Ability of asthmatics with and without respiratory arrest to detect added resistive loads

Current perspectives on symptom perception in asthma: a biomedical and psychological review

Symptom perception in patients with asthma is often inadequate. Patients may fail to perceive serious airway obstruction or suffer from breathlessness without objective cause. These extremes are associated with fatal asthma and excessive use of medicines, respectively. This article covers symptom perception in a multidisciplinary perspective. A presentation of current definitions and methods for studying symptom perception in asthma is followed by a summary of theories on the origin of breathlessness. Next, biomedical and psychological factors influencing symptom perception are examined. Preliminary biomedical research emphasizes neural pathway impairment, but causal factors remain inconclusive, particularly regarding the overperception of symptoms. Psychological studies suggest that the accuracy of symptom perception is influenced by (a) competition between asthmatic and nonasthmatic sensory information, (b) negative emotions, and (c) acquired response tendencies (e.g. habituation to symptoms, repression of symptoms, selective perception, and false interpretation of symptoms). These factors may favor either blunted perception or overperception. Empirical data in support of psychological factors are still insufficient. Methodological problems and procedures to improve symptom perception are discussed.

The impact of severe asthma on schoolchildren

Episodic airway obstruction and hypoxia are potentially life-threatening to children with asthma and may account for neuropsychological impairment. Moreover, living with this chronic disease may severely disrupt children's emotional functioning. The general functioning of 25 children with severe asthma aged 10-13 years was tested by a comparison with 25 matched normal controls. Testing included variables with relevance to normal daily functioning: memory, concentration, school performance, physical condition, subjective symptoms after exercise, and negative emotions. The results showed that children with asthma did not significantly deviate from controls. They reported more dyspnea after physical exercise, which could not be attributed to lung function. Differences in school performance were not significant. It was concluded that children may generally adapt well to living with asthma.

Magnitude estimation of inspiratory resistive loads in children with life-threatening asthma

The perception of inspiratory resistive (R) loads was studied in nonasthmatic children and in children with a history of life-threatening asthma. It was hypothesized that the children with life-threatening asthma would have a reduced sensitivity to added mechanical loads as measured by magnitude estimation of resistive loads (ME). The subjects were screened from the experimenter and seated in a sound-isolated room in a lounge chair facing an oscilloscope, and they respired through a nonbreathing valve with the inspiratory port connected to the loading manifold. The oscilloscope displayed the inspiratory V, and each subject was required to inspire to the same peak V for each breath. The subject's inspiratory background R was measured by the interrupter method. Five magnitudes of R loads and no-load were presented randomly 10 times each for a single inspiration after the illumination of a light cue. The subjects were initially given a training trial breathing to the V target. The loads were presented in two trials. The load was estimated using the modified Borg scale. The slope of the log-log relationship between R load magnitude and the ME is a measure of the sensitivity of the subject to R loads. The slope for children with life-threatening asthma was significantly less than that for asthmatic and nonasthmatic children. There were no significant differences in the slope related to race, sex or age in the nonasthmatic children or in the asthmatic children. The reduced sensitivity to increased R loads suggests that these children are at risk of a life-threatening asthmatic attack in part because of an underestimation or delay in the perception of the increased mechanical load that occurs during an asthmatic attack.

Habituation to prolonged airflow obstruction

The hypothesis that absence of dyspnea during airflow obstruction is caused by habituation to sensory information was tested. Adolescents without respiratory disease breathed through a mouthpiece interrupting airflow analogous to approximately 64% reduction in forced expiratory volume in 1 sec. They were randomly assigned to labored breathing for 1 min, 30 min, or twice 30 min (with a 30-min interval in between). Dyspnea was measured pretest without mouthpiece and posttest with mouthpiece in. Results showed no significant difference in posttest dyspnea between conditions. Dyspnea remained remarkably mild. Severe secondary symptoms (excessive saliva) during the experiment made habituation unlikely and the results were interpreted in favor of the alternative hypothesis: lack of or mild dyspnea is associated with a low-anxiety situation without connotation of suffocation, irrespective of level of airflow obstruction.

Perception of breathlessness during early and late asthmatic responses

We looked at the perception of breathlessness associated with bronchoconstriction during early (EAR) and late (LAR) asthmatic responses to inhaled antigens and its correlation with the rate of fall of expiratory flows. Twenty-eight asthmatics were studied (12 male, 16 female, 18 to 38 yr of age). Breathlessness was evaluated on a modified Borg scale (0 to 10) before each FEV1 measurement, obtained at regular intervals for as long as 8 h after the antigen challenge. The rate of the fall in FEV1 was calculated from the maximal percent fall obtained during the EAR or the LAR and the time lapse from the onset of the reaction to the maximal fall in FEV1. Ten subjects had an isolated early and 18 had a dual asthmatic response after allergen challenge. Dual responders perceived a similar percent fall in FEV1 (mean percent fall: EAR, 20.7 +/- 1.6%; LAR, 21.5 +/- 1.6%) more intensely during the EAR than during the LAR, with median Borg scores (range) of, respectively, 2.0 (0.5 to 4) and 0.5 (0 to 3.0) (n = 18, p < 0.001). The median rate of the fall in FEV1 was: EAR, 2.09 (0.77 to 6.6) %/min; LAR, 0.11 (0.05 to 0.36) %/min (n = 18, p < 0.001). The rate of the fall in FEV1 during either EAR or LAR was strongly correlated with the Borg scores; the slower the fall, the weaker the perception (p < 0.001). We conclude that LAR are poorly perceived compared with EAR and that this may be due to the temporal adaptation to the slow and progressive bronchoconstriction in LAR.