Altitude Flashcards
What are some effects of rapid ascent (loss of cabin pressure)
HYPOXIA
This causes some effects: sleepy false sense of well-being impaired judgement Blunted pain perception Increasing errors on simple tasks Decreased visual acuity Clumsiness TremorsLoss of consciousness or even death
What is the effect of ascent to moderate altitude (acute mountain sickness)?
Occurs of matter of hours/days
Hypoxia and Hypocapnia +Alkalosis
This causes some effects: Headache, Dizziness Breathlessness at rest Weakness Malaise Nausea, anorexia Sweating, palpitations Dimness of vision, partial deafness Sleeplessness Fluid retention Dyspnea on exertion
Whats the relationship between altitude and loss of consciousness?
How long a person can stay conscious is inversely proportional to their altitude
At very high altitudes you would lose consciousness almost instantly
Totale barometric pressure is 47mmHg at 63,000 feet, water boils at this pressure - all your body fluids would boil.
What is the relationship between partial pressure and altitude
As you ascend to greater altitudes, the ambient pressure decreases and is not linear
Barometric pressure decreases more rapidly at lower altitudes
Closer to the surface of the earth, more pressure because you have more pressure pushing down
What is the difference between the changes in water pressure and O2 pressure at high altitudes
Water changes in a linear fashion
water: pressure = water density X water column of height X gravity
Fraction of water in air stays a constant 0.21
Air does not because it is compressible and a non linear function
How does the increased altitude effect alveolar ventilation?
Inspired PO2 is lower so arterial PO2 is lower, arterial chemoreceptors increase ventilation
this will end up decreasing CO2
What is the revised equation for Alveolar Air at different altitudes?
PAO2 = FiO2 (Pb - PH2O) - PACO2/R
PAO2 = alveolar oxygen FiO2 = inspired air Pb = barometric pressure PH2O = water pressure PACO2 = alveolar CO2 R-Value = .8
How is the PiO2 (PO2 of inspired air) calculated?
PiO2 = FiO2 X (Pb - PH2O)
FiO2 = inspired air Pb = barometric pressure PH2O = water pressure R-Value = .8
What chemoreceptors primarily respond to altitude changes (Hypoxic environment)
The arterial chemoreceptors respond to the hypoxic changes, central do not.
Response usually isn’t all that impressive until PaO2 gets to around 60mmHg
Arterial chemoreceptors never adapt to hypoxic conditions
PaO2 = Arterial O2
How does hyperventilation in response to increased altitude affect the body?
Body breathes in excess of what is required to keep PaCO2 around 40mmHg
Alveolar and Arterial PaCO2 should normally be equal
If patients PaCO2 falls then the patient will experience respiratory alkalosis
When treating acute mountain sickness one should think about respiratory alkalosis
What is the price of increasing PAO2 by hyperventilation?
Hypocapnia and respiratory alkalosis
Central chemoreceptors are trying to say “breathe less” as CO2 is leaving the CSF through the BBB, central thinks its hypocapnia and doenst want to breath any more
Most people get a small amount of cerebral edema
Renal system tries to retain H ions and get rid of HCO
Whats happening with PaO2 and PAO2 and PACO2 at higher altitudes
all are lowered
What are the effects of high altitude on the mechanics of breathing?
Increases work of breathing, triggers bigger tidal volumes (hyperventilate through this path)
Elastic work of breathing increased (due to larger tidal volumes)
Increase resistance due to dynamic compression -THE BIGGEST REASON
Chemo receptors trigger broncho constriction
How does perfusion change at higher altitudes?
Arterial chemorecptors increase CO - pulmonary artery pressure increases - recruitment and distention - decreased PVR
V/Q relationship is probably better because of more uniform ventilation and perfusion of top of lung
How does HPV work at high altitudes?
If PO2 of alveoli is low than HPV will kick in
How does the pressure gradient effect diffusion at higher altitudes?
At normal altitude Mixed venous is at around 40 and Alveolar PO2 is around 100, there is a larger pressure gradient so O2 passes over quickly and they reach equilibrium faster, which makes this a perfusion-limited relationship
At higher altitudes Mixed venous is around 22 and the highest Alveolar PO2 will go is around 45, smaller pressure gradient so it will take longer for it to reach equilibrium
What mechanisms can help offset the diffusion problems caused by high altitudes?
Increased CO will allow more blood flow through the pulmonary capillaries so more blood will be oxygenated
Increased CO will cause increased recruitment and distention which will increase surface area
Whats the difference between alveoli in the top of the lung at higher altitudes as opposed to normal altitudes?
Better ventilated and perfused than normal conditions
At normal conditions the bottom portion of the lungs are much more ventilated and perfused
What are some of the benefits and disadvantages of HPV at high altitudes?
Normally HPV is good because it will direct blood towards better ventilated alveoli but if the who lung is hypoxic due to low O2 at high altitudes, it won’t help
This can cause pulmonary edema and greatly increase after load on RV
What 3 effects can altitude have on the mechanics of breathing?
- Work of breathing goes up
- Alveolar ventilation is more uniform
- Both CO and HPV will increase which will increase workload on RV, this will result in more recruitment of pulmonary capillaries which will increase surface area
How does increased altitude effect the oxy-hemoglobin curve?
Most likely move the curve to the left because PCO2 will decrease and pH will increase
Loading of O2 will be enhanced but unloading will be hindered
Body creates more RBCs in order to try and compensate
Body will increase the production of 2,3 DPG
What CNS problems does high altitude cause?
High CSF pH due to CO2 ions leaving
Normally low arterial pCO2 would cause constriction but the low pO2 overrides this causing vasodilation, hydrostatic pressure increases and fluid leaves the capillaries and accumulates in the brain
