Wearing face masks while climbing stairs influences respiratory physiology.

During the COVID-19 pandemic wearing face masks was mandatory. Nowadays, face masks are still encouraged indoors, especially in hospitals. People climbing stairs with masks describe unpredictable dyspnea. In this study, healthy adults climbed 5 floors with and without a mask. Various cardio-respiratory parameters were measured, including O 2 -saturation (O 2 -Sat) and end-tidal CO 2 (EtCO 2 ), at baseline and on the top floor. Subjective indexes, such as Borg's scale, were evaluated. Thirty-two volunteers (16 males), median age 39 years (IQR 32.5-43), median BMI = 23.6 (IQR 21.5-25.1), with good fitness levels, participated. Comparing baseline to end-activity, median (IQR): O 2 -Sat change was -1.0% (-2-0) without mask, versus -3.0% (-4-0) with mask, p = 0.003; EtCO 2 + 7.0 (+3.3-+9) without mask, versus +8.0 (+6-+12) with mask, p = 0.0001. Hypercarbia was seen in 5 (15.6%) participants without mask, median = 48 mmHg (IQR 47.5-51), and in 11 (34%) participants with mask, median = 50 mmHg (IQR 47-54), p < 0.001. Desaturation (O 2 -Sat < 95%) was seen in 5 (15.6%) participants without mask, median = 94% (IQR 93%-94%), and in 10 (31%) participants with mask, median = 91.5% (IQR 90%-93%), p = 0.06. Regression analysis demonstrated that only male sex was significantly associated with abnormal EtCO 2 (OR = 26.4, 95% CI = 1.9-366.4, p = 0.005). Ascent duration increased from median (IQR) of 94 s (86-100) without mask to 98 s (89-107) with mask, p < 0.001. Borg's scale of perceived exertion (range 0-10) increased from median (IQR) of 3.0 (2.5-3.87) without mask to 4.0 (3.0-4.37) with mask, p < 0.001. To conclude, during routine daily activities, such as stair-climbing, face masks cause dyspnea, and have measurable influences on ventilation, including true desaturation and hypercapnia, especially in males.