Dyspnea affective response: comparing COPD patients with healthy volunteers and laboratory model with activities of daily living

Abstract

Background: Laboratory-induced dyspnea (breathing discomfort) in healthy subjects is widely used to study perceptual mechanisms, yet the relationship between laboratory-induced dyspnea in healthy volunteers and spontaneous dyspnea in patients with chronic lung disease is not well established. We compared affective responses to dyspnea 1) in COPD patients vs. healthy volunteers (HV) undergoing the same laboratory stimulus; 2) in COPD during laboratory dyspnea vs. during activities of daily living (ADL).

Methods: We induced moderate and high dyspnea levels in 13 COPD patients and 12 HV by increasing end-tidal CO2 (PETCO2) during restricted ventilation, evoking air hunger. We used the multidimensional dyspnea profile (MDP) to measure intensity of sensory qualities (e.g., air hunger (AH) and work/effort (W/E)) as well as immediate discomfort (A1) and secondary emotions (A2). Ten of the COPD subjects also completed the MDP outside the laboratory following dyspnea evoked by ADL.

Results: COPD patients and HV reported similar levels of immediate discomfort relative to sensory intensity. COPD patients and HV reported anxiety and frustration during laboratory-induced dyspnea; variation among individuals far outweighed the small differences between subject groups. COPD patients reported similar intensities of sensory qualities, discomfort, and emotions during ADL vs. during moderate laboratory dyspnea. Patients with COPD described limiting ADL to avoid greater dyspnea.

Conclusions: In this pilot study, we found no evidence that a history of COPD alters the affective response to laboratory-induced dyspnea, and no difference in affective response between dyspnea evoked by this laboratory model and dyspnea evoked by ADL.

Figure 1

Plot of BDVAS and A₁ ratings during limited volume ventilation as a function of change in stimulus intensity (∆P_ETCO₂). The BDVAS was used to continuously rate breathing discomfort throughout a trial lasting 10 to 15 min; the value shown in this graph is the mean BDVAS over the final 30 seconds of the trial. BDVAS scale ranged from zero to ‘stop now’, which indicated that the subject had reached his or her limit of tolerance. A₁ was assessed immediately following the trial, and the subject was asked to focus on the last 30 seconds of the trial when responding. The A₁ scale of unpleasantness ranged from ‘neutral’ to ‘unbearable’.

Figure 2

Plot of ‘unpleasantness’ (A₁) as a function of air hunger intensity for two groups of subjects, COPD patients (open circles, dashed line) and healthy controls (closed circles, solid line). Both groups were exposed to moderate and high stimuli. There was no difference between the groups. The A₁ scale of unpleasantness ranged from ‘neutral’ to ‘unbearable’; the air hunger scale ranged from zero (‘none’) to ‘as intense as I can imagine’.

Figure 3

Plot of anxiety rating (panel 3a) and frustration rating (panel 3b) vs. unpleasantness (A₁) for healthy subjects (closed circles, solid line) and COPD patients (open circles, dashed line). Ratings are for the last 30 seconds of moderate intensity and high intensity laboratory stimuli. Scale maxima were defined as ‘Unbearable’ for unpleasantness and ‘most I can imagine’ for emotion. Error bars reflect standard errors.

Figure 4

Plot of Unpleasantness (A₁) as a function of air hunger rating for the 10 COPD subjects who completed daily questionnaires at home. Open circles connected by line represent dyspnea during moderate and high P_ETCO₂ during restricted ventilation in the laboratory; closed circle represents dyspnea experienced during activities of daily living, such as walking or climbing stairs. Scale maxima were defined as ‘Unbearable’ for unpleasantness and ‘as intense as I can imagine’ for air hunger. Error bars reflect standard errors.

Figure 5

Plot of anxiety (5a) and frustration (5b) ratings as a function of unpleasantness rating in COPD subjects during dyspnea caused by activities of daily living (ADL) and by a laboratory stimulus evoking air hunger. Open circles connected by line represent dyspnea during moderate and high P_ETCO₂ during restricted ventilation in the laboratory; closed circle represents dyspnea experienced during activities of daily living, such as walking or climbing stairs. Scale maxima were defined as ‘Unbearable’ for unpleasantness and ‘most I can imagine’ for emotion. Error bars reflect standard errors.