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Non-invasive and Unrestrained Monitoring of Human Respiratory System by Sensorized Environment

Abstract

This report describes a living-space-shaped system for non-invasively and unrestrainedly monitoring the human respiratory system and intelligibly reporting its results. This environmental system consists of sensorized furniture: 1) a ceiling dome microphone, 2) a pressure sensor bed, and 3) a washstand display. The ceiling dome microphone consists of a ceiling dome, a lighting fixture, and an omnidirectional microphone. The ceiling dome microphone can detect not only snoring sounds but also normal breathing sounds, i.e., airflow at the mouth and nose. The pressure sensor bed has 210 tactile sensors and can monitor body movement, breath curve and posture. By analyzing the breath curve, the system can estimate oxygen desaturation frequency. By integrating the above functions, for example, the system can find obstructive apnea, which is a typical apnea such that the patient cannot inhale the air despite of breath effort and that the concentration of the oxygen in blood falls. The washstand display can provide information related to the conditions of the respiratory system in the person's daily life. To prove the effectiveness of the integrated system, experiments are conducted for a patient suffering from breath disorder.

Introduction

Daily living space works to enable our lives. Engineering on daily living space enables to improve and augment human support functions in our daily living spaces through analyzing implicit functions based on careful observation of the spaces, characterizing them in an explicit form, clarifying functions to be improved and augmented, realizing the desired functions by engineering components, and finally integrating the realized function into the daily living space in a natural form. Daily personal healthcare support at home is one of the most necessary functions our daily living space should have in a near future. To realize such a function in socially acceptable form, an unrestrained and non-invasive means of observing physiological status is the key technology. This report describes a sensorized environment for non-invasively and unrestrainedly monitoring the human respiratory system. The environment consists of a sensing part for robustly and naturally observing inhabitants, 2) a digital human model for understanding conditions of the human respiratory system from observed data, and 3) a presenting part for letting them utilize understood information.

Non-nvasive and Unrestrained Monitoring by Sensorized Living Space

The human respiratory system is very complex. Therefore, it requires monitoring with many sensors such as pressure sensors to monitor the chest and abdomen's movement, thereto for airflow around the nose and mouth, a contact-type of microphone for snoring, oximeters for oxygen saturation, and mercury sensors for posture(Figure 1 (B)). Since these sensors need to be attached directly to the person, they impose much physiological or mental burden on him or her.

Figure 1: Environment Sensorization

Indeed, the conventional contact-type sensors can monitor physiological values certainly as long as they are used adequately. Actually, however, they very often fail to monitor continuously. For example, in 48 percent of the cases (21 of 43 cases) in the clinical study the authors conducted, the monitoring system failed to measure the physiological values continuously enough to diagnose disease. This suggests that even in a hospital where more priority is given to accurate monitoring than to comfortable monitoring, non-invasive and unrestrained monitoring is required to minimize this failure.

The developed living space, SELF (Sensorized Environment for LiFe) is sensorized as shown in Figure 1. In this study, sensorization meansmaking the room itself a sensor for inputting human daily behavior by embedding sensors into the room invisibly to keep the room's appearance natural and maintain its original function. The figure explains main components of the typical conventional computers are transformed to the room. For example, a keyboard, which is a kind of touch sensor, becomes a bed-shaped touch sensor. A microphone is embedded into a lighting fixture. A display is embedded into a washstand. Figure 1 (C) shows the photograph of the constructed bed room. SELF supports daily healthcare at home as follows: 1) SELF observes a person using the pressure sensor bed and the ceiling dome microphone when he or she goes to bed and sleeps, 2) SELF reports useful information to the person using the washstand display when he or she goes to the washstand typically after waking up or before going to bed.

Environment Sensorization

This section describes a pressure sensor bed and a ceiling dome microphone as an example of the sensorized environment. Sensors are embedded in both systems invisibly.

Pressure sensor bed

The pressure sensor bed consists of a pressure distribution sensor array, a controller, and a bed. The pressure distribution sensor has 210 Force Sensing Resistors (FSRs) which are set at 7[cm] intervals. An FSR is a thin film sensor made from piezoresistive polymer. The sampling frequency of the pressure image is 20 [Hz]. The measuring range of each pressure sensor is 0 to 1[kg]. The pressure sensor bed is used for monitoring the breath curve, oxygen desaturation (*1) frequency, posture, and body movement.

Based on the fact that Cheyne-Stokes-like breathing occur at high probability in oxygen desaturation, the pressure sensor bed can estimate oxygen desaturation frequency by measuring Cheyne-Stokes-like breathing (*2) frequency. Figure 2 compares the frequency of Cheyne-Stokes-like breathing and oxygen desaturation 4%(*3) at an interval of 10 minutes with 3 patients with disease of different seriousness.

Figure 2: Comparison of histogram of Oxygen desaturation 4% (OD4) detected by conventional sensor and Cheyne-Stokes-like breathing detected by pressure sensor bed.

(*1) Oxygen saturation (SpO2) expresses the percentage of oxyhemoglobin molecules to all hemoglobin molecules and is almost 100% in healthy subjects. Oxygen desaturation means the percentage falls for some reasons. Doctors find oxygen saturation monitoring important physiologically to judge whether respiration is normal.

(*2) It is a kind of periodic respiration. The authors defined Cheyne-Stokes-like breathing as the breath with respiration effort without ventilation accompanying gradual increase and gradual decrease, or sudden increase and gradual decrease.

(*3) Oxygen desaturation 4% means oxygen saturation falls 4%. From Figure 2, a high correlation was confirmed between the Cheyne-Stokes index monitored by the pressure sensor bed and oxygen desaturation 4% index.

Ceiling dome microphone

The authors invented the ceiling dome microphone which consists of a ceiling dome, a lighting fixture, and a omnidirectional microphone. This device has two functions: indirect lighting and gathering sound. The ceiling dome is used to reflect both light and sound. A microphone is set at the focal point of the reflector. The diameter of the dome is 900[mm]. The device enables detection not only snoring sounds but also normal breathing sounds with high sensitivity while keeping the room's appearance natural. It is positioned above the bed. The gain obtained by the ceiling dome is maintained at more than 20[dB] for high frequency sounds of more than 6[kHz]. Since the frequency of normal breathing sounds ranges from 5 to 15 [kHz], this device can detect breathing sounds, i.e., air flow at the mouth and nose.

Figure 3 shows an example of breathing sounds detection using the ceiling dome microphone. Room's background noise includes such noises as those of an air conditioner and a computer. The figure shows that both the inhalation and exhalation component of the breath cycle are detected quite clearly.

Figure 3: Detection of normal breathing sounds by ceiling dome microphone.

Understanding Internal Status based on a Model of Human Functions

Human respiratory system

Figure 4 shows physiology and physics of human respiration, and a method for monitoring conditions of the human respiratory system. The human respiratory system deeply relates to brain activity, the circulatory system, respiratory organs such as lung, respiratory muscles such as diaphragm, peripheral organs such as nasal cavity and oral cavity, human posture and so forth as shown in Figure 4 (a). To monitor conditions of the human respiratory system, a model of the respiratory system for estimating the conditions from sensor data is necessary. This section describes the developed model of the human respiratory system and a method of estimating the conditions using the model.

Figure 4: Physiology, physics and measuring method of human respiratory system.

Physiology of human respiratory system

Respiration keeps oxygen and carbon dioxide in body fluids within a constant range. Tidal air is controlled by respiratory muscles such as the diaphragm and intercostals based on the oxygen and carbon dioxide concentration detected by some internal sensors. The sensors exist in carotid body of the common carotid artery and central chemosensitive area of the medulla oblongata. The control of the human respiratory system is shown in Figure 4 (b).

Non-invasive and unrestrained monitoring of human respiratory system

The followings are physiological values that the developed human model can estimate from sensor data. Physics of the human respiratory system and the methods for monitoring these physical values are outlined in Figure 4.

Evaluation of estimation function of SELF

The authors conducted experiments for a real patient suffering from Sleep Apnea Syndrome. Figure 5 compares physiological values measured by a conventional system and that estimated by the developed system. Apnea estimation by our system is done using both a detecting function of snoring sounds and a monitoring function of the amplitude of breath curve. If the amplitude is less than a certain threshold and that there are no snoring/breathing sounds, the system finds obstructive apnea. Obstructive apnea is a typical apnea such that the patient cannot inhale the air despite of breath effort and that the concentration of the oxygen in blood falls. Oxygen desaturation estimation is done by analyzing the change of the amplitude of breath curve. The figure shows the system can estimate apnea correctly in 8 of 10 cases. The figure also shows the system can estimate ogygen desaturation in 9 of 10 cases.

Figure 5: Comparison monitoring and estimating function of SELF with conventional one.

Presenting Environment

This section reports a washstand display as an examples of an information providing furniture. The washstand tends to be used every morning and night, which means if the washstand has a function of providing information as well as mirroring the inhabitant, it is able to convey periodically. According to questionnaire survey conducted by us, women spend at the washstand from 30 minutes to 1 hour a day. Since there are enough time to read information from the washstand, the washstand is one of the most suitable place for providing a person with useful information. Figure 6 shows the developed washstand display. It consists of a liquid crystal display (LCD) having a touch sensor and a vision system. The LCD is used for displaying not only a person's face but also some health information analyzed by SELF.

Figure 7 shows the image displayed on the LCD. The health information is displayed around the face. This report consists of weekly and daily information on the changes in health condition and is expressed with bar graphs and text. Changes to be notified to the person are determined based on the average condition of the person and of other people. For the basis of information on the average condition of people, we used a medical textbook.

Figure 6: Constructed washstand display
Figure 7: Example of output of washstand display

Conclusions

This report describes a sensorized environment for non-invasive and unrestrained monitoring the human respiratory system. The system consists of 1) a sensorized environment for robustly and naturally observing inhabitants, 2) a human model for understanding conditions of the human respiratory system, and 3) a presenting environment for letting them utilize analyzed information. As examples of the sensing and presenting environment, this report reports the daily living space (SELF) which has a ceiling dome microphone, a pressure sensor bed, and a washstand display. The experiments conducted for a real patient suffering from Sleep Apnea Syndrome proved the developed system can estimate apnea, oxygen desaturation frequency using sensory data from the pressure sensor bed and the ceiling dome microphone.

References

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