Chapter 9 Flashcards
What is the Fick equation for exercise testing?
VO2 = Z (CaO2 - CvO2) VO2 = VE (FIO2 - FEO2)
What happens to diffusing capacity during exercise?
Increases threefold
What increases most in exercise? Ventilation or blood flow?
Ventilation
CO increase in only 1/4 the increase in ventilation
What happens to V/Q mismatch in elite athletes at the end of exercise?
V/Q mismatch can develop because of mild degrees of interstitial pulmonary edema
What changes happen in peripheral tissues with exercise?
capillaries open up, reduce diffusion path length to the mitochondria
peripheral vascular resistance falls
What physiologic changes at high altitude?
- Hyperventilation *** most important for acclimatization
- mechanism: hypoxic stimulation of peripheral chemoreceptors
- maximum breathing capacity increases bc air is less dense - Polycythemia
- increases O2-carrying capacity
- stimulus for increased production of RBC is hypoxemia (releases EPO from kidney which stimulates bone marrow) - Increased number of capillaries per unit volume in peripheral tissues
- Increased oxidative enzymes in peripheral tissues
- Shift in O2 dissociation curve:
rightward shift with moderate altitude (increased 2,3 DPG from respiratory alkalosis)
Leftward shift with extreme altitude due to respiratory alkalosis - Pulmonary vasoconstriction
- deleterious
- causes pulmonary edema
How does the mixed venous blood compare for individual at altitude and at sea level?
Actually very similar
Even though PiO2 is very different, the acclimatization mechanisms actually make it so that the mixed venous blood is not very different.
What are the effects of O2 toxicity?
Pulmonary edema
Retrolental fibroplasia (babies)
CNS stimulation - leads to convulsions (can happen with diving and high PiO2)
Does absorption atelectasis happen faster breathing 100% O2 or RA? Why?
Faster with 100% O2
The venous blood partial pressure is very low when breathing in 100% O2 because there is no N2 stenting effect (all N2 is washed out)
- the fall in PO2 from arterial to venous blood is greater than the rise in PCO2 because of the steep slope of CO2 dissociation curve compared to O2 dissociation curve
What happens in space flight?
- Deposition of inhaled aerosol is altered because there is no sedimentation
- Thoracic blood volume increases because blood is not pooled in legs - increases pulmonary capillary blood flow and diffusing capacity
- Cardiovascular deconditioning when reurned to earth - postural hypotension when returning to earth
Diving
What happens to work of breathing when diving?
Increased work of breathing because of increased density of gas at depth
Why does decompression sickness happen?
N2 is normally poorly soluble
at high partial pressure, it dissolves into fat (high N2 solubility) but blood supply is poor to fat, so it diffuse out slowly bc of low solubility
Takes hours to reach equilibrium
With ascent. N2 is released as air bubbles and this can cause pain (bends) or CNS disturbances
Why does a Helium-oxygen mixture prevent decompression sickness?
Helium has low solubility and low molecular weight.
- low solubility means it won’t dissolve in tissues (1/2 as soluble as N2)
- low molecular weight (1/7 N2) means it diffuses out of tissue rapidly
Diffusion constant = sol / sqrt(MW)
ALSO has low density which decreases the work of breathing
Re = 2rvd/n d = density
lower Re means more laminar flow (<2000)
What are the consequences of diving?
Decompression sickness
Inert gas toxicity (N2 affects CNS)
O2 toxicity (pulm edema, stimulates CNS)
What can hyperbaric O2 treat?
Decompression sickness
CO Hb poisoning (left shifted O2 dissociation curve)
Gas gangrene
Note: high risk of fire and explosion, therefore O2 given by mask in the chamber
