14. Hypoxia Flashcards
Define hypoxia
A disease where there is inadequate oxygen supply to the tissues
Define hypoxaemia
A low concentration of oxygen in the blood - describes the environment
What is considered to be hypoxaemia?
O2 of less than 8kPa
What factors can put your body under hypoxic stress?
Disease
Altitude
How does the partial pressure of O2 change with increasing altitude?
It decreases as the barometric pressure decreases due to Dalton’s law
What is the saturation of blood and partial pressure arriving at the gas exchange surface?
75% saturated with a partial pressure of 5.3 kPa
Where does bronchial drainage return to?
It returns to the pulmonary veins and dilutes the blood decreasing saturation to 97%
What is the pKa of fully oxygenated blood?
at 100% = 13.5 kPa
What happens to the mean pO2 in the alveolar space and in the arterial blood with age?
It decreases
Define polycythaemia
An abnormally increased concentration of haemoglobin in the blood
Define oxygen cascade
This describes the decreasing oxygen tension from inspired air to respiring cells
What is the amount of gas that will diffuse across a membrane proportional to?
Surface area for gas exchange Diffusion constant (CO2 is faster than O2 Diffusion gradient
Describe the changes in the partial pressure of oxygen in ambient air down to the veins?
Ambient air - 21.3kPa Upper airways air -20kPa Alveolar air - 13.5kPa this can vary depending on hypoventilation and hyperventilation Post-alveolar capillaries -13.5kPa Arteries - 13.3kPa bronchial drainage Tissues - variable depends on exercise Veins - 5.3kPa
How much of the haemoglobin desaturates when going form the arteries to the veins?
25%
What is the proportions oxygen transported?
2% is dissolved
98% bound to haemoglobin
What does the big drop in the partial pressure of O2 from the arteries to the tissues associated with?
A big unloading of haemoglobin. The drop in partial pressure of O2 isn’t what is keeping you alive.
What are the factors affecting the oxygen cascade?
Alveolar Ventilation
Ventilation/Perfusion matching
Diffusion capacity
Cardiac output
What is the shape of the oxygen cascade in really hypoxic air?
Everything decreases
When exercising what system is used for energy in the first 10 seconds?
The first 10 seconds uses ATP and ATP-Phophocreatine system
When exercising what system is used at 400m?
lactic acid
For exercise longer than 60 seconds what method of energy production is used?
aerobic respiration
What happens to the demand for energy when you exercise?
Increase in demand for energy, increase in the demand for oxygen, increase ventilation and increase cardiac output thus increasing oxygen delivery. You also increase fuel utilisation and carbon dioxide produced
Define VO2 max?
The capacity to deliver oxygen to tissues is termed VO2 max
In sub-maximal exercise how many L/min of ventilation is required to meet the metabolic demand?
40 L/min
Describe the change in ventilation with submaximal exercise?
There is a rapid rise followed by a steady rise in ventilation until the supply meets the demand
What happens after ventilation?
Repaying the oxygen debt
Where does the oxygen debt come from?
Intramuscular ATP, phosphocreatine and myoglobin
When exercise initial begins describe the breathing rate?
The breathing rate rapidly increases from 12 to 20 breathes per minute
When exercise initially begins why does the ventilation rate become stable?
increasing tidal volume is more efficient at increasing ventilation than increasing respiratory rate
What happens to the respiratory rate when the TV starts to plateau?
The respiratory rate starts to increase because it is inefficient to increase the tidal volume. The TV will not reach vital capacity because it is energy inefficient
What are five challenges of altitude?
Hypoxia Thermal stress Solar radiation Hydration Dangerous
Define accommodation
A rapid physiological change in response to a change in the oxygen environment
Define acclimatisation
Phsiology becomes more efficient so you can get as much out of the air as possible
What happens during acclimatisation?
Arterial partial pressure of O2 increases but CO2 falls. Erythropoietin is secreted from the renal cortex
What does low arterial partial pressure of O2 stimulate?
Increased ventilation to increase alveolar partial pressure of O2 - hypobaric hypoxia
What are some innate/developmental adaptations of those living in altitude?
Barrel Chest
Increased Haematocrit
Larger heart - Pulmonary vasculature constricts in response to hypoxia so a stronger heart is required to push blood throgh higher resistance circuit
Increased mitochondrial density
Describe chronic mountain sickness
Secondary polcythaemia (as a result of hypoxia). This is a problem because this higher proportion of RBC leads to increased viscosity of the blood
What is associated with acute mountain sickness?
High altitude cerebral oedema and high altitude pulmonry oedema. They are both associated with low oxygen environments
Ataxia - impaired ability to coordinate movement
What is the consequence of AMS?
I may develop into HAPE or HACE
What is HACE?
High altitude cerebral oedema
What is the physiology behind HACE?
Due to vasodilation of the vessels in response to hypoxaemia, the increased blood flow means there is more fluid leakage resulting in an increase in ICP
What is HAPE?
High altitude pulmonary oedema
What is the physiology behind HAPE?
Due to vasoconstriction of pulmonary vessels in response to hypoxia, there is increased pulmonary pressure, permeability and fluid leakage from capillaries. If the fluid produced exceeds the lymph drainage there is oedema
How do treat HACE?
Immediate descent, O2 therapy and dexamethasome
How do you treat HAPE?
Descent, hyperbaric O2 therapy, nifedipine, sildenafil
Define respiratory failure
The ineffective ability to exchange gas between the lungs and the blood
What are the types of respiratory failure?
Type I: Hypoxic respiratory failure
Type II: Hypercapnic respiratory failure
Type III: Mixed respiratory failure
What is indicative of Type I respiratory failure?
PaO2 < 8 kPa
What is indicative of Type II respiratory failure?
PaCO2 > 6.7 kPa
What is indicative of Type III respiratory failure?
PaO2 < 8 kPa
PaCO2 > 6.7 kPa
What systems help to maintain PaO2 and PaCO2?
Mechanisms within the blood, renal system and respiratory system
What are the main determinants of arterial gas tensions?
Alveolar ventilation and gas exchange
What is type I respiratory failure?
Typically a ventilation/perfusion mismatch in the lungs; perfused alveoli are hypoventilated or perfused alveoli are hypoperfused
What is type II respiratory failure?
Typically hypoventilated lungs; inadequate gas exchange as alveolar air stagnates and concentration gradients are poor