Alveolar pressures are not isolated from atmosphere!
As depth increases,
P
across chest wall increases
Depths below 100 result in the BIG SQUEEZE
A Bonus from the 440 Staff! Not in your Textbook!
Pressures:
| Depth | P (atm) | P (mm Hg) | Vol |
| 0 | 1 | 760 | 1 L |
| 33 | 2 | 1520 | 0.5 |
| 67 | 3 | 2280 | 0.33 |
| 100 | 4 | 3040 | 0.25 |
| 200 | 7 | 5320 | 0.14 |
| 300 | 10 | 7600 | 0.10 |
Partial Pressures of Gases in Air
| Gas | 0 | 33 | 100 | 200 |
| Air | 760 | 1520 | 2280 | 5320 |
| O2 | 160 | 320 | 640 | 1120 |
| N2 | 600 | 1200 | 2400 | 4200 |
Free Dive Limitations
Alveolar pressures are not isolated from atmosphere!
As depth increases, P
across chest wall increases
Depths below 100 result in the BIG SQUEEZE
SCUBA
Function of Regulator:
Deliver same volume of gas per minute as at sea level
However 1L of gas now occupies less volume depending upon depth
Must purge breathing tubes
As depth increases, air supply lasts less time
Pgas dissolved in plasma and body fluids depends upon P
of that gas
As depth and P increases, so does gas dissolved in blood
Suddenly decrease P, gas comes out of solution!
---->the Bends
Decompression
To combat the bends, decompression is required
Slow release of gases from body fluids due to stepwise decrease of
pressure
Decompression tables: Time and depth
Decompression after 1 hour at 200
10 min @ 50
17 min @ 40
19 min @ 30
50 min @ 20
84 min @ 10
Total Time = 3 hours
Gases at High Pressure
Nitrogen Narcosis or Rapture of the Deep
CO2 narcosis
O2 toxicity due to free radicals at PO2 > 1520
mm Hg
nausea, twitching, disturbed
vision, disorientation, dizziness --> coma
Solutions
Replace N2 with inert gas, Helium
Remove CO2 with increased air flow as depth increases
Increased depth decreases air supply time
e.g., 1 hour tank
lasts 1/4 hr at 100
Diving Mammals
How can a Whale dive for 1 hour, a Weddell seal for 15 minutes, and
a Peking duck for > 5 minutes?
How long can you hold your breath?
Physiological Adaptations
Hematocrit --> No
Hemoglobin (1.5X increase)
Myoglobin (7X increase)
Tidal volume
>80% of lung volume
exhale before a dive!! prevents the bends
O2 consumption decreases during a dive
Cardiac Output decreases to 20% of that at rest on surface
Vasoconstriction of major arteries
Blood flow to skeletal muscles reduced to almost 0
Reflex bradycardia
temperature dependent
all mammals
can be learned
Sphincter on posterior vena cava
decrease CO
Delivers blood to critical
Summary
Selective delivery of blood
O2 to CNS & heart
Prevent CO2 from reaching CNS
Decreased O2 consumption
Increased O2 stores in blood and muscle