Airway and Tissue Resistance in Wheezy Infants

Abstract

We partitioned total respiratory system resistance into airway (Raw) and tissue (Rti) resistance in 16 sedated infants (age 15 to 88 wk) with a history of wheezing disorders before and after inhalation of albuterol. Using systems identification methods, airway (Raw-z) and tissue resistance (Rti-z) were extracted from measurements of respiratory system transfer impedance (Ztr[omega]) over a wide frequency range (typically, 4 < f < 140 Hz). Baseline Raw-z (80.6 +/- 31.5 cm H(2)O/L/s) was significantly (p < 0.01) reduced after albuterol inhalation (60.6 +/- 22.2 cm H(2)O/L/s) but pre- and postalbuterol Rti-z were not significantly different (2.3 +/- 1.7 and 2.7 +/- 2.4 cm H(2)O/L/s, respectively). Raw-z was compared with airway resistance measured with whole-body plethysmography (Raw-p) in 10 of the 16 infants. Raw-z and Raw-p were significantly different in baseline as well as postalbuterol conditions (86.4 +/- 36.9 versus 19.0 +/- 7.0, and 60.6 +/- 22.0 versus 22.5 +/- 14.7, respectively) and they were not correlated. There was no significant difference between Raw-p under baseline and postalbuterol conditions. We conclude that airway resistance estimated from Ztr measurements comprises the major portion of total resistance (approximately 97%) in infants with wheezing disorders in baseline as well as post-beta agonist inhalation, and it is significantly reduced by albuterol inhalation.

Combined body plethysmographic, spirometric and flow volume reference values for male and female children aged 6 to 16 years obtained from "hospital normals"

“…Since¯ows are lower and more variable in children, the assessment of R e measured at every sample point of the resistance loop by computerised analysis is more accurate than the assessment of R tot measured at the peak pressure points [15,17] and may be preferred. It is now more often used also in adults and even in infants [9]. …”

Is forced oscillation technique the next respiratory function test of choice in childhood asthma

“…The reported Rrs variable includes, in the same measurement, the Rrs of the airway, that of the chest wall, and that of the lung tissue. As airway Rrs dominates Rrs in the mid frequencies[ 26 ], it can be considered a surrogate of airway resistance[ 27 , 28 ]. As frequency decreases to below approximately 4 Hz Rrs will increasing include peripheral respiratory resistance and be reflective of the peripheral airways and the lung.…”

Standards for infant respiratory function testing:what(ever) next?

“…Inevitably, in the time available it has not been possible to tackle all current tests, nor the specialized circumstances in which they may be applied. Thus considerable further work is still required to produce similar standards for oesophageal manometry [18], forced expiratory manoeuvres from raised lung volumes [19–25], oscillation mechanics [26–33] and ventilation inhomogeneity [30, 34]. Similarly, guidelines still need to be produced with respect to the use of these measurements in clinical trials, on the intensive care unit and when assessing bronchial responsiveness in infants and young children.…”