Spirometry is the most basic and frequently performed test of pulmonary function, measuring the ventilatory function of the respiratory system i.e. the ability to move air into and out of the lungs. These measurements of the so-called dynamic lung volumes and of maximal flow rates have been used to tell us about the mechanical properties of the lungs. When used appropriately, spirometry can play an important role in the detection, prevention and quantification of diseases affecting the respiratory system (American College of Occupational and Environmental Medicine, 2004)
Spirometry may reflect one’s ability to increase the depth of breathing during exercise. These volumes will be influenced by a number of factors including pulmonary congestion, cigarette smoke, exercise habits and the health and integrity of the muscles in the thoracic cavity. Since pulmonary volumes are easily measured, it is logical to assess them as part of the health assessment.
It is important to appreciate that spirometry is based on a maximal, forced expiratory manoeuvre. It’s clinical value is critically dependent on the correct operation and accuracy of the spirometer, performance of the correct breathing manoeuvre and use of relevant predicted normal values. This accuracy is effort-dependent, requiring a subject’s full understanding, cooperation and effort.
Measurements of Ventilatory Function
The clinically useful measurements obtained from properly performed spirometry tests are the Forced Vital Capacity (FVC), the Forced Expiratory Volume in One Second (FEV1.0), the Forced Expiratory Ratio (FER) and the Peak Expiratory Flow Rate (PEFR).
These measurements are usually compared with average values ‘predicted’ for a subject based on their gender, age, height and race. The presence of ventilatory abnormality can be inferred if any of FEV1.0, FVC, PEF or FER values are outside of the normal range
Forced Vital Capacity (FVC):
Definition: the volume of air expelled by a maximum expiration after a maximum inspiration.
The FVC is influenced by a number of factors including age, gender and height. One’s vital capacity reaches maximal potential in the early to mid thirties, often when strength levels are peaking as well. Taller people tend to have larger pulmonary volumes than their shorter peers do and males tend to have higher values than females.
There are many reasons why a person’s FVC is lower than normal, e.g. bronchitis, emphysema, asthma and other disorders of the lungs. Being overweight can often reduce lung volume since the diaphragm has little room to move downwards and excess fat on the chest wall restricts the expansion of the lungs.
Forced Expiratory Volume in One Second (FEV 1.0) :
Definition: this is the volume of air expired in the first second of maximal expiration after a maximal inspiration and is a useful measure of how quickly full lungs can be emptied.
The (FEV 1.0) depends on a number of factors such as clear airway tubes and clean air sacs (alveoli). It also depends on the strength of the inter-costal muscles, the diaphragm and the muscles in the back, neck and abdomen. Values are most certainly affected by smoking and pulmonary disorders.
FVC & FEV1.0 – Method of assessment
(Adapted from ACOEM, 2004)
- Testing should be conducted at ambient temperatures between 17 – 40°C. However, temperatures > 23° C are preferable to avoid a large temperature difference between the spirometer temperature and body temperature.
- Trainer describes and demonstrates the test, and enthusiastically coaches the client.
- Stand erect and limit leaning forward during the test (the client can sit if required since results between positions are very similar in adults)
- Apply a nose clip to the client’s nose (this is recommended but not essential)
- Take a couple of preparation breaths, then take a maximum inhalation (in-breath).
- Hold the micro-spirometer still, ensuring no movement, and seal lips around the mouthpiece.
- Breathe air out ‘as fast and as far as you can’ until the lungs are completely empty. This should mean an expiration of at least 6-10 sec, unless subject must stop due to discomfort, airways obstruction, or old age.
- Ensure a smooth, rapid take off with no hesitation, cough, leak, tongue obstruction, glottis closure, valsalva or early termination
- Repeat for a minimum of 3 (maximum of 8) and record the highest values for both FVC and FEV1.0.
- For reproducibility, the highest and second highest FVC and FEV1.0 values should differ by no more than 0.2L.
- The highest FVC and FEV1.0 values should be used, even if they are not achieved in the same manoeuvre.
- Use the appropriate table to get the upper and lower limits of normal lung strength and size and compare to achieved results.
Forced Expiratory Ratio (FER):
This is the FEV1.0 expressed as a ratio or percentage of the FVC and gives a clinically useful index of airflow limitation.
Assessment of:lung efficiency, percentage (%)
FER is more important than the actual FEV1.0 value. Normally, about 80% of the vital capacity can be expelled in one second; less than 75% should cause concern. Smokers commonly have ratios in the mid 60s to low 70s and emphysema patients are often as low as 28 – 32%. An FER that is below the lower limit of a subject’s normal range for this ratio indicates probable airway obstruction.
Peak Expiratory Flow Rate (PEFR):
Definition: this is the maximal expiratory flow rate achieved and occurs very early in the forced expiratory manoeuvre.
Assessment of: lung power, litres per minute (L/min)(sometimes expressed as L/sec)
The ability to generate high velocities of exhaled air from the lungs is associated with low airway resistance and increased respiratory muscle tone.
This value indicates the overall functional health of the lungs and will identify respiratory limitations during exercise. Gender, age and height also influence norms for this particular measure.
PEFR – Method of assessment
(Adapted from NACA, 2003)
1. It is preferred to adopt a standing position for the assessment
2. A nose clip for this assessment is not necessary
3. Hold the peak flow meter in one hand, with fingers not restricting the dial
4. Take a maximal inspiration and exhale into the mouthpiece with maximum effort as if blowing in a ‘pea shooter’
5. Ensure that there is a good seal around the mouthpiece and that there is no cough during the expiration
6. The blow duration should last for approximately 1 to 2 seconds
7. There should be a minimum of 3 acceptable blows and the best score recorded
8. Use the normative data tables for lung power, and compare to achieved results
9. Note results and monitor against your best ever PEFR
The PEFR tabulated results were obtained from the National Asthma Council Australia (NACA, 2003).
Sources of Measurement Error
Spirometry is simple but fraught with technical pitfalls that can invalidate the pulmonary function measurements. Failure to obtain full understanding, cooperation and effort from a client during any part of the test usually results in an underestimation of the true pulmonary function. The trainer demonstrating the test often facilitates the vigorous effort required for spirometry.
Common patient-related problems when performing the FVC manoeuvre are:
- submaximal effort
- leaks between the lips and mouthpiece
- incomplete inspiration or expiration (prior to or during the forced manoeuvre)
- hesitation at the start of the expiration
- cough (particularly within the first second of expiration)
- glottis closure (suspected if flow ceases abruptly)
- obstruction of the mouthpiece by the tongue (to correct, place the mouthpiece well into the mouth and bite it lightly)
- vocalisation during the forced manoeuvre (will reduce flow)
- poor posture
- non-calibration of equipment
Once again, demonstration of the procedure will prevent many of these problems, remembering that all effort-dependent measurements will be variable in patients who are uncooperative or trying to produce low values.
Other Factors Affecting Lung Function
- gender: for a given height and age, males have a larger FEV1.0, FVC, and PEFR but a slightly lower FEV1.0/FER%
- age: FEV1.0, FVC, and PEFR increase and FER decrease with age until about 20 years old in females and 25 years in males. After this, all indices gradually fall, although the precise rate of decline is probably masked due to the complex interrelationship between age and height. The fall in FER with age in adults is due to the greater decline in FEV1.0 than FVC
- height: all indices other than FER increase with standing height
- ethnic origin: Caucasians have the largest FEV1.0 and FVC and, of the various ethnic groups, Polynesians are among the lowest. Values for African Americans are 10-15% lower than for Caucasians of similar age, sex and height because for a given standing height their thorax is shorter. Chinese have been found to have an FVC about 20% lower and Indians about 10% lower than matched Caucasians. There is little difference in PEFR between ethnic groups
Contraindications to Spirometry
(taken from BUPA, 1999)
The latest advice is incorporated in the following bullet points (additionally caution is required with clients with aortic stenosis, recent eye and ear surgery):
- recent pneumothorax – forced effort may rupture the healed pleural membrane and cause a reoccurrence of the pneumothorax. It is acceptable to wait 2 to 3 months after the pneumothorax before spirometry takes place
- recent chest pain – if the cause is pulmonary like a pulmonary embolism or consolidation then the accuracy of spirometry is reduced
- due to pain on effort – pain of cardiac origin like angina or a recent MI should be treated with caution as the effort and possible hypoxia may overstress the client. There is no real reason not to undertake lung function tests after an MI or chest pain but it is probably wise to wait for about 3 weeks
- recent stroke – there is no particular evidence of harm after a stroke but it is probably best to wait for at least a month. The main problem is clients not being able to co-ordinate well enough to perform the procedure
- ear problems – stable perforations are not a contraindication but the results may be inaccurate due to escaping air via the ear canal. Recent surgery within the last 12 months on the middle and inner ear should be treated with caution as increased pressure may cause damage
- eye problems – a very recent eye operation or eye trauma remains a contraindication until further information is available
- abdominal surgery – recent surgery within the past 2 to 3 weeks may limit the accuracy of the procedure due to pain
- acute back problems – there is a risk of worsening a back problem due to straining and raised intra-abdominal pressure
- blood pressure – a raised BP is a theoretical risk for spirometry but in practical terms should not exclude clients. If the BP is markedly raised as in severe hypertension i.e. BP is greater than 200/110mmHg then spirometry should be avoided until the blood pressure is treated and under control
American College of Occupational and Environmental Medicine (2004). http://www.acoem.org
American Thoracic Society (ATS) (2004). http://www.thoracic.org/copd.BUPA (1999) Clinical Handbook. BUPA Health Services.