Cardiovascular System, Lecture 4

Question 1

Cardiac Cycle - electrical - electrocardiogram

Answer 1

cardiac cycle - events associated with a single heart beat; a number of representations
- electrical representation - combined all individual APs of atria and ventricles together generates an electrical curent in extracellular fluid forming electrocardiogram (ECG)
- all the individual APs come together to make ECG
- electrical representation of a cardiac cycle

Question 2

ECG key components

Answer 2

amplitude (mV)
waves:
- P wave: atrial depolarization
- QRS complex: ventricular depolarization (atrial repolarization simultaneously)
- T wave: ventricular repolarization
(mainly depolarization and repolarization)
duration (msec):
segments - periods between waves
- PR segment: AV nodal delay (timing is critical factor)
- ST segment: time during which ventricles are contracting and emptying
- TP segment: time during which ventricles are relaxing and filling

Question 3

Cardiac Cycle - volume, pressure, sounds (diastole - ventricular filling)

Answer 3

• blood moving into left ventricle as left atrial pressure > left ventricle pressure
• near end left ventricle filling gets left atrium systole pushing final blood volume into left ventricle
• left ventricle at fulled volume (end diastole volume; EDV)
• phases ends when start ventricular systole as left ventricular pressure > left atrial pressure
• 1st heart sound (S1; lub), associated with closure of bicuspid valve

Question 4

Cardiac cycle - volume, pressure, sounds (systole - isovolumetric contraction)

Answer 4

• bicuspid valve closed: left ventricular pressure > left atrial pressure
• aortic valve closed: left ventricular pressure < aortic pressure
• left ventricular systole but no change in ventricle volume
• rapid increase in left ventricular pressure
• there is a period where the bicuspid and aortic valve are both closed, short phase where it becomes isovolumetric contraction (same amount of volme - nothing comes in or out)
• when blue line crosses the red the next one begins, the aortic valve opens, the end-systolic volume

Question 5

Cardiac Cycle - volume, pressure, sounds (systole - ventricular ejection)

Answer 5

• aortic valve opens: left ventricular pressure > aortic pressure
• left ventricle ejection beings into systemic circulation (rapid ejection at first, then slower)
• left ventricular pressure rises, peaks, decreases until: left ventricular pressure < aortic pressure
• ends left ventricle ejection
• 2nd heart sounds (S2; dub), associated with closure of aortic valve

Question 6

Cardiac Cycle - volume, pressure, sounds (diastole -isovolumetric relaxation)

Answer 6

aortic valve closed: left ventricular pressure < aortic pressure
bicuspid valve closed: left ventricular pressure > left atrial pressure
- left ventricular diastole but no change in left ventricle volume
- left ventricle at lowest volume (end systolic volume; ESV)
volume ejected: stroke volume (SV)
- difference between end diastolic and end systolic volumes (SV = EDV - ESV)
- rapid decrease in left ventricular pressure

Question 7

Cardiac Cycle - volume, pressure, sounds (diastole -ventricular filling)

Answer 7

• bicuspid valve opens: left ventricular pressure < left atrial pressure
• blood beings moving from left atrium into left ventricle (rapid filling at first, then slower)
• near end left ventricle filling get left atrium systole and start next cardiac cycle
  at rest: heart rate (HR) ~75 bpm; cardiac cycle duration ~0.8 seconds
• atria - 0.7 sec diastole/ 0.1 sec systole
• ventricle - 0.5 sec diastole / 0.3 sec systole
• increase HR both systole and diastole duration decrease; diastole decreases more