Fig. 2. Cardiovascular and respiratory parameters during the study are shown in three time epochs: before, during, and a 6-h period after the CO₂ inhalation.

Data are presented as medians with ranges in the entire cohort. a Heart rate (HR) decreased from a median 108/min (87–134) to 97/min (82–122) during CO₂ inhalation. After the CO₂ administration, the HR reduced further to 88/min (75–120); (p = 0.007, Friedman test). The mean arterial blood pressure (MABP) and peripheral oxygen saturation (SpO₂) did not change and remained in the physiological range throughout the three time epochs. (MABP medians: pre-study: 47 mm Hg (44–56); during: 47 mm Hg (40–52); post-study: 46 mm Hg (40–49); (p = 0.07, Friedman test). SpO₂ medians: pre-study: 100% (98–100); during: 99% (97–100); post-study: 97% (93–100); (p = 0.07; Friedman test). b The respiratory rate and tidal volumes changed significantly over the three study epochs. Respiratory rate was 42/min (24–53) and 42/min (25–58) before and during the CO₂ inhalation, respectively, and reduced to 28/min (19–49) in the post-study period (p = 0.008; Friedman test). Peak tidal volumes were the following: pre-study: 5.0 mL/kg (2.8–7.3); during: 10.3 mL/kg (5.3–16.6); and post-study: 4.9 mL/kg (3.9–8.7); (p = 0.002; Skillings–Mack test).