Development of a Respiratory Inductive Plethysmography Module Supporting Multiple Sensors for Wearable Systems

Abstract

In this paper, we present an RIP module with the features of supporting multiple inductive sensors, no variable frequency LC oscillator, low power consumption, and automatic gain adjustment for each channel. Based on the method of inductance measurement without using a variable frequency LC oscillator, we further integrate pulse amplitude modulation and time division multiplexing scheme into a module to support multiple RIP sensors. All inductive sensors are excited by a high-frequency electric current periodically and momentarily, and the inductance of each sensor is measured during the time when the electric current is fed to it. To improve the amplitude response of the RIP sensors, we optimize the sensing unit with a matching capacitor parallel with each RIP sensor forming a frequency selection filter. Performance tests on the linearity of the output with cross-sectional area and the accuracy of respiratory volume estimation demonstrate good linearity and accurate lung volume estimation. Power consumption of this new RIP module with two sensors is very low. The performance of respiration measurement during movement is also evaluated. This RIP module is especially desirable for wearable systems with multiple RIP sensors for long-term respiration monitoring.

Wearable Sensors

“…5.09.4.1.1.1 Inductive plethysmography (Adams, 1996;Milledge and Stott, 1977;Wu et al, 2009;Zhang et al, 2012) An RIP consists of two sinusoidal wire coils insulated and placed within two 2.5 cm (about 1 inch) wide, lightweight, elastic, and adhesive bands. The transducer bands are placed one around the rib cage under the armpits and the other around the abdomen at the level of the umbilicus.…”

Recycling cardiogenic artifacts in impedance pneumography

“…Cardiogenic artifacts come from the blood volume movement in the thorax [1] and may mask the physiological information in which we have interest. Examples of measurements in which cardiogenic artifacts may be observed include the impedance pneumography (IP) [5,12,25], the respiratory inductive plethysmography (RIP) [30], thoracic or abdominal movements recorded via piezo-electric band [10], the capnogram [20], the electroencephalogram [24] and the esophageal pressure signal [18]. Published algorithms intended for clinical deployment have focused on removing cardiogenic artifacts using techniques such as digital filtering [15,26], adaptive filtering [12,29], template subtraction via the electrocardiogram [18,19], the synchrosqueezing transform [11], or blind source separation [24].…”

A Wearable Contactless Sensor Suitable for Continuous Simultaneous Monitoring of Respiration and Cardiac Activity

“…For this reason, a number of sensors suitable for respiration pattern monitoring during sleep have been reported. Some of these sensors require skin contact (e.g., systems that utilize electrodes like impedance plethysmography), while others are based on calibrated displacement sensors or inductive sensors that are embedded in tightly fitted jackets/garments (e.g., inductive plethysmography and strain-gauge plethysmography) [3][4][5][6][7][8][9][10][11].…”

“…Inductive and strain-gauge plethysmography systems allow easy detection of breathing pattern disruption and are commonly employed as part of more complex "sleep disorders" monitoring systems [11,12]. Respiratory effort is an important measurement particularly during sleep as the differences in phase between chest and abdomen movements during respiration (or attempted respiration) are linked to obstructive apnoea and other sleep disorders [1,11,13,14].…”