Physiology of the heart II. Cardiac electrophysiology The heart as a ...

Cardiac soundsauscultation on the chest1. (systolic) sound: contraction, valves, ejection of blood2. (diastolic) sound: valves, can be split3. (diastolic) sound: cuspidal valves during rapid filling4. (late diastolic) sound: atrial contraction3The jugular pulse• Fluctuations in the right atrial pressure causepressure oscillations in the jugular vein.• Physiologically only visible during increasedvenous pressure (weight lifting, Valsalvamanouvre).42

carotid pulsejugular pulse5Normal jugular venous pulse:A, a positive wave due to contraction of the right atrium;C, a positive deflection due to bulging of the tricuspid valve toward the atria atthe onset of ventricular contraction;X, a negative deflection due to atrial relaxation during the ventricular systole;V, a positive deflection due to filling of the right atrium against the closedtricuspidal valve during ventricular contraction;Y, a negative deflection due to emptying of the right atrium upon ventricularrelaxation.63

Starling’sheart-lungpreparationresistancevenous reservelungsaorta pressureventricularfilling pressureventricular volume7Starling’s heart-(lung) preparation84

ActivepressurePressureDiastolic volumePressureActivepressureDiastolic volume9105

11Adaptation to:increased venous return (preload):change in body position, respiration…increased peripheral resistance (afterload)pressure increases in the aortasympathetic stimulation (positive inotropic effect)diastolic and systolic reserve126

Frank Starling law of the heart• stroke volume of the heart increases in responseto an increase in the volume of blood filling theheart (the end diastolic volume)or• the strength of the heart's systolic contraction isdirectly proportional to its diastolic expansion(end diastolic volume)13resting length (diastolic volume) determines the contraction force„Frank-Starling mechanism”Ca ++ sensitivity increases (Ca ++ channels?)works also in isolated heartcontraction force may increase without change in length„positive inotropic effect”background: intracellular Ca ++ increaseseffect of sympathetic stimulation14147

Rhythmic excitation of the heart• special features: automatic and rhythmic• where is it coming from?Stannius, the ligatures and the frog heart15The Stannius ligature168

Rhythmic excitation of the heart• special features: automatic and rhythmic• Stannius and the frog heart• nomotop (natural) pacemaker (SA node)• heterotopic (ectopic) pacemakers• extrasystole17189

19sinoatrial nodeaction potentialsatrial musclesAV nodeHis bundleTawara branchPurkinje fibresventricle muscles2010

• fast AP (atrium, ventricle, Purkinje), more negative, steeper, largeramplitude → Na channels• slow AP (SA and AV node), less negative, less steep, smalleramplitude → no voltage dep. Na channels• conduction speed of fast APs: 0.3-1-4 m/s,• conduction speed of slow APs: 0.02-0.1 m/s21actual pacemakerslow APthresholdmaximaldiastolicpotentialslowdiastolic depol.(pacemaker pot.)potencial pacemakerwhat ions ???thresholdmyocardiumfast APrestingpot.threshold2211

23-70.0 mV2412

sympathetic β1 receptorstimulationnormalheart rate decreasesduring vagal nervestimulationVagal stimulationnormalACh252613

Regulation of the cardiac pumping function1. Frank - Starling mechanism: intrinsic regulation2. Neural regulation• parasympathetic- (n. vagus – ACh - muscarinergic)negative chronotropy, dromotropy, bathmotropyinotropy (not in the ventricles)• sympathetic- (NA- β1 receptor)positive chronotropy, dromotropy, bathmotropyinotropy, lusitropy + vasodilation3. Humoral: Adrenalin, NA4. Effect of Ca ++ and K + 2827speed of depolarization (V/s)membrane potential (mV)resting membrane potential (mV)14