Boudewijn, I.M. (2012) The role of small airway dysfunction in asymptomatic airway hyperresponsiveness. thesis, Medicine.
Full text available on request.Abstract
Introduction: Airway hyperresponsiveness (AHR) is a hallmark of asthma, but can also be present in healthy subjects without any respiratory symptoms. It is unclear why these asymptomatic subjects with AHR do not experience symptoms. Most studies on asymptomatic AHR have investigated large airways and showed various levels of airway inflammation and remodeling. Thus far, little is known about the role of small airways in asymptomatic AHR. Aim: We assessed whether subjects with asymptomatic AHR have more small airway dysfunction than controls and less small airway dysfunction than asthma patients both at baseline and during a methacholine provocation test. Furthermore, we investigated whether small airway dysfunction during a methacholine provocation test is associated with dyspnea perception. Methods: Methacholine provocation tests were performed in subjects with asymptomatic AHR, asthma patients and controls (n=15 per group). AHR was defined as a provocative concentration of methacholine inducing a 20% fall in FEV1 (PC20) ≤ 8mg/ml. Small airway function was assessed with impulse oscillometry (IOS) before (baseline) and during provocation, by measuring the difference in resistance at 5Hz and 20Hz (R5-R20) and reactance at 5Hz (X5). An increase of R5-R20 and a decrease of X5 reflect small airway dysfunction. Dyspnea perception was assessed with the modified Borg scale. For all IOS variables and the Borg dyspnea score, we calculated the values at PC20. Results: At baseline, small airway function (R5-R20 and X5) was comparable in asymptomatic AHR and controls. Asthma patients had more baseline small airway dysfunction than subjects with asymptomatic AHR, i.e. a higher R5-R20 and lower X5. Large airway parameters, i.e. the resistance at 20Hz (R20) and FEV1, were similar in all groups. During provocation, R5-R20 was lower and X5 was higher in asymptomatic AHR than in asthma. Again, R20 was similar in both groups. An increase in small airway dysfunction at PC20 was significantly associated with an increase in Borg dyspnea score at PC20 in asymptomatic AHR (R5-R20 rs=0.66, X5 rs= -0.64). Conclusion: At baseline, small airway function is comparable in subjects with asymptomatic AHR and in controls, whereas asthma patients have more baseline small airway dysfunction. Also, during provocation, subjects with asymptomatic AHR have less small airway dysfunction than asthma patients. We hypothesize that asymptomatic subjects with AHR experience less symptoms because they have less small airway dysfunction. The latter is supported by the fact that the degree of small airway dysfunction influences dyspnea perception in these subjects.
| Item Type: | Thesis (Thesis) |
|---|---|
| Supervisor name: | Supervisor: and Berge, Dr. M. van den and Department of Pulmonary diseases and University Medical Center Groningen |
| Faculty: | Medical Sciences |
| Date Deposited: | 25 Jun 2020 10:55 |
| Last Modified: | 25 Jun 2020 10:55 |
| URI: | https://umcg.studenttheses.ub.rug.nl/id/eprint/1576 |
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