Journal of Medical and Biological Engineering

, Volume 37, Issue 2, pp 288–297

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

  • Mehdi Shokoueinejad
  • Arman Pazouki
  • Jake Levin
  • Fa Wang
  • Chris Fernandez
  • Samuel Rusk
  • Ícaro dos Santos
  • Ashley Mulchrone
  • Jerome Dempsey
  • John G. Webster
Original Article
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Abstract

We present the device design, simulation, and measurement results of a therapy device that potentially prevents sleep apnea by slightly increasing inspired CO2 through added dead space (DS). The rationale for treatment of sleep apnea with CO2 manipulation is based on two recently reported premises: (i) preventing transient reductions in PaCO2 will prevent the patient from reaching their apneic threshold, thereby preventing “central” apnea and instabilities in respiratory motor output; and (ii) raising PaCO2 and end-tidal CO2, 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 CO2 in the device, thus enabling the transient simulation of CO2 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 CO2 concentration were obtained for the maximum/minimum device volume; 3.4 and 2.4 mol/m3 for the DS volumes of 1.2 and 0.5 × 10−3 m3, respectively. In all case studies, the CO2 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%.

Keywords

Sleep apnea Inspired carbon dioxide CO2 Computational fluid dynamics Transport of diluted species 

Abbreviation

PaCO2

Atrial Pressure of Carbon Dioxide in Arterial Blood

PETCO2

End tidal CO2

\(\varvec{x}_{{\varvec{O}_{2}}}\)

Concentration of O2

\(\varvec{x}_{{\varvec{CO}_{2}}}\)

Concentration of CO2

\(\varvec{x}_{{\varvec{O}_{2},1}}\)

Chamber O2 concentration before inhale

\(\varvec{x}_{{\varvec{O}_{2},2}}\)

Chamber O2 concentration after inhale

\(\varvec{x}_{{\varvec{O}_{2},3}}\)

Chamber O2 concentration after exhale

\(\varvec{x}_{{\varvec{O}_{2},\varvec{in}}}\)

Inlet air O2 concentration

\(\varvec{x}_{{\varvec{CO}_{2},2}}\)

Average CO2 concentration after inhale

\(\varvec{y}_{{\varvec{O}_{2},1}}\)

Average inhale air O2 concentration

\(\varvec{y}_{{\varvec{O}_{2},2}}\)

Average exhale air O2 concentration

\(\varvec{c}_{{{\mathbf{n}},1}}^{{{\mathbf{ave}}}}\)

Average CO2 concentration after inhale where n is the breathing cycle number

\(\varvec{c}_{{{\mathbf{n}},2}}^{{{\mathbf{ave}}}}\)

Average CO2 concentration after exhale in nth breathing cycle

\(\varvec{v}_{\varvec{b}}\)

Air velocity at the inlet boundary

TV

Tidal Volume

RV

Reservoir Volume

\({\boldsymbol{\gamma}}\)

Main reason to introduce \({\boldsymbol{\gamma}}\) in the equations is to (i) account for imperfect mixing in small volume, e.g. due to undeveloped flow and (ii) account for any unforeseen parameter that can affect the mixing of CO2 and fresh air

Copyright information

© Taiwanese Society of Biomedical Engineering 2017

Authors and Affiliations

  • Mehdi Shokoueinejad
    • 1
    • 4
  • Arman Pazouki
    • 2
  • Jake Levin
    • 1
  • Fa Wang
    • 3
  • Chris Fernandez
    • 1
  • Samuel Rusk
    • 3
  • Ícaro dos Santos
    • 1
  • Ashley Mulchrone
    • 1
  • Jerome Dempsey
    • 4
  • John G. Webster
    • 1
  1. 1.Department of Biomedical EngineeringUniversity of Wisconsin-MadisonMadisonUSA
  2. 2.Department of Mechanical EngineeringCalifornia State UniversityLos AngelesUSA
  3. 3.Department of Electrical EngineeringUniversity of Wisconsin-MadisonMadisonUSA
  4. 4.The John Rankin Laboratory of Pulmonary Medicine, Medical Sciences CenterUniversity of Wisconsin-MadisonMadisonUSA

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