The 6-minute walk test (synonyms: 6MGT; 6-min-walk distance, 6MWD) is a standardized procedure for objective assessment, determination of severity, and progression of exercise limitation attributable to cardiopulmonary causes. The evaluation of the effectiveness of therapeutic measures, physical training and the success of an invasive surgical procedure also play an important role. With the help of this exercise test, a statement can also be made about the prognosis of the disease in question. Primarily, the 6-minute walk test has been developed for the evaluation (assessment) of chronic obstructive pulmonary disease (COPD).
Indications (areas of use)
Follow-up and severity assessments of the following diseases (exemplary):
- Chronic obstructive pulmonary disease (COPD).
- Heart failure (cardiac insufficiency) – Massive limitation of cardiac output due to disease of the heart or even the lungs.
- Pulmonary fibrosis – Disease of the lung tissue characterized by increased formation of connective tissue between the alveoli (air sacs) and the blood vessels surrounding them; there are numerous clinical pictures that can lead to pulmonary fibrosis.
- Pulmonary arterial hypertension (PAH) – pulmonary vascular hypertension that either occurs without an identifiable cause (such as idiopathic pulmonary arterial hypertension, IPAH) or manifests in the setting of another condition, such as cirrhosis of the liver or certain congenital heart diseases. In the context of these diseases, there is an increase in vascular resistance within the pulmonary vasculature and a subsequent increase in blood pressure within it. As the disease progresses, this change leads to increased stress on the right heart (right ventricle, right atrium). The causes of this disease are varied and extensive, so they will not be discussed in detail here.
In addition, therapy effects can be assessed, for example, within a rehabilitation and subsequently optimized.
Contraindications
- Walking disability
- Lack of compliance of the patient
In addition, in the context of any disease that is aggravated by physical exertion, the performance of an exercise test is contraindicated (eg, myocardial infarction – myocardial infarction).
The procedure
The 6-minute walk test assesses a patient’s physical capacity: The test determines the walking distance covered by the patient within 6 minutes on level terrain and defined route. If possible, the longest walking distance should be aimed for. A circular route of 25 m in length is optimal for the test, as walking distances that are too short can impair the results. First, the patient is instructed by means of a standardized information text that he must run or walk the longest distance possible for him within the 6 minutes. Before the walking test, a rest period of about 5 minutes should be observed, during which neither walking nor talking should take place. During the walking test, changes of pace and pauses are allowed, the patient determines his own speed. The use of necessary walking aids or assistance from another person is allowed. The patient should be motivated to achieve the maximum performance for him. Walking distance is recorded in meters, and the following vital signs are also obtained by pulse oximetry:
- Respiratory rate
- Pulse rate
- Oxygen saturation (SpO2) (value that describes what proportion of hemoglobin (red blood pigment) in the blood is loaded with oxygen and gives an indication of the effectiveness of oxygen uptake by the lungs).
In addition, blood pressure is measured. Before and after the examination, a blood gas analysis (BGA; determination of blood gases, blood pH and electrolytes from a blood sample) is performed. Furthermore, before and after the walking test, the subjectively perceived breathing restriction of the patient is determined by means of the so-called Borg scale. The Borg scale is an assessment method for evaluating the severity of dyspnea (subjective shortness of breath) used in cardiology (heart medicine), pulmonology (lung medicine) and sports medicine. The evaluation is performed either by a physician using a patient interview or by the patient himself through a questionnaire.The Borg scale records the respiratory distress felt during the last 24 hours on a scale of 1-10. The assessment of the walking distance is carried out by means of Troosters’ so-called prediction formula. This formula is used to determine a target value that is compared to the patient’s actual value. Age, weight, height as well as gender are included in the calculation:
6MWD (m) = 218 + (5.14 x height [cm] – 5.32 x age [years]) – (1.8 x weight [kg] + 51.31 x sex [women: 0; men: 1]).
Prognostically, the comparison with normal values of healthy subjects is groundbreaking: trained healthy subjects walk more than 1,000 m, untrained walk about 700-800 m within the 6 minutes, the performance of women is slightly lower than that of men. If the walking distance is less than 300 m, the prognosis can be assumed to be limited.
Possible complications
With consideration of contraindications, complications are not usually expected. Physical exhaustion limits the examination; if the patient is too exhausted, the examination should be discontinued. Further notes
- In patients with chronic obstructive pulmonary disease (COPD) and reasonably intact knee joints, the one-minute stand-up test is also informative in determining pulmonary performance.
