Effect of electronic compensation on plethysmographic airway resistance measurements.
OBJECTIVE
To compare the performance of a plethysmograph which incorporated electronic compensation (Jaeger) to one which incorporated a heated humidified breathing system (Hammersmith plethysmograph).


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


METHODS
In vitro and in vivo comparison.


METHODS
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).


CONCLUSIONS
These results suggest plethysmographs which incorporate electronic compensation may be inappropriate for use in infants and very young children.
Division of Asthma, Allergy and Lung Biology, King's College London-MRC Asthma Centre, London, United Kingdom.
Simon
S
Broughton
Gerrard F
GF
Rafferty
Anthony D
AD
Milner
Anne
A
Greenough
D000402:Airway Obstruction / Q000175:diagnosis*; D000403:Airway Resistance / Q000502:physiology*; D004582:Electronics, Medical; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007223:Infant; D008297:Male; D010993:Plethysmography, Whole Body / Q000295:instrumentation* / Q000379:methods*