Development of a smart active respirator for comfortable and hygienic breathing

Rapid spreading and the high mortality rate made the current COVID-19 pandemic a global emergency.^1,2 This disease is predominantly characterized by a fever and dry cough often leading to respiratory and multi-organ failure.³ The SARS-CoV-2 virus is extremely contagious in humans owing to human-to-human transmission.⁴ In the current scenario, the maintenance of a healthy lifestyle to have an efficient immune system is the only preventive measure against COVID-19.^5–8 In this regard, effective precautionary measures, as recommended by the World Health Organization (WHO), are essential to decrease the rate of transmission of the virus.^9,10 The WHO recommended precautionary measures including regular washing of hands with soap and water or with an alcohol-based hand sanitizer, and wearing facial masks along with maintenance of social distancing.¹¹ Therefore, masks have become an integral part of our day-to-day life. Even after the roll-out of the vaccine, the use of a face mask is mandatory.¹² It is reasonable to assume that the current need to wear facial masks will remain an integral part of public hygiene and health not only in the upcoming days but possibly also in the post-COVID-19 era.

Each of the various types of masks that are available in the present market has its drawbacks. For example, the normal smart pro mask (SPM) users are forced to rebreathe the exhaled carbon dioxide (CO₂), as the CO₂ continues to circulate between the face and the mask, and there is no provision for the CO₂ to escape.¹³ This rebreathing can cause several adverse health effects, such as increased blood pressure, increased heart rate, chest pain, and hypercapnia.^14,15 The problem becomes more evident in patients suffering from chronic obstructive pulmonary disease (COPD), in children and elderly people.^16,17 Considering its low exhalation force, the exhaled CO₂ gets easily trapped between the mask and the face.¹⁸ Similar problems appear during inhalation, as the fresh air cannot enter through the mask due to its lack of sufficient inhalation force.

Furthermore, moisture settles on the covered area of the face of the user causing huge discomfort.^19,20 Due to the thick fabric-like material of the mask and lack of options for clearance, the covered area becomes prone to moisture deposition.⁸ Moreover, since the human exhaled air is usually warmer than the ambient temperature, it creates sweat, adding to the discomfort.¹³ In addition, the voice clarity gets severely perturbed due to acoustic attenuation by the mask fabric, which often hinders natural conversations.²¹ 

In the present work, we have developed a battery-powered especially programmed active respirator, which when attached to the commercially available N95 masks, helps in breathing oxygen by providing fresh atmospheric air, not only by preventing rebreathing of CO₂, but also by lowering the discomfort of sweating and heating. The developed active respirator pumps to push out the circulating CO₂ and helps in the inhalation of oxygen. The developed system can also maintain normal acoustic wave propagation and helps in pursuing natural conversation.

Figure 1(a) schematically describes the detailed outer design of the mask with the proposed active respirator. The present invention can be powered by any form of an external source, such as an external battery, power bank, USB charging devices, mobile charging stations, and electric or solar-powered systems. Recharging the respirator for 6 h will generate usage of 12 h. However, the mask with the attached respirator acts as a commercially available conventional N95 mask, if the active respirator is not charged.

Figure 1(b) demonstrates the construction of the active respirator. The base section of the active respirator (A) consists of a baseplate, which holds the weight of the entire unit and serves as the interface with human skin. Section (B) holds the air circulator and creates clearance for the physical movement of the circulator. The circulator (C) forms the basis of the innovation and is connected via concealed electrical wires with the battery pack. A special programming was developed and optimized to control the circulator for normal respiration, positive air pressure for clearance of CO₂, and moisture. The following section (D) holds the air filter, which acts as an SPM filter and the valve (E) ensures unidirectional airflow. The entire setup is integrated with an N95 tri-layer mask fabric, the cloth part of which is easily replaceable, as shown in Fig. 1(b).

Thus, the battery-operated motorized respirator of the present invention creates positive pressure and removes the trapped air from the space between the mask and the covered area of the face. The integrated electronics require a 5 V source with current usage of 0.2 A. The proposed device circulates air through appropriate channels to maintain the humidity as well as the temperature of the enclosure chamber and does not allow the formation of air pockets. The generated airflow maintains the supply of fresh O₂ essential to the physical and mental well-being of an individual as well as removes the toxic carbon dioxide.

Moreover, the weight of a commercially available N95 mask is 9.93 g, whereas that of the active respirator is approximately 4 g. Thus, the addition of the active respirator to the mask does not compromise the comfortable maneuverability of a user. Additionally, the added weight of the active respirator does not change the maneuverability, which is evident from the picture of the human volunteers wearing the prototype [Fig. 1(a) inset, supplementary material video file multimedia Fig. 6 (Multimedia view)].

To demonstrate the concentration of CO₂ in the exhaled air, the experimental arrangement includes a CO₂ sensor placed in between the face and the mask. All experiments were performed according to the Institutional Ethics Committee of NRS Medical College and Hospitals. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article. The experimental setup was designed with one MG-811 CO₂ Sensor Module (Sandbox Electronics, China) to measure the concentration of atmospheric CO₂.

To exemplify the maintenance of thermal stability while using the proposed innovation, a standard temperature sensor AM2302/DHT22 (Adafruit) was used to detect the ambient temperature.

To show that the present innovation aids in the maintenance of normal acoustic wave propagation, and during the conversation, Landmark Tiny LM-BT1061 Wireless Bluetooth Speaker was used as a source, and Samsung Galaxy A7 mobile was used to record the audio from the speaker.

A graphic user interface was developed using LabVIEW software (National Instruments) for signal acquisition, data analysis in a real-time mode, and subsequently generating the final results in both graphical and numerical forms.

In order to estimate the particle size, an in vitro experiment was performed. A 668 nm wavelength LASER light was incident on an experimental setup to verify the filtration capability of the innovatively designed Bose shield with respect to the conventional N95 mask. The images of the particulates generated from the smoke generator were captured by a Samsung Galaxy A7 mobile.

The conventional masks that are available in the markets have the major limitations of trapping of CO₂ in the air pocket formed in between the mask and the face, which in turn creates CO₂ poisoning, excess humidity, and loss of speech clarity.^14,22 The following experiments have been performed with our self-developed active respirator to overcome the aforementioned limitations.

Figure 2(a) schematically describes the experimental arrangement which includes a CO₂ detector placed in the air pocket created in between the face and the mask. It is observed that when the face is covered by an N95 mask for a prolonged period of time, the CO₂ level in the air pocket starts increasing. Thereafter, when the respirator attached to the N95 mask is turned on, the relative CO₂ concentration starts to decrease. Figure 2(b) shows the plot of relative CO₂ concentration in three different situations. In the first case (control), when no mask was worn, the relative CO₂ concentration was 100%. Hence, when a conventional N95 mask was worn, it was observed that the relative CO₂ concentration increased by 50%, which was subsequently reduced to 16.67% when the active respirator was turned on. The present invention includes an especially designed battery-operated motorized respirator that creates positive pressure and removes the trapped CO₂-rich air from the space between the mask and the face, hence, minimizing the chance of rebreathing of the toxic CO₂-rich air. Consequently, the unique design of the mask provides an option for oxygen to enter through the mask for inhalation by creating a pressure gradient, which helps to maintain normal respiration.

To demonstrate the temperature stability of the developed system, the experimental arrangement which includes a thermal sensor placed in between the face and the mask was used as schematically described in Fig. 3(a). According to the static PMV/PPD model by Fanger, at a “drybulb” temperature of 24–30 °C, thermal comfort is felt regardless of the corresponding relative humidity (%).^23,24 In our study, it was observed that the detected temperature is 29 °C [Fig. 3(b)] when the mask was not worn, which then started rising as soon as the commercially available N95 mask was worn; due to the thick material of the mask, the enclosed area becomes prone to moisture, which results in moisture settlement in the covered area. Owing to the body temperature of the subject, the human exhaled air is warmer than the ambient temperature. This temperature difference creates sweating, resulting in discomfort or loss of thermal comfort. However, a distinct fall in detected temperature was observed when the developed active respirator attached to the mask was turned on. The exhaled breath temperature (EBT) came down to 26.7 °C [Fig. 3(b)], which reached the comfort temperature range as demonstrated by Fanger. Thus, it can be stated that irrespective of the humidity, thermal comfort would be felt by the individuals wearing the newly developed active respirator regulated mask. Hence, the present innovation provides a motorized option for the escalation of the moisture created in the space between the mask and the face. The present design consists of an external active exhalator that helps in evaporating the sweat droplets utilizing the principles of latent heat and through creating a cooling effect, which provides comfort to the subject.

Figure 4(a) schematically describes the next set of experimental arrangements for the determination of voice clarity. The setup includes a speaker covered by the mask in such a way that the speaker is parallel to the active respirator. A user-friendly smartphone (Samsung Galaxy A7) was placed 10 cm away from the above arrangement to record the sound from the speaker by the “voice recorder” application. The speaker was Bluetooth operated by another smartphone (Samsung Galaxy A7), and individual frequencies (100 Hz, 1 KHz, 10 KHz, and 12 KHz) were played by an application named “frequency generator,” one at a time. For each set of frequencies, three individual cases were studied. Initially, the speaker was left uncovered and the sound was recorded for 10 s. For the second part of the study, the speaker was covered with the commercially available N95 mask and the sound was recorded. It was observed that the relative volume intensity decreased. Finally, the Bluetooth speaker was covered by the respirator-attached N95 mask and sound was recorded like the previous two cases. It was found that the relative volume was recovered significantly due to the use of active respirator. The relative comparison study is shown in Fig. 4(b). The voice quality of the subject, which is severely perturbed due to acoustic attenuation by the mask fabric, can thus be reinstated. Hence, the present innovation provides an option to maintain normal acoustic wave propagation and help during the conversation.

An in vitro experimental setup was developed for the verification of filtration capability of the Bose shield with respect to the conventional N95 mask [Fig. 5(a)]. The experimental setup consists of two chambers (1 and 2), and the Bose shield was acting as a partition between these two chambers. The outer layer of the mask was exposed to a smoke generator fixed to chamber 1 (source of particulates). Chamber 2 was securely placed in the inner layer, where two pairs of laser detector were attached for the detection of optical density and particle sizes. The light profiles of the LASER beams in both the chambers were captured by a 24 MP, f/1.7 camera (Samsung). Figs. 5(b) and 5(c) show a spatial distribution of laser light profiles in the chambers 1 and 2, respectively.

The acquired pictures are analyzed pixelwise. The images were converted to the gray scale for detection of the intensity (I) of the particular position with an increasing scattering angle.

The diameter of particles in colloidal suspension can be estimated from the following well-known Rayleigh scattering equation (1). The intensity I of light scattered by any one of the spheres of diameter “d” and refractive index “n” from a beam of light of wavelength “λ” and intensity “I₀” are given by

where R is the distance to the particle from the detector and θ is the scattering angle.

Our experimental setup dictates the use of the LASER with distinct wavelength of 668 nm.

The above equation can be re-written as follows:

Therefore,

where K = 1.516 × 10⁻²⁹. Fig. 5(d) shows estimated particle size distribution in the chambers. It can thus be observed through the in vitro experiments that the filtration capability of the Bose shield does not deter from that of the standard N95 mask.

In the present study, a battery-powered active respirator was introduced in an otherwise standard passive mask. Due to this novel addition, the subject can breathe fresh oxygen with every breath. All other conventionally used masks are not accompanied by a battery-powered respirator, and as a result the exhaled CO₂ accumulates in between the mask and the covered portion of the face. This results in the rebreathing of the CO₂, which is toxic to health. The rebreathing of the exhaled CO₂, which causes CO₂ poisoning, can be avoided to a great extent by the battery-powered respirator, where the moisture settlement in the nose and mouth area will be reduced. The voice of the subject will also be heard by the surrounding people with a lot of clarity. Currently, no other mask can provide these excellent features like the Bose shield. In our in vitro experiment, the intactness of particulate filtration capability in the active respirator improvised N95 mask is also demonstrated. Moreover, the one-time cost of the active respirator being $3 is comparable to the standard commercially available N95 mask in the USA, which costs about $1. The developed replaceable active respirator can be fitted to any N95 mask revealing the cost effectiveness of the technology. To our understanding, the novel Bose shield can reduce CO₂ rebreathing in respiratory protective devices (RPDs) significantly and promises to be an excellent choice for laborers who inevitably wear them for long hours.

S.K.P. acknowledges Abdul Kalam Technology Innovation National Fellowship (INAE/121/AKF) from the Indian National Academy of Engineering, and Science and Engineering Research Board (SERB), Department of Science and Technology (DST), Government of India. S.K.P. also acknowledges Paulmech Infrastructure Pvt. Ltd. for the support. The authors would like to acknowledge the Deanship of Scientific Research at Umm Al-Qura University for supporting this work by Grant No. 22UQU4092426DSR01.

The authors have no conflicts to disclose.

N.B. developed the instrument and was involved in the planning of the study, coordinated data collection, carried out the primary analyses, and drafted an initial manuscript. S.S. was involved in the design and development of the instrument and reviewed the manuscript. R.G. was involved in the development of the device and revised the manuscript. A.A. analyzed the data, interpreted it, and revised the manuscript. A.H. was involved in the design and development of the instrument and reviewed the manuscript. M.G. made a substantial contribution to data acquisition and interpretation. S.G. analyzed the data and reviewed the manuscript. P.M. planned the study, interpreted the data, and reviewed the manuscript. S.N. analyzed the data and reviewed the manuscript. S.A. made a substantial contribution to data acquisition and interpretation. S.K.P. conceptualized and planned the study, interpreted the data, and revised the manuscript.

The data that support the findings of this study are available from the corresponding authors upon reasonable request.