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1 Department of Biomedical Engineering, Boston University, Boston, MA, USA
2 Pulmonary Division, Brigham and Women's Hospital, Boston, MA, USA
* To whom correspondence should be addressed. E-mail: klutch{at}bu.edu.
Measures of airway resistance (Raw) during a deep inspiration (DI) suggest that the asthmatics possess stiffer, more reactive airway smooth muscle. There is evidence that one can enhance airway reactivity in healthy lungs by prohibiting a DI for an extended period. The current study had two goals. First, we determined if the maximum dilation capacity of asthmatics depended on the rate of the DI. Second, we investigated whether the enhanced reactivity in healthy humans might derive from additional mechanisms not present in asthmatics. For the first goal we tracked Raw in seven healthy and seven asthmatic subjects during a non-coached DI, a DI with a 5-10 sec breathhold at TLC and a rapid DI. We found that the minimum resistance (Rmin) achieved at TLC was independent of the manner in which the DI was performed. For the second goal we tracked the rate of return of Raw after a DI as well as the dynamic lung elastance (EL) before and after the DI, at baseline and after bronchial challenge. A drop in EL post DI would be indicative of reopening of lung regions and/or reduced heterogeneities. The data show that constricted healthy but not asthmatic subjects produce longer lasting residual dilation. Hence, a portion of the enhanced reactivity in healthy subjects response to prohibition of DIs is likely due to airway closure and/or atelectasis that can be ablated with a DI. We conclude that preventing DIs does not insure that healthy subjects will transition entirely to an asthmatic-like hyper-reactive lung state.
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