1. Cardiac Cycle Setting the Tempo

2. Cardiac Cycle – Overview
Events of each heartbeat
Highly coordinated so that both atria contract together and then both ventricles contract together
Divided into two phases:
Systole
contraction of heart muscle
Diastole
relaxation of heart muscle

3. Overview cont’d Time for each cycle is influenced by autonomic nerves.
Two regulatory nervous systems affect the cardiac cycle:
Sympathetic nervous system
Prepares the body for stress. Increases heart rate.
Parasympathetic nervous systems
Returns the body to normal resting state following stress

4. Cardiac Cycle cont’d
Cardiac muscles are able to contract without being stimulated by external nerves.
Called myogenic muscle
allows your heart to beat without a continual reminder
Also able to recover quickly; the only rest they get is small time between beats.
Normal heart rate at rest is about beats per minute

5. Stages of the Cardiac Cycle
Atria contract.
Ventricles contract.
Heart relaxes and fills.

6. Stages of the Cardiac Cycle
Atria relax
causes them to fill with blood
Atrial walls contract
Forces the AV valves open, and blood flows into the ventricles filling them up
Ventricles contract
Forces the AV valves shut, pushes blood into the arteries.
The ventricles relax
Backflow prevented by closing of aortic and pulmonary valves
Diastole
Systole

7. Heart Beat - Sounds Caused by the closing of the heart valves
Lubb – AV (atrioventricular) valves close
Dubb – Semi lunar valves close
Heart murmurs are caused by an incomplete seal on a valve
Blood leaks past the closed valve, or flows backwards in the heart.
causes a whoosing, or gurgling sound

8. Heart Beat - Intrinsic Control
Heart has its own intrinsic system to conduct signals that trigger muscle contractions.
Autorhythmic - cardiac muscle can contract without stimulation from the nerves.
The autonomic nervous system does have inputs to the heart and normally regulates heart rate.
Nodal tissue - 2 areas in the heart
Has both muscular and nervous characteristics
Can generate action potentials to cause contraction
Sinoatrial (SA) node and atrioventricular (AV) node

9. Heart Beat – The Pacemaker
Sinoatrial Node (SA)
A bundle of specialized nerves and muscles
located where the vena cava enter the right atrium. (#1)
Sends a signal over the two atria
Atrioventricular node (AV) (#2).
Located in the lower part of the right atrium close to the tricuspid valve
picks up electrical impulses

10. Heart Beat – The Pacemaker
AV Node sends nerve impulses via the Purkinje Fibres (#4)
two large nerve fibres
run through the septum,
Each nerve impulse triggers cardiac contraction
Atria contract first, followed by ventricles.

11. Heart Beat Tachycardia Bradycardia Fast heart beat
heart rate exceeds 100 beats per min
can result from exercise or from the consumption of such drugs as caffeine or nicotine.
Bradycardia
Slow heart beat
Heart beat lower than 60 bpm
Can result from degeneration of the muscle (age), and disease.

12. Blood Pressure

13. Blood Pressure
A measure of the pressure or force of blood against the walls of your arteries
Systolic pressure
the pressure when your heart contracts and pushes blood out
Highest pressure
Diastolic pressure
the lowest pressure when the heart relaxes between beats
Normal blood pressure is below 120/80 mm Hg.
High blood pressure is consistently more than 140/90 mm Hg

14. Factors affecting Blood Pressure
Cardiac output
This is the volume of blood pumped from the heart each minute
Increased output will increase blood pressure.
Raising your heart rate increases output!

15. Factors affecting Blood Pressure
Arteriolar resistance
This is how much the arterioles resist the flow of blood.
Diameter of the arterioles is regulated by muscles in their walls
Arteriolar Constriction reduces blood flow, causing higher blood pressure.
Arteriolar dilation opens vessels and increases blood flow, decreasing blood pressure

16. High Blood Pressure Factors
High Blood Volume
High Salt levels cause excess water in our blood increasing our blood volume
Increased Cardiac Output
Tachycardia
Overactive Sympathetic Nervous System
Arteriolar Constrictors
Caffeine and Nicotine
Cold
Blockages in the arteries
Caused by arteriosclerosis

17. Low Blood Pressure Factors
Low Blood Volume
Dehydration
Starvation (anorexia)
Bleeding
Decreased Cardiac Output
Bradycardia
Insufficient volume of blood being pumped
Valve problems
Arteriolar Dilation
Heat
Brain injury
Arteriolar walls stop contracting

18. Mapping the Heart Beat Electrocardiogram (ECG or EKG)
test that measures the electrical activity of the heart.
Traces how long the electrical wave takes to pass through your heart
Printed on paper covered with a grid of squares each represents 0.04 seconds.
25 squares = 1 second
ECG’s printouts are usually is 6 seconds; a "six second strip."
Changes in electrical current reveal normal or abnormal events of the cardiac cycle.
Determines if
activity is normal, fast or irregular.
heart is enlarged or overworked.

19. Interpreting ECG P wave QRS complex T wave
first little hump – atria receives signal and contracts
QRS complex
Ventricles receive signal and contract
May just be an RS… this is still normal
R wave is the first wave ABOVE the midline
T wave
Recovery of the heart

21. Normal Rhythm
Bradycardia
Tachycardia
Abnormal Rhythym
V-Tach (NO QRS)