A maturational model for the study of airway smooth muscle adaptation to mechanical oscillation

Superimposed pressure oscillations: An alternative to treat airway hyperresponsiveness in an acute sensitized airways mouse model

The main driving mechanism during an asthma attack is the hyper-constrictions of airway smooth muscle (ASM), which reduces the airway lumen and makes normal breathing difficult. In spite of some noticeable side effects, bronchodilator drugs such as salbutamol are used to alleviate these symptoms by inducing temporary relaxation of the contracted ASM. In vitro studies have shown that mechanical oscillation can induce relaxation in isolated contracted ASM obtained from healthy subjects but not from asthmatics. To date, little is known about in vivo ASM behaviours, in particular in asthmatic subjects. This in vivo study aims at determining the effect of various superimposed pressure oscillation (SIPO) patterns (different to those occurring during normal breathing) on sensitized airways during an ACh challenge (mimicking an asthmatic attack) and comparing it with the effect of a widely studied broncho-relaxant drug, Isoproterenol (ISO). The study shows that superimposed pressure oscillation in the range of 5-15Hz induces approximately 50% relaxation on pre-constricted sensitized airways in vivo; however, this behaviour was not observed at 20Hz. Our finding suggests that mechanical oscillation, particularly SIPO, may act as a bronchodilator and achieve ASM relaxation.

The relation between age and time to maximal bronchoconstriction following exercise in children

BACKGROUND

The exercise challenge test (ECT) is a common tool for assessment of asthma in children. Many studies suggest that the "time to maximal bronchoconstriction" (Nadir-t) after exercise challenge in asthmatic children may be age-dependent, although this has never been systematically studied. Such findings may influence epidemiological surveys where the schedule of post-exercise measurements is trimmed. This study systematically assesses the relation between age and time to maximal bronchoconstriction post-ECT.

METHODS

Data were collected retrospectively from 131 subjects (87 male; 3-18 years) who were referred for ECT. The routine ECT was performed according to ATS recommendation of a 6-min run. Spirometry was measured at 1, 3, 5, 10, 15, and 20 min post-exercise. The post-exercise nadir of FEV1 (%baseline) (FEV1-nadir) and the time to maximal fall in Nadir-t (minutes) were sought and values were related to age.

RESULTS

Baseline FEV1 values (mean+/-SD) were 90.5+/-13.8% predicted. FEV1-nadir was -23.6+/-11.7% from baseline values. The Nadir-t was reached at 5.1+/-2.6 min (range 2-12 min). A positive correlation between children's age and Nadir-t was observed (r2=0.542; SD of residuals=1.79; p<0.001), regardless of FEV1-nadir, whether the cutoff of point was -10% or -15% of baseline FEV1. Children <10 years of age showed Nadir-t at 3.4+/-1.7 min post-exercise and older children at 6.6+/-2.5 min post-exercise (p<0.0001).

CONCLUSION

Our results indicate that the time to maximal bronchoconstriction is age-dependent in children and adolescents, and imply that the schedule of post-exercise FEV(1) measurements should be cautiously trimmed.