Flying Over Everest Flashcards
Problems for Bar-headed goose flight at 9000m?
VERY low PO 2 roughly 1/3 of sea level PO 2 .
Affects of thinner air on flight reduces drag BUT also reduces lift generation during flight for any given air speed.
Overall power required to fly at 9000m is over 50% greater than at sea level.
Cold
Lung Air Sac System - Structure in birds?
It is separated into the lung (gas exchanging part) and a series of air sacs.
Gas exchange tissue = parabronchi
These are tiny tubes that permeate the lung tissue. Air capillaries branch off these.
No alveoli and no diaphragm!
Air flow:
The air sacs drive a continuous uni-directional flow of air.
Aerodynamic valve system ensures gas flows in the same direction through the parabronchi during inspiration and expiration.
Diff between avian and mammalian air flow?
The mammalian lung doesn’t empty with each expiration, it is a pool pattern of ventilation.
Mammalian anatomical dead space volume is far greater.
Ventilatory structures need to be freely distortable
Gas exchange structures require thin walls. In birds, lung parenchyma is rigid, in mammals, the lung is deformable. Benefits for blood gas barrier function as in avians, allows thinner, more uniform BGB.
Result: PaO2 closer to PiO2
Diff between avian and mammalian Blood gas barrier?
The BGB is much thinner compared to mammals, yet the integrity of the capillary walls is maintained.
Pulmonary capillary walls are less vulnerable to damage when transmural capillary pressures are high.
BGB is a uniform thickness.
Diff between avian and mammalian responses to hypoxia?
Respiratory system of birds generally more responsive to environmental hypoxia than mammals.
HVR (hypoxic ventilatory response) of BHG is significantly greater then other waterfowl species that migrate at low altitudes.
Possibly linked to lung mechanics higher peak inspiratory flows due to enhanced mechanical capacity.
Breathing frequency is coordinated with beat frequency. This is thought to reduce the energetic cost of breathing.
Diff between avian and mammalian responses to hypocapnia?
In Mammals:
Hyperventilation > Blow off CO2 > Hypocapnia > Cerebral vasoconstriction
This overrides the vasodilatory stimulus of hypoxaemia.
Birds:
Are less affected by hypocapnia meaning they maintain a higher cerebral blood flow when hyperventilating.
They are therefore capable of achieving a higher PaO2
What is hypoxic pulmonary vasoconstriction and how does it help in response to hypoxia?
Regional restriction of blood capillaries is used to match ventilation to flow
In hypoxia, constriction is GLOBAL.
When O2 levels are low, you need an increase in blood flow to the lungs
Global constriction increases cardiac work and pulmonary artery pressure (PAP)
A high PAP is a characteristic response of lowland mammals or birds to hypoxia.
If this is severe, it can result in pathology e.g.pulmonary odema
Why is pulmonary pressor response attenuated in BHG?
A reduced/lacking vasoconstrictor response suggests there is no reduction in blood flow, thus meaning the parabronchus of BHG is more homogenously perfused.
Not likely to suffer from pathologies associated with increasing PAP upon hypoxic exposure, as seen in lowland mammals.
Hb adaptation in BHG?
Oxyhemoglobin curve shifted to left. Lower p50. Due to single a.a. Mutation. Changes Hb state from T (deoxy) to R (oxygenated) state.
Conformational change that can only occur in relatively high O2 conditions
Hb can become oxygenated when less O2 is available
Bonus:
CaO2 is roughly twice as great in BHG at very high altitudes compared to pekin ducks.
