Airway resistance estimation by best fit analysis in very premature infants

Abstract

Plethysmographic measurement of airway resistance (R(aw)) has been determined by single-point analysis, usually at 50% of maximum inspiratory flow (MIF). Computer-assisted (best fit) analysis, however, allows R(aw) to be calculated by applying a regression line to any portion of the plethysmograph pressure-flow loop. We determined whether the results of best fit analysis using a computer program, sampling at 200 Hz, were influenced by the portion of the inspiratory loop analysed and if best fit or single-point analysis gave more reproducible results. Twenty infants of median gestational age 26 (range 24-28) weeks, were studied at a median age of 12 (12-14) months corrected for prematurity. R(aw) was calculated by best fit analysis between 0 and 33% MIF, 0 and 50% MIF and 0 and 67% MIF and single-point analysis at 50% of MIF. Similar mean R(aw) values were obtained by best fit analysis between 0 and 33% MIF (2.79 kPa/(l/s)) and 0 and 50% MIF (3.01 kPa/(l/s)) and single-point analysis at 50% MIF (2.86 kPa/(l/s)), but best fit analysis between 0 and 67% gave higher results (3.60 kPa/(l/s)), p < 0.0001. Within the linear portion of the inspiratory loop, the mean intrasubject coefficient of variation was lowest for best fit analysis between 0 and 50% MIF. Best fit computerized analysis between 0 and 50% MIF is recommended as the analysis of choice.

Very prematurely born infants wheezing at follow-up: lung function and risk factors

“…Airways resistance (R aw ) was calculated electronically using an established formula by applying a regression line to the selected portion of the loop. R aw was calculated during initial inspiration between 0 and 50% maximal inspiratory flow, and during expiration between 0 and 50% maximal expiratory flow 14. During all R aw measurements, the computer calculated the apparatus resistance of the selected portion of the individual breath by relating ΔP ao to Δflow and then subtracted this value from the total measured resistance.…”

Respiratory function of very prematurely born infants at follow up: influence of sex

“…All channels were calibrated before each patient test, as previously described. 11 FRC pleth was calculated from a minimum of three end inspiratory occlusions. A time based trace of all four data channels and an x/y plot of V pleth /Pao during each occlusion were displayed by the computer.…”

Plethysmograph and interrupter resistance measurements in prematurely born young children

“…Details of the plethysmograph and calibration techniques are given elsewhere. 23 The plethysmograph was sealed, and functional residual capacity (FRC pleth ) measured from a minimum of three end inspiratory occlusions. Raw was then determined from a minimum of five technically acceptable breaths.…”