The COSMIC Bubble Helmet: A Non-Invasive Positive Pressure Ventilation System for COVID-19

Goal: COSMIC Medical, a Vancouver-based open-source volunteer initiative, has designed an accessible, affordable, and aerosol-confining non-invasive positive-pressure ventilator (NIPPV) device, known as the COSMIC Bubble Helmet (CBH). This device is intended for COVID-19 patients with mild-to-moderate acute respiratory distress syndrome. System Design: CBH is composed of thermoplastic polyurethane, which creates a flexible neck seal and transparent hood. This device can be connected to wall oxygen, NIPPVs including Continuous Positive Airway Pressure and Bi-level Positive Airway Pressure, and mechanical ventilators. Discussion: Justification of CBH design components relied on several factors, predominantly the safety and comfort of patients and healthcare providers. Conclusion: CBH has implications within and outside of the pandemic, as an alternative to invasive mechanical ventilation methods. We have experimentally verified that CBH is effective in minimizing aerosolization risks and performs at specified clinical requirements.

The promise of helmet based NIPPV has led to the development of the COSMIC Bubble Helmet NIPPV. As a subset of COSMIC Medical, our Project Bubble Helmet team has collaborated on the design, technical writing, and manufacturing of this adapted device. While this design aims to tackle virus aerosolization and ventilatory demands in patients with ARDS due to COVID-19, CBH has applications in patients with respiratory distress of any etiology.

II. REQUIREMENTS
The requirements were defined through literature review, consultation with key stakeholders including doctors and respiratory therapists. Assumptions in the benchmarking tests of the bubble helmet are detailed below.

A. CO2 Accumulation Justification
A concern for helmet-based ventilation is the potential for CO2 accumulation and rebreathing in the helmet. Taccone's study on the effects of helmet ventilation on carbon dioxide rebreathing was carried out in healthy volunteers (n=8) and provided evidence that CO2 levels are not related to the applied PEEP or hood volume [16]. Taccone's research builds upon previous studies demonstrating that the hood's CO2 concentration is independent of the PEEP and depends on the gas flow [17]. This substantiates the assumption that CO2 accumulation is dependent on flow and thus tested in detail for the CBH (below).

B. Operational Noise Level Justification
Another problem for helmet delivery of CPAP with the helmet is the noise level for the patient. A recent study of two alternative NIV helmets, the StarMed and Dimar hoods, reported similar performances in noise levels at a gas flow of 40 L/min compared to 20 L/min (74 dBA vs. 52 dBA respectively) [18]. The authors also suggest that a diffuser filter should not be used with gas flows over 30 L/min because it will amplify the sound pressure.

III. FUNCTIONALITY TESTING DATA
The CBH has been tested iteratively throughout its development to inform its design and ensure its efficacy. These tests included benchmark testing to evaluate its performance, ensure safe airflow characteristics, and usability testing to assess its suitability for use by healthcare providers.

A. Leakage Test
The purpose of the leakage test was to measure the losses in airflow due to leaks in the helmet by quantifying air dispersion levels. Measuring air dispersion allows a quantitative measure of the helmet's structural integrity and its ability to control aerosolized viral spread under operating conditions. Air dispersion should be minimized to avoid contamination of the environment. By observing the difference between inflow and outflow, the rate of leakage can be determined. The leakage was compared to that of the StarMed CPAP Hood, which is a Health Canada and FDA-cleared equivalent ( Figure 2).
The CBH registers consistently lower air leakage than the StarMed hood at PEEP valve settings of 5, 10, and 15 cmH2O. In a recent study performed by Feriolin, the StarMed helmet with air cushion had a negligible air dispersion radius compared to the one-meter air dispersion radius of high-flow nasal cannula [19]. The leakage testing performed provides evidence that the CBH has lower rates of air leakage compared to CaStar StarMed helmet and can reduce virus aerosolization from air dispersion.

B. CO2 Accumulation Test
The CO2 accumulation test evaluates the accumulation of CO2 within the CBH when in use. With a healthy test subject and a CO2 monitoring probe, the helmet was tested with a range of flow rates to determine the flow necessary to prevent dangerous CO2 rebreathing.
We demonstrated that with two human subjects, one male and one female, a minimum flow rate of 30L/min is required to prevent an increase in FiCO2 above 7.6mmHg based on the ISO 17510 ( Figure S1). The subjects in these experiments were healthy young adults in a sitting resting position. The recommended level for therapeutic patient use will be determined in a future clinical trial feasibility study of the CBH and beyond the scope of this experiment. We demonstrated that in our small sample, the CBH is safe and comfortable to use for the duration of the experiment (approx. 60 minutes). Subjects

Supplementary Materials
The CO2 accumulation in prolonged wear over several hours.

C. PEEP Range Test
The PEEP range test evaluated the performance of the CBH at different PEEP pressures. The pressure setting of the PEEP valve and the flow rate from the flow source was varied, while the pressure readings within the helmet were observed as seen in Figure S2.
The results for pressure containment were nearly identical between the CBH and the StarMed hood. The pressure inside the helmet was dependent on the flow rate in addition to the PEEP valve setting. This proved that the helmet can withstand high pressures of 30 cmH2O without observed failure of the components: hood, neck seal, and straps. It was further observed that the pressure in the hood is highly dependent on the flow at higher flow rates (>120 L/min).

IV. USABILITY TESTING
The usability test includes several factors that would be considered essential to our design and device effectiveness. Four (4) tests were conducted as part of the usability testing. Hood visibility -test subjects successfully performed tasks such as reading a book, working on a laptop, and using a mobile phone. Observers were able to see test subjects' facial expressions well. Ease and timeliness of donning and doffing of the CBH was tested, which is a vital factor in the event of an emergency. The COSMIC bubble helmet allows for quick donning by a single healthcare provider with an able and cooperative patient or two providers depending on the setting. Donning can be performed in less than 30 seconds and doffing Fig. S2. As the inspiratory flow increases, pressure within the helmet increases as well. This graph shows that at higher inspiratory flow rates, pressure is highly dependant on the flow (n=2). by healthcare providers and/or patients takes less than 15 seconds. In the event of an emergency, the helmet's soft construction allows for emergency removal using a pair of scissors. The set-up and assembly test were used to assess the time required for healthcare providers to set up the helmet. With manual provided, the time required for a test subject to assemble the helmet was measured and observed. Based on our own results, device set-up time approximated five minutes. Operating noise of the helmet was also tested to ensure that the helmet was comfortable enough to be worn for extended periods of time, which may be required for NIV treatment. This test evaluated the comfort of wearing the helmet for up to 12 hours. Based on our results, operating noise did not exceed 87 decibels (dB). As per Usability Specification 5 our measured operating noise does not exceed that of the Canadian Federal Noise Regulation.