Comparative Study Of The Effect Of N95 Facemask And Powered Air-purifying Respirator (2 Fans, N95 Filter) On Cardiovascular Parameters Of Healthy Individuals During Exercise

Abstract: N95 masks filter 95% of the small particles and respiratory droplets (>0.3 µm diameter).  Therefore, they are widely used both by the general public and health workers during the pandemic. When physical activity or exercise is performed wearing an N95 mask, it induces a hypercapnic environment.  The heat burden is also increased leading to discomfort and reduced compliance. This study compared physiological effects and subjective perceptions while wearing an N95 mask and powered air-purifying respirator (PAPR) (2 fans, N95 filter) during incremental exercise.  ECG, respiratory movement, SpO2, and temperature inside the mask were recorded and perception of discomfort was also assessed. Heart rate variability (HRV) values during baseline were within normal limits in both the mask conditions signifying that cardiac autonomic tone is comparable.  During incremental exercise, the fall in SpO2 was significantly lesser in PAPR as compared to the N95   mask at 60–70% and 70–80% of the maximum achievable heart rate. The temperatures inside both the mask conditions were significantly higher than the ambient temperature. The scores of humid, hot, breath resistance, and fatigue were significantly lower in PAPR than N95 mask. In situations where prolonged use of the mask is required with strenuous physical exertion or exercise, PAPR could be preferred over an N95 mask.

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Keywords: Cardiopulmonary exercise test (CPET), COVID-19, HRV, N95 mask, PAPR

Introduction

The novel SARS COV-2 virus can be transmitted through respiratory droplets and physical contact which is highly   transmissible1). The WHO declared COVID-19 as a global pandemic on 11th March, 20202). The cases are still increasing worldwide. It is mandatory to wear the mask in public places to prevent infection and also to prevent the spread. There are various types of masks available like surgical masks, N95 facepiece respirators, powered air-purifying respirators (PAPR), etc. Surgical masks reduce the transmission from the wearer to the patient, hand-to-face contact, and facial contact with large droplets, while N95 facepiece respirators filter the small airborne particles,   tightly fit to the face. N95 mask filters 95% of the small particles (>0.3 µm diameter)3). Therefore, they are widely used by healthcare workers for self-protection during this pandemic.

As the N95 mask is tight fitting and has a fine pore size it causes increased resistance to airflow. This also increases temperature and humidity which in turn leads to moisture condensing on the surface of the mask. This in turn impairs the respiratory heat loss and increases the heat burden4). There is also an increase in discomfort on prolonged usage of masks and this leads to a lack of compliance5).

When exercise is done with an N95 facemask the above problems are aggravated. Previous studies have noted that exercising with an N95 mask induces a hypercapnic hypoxic environment due to inadequate oxygen uptake (O2 ) and carbon dioxide (CO2 ) removal but in healthy individuals, without any cardiovascular comorbidities or risk factors the parameters such as heart rate (HR), a saturation of peripheral oxygen (SpO2 ) and end-tidal carbon dioxide (ETCO2) were within physiological limits even during strenuous exercise6,  7). However, exercise remains a physiological antidote to risk factors for cardiometabolic diseases8) and it lessens the chances of acute respiratory distress syndrome (ARDS) associated with COVID-199).

PAPR has possible features to ameliorate the issues of airway resistance and thermal discomfort. It has a motor that draws air through a filter and delivers the filtered air under positive pressure to the mask10). It enhances the comfort of wearing a mask by solving heat-related issues via the cooling effects of air currents which leads to an increase in compliance and the duration of work cycles as compared to the N95 mask11). However, its impact on physiological parameters during exercise remains to be seen.

The present study was undertaken to compare the physiological effects and subjective perceptions while wearing  PAPR (2 fans, N95 filter) and N95 mask during incremental exercise in humans.

Materials and Methods

This was a cross-over, self-control study conducted in the Department of Physiology, All India Institute of Medical  Sciences (AIIMS), New Delhi after approval from the institute ethics committee (Ref. No.: IEC-1222/04.12.2020 RP- 26/2020). 21 healthy volunteers were recruited for the study. Subjects with a recent history of coronary artery disease, chronic smoking, alcoholism, and taking vitamin supplements within a week of the study were excluded. The subjects were instructed to report to the laboratory after a light breakfast/meal at least 2 hours before the study. The subjects were asked to empty their bladder before the recording.  All the subjects recruited were healthcare workers who did not have prior exercise training. Written informed consent was taken from all the healthy volunteers after an explanation of the nature, purpose, and duration of the study. Each subject performed the test two times: (1) with PAPR (2 fans,  N95 filter) and (2) with N95 mask. Randomization was done while allotting each subject’s sequence of intervention. After that, electrodes were placed to record Lead II   electrocardiogram by digital data acquisition system (Powerlab™, AD Instruments, Australia). The respiratory Belt  Transducer was fixed around the chest at the level of the 4th  intercostal space to record respiratory movements. Temperature Probe was put inside the mask to record the temperature of the microenvironment of the facemask. During the exercise, a different ECG configuration was used. Wireless 12  Lead ECG (COSMED, Italy) was placed to record the electrocardiogram and the heart rate was derived from it during exercise. A pulse oximeter was put on the index finger of the subject to record the percentage of O2  saturation of hemoglobin (SpO2 ). The bicycle ergometer (Carnival, Netherlands)   was used to do the exercise using a 10W/minute incremental exercise protocol using OMNIA 1.4 (CPET) software  (COSMED, Italy). The recording setup is shown in Fig. 1.  The testing room was air-conditioned with ambient temperatures at 22–23°C and relatively low humidity (<50%).

Mask

We used disposable FFP2/N95 protective face masks  (Suvayu SV9500, India) and PAPR (2 fans and N95 filter)  (Moksha mask, PQR Technologies Pvt. Ltd., India). It uses two small DC fans – one for inhalation and one for exhalation. The first small DC fan pumps in the air from outside, after filtering it through the N95/ BFE95 or any such filter, and delivers purified air to the user while the second fan throws out the exhaled CO2  and moisture-laden air. The fan is rotating at 8,000 rpm (Fig. 2).

Baseline recording

A brief medical history was taken to rule out comorbidities and disease states that might affect the exercise capacity of the subject. After giving five minutes of resting period five minutes of ECG recording is selected for computing short-term heart rate variability (HRV). Standard procedure was used to record HRV12) during this period, resting heart rate, SpO2, and temperature levels in the mask are noted.

Incremental exertion test (IET) 

Each subject performed two incremental exertion tests  (IET), one with FFP2/N95 mask and one with a PAPR mask.  Tests were performed at the same time of day with a minimum of 48 hours between two tests. All the subjects were given a warm-up of 3 minutes to familiarise themselves with the exercise protocol. IET was performed on an (electronically braked) bicycle ergometer (COSMED, Italy) at a constant speed of 60 revolutions per minute (rpm). The test began at a workload of 0 W with an increase of 10W within 1 min  (as a ramp) until 80 percent of maximum heart rate was achieved. Maximum heart rate was calculated using the standard formula (220- Age).

Quantification of comfort/discomfort

We used a questionnaire after exercise to quantify the following ten domains of comfort/discomfort of wearing a mask: humidity, heat, breathing resistance, itchiness, tightness, saltiness, feeling unfit, odor, fatigue, and overall discomfort4). The perception of discomfort was assessed after 10 minutes of IET.

Statistical analysis

All values are expressed as mean ± standard deviation unless otherwise stated, and the significance level was p<0.05. Data were analyzed using GraphPad Prism  9 (GraphPad Software Inc., California, USA). The normal distribution of the data was evaluated by the Shapiro–Wilk test. Two-factor repeated ANOVA with Bonferoni’s post hoc test for multiple comparisons was done to determine if there was a change following masking.

Results

Subject characteristics

Subjects of this study consisted of 21 subjects of whom 9 (43%) were females and 12 (57%) were males (mean age, 28 ± 4 years, range 22–35). Resting average heart rate was not significantly different between the two conditions i.e., N95 mask group and PAPR (2 fans, N95 filter) condition (Table 1). 

Heart rate variability during baseline

The parameters of time domain - SDSD, RMSSD, frequency domain - LF, HF, Total Power & LF/HF Ratio and non-linear analysis – SD1/SD2 Ratio were within normal range and showed no significant difference between N95   mask and PAPR (2fans, N95 filter) (Table 2).

Parameters studied during incremental exercise test 

a) Change of SpO2 : 

During the incremental exercise, a fall in SpO2 was noted in both the N95 mask and PAPR (2 fans, N95 filter) at various percentages of maximum achievable heart rate. But this fall was significantly lesser in PAPR (2 fans, N95 filter) as compared to the N95 mask at 60–70 and 70–80 percent of the maximum achievable heart rate. While at 30–40, 40–50, and 50–60 percent of the maximum achievable heart rate, the mean values showed no significant difference (Fig. 3).

A significantly lesser percentage fall of SpO2  was noted in  PAPR (2 fans, N95 filter) as compared to the N95 mask. In  PAPR (2 fans, N95 filter) group, 3 out of 21 subjects showed > 5% SpO2  fall compared to 9 out of 21 subjects in  N95 mask group above 60% of maximum achievable heart rate (Fig. 4).

b) Change in temperature inside the mask:

The temperatures inside both the masks (N95 mask and  PAPR) were significantly higher than the ambient temperature (22.31 ± 0.06) both at rest and during incremental exercise (32.93 ± 0.93, 32.72 ± 1.07). But there was no significant difference between the N95 mask and PAPR (2 fans, N95   filter) (Fig. 5).

Perception of discomfort after wearing N95 mask and PAPR (2 fans, N95 filter):

The scores of humid, hot, breath resistance, and fatigue were significantly higher in the N95 mask than in PAPR (2 fans,  N95 filter) (Fig. 6).

Discussion

The results from the study demonstrate that percentage oxygen saturation, microclimate inside the mask, and subjective ratings were significantly and equally influenced by the wearing of the N95 mask and PAPR (2 fans, N95 filter) at rest.

Heart rate variability during baseline recording was comparable to the normative values from our lab12) and those provided by HRV Task Force 199613) in both the masks, signifying that cardiac autonomic tone remains normal and there is no abnormal alteration in parasympathetic and sympathetic tone using either mask. To our knowledge,   this is the first study to report this finding.

In our study, during incremental exercise there was no significant difference in the fall of SpO2 till 60% of HRmax after that there was a significant difference in the fall of SpO2  noted between both the mask conditions. 9 out of 21 subjects wearing N95 masks had a SpO2  fall of more than 5%, signifying that there could be a subset of the population who are more susceptible to SpO2  fall. While using PAPR (2 fans, N95 filter), the fall in SpO2  during all intensities of the exercise was minimal, only 3 out of 21 subjects had a fall of more than  5%. Powell et al. found that during low-to-moderate exercise there was no significant difference in cardiopulmonary variables such as SpO2, transcutaneous carbon dioxide (tcPCO2 ), heart rate (HR), respiratory rate (RR) during wearing of N95 mask and PAPRs. This was attributed to the fact that cardiovascular parameters are more impacted by the intensity of exercise rather than the types of masks  (N95 and PAPR)14). Similar findings were observed with  N95 masks during low-intensity physical activity in the treadmill studies done by Roberge et al 6). However, they also found that there was a 3% increase in inhalation and exhalation resistance when exhaled moisture was retained by the N95 mask15). Epstein et al. noted that exercising with an N95 mask was associated with a significant but mild increase in end-tidal carbon dioxide (EtCO2 ) levels and the differences were more prominent when the intensity of exercise was increased7). In the N95 mask, we found that sweating, humidity, heat perception and fatigue were significantly higher than PAPR (2 fans, N95 filter) during strenuous exercise (> 60% of HRmax) and this in turn increased the breath resistance. When breath resistance increases during strenuous exercise, the work of respiratory muscles is increased, and prolonged inspiratory activity would lead to more negative intrathoracic pressure and finally increase the preload16).  And the after load also increases due to the raised transmural left ventricular pressures17). These findings could be more pronounced in subjects with obstructive lung diseases and cardiovascular disorders with low cardiac output.

In the current study, the temperatures inside both masks were significantly higher than those of ambient temperature but the differences between the two microenvironments were negligible during incremental exercise. A slight decrease in temperatures (at 60–70% HRmax) inside the N95   mask during exercise could be attributed to the cooling effect of sweating18). But in PAPR (2 fans, N95   filter), there is an air current that is maintained, which reduces the sweating, humidity, and heat accumulation inside the mask. In individuals sensitive to thermal stress,   sweating might be increased and a fall in SpO2 might be exaggerated.

Use of PAPR (2 fans, N95 filter) could be preferred over N95 mask for high-intensity workouts, athletic or sports training, factory workers, health care workers, workspaces without air conditioning, spectators in stadiums and music concerts, military training, etc. But for universal acceptability of PAPR (2 fans, N95 filter), there is a need to develop lighter, less bulky, more accessible, and cost-effective models.

Limitations of the present study include the relatively low number of subjects (12 males, 9 females). Due to  COVID pandemic restrictions, studies without wearing the mask could not be done and spirometry parameters could not be assessed. The study was performed in a laboratory where the ambient temperature was maintained so we can’t comment on the impact of these masks in hot, humid environments.

In future studies, the other cardiopulmonary parameters such as EtCO2, lung volume changes, VO2  max, and arterial blood gas parameters at different stages of exercise could be assessed in real-time. The effect of different fan speeds and pressure changes inside the masks could be assessed to further elucidate the mechanisms involved. And further, these findings could help us to create an automated mask that would eliminate the increase in breath resistance.

Conclusion

During resting conditions and mild physical activity, the use of both N95 and PAPR (2 fans, N95 filter) did not affect autonomic and cardiovascular parameters. But during heavy exercise (at 60–70% and 70–80% of HRmax) fall in  SpO2  was significantly lesser in PAPR (2 fans, N95 filter)   as compared to the N95 mask. In conditions where prolonged use of the mask is required with high intensity of work or exercise and strenuous physical exertion, PAPR (2 fans, N95   filter) could be preferred over N95 mask.

Acknowledgments

We would like to express our thanks to the research section for their support for the study and for initiating a collaborative research agreement with PQR Technologies Pvt. Ltd.,  India. We would also like to thank PQR Technologies Pvt.  Ltd., India for providing the PAPR (2 fans, N95 filter)-“Moksha mask” for the study.

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