Descriptors of breathlessness in healthy individuals: distinct and separable constructs.

STUDY OBJECTIVES: We tested the hypothesis that descriptors of breathlessness represent distinct and separable cognitive constructs, and predicted that the use of descriptors of breathlessness by healthy individuals is the same as their use by patients with cardiopulmonary disease. DESIGN: Cluster analyses obtained in healthy individuals were compared with those obtained previously in patients who complained of breathing discomfort. In addition, we used multidimensional scaling (MDS) techniques to analyze relationships among descriptors in healthy individuals. SETTING: Public university. PARTICIPANTS: The participants were 100 healthy individuals (48 men and 52 women) ranging in age between 18 and 65 years (mean, 27.9+/-11.7 years). MEASUREMENTS AND RESULTS: Participants judged the dissimilarity among pairs of 15 descriptors of breathlessness that were used previously to examine the experience of dyspnea in patients who complained of breathing discomfort. Cluster analysis solutions obtained in the healthy individuals were virtually identical to those obtained previously in patients. Three dimensions (attributes) of breathing discomfort were uncovered with MDS: "Depth and frequency of breathing," "Perceived need, or urge, to breathe," and "Difficulty breathing and phase of respiration." The results did not depend on age, sex, levels of education, or the presence of uncomfortable awareness of breathing with activities. CONCLUSIONS: The relations among descriptors of breathlessness obtained in healthy individuals support the contention that the association of different clusters with different disease states reflects distinct and separable cognitive constructs that are not simply dependent on the presence of an underlying pathophysiology or on a specific disease condition. Our results in healthy individuals also suggest that distinct qualities of breathlessness relate to different physiologic mechanisms underlying respiratory discomfort.

Event-related potentials to inspiratory flow-resistive loads in young adults: stimulus magnitude effects.

Event-related potentials were recorded to brief presentations of four levels of inspiratory flow-resistive loads in young adults. We labeled the loads according to the level of resistance they provided subjectively: sub-threshold (0.34 cmH2O/l per s), near-threshold (4.01 cmH2O/l per s), intermediate (10.4cmH2O/l per s), and near-occlusion (57.5 cmH2O/l per s). No discernible ERPs were elicited by the undetected, sub-threshold stimulus but late components of the ERP (P2, N2, and P3) were observed to each of the three larger stimuli. They were related, in part, to behavioral judgments obtained during the stimulus periods. Both the latency and amplitude of the ERP components varied systematically as a function of stimulus magnitude, in a manner comparable to that observed in ERP paradigms using auditory and visual stimuli. Thus, the data show that event-related potentials to breathing are sensitive to physiologic effects of resistive loads present at the onset of inspiration. Respiratory ERPs may be used to infer sensory and perceptual responses to increases in airflow resistance and, accordingly, may relate to the perception of airflow obstruction in patient populations.

Language of dyspnea in assessment of patients with acute asthma treated with nebulized albuterol.

To investigate whether the language of dyspnea provides relevant clinical information in addition to that provided by ratings of overall dyspnea intensity when assessing subjective response to therapy, we conducted a prospective study in a cohort of 25 patients with acute asthma presenting to the emergency department of a tertiary care hospital. Patients received nebulized albuterol treatments every 20 min with a maximum of three doses. At presentation and after each treatment, patients completed spirometry, rated overall dyspnea intensity on a modified Borg scale, and selected phrases that described qualities of breathlessness from a 15-item questionnaire. Paired Student's t tests revealed significant improvements in FEV1 (from 1.39 +/- 0.66 L to 1.80 +/- 0.76 L, p < 0. 001) and reductions in dyspnea intensity (from 5.12 +/- 2.08 to 2.82 +/- 1.59, p < 0.001) after the first albuterol treatment. Dyspnea intensity continued to decrease significantly in response to the second treatment, modified Borg rating 2.26 +/- 1.52, although there was no positive bronchodilator response. The results from Cochran Q tests revealed that the frequency of the experience of "chest tightness" decreased significantly across the phases of treatment. However, the sensations of "work" or "breathing effort" persisted at the same time that the FEV1 revealed ongoing airways obstruction. We conclude that attention to the language of dyspnea would alert health care providers to residual air flow obstruction despite decreases in overall dyspnea intensity.

Descriptors of breathlessness in cardiorespiratory diseases.

The purposes of this study were: to examine the decriptors of breathlessness chosen by a large sample of patients with cardiorespiratory disease; to determine test-retest reliability of a patient's selection of the descriptors; and to assess whether a patient's recall of the experience of breathlessness is the same as that provoked by physical activity. Questionnaire data were collected at an initial visit for patients who complained of breathlessness and at a second visit in a subgroup of patients. A total of 218 patients who sought medical care for difficulty breathing due to one of seven different conditions were recruited from an outpatient pulmonary disease clinic at a university medical center. Patients selected statements that described qualities of breathlessness from a 15-item questionnaire and completed pulmonary function tests. At a subsequent visit (4 to 15 d later) a subgroup of 16 patients with chronic obstructive pulmonary disease (COPD) repeated the questionnaire at rest (to assess reliability) and after walking in a hallway to provoke a moderate intensity of breathlessness (to compare recall with direct experiences). The relationship among descriptors was evaluated by cluster analysis. The "work/effort" cluster was common for all diagnoses. Each condition was characterized by more than one cluster except COPD. Each diagnosis was associated with a unique set of dusters (e.g., asthma with "work/effort" and "tight," interstitial lung disease with "work/effort" and "rapid" breathing). Percent agreement for all descriptors selected at Visits 1 and 2 (recall) was 79% (r = 0.82; p = 0.001). Percent agreement at Visit 2 between descriptors for recall and for breathlessness provoked by walking was 68% (r = 0.69; p = 0.004). We conclude that patients with different cardiorespiratory conditions experience distinct qualities of breathlessness. Patients' recall of their sensations of breathlessness is reliable and comparable to dyspnea with walking. Employing a questionnaire containing descriptors of breathlessness may help to establish a specific diagnosis and to identify mechanisms whereby a specific intervention relieves dyspnea.

Highlights of the annual meeting of the International Society for the Advancement of Respiratory Psychophysiology and the 14th International Symposium on Respiratory Psychophysiology.

This article provides a review of selected presentations and events that highlighted the annual meeting of the International Society for the Advancement of Respiratory Psychophysiology (ISARP) and the 14th International Symposium on Respiratory Psychophysiology, Toronto, Ontario, Canada, October 1995. The meeting, which was scheduled as a satellite to the 35th annual meeting of the Society for Psychophysiological Research, included two workshops (Diana M. Innocenti on "Identification of Individual Breathing Patterns and Introduction to the Reeducation of Dysfunctional Patterns in Hyperventilation, Asthma, and Emphysema" and Richard N. Gevirtz on "Respiratory and Psychophysiological Factors in the Diagnosis and Treatment of Functional Cardiac and Panic Disorders"), two symposia (one on "Breathing Retraining: Issues and Applications" and one on "Capnography and Hyperventilatory Hemodynamics"), three invited addresses (Hans Folgering on "Rehabilitation of Patients with Exercise Hypoxemia"; David Stubbing on "Assessing Impairment, Disability, and Handicap in Chronic Lung Disease"; and Robert Banzett on "Hypercapnia-Induced Air Hunger"), three panel sessions (one on "Respiratory Psychophysiology of Airway Obstruction," one on "Applied Respiratory Psychophysiology," and one on "Hyperventilation and Panic: Psychological Aspects"), and a poster session.

Gender affects the detection of resistive loads.

Gender differences were observed on a respiratory-resistance detection task. Men (n = 35) exhibited significantly lower thresholds for air flow resistance than women (n = 45).

Event-related potentials to airway occlusion in young and old subjects.

Event-related potentials (ERPs) were recorded to both inspiratory and expiratory airway occlusion in young (21-28 years) and old (55-67 years) subjects under both attend and ignore conditions. Early and late components of the ERP (N1, P2, N2, P3) were observed to both types of occlusions in both conditions. Variations in these components were consistent in both direction and degree with those observed in oddball tasks employing exteroceptive stimuli. ERPs for breathing may serve to clarify sensory attributes of respiratory stimuli in humans and to identify central processing abnormalities in patient populations.

Effects of detection and classification of resistive and elastic loads on endogenous event-related potentials.

Resistive and elastic loads added to inspiration are readily detected, and detection latencies vary as a function of load magnitude and load type. In the present study, we recorded endogenous event-related potentials (i.e., N2 and P3) to the detection and classification of large (15.0 cmH2O.1-1.s and 70.0 cmH2O/l) and small (1.45 cmH2O.1-1.s and 19.0 cmH2O/l) loads equated for subjective magnitude in 14 men (mean age 21.14 yr). In blocks of trials comprised of either large or small loads, subjects made a button-press response upon detecting a load and then classified the load as resistive or elastic. Loads were presented briefly (for approximately 200 ms) early in inspiration and at the same level of inspiratory pressure. For loads of comparable magnitude, subjects detected equivalent numbers of resistive and elastic loads but could not discriminate reliably between load types. On the other hand, the latency of N2 was shorter to larger than to smaller loads, to resistive than to elastic loads, and to correct than to incorrect load classifications. The latency of P3 was affected similarly by load magnitude and load type. These findings demonstrate that event-related potentials are elicited by brief presentations of resistive and elastic loads and that N2 and P3 latencies vary reliably as a function of load magnitude and load type. Most importantly, event-related potential latencies are sensitive to load type and to classification accuracy even when resistive and elastic loads are not distinguishable subjectively.

Effects of feedback on the ability of asthmatic subjects to detect increases in the flow-resistive component to breathing.

Improved perception of increases in airflow resistance may have implications in asthma self-management. Two experiments that evaluated effects of feedback on the detection of flow-resistive loads are summarized. In the first experiment, detection ability of asthma patients who received feedback about the correctness of their responses in a signal-detection task was compared with that of asthma patients who did not receive feedback. Experiment 1 showed that subjects in the feedback condition detected the presence of flow-resistive loads more accurately than subjects in the no-feedback condition. In the second experiment, effects of feedback were compared between asthmatic and nonasthmatic subjects. Experiment 2 showed that effects of feedback training were equivalent in subjects with and without asthma.

Signal-detection outcomes on heartbeat and respiratory resistance detection tasks in male and female subjects.

Male and female subjects were compared on heartbeat, respiratory resistance, and light-tone signal-detection tasks. Subjects judged whether a series of 10 tones was coincident with their heartbeats; whether an external load added to the airway was either present or absent during targeted inspiratory cycles; and whether a series of 10 light flashes was matched with auditory tones presented following a fixed delay of either 50 or 100 ms. Nonparametric indices of perceptual sensitivity and response bias indicated that men were more sensitive than women on the resistive load task (p < .05) and on the heartbeat task (p = .07). Performance on the light-tone task was virtually identical. All subjects used a stricter criterion on the respiratory resistance task than on either the heartbeat or the light-tone task; women employed a stricter criterion than men on the heartbeat task. The gender differences may be understood in terms of lateralization of central processing of somesthetic sensory information.

EMG stability as a biofeedback control.

Factors that may confound comparisons between electromyographic (EMG) biofeedback training and its control conditions include feedback quality and experience of success. We investigated the usefulness of a control procedure designed to overcome these potential sources of confounding. The procedure consisted of training muscle tension stability. We used it as a control for frontal EMG relaxation training in children with asthma. To equate the groups for feedback quality and experience of success, we gave each child in the control condition audio feedback decreasing in pitch when muscle tension was at or near baseline levels, and feedback increasing in pitch when muscle tension was either substantially above or below baseline levels. Children in both groups were instructed to decrease the pitch of the tone. In comparison to children in the relaxation condition, the children in the control condition exhibited stable levels of muscle tension throughout eight training sessions. We concluded that feedback for stable muscle tension may be a useful control procedure for EMG biofeedback training whenever experimental and control procedures differ in either feedback quality of degree to which they permit subjects to experience success.

A factor analysis of dyspnea ratings, respiratory muscle strength, and lung function in patients with chronic obstructive pulmonary disease.

The purpose of this study was to demonstrate that clinical ratings of dyspnea and physiologic function are separate dimensions underlying the pathophysiology of chronic obstructive pulmonary disease (COPD). We used principal-components factor analysis to confirm these dimensions using data collected prospectively in 86 symptomatic patients with COPD. Three different instruments were used to rate dyspnea: a modified Medical Research Council (MRC) scale, the oxygen cost diagram (OCD), and the baseline dyspnea index (BDI). Measures of physiologic function included standard spirometric measures (forced vital capacity [FVC] and forced expiratory volume in one second [FEV1]) and maximal inspiratory (PImax) and expiratory (PEmax) mouth pressures. Age of the 65 male and 21 female subjects was 62.9 +/- 1.2 yr (mean +/- SEM). All three clinical scales were significantly correlated with physiologic function (range of r values, 0.32 to 0.45; p less than 0.05), except for the relationship between the MRC scale and PEmax (r = -0.14; p = NS). The factor analysis yielded three factors that accounted for 71.9% of the total variance of the data: clinical ratings of dyspnea (MRC scale, OCD, and BDI) loaded on the first factor; maximal respiratory pressures and gender loaded on the second factor; and lung function and age loaded on the third factor. Additional post hoc factor analysis provided similar results when the sample was divided into two subgroups by randomization, by severity of dyspnea ratings, or by severity of airflow obstruction. We conclude that dyspnea ratings, maximal respiratory pressures, and lung function are separate factors or quantities that independently characterize the condition of patients with COPD.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term effects of biofeedback-induced facial relaxation on measures of asthma severity in children.

We studied the effects of electromyographic biofeedback on measures of asthma severity in children. Fifteen children received biofeedback training to reduce facial tension, and 14 children, who served as controls, received biofeedback training to maintain facial tension at a stable level. Assignment to experimental condition was random. As a result of training, electromyographic levels decreased in children trained in facial relaxation and remained fairly constant in children trained in facial tension stability. Biofeedback training was augmented for children in both groups by having them practice their facial exercises at home. Each child's condition was followed for a five-month period subsequent to biofeedback training. Throughout the experiment, the following measures of asthma severity were monitored: lung function, self-rated asthma severity, medication usage, and frequency of asthma attacks. In addition, standardized measures of attitudes toward asthma, self-concept, and chronic anxiety were recorded at regular intervals. As compared to the facial stability subjects, the facial relaxation subjects exhibited higher pulmonary scores, more positive attitudes toward asthma, and lower chronic anxiety during the follow-up period. Subjects in the two groups, however, did not differ on self-rated asthma severity, medication usage, frequency of asthma attacks, or self-concept. Based on the improvements we observed in pulmonary, attitude, and anxiety measures, we concluded that biofeedback training for facial relaxation contributes to the self-control of asthma and would be a valuable addition to asthma self-management programs.

Measurement of respiratory sensation in interstitial lung disease. Evaluation of clinical dyspnea ratings and magnitude scaling.

To evaluate measurements of respiratory sensation in ILD, we compared ratings of breathlessness from three clinical scales with the perceived magnitude of added elastic loads in 20 symptomatic ILD patients. Dyspnea ratings were obtained by two independent observers for each clinical method. Perceived magnitude of four elastic loads was selected from the Borg category scale; these estimates were summarized using the psychophysical power function equation. Ten age-matched healthy subjects also scaled the magnitude of added elastic loads. Dyspnea ratings from the three clinical scales were significantly interrelated. Mean exponents for mouth pressure developed during elastic loading were similar in the patient and control groups. Dyspnea ratings and exponents for elastic loads were not significantly correlated in ILD patients. Of the physiologic parameters examined, Dsb and gas exchange during exercise correlated significantly with clinical dyspnea ratings; none correlated with the exponent for added elastic loads. These data demonstrate that clinical dyspnea ratings provide valid measures of breathlessness in patients with ILD which are independent of the perception of respiratory loads.

Targeted inspiratory muscle training improves respiratory muscle function and reduces dyspnea in patients with chronic obstructive pulmonary disease.

STUDY OBJECTIVE: To examine the effects of targeted inspiratory muscle training on respiratory muscle function, clinical ratings of dyspnea, and perception of resistive loads in symptomatic patients with chronic obstructive pulmonary disease. DESIGN: Randomized, placebo-controlled trial with an 8-week treatment period. SETTING: Outpatient pulmonary clinic and pulmonary function laboratory. PARTICIPANTS: We studied 19 patients with moderate to severe chronic obstructive pulmonary disease, assigning 10 patients to an experimental group and 9 to a control group. INTERVENTIONS: Patients in both groups trained for 15 minutes twice each day using a device that provided breath-to-breath visual feedback of training intensity. Patients in the experimental group trained at six increasing levels of inspiratory resistance, whereas the patients in the control group trained at a constant, nominal level of resistance. MEASUREMENTS AND RESULTS: Although there was no statistically discernible difference in the effects of targeted muscle training on the mean difference in maximal inspiratory pressures between the two groups (9.83 cm H2O; 95% CI, -7.37 to 27.03), patients in the experimental group did show a significant increase in inspiratory muscle strength (15.03 cm H2O; P = 0.01). Experimental subjects also had decreased dyspnea after 8 weeks of training compared with control subjects (P = 0.003). Improvements in physiologic values and in dyspnea ratings were correlated. The perception of added resistive loads was not affected by inspiratory muscle training. CONCLUSIONS: Targeted inspiratory muscle training may enhance respiratory muscle function and reduce dyspnea in symptomatic patients with moderate to severe chronic obstructive pulmonary disease.

Human breathing pattern responses to loading with increased background impedance.

We determined the influence of the background level of mechanical impedance on the respiratory responses to very small mechanical loads, at or below the threshold for conscious perception. We used a pseudorandom load application technique to estimate the immediate pattern responses from the zeroth lag of the cross correlation between the load application sequence and the respiratory pattern components of tidal volume (VT), inspiratory and expiratory time (TI and TE), and the instantaneous respiratory frequency (f), minute ventilation (VI), and mean inspiratory flow (VT/TI). Elevation of the background resistance served to reduce the TI and TE responses to small perturbations in resistance from those in the control background state, which resulted in generally smaller perturbations of f, VI, and VT/TI. Elevation of the background elastance, however, served to initiate a TI reduction not seen in the control state but did not appreciably affect the rest of the pattern responses to the load perturbations. Thus the neural reflexes involved in breath-by-breath pattern regulation are modulated by the background level of the respiratory impedance, as well as by the type and size of the load perturbation.

Prediction of peak oxygen consumption in obstructive airway disease.

The hypothesis of this study was that non-exercise variables can be used to reliably predict peak oxygen consumption (VO2) in patients with obstructive airway disease (OAD). We also evaluated the impact of symptoms on exercise capacity. Selected predictor variables included age, lung function, respiratory muscle strength, gas exchange, and the Baseline Dyspnea Index (BDI). In 40 patients peak VO2 was 19.9 +/- 8.7 (mean +/- SD) ml.kg-1.min-1 during progressive, incremental exercise until limited by symptoms on a cycle ergometer. Multiple regression analysis yielded three significant predictors: forced expiratory volume in one second (FEV1), age, and BDI. Peak VO2 (ml.kg-1.min-1) = 5.5 (FEV1) - 0.3 (age) + 0.8 (BDI) + 19.3 (R2 = 0.79; SEE: 4.2 ml.kg-1.min-1). Comparisons between patients who stopped exercise because of breathlessness (N = 14) and those who stopped because of leg fatigue (N = 18) showed that lung function, inspiratory muscle strength, and peak VO2 were significantly reduced in the former group compared to the latter. Peak exercise ventilation (VE)/MVV ratio was similar in the breathless (95.3 +/- 23.8%) and leg fatigue (86.8 +/- 20.3) groups, but peak heart rate (HR)/pred. HRmax ratio was significantly higher in the leg fatigue group (86.8 +/- 12.6%) than in the breathless group (75.1 +/- 8.6%) (P = 0.006). We conclude that lung function, age, and the clinical rating of breathlessness reliably predict peak VO2 in patients with symptomatic OAD. Moreover, peak exercise performance in OAD appears to be affected by different physiological factors which may be distinguished by the major symptom limiting exercise.

Measures of asthma severity recorded by patients.

Twenty-nine children with asthma made daily recordings of the severity of their asthma for 8 months. Each child recorded four measures of severity: a medication usage score, a morning peak expiratory flow rate (PEFR), an evening PEFR, and a subjective rating of overall severity. We determined the relationships between the four measures. Except for the morning and evening PEFRs, the relationships between the measures were weak; the PEFR measures were highly related to one another. The relationship between PEFR scores and medication usage scores increased following biofeedback relaxation training.