A Modeling Study on Inspired CO2 Rebreathing Device for Sleep Apnea Treatment by Means of CFD Analysis and Experiment

We present the device design, simulation, and measurement results of a therapy device that potentially prevents sleep apnea by slightly increasing inspired CO 2 through added dead space (DS). The rationale for treatment of sleep apnea with CO 2 manipulation is based on two recently reported premises: (i) preventing transient reductions in P aCO 2 will prevent the patient from reaching their apneic threshold, thereby preventing “central” apnea and instabilities in respiratory motor output; and (ii) raising P aCO 2 and end-tidal CO 2 , even by a minimal amount, provides a strong recruitment of upper airway dilator muscles, thereby preventing airway obstruction. We have also provided the simulation results, obtained from solving the Navier–Stokes (NS) equations within the device volume. Therein, the NS equations are coupled with a convection–diffusion equation that represents the transport of CO 2 in the device, thus enabling the transient simulation of CO 2 propagation. Using this procedure, a prototype of variable volume dead space reservoir device was designed. Volumetric factors influencing carbon dioxide increases in the added reservoir (open-ended DS) were investigated. The maximum/minimum amount of CO 2 concentration were obtained for the maximum/minimum device volume; 3.4 and 2.4 mol/m 3 for the DS volumes of 1.2 and 0.5 × 10 −3 m 3 , respectively. In all case studies, the CO 2 buildup reached a plateau after approximately 20 breathing cycles. The experimental measurement results are in agreement with the simulation and numerical results obtained using the proposed simplified modeling technique, with a maximum relative error of 3.5%.