Airway resistance estimation by best fit analysis in very premature infants

Lung function at follow-up of infants with surgically correctable anomalies

Infants with congenital diaphragmatic hernia (CDH) or anterior wall defects (AWD) can suffer abnormal antenatal lung growth, the risk, however, may be greater for CDH infants. The objectives of this study were to test the hypothesis that following surgical correction, CDH infants would have worse lung function at follow-up than AWD infants and to determine whether fetal lung volume (FLV) results correlated with the lung function results at follow-up. Thirteen infants with CDH and 13 infants with AWD had lung function measurements at a median age of 11 (range 6-24) months; 17 of the infants had had their FLV assessed. Lung function was assessed by plethysmographic measurement of lung volume (FRCpleth) and airway resistance (Raw). In addition, functional residual capacity was assessed by a helium gas dilution technique (FRCHe); tidal breathing parameters (T(PTEF) :Te) and compliance and resistance of the respiratory system (Crs and Rrs, respectively) were also determined. FLV was assessed using three-dimensional (3D) ultrasound and virtual organ computer aided analysis. The CDH compared to the AWD infants had a higher median FRCpleth (41 ml/kg vs. 37 ml/kg, P = 0.043) and a lower median Crs (1.45 ml/cm H(2) O/kg vs. 2.78 ml/cm H(2) O/kg, P = 0.041). FRCpleth results correlated significantly with FLV results (r = 0.721, P < 0.001). In conclusion, infants with CDH had significantly different lung function at follow-up than AWD infants. Our findings suggest FLV results may predict lung function abnormalities at follow-up in infants with surgically correctable anomalies.

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

OBJECTIVES

To determine whether abnormalities of lung volume and/or airway function were associated with wheeze at follow-up in infants born very prematurely and to identify risk factors for wheeze.

DESIGN

Lung function data obtained at 1 year of age were collated from two cohorts of infants recruited into the UKOS and an RSV study, respectively.

SETTING

Infant pulmonary function laboratory.

PATIENTS

111 infants (mean gestational age 26.3 (SD 1.6) weeks).

INTERVENTIONS

Lung function measurements at 1 year of age corrected for gestational age at birth. Diary cards and respiratory questionnaires were completed to document wheeze.

MAIN OUTCOME MEASURES

Functional residual capacity (FRC(pleth) and FRC(He)), airways resistance (R(aw)), FRC(He):FRC(pleth) and tidal breathing parameters (T(PTEF):T(E)).

RESULTS

The 60 infants who wheezed at follow-up had significantly lower mean FRC(He), FRC(He):FRC(pleth) and T(PTEF):T(E), but higher mean R(aw) than the 51 without wheeze. Regression analysis demonstrated that gestational age, length at assessment, family history of atopy and a low FRC(He):FRC(pleth) were significantly associated with wheeze.

CONCLUSIONS

Wheeze at follow-up in very prematurely born infants is associated with gas trapping, suggesting abnormalities of the small airways.

Effect of electronic compensation on plethysmographic airway resistance measurements

OBJECTIVES

To compare the performance of a plethysmograph which incorporated electronic compensation (Jaeger) to one which incorporated a heated humidified breathing system (Hammersmith plethysmograph).

WORKING HYPOTHESIS

The performance of a plethysmograph which incorporated electronic compensation would be impaired compared to that which incorporated a heated humidified system.

STUDY DESIGN

In vitro and in vivo comparison.

PATIENT SELECTION

Eleven children, median postnatal age 13 (range 5-15) months.

METHODS

In vitro, the plethysmographs were assessed using known resistances (1.94, 4.85, and 6.80 kPa, equivalent to 20, 50, and 70 cm H(2)O/L/sec, respectively). In vivo, comparison was made of the results of children studied in both plethysmographs.

RESULTS

In vitro, the resistance results of the two plethysmographs were similar to each other and to the known resistances. In vivo, the median "effective" airways resistance result of the Jaeger (4.15 kPa/L/sec) was significantly higher than the inspiratory resistance of the Hammersmith plethysmograph (3.0 kPa/L/sec), but the median inspiratory resistances of the Jaeger were significantly lower than those of the Hammersmith plethysmograph (2.8 kPa/L/sec vs. 3.0 kPa/L/sec). The mean within patient coefficient of variability for inspiratory resistance of the Jaeger plethysmograph (16.7%) was significantly higher than that of the Hammersmith plethysmograph (11.6%) (P = 0.014).

CONCLUSION

These results suggest plethysmographs which incorporate electronic compensation may be inappropriate for use in infants and very young children.

Plethysmograph and interrupter resistance measurements in prematurely born young children

BACKGROUND

Airways obstruction in premature infants is often assessed by plethysmography, which requires sedation. The interrupter (Rint) technique does not require sedation, but has rarely been examined in children under 2 years of age.

OBJECTIVE

To compare Rint results with plethysmographic measurements of airway resistance (Raw) in prematurely born, young children.

DESIGN

Prospective study.

SETTING

Infant and Paediatric Lung Function Laboratories.

PATIENTS

Thirty children with a median gestational age of 25-29 weeks and median postnatal age of 13 months.

INTERVENTIONS AND MAIN OUTCOME MEASURES

The infants were sedated, airway resistance was measured by total body plethysmography (Raw), and Rint measurements were made using a MicroRint device. Further Raw and Rint measurements were made after salbutamol administration if the children remained asleep.

RESULTS

Baseline measurements of Raw and Rint were obtained from 30 and 26 respectively of the children. Mean baseline Rint values were higher than mean baseline Raw results (3.45 v 2.84 kPa/l/s, p = 0.006). Limits of agreement for the mean difference between Rint and Raw were -1.52 to 2.74 kPa/l/s. Ten infants received salbutamol, after which the mean Rint result was 3.6 kPa/l/s and mean Raw was 3.1 kPa/l/s (limits of agreement -0.28 to 1.44 kPa/l/s).

CONCLUSION

The poor agreement between Rint and Raw results suggests that Rint measurements cannot substitute for plethysmographic measurements in sedated prematurely born infants.

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

OBJECTIVE

To test the hypothesis that male compared with female prematurely born infants would have worse lung function at follow up.

DESIGN

Prospective follow up study.

SETTING

Tertiary neonatal intensive care units

PATIENTS

Seventy six infants, mean (SD) gestational age 26.4 (1.5) weeks, from the United Kingdom oscillation study.

INTERVENTIONS

Lung function measurements at a corrected age of 1 year.

MAIN OUTCOME MEASURES

Airways resistance (Raw) and functional residual capacity (FRC(pleth)) measured by whole body plethysmography, specific conductance (sGaw) calculated from Raw and FRC(pleth), and FRC measured by a helium gas dilution technique (FRC(He)).

RESULTS

The 42 male infants differed significantly from the 34 female infants in having a lower birth weight for gestation, requiring more days of ventilation, and a greater proportion being oxygen dependent at 36 weeks postmenstrual age and discharge. Furthermore, mean Raw and FRC(pleth) were significantly higher and mean sGaw significantly lower. After adjustment for birth and current size differences, the sex differences in FRC(pleth) and sGaw were 15% and 26% respectively and remained significant.

CONCLUSION

Lung function at follow up of prematurely born infants is influenced by sex.

Limitations of electronic compensation for measuring plethysmographic airway resistance in infants

Electronic compensation to overcome thermal artifacts during plethysmographic estimations of airway resistance is now used routinely in adults and school-age children, and was shown to be a valuable means of discriminating airway function between preschool children with and without lung disease. A similar system is now commercially available for infants, which could increase the applicability of this technique. However, we noted marked discrepancies in electronically calculated values of airway resistance in this age group, both with respect to absolute values displayed and marked within-subject variability on a single test occasion. The aim of this technical report is to summarize our recent findings in order to alert other users to potential problems. Airway resistance (R(aw)) was measured in 62 infants (28 with cystic fibrosis (CF); 34 healthy). Three to five epochs of quiet regular tidal breathing were collected in each infant. Marked within-subject, within-test variability was observed, with the median coefficient of variation (CV) being 9.1% (range, 1.2-52.6%) within and 8.5% (0.1-112%) between epochs. Among healthy infants, R(aw) varied from 0.1-6.4 (kPa x liter(-1) x sec), with no relationship to either body or lung size and complete overlap of results with those from infants with CF, despite abnormal lung function in the latter when assessed by other means. The marked within- and between-subject variability in healthy infants, and lack of discriminative power of R(aw) when derived from electronically compensated values, currently preclude application in either clinical or research studies.