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Figure 1.6 CPAP treatment of sleep apnea[20] B. Bi-level positive airway pressure (Bi-PAP) Bi-PAP was introduced into use in the 1990s. A problem with CPAP is that the patient has to exhale against the extra pressure. However, with Bi-PAP, pressure can be set at a higher level for inhalation and lower for exhalation. This is helpful for the patient’s exhalation and makes it easier for compliance. Bi-PAP is more expensive than CPAP [21]. C. A-PAP The Auto-adjustable-CPAP or Automatic-CPAP [22] prototype was firstly developed in the early 1990s [23]. When in use, it is firstly set to a low pressure level which reduces the extra pressure comparing to CPAP. There is a sensor in the APAP. Once the sensor detected a “specific pressure characteristics of air” which indicates an obstruction is happening, the machine will automatically raise the pressure to keep the patient’s upper airway open. When obstruction is absent, the pressure drops gradually to the minimum pressure. This keeps the overall average pressure much lower than traditional CPAP and makes the patient more comfortable [24]. 6
1.3 Literature survey A literature survey was carried out on CPAP, the inhaled air quality requirement under such pressurized respiration and mathematical modelling of the machine. 1.3.1 Delivered air quality and the problem of condensation when using CPAP When using CPAP, besides the provision of pressure, there are other conditions to consider for patients’ safety, comfort and compliance. There are: 1.3.1.1 CPAP pressure consideration When a CPAP is used for remedy, its pressure should be set high enough to have the remedy effect and should not be too high to disturb patient’s sleep and increase mouth leak [25]. 1.3.1.2 Carbon dioxide limit in inhaled air The Occupational Safety and Health Administration (OSHA) standard for carbon dioxide is an eight-hour time-weighted average (TWA) of 5,000 ppm (0.5% of weight) with a short term 15-minute average limit of 30,000 ppm (3% of weight) [26]. They are 0.325% and 1.95% by volume respectively. The average carbon dioxide (CO2) content of exhaled air is 3.7% CO2 by volume [27], which is equivalent to about 5% CO2 by weight. This is 10 times the limit. This means if assuming CO2 concentration in the exhaled air is evenly distributed, the exhaled air should be no more than 9% in inhalation. Another phenomenon observed is that at the lower pressure settings, there is higher CO2 percentage in the inhaled air [28]. This also becomes a limitation when considering the possibility of higher pressure induced sleep disturbance and mouth leak [29]. More discussions are in below sub-sections. 1.3.1.3 Humidity and temperature of inhaled air The American National Standards Institute suggested a minimum absolute humidity of 10 mg/L at no lower than 22°C for non-intubated patients [30]. The 10 mg/L is equivalent to air at 22°C and 50% relative humidity which means that the normal room 7
Page 1 and 2: The Effects of CPAP Tube Reverse Fl
Page 3 and 4: Acknowledgement First of all, I wou
Page 5 and 6: When deep breathing induced reverse
Page 7 and 8: 2.4.1 Reverse flow calculation ....
Page 9 and 10: 5.3.1 Thermal dynamic model under s
Page 11 and 12: XI.3 Steady state mask thermal bala
Page 13 and 14: List of Figures Figure 1.1 Obstruct
Page 15 and 16: Figure 5.10 Comparison between expe
Page 17 and 18: Figure 6.13 Fluctuation of airflow
Page 19 and 20: Table 5.3 Comparison of condensatio
Page 21 and 22: Nomenclature Symbol Meaning of the
Page 23 and 24: CMFeO CMFet C O C t Concentration o
Page 25 and 26: m C 23 m Ca m cv m Cw m store m i m
Page 27 and 28: Nu Cp Nu dir Nu Ti Nu To Nuwsn Nuws
Page 29 and 30: QMor QMwst QTastn QTicn QTin Q
Page 31 and 32: R Mic R Moc R Ticn R Toc R Torn Mas
Page 33 and 34: V Capacity of the container m 3 V C
Page 35 and 36: 1.1 Background Chapter 1 Introducti
Page 37 and 38: The MRD is worn in user’s mouth w
Page 39: Figure 1.4 CPAP machine Figure 1.5
Page 43 and 44: CPAP fluid dynamic performance with
Page 45 and 46: Chapter 2 Mathematical Modelling of
Page 47 and 48: 2.3 Fluid dynamic analysis This sec
Page 49 and 50: If there are minor pressure drops,
Page 51 and 52: Figure 2.6 Pressure sensor - Honeyw
Page 53 and 54: The pressure readings were taken af
Page 55 and 56: Figure 2.12 Experimental set up for
Page 57 and 58: 2.3.4 Chamber air space mass balanc
Page 59 and 60: From the above analysis, the pressu
Page 61 and 62: Figure 2.18 Full face mask and the
Page 63 and 64: Inserting Eq. (2.26) and Eq. (2.27)
Page 65 and 66: Where n( ) t is the airflow proper
Page 67 and 68: However in reality, mixing turns ou
Page 69 and 70: Chapter 3 Mathematical Modelling of
Page 71 and 72: An Environment Control Chamber (Vö
Page 73 and 74: Figure 3.4 Thermal enthalpy gain of
Page 75 and 76: Figure 3.6 Heating element beneath
Page 77 and 78: Figure 3.8 Chamber water heat balan
Page 79 and 80: Table 3.1 Thermal resistance from h
Page 81 and 82: 3.3.1.2 Heat balance at the outer s
Page 83 and 84: 3.3.2 Heat flow from chamber water
Page 85 and 86: through ADU which is a function of
Page 87 and 88: It is assumed that the direct impac
Page 89 and 90: Sc a a (3.47) Dwa Analogous to th
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and keep them in gaseous status. On
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through the walls and natural conve
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Where d Ca is the specific humidity
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TTa ( n1) is also considered as inl
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R Torn 2 2 ATlor ( TTWn T )( TTWn
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condensation severity but cannot ca
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condensation has occurred at all or
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The inlet is the air from HADT duri
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3.9 Average temperature of inhaled
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Table 4.1 Inputs to the fluid dynam
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Figure 4.2 Simulink TM model for fl
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Table 4.4 Outputs from the overall
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Gain block after input 1 is to conv
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Figure 4.7 Varying Transport Delay
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4.2.5 Mask mixing calculation subsy
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4.3 Computational model of thermal
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Figure 4.11 Block diagram of CPAP t
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Figure 4.13 Simulink TM model for t
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The outputs are listed in Table 4.1
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Figure 4.16 Dynamic chamber-air the
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Figure 4.17 HADT lump thermal balan
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Figure 4.18 Steady state HADT lump
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Figure 4.19 HADT lump air dynamic f
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Figure 4.21Steady state mask full t
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4 Temperature of airflow from HADT
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Average evaporation rate subsystem
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HADT and connects those upstream se
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The experiment was also carried out
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air flowing through the elbow, a ce
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expansion from the elbow to the mas
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Figure 5.12 Environmental control r
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Table 5.1 shows the combinations of
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Figure 5.17 Comparison of model out
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The comparison of experimental resu
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5.3.1.4 Airflow temperature at the
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flow rate had been even further inc
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Figure 5.31 Comparison of condensat
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Table 5.3 Comparison of condensatio
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3. The corrugated grooves on the HA
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5.3.2.1 Validation of evaporation r
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The experiment observation showed t
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Figure 6.1 Reverse flow under diffe
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It can also be seen in Figure 6.2 t
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within the same period. However, wh
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Figure 6.6 Comparison of evaporatio
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Figure 6.8 Airflow velocity in HADT
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Figure 6.11 Airflow velocity in HAD
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In Figure 6.14 the blue curve repre
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6.3.3.1.2 Comparison when heating e
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This vaporization potentiality (coi
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Figure 6.20 In-tube condensation of
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When using different sized masks, t
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Figure 6.23 Average specific humidi
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The average specific humidity in an
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Table 6.5 Comparison of average spe
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6. The deep breathing and reverse f
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Appendices Appendix I Regression of
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Appendix I. Regression of the press
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Figure I. 1 Tested results and the
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Appendix II. Regression of the pres
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Table III. 2 Airflow temperature an
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Appendix IV. The corrugated HADT ou
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The total area of the complicated c
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Figure V. 1 Regression of saturated
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This ratio can be regressed against
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Appendix VII. Details of the CPAP f
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VII.4 The mask pressure subsystem F
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Inputs to this water-centred subsys
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Input port number Input Unit 1 Heat
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input 4 is the portion of impact ar
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VIII.2.3 Water surface mass transfe
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This subsystem also contains two su
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VIII.2.5 Chamber wall 1 heat transf
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Figure VIII. 13 Wall 1 outer surfac
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Wall 2 and 3 inner surface temperat
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Figure VIII. 17 Chamber wall 2 and
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Inputs to this subsystem are listed
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Appendix IX. Details of steady stat
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Figure IX. 3 The HADT lump wall out
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Appendix X. Details of HADT lump ai
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2 Absolute value of airflow velocit
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Figure X. 5 HADT lump inlet absolut
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Figure XI. 2 Steady state mask mixi
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Figure XI. 4 Steady state mask wall
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Input port number Input Unit 1 Aver
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Appendix XII. Details of mask air d
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4 Length of the triangular plate in
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8 Length of the triangular plate in
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Appendix XIII. Details of the auxil
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XIII.3 Breath load average subsyste
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Figure XIII. 7 Average evaporation
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XIV.1.2 Under normal ambient temper
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XIV.2.3 Under high ambient temperat
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XIV.4 Airflow temperature at the en
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XIV.5.2 Under normal ambient temper
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XIV.6.3 Under high ambient temperat
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Appendix XVI. Regression of kinetic
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Figure XVII. 2 Condensation/evapora
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Figure XVIII. 2 Condensation/evapor
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at point C. Right after that, here
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Appendix XIX. Coefficient and param
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Average water thermal conductivity
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Appendix XXI. Fluid dynamic and the
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The lung simulator drives the air.
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Appendix XXII. Model user instructi
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The input blocks and their values a
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Dynamically fluctuating air tempera
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References [1] Good sleep advice. W
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[28] Schettino GPP, Chatmongkolchar
Page 317:
[60] Marek R, Straub J. Analysis of
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