Performance of impedance and inductance ventilation sensors on premature infants during natural breathing, motion, and airway obstruction

We measured ventilation from infants by impedance plethysmography (IP) and respiratory inductance plethysmography (RIP) on the ribcage (re) and abdomen (abd) in order to characterize sensor performance during unrestrained sleep. We recorded airflow using a pneumotachometer (PT) attached to a standard infant mask gently sealed over the face. For each subject, we recorded spontaneous respiratory activity for one hour, and occluded the PT three times for approximately 5 s to simulate obstructive apnea. We determined the error between sensor estimates of breath amplitude and PT measurements of tidal volume during quiet breathing, motion, apnea and simulated airway obstruction. For the thirteen infants studied, no other individual sensors resulted in lower bias (mean error) or limits of agreement (bias±2SD of errors) than IP(rc). IP(rc) measurements of tidal volume during quiet breathing of 10.0 ml had a mean bias of 0.8 ml, with limits of agreement from -5.6 to 7.2 ml. During motion, spontaneous apnea and airway obstruction, the IP(rc) bias increased to 7.6±8.4, 4.8±4.2, and 7.6±4.2 ml (mean±2SD), respectively. The combination of RlP(abd) and RlP(rc) was not significantly more accurate than IP(rc). IP(rc) measurements obtained at 35 kHz and 185 kHz appeared similar, and IP(abd) measurements were the most unreliable.