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Title: The measurement of lung mechanics during neonatal intensive care
Author: Thomson, Anne H.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1986
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The aim of this thesis was to establish methods of measuring the mechanical properties of the respiratory system in small infants while they were being ventilated in the intensive care unit. A double pneumotachograph system which fitted in the ventilator bias flow-circuit was used to measure flow, overcoming the problems of adding resistance or dead space to the infant's breathing circuit. Two methods for measuring compliance in infants (< 1500 g) breathing spontaneously through endotracheal tubes were assessed. The traditional measurement of dynamic lung compliance (Cdyn) using oesophageal pressue was compared with a technique for measuring total respiratory compliance (Crs) based on the utilisation of the Hering-Breuer reflex (Olinsky 1976) and using airway pressure. Values of Cdyn were poorly reproducible and correlated poorly with Crs and this was due to variability and inaccuracy of oesophageal pressure measurement in infants with chest wall distortion. Total respiratory compliance was reliably measured in intubated infants both when breathing spontaneously and when fully ventilated. Another approach based on the passive expiratory flow-volume relationship (Zin 1982) was developed for use in ventilated infants. The expiratory time constant (Trs) was measured and total respiratory resistance (Rrs) calculated from the relationship Trs = Rrs.Crs. This technique was validated by adding resistive loads and deriving new volumes for Rrs from the altered Trs. The first measurements of the time constant and respiratory resistance of preterm infants during the acute stage of illness were made using this technique. Representative mean values from 12 infants < 1500 g with hyaline membrane disease were Crs = 0.41 ml.cmH2O-1; Trs = 0.073 s; Rrs = 219 cmH2O.ℓ-1.s. A computerised technique was developed to enable these measurements to be made at the cotside. This provided a preliminary model for a lung function monitor to assess mechanical lung function continuously during neonatal ventilation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Medicine