Medical notes For MBBS students

  Heart Working As A Pump Duration of cardiac cycle & heart rate: Duration of cardiac cycle = 0.8 sec at heart rate = 70 beats/min. • When heart rate increases duration of cardiac cycle decreases. Diastole is more affected as compared to systole with rapid heart rate. At heart rate = 180 / min, cardiac cycle duration 0.33 sec: (systole = 0.18 sec, diastole 0.15 sec). QUESTION At a very rapid heart rate: Cardiac output decreases, Why??? ANSWER Because diastole becomes too short →→→ ventricular filling decreases → decrease stroke volume & decrease in cardiac output, in spite of increase in heart rate. Pressure changes in Atria during the Cardiac Cycle: Atrial systole duration = 0.11 sec Atrial diastole duration = 0.7 sec Atrial systole + Atrial diastole = 0.8 sec = cardiac cycle. • Atrial diastole > Atrial systole, because basic function of atria is to receive blood from large veins & it can receive blood only when it is relaxed. 3 waves can be recorded from atria whic...

DEFINITION OF CARDIAC CYCLE • Period between start of one beat to start of  next. ⚫ It consists of one complete heart beat. It consists of one systole & one diastole. INITIATION OF CARDIAC CYCLE : • Initiated by Cardiac Impulse, which originates from SA node . • EVENTS THAT OCCUR IN THE CARDIAC CHAMBERS DURING CARDIAC CYCLE Pressure Changes . Volume Changes . Production of Heart Sounds   Closure & Opening of Cardiac Valves . Electric Changes /ECG recording VENTRICULAR SYSTOLE 0.31 sec (Peak of R wave of QRS complex to the end of T wave) :  consists of following:  ISO-VOLUMETRIC CONTRACTION 0.06 sec MAXIMUM EJECTION (2/3) 0.11 sec REDUCED EJECTION (1/3) 0.14 sec VENTRICULAR DIASTOLE  0.52sec (End of T wave to the peak of R wave of QRS complex): consists of following: PROTODIASTOLE 0.04 sec ISO-VOLUMETRIC RELAXATION 0.06 sec RAPID INFLOW 0.11 sec SLOW INFLOW / DIASTASIS 0.2 sec ATRIAL SYSTOLE (after P wave) 0.11 sec So, 8 Phases of CARDIAC CYCLE= 0.8 sec. ...