Hospitalization trends for paediatric asthma in eastern Finland: a 10-yr survey

Dynamic hyperinflation during the 6-min walk test in severely asthmatic subjects

We tested the hypothesis that dynamic hyperinflation develops in severe asthmatic subjects during exercise. Changes in inspiratory capacity (IC) were measured during the 6-min walk test (6MWT) in severe asthmatic subjects compared with chronic obstructive pulmonary disease (COPD) subjects with a similar degree of bronchial obstruction. We assessed whether changes in IC were associated with changes in dyspnoea perception.

27 severe asthmatic subjects (10 males and 17 females) and 43 COPD subjects (35 males and eight females) were recruited. The two groups performed similarly in the 6MWT (p=0.90). At the end of the test, the Borg score increased significantly in both groups (mean difference: for asthmatic subjects 1.7±1.6; p<0.0001; for COPD subjects 3.1±1.9; p<0.0001). IC measured at the beginning of 6MWT was not different between groups (2.25±0.47 L in asthmatic subjects versus 2.38±0.60 L in COPD subjects; p=0.32) and decreased in both groups (mean difference: for asthmatic subjects 0.160 L; p=0.02; for COPD subjects 0.164 L; p<0.0001). However, changes in IC were significantly associated with changes in the Borg score in the COPD group (r²=0.17; p=0.006), but not in the asthma group (r²=0.06; p=0.20).

In severe asthmatic subjects, IC significantly drops during the 6MWT to the same extent as COPD subjects with a similar degree of lung impairment, indicating the development of dynamic hyperinflation. Contrary to COPD, in asthmatic subjects the occurrence of dynamic hyperinflation was not associated with changes in dyspnoea perception.

Severe asthma is characterised by occurrence of dynamic hyperinflation during exercise; inspiratory capacity drops in severe asthmatic subjects during the 6MWT to the same extent as in COPD subjects with similar lung impairmenthttp://ow.ly/InfQ30jjivW

Mechanisms, measurement and management of exertional dyspnoea in asthma: Number 5 in the Series "Exertional dyspnoea" Edited by Pierantonio Laveneziana and Piergiuseppe Agostoni

Asthma is a heterogeneous condition, with dyspnoea during exercise affecting individuals to a variable degree. This narrative review explores the mechanisms and measurement of exertional dyspnoea in asthma and summarises the available evidence for the efficacy of various interventions on exertional dyspnoea. Studies on the mechanisms of dyspnoea in asthma have largely utilised direct bronchoprovocation challenges, rather than exercise, which may invoke different physiological mechanisms. Thus, the description of dyspnoea during methacholine challenge can differ from what is experienced during daily activities, including exercise. Dyspnoea perception during exercise is influenced by many interacting variables, such as asthma severity and phenotype, bronchoconstriction, dynamic hyperinflation, respiratory drive and psychological factors. In addition to the intensity of dyspnoea, the qualitative description of dyspnoea may give important clues as to the underlying mechanism and may be an important endpoint for future interventional studies. There is currently little evidence demonstrating whether pharmacological or non-pharmacological interventions specifically improve exertional dyspnoea, which is an important area for future research.

Expiratory flow limitation definition, mechanisms, methods, and significance

When expiratory flow is maximal during tidal breathing and cannot be increased unless operative lung volumes move towards total lung capacity, tidal expiratory flow limitation (EFL) is said to occur. EFL represents a severe mechanical constraint caused by different mechanisms and observed in different conditions, but it is more relevant in terms of prevalence and negative consequences in obstructive lung diseases and particularly in chronic obstructive pulmonary disease (COPD). Although in COPD patients EFL more commonly develops during exercise, in more advanced disorder it can be present at rest, before in supine position, and then in seated-sitting position. In any circumstances EFL predisposes to pulmonary dynamic hyperinflation and its unfavorable effects such as increased elastic work of breathing, inspiratory muscles dysfunction, and progressive neuroventilatory dissociation, leading to reduced exercise tolerance, marked breathlessness during effort, and severe chronic dyspnea.

Methods for Assessing Expiratory Flow Limitation during Tidal Breathing in COPD Patients

Patients with severe COPD often exhale along the same flow-volume curve during quite breathing as during forced expiratory vital capacity manoeuvre, and this has been taken as indicating expiratory flow limitation at rest (EFL_T). Therefore, EFL_T, namely, attainment of maximal expiratory flow during tidal expiration, occurs when an increase in transpulmonary pressure causes no increase in expiratory flow. EFL_T leads to small airway injury and promotes dynamic pulmonary hyperinflation with concurrent dyspnoea and exercise limitation. In fact, EFL_T occurs commonly in COPD patients (mainly in GOLD III and IV stage) in whom the latter symptoms are common. The existing up-to-date physiological methods for assessing expiratory flow limitation (EFL_T) are reviewed in the present work. Among the currently available techniques, the negative expiratory pressure (NEP) has been validated in a wide variety of settings and disorders. Consequently, it should be regarded as a simple, non invasive, most practical, and accurate new technique.

Regional pulmonary perfusion, inflation, and ventilation defects in bronchoconstricted patients with asthma

RATIONALE

Bronchoconstriction in asthma leads to heterogeneous ventilation and the formation of large and contiguous ventilation defects in the lungs. However, the regional adaptations of pulmonary perfusion (Q) to such ventilation defects have not been well studied.

METHODS

We used positron emission tomography to assess the intrapulmonary kinetics of intravenously infused tracer nitrogen-13 ((13)NN), and measured the regional distributions of ventilation and perfusion in 11 patients with mild asthma. For each subject, the regional washout kinetics of (13)NN before and during methacholine-induced bronchoconstriction were analyzed. Two regions of interest (ROIs) were defined: one over a spatially contiguous area of high tracer retention (TR) during bronchoconstriction and a second one covering an area of similar size, showing minimal tracer retention (NR).

RESULTS

Both ROIs demonstrated heterogeneous washout kinetics, which could be described by a two-compartment model with fast and slow washout rates. We found a systematic reduction in regional Q to the TR ROI during bronchoconstriction and a variable and nonsignificant change in relative Q for NR regions. The reduction in regional Q was associated with an increase in regional gas content of the TR ROI, but its magnitude was greater than that anticipated solely by the change in regional lung inflation.

CONCLUSION

During methacholine-induced bronchoconstriction, perfusion to ventilation defects are systematically reduced by a relative increase in regional pulmonary vascular resistance.