Development of an apnea detector for neonates using diaphragmatic surface electromyography.

Respiratory diseases are among the most important and serious conditions that can affect the newborn baby. A cessation of breathing, longer than 15 seconds, or accompanied by hypoxia or bradycardia, is called apnea of prematurity (AOP) and has been found in more than 50% of premature infants. An apnea detector used in infant monitoring has been designed and constructed and is intended to be applied in a clinical environment. Diaphragmatic surface EMG has been used as the technique for detecting apnea episodes due to a direct relation with the respiratory drive. Both obstructive and central apnea can be determined as well as heart rate. Good performance and feasibility have been shown by the prototype.

Descending aortic flow contribution to intrathoracic impedance-development and preliminary testing of a dual impedance model.

OBJECTIVE: Impedance measurement of cardiac output has struggled to become established partly because there have been only a few attempts to establish a sound theoretical basis for this measurement. Our objective is to demonstrate that there is valuable aortic flow information available from an intrathoracic impedance signal which may eventually be useful in the measurement of cardiac output by impedance technology. METHODS: A model, using dual impedance measurement electrodes and the change in impedance when blood flows, has been developed based on an intrathoracic impedance model of the descending aorta and esophagus. Using this model as the basis for measurement by an esophageal probe, we provide solutions to the velocity of blood flow in the descending aorta. RESULTS: Five patients were studied. Only three patients had suitable signals for analysis but the aortic flow profiles from these three patients were consistent and realistic. CONCLUSION: Aortic blood flow information may be obtained from the intrathoracic impedance signal using this dual impedance method.

A probe for organ impedance measurement.

In this paper, we describe the theory and practical implementation of an electrical impedance probe for making in vivo measurements of the electrical admittance of living tissue. The probe uses concentric annular electrodes and is shown to sample a more localized, yet greater, volume of tissue than the standard four-electrode probe. We have developed a mathematical model for the conduction of current between the probe electrodes assuming that we are investigating a uniform, isotropic, semi-infinite region and taking into account the contact impedance between the electrodes and the organ. The electric fields produced by the probe have been calculated by solving a weakly singular Fredholm integral equation of the second kind. The size and position of the probe electrodes have been optimized to maximize both the accuracy in the admittance measurement and insensitivity to contact impedance. A probe and driving hardware have been constructed and experimental results are provided showing the accuracy of admittance measurements at 50 and 640 KHz.