into the large arteries
2) Rate of blood flow out of the large arteries to enter smaller arteries and arterioles
3) Arterial wall compliance
What is pulse pressure?
Systolic blood pressure - diastolic blood pressure
What effect does aortic insufficiency (aortic valve regurgitation) have on pulse pressure?
Increases pulse pressure
As blood leaks back into the ventricle through the aortic valve during ventricular diastole, decreasing the pressure in the aorta during diastole
Systolic blood pressure is the same/ slightly elevated
Greater difference between systolic and diastolic pressure
How does first degree heart block usually present in an ECG?
Prolonged PR interval
PR interval is normally 0.12-0.20 seconds
PR interval consistently longer than 0.20 seconds (greater than 5 small boxes) in 1st degree AV block
1:1 ratio between P waves and QRS complexes maintained
Indicates conduction through the AV node is slowed
How does second Degree AV Block Type I usually present in an ECG?
(Wenckebach block or Mobitz Type I AV block)
Progressive PR interval prolongation with each beat until a P wave is not conducted - increasing delay of AV nodal conduction until a P wave fails to conduct through the AV node
1:1 P wave to QRS complex ratio is NOT maintained
Irregular R-R interval
Indicates varying failure of conduction through the AVN
can be caused by AV blocking medications/ increased vagal tone/ AVN ischemia during an inferior MI
How does second Degree AV Block Type II usually present in an ECG?
(Mobitz Type II AV block)
AVN becomes completely refractory to conduction on an intermittent basis - some P waves not followed by a QRS complex since it does not conduct through the AV node to the ventricles
The PR interval may be normal or prolonged, but it is always constant in length
Indicates significant conduction disease in this His-Purkinje system and is irreversible, pemament pacemaker is required
How to work out how long each heartbeat is
60 (secs) / heart rate (beats per min)
How does sympathetic stimulation have a positive inotropic effect?
NA and A activate beta 1 adrenoceptors
Activates adenylyl cyclase
Causes increase in cAMP
Increases intracellular Ca2+
How does parasympathetic stimulation have a negative inotropic effect?
Activate M2 receptors
Linked to adenylyl cyclase
Causes decrease in cAMP
Decreases intracellular Ca2+
How does parasympathetic stimulation have a negative chronotropic effect?
ACh released increases nodal cells’ permeability to K+
This decreases the slope of the pacemaker potential
and hyperpolarizes the membrane potential
How does sympathetic stimulation shorten phase 2 of ventricular action potentials?
cAMP activates protein kinase A
That phosphorylates the delayed rectifier K+ channels responsible for moving phase 2 to phase 3
Means a faster repolarisation, shortening the action potential
Cardiac output =
Stoke vol x heart rate
