Unit 3 - Cardiac Physiology Flashcards
end diastolic volume (EDV)
amount of blood in ventricles after filling
normal = 135 ml
end systolic volume (ESV)
amount of blood left in ventricles after ejection
ESV = EDV - SV
normal = 65 ml
stroke volume (SV)
volume of blood pumped by each ventricle in one contraction
normal SV = 70 ml
cardiac output (CO) & formula
- amount of blood pumped by each side of the heart in one minute
CO = HR x SV
normal CO = 70 (HR) x 70 ml (SV) = about 5 L/min
ejection fraction (EF)
ratio of stroke volume to EDV
SV / EDV
Normal EF is about 50%
Ventricles only eject about half of blood they receive
Determinants of Stroke Volume
- preload
- contractibility
- afterload
preload
- stretch of the heart prior to contraction
- blood available for pumping
- the more blood that comes back to the heart, the stronger the ventricle contraction
contractibility
force of contraction
afterload
- resistance (pressure) against which heart needs to pump
intrinsic control of stroke volume
the heart’s inherent ability to vary stroke volume
vagal tone
effect the parasympathetic NS has on HR.
- decreases the intrinsic rate of SA node to maintain normal HR at rest
what is RMP of auto rhythmic cells?
-60 mv
what is RMP of contractile cells?
-90 mv
AP of auto rhythmic cells
RMP = -60 mv TP = -40 mv maximum = 0
AP of contractile cells
RMP = -90 mv TP = -70 mv max = +30 mv
What do the following waves represent on an ECG?
- P wave
- QRS wave
- T wave
- P wave - atrial depolarization
- QRS wave - ventricular depolarization
- T wave - ventricular depolarization
What comprises the slow drift to threshold (aka PACEMAKER POTENTIAL)?
- Decreased permeability for K+
- Increased permeability of Na+ (flow inward) = FUNNY CHANNELS = voltage gated channels that open in hyperpolarized state
- Increased permeability (inward) of Ca2+ = TRANSIENT Ca2+ channels
Na+ FUNNY channels
Open at hyperpolarization
Aid in slow depolarization toward Threshold Potential
Close halfway to Threshold Potential
Transient t-type Ca2+ channels
Open at hyperpolarization
Aid in pacemaker potential (slow depolarization)
Close at Threshold Potential
What happens at TP in an autorythmic cell?
Ca2+ L-type (long lasting) channels open
Lead to large influx of positively charged ions = rising phase of action potential
What make the 2 phases of Pacemaker Potential?
- INITIAL PHASE - Takes off from RMP (-60 -> -40)
- K+ stays in cell
- Na+ funny channels open - Na+ enters cell - SECOND PHASE - takes it to TP
- Transient (T-type) Ca2+ channels open
Rising phase of AP
T-type ca2+ channels close
L-type CA2+ channels open
Takes it all the way to too
Falling Phase
VG K+ channels open - begin leaving cell
Ca2+ L-type channels close
Cell becomes more negative;
After AP, slow closure of K+ cause hyperpolarization
imaginary triangle used in determining the positions of ECG leads?
Einthoven’s triangle
