Cardiac beat

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Cardiac beat

• Prof.Lammers
• CVS module/Week

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The cardiac cycle

• The cardiac cycle the sequence of events from
  the beginning of one heart beat to the next one.
• It is made of
• Systole the phase of contraction and pumping
  blood
• Diastole the phase of relaxation and filling

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The events during Systole Diastole

• Diastole is made of three main phases
• Early diastole rapid ventricular filling.
• Middle diastole ventricular filling in slower
  rate.
• Late diastole contraction of the atrium to pump
  extra 25 of blood to the ventricles.

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The events during systole and Diastole

• Systole is made of three phases
• Isovolemic contraction after filling, AV valve
  closes the semilunar valves is still
  closed?pressure raise rapidly in the ventricles.
• Ejection when the pressure in the ventricles is
  higher than the pressure in the aorta/pulmonary
  artery? semilunar valve open?pumping blood out.
• Isovolemic relaxation after blood is pumped,
  pressure in the ventricles decreases blood will
  try to flow back but the atrium pressure is
  higher than the ventricle? AV valves open?EARLY
  DIASTOLE

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Pressure-Volume loop

• Phase I ventricular filling? ? volume but
  pressure is 0
• Phase II isovolemic contraction ? volume is
  constant but the pressure?
• Phase III ejection ? volume decreases and the
  pressure increases slightly and then decrease
• Phase IV isovolemic relaxation ? volume is
  constant but the pressure decreases to 0.

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Phase III
Phase IV
Phase II
Phase I
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Regulation of the heart

• Intrinsic regulation of the heart is by
  Frank-Starlings low ?Blood volume??Stretching
  of the heart??force of contraction.
• This is explained by the fact that when the
  muscle stretch?the actin myosin filaments are
  brought to an optimal length degree of
  integration for force contraction.

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Regulation of the heart

• Extrinsic regulation of the heart is by the
  sympathetic and parasympathetic system.
• The sympathetic system ?heart rate (
  chronotropic effect) ?force of contraction (
  ionotropic effect)
• The parasympathetic system (vagus nerve) ? heart
  rate and had minimal effect on the force of
  contraction