cardiovascular principles Flashcards
how is a regular spontanous action potential generated in the SA node
- the spontaneous pacemaker potential takes the membrane potential to a threshold
- every time the threshold is reached an action potential is generated
what is vagal tone
- the vagus nerve (parasympathetic supply to the heart) exerts a continuous influence of the SA node under resting conditions.
- vagal tone dominates under resting conditions
- the vagal tone slows the intrinsic heart rate from 100bpm to produce a normal resting heart rate of 70bpm
what is the normal resting heart rate and what is the term for a heart rate above it and below it
- 60-100bpm
- tachycardia = resting heart rate above 100bpm
- bradycardia = resting heart rate below 60bpm
what effect does the vagal stimulation have on the SA and AV node
- Slowed rate of firing from the SA node
- Increase in AV nodal delay
what are the phases of ventricular muscle action potential
0 = fast Na2+ influx 1 = closure of Na2+ channels and transient K+ efflux 2 = mainly Ca2+ influx 3 = closure of Ca2+ channels and K+ efflux 4 = resting membrane potential
what are the standard limb leads
- lead 1 = RA-LA
- lead 2 = RA-LL
- lead 3 = LA-LL
what does the P wave show
atrial depolarisation
what does the QRS complex show
ventricular depolarisation
what does the T wave show
ventricular repolarisation
what does the PR interval show
largely AV node delay
what does the ST segment show
represents the interval between ventricular depolarization and repolarization.
what does the TP interval show
diastole
what is the refractory period on an ECG
the period following an action potential in which it isn’t possible to produce another action potential
how are the cardiac monocytes electrically coupled
gap junctions - these protein channels form low resistance electrical communication pathways between neighbouring monocytes
what provides mechanical adhesion between cardiac cells
desmosomes - they ensure that the tension developed by one cell is transmitted to the next
what produced muscle tension
sliding of actin filaments on myosin filaments
define stroke volume
the volume of blood ejected by each ventricle per heart beat
-SV=EDV(end diastolic volume)-ESV(end systolic volume)
what affects the stroke volume
- Cardiac preload
- Cardiac afterload
- Myocardial contractibility
what is blood pressure
the outwards hydrostatic pressure exerted by the blood on the blood vessels
what is the ideal blood pressure for an adult under 80 yrs
120/80 to 90/60mmHg
what bp is hypertension
140/90mmHg and day time average of 135/85mmHg
what is pulse pressure
difference between the systolic and diastolic blood pressures
- normally between 30 and 50 mmHg
what is the mean arterial blood pressure
the average arterial blood pressure during a single cardiac cycle which involves contraction and relaxation of the heart
- MAP = [(2X diastolic) + systolic] divided by 3
- MAP = CO X SVR
- a MAP of at least 60mmHg is needed to perfuse vital organs like the brain, heart and kidneys
what factors can change the mean arterial blood pressure
- heart rate
- stroke volume
- systemic vascular resistance