Carriage of Oxygen Flashcards
Describe the oxygen cascade.
- INSPIRED Gas - affected by inspired oxygen concentration/barometric pressure and altitude (reduced air pressure)
- ALVEOLAR Gas - Affected by alveolar ventilation/oxygen consumption/presence of water vapour in inspired gas
- VESSEL BLOOD - affected by ventilation and perfusion of alveoli, and haemoglobin binding
- CELLULAR OXYGEN - affected by blood flow/Hb concentration
What happens with oxygen partial pressures as you go down the oxygen cascade from the atmosphere to the tissues?
DECREASES
What is the effect of partial pressure on gas solubility?
- HENRY’S LAW - Amount of given gas that dissolves in a given type/volume of liquid proportional to partial pressure of gas in equilibrium with liquid
- BLOOD - Oxygen amount dissolved in blood proportional to partial pressure
Describe the behaviour of gases with respect to their partial pressures.
- If partial pressure in gas phase increased, concentration of gas in liquid phase increases proportionally
- Partial pressure of gas in solution = partial pressure of gas in mixture when in equilibrium
Why are mechanisms involved in oxygen transport in the blood?
- Resting oxygen consumption of body cells - 250 ml/min
- RESTING - rate of transport to tissues is 15 ml/min. STRENUOUS - rate is 90 ml/min
How does hyperbaric oxygen increase dissolved oxygen?
- At normal pressures, dissolved oxygen provides 3ml of O2 per litre
- Doubled at 2 atmospheres
- Increased by factor of 5 with 100% oxygen
- Used during carbon monoxide poisoning
What are the 2 ways oxygen is present in blood?
- Bound to haemoglobin - 98.5%
- Physically dissolved - 1.5%
Describe oxygen binding to Hb.
- Reversible
- 4 haem groups - each bind to O2
- Fully saturated - when all Hb present carrying maximum O2 load
- PO2 - determines percent saturation of Hb with O2
Describe HbF (fetal haemoglobin)
- Greater oxygen affinity than adult haemoglobin
- Greater saturation at lower partial pressures of oxygen
- Dissociation curve to left of adult Hb
Describe HbS (sickle cell haemoglobin)
- Hypoxia induces change in shape of RBC
- Causes vessel blockage and tissue damage
- Reduced affinity and reduced oxygen saturation at greater partial pressures
What is the formula for oxygen delivery index?
- Oxygen content of arterial blood x cardiac index
- CARDIAC INDEX - cardiac output in relation to body surface area
What is the formula for oxygen content of arterial blood?
- 1.34 x haemoglobin concentration x percentage saturation with oxygen
- 1.34 BECAUSE this is how much 1 gram of Hb carries when fully saturated
What can impair oxygen delivery to tissues?
- Reduced levels of oxygen in environment
- Respiratory disease/shunts/reduced perfusion of ventilated lung
- Heart failure - reduced cardiac output
- Anaemia - reduced carriage of oxygen
What does partial pressure of inspired oxygen depend on?
- Atmospheric pressure (reduces at high altitudes)
- Proportion of oxygen in gas mixture
What is the formula for partial pressure of oxygen in alveolar air?
- PARTIAL PRESSURE OF O2 IN INSPIRED AIR - (PARTIAL PRESSURE OF CO2 IN ARTERIAL BLOOD/0.8)
- 0.8 because this is usual RER ( VCO2/VO2)
What contributes to shape of the oxygen dissociation curve?
- Sigmoid shape due to co-operative binding of oxygen to Hb influencing affinity for O2
- Cooperativity causes conformational changes in shape of Hb
- Flattens when all sites occupied
- Dose response curve of 4 separate reactions superimposed on each other
What is the significance of the sigmoid curve?
- FLAT UPPER PORTIONS - moderate fall in partial pressure of alveolar oxygen won’t affect oxygen loading - no fall in Hb saturation
- STEEP LOWER PART - small drop in capillary PO2 = peripheral tissues get lots of oxygen
What is the Bohr effect and what causes it?
- Shift of dissociation curve to right i.e increased release of O2 to tissues
- Caused by raised [H+], temperature, 2,3 BPG and hypercapnia
What can cause the oxygen dissociation curve to be shifted to the left?
- ALKALOSIS
- Increased cardiac output
What are the effects of shifts of the curve to left/right?
- LEFT - greater oxygen affinity of Hb. Reduced release to tissues.
- OPPOSITE for RIGHT
Describe myoglobin.
- Present in skeletal and cardiac muscle
- Each molecule contains one haem group
- No cooperative binding so dissociation curve is hyperbolic
- Oxygen released at low partial pressures. Short term storage during anaerobic conditions
What does myoglobin presence in blood indicate?
Muscle damage
What makes respiration less effective?
- Mitochondrial disease
- Fewer mitochondria
- Genetic abnormalities
What is the effect of low haemoglobin levels?
- Less oxygen can be carried
- OPPOSITE FOR WHEN Hb LEVELS ARE RAISED - example during acclimitisation
Describe what occurs to CO2 during oxygen carriage. PART 1
- Produced in tissues
- Converted to H+ and HCO3- by carbonic anhydrase
- Can be carried dissolved in blood or bound to proteins
Describe what occurs to CO2 during oxygen carriage. PART 2
- Ions reconverted back to CO2
- CO2 readily transferred across alveolar membrane - CO2 exchange rarely a problem unless severe lung disease
