What do masks mask? A study on transdermal CO monitoring.

Medical professionals have complained of extreme discomfort and fatigue from continuous wearing of N95 respirators (N95) overlaid with surgical masks (SM) and face shields (FS) during COVID-19 pandemic. However, there are no reports on the effect of face coverings on transdermal CO (TrCO) levels (a measure of blood CO) during moderate activity. In this study, real-time monitoring of TrCO, heart rate and skin surface temperature was conducted for six subjects aged 20-59 years with and without wearing personal protective equipment (PPE). We initially studied the effect of wearing PPE (N95+SM+FS) at rest. Then, the effect of moderate stepping/walking activity (120 steps per minute for 60 min) while wearing PPE was evaluated. In addition, we investigated the effect of exercising intensity with different masks. We observed a significant difference (p < 0.0001) in TrCO levels between without and with PPE during moderate exercise, but not while resting. TrCO levels were correlated to exercise intensity independently with masking condition and breathability of masks. For the first time, we present data showing that a properly fitting N95 worn along with SM and FS consistently leads to elevated TrCO under moderate exertion, which could contribute to fatigue over long-term use.