Evaluation of Ultrasound-Based Sensor to Monitor Respiratory and Nonrespiratory Movement and Timing in Infants

Abstract

Goal To describe and validate a non-contacting sensor that used reflected ultrasound to separately monitor respiratory, non-respiratory, and caretaker movements of infants. Methods An In-Phase and Quadrature (I&Q) detection scheme provided adequate bandwidth, in conjunction with post-detection filtering, to separate the 3 types of movement. The respiratory output was validated by comparing it to the electrical activity of the diaphragm (Edi) obtained from an infant ventilator in 11 infants. The non-respiratory movement output was compared to movement detected by miniature accelerometers attached to the wrists, ankles, and heads of 7 additional infants. Caretaker movement was compared to visual observations annotated in the recordings. Results The respiratory rate determined by the sensor was equivalent to that from the Edi signal. The sensor could detect the onset of inspiration significantly earlier than the Edi signal (23+/−69ms). Non-respiratory movement was identified with an agreement of 0.9 with the accelerometers. It potentially interfered with the respiratory output an average of 4.7+/− 4.5% and 14.9+/1 15% of the time in infants not requiring or on ventilatory support, respectively. Caretaker movements were identified with 98% sensitivity and specificity. The sensor outputs were independent of body coverings or position. Conclusion This single, non-contacting sensor can independently quantify these three types of movement. Significance It is feasible to use the sensor as trigger for synchronizing mechanical ventilators to spontaneous breathing, to quantify overall movement, to determine sleep state, to detect seizures, and to document the amount and effects of caretaker activity in infants.

Contactless Mapping of Thoracic and Abdominal Movements: Applications for Seismocardiography

“…The first patents for non-contact measurement of body movement with ultrasound were filed in the 70s. More recently, a team described and validated a single channel, non-contacting ultrasound-based sensor for respiratory, non-respiratory, and caretaker movement of infants in an intensive care [8]. The technical capability for high frequency acoustical 3D surface vibrometry only starts to develop recently [9][10].…”

A System for Monitoring Breathing Activity Using an Ultrasonic Radar Detection with Low Power Consumption

“…For showing the advantages of the current study over the existing literature, we have compared the correlation coefficient of the proposed system with the most relevant literature [27,35,36] when the subjects were fully-clothed. At a distance of 0.5-1 m, the proposed system had a correlation coefficient of 0.96 in comparison with 0.93 [35], 0.93 [36], and 0.9063 [27]. Although the results obtained in this study have verified the effectiveness and accuracy of the ultrasonic radar detection to extract the abnormal breathing syndromes at different distances up to 3 m, it also has some limitations.…”

“…There have been several attempts to devise direct and indirect techniques to monitor breathing activity while minimizing discomfort. These techniques include direct contact such as magnetic induction [14][15][16][17], microphone [18,19], and capacitive [20][21][22][23], and indirect contact (contactless) such as electromagnetic radar detection [24][25][26][27][28][29], laser radar detection [30][31][32][33], ultrasonic radar detection [10,[34][35][36][37], thermographic imaging [38][39][40][41][42][43], and video camera imaging [44][45][46][47][48][49][50]. Each of these techniques, however, requires different process monitoring and has benefits and drawbacks that may make it more or less appealing to use under different circumstances as discussed in reference [51].…”

“…The limitations include that the system was somewhat limited to an unclear region of interest in the case of the presence of a cannula or breathing mask and the low signal to noise ratio when the distance to the subject increased. Respiratory and non-respiratory movement was also detected wirelessly using an ultrasonic sensor by Heldt et al [36]. The sensor head was placed at a distance of 0.15-0.5 m above the subject (infant) and was focused on the sound signal from the thoracic region.…”

A low-power thermal-based sensor system for low air flow detection

“…This rapidly increasing trend in the use of air flow sensing systems is being dictated by the sensor type, power consumption, linearity, and form factor of the system. The several types of sensors being utilized for low air flow measurements can be broadly categorized as thermistors thermopiles [1], pyroelectric elements [2], pn junctions [3], intensity modulated fiber optic [4], ultrasound based [5], micro-electro-mechanical systems based [6], capacitive based [7]–[8], electromagnet based [9]–[10], resonating microbridges [11] and prandtl tubes [12] among others. One category of air flow sensor uses an indirect measurement such as the air temperature [13], volume or pressure [14] to determine the air flow.…”