Lecture 2.docx

Objectives:  Changes in pressure in the ventricles and atria, aorta and veins during diastole and systole  Changes in blood volume in the ventricle, atria, aorta and veins during CC  Typical values for pressures and volumes in diastole and systole and their units  Concept of timing of these processes in rest and with increasing heart rate  How and when AC and SL valves open and close  How and when the heart sounds can be heard The Beating Heart:  70BPM, 100,800 per day, 36,792,000 per year, 2,943,360,000 a lifetime (80 years)  Missing beats: 1-2 creates no problem  5-6 would render you unconscious  5 minutes would damage your heart and require clinical help  Greater than 10 minutes would be fatal  All Cardiac Processes: excitation, contraction, relaxation, valves open, valves closed all need to occur at the right time in the right direction- important for normal physiological function Cardiac Cycle:  A complete set of contraction and relaxation of the heart  Two Phases:  Diastole: ventricles relaxed  Systole: ventricles contracting  Mechanical events: pressure and flow changes  Electrical events: ECG- electrical stimulus and its conduction generates an ECG  Valvular events: heart sounds (closure of valves) Complex Slide: must understand:  Wigger‟s Diagram:  Indicates: different pressures, blood flow/velocity, heart sounds, ECG, systole and diastole.  Studying: take the blank figure/copy it a few times, and try to draw the diagrams yourself to understand cardiac cycle Diastole 1: Isovolumetric relaxation:  All valves are shut  No blood flow, no change in blood volume in ventricle  Minimal ventricular volume (end systolic volume (ESV))  Ventricles relaxing  Atrial pressure lower than ventricular atrium fills with blood returning to heart  Elevates atrial pressure above ventricular pressure  AV valve opens passively and ventricles will be filled. Diastole 2: ventricular filling:  AV valves open passively, ventricular filling begins  90% ventricular filling occurs passively down pressure gradient  During Late Diastole, atrial depolarisation occurs (first)- this is the P wave on the ECG  Therefore get atrial contraction, pressure rises, and so last 10% of blood is pushed into ventricle from atrium- “top up” into ventricles  End Diastolic Volume (EDV)- at rest is around 130mL (in humans) Systole 1: Isovolumetric Contraction  Ventricles depolarise (QRS complex on ECG)  Electrical signal travels down conduction pathway; after „top up‟ the ventricles will begin contraction  This develops tension- ventricular pressure rises  AV valve closes = first heart sound (S1)  If pressure is larger in ventricle than in atrium, the valves will close. At that point, all valves are shut again  No blood flow; no blood volume change.  Therefore: Isovolumetric, isometric contraction (pressure in left and right ventricles lower than that in pulmonary artery and aorta therefore valves closed).  Ventricular pressure is Systole 2: Ventricular ejection:  Aortic valve opens: blood ejected into aorta  Arterial blood volume and arterial pressure increase  LVP and AP rise in parallel  2/3 of blood ejection occurs in first 1/3 of ejection time- rapid ejection  Late systole: both LVP an dAP fall, reduced ejection  Repolarisation of ventricles- T wave in ECG  LVP falls below AP therefore semilunar valves close  2 ndheart sound (S2) (made up of aortic (a) and a pulmonary component (P)  Closure of semilunar valves marks the end of systole and beginning of diastole  Cardiac cycle re-enters Isovolumetric relaxation  End systolic volume (ESV) at rest is approximately 60mL IMPT: the Wigger‟s diagram represents the cycle in time, but will lengthen or shorten depending on the heart rate- we assume here, that it is describing a cardiac cycle lasting one second (60BPM). Wigger‟s Diagram:  Diastole: ventricles relaxed  Diastole 1: 0.05s: all valves shut (S2), isovolumetric relaxation in left and right ventricles  Diast