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 Challenge: can you write these as numeric equations? 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 Heart rate = # beats minute 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

Control of Cardiac Output and Blood Pressure Parasympathetic & sympathetic nerves to smooth muscle of arterioles

What is the effect of exercise on cardiac output? Get out your calculators! Heart rate (beats/min) Stroke Volume (cm3/beat) Cardiac Output (cm3/min) At rest 75 During exercise 180 120 5,625 21,600

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 sphygmomanometer 1. 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 Carotid artery Radial 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

Questions A person’s blood pressure should be measured when they are resting and relaxed. Explain why. People with high blood pressure sometimes have swelling in their legs and feet. Explain how this happens Low blood pressure can cause fainting. Explain why. 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