We measured in 130 (61 girls) children aged 3--14 yr respiratory resistance (Rrs), with the oscillation technique, between 4 and 9 Hz. Rrs, at both 4 and 9 Hz, decreased as a function of height (r = 0.74, P less than 0.001). No statistical difference was found between boys and girls. Frequency dependence of resistance (Rrs 4 Hz-Rrs 9 Hz) was found in children at all ages, and decreased with increasing height (r = 0.50, P less than 0.001). We suggest that frequency dependence of resistance in children can be explained on the basis of an increased peripheral resistance, which produces an asynchronous distribution of tidal volume between dead space and lung parenchyma. During growth peripheral resistance decreases and Rrs bcome less frequency dependent to reach at about 15--16 yr independency of frequence.

Movements of the suprasternal fossa during spontaneous breathing monitored with the surface inductive plethysmograph (SIP) have been shown to reflect changes of intrapleural pressure in conscious humans. Calibration of this device in anesthetized intubated dogs was accomplished by adjusting the electrical gain of its analog waveform to be equivalent to changes of airway pressure during inspiratory efforts against an occluded airway. This procedure, denoted the occlusion test, was also used to identify the site of esophageal balloon catheter placement for its recording of intrapleural pressure deflections. The validity of SIP-derived estimates of inspiratory and expiratory pulmonary resistances and lung compliance was established by finding close agreement with measurements obtained with intraesophageal pressure changes during 1) unimpeded spontaneous breathing, 2) inspiratory resistive loading, 3) bronchoprovocation with aerosolized carbachol, 4) mechanical ventilatory modalities, and 5) induced pulmonary edema. Therefore, movements of the suprasternal fossa with respiration can be reliably transformed into quantitative or semiquantitative changes of intrapleural pressure in anesthetized intubated dogs during major alterations of pulmonary mechanics.

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