The normal oxygen saturation or SpO2 of a healthy person is 95 – 100 %. These numbers generally stay unchanged during moderate intensity exercises and may even increase a little, because one is breathing faster and deeper, resulting in better lung ventilation.
During vigorous short-term exercise, like in soccer, you may notice a small drop in blood oxygen saturation of about 1 – 2 %. When you stop exercising, the SpO2 will return to your baseline reading quickly.
When a person complains of shortness of breath, the doctor will take down a medical history, perform a physical examination and may order some tests. Diseases of the heart, lungs, kidneys or liver may present with shortness of breath.
The most common functional impairment in patients with lung disease is impaired gas exchange. In the early stages of many lung diseases, the oxygen saturation is maintained or is normal at rest, but when the lung is challenged with increasing demand, like during exercise, the oxygen saturation may drop.
The 6MWT is used to assess the functional capacity of a person. The 6MWT is also a simple test to evaluate gas exchange impairment during exercise. It is widely used, and is considered the gold standard, to evaluate patients with chronic respiratory disorders like COPD and ILD. However, it is not feasible to perform the 6MWT in many office-based practices, which generally, do not have the flat, straight 30-m corridor required for the test.
There is evidence in the literature, suggesting that the 1MSTST be used as an alternative to the 6MWT for measuring a person’s functional capacity and in detecting exercise induced gas exchange impairment. Both tests have a good correlation, and the advantage of the 1MSTST is that it causes less hemodynamic stress for patients than the 6MWT. The 1MSTST is well tolerated, easy to perform, understood, and interpreted; and does not require special hardware. The mean number of 1MSTST repetitions reported in the literature achieved ranged from 8 repetitions (patients with stroke) to 50 repetitions (young men).
The 1MSTST has been validated for use in COPD and ILD of various aetiologies.
There are many uses for the 1MSTST:
The 1MSTST is used to identify subjects with low exercise capacity or preserved exercise capacity.
The 1MSTST is used to detect exercise-induced gas exchange impairment early in the course of ILD, before changes in resting DLco and PaO2, hence making the early clinical diagnosis of ILD possible. The resting DLco is a specific but an insensitive predictor of abnormal gas exchange during exercise. The DLco is the diffusing capacity of lung for carbon monoxide is a measure of the efficiency of lung gas transfer.
The 1MSTST is used to measure the effectiveness of a pulmonary rehabilitation programme as an improvement of three repetitions is consistent with physical benefits.
To perform the 1MSTST place a chair of standard height (46 cm), without arm rests, against a wall to prevent the chair moving and person falling during the test. Seat the person upright on the chair with knees and hips flexed at 90°, feet placed flat on the floor and a hip-wide apart, with arms held stationary by placing the hands on the hips. The person is asked to perform repetitions of standing upright and then sitting down in the same position at a self-paced speed, safely and comfortably, as many times as possible for 1 minute. The person should not use the arms for support while rising or sitting. The person is permitted to rest during the one-minute period.
The patient is given the following instructions:
“The purpose of the test is to assess your exercise capacity and leg muscle strength. The movement required is to get up from this chair with the legs straight and sit back continuing the repetitions as fast as possible within one minute. I will give you the countdown ‘3, 2, 1 Go’ as an indication to start and I will tell you when we are at the 15 remaining seconds. If required, you can make a break and resume the test as soon as possible”.
The patient should be able to perform a minimum of 5 repetitions.
The SpO2 and heart rate are noted before and immediately after the 1-minute test. The SpO2 and hear rate are noted for a further 1 minute following the test, during recovery, as oxygen desaturation can continue for up to a minute after stopping the test. The number of sit-stand repetitions are recorded for the first 1 minute of the test.
In early lung disease, a person at rest, may have a normal SpO2 of 95 – 100 %. However, during exercise the SpO2 may drop because of increased oxygen demand and the presence of impaired gas exchange in the diseased lungs.
POSITIVE TEST. A SpO2 drop of 3% or more is considered a positive test. A positive test may indicate the presence of lung disease which requires medical attention.
DO NOT perform the 1MSTST in the following situations.
1. When the resting SpO2 is already abnormal at 94% or less.
2. When the person is immobile or using walking aids.
3. During advanced pregnancy.
4. Following recent abdominal surgery or heart attack.Fo
F STOP the 1MSTST when you notice the following:
1. Feeling faint or giddy.
2. Vision becoming dim or blur.
3. SpO2 falling more than 3% from baseline. (Calculate the value before starting the test. Example: when the resting SpO2 is 96%, stop the test when the SpO2 fall to 93% or lower.)
4. Sensation of breathlessness which is severe or unbearable.
5. Occurrence of chest pain
You MUST CONSULT a doctor when the test is positive.
The 1MSTST is currently being evaluated for use in respiratory illnesses other than COPD and ILD.
The IMSTST is being used in some EDs or emergency departments to quickly identify exercise induced oxygen desaturation caused by lung disease, so a decision can be made regarding patient discharge, with or without enhanced monitoring, or hospitalisation.