Abstract
Introduction: MBNW requires little cooperation beyond steady breathing, but some subjects (eg. children) may breathe irregularly. Historical studies examining the effect of changing respiratory rate and depth on ventilation distribution indices1,2 have contradictory findings. We aimed to examine the impact of rate and depth of breathing on Lung Clearance Index (LCI), and 2 indices of ventilation inhomogeneity (Scond and Sacin).
Methods: Each subject performed at least 3 MBNW tests at each of 3 breathing patterns (BP). A visual signal provided a frequency target and an auditory signal guided tidal volume (Vt). We compared mean LCI, Scond and Sacin between the different BP using repeated measures ANOVA. Sensitivity analyses were performed with and without outliers for validation.
Results: We studied 19 healthy adults but excluded 2 for technical reasons. There were significant differences in LCI and Sacin with BP (p<0.01), but no significant differences in Scond (p=0.117). Increasing Vt from 0.6 to 1.0L reduced LCI and Sacin. Increasing frequency from 15 to 30bpm increased LCI and Sacin.
Discussion: We confirmed an earlier report on 4 adults that increasing Vt reduces ventilation inhomogeneity within acinar airways1; in contrast we found no effect on Scond. Frequency also influenced some indices of ventilatory homogeneity. We recommend that both Vt and frequency are controlled.
(1)Crawford A et al1986.RespirPhysiol;66(1):11-25.
(2)Bouhuys AA et al1961.JApplPhysiol;16:I039-I042.
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