Interindividual differences in dyspnea during acute hypoxic exercise in healthy adults: A single exposure to simulated altitude at ~9000 ft

Figures

• 

  FIGURE 1. Visual schematic of the experimental visit. Participants completed a 90‐min testing session in a simulated altitude facility under normobaric hypoxic conditions (FIO2 ≈ 15 ± 0.1%, ~9000 ft). The protocol included supine heart rate variability, a vascular occlusion test, and submaximal cycling at 60% heart rate (HR) reserve. Heart rate and vastus lateralis muscle oxygen saturation were measured continuously.

• 

  FIGURE 2. Interindividual variability in dyspnea during submaximal cycling. Dyspnea (immediate perception domain of the Multidimensional Dyspnea Profile; sum of sensory qualities and breathing discomfort) was assessed at 10, 20 and 30 min during cycling at 60% heart rate reserve under normobaric hypoxic conditions (FIO2 ≈ 15 ± 0.1%, ~9000 ft). Thin lines represent individual participants (n = 22). Females are shown as solid lines and males as dashed lines. Sex‐specific means are shown as bold gray lines, and the overall mean is shown in black.

• 

  FIGURE 3. Relationship between dyspnea and muscle oxygen saturation. Dyspnea (immediate perception domain of the Multidimensional Dyspnea Profile; sum of sensory qualities and breathing discomfort) at 10 (a), 20 (b), and 30 (c) min of cycling at 60% heart rate reserve under normobaric hypoxic conditions (FIO2 ≈ 15 ± 0.1%, ~9000 ft) is plotted against skeletal muscle (vastus lateralis) oxygen saturation (SmO2). SmO2 is expressed as the change from rest (Δ) and quantified as the area under the curve (AUC), representing the integrated local deoxygenation response during exercise. Males are shown as circles and females as triangles. Each panel included 22 participants.