Presented at the Neonatal Society 2001 Autumn Meeting.
Primhak RA1, Jackson MJ1, Milnes P2, Smallwood R2, Brown BH2
1 Departments of Child Health, University of Sheffield Children’s Hospital, Sheffield, S10 2TH
2 Medical Physics, University of Sheffield Children’s Hospital, Sheffield, S10 2TH
Background/Aims: We have previously shown that electrical impedance tomographic spectroscopy (EITS) using 16 electrodes can be used to image neonatal lungs and that neonatal lungs differ from adult lungs in their impedance spectra1. The current study used an 8-electrode system to verify the differences between neonatal and adult lungs, and to look at changes in the first 3 years of life.
Methods: A Mark 3.5 Sheffield 8-electrode EITS system was used to study 17 stable preterm neonates, 42 healthy subjects aged 6 hours to 36 months and 10 healthy adults. Data were collected at 25 frames per second at 30 frequencies from 2 kHz to 1.6 MHz. Four 1 minute epochs of tidal breathing were collected. Total thoracic and individual lung impedance and the frequency spectra of lung impedance were measured. An adult lung model developed by Nopp2 was modified using current knowledge of neonatal lung morphology and data from CT images of a healthy infant.
Results: The mean impedivity of the lung, corrected for chest circumference, was approximately three times higher in the adults than in the neonates. 75% of this increase occurred in the first year of life. The differences in frequency spectra observed in neonatal and adult lungs correspond to those predicted by the model (Figure).
Conclusions: Impedance changes are likely to reflect morphological changes in lung architecture, in particular the alveolarisation of lung, and the changes in air-tissue ratio. A functional electrical model raises the possibility of estimating alveolar size and number in individual patients.
References
1. Smallwood et al. Physiological Measurement 1999;20:401-13
2. Nopp et al. Med & Biol. Eng & Comp 1997;35, 695-702