The 6-minute walk test (6MWT) in pulmonary arterial hypertension

Nowadays, pulmonary health is in the spotlight like never before, mainly due to the ongoing COVID-19 epidemic that has caused chaos in every area of human society. Unfortunately, COVID-19 is not the only complex pulmonary condition, as there are others that also have a poor prognosis. A good example is pulmonary arterial hypertension that is a rather uncommon condition, but coupled with high difficulty and expenses in diagnosis, management, and treatment.

In this blog you will learn:

• What is pulmonary hypertension?
• What are the morbidity and burden of pulmonary hypertension?
• How is the 6-minute walk test (6MWT) used in patients with pulmonary hypertension?

What is pulmonary hypertension?

Pulmonary arterial hypertension (also known as PH, PHTN or PAH) is a cardiopulmonary condition characterised by a progressive increase in pulmonary vascular resistance and arterial pressure that leads to right heart failure and premature death [1, 2, 3]. The exact cause of primary PH is unknown (but the condition may be heritable in some individuals), as is the worldwide prevalence, although there is concrete data for some countries [4, 5, 6]. Estimated prevalence of PH is around 12.4 patients per million in the United States, 15 patients per million in France and up to 52 patients per million in Scotland [7, 8, 9]. These are quite low numbers in comparison with, for example, chronic obstructive pulmonary disease (COPD), which is estimated to afflict up to 7.6 % of the world’s population [10].

There are many possible causes for PH, cardiovascular or pulmonary in nature and a nearly equal number to those of other aetiologies, leading healthcare organisations and professional bodies to categorise the disease in several distinct groups. According to the World Health Organization (WHO) PH is categorised in five groups [11, 12]:

• Group 1: PH that is idiopathic, heritable, drug- or toxin-induced or associated with conditions such as HIV infection or connective tissue disease [13].
• Group 2: PH due to left heart disease; left ventricular systolic or diastolic dysfunction and congenital cardiomyopathies [13].
• Group 3: PH due to lung diseases and/or chronic hypoxia; COPD, interstitial lung diseases, and alveolar hypoventilation disorders amongst others [13].
• Group 4: PH due to chronic arterial obstruction, i.e. chronic thromboembolic pulmonary hypertension (CTEPH) [13].
• Group 5: PH with unclear or multifactorial mechanisms – the most complex and widest group of causes [13]. It includes haematological disorders (e.g. chronic haemolytic anaemia), systemic disorders (e.g. sarcoidosis), metabolic disorders (e.g. thyroid disorders), and others.

Treatment of each type of PH generally greatly varies, although there is some overlap. The common denominator for all is the significant cost and associated high burden for both the patient and healthcare.

What are the morbidity and burden of pulmonary hypertension?

There is no cure for PH, regardless of aetiology, and healthcare professionals can at best mitigate symptoms and treat the underlying causative disease. Treatment options are both pharmacological and surgical, including pulmonary thromboendarterectomy and ultimately, lung transplantation [14, 15]. Regardless of the exact treatment regime for each patient, the costs are significant.

It is estimated that in the United States the average total health care costs associated with PH per patient are approximately USD 98,243 for the 12-month follow-up period [16]. Data for other countries is scarcer and more ambiguous. One study found that the total treatment costs for 384 patients hospitalised in France in 2013 were in the ballpark of EUR 3,640,382 [17].

Patients’ suffering, both physiological and psychological, is also significant [18-22]. They have higher rates of depression, panic and anxiety disorders, and a generally reduced quality of life [23-25]. Additionally, there is evidence that depressive symptoms are associated with worse physical functioning as assessed by the 6MWT [26].

How is the 6-minute walk test (6MWT) used in patients with pulmonary hypertension?

Correlation between the 6MWT and depression is not the only useful diagnostic indicator of this simple yet comprehensive assessment tool in patients with PH. The 6MWT is useful as a prognostic indicator of long-term PH-related mortality and risk of hospitalisation; a study found that patients who could walk at least 400 metres in the assigned time (6 minutes) had on average the best outlook [27]. It is also used for following disease progression and for assessing functional capacity, which may have a value by itself or is just another health parameter in more in-depth diagnostic investigation [28, 29].

Changes in functional capacity have long been used in the evaluation of the effectiveness of new pharmaceuticals and other therapeutic interventions in a variety of diseases and PH is no exception [30, 31]. The 6MWT is a useful metric in assessing the effectiveness of treatments and treatment regimens for specific patients, who should experience a meaningful degree of improvement in their functional capacity as result. What is a meaningful improvement is a matter of some debate and may differ from patient to patient. In other words, clinicians should aim to improve the patient’s well-being and be aware of a relative change in walking distance as a product of their efforts and less concerned with absolute walking distance [32].

The 6MWT is a valuable tool in the management of pulmonary hypertension and for assessing the efficiency of treatment regimens and following disease progression.

Interested in finding out more about the use of the 6MWT in the management of other conditions? Read about assessing heart failure, assessing respiratory function and assessing the functional fitness of seniors.