Higher Order Thoughts

1
Higher Order Thoughts

• Team 3

2
Some friends climb up to the top of a mountain
that is 16,000 ft. above sea level. They live at
sea level and it only takes them 2 days to reach
the peak.

• Introduction

3
Change in PaO2

• PaO2 is the partial pressure of oxygen in the
  arterial blood
• As the friends trek up the mountain. the PaO2
  would decrease due mainly to the PaO2 of the
  atmospheric air
• The barometric pressure at 16,000 ft. will be
  much less then the barometric pressure of 760
  mmHg at sea level
• Drop in atmospheric pressure leads to a drop in
  the PaO2 of atmospheric air (0.21 X atm PaO2)
  (0.21 is the percent oxygen in the air)
• A decrease in PaO2 in the atmosphere yields less
  O2 available for inspiration and therefore a drop
  in arterial PaO2
• Also, because the climbers are exerting
  themselves, the tissues will be consuming more
  oxygen for energy, this too contributes to the
  drop in PaO2

4
Response to Low PaO2

• The peripheral chemorecptors are stimulated by a
  decrease in arterial PaO2 as well as a an
  increase in H concentration
• Once the arterial PaO2 drops to 60 mmHg then
  there will be an increased ventilation
• The peripheral chemoreceptors increase their rate
  of synaptic firing to the brainstem when the
  arterial PaO2 is low
• This triggers the medullary inspiratory neurons
  and leads to an increase in ventilation to
  provide more oxygen to the alveoli

5
Change in PaCO2

• Hyperventilation leads to an increased loss of
  CO2 therefore decreasing arterial PaCO2
• An increased loss of CO2 would consequently lead
  to a decrease of H ions and cause alkalosis
  throughout the body

6
Change in Pulmonary Artery Pressure

• The pulmonary arteries normally have a low blood
  pressure due to low resistance (compared to
  systemic blood pressure)
• However, when the partial pressure of oxygen is
  low, it leads to vasoconstriction of the
  pulmonary vessels because there is a
  ventilation-perfusion inequality.
• This leads to an increase in pulmonary blood
  pressure.
• When oxygen is low in the lungs, it is also low
  in the pulmonary blood.
• This causes the lungs to divert blood flow away
  from the areas of the lungs that arent getting
  oxygen.
• This happens because the body tries to maximize
  the efficiency of oxygen delivery.

7
The Villagers

• On the way up the mountain, the climbers meet
  some villagers who have lived at an altitude of
  14,000 ft. their entire lives.

8
Acclimitization

• Table 13-12
• -Peripheral chemoreceptors stimulate ventilation
• -Increase in erythropoietin leads to an increase
  in red blood cell synthesis which increases
  erythrocyte and hemoglobin concentration in the
  blood
• -DPG increases and this shifts the hemoglobin
  dissociation curve to the right leading to an
  increase of oxygen unloading in the tissues
  (however can lead to an impairment of oxygen
  loading in the lungs with is detrimental)
• -Increase in capillary density, mitochondria, and
  muscle myoglobin occur ? increase oxygen transfer
• -peripheral chemoreceptors stimulate and
  increased loss of sodium and water in the urine
  which reduces plasma volume in order to increase
  the concentration of erthyrocytes and hemoglobin
  in the blood

9
Mountain Dwellers vs. Sea Level Climbers

• Hemoglobin Content
• Dwellers- would have an increased hemoglobin
  content compared to the climbers due to an
  increased production of erythropoietin in the
  kidneys causing an increased synthesis of
  erythrocytes
• Climbers- lower levels of hemoglobin because the
  body has not had to time to increase the number
  of erythrocytes in order to increase the amount
  of oxygen transferred throughout the body (would
  likely see a sharp increase in erythropoietin
  production but this would not lead to a
  sufficient increase in erythrocytes yet)

10
Mountain Dwellers vs. Sea Level Climbers

• Hypoxia is a deficiency of oxygen at the tissue
  level
• Hypoxia due to a decrease in arterial PaO2 is
  hypoxic hypoxia

11
Mountain Dwellers vs. Sea Level Climbers

• Hypoxic Ventilatory Response
• Dwellers- Have a blunted response because they
  are used to lower levels of O2 available. They
  have acclimitized to the lack of oxygen and
  therefore are able to tolerate less O2 due to the
  adaptations previously discussed. The
  chemoreceptors will likely have acclimitized to
  these levels as well.
• Climbers- Have a quicker hypoxic ventilatory
  response because they are not adapted to the
  lower PaO2. Lower PaO2 would trigger the
  peripheral chemoreceptors and in response,
  trigger increased ventilation

12
Mountain Dwellers vs. Sea Level Climbers

• Hypercapnic Ventilatory Response
• Dwellers Unchanged
• Climbers Unchanged
• This is because, due to the increased
  ventilation, the body will be removing CO2 from
  the body, and the level of CO2 will not be
  increased.
• Therefore, the dwellers have no advantage over
  the climbers because neither groups have
  developed hypercapnia.

13
Moutain Sickness Strikes

• Once they reach the summit, one of the climbers
  becomes short of breath and has a severe
  headache. However, the climbers only brought
  along a basic first aid kit and have to decide
  the best course of action

14
Help!

• The best course of action would be to give the
  climber water and get him safely down the
  mountain.
• The increased ventilation leads to an increase in
  H2O loss during breathing. The air is extremely
  cold and dry so this contributes to the loss of
  water because little water is taken in.
• Rehydration will give the climber more strength
  to make it back down the mountain.
• Once he gets to the bottom of the mountain he
  should get better quickly.

15
References

• Bhaumik, Gopinath Ram P. Sharma Deepak Dass
  Himmat Lama Shri K. S. Chauhan Shivu S. Verma
  William Selvamurthy P. K. Banerjee, Hypoxic
  Ventilatory Response Changes of Men and Women 6
  to 7 Days after Climbing from 2100 m to 4350 m
  Altitude and after Descent. High Altitude
  Medicine Biology. Aug 2003, Vol. 4, No. 3
  341-348.
• Dane, Gabrielle. "Reading Ophelia's Madness."
  Exemplaria 10.2 (1998). 12 July 2005
  lthttp//web.english.ufl.edu/english/exemplaria/dan
  efram.htmgt.
• Http//www.mounteverest.net/expguide/survivalrules
  .htm
• Http//www.nationalgeographic.com/everst/
• Katayama, Keisho Hiroshi Matsuo Koji Ishida
  Shigeo Mori Miharu Miyamura Intermittent
  Hypoxia Improves Endurance Performance and
  Submaximal Exercise Efficiency High Altitude
  Medicine Biology. Aug 2003, Vol. 4, No. 3
  291-304.
• Loeppky, Jack A. Milton V. Icenogle Damon Maes
  Katrina Riboni Pietro Scotto Robert C. Roach
  Body Temperature, Autonomic Responses, and Acute
  Mountain Sickness High Altitude Medicine
  Biology. Aug 2003, Vol. 4, No. 3 367-373.
• West, John B., Understanding Pulmonary Gas
  Exchange Ventilation-Perfusion Relationships
  American Physiological Society. 2004.
• West, John B., Human Physiology at Extreme
  Altitudes on Mount Everest. Science, New
  Series, Vol. 223, No. 4638 (Feb. 24, 1984),
  784-788.
• White, David P. Kevin Gleeson Cheryl K.
  Pickett Anne M. Rannels Allen Cymerman John V.
  Weil Altitude Acclimatization Influence on
  Periodic Breathing and Chemoresponsiveness During
  Sleep. J. Appl. Physiol, 63(l) 401-412, 1987.
• Widmaier, Eric P. Raff, Hershel Strang, Kevin
  T. Human Physiology The mechanisms of Body
  Function 10th Edition. 2006. Boston, MA