Reduction of motion artefacts during paediatric/infant apnoea monitoring

APNOEA IS generally agreed to be the cessation of airflow for more than 20 s (POTSlC, 1989; GUILLEMINAULT et al., 1975), and it has been reported to occur in 30-95% of premature infants during sleep (BOUTERLnVE-YOUNG and SMITH, 1950). It has been proposed that this may be due to 'a failure to respond to the metabolic and mechanical stress imposed by the first experience with nasopharyngitis, or a dysfunction of the autonomic nervous system due to a transient anatomic or functional defect of the neuron or a temporary deficiency of a metabolite or neurotransmitter' (KELLY and SHANNON, 1979). Such vulnerabilities decrease with age (KELLY et al., 1978). Owing to the possible connection between sleep apnoea and Sudden Infant Death Syndrome (SIDS), infants believed to be at risk of SIDS are monitored for apnoeic episodes. As instances of bradycardia are common in central apnoea ('WARBURTON et aL, 1977; KULKARa, 1991; SAHAKIAN et aL, 1985), a combination of impedance pneumography and electrocardiography is the most commonly used acquisition system for apnoea detection (SAHAKL~ et al., 1985). Impedance pneumography, however, is prone to several problems including susceptibility to false breath detections due to the subject's motion artefacts, difficulty in detecting obstructive apnoea, changes in intrathoracic blood volume and venous return (which cause changes in the thoracic impedance), and cardiogenic artifacts (WARBURTON et al., 1977; NnacDc, 1987; UPTON et aL, 1990; JEFFERY et al., 1981). Movement artefacts, cardiogenic artefacts or breathing efforts during obstructive apnoea can cause fluctuations in the chest wall impedance that may resemble ventilatory fluctuations, and thus may be mistaken for ventilation. Although some attention has focused on breath-detection algorithms, much less attention has focused on the types of electrodes. Most electrodes used for ventilation monitoring were designed for ECG monitoring. Thus determining which factors are beneficial for ventilation monitoring may improve electrode design for apnoea monitoring, thereby improving impedance pneumography. Previous studies have shown that electrodes with good stability, strong adhesion, low face-to-face impedance, low transthoracic-plus-electrode impedance and a large effective