Cardiovascular Physiology Part B: Cardiac Cycle

Question 1

3 Components of Cardiac Cycle

Answer 1

1. Electrical Activity (ECG)
2. Mechanical Activity
3. Blood flow through heart

Question 2

Electrical Activity (ECG)

• due to:
• measured using:
• waves are:

Answer 2

1. small currents due to depol/repol. of heart move through salty body fluids
2. potential difference measured on body surface using electrode pairs: one pair = a lead
3. recording seen as waves
   = sum of electrical activity of ALL myocardial cells (NOT an AP)

Question 3

ECG Waves:

P wave

Answer 3

atrial depolarization -> followed by contraction

Question 4

ECG Waves:

QRS wave

Answer 4

ventricular depolarization -> contraction

- also atrial repolarization (relaxation) - masked by larger ventricle electrical event (larger muscle mass)

Question 5

ECG Waves:

T wave

Answer 5

ventricular repolarization -> followed by relaxation

Question 6

ECG Intervals:

P-Q

Answer 6

atria contracted, signals passing through AV node

Question 7

ECG Intervals:

S-T

Answer 7

ventricles contracted, atria relaxed

Question 8

ECG Intervals:

T-P

Answer 8

heart at rest

Question 9

What is it called when resting HR is more than 100 bpm?

Answer 9

Tachycardia

Question 10

What is it called when resting HR is less than 60 bpm?

Answer 10

Bradycardia

Question 11

What is it called when conduction through AV node is slowed, get an increased P to Q interval -> ventricles may not contract after each atrial contraction?

Answer 11

Heart Block

Question 12

Systole

Answer 12

contraction, emptying

-initiated by electrical activity

Question 13

Diastole

Answer 13

relaxation, filling

-initiated by electrical activity

Question 14

Complete heart beat =

Answer 14

diastole + systole of atria AND diastole + systole of ventricles

Question 15

Average resting HR

Answer 15

75 beats/min.

= 0.8sec/beat

Question 16

What happens in 1 beat (0.8sec)?

Answer 16

1. atria in systole for 0.1 sec, then diastole for 0.7 sec
2. ventricles enter systole after atria (0.1 sec delay at AV node)
   ∴ ventricles begin systole as atria begin diastole ⇒ in systole for 0.3 sec, then diastole for 0.5 sec

Question 17

Blood flow to the heart is due to…

Answer 17

1. Emptying pressure changes (high P -> low P)
2. Valves
3. Myocardial contraction

Question 18

Path of blood flow

Answer 18

Vena Cava and Pulmonary Veins
Atria relaxed 
Ventricles relaxed
Atria contract
Ventricles contract and Atria relax
Ventricles relax

Question 19

What happens during Ventricular Systole?

Answer 19

1. higher P in ventricles than atria forces AV valves shut ⇒ turbulence of blood gives first heart sound (= LUB) - shortly after QRS wave starts
2. P rises - higher P in ventricle than aorta/pulm trunk pushes semilunar valves open ⇒ blood enters vessels

Question 20

What happens during Ventricular Diastole?

Answer 20

1. P drops - higher P in aorta/pulmonary trunk than ventricles forces semilunar valves to shut ⇒ turbulence ⇒ 2nd heart sound (= DUB) – mid-T wave
2. AV valves open when P in ventricles drops below P in atria

Question 21

What is turbulent flow?

Answer 21

heart sounds noisy due to blood turbulence when valves shut

Question 22

What is Laminar flow?

Answer 22

no sound

Question 23

What are Korotkoff Sounds?

Answer 23

Turbulence heard in brachial artery during blood pressure measurements:

begin: systole pressure
stop: diastole pressure
- due to cardiac cycle events