Control of Heartbeat and Monitoring Blood Pressure

Learning objectives

Define heart rate, stroke volume & cardiac output

List the main factors affecting blood pressure

Measure & accurately record heart rate & blood pressure, using equipment safely

Control of Heartbeat – a review

On your mini whiteboards, summarise what you remember about this!

Definitions

Heart rate: number of heartbeats per minute

Stroke volume: volume of blood (cm3) pumped by heart in 1 beat

Cardiac output: stroke volume multiplied by the heart rate gives the amount of blood (cm3) pumped by heart in 1 minute

Challenge: can you write these as numeric equations?

Heart rate = # beatsminute

Stroke Volume = blood cm3

beat

Cardiac Output = blood cm3 X # beats = blood

beat minute minute

Cardiac Output

Can be changed by a number of factors:› Cardiovascular centre in brain› Hormones e.g. adrenaline› Stretching of cardiac muscle

Parasympathetic & sympathetic nervesto smooth muscle of arterioles

Control of Cardiac Output and Blood Pressure

Heart rate(beats/min)

StrokeVolume

(cm3/beat)

CardiacOutput

(cm3/min)

At rest 75 75

Duringexercise

180 120

5,625

21,600

What is the effect of exercise on cardiac output? Get out

your calculators!

Blood Pressure Blood needs to flow through vessels at

a certain pressure. If pressure is too low, exchange of nutrients and gases within the tissues will not happen efficiently.

This is why blood pressure is a vital measurement taken by doctors and nurses.

Blood pressure is measured using a sphygmomanometer and is recorded in mmHg (millimetres of mercury)

Blood Pressure Measured in blood vessels (artery)

Determined by cardiac output and resistance to flow of blood in vessels

Resistance to flow affected by diameter of blood vessels

Narrower vessels (vasoconstriction)

Wider vessels (vasodilation)

Factors affecting blood pressure Cardiovascular centre

› Diameter of blood vessels controlled by stimulation of sympathetic and parasympathetic nerves

Smoking› Nicotine causes vasoconstriction› Build up of fatty deposits in vessels

Diet› High fat diet leads to build up of fatty deposits

in blood vessels Adrenaline

› Causes selective vasoconstriction & vasodilation

Increase in blood viscosity › Excess water loss (sweating/excessive

urination)

Diastolic and Systolic Pressure Definitions

Get out your mini-whiteboards

Write down the meanings of the words ‘systolic’ and ‘diastolic’.

Compare your answers with the others on your table.

Recording blood pressure Systolic blood pressure:

› Maximum blood pressure› Occurs when ventricles are contracting (at the

end of the cardiac cycle) Diastolic blood pressure:

› Minimum blood pressure› Occurs when ventricles are relaxed and filled

with blood (at the beginning of the cardiac cycle)

We record blood pressure as: Systolic BP/Diastolic BP› e.g. 120/80 mm Hg

Diastolic pressure gives clearest indication of resistance to flow in blood vessels

Rough estimate of systolic BP is your age +100

Systolic and Diastolic Pressure

Measuring blood pressure

Sphygmomanometer

How to use a sphygmomanometer1. Place the stethoscope ear pieces around your neck and wrap the cuff

of your sphygmomanometer tightly around your upper arm. 2. Locate the pulse of your brachial artery by tracing your finger down

your bicep down toward the crook, or inside elbow, of your arm. You should find the brachial pulse about an inch or so above this crook.

3. Put the ear pieces of the stethoscope into your ears and place the round, metal end of the stethoscope over the pulse of your brachial artery.

4. Tighten the stopcock on the sphygmomanometer bulb and squeeze the bulb of your sphygmomanometer multiple times to inflate the cuff around your upper arm. The cuff should be inflated until you've reached 180 mm of pressure. You will be able to determine how much pressure you've pumped into the sphygmomanometer cuff by reading the blood-pressure meter in front of you.

5. Release the bulb stopcock slowly and gradually. This will let the air out of the cuff, allowing you to make a blood pressure reading.

6. Note the number on the meter when you first hear your pulse through the stethoscope. Then note the number when the last pulse sound comes through the stethoscope. Record these two numbers by placing the higher number over the lower number to determine your current blood pressure.

Finding your pulse

Radial artery

Carotid artery

Challenge for Today! Watch the demonstration of how to use

the sphygmomanometer In your book, record:

› Your blood pressure three times and average the results

› Your heart rate three times and average the results

Questions1) A person’s blood pressure should be

measured when they are resting and relaxed. Explain why.

2) People with high blood pressure sometimes have swelling in their legs and feet. Explain how this happens

3) Low blood pressure can cause fainting. Explain why.

4) Nicotine in cigarette smoke causes the muscle fibres in arteriole walls to constrict. Explain how this causes blood pressure to increase.

Learning objectives

Define heart rate, stroke volume & cardiac output

List the main factors affecting blood pressure

Measure & accurately record heart rate & blood pressure, using equipment safely