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Sleep apnoea: A model of airway drying during nasal positive air
pressure breathing
David White School of Engineering
• Olfaction • Heating and
humidifying inhaled air
• Recovering heat and moisture from exhaled air
• Filtration
Role of the nose
Affects 6% of adult population. •3 times as likely to have car accidents. •Causes excessive sleepiness whist awake. Suffer other symptoms such as: •irritability •Depression •sexual dysfunction •Learning •memory difficulty associated with: •irregular heartbeat •high blood pressure •heart attack •Stroke
Obstructive Sleep Apnoea (OSA)
Many n-CPAP patients use supplementary humidification to relieve airway drying symptoms.
in-vivo
nasal morphology
in-vitro
airway surface liquid supply
in-silico Computer simulation
Nasal Model
Produce a computational model for use by engineers and physiologists to investigate nasal conditions during ambient and pressurised breathing.
(in-vivo) Nasal Geometric Properties Cross-Sectional Area
Cross-Sectional Perimeter Volume
Surface Area
congested patent
Hydraulic diameter distribution along patent and congested airways at ambient pressure.
∆ = Hanna (1983), ○ = Craven et al. (2007).
(in-vitro) ASL Water Supply
Button, B. & Boucher, R.C. (2008)
ASL top up When ADO>200nM P1 receptor A2b opens Cl- channel – fluid leaves cell Na+ channel closes – no extracellular fluid entry CBF increases When ATP>1nM P2Y2 receptor open Cl- channel – fluid leaves cell CBF increases
ASL reduction When ADO<200nM P1 receptor A2b closes Cl- channel – no fluid exit Na+ channel opens – extracellular fluid enters cell CBF decreases When ATP<1nM P2Y2 receptor closes Cl- channel – no fluid exit CBF decreases
Purinergic Regulation
τ P P
Wen, J. et al. (2008)
Tissue Pressure and Shear Tidal Forces
Patm
+Patm
-Patm
nose
airflow direction
Tissue
inhale
exhale
Schematic representation of apparatus set up
ON
CPAP air delivery unit
U-tube manometer
Transport ventilator
Tissue bath
Incubator cabinet
Air-flow restrictor
Desiccant
Air vent
Bovine tracheal maximal water flux during ambient and augmented pressure
(in-silico) Computational Nasal
Air-Conditioning Model
Right Nasal Cavity
• Heat/water flux • ASL height • Cellular water supply • ASL boundary location
Tissue Compliance
Tissue Water Supply
Nasal Mask
• Pressure • Temperature • Humidity
Nasopharynx
• Pressure • Temperature • Humidity
Left Nasal Cavity
• Heat/water flux • ASL height • Cellular water supply • ASL boundary location
Tissue Compliance
Tissue Water Supply
Flow
Pa
rtiti
onin
g
Flow
Pa
rtiti
onin
g
Naso-
pharynx
Right Airway
R1 R2 Rn
R1 R2 Rn
Left Airway
Nasal
Mask
Inhalation inter-airway temperature (Ta), absolute humidity (AH), molar water flux (N), heat flux (Q) and ASL water equivalent height (He,ASL) distribution from rest to maximal change. Mask pressure ambient, AH=9.2g H2O/m3 dry air (T=23°C, RH=45%). ∆ = Keck et al. (2000), ○ = Wiesmiller et al. (2007), ◊ = Lindemann et al. (2001), = Hanna (1983), □ = Lindemann et al (2002).
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 1 2 3 4 5 6 7Time (s)
Inhalation
Ambient Breathing
Ambient Breathing
n-CPAP Breathing
Acknowledgements
Assoc. Prof. Brett Cowan and Dr Beau Pontré, both from the Centre for Advanced MRI (CAMRI), University of Auckland.
Dr Jim Bartley & Dr Randall Morton, Counties Manukau District Health Board & University of Auckland .
Dr Robin Hankin, School of Computing and Mathematical Sciences, AUT.
Dr Susan McGlashan, University of Auckland
in-vivo Nasal Morphology
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 1 2 3 4 5 6 7Time (s)
Inhalation
Simultaneously solve for Tm(k), Cm(k) and N(k):
(3.33)
(3.37)
CASL(k) = linear fit (3.36)
Given state variables Ta(k-1), Ca(k-1) from the previous segment
Read Dh(x) from morphology data A(k), P(k))
Calculate Vi(k) from Dh(k), ma and 𝜌a
Calculate Red(k) from Vi(k), Dh(k),υ
Calculate Nu(k) from Dh(k), Red(k) and Pr (k)
Solve ODE
(3.9)
Determine hc(k) from Nu(k) and kt,
𝑇𝑎,𝑘 = 𝑇𝑎,(𝑘−1) + 𝑑𝑇𝑎
Determine Le(k) α, and DAB
Calculate hm(k) from hc(k), 𝜌a, Le(k) and Cp,a
Solve ODE (3.14)
𝐶𝑎,𝑘 = 𝐶𝑎,(𝑘−1) + 𝑑𝐶𝑎
Update Ta(k)
Update Ca(k)
Normal Hydration Severely Dehydrated
Water Equivalent Height (He,asl)
10 µm
0 µm
Schematic representation of ASL water equivalent height of 10 µm representing the hydration difference between normal and severely dehydrated ASL. Diagram adapted from Button et al (2012).
Pres
sure
(cm
H2O
)
Time (sec)
2 mmH2O
Airflow Stress Stimulation
20 c
mH 2
O
Factor of 100 x