RESUMO
BACKGROUND: Magnetic induction measurement (MIM) allows the identification of resistance in biologic tissues by alternating magnetic fields. These occur when well-conducting (blood) and poor-conducting matter (air) is moved through the thorax during heart and lung activity. As a result, allocation of the resistance changes and the total resistance of the thorax is shifted. By using coils, these changes can be registered in a non-contact manner and recorded. To date, this measuring principle was employed only in adult volunteers or in full-grown pigs. A neonatal animal model has not yet been described. The aim of this study was to test the hypothesis that non-contact monitoring of heart and lung activity using MIM in a porcine newborn piglet model can be applied in order to evaluate neonatal disorders of heart and lung activity in the future. MATERIALS AND METHODS: By using five coils (three measurement and two excitation coils), placed at the bottom of an experimental incubator, magnetic induction changes, depending on the heart and lung activity in 16 analgosedated piglets, were simultaneously measured and compared with pulse oximetry and airflow detection (flow resistance and pressure differential sensor) as reference signals. In addition, spontaneous breathing, including apnea, CPAP (continuous positive airway pressure to prevent end-expiratory alveolar collapse, flow 8 l/min; pressure 5 cm H(2)O), mechanical ventilation (inspiratory pressure 14 cm H(2)O; frequency 40/min) and high frequency oxygenation ventilation (HFOV, ventilation method in lung failure) (frequency 10 Hz, mean pressure 10 cm H(2)O, amplitude 1.5) were performed. Lung activity with MIM compared with the reference signal was estimated with a detection rate (%) of "correct registered lung activity". To quantify the analogy between MIM and reference signal for heart activity, the concordance correlation coefficient after Lin (95% confidence interval) and the Bland-Altman plot were calculated. RESULTS AND DISCUSSION: The detection rate for breathing [%] of MIM compared with the reference signal under CPAP was 88% [95% CI: (87.1%; 88.5%)], mechanical ventilation 91% [95% CI: (90.3%; 91.2%)] and under HFOV 95% [95% CI: (94.7%; 94.9%)]. For heart activity, during apnea the difference between MIM and reference signal was 1.1 bpm (+/-11.3 SD) in apnea and during HFOV 5.3 bpm (+/-26.4 SD). Under spontaneous breathing it was not possible to achieve a correlation. Owing to interference problems, registration of heart activity with MIM during simultaneous breathing activity (CPAP, conventional mechanical ventilation, HFOV) was insufficient. CONCLUSION: Non-contact monitoring of lung activity using MIM in a neonatal piglet model is possible under specific conditions. These results might be a basis for the development of non-invasive parameters in neonatology. It also provides the possibility of obtaining more information about the characteristics of lung activity of the newborn.
