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Chapter: Medicine Study Notes : Cardiovascular

Physiology and Anatomy - Cardiovascular

CO = MAP/TPR (ie flow = pressure / resistance)

Physiology and Anatomy




·        Cardiac Output (CO):

o   CO = MAP/TPR (ie flow = pressure / resistance)

o   CO = SV * HR

o   Normal adult at rest = 5 L/min

o   Can be measured with Doppler/echo

·        Mean Arterial Pressure:

o   MAP = Cardiac Output*TPR

o   MAP = Diastolic + 1/3(systolic-diastolic)

·        Stroke volume:

o   SV = End diastolic volume – end systolic volume

o   Normal 60 – 80 ml

·        Ejection fraction = ESV/EDV.  Determined by:


o   Preload (=EDV): dependent on blood volume, venous tone, posture, intrathoracic pressure, peripheral muscle pump, and atrial contraction (20% of filling). Affects stroke volume through Starling‟s Law: ­myocardial fibre length (ie filling) ® ­SV until ventricle is over-stretched. Can be measured for the left ventricle using pulmonary artery/capillary wedge pressure (CAWP) and for the right using central venous pressure


o   Force of Contraction (Inotropy): Shifts Starling Curve up and to the left. Increased by sympathetic stimulation, ­Ca, ­thyroxine, ­angiotensin, drugs, ­temp, ­HR. Decreased by acidosis, hypoxaemia, ­K, drugs (general anaesthetics, beta blockers)


o   Afterload = tension in the ventricular wall at the end of systole. Results from ventricular distension, elasticity of arterial walls and arterial network resistance. Measure with arterial catheter


o   Changes given certain shock states:

·        Peripheral vascular resistance:

o   Resistance proportional to radius to the power of 4

o   = (Mean aortic pressure – right atrial pressure)/cardiac output


Cardiac Anatomy


·        Heart Valves:

o   Mitral valve (left AV): anterior and posterior leaflets

o   Tricuspid valve:  anterior, posterior and septal cusps

o   Aortic valve: left, right and posterior cusps

o   Pulmonary valve: left, right and anterior cusps

·        Blood supply:


o   Left main stem (LMS) ® LAD (anterior wall of LV and anterior 2/3 of septum) and Circumflex (lateral wall of left ventricle and most of the posterior wall of the LV). Also supplies AV node, and SA node in 60%


o   Right coronary artery ® right atrium, right ventricle (except for left part of anterior wall), right posterior and inferior walls of LV and posterior 1/3rd of septum

·        Pericardial effusion: normal content of pericardial sac = 50 ml. Effusion can be serous, chylous or haemorrhagic. Sign of pericarditis but also accompanies MI


Regional Blood Flow

·        Cerebral Perfusion:


o  Cerebral blood flow (CBF) = [MAP – ICP (or CVP, whichever is greatest)]/cerebral vascular resistance


o  Minimal desirable perfusion pressure is 60 mmHg. This is reduced by ¯arterial pressure, ­venous pressure, constriction/spasm of cerebral vessels or ­intra-cranial pressure (ICP)


o  Autoregulation keeps CBF at 50 ml/100g/min.  Less than 15 ® changes in electrical activity

·        Coronary Perfusion:

o  Perfused during diastole

o  Coronary perfusion = (Mean diastolic pressure – VEDP)/Coronary Vascular Resistance

o  So treat poor perfusion with:

§  High diastolic pressure (eg systemic vasoconstrictor - a agonist)

§  Reducing end diastolic ventricular volume (prevent volume overload)

§  Decrease coronary vascular resistance (eg coronary vasodilator)

§  Slow heart rate ® longer diastolic phase (eg beta blockers)

§  ¯Preload (nitrates and Ca channel blocker)

§  O2 therapy and maintain haemoglobin

·        Renal Perfusion:


o  Normally autoregulated down to 80 mmHg systolic. When BP ¯, renal blood flow ¯¯ ® renal failure and acute tubular necrosis


o  Treatment:


§  Colloid/saline ® ­ BP

§  Dopamine 2 – 5 mg/kg/min ® ¯renal vascular resistance


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