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.

A humidifier system for neonatology that functions according to the 'membrane humidification' principle was subjected to a performance test in our laboratory. Humidification and heating of the respiratory gases took place in a module consisting of a net of hollow fibres placed inside the incubator. In 18 measurement combinations flow, respiratory gas temperature, and incubator temperature were varied. At respiratory gas temperatures within the range of 33-37°C the minimum international standard for the absolute air humidity in the respiratory gas was saturation. The module should be installed inside the incubator in order to keep a possible temperature drop along the tubing path to the patient as low as possible and so avoid formation of condensation. In addition, the membrane serves as a bacterial filter. The inspiratory gas temperature is measured near to the patient (20 cm from the Y piece), by means of a sensor, and is adjusted to the set temperature by servocontrol. There is an automatic cut-out mechanism to reduce the risk of exposure to dangerously high inspiratory gas temperature and an alarm in case of low inspired gas temperature and inadequate function of the pump. Methods of measurementThe respiratory gas temperature was measured by means of thermoelements (NiCr-Ni: Impac Tastotherm D 700). We recorded the deviations between set temperature and inspiratory gas temperature near the endotracheal tube (6 cm from the Y piece). In addition, the air temperature drop inside the inspiratory tubing system was measured at two different points (20 and 6 cm from the Y piece). The relative air humidity near the endotracheal tube was measured in the inspiratory circuit at a distance of 3 cm from the Y piece by means of a capacitive measurement technique (Rotronic Hygroskop DT). The thermoelements and the capacitive sensors are not supplied with the commercial humidification system. The absolute air humidity was calculated from the respiratory gas temperatures and the relative humidity.The measurements were carried out at different ambient temperatures inside the incubator (33, 35, 37°C). The set flow of the ventilator was modified: 2, 6, and 16 1/minute.The setpoint temperature of the humidifier was 34 and 37°C. After modification of these parameters and a period of 15 minutes for stabilisation the measurements were carried on for a time of 60 minutes for each combination of temperatures and gas flow. The average of two measurements of inspiratory gas temperatures and relative humidity during this plateau phase were calculated. The ventilator circuit was connected to an artificial lung (volume 50 ml) inside the incubator. The measurements were performed in a single wall incubator at a room temperature of about 26°C. Ventilator parameters (Drager Babylog 1) were: frequency 45/minute, inspiratory: expiratory ratio 1:2, peak pressure 20 mm Hg, positive and expiratory pressure 4 mm Hg. The results were recorded simultaneously on a recording instrument (BBC Goerz Metrawatt SE 460). Results RELATIVE AIR HUMIDI...

No controlled clinical tests regarding the importance and long term effects of different levels in the inspiratory air are so far available for the ventilatory treatment of neonates.

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