Testing for desaturation in chronic lung disease
Kathryn Watson is the lead author on a study comparing the one-minute sit-to-stand test to the six-minute walk test for detecting which people with advanced lung disease are likely to desaturate with exercise.
Your study examined whether the one-minute sit-to-stand test is a suitable substitute for the six-minute walk test in terms of identifying people with chronic lung disease who desaturate with exercise and for prescribing exercise (such as in a pulmonary rehabilitation program). Why is investigating the one-minute sit-to-stand test an important issue?
With the rise in platforms supporting telerehabilitation and with the recent restrictions imposed due to the COVID-19 pandemic, physiotherapists are exploring assessment options that can be delivered remotely and with minimal time commitment, such as the one-minute sit-to-stand test.
While the use of this assessment tool gained popularity in recent times, few studies have compared cardiorespiratory and symptom responses measured during the six-minute walk test and the one-minute sit-to-stand test respectively in people with an advanced lung disease.
We wanted to determine whether it is appropriate to use this tool in a population with advanced lung disease to detect desaturation and whether the results of this test can be used to estimate six-minute walk distance, which is the gold standard measure used to prescribe walking training in pulmonary rehabilitation programs.
Can you briefly summarise your study design?
This study presented data that was collected prospectively during routine clinical practice from all adults known to the Advanced Lung Disease Unit at Fiona Stanley Hospital who completed a six-minute walk test and a one-minute sit-to-stand test between September 2021 and January 2022.
Patients treated by the Advanced Lung Disease team all have a chronic lung disease and are being considered for specialist interventions (eg, lung transplant) or enrolment in pharmaceutical trials.
All recruited participants were exacerbation-free at the time of assessment and the six-minute walk test was performed prior to the one-minute sit-to-stand test with at least 20 minutes of rest between tests.
The outcomes from the two tests were analysed to determine whether cardiorespiratory and symptom responses were comparable.
What outcomes did you measure?
In addition to participant characteristics (eg, age, gender, height, weight and lung function), we collected data on lowest oxygen saturation, pulse rate, shortness of breath and leg fatigue on completion of the six-minute walk test and the one-minute sit-to- stand test as well as oxygen saturation and pulse rate measured at the end of the first minute of the six-minute walk test.
What did you find with respect to the one-minute sit-to-stand test’s ability to identify people who desaturate during exercise?
Kathryn Watson's study on testing for desaturation in chronic lung disease was published in the April 2023 issue of the Journal of Physiotherapy.
The one-minute sit-to-stand test elicited less desaturation than the six-minute walk test and classified a smaller proportion of people as ‘severe desaturators’ on exertion.
While the difference in lowest oxygen saturation between tests of three per cent to five per cent might seem small, when the lowest oxygen saturation was used to develop thresholds to classify people as mild, moderate or severe desaturators, there was a clear disparity between the tests.
We found that 83 per cent of those who were classified as severe desaturators on the six-minute walk test were classified as only mild or moderate on the one-minute sit-to-stand test and 80 per cent of those who were classified as moderate desaturators on the six-minute walk test were classified as mild desaturators on the one-minute sit-to-stand test.
It is therefore inappropriate to use the lowest oxygen saturation recorded during a one-minute sit-to-stand test to make decisions about whether strategies are needed to prevent severe desaturation during walking-based exercise.
What did you find with respect to the one-minute sit-to-stand test’s ability to predict the result on the six-minute walk test?
The equation representing the relationship between tests was identified as six-minute walk distance (m) = 247 + (seven × the number of transitions achieved during the one-minute sit-to-stand test).
Although clinicians may be tempted to use this equation to estimate the six-minute walk distance using the number of transitions achieved during the one-minute sit-to-stand test, the association between the two explained less than 50 per cent of the variance in the measure of six-minute walk distance.
The estimate of six-minute walk distance derived from this equation should therefore be used with caution.
So the one-minute sit-to-stand test is not helpful when prescribing walking-based exercise?
That’s right. We really need to continue to use the six-minute walk test to prescribe walking-based exercise, assess desaturation and monitor the response to pulmonary rehabilitation programs in this group.
Where does research in this area need to go now?
The next steps should be to identify whether changes to the one-minute sit-to-stand test could be implemented to make it appropriate for prescribing walking-based exercise in this population.
It has been previously suggested that the length of the one-minute sit-to-stand test is the limitation to its use and potential adaptations could include assessing whether a longer test elicits closer results to the six-minute walk test or whether a longer monitoring period after the cessation of the test would produce different results.
>> Kathryn Watson is one of the lead physiotherapists in the Advanced Lung Disease Unit at Fiona Stanley Hospital, working with patients pre- and post-lung transplant. She has over 10 years of experience working with patients with chronic lung disease in a variety of clinical settings.
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