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Spirometry Overview

Spirometry Overview Document©
Author: Oisin Mcmanigan

In its simplest terms spirometry is the measurement of airflow and volumes that can be exhaled from the lungs from maximum inhalation to maximum exhalation, to assess the efficiency of the physical properties of the respiratory tract

Who uses Spirometers?

  • General practitioners
  • Practice nurses
  • Hospital Respiratory Laboratories
  • Occupational Health Nurses
  • Health/Fitness personnel
  • Pharmaceutical companies
  • Specialist units e.g cystic fibrosis units, Lung transplant units

Objectives of Spirometry

  • Detects early lung dysfunction
  • Aids diagnosis
  • Predicts future mortality / morbidity
  • Provides evidence of disease progression
  • Monitors response to treatment, course of a chest infection
  • Monitors the effects of environmental conditions
  • PEFR may underestimate the degree of airways obstruction, and cannot differentiate between obstructive/restrictive disorders

Why Spirometry>

Spirometry gives us a good indication of what is happening in the lungs, it helps aids diagnosis of diseases and can differentiate between diseases.

Why Micro Medical spirometers?

  • Micro Medicals' unique digital volume transducers- turbines are unaffected by temperature, humidity, altitude unlike other flow measuring devices.
  • Turbine spirometers are clinically proven to be very stable and do not need regular recalibration
  • Micro Medical spirometers are small handheld portable devices which allow them to be used in places away from the traditional lung function laboratory in the hospital.

How does the turbine work?

There are two types of turbine :- unidirectional measures flow only one way expiratory Bidirectional measures flow in two directions expiratory and inspiratory

Most G.P’, Occupational health nurses, Pharmaceutical trials tend only measure expiratory flows. Hospital pulmonary laboratorys tend to use both expiratory and inspiratory flows. Inspiratory flows give us information on intra or extra thoracic problems (those outside the lungs).

The number of rotations is proportional to the volume of air passed through the transducer and the frequency of rotation is proportional to the flow rate. The LED’s produce infra red beams which are interrupted by the vane twice per rotation which is then sensed by the phototransistors.

The gold standard turbine was created due to the increased interest in COPD and the low flows, which are created by individuals suffering from COPD.

Which instraments measure which flows?

Unidirectional - Micro, Microplus, MicroGP, MicroDL, MicroDiaryCard
Bi-directional - MicroLoop, MicroLab, SuperSpiro

Preparation of the patient

Ideally the patient should avoid:

  • Smoking for 24 hrs prior to the test
  • Vigorous exercise for 30 minutes prior to the test
  • Taking a short acting bronchodilator within 4 hrs prior to the test
  • Consuming alcohol for 4 hrs prior to the test

The purpose and nature of the test should be fully explained to the patient

  • Record the age, height, race and gender
  • Demonstrate the test where necessary
  • Record the date and time (the majority of Micro Medical spirometers record this automatically)
  • The patient should be seated upright in a chair with arms (for safety reasons in case of dizziness, and encourages patient compliance- when standing patients bend over during the manoeuvre)
  • Loosen any restrictive clothing

Errors of technique

  • Inadequate inspiration
  • Slow start to expiration
  • Premature termination
  • Coughing, vocalizing or puffing from the cheeks
  • Extra breath taken
  • Mouthpiece obstructed
  • Poor posture
  • Many Micro Medical spirometers have in-built ATS (American Thoracic Society) safety checks which advise the user of many of the above errors.

INDICES MEASURED

  • VITAL CAPACITY (VC) - Volume of air expired from the lungs from maximal inspiration using a slow/relaxed manoeuvre.
  • FORCED VITAL CAPACITY (FVC) - Volume of air that can be forcibly expelled from the lungs from a position of maximal inspiration.
  • FORCED EXPIRATORY VOLUME IN THE 1ST SECOND (FEV1) - Volume of air forcibly expelled in the first second - following a maximal inspiration
  • FEV1/FVC RATIO - This is the FEV1 expressed as a percentage of the FVC
  • FEV1/FVC x 100= FEV1% (sometimes shown as FER) - Normal value 70%
  • PEFR - Peak expiratory flow rate

Performing a test

VITAL CAPACITY

The patient is instructed to blow out from a position of maximal inspiration at a sustained and comfortable speed until no further air can be exhaled. In healthy individuals the VC and the FVC results will be extremely similar, in patients with COPD there will be a large difference between the VC and FVC due to the airways collapsing and trapping air during the FVC.

  • Always performed before a forceful manoeuvre
  • Performed wearing a nose clip
  • Maximum of 4 attempts

FEV1 AND FVC

The patient is instructed to breath in as fully as possible, and encouraged to blow out as hard and fast as possible until no further air can be exhaled

  • Forceful manoeuvre
  • Maximum of eight tests to be performed in one session

Acceptability

  • 2 technically acceptable VC's
  • At least two readings of FEV1 that are within 5% or 100ml of each other
  • Recording continued long enough for a plateau to be reached on a volume time plot - no variation in flow for two seconds
  • Traces smooth and free from any irregularities

Interpretation of Results

1. Obstructive Airways Disease

Any disease that affects the patency of the airways due to:

1. Excessive mucus production
2. Inflammation
3. Bronchoconstriction

  • Obstructive patterns are characterized by a reduced FEV1 and FEV1% In healthy individuals the FEV1 is above 80% of the individuals predicted value
  • Healthy individuals can usually complete a forced manouevre in approximatly 4 seconds Individuals with COPD take much longer resulting in a reduced FEV1 in severe cases the manouevre can take up to 15 seconds.
  • The classification of obstruction, is assessed by using the actual FEV1 as a % of the patients predicted

Mild COPD FEV1% of predicted 60-80%

Modorate COPD FEV1% of predicted 40-59%

Severe COPD FEV1% of predicted < 40%

2. Restrictive Airways Disease

Any disease that affects the lung tissue or the inability of the lungs to expand due to:

1. Fibrosis or scarring
2. Full inflation not possible
3. Respiratory muscle weakness

  • Restrictive patterns are characterized by a reduced FEV1 and FVC with a normal or high FEV1%
  • In healthy individuals the FEV1% is greater than 70%

3. Combined Airways Diseases

  • Any disease that affects both the airways and the lungs
  • All results will be reduced in mild cases and it is often difficult to differentiate between a combined and an obstructive pattern.

Where does the Micro CO and Smokecheck come into this scheme?

The MicroCO and the Smokecheck were designed to help in smoking cessation, both devices are used for simple screening of exhaled carbon monoxide on the breath. They are a powerful incentive device which allow the user, to see their levels of CO and then encourage abstinence from smoking.

The difference between the two devices:

1. The MicroCO measures in individual ppm and gives an indication of %COHb(carboxhaemoglobin-the amount of the bodies blood that cannot pickup oxygen as the red blood cell is attached to carbon monoxide)
2. The Smokecheck measures in ppm bands as opposed to individual ppm's and does not give a measurement of %COHb
3. The MicroCO has a comm Ports connection and can be used with Cobra software Which will display a graph of the results and %COHb.

It is well known that 20% of all smokers will develop COPD, and of all individuals suffering with COPD smokers account for 80%. Besides the respiratory problems that smokers develop there are also cardiac and circulatory problems, the increased risk of cancer.

As a result the MicroCO/Smokecheck and spirometers are intrinsically linked.


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