Fig. 2. The arterial-to-end-tidal partial pressure difference (Δco²) for each device/cannula and patient group. Individual data points are plotted along with mean and 95% confidential interval for 20 normal weight patients (defined as a body mass index < 30 kg/m²) without a diagnosis of obstructive sleep apnea (Non-obese non-OSA), 20 obese patients (body mass index > 35 kg/m²) without a diagnosis of obstructive sleep apnea (Obese non-OSA), and 20 obese patients with polysomnography-diagnosed obstructive sleep apnea (Obese OSA). *  P < 0.05; **  P < 0.01.