What is spirometry?

When we are having trouble breathing, our doctor might suggest a test called spirometry. It is a common office test used to assess how well our lungs work by measuring how much air we inhale, how much we exhale and how quickly we exhale.

Why is it done?

Doctor may suggest a spirometry test if he or she suspects  symptoms which are caused by a chronic lung condition such as:

• Chronic bronchitis

• COPD

• Pulmonary fibrosis

• Asthma

• Emphysema

 

If one already has been diagnosed with a chronic lung disorder, spirometry can be used periodically to check how well his/her medications are working and whether breathing problems are under control. Spirometry may be ordered before a planned surgery to check if our lung function is adequate for the rigors of an operation. Additionally, spirometry can be used to screen for occupational-related lung disorders.

Spirometer :

Spirometer is a biomedical device which measures lung capacity and lung volume. The construction of a spirometer is pretty simple. Mainly it has a container which gathers gas. For the understanding purpose of the basic working principle of a spirometer, we have to look into the basic construction of a spirometer.

Working Of Spirometer :

Water Seal Spirometer

Most of the respiratory measurements can be adequately carried out by the classic water-sealed spirometer . This contains an upright, water filled cylinder which consists of  an inverted counter heavy bell. When we breathe into the bell the volume of gases trapped inside changes, and the change in volume is converted into vertical motion, which is noted on the moving drum of a Kymograph. The excursion of the bell will be proportional to the tidal volume. For most purposes, the bell has a capacity of the order of 6-8 1.  The normal spirometer is just  capable of responding completely to slow respiratory rates and not to rapid breathing unless a special light weight bell is provided ,  sometimes encountered after anesthesia. In addition , the frequency response of a spirometer should be adequate for the measurement of the forced expiratory volume. The instrument should have no hysteresis, ie. the exact same amount of  volume should be achieved whether the spirometer is being filled or being emptied to that volume.
As the water-sealed spirometer consists of moving masses in the pattern of the bell and counter- weights, this leads to the usual problems of inertia and possible oscillation of the bell. This can lead to an overestimation of the expiratory volume. A recommended compensation is by the use of a spirometer bell having a greater diameter and which will fit closely over the central core of the spirometer, so that the area of water which is covered by the bell is little  in relation to that of the water tank. If the spirometer is being used for time-dependent parameters, then it should also have a quick response time, with a flat frequency response up to 12 Hz. This requirement applies also to the recorder used in conjunction with the recording device, not only to the spirometer.

Since the input is air flow and the output is volume displacement the spirometer is a mechanical integrator. An electrical signal which is proportional to  the volume displacement may be achieved  by using a linear potentiometer that is connected to the pulley section of the spirometer. The spirometer is a heavily damped device so that small changes in inspired and expired air volumes should not be noted. The spirometers can be shaped with a linear motion potentiometer, which will directly convert spirometer volume changes directly into an electrical signal. This  signal can be used to feed a flow-volume differentiator to the evaluation and storing of data. The response  is generally± 1% to 2 Hz and 10% to 10 Hz. 

Tests which are done using the spirometer are not analytical. Also, they are not fully objective because the results  depend on the cooperation of the patient and the coaching efforts of a good respiratory technician. There have been efforts to develop electronic spirometers which may  give  greater information-delivering and time-saving capabilities. Also, there have been efforts to achieve  more detailed

diagnostic information than spirometry alone can provide. To calculate results manually from the graph of the mechanical volume spirometer needs considerable time. To transform the movement of the bell transducers have been designed, bellows or piston of volume spirometers into electrical signals. These are then used to compute the numerical results electronically. Because of the  popularity and lower cost of personal computers have made them an attractive method of automating both the volume and flow spirometers. If an accurate spirometer is connected to a personal computer with a well software program has the potential of allowing untrained person to achieve  accurate results.

 

 The Spirometry Extension displays and measures respiratory parameters like :  

• Tidal volume

• Minute ventilation

• Respiratory rate

• Peak inspiratory flow (PIF) 

• Peak expiratory flow (PEF) 

• Forced vital capacity (FVC)

• Forced expiratory volume in 1 second (FEV1)

BTPS correction :

Spirometry must be corrected for our body temperature and ambient pressure which is saturated with water vapors (BTPS). This is done to correct  the difference between the volume of air in the lungs (at 37°C) and the volume measured by the spirometer (at room air temperature). Where barometric pressure may not be inputted, For the correction factor used, the spirometer should have a pressure range.

 

 

Sensors Used in spirometer :

Pressure sensor :

 When implementing a spirometer is a transducer which converts the air flow into an electrical signal, which is  then processed by electronic means. To obtain this, the MED-SPI demo uses an integrated silicon pressure sensor from Freescale, the MPXV7025DP. It is a difference.

 

Benefits :

1. A spirometer can be used for many of reasons like testing of Pulmonary Function Tests

2. Many lung diseases can be cured by using a Spirometer.

3. They can assess the result of the medication or not the medication needs to be adjusted

4. The progress of the disease treatment can be measured.

5. Before someone undergoes surgery, they are most favorable for checking the lung function.

6. if chemicals in the work environment affect lung function they can measure.

7. Can find the reason of shortness of breath and other lung-related diseases and problems

 

Risks :

Generally Spirometry is a quite safe test. We  may feel short of breath or dizzy for a while after the test is performed.

Because this test  needs some exertion, it can not be performed if we've had a recent heart attack or any other heart condition. Rarely, the test triggers serious breathing problems.

Blog By :

Srushti Hamand

References :

https://www.lung.org/lung-health-diseases/lung-procedures-and-tests/spirometry

https://en.wikipedia.org/wiki/Spirometry