The impact of panic disorder on interoception and dyspnea reports in chronic obstructive pulmonary disease
Introduction
Chronic obstructive lung disease (COPD) is common, underdiagnosed and increasing in prevalence both in industrialized and developing nations. Anxiety symptoms are common in patients with COPD and the prevalence of specific anxiety disorders is estimated to be 3–10 times higher in patients with COPD compared to the general population. Panic disorder is one of the most common anxiety disorders in COPD. The prevalence of panic disorder has been estimated at 1–3% in community populations, 4–8% in primary care populations, and 8–32% in populations with COPD (Brenes, 2003). Several studies have examined the association of panic disorder with COPD as well as with other respiratory diseases, especially asthma. Primary interest in this association stems from the many overlapping symptoms that these illnesses share such as smothering sensations, choking, hyperventilation, dyspnea, and increased anxiety (Battaglia and Ogliari, 2005, Meuret et al., 2006, Nardi et al., 2009, Perna et al., 2004). Although few studies have examined the impact of panic disorder specifically, many studies have found that comorbid anxiety disorders are associated with increased symptom burden in patients with COPD, including decreased quality of life, more severe dyspnea, greater disability, and impaired functional status (Aydin and Ulusahin, 2001, Beck et al., 1988, Weaver et al., 1997). Anxiety is also a significant predictor of the frequency of hospitalizations for acute exacerbations of COPD (Yohannes et al., 2000).
Several mechanisms have been proposed to attempt to explain the increased risk of panic disorder in patients with COPD and other respiratory illnesses. From a cognitive-behavioral perspective, emotional sensitivity to somatic sensations may lead to greater anxiety when these bodily cues are encountered. The disposition toward this type of heightened reaction has been termed anxiety sensitivity (AS). Patients with high anxiety sensitivity may become vigilant to somatic sensations and react to these sensations with anxiety, and further physiological arousal. In addition, longitudinal experience with exacerbations of respiratory disease may generate fearful or catastrophic beliefs about respiratory symptoms, which, in turn, provoke panic attacks. Supporting this theory, COPD patients with PD scored higher on the Agoraphobic Cognitions Questionnaire and the Body Sensations Questionnaire than COPD patients without PD (Porzelius et al., 1992). More recently, women with COPD scored twice as high on the Anxiety Sensitivity Index than men and were three times more likely to have PD (Laurin et al., 2007). COPD can be associated with near-death episodes, need for ventilatory support, and other illness experiences, which could understandably influence the development of these frightening thoughts.
A large number of studies have explored the “interoceptive sensitivity” hypothesis of panic disorder (Ehlers and Breuer, 1992, Reiss et al., 1986), which states that patients with panic disorder are characterized by an enhanced ability to accurately detect arousal-related bodily sensations. This enhanced interoceptive sensitivity is thought to increase the probability that such individuals will experience arousal-related somatic sensations and then respond to them with anxiety (Ehlers, 1993). Evidence for greater accuracy in the detection of somatic activity in PD has been mixed. More consistently, however, individuals with PD report worse symptoms in response to a variety of physiological provocations, such as voluntary hyperventilation or CO2 inhalation (Gorman et al., 1994, Griez et al., 1990).
Very few studies have examined the characteristics of PD in patients with COPD. Previous work has either described associations between anxiety symptoms or panic disorder and COPD outcome variables (e.g., quality of life, hospital admissions), or has sought to test treatments for PD comorbid with COPD that were based on those supported for the treatment of PD alone. One study investigated the relationship between pulmonary function, catastrophic thoughts about anxiety, and panic attacks in patients with COPD (Porzelius et al., 1992). COPD patients with panic attacks did not differ from those without panic attacks on demographic variables, pulmonary function tests, or general activity levels; but they did have more agoraphobic thoughts and greater fear of bodily sensations. However, this study did not examine PD per se, and may have limited relevance to this disorder, since 36% of the general population has experienced panic attacks, while only 2–3% develop PD. One recent study examined the perception of inspiratory resistive loads in patients with PD or panic attacks and COPD (Livermore et al., 2008). Participants in this study with COPD and panic reported greater dyspnea in response to increasing inspiratory resistive loads than participants with COPD alone and healthy controls. But, again, only 9 of 20 individuals in the ‘COPD with panic’ group actually had PD. Furthermore, this study only measured dyspnea intensity ratings to resistive loads but did not test for differences in perceptual detection of loads.
In the current study, we used inspiratory resistive loads to compare interoceptive sensitivity and symptom intensity in COPD subjects without or with PD and in healthy control subjects. We hypothesized that participants with COPD and PD would show no differences in interoceptive sensitivity, as indexed by respiratory load detection threshold, but would report greater dyspnea in response to inspiratory resistive load breathing. We also predicted that anxiety sensitivity would significantly account for the higher dyspnea reports in participants with panic disorder.
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Participants
Participants with COPD and PD (COPD-PD), COPD without a psychiatric disorder (COPD-NP), and healthy controls were recruited from the outpatient mental health and primary care clinics at a University healthcare system. Participants were matched for age, sex and BMI. Potential participants were excluded for the presence of other current Axis-I psychiatric disorders, the presence of other major medical illness, or the current use of opiate or benzodiazepine medications. Individuals with PD were
Results
Subject characteristics are shown in Table 1. There were no significant differences between groups in age, sex, or BMI. Subject groups did differ on ASI scores (F(2, 25) = 10.70, p < 0.001). COPD-PD participants had significantly higher ASI scores than COPD-NP and controls participants. COPD-NP and healthy control participants did not differ on ASI scores.
On the respiratory load detection task, there were no group differences in ΔR50 (F(2, 25) = 1.69, p = 0.204). On the dyspnea rating task (Fig. 1),
Discussion
We examined interoceptive sensitivity and symptom intensity reports in COPD and panic disorder using inspiratory resistive loads. We tested the hypotheses that individuals with COPD and PD would show no differences in interoceptive sensitivity, as indexed by respiratory load detection threshold, but that they would report greater dyspnea intensity in response to inspiratory resistive load breathing. Our results support both hypotheses. In our first task, PD was not associated with hightened
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