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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Atmospheres and Decompression• Emergency and explosive
decompression• Denitrogenation and decompression sickness• Tissue
models• Physics of bubble formation• Atmosphere constituent
analysis
1
© 2019 David L. Akin - All rights reserved
http://spacecraft.ssl.umd.edu
http://spacecraft.ssl.umd.edu
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Effective Performance Time at Altitude
2
Altitude, m Altitude, ft Effective Performance Time5500 18,000
20-30 minutes6700 22,000 10 minutes7600 25,000 3-5 minutes8500
28,000 2.5-3 minutes9100 30,000 1-2 minutes
10,700 35,000 0.5-1 minute12,200 40,000 15-20 seconds13,100
43,000 9-12 seconds15,200 50,000 9-12 seconds
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Cabin Depressurization Rates• Fliegner’s Equation
– t=time of decompression (seconds)– A=cross-sectional area of
opening (square inches)– V=cabin volume (cubic feet)– P=initial
cabin pressure (psia)– B=external ambient pressure (psia)
• Decent approximation for aircraft cabins
3
t = 0.22VA
P − BB
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Cabin Depressurization Rates• Haber-Clamann Model
– tc=time constant for cabin (sec)– V=cabin volume (cubic feet)–
A=area of opening (square feet)– C=speed of sound (1100 ft/sec)–
t=time of depressurization (sec)– P=initial cabin pressure (psia)–
B=external ambient pressure (psia)
– 4
tc =V
ACt = tc [1.68 ln ( PB ) + 0.27]
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Cabin Depressurization Rates• Violette’s Equation
– t=time of depressurization (sec)– V=cabin volume (cubic
meters)– A=area of opening (square meters)– P=initial cabin
pressure– B=external ambient pressure
5
t =V
220Acosh−1 ( PB )
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
S/C Depressurization (Sonic Orifice)• External environment at
zero pressure• Any hole is a sonic orifice• Mass flow rate
• Switch to pressure (ideal gas, isentropic)
vflow = γRT
·m =dmdt
= ρvflowAorifice
dmdt
= APoγ
RTo (2
γ + 1 )γ + 1γ − 1
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Sonic Orifice Analysis (2)
dm
dt= 0.04042
APop
To
For air, � = 1.4; R = 287J
kg K
Isothermal: t =0.086
To
VA
ln ( PoPf )
Solve for time to reach final pressure Pf
Adiabatic: t =0.43
To
VA ( PoPf )
0.143
− 1
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
S/C Depressurization (Bernoulli)• Bernoulli’s Law
• g=0• Interior and exterior to spacecraft
• Inside vo~0, outside Pe=0
8
P +1
2⇢v
2 + ⇢gh = constant
Po
+1
2⇢v2
o
= Pe
+1
2⇢v2
e
Po
=1
2⇢v2
e
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Bernoulli Analysis (2)
ve
=
s2P
o
⇢
dm
dt= ⇢Av
e
= A⇢
s2P
o
⇢= A
p2⇢P
o
⇢ = m/V
dmpm
= A
r2P
o
Vdt
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Cabin Leak Pressure Loss
10
0"
2"
4"
6"
8"
10"
12"
14"
16"
0" 50" 100" 150" 200" 250" 300" 350"
Cabin&Pressure&(p
si)&
Depressuriza1on&Time&(sec)&
Bernoulli" Sonic"Nozzle"
10 m3 cabin volume 1 cm2 leak area
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Lung Overpressure Following Decompression
11
From Nicogossian and Gazenko, Space Biology and Medicine -
Volume II: Life Support and Habitability, AIAA 1994
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Violette’s Explosive Decompression Limits
12
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Caissons• Pressurized chambers
for digging tunnels and bridge foundations
• Late 1800’s - caisson workers exhibited severe symptoms– joint
pain– arched back– blindness– death
13
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Brooklyn Bridge• Designed by John Roebling, who
died from tetanus contracted while surveying it
• Continued by son Washington Roebling, who came down with
Caisson Disease in 1872
• Competed by wife Emily Warren Roebling
• 110 instances of caisson disease from 600 workers
14
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Decompression Sickness (DCS)• 1872 - Dr. Alphonse Jaminet noted
similarity
between caisson disease and air embolisms• Suggested procedural
modifications
– Slow compression and decompression– Limiting work to 4 hours,
no more than 4 atm– Restricting to young, healthy workers
• 1908 - J.B.S. Haldane linked to dissolved gases in blood and
published first decompression tables
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Supersaturation of Blood Gases• Early observation that “factor
of two” (50% drop in
pressure) tended to be safe• Definition of tissue ratio R as
ratio between
saturated pressure of gas compared to ambient pressure
• 50% drop in pressure corresponds to R=1.58
(R values of ~1.6
considered to be “safe”)
16
R =PN2
Pambient= 0.79 (nominal Earth value)
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Tissue Models of Dissolved Gases• Issue is dissolved inert gases
(not involved in
metabolic processes, like N2 or He)• Diffusion rate is driven by
the gradient of the
partial pressure for the dissolved gas
where k=time constant for specific tissue (min-1)P refers to
partial pressure of dissolved gas
17
dPtissue(t)dt
= k [Palveoli(t)� Ptissue(t)]
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Solution of Dissolved Gas Diff. Eq.• Assume ambient pressure is
piecewise constant
(response to step input of ambient pressure)• Result is the
Haldane equation:
• Need to consider value of Palveoli
where Q=fraction of dissolved gas in atmosphere ΔPO2=change in
ppO2 due to metabolism
18
Ptissue(t) = Ptissue(0) + [Palveoli(0)� Ptissue(0)]�1� e�kt
⇥
Palveoli =�
Pambient � PH2O +1�RQ
RQPCO2
⇥Q
Palveoli = (Pambient � PH2O � PCO2 + �PO2)Q
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Linearly Varying Pressure Solution• Assume R is the (constant)
rate of change of
pressure - solution of dissolved gases PDE is
• This is known as the Schreiner equation • For R=0 this
simplifies to Haldane equation• Produces better time-varying
solutions than
Haldane equation• Easily implements in computer models
19
Pt(t) = Palv0 + R�
t� 1k
⇥�
�Palv0 � Pt0 �
R
k
⇥e�kt
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Tissue Saturation following Descent
20
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Tissue Saturation after Ascent
21
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Effect of Multiple Tissue Times
22
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Haldane Tissue Models• Rate coefficient frequently given as time
to evolve
half of dissolved gases:
• Example: for 5-min tissue, k=0.1386 min-1• Haldane suggested
five tissue “compartments”: 5,
10, 20, 40, and 75 minutes• Basis of U. S. Navy tables used
through 1960’s• Three tissue model (5 and 10 min dropped) • 1950’s:
Six tissue model (5, 10, 20, 40, 75, 120)
23
T1/2 =ln (2)
kk =
ln (2)T1/2
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Workman Tissue Models• Dr./Capt. Robert D. Workman of Navy
Experimental Diving Unit in 1960’s• Added 160, 200, 240 min
tissue groups• Recognized that each type of tissue has a
differing
amount of overpressure it can tolerate, and this changes with
depth
• Defined the overpressure limits as “M values”
24
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Workman M Values• Discovered linear relationship between
partial
pressure where DCS occurs and depth
M=partial pressure limit (for each tissue compartment)M0=tissue
limit at sea level (zero depth)ΔM=change of limit with depth
(constant)d=depth of dive
• Can use to calculate decompression stop depth
25
M = M0 + �Md
dmin =Pt �M0
�M
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
PADUA (Univ of Penn.) Tissue ModelTissue T1/2 (minutes) M0
(bar)
1 5 3.042 10 2.5543 20 2.0674 40 1.6115 80 1.5816 120 1.557 160
1.528 240 1.499 320 1.4910 480 1.459
26
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Bühlmann Tissue Models• Laboratory of Hyperbaric Physiology at
University
Hospital, Zurich, Switzerland• Developed techniques for
mixed-gas diving,
including switching gas mixtures during decompression
• Showed role of ambient pressure on decompression (diving at
altitude)
• Independently developed M-values, based on absolute pressure
rather than SL depth
• “Zurich” 12 and 16-tissue models widely used
27
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Bühlmann M-Value Models• Modifies Workman model by not assuming
sea
level pressure at water’s surface
Pamb=pressure of breathing gasb=ratio of change in ambient
pressure to change in tissue pressure limit
(dimensionless)a=limiting tissue limit at zero absolute
pressure
• ZH-L16 model values for a and b
28
M =Pamb
b+ a
a = 2 T�13
1/2 < bar > b = 1.005� T� 121/2
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Physics of Bubbles• Pressure inside a bubble is balanced by
exterior
pressure and surface tension
where γ=surface tension in J/m2 or N/m (=0.073 for water at
273°K)
• Dissolve gas partial pressure Pg=Pamb in equilibrium
• Gas pressure in bubble Pint>Pamb due to γ• All bubbles will
eventually diffuse and collapse
29
Pinternal = Pambient + Psurface = Pambient +2�r
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Critical Bubble Size• Minimum bubble size is defined by point at
which
interior pressure Pint = gas pressure Pg
• rrmin - bubble will grow • r=rmin - unstable equilibrium
30
rmin =2�
Pg � pambient
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Bubble Formation and Growth• In equilibrium, external pressure
balanced by internal
gas pressure and surface tension• Surface tension forces
inversely proportional to radius
31
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
“Clinical” Discussion of DCS• Tissue models are predictive, not
definitive• Every individual is different
– Overweight people more susceptible to DCS– Tables and models
are predictive limits - there will be
“outliers” who develop DCS while adhering to tables
• Doppler velocimetry reveals prevalence of bubbles in
bloodstream without presence of DCS symptoms - “asymptomatic
DCS”
32
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Implications of DCS in Space Flight• Drop from sea level
pressure to ~4 psi, 100% O2
pressure– Equivalent to ascent from fully saturated 120 ft dive
– Launch in early space flight– Extravehicular activity from
shuttle or ISS
• To have “safe” (R=1.4) EVA from shuttle requires suit pressure
of 8.2 psi
33
R =PN2Pamb
=14.7(0.78)
4= 2.87
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Current Denitrogenation Approaches• Depress to 10.2 psi for
12-24 hours prior to EVA
– Full cabin depress in shuttle– “Campout” in air lock module of
ISS
• Exercise while breathing 100% O2• In-suit decompression on
100% O2 (3.5-4 hours)
34
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Historical Data on Cabin Atmospheres
35
from Scheuring et. al., “Risk Assessment of Physiological
Effects of Atmospheric Composition and Pressure in Constellation
Vehicles” 16th Annual Humans in Space, Beijing, China, May 2007
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Spacecraft Atmosphere Design Space
36
from Scheuring et. al., “Risk Assessment of Physiological
Effects of Atmospheric Composition and Pressure in Constellation
Vehicles” 16th Annual Humans in Space, Beijing, China, May 2007
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Effect of Pressure and %O2 on Flammability
37
from Hirsch, Williams, and Beeson, “Pressure Effects on Oxygen
Concentration Flammability Thresholds of Materials for Aerospace
Applications” J. Testing and Evaluation, Oct. 2006
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Atmosphere Design Space with Constraints
38
from Scheuring et. al., “Risk Assessment of Physiological
Effects of Atmospheric Composition and Pressure in Constellation
Vehicles” 16th Annual Humans in Space, Beijing, China, May 2007
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Decompression/Neurovestibular Physiology ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
0.0#
2.0#
4.0#
6.0#
8.0#
10.0#
12.0#
14.0#
0# 200# 400# 600# 800# 1000# 1200#
Tissue
&Nitrogen
&Pressure&(psi)&
Time&(min)&
5*min#.ssue# 80*min#.ssue# 240*min#.ssue#
EVA Denitrogenation - 14.7 psi Cabin
39
Suit Pressure 4.3 psi 100% O2
Cabin Atmosphere 14.7 psi 21% O2
R Value = 1.4
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Decompression/Neurovestibular Physiology ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
0.0#
1.0#
2.0#
3.0#
4.0#
5.0#
6.0#
0# 200# 400# 600# 800# 1000# 1200#
Tissue
&Nitrogen
&Pressure&(psi)&
Time&(min)&
5+min#/ssue# 80+min#/ssue# 240+min#/ssue#
EVA Denitrogenation - 8.3 psi Cabin
40
Suit Pressure 4.3 psi 100% O2
Cabin Atmosphere 8.3 psi 32% O2
R Value = 1.4
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Pulmonary Physiology and Decompression ENAE 697 - Space Human
Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Constellation Spacecraft Atmospheres
41
from Scheuring et. al., “Risk Assessment of Physiological
Effects of Atmospheric Composition and Pressure in Constellation
Vehicles” 16th Annual Humans in Space, Beijing, China, May 2007