HK 3810 Package 1 notes.docx

15min driven by purkinje fibres instead of av node

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15/min driven by purkinje fibres instead of AV node which is why the rate is slower Atrial fibrillation o All you get are QRS waves o No P waves o Atria does not contract sequentially, no organized change in membrane potential o Re-entry loop of AP at the wrong spot o Not life threatening o Consequence of connecting cells through gap junctions bc gap junctions are bidirectional o Atria contract before ventricle Ventrical fibrillation o Irregular heart rhythm due to lack of coordinated contraction o No QRS wave, P wave not visible o Life threatening o Ventricles not contraction, no blood pumping o When this is happening, you need to do CPR to start manually working the heart, as well as use a defibrillator o Defibrillation puts cells of the heart into refractory periods through depolarization all at the same time, then SA node initiates AP (which has the fastest rate) and starts organized electrical activity Mechanics Pressure/volume relationships in the ventricle Pressure is relative to atmospheric pressures; set atmospheric pressure = 0 Left ventricular pressure and volume o Start out when ventricle is relaxed (in diastole), meaning it has not received an AP but it is about to receive one, ventricle is filling at this time o Atrial contraction occurs, so there is an increase in pressure and volume o Ventricular contraction occurs (in systole), so the AP came from the purkinje fibres and the AP is now in ventricular myocytes, trigger Ca2+ is present and muscle starts to contract; mitral valve closes and ventricular pressure increases o Since we are contracting against a fixed volume that cannot go anywhere, there is no change in volume, but pressure increases; this is called the isovolumetric contraction bc at this time aortic pressure > ventricular pressure o Volume starts to eject when aortic valve opens due to the ventricular pressure overcoming aortic pressure
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HK 3810 Package 1 o Ventricular relaxation occurs when ventricular pressure is lower than aortic pressure and then aortic valve closes o Isovolumetric relaxation occurs when there is no change in volume but pressure decreases o Ventricular pressure < atrial pressure causing mitral valve to open o There is a period of rapid filling of the ventricle through the pulmonary veins, through the atria, through the open valve and right into the ventricle o EDV – end diastolic volume, the volume that the heart has to pump; max amount of blood available per stroke of the heart o ESV – end systolic volume Stroke volume = the amount you ejected = EDV-ESV =130-50 mL =80mL Blood pressure = systolic pressure/diastolic pressure = 120mmHg/80mmHg MAP = 100mmHg Output from the heart - EDV SV = EDV-ESV (volume ejected/beat) CO = SV x HR (volume/min) CO = (EDV-ESV) x HR At rest: CO = 80 mL/beat x 70 bpm = 5.5 L/min Exercising: CO = 130 mL/beat x 180 bpm = 23 L/min EDV is the volume at the end of diastole, which is the volume from the venous compartment o ex. EDV = 150 mL ESV = 50 mL SV = 80 mL o If we increase EDV (preload)
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  • Fall '16
  • Coral Murrant
  • AP

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