An electrocardiogram records the electrical activity spreading through the heart during each phase of the cardiac cycle. Recording electrodes are placed on the body and transmitted to a machine called an electrocardiograph.
The P wave = Contraction of the atria
The QRS complex = Contraction of the ventricles
The T wave = Relaxation of the ventricles
The electrocardiogram can be used to find the heart rate and it can give important information about the condition of the heart muscle following a heart attack.
The leads are attached on the left arm, right arm, ankle and chest on the patient.
They are attached with conducting gel to ensure good electrical contact.
Abnormal Electrocardiogram Patterns
Tachycardia - This is where the heart beats too fast. Normal resting heart rate is 60-80 bpm. But in tachycardia, the heart rate increases to more than 100 bpm.
Arrythmia - The conducting system of the muscle cells of the heart has been damaged. Normally there will be 2P waves to every QRS complex, the atria will be beating normally but the ventricles will be contracting at a slower rate and not all the blood squeezed out of the ventricles before they contract.
Bradycardia - The heart is beating much more slowly than the resting rate of 60-80 beats per minute .
Ventricular Fibrillation - There is random depolarisation of the muscle cells in the ventricles. The heart beat becomes uncoordinated. The blood pressure drops rapidly.
A person with VF woud collapse due to a heart attack. There will be a reduced oxygen supply to the heart muscle as a branch of the coronary artery is blocked with a clot. Paramedics would then try to restore a normal rhythm to the patient's heart by applying a high voltage to the heart muscle using a defibrillator. The idea is to depolarise all the muscle cells of the ventricles at the same time so they start up in the correct sequence.
Peak Flow (Peak expiratory flow)
A peak flow meter is used to measure peak flow.
- Take a deep breath
- Blow as hard as possible into the mouth piece
- Record peak flow from sliding scale on the side
- Repeat two more times and take the highest value
Peak flow measures the rate of air flow out of the lungs in dm3/m
A student with asthma shows a low peak flow reading because the bronchioles are narrowed because muscles in the walls contract and further narrowing occurs due to excess mucus production.
The normal range of values for peak flow are 400 - 600 dm3/m
A spirometer is an apparatus for measuring the volume of air inspired and expired by the lungs. The spirometer records the amount of air and the rate of air that is breathed in and out over a specified period.
Tidal volume is the volume of air that is breathed in and out in one ventilation cycle. The normal range of values for tidal volume = 400 - 500 cm3
Vital capacity is the maximum amount of air you can breathe in and out. The normal range of values for vital capacity are male - 4.8 dm3 and female 3.1 dm3.
Residual Volume is the volume of gas remaining in the lungs after a person has breathed out as much as they can. RV = 1200cm3
Expiratory Reserve Volume is the extra air that a person can force out of their lungs after a normal expiration.
Inspiratory Reserve Volume is the extra air that a person can force into their lungs after a normal inspiration.