Why Do Some Clinicians Continue to Demand Objective Measures in the Face of a Subjective Sensation? The Curious Case of Chronic Breathlessness

Chronic symptoms such as pain or breathlessness have a lot in common. Decades ago, some clinicians would refuse to accept that a person had pain if there wasn’t some objective evidence on a plain X-ray. The advent of increasingly sophisticated imaging with finer resolution had many clinicians keen to find an anatomic correlate to support someone’s complaint of pain. Ever more sophisticated imaging has shown that this assumed correlation between symptom and pathology is often not present. For many people there is still nothing to see on scans that explains their symptoms (and for others unexpected abnormal radiologic findings are associated with no pain). We have learned that the lack of findings does not mean that a person is not experiencing pain. The International Association for the Study of Pain (IASP) accepted that pain is a subjective sensation and that we need to listen to people’s assessment of the symptom. ¹ While there has been over-treatment of some chronic pain with opioids (contributing to the opioid crisis in the United States), the basic idea that pain is a subjective symptom to be taken seriously remains relevant. Investigations of pain then complement the person’s self-report, seeking reversible causes.

Objective findings (signs) do not always directly match perceptual experiences that can only be described by personal experience (symptoms). It is easy to overlook that ‘objective’ does not necessarily mean ‘accurate’. ²

Yet, one-quarter of the way through the 21st century, there are still clinicians doing the equivalent with people who experience chronic breathlessness. ³ It is not uncommon to hear: “Your pulmonary function tests don’t look too bad.” or “Your six-minute walk test hasn’t changed that much.” Often such statements are followed almost immediately by “Are you still taking your inhalers as directed?.” This approach is not without consequences. Clinicians’ reliance on physiological measures can invalidate the person’s experience of breathlessness and, therefore, result in missed opportunities to respond. ⁴ Many routinely used objective investigations of respiratory well-being and people’s sensations of breathlessness correlate poorly. For example, people can experience no breathlessness despite a low oxygen saturation while hiking at altitude, and others can feel significant breathlessness from asthma with normal saturation at sea level.

These observations are not new. A study more than 35 years ago in 93 people with chronic obstructive pulmonary disease (COPD) showed a very poor correlation between the baseline Borg scale dyspnea index and three frequently used measures of lung function: forced expiratory volume in one second (FEV₁), forced vital capacity (FVC), and forced expiratory flow at 25 − 75% of forced vital capacity (FEF_25–75). Furthermore, there was almost no correlation (r = 0.05) between improvement in lung function after bronchodilator therapy and changes in the subjective sensation of breathlessness. ⁵ In the 65 people with baseline Borg scores of ≥2 treated with a single dose of salbutamol 200 mcg, two groups of interest arise: (1) people with marked improvement in breathlessness sensation and minimal change in post-bronchodilator FEV₁ (one in four people); and (2) people with a marked improvement in FEV₁ and no change in breathlessness (one in six people). Overall, 43% of people had subjective outcomes not congruent with changes in their pulmonary function tests.

Similarly, in a cohort of 25 people with idiopathic pulmonary fibrosis (IPF), FEV₁ was not correlated with Borg scores, despite breathlessness scores being much higher in the cohort with IPF than in 50 healthy controls. ⁶

Other self-reported breathlessness measures, such as the Medical Research Council (MRC) breathlessness scale, ⁷ correlate better with functional tests because they measure activity limited by breathlessness. For example, in another cohort of 25 people with IPF, the correlation between the MRC scale and six-minute walk distances ⁸ was strong (r = −0.781, p < 0.001). Importantly, in a multiple logistic regression, the only relationship to remain significant for disease severity was MRC breathlessness. These findings are also seen in the relationship between MRC and shuttle walk test results in people with COPD. ⁹

Newer instruments, such as the Dyspnea-12 (D-12) ¹⁰ and Multidimensional Dyspnea Profile (MDP), ¹¹ specifically assess sensations of breathlessness (discomfort, sensory qualities, emotional responses). Their scores consistently demonstrate moderately significant positive correlations with other self-reported breathlessness instruments [COPD assessment test (CAT), ¹² Hospital Anxiety and Depressions Scale (HADS) ¹³ and modified Medical Research Council (mMRC) breathlessness scale ¹⁴ ] but weak negative correlations with pulmonary function (FEV₁% predicted). ¹⁵

At a population level, most chronic breathlessness is attributed to lung disease. ¹⁶ As such, it is important to make a clinical diagnosis that delineates the potential etiologies and actively seek reversible causes of chronic breathlessness as part of a comprehensive approach to a person who presents with this disabling symptom. ¹⁷ For example, newer treatments for interstitial lung disease (ILD) can slow and even reverse the disease process, making accurate diagnosis imperative. If indicated clinically, perform pulmonary function tests to explore the nature of any lung disease as part of a systematic approach to the diagnosis of the cause(s) of a person’s dyspnea. ¹⁸ These are important and relevant investigations, but as with pain, test results are complementary to a person’s report of breathlessness, and relief of breathlessness as a symptom is a key goal in parallel.

Person-centered care is considered fundamental to the services that we provide. Moreover, the importance of patient-reported outcomes and patient-reported experience measures is widely advocated and espoused ¹⁹ but often undervalued by clinicians. In the case of breathlessness, appreciating its subjective nature is critical to understanding the lived experience of literally hundreds of millions of people around the world. It is also important to recognize that for many people breathlessness, especially in advanced illness, is a more feared and fearsome symptom than pain. While pain can be excruciating, few people think they will die of pain, whereas many people worry that they will die of breathlessness or with the symptom still uncontrolled. As such, a person’s self-report of the severity and impacts of breathlessness should be assessed routinely and treated seriously as a target for improving quality of life, independent of measures of lung function, especially in hospice and palliative care where underlying disease management is no longer an option.

In clinical practice and in research, a person can have chronic breathlessness despite relatively normal measures that we routinely evaluate for respiratory function. Equally, breathlessness is worthy of treatment even when pulmonary function tests are unavailable. Likewise, self-attribution and self-reported impacts of breathlessness should not be treated as any less informative.

Person-centered care means we need to recognize the views, perceptions, and descriptions of people’s experiences. People should not have their experiences dismissed as though they are poor historians, cognitively challenged, melodramatic, in denial, or just plain wrong. Subjective patient-reported measures for each person are surprisingly reproducible as are pulmonary function tests—they just don’t correlate with each other. While clinical correlates and tests are essential adjuncts to understanding, respecting patients’ reports of their symptoms is fundamental for understanding their experiences individually and, when aggregated, across the population.