Recommendations on the use of exercise testing in clinical practice

To the Editors:

Congratulations to the European Respiratory Society (ERS) Task Force for updating their classic report on Clinical Exercise Testing 1 on its 10th anniversary. The original report 2 was the first to summarise the collective views on exercise testing of workers in the respiratory field, and the update provides an opportunity for reinterpretation in light of developments since 1997.

These new developments have included: 1) the emergence of evidence that cycle ergometry may not reproduce the respiratory symptoms of chest patients who are not cyclists; 2) an increased interest in the contribution of pattern of breathing to exercise limitation; and 3) a growing impression that ergometry may be beyond the competence of some lung function laboratories. The latter might have contributed to the paucity of material on exercise that was presented at the 2006 ERS Annual Congress.

We are concerned that these and related topics are not addressed adequately in the report, and so make additional suggestions for consideration by the Task Force.

Exercise capacity contributes to the management of both respiratory and cardiac patients and its assessment is an essential component of cardiopulmonary exercise testing 3. However, whilst the equipment, some protocols and a need to identify the affected bodily systems are shared, the requirements of the two disciplines subsequently diverge. Cardiologists rightly focus on indices of cardiac and circulatory function. In the case of exercise there are rigid guidelines and these give the technicians control of the tests. Respiratory physicians can usefully focus on how lungs that are damaged by disease adapt to the challenge of exercise and how the response can be improved. The circumstances of the test are often pragmatic with the patient in control, so the conduct of the test requires a flexible approach; respiratory technicians adjust to this, but some cardiac technicians feel insecure. Thus, the differences between the two types of assessment operate at a number of levels and for optimal results they should be borne in mind, not ignored. The respiratory dimension, which includes daily living as well as exercise limitation, is the remit of “respiratory exercise testing” and we commend this term in preference to “clinical exercise testing”, which glosses over the differences; the latter term is, in this context, essentially nonspecific and has implications for testing disorders outside the thorax.

Apart from for exercise-induced bronchoconstriction there has been no change to the previous recommendation of the ERS and American Thoracic Society that cycle ergometry is the method of choice 2, 3. This mode of exercise has the advantage that the patient is seated, so is accessible and feels secure. The patient can usually perform what is required and the method lends itself to a progressive protocol. In addition, the test occupies a minimum amount of space in the laboratory and is relatively cheap. The case against cycle ergometry is that respiratory patients usually experience breathlessness during walking or mounting stairs, not cycling, which few patients undertake and which uses different muscles. At the end of a symptom-limited cycling test a patient who experiences breathlessness during daily living may give up on account of fatigue 4; this has somewhat different features. As a result, the score for breathlessness during daily living cannot be predicted from that obtained on a cycle ergometer 5. This is despite cycling, on average, being associated with a relatively shallow, more rapid pattern of breathing than walking 6, 7; such a pattern increases the ventilation minute volume 8, 9 so could predispose to breathlessness. Exercise training on a cycle ergometer might be expected to improve performance during cycling, but not necessarily the exercise capacity and quality of life during daily living.

The differences between the responses to cycling and walking do not appear to be in dispute, and have led some laboratories to replace ergometry with timed walking or shuttle tests. Such tests are fine for assessing exercise capacity, but not for exploring mechanisms. For this, the exercise should normally be carried out on a treadmill using a progressive protocol 10, 11 with the end-point determined by the patient (symptom limited). However, a cycle ergometer should be available for those few patients who find a treadmill daunting. The minimal information is of ventilation, including breathing frequency and tidal volume (pattern of breathing), gas exchange, electrocardiography, body muscle and fat and pulse oximetry. The current additional procedures for assessing dynamic hyperinflation 1 may be more appropriate for specialist laboratories. However, hyperinflation during the course of a progressive symptom limited test reduces the ability to inspire and hence the tidal volume. This reduction is usually apparent on a graph relating ventilation to tidal volume 12, 13; such a change might provide sufficient information for routine clinical purposes and this possibility merits investigation.

Breathlessness on exertion during daily living and the associated quality of life are related more closely to an increase in the ventilatory cost of exercise than to impaired lung function 14. This ventilatory burden can be represented by the ventilation at an oxygen uptake of 1.0 L·min⁻¹ (45 mmol·min⁻¹; designated V′_E,st) which is the level needed for many daily tasks, including the ability to undertake light work 15. In healthy subjects, the average V′_E,st is ∼23–25 L·min⁻¹, but in respiratory patients values >40 L·min⁻¹ are not uncommon; this high ventilatory burden can only be identified by an exercise test. Examples of conditions where high levels may occur are given in the ERS recommendations 1. The differential diagnosis is functional breathing, but in our experience differentiation is possible using the results of an exercise test 16, 17. The report states that an exercise test cannot uniquely affect diagnosis, but this is possibly too modest; in our view the exploration of such cases should be within the scope of a routine lung function laboratory. In chronic obstructive pulmonary disease the case for respiratory exercise testing is well established 1 and, since the condition is ubiquitous, the exercise assessment should again be conducted at the district level.

In summary, the mechanisms that underlie an increase in ventilation during daily living can be important for diagnosis and clinical management. They are investigated by what is appropriately described as respiratory exercise testing. This differs from cardio-respiratory exercise testing and clinical exercise testing in that the operators focus both mentally and practically on the respiratory consequences of lung diseases. The assessments should preferably be performed using a treadmill, not a cycle ergometer, and, for clinical purposes, be undertaken at the nearest convenient lung function laboratory. Neglect of these aspects detracts from the report of the Task Force: the recommendations should be updated further.