Weighing up the evidence–a systematic review of measures used for the sensation of breathlessness in obesity

International Journal of Obesity (2013) 37, 341–349 & 2013 Macmillan Publishers Limited All rights reserved 0307-0565/13 www.nature.com/ijo REVIEW Weighing up the evidence–a systematic review of measures used for the sensation of breathlessness in obesity Y Gerlach, MT Williams and AM Coates Breathlessness on exertion is common in people with obesity. Assessments of breathlessness may include sensation (intensity, sensory quality or unpleasantness) and/ or the behavioral/emotional consequences of the sensation (respiratory-related functional impairment, disability or quality of life). This systematic review of primary studies published since 2005 evaluated how has the sensation of breathlessness been assessed in adults with increased adiposity. A total of 41 articles were retained from the systematic search strategy resulting in 20 instruments. The Modified Borg Scale (perceived exertion-intensity), the Medical Research Council (MRC) Scale and Baseline Dyspnea Index (BDI; both assess respiratory-related functional impairment) were, respectively, the most frequently reported instruments. Few instruments had been tested for reliability and validity in people with increased adiposity. Visual Analog Scale, Modified Borg Scale, descriptors of sensory quality, MRC and BDI can be recommended as instruments based on their psychometric properties (reliability (correlations 40.8) and concurrent validity (correlation with severity of airways obstruction and walking distance)). A greater number of instruments were identified that assessed the consequences of the breathlessness rather than breathlessness as a sensation. If sensation drives behavior, comprehensive data on the sensation of breathlessness might assist in understanding the behavioral consequences of interventions. International Journal of Obesity (2013) 37, 341–349; doi:10.1038/ijo.2012.49; published online 24 April 2012 Keywords: overweight; dyspnoea; breathlessness; assessment; instruments INTRODUCTION Breathlessness and distress with breathing (dyspnea) are common symptoms in people with increased adiposity (overweight body mass index (BMI) 25–29.9 kg m  2 or obese X30 kg m  2).1,2 Among other musculoskeletal, metabolic and cardiovascular alterations, people who are overweight or obese display a number of respiratory physiological alterations in pulmonary volumes, flows and capacities, respiratory mechanics, gas exchange, control of breathing and respiratory muscle function.3,4 These physiological mechanisms underpin the functional increase in the work of breathing resulting in breathlessness. It has been suggested that these respiratory alterations may be more related to the distribution of adiposity (waist circumference or waist to hip ratio) rather than BMI.5,6 Increased adiposity not only predicts the presence and severity of chronic breathlessness, but also severity of breathlessness is strongly associated with increased BMI and decreased physical activity.7 Although breathlessness is usually seen as a comorbid effect of increased adiposity, in other chronic conditions where breathlessness is a feature (chronic obstructive pulmonary disease or heart failure), the uncomfortable or distressing sensation of breathlessness leads to early cessation of exercise and facilitates sedentary behaviors resulting in adverse health outcomes (reduced cardiovascular fitness and muscle strength).8 During the past century our understanding of the sensation of breathlessness has evolved from a simple model of respiratory center stimulation (neurochemical model), to the recognition that receptors including muscle (tension), joint (position sense and displacement), irritant, vascular and airways receptors can modify ventilation (neuromuscular model; Figure 1). In the late 1900s, the contribution of physiological, psychological, cognitive, social and environmental factors to the sensory experience of breathlessness was recognized through the American Thoracic Society’s definition of dyspnea.8 A gated neuromatrix model for dyspnea has emerged during the past decade, which integrates afferent inputs from the receptors and systems within the body as well as cortically mediated processes for memory, associations and attention.9,10 Where afferent information exceeds a threshold (gate open by increased input from the periphery or consciously directed attention), the individual consciously appreciates intensity and sensory quality (descriptors) of the sensation of breathlessness.10 A second gating system is involved in determining whether the sensation is pleasant/unpleasant, presumably through comparison of the current sensation with past experiences/expectation of the degree of breathlessness in similar contexts. Where the sensation is perceived to be unpleasant (that is, dyspnea rather than breathlessness) limbic structures associated with fear or alarm are activated evoking an immediate emotional (fear, anxiety and frustration) and behavioral response (cessation or avoidance of physical activity).10 In conditions where breathlessness is a common symptom (obesity, obstructive and restrictive respiratory disorders), the disparity between motor output and resultant work of breathing is the most likely mechanism underpinning the conscious awareness of a sensation of breathing discomfort or distress.10–15 Nutritional Physiology Research Centre, Sansom Institute for Health Research, School of Health Sciences, University of South Australia, Adelaide, Australia. Correspondence: Y Gerlach, Nutritional Physiology Research Centre, Sansom Institute for Health Research, School of Health Sciences, University of South Australia, City East Campus, Adelaide 5001, Australia. E-mail: Received 9 November 2011; revised 27 February 2012; accepted 4 March 2012; published online 24 April 2012 Measures of sensation of breathlessness in obesity Y Gerlach et al 342 Dyspnoea model Neuromatrix Neuromuscular Discordance between drive and ventilatory function Neurochemical Carbon dioxide, oxygen drive ventilation ←1920 Era 1940 1950 1960 1970 1980 1990 2000 → Lab-based physiological impairment tests Respiratory related functional impairment Field-based physiological impairment tests Breathlessness intensity Respiratory related quality of life Breathlessness sensory quality (descriptors) Breathlessness unpleasantness Assessment domains Figure 1. 1930 Evolution of dyspnea mechanisms and breathlessness assessments. In many ways, assessments of breathlessness in chronic conditions reflect the contemporary understanding of the mechanisms giving rise to the symptom (Figure 1). To better understand the etiology, pathogenesis and response to intervention, breathlessness assessments have diversified from measures of the severity of physiological impairment (for example, pulmonary function tests, arterial blood gas analysis, exercise performance) to include assessments of how breathlessness impairs functional activities (for example, the New York Heart Clas (...truncated)