Cardiac Cycle Setting the Tempo

Cardiac Cycle – Overview

• Events of each heartbeat– Highly coordinated so that both atria

contract together and then both ventricles contract together

• Systole– contraction of heart muscle

• Diastole– relaxation of heart muscle

Overview cont’d

• Time for each cycle is influenced by autonomic nerves.

• Two regulatory nervous systems– Sympathetic nervous system

• Forms a division of the autonomic nervous system• Prepares the body for stress increases heart rate.

– Parasympathetic nervous systems• Returns the body to normal resting state following

stress

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 60-80 beats per minute

12-5

Stages of the Cardiac Cycle

• Fig 12.5

Heart Beat - Sounds

• Caused by the closing of the heart valves– Lubb – AV 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

12-7

Heart Beat - Intrinsic Control

• Heart has its own intrinsic conduction system

• Autorhymicity-unlike skeletal muscle, cardiac muscle can contract without neural stimulation

• The autonomic nervous system does has inputs to the heart and normally regulates rate

• Nodal tissue-2 areas in the heart• Has both muscular and nervous characteristics• Can generate action potentials to cause

contraction• SA node and AV node

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). – Located the lower part

of the right atrium close to the tricuspid valve (#2)

– picks up electrical impulses

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.

Heart Beat

• Tachycardia – 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), disease

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.

Interpreting ECG

• P 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

http://nursingpub.com/wp-content/uploads/2010/12/ventricular-tachycardia.gif

Normal Rhythm

Bradycardia

Abnormal Rhythym

Tachycardia

V-Tach (NO QRS)

Blood Pressure

Blood Pressure

• A measure of the pressure or force of blood against the walls of your arteries

• Systolic– the pressure when your heart contracts and pushes

blood out – Highest pressure

• Diastolic – 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

Our Heart the Pump

Diastole

Systole

Sphygmomanometer

• Measures blood pressure indirectly– Measures the pressure exerted by blood

in the brachial artery

• Blood flowing through the brachial artery makes no noise– A stethoscope is placed below the cuff

to listen for the blood

• The cuff is placed around your arm and brachial artery.– Air is pumped into the cuff until

circulation is restricted.

Sphygmomanometer

• Pressure is slowly lowered until the blood is able to flow past, this is the systolic pressure– Doctors will hear this blood rushing

through as a beat

• Pressure continues to be lowered until the noise disappears– This is the diastolic pressure– Blood no longer needs to force the

artery open to pass through.

Blood Pressure Clip

Factors affecting Blood Pressure

• Cardiac output– The volume of blood pumped from the heart

each minute– Increased output will increase blood pressure.

• Raising your heart rate increases output!

Factors affecting Blood Pressure

• Arteriolar resistance– Diameter of the arterioles is regulated by muscles

in their walls• Arteriolar Constriction reduces blood flow, causing

higher blood pressure. • Arteriolar dilation, opens vessels increases blood flow

and decreases blood pressure

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 artheriosclerosis

Low Blood Pressure Factors

• Low Blood Volume– Dehydration– Starvation (anorexia)– Bleeding

• Decreased Cardiac Output– Bradycardia– Insufficient stroke volume– Valve problems

• Arteriolar Dilation– Heat– Brain injury

• Arteriolar walls stop contracting