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Karan - MBBS Year 1: Respiratory Week 1 > Carriage of Oxygen > Flashcards

Carriage of Oxygen Flashcards

1
Q

Describe the oxygen cascade.

A
  • 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
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2
Q

What happens with oxygen partial pressures as you go down the oxygen cascade from the atmosphere to the tissues?

A

DECREASES

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3
Q

What is the effect of partial pressure on gas solubility?

A
  • 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
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4
Q

Describe the behaviour of gases with respect to their partial pressures.

A
  • 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
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5
Q

Why are mechanisms involved in oxygen transport in the blood?

A
  • 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
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6
Q

How does hyperbaric oxygen increase dissolved oxygen?

A
  • 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
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7
Q

What are the 2 ways oxygen is present in blood?

A
  • Bound to haemoglobin - 98.5%
  • Physically dissolved - 1.5%
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8
Q

Describe oxygen binding to Hb.

A
  • 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
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9
Q

Describe HbF (fetal haemoglobin)

A
  • Greater oxygen affinity than adult haemoglobin
  • Greater saturation at lower partial pressures of oxygen
  • Dissociation curve to left of adult Hb
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10
Q

Describe HbS (sickle cell haemoglobin)

A
  • Hypoxia induces change in shape of RBC
  • Causes vessel blockage and tissue damage
  • Reduced affinity and reduced oxygen saturation at greater partial pressures
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11
Q

What is the formula for oxygen delivery index?

A
  • Oxygen content of arterial blood x cardiac index
  • CARDIAC INDEX - cardiac output in relation to body surface area
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12
Q

What is the formula for oxygen content of arterial blood?

A
  • 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
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13
Q

What can impair oxygen delivery to tissues?

A
  • Reduced levels of oxygen in environment
  • Respiratory disease/shunts/reduced perfusion of ventilated lung
  • Heart failure - reduced cardiac output
  • Anaemia - reduced carriage of oxygen
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14
Q

What does partial pressure of inspired oxygen depend on?

A
  • Atmospheric pressure (reduces at high altitudes)
  • Proportion of oxygen in gas mixture
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15
Q

What is the formula for partial pressure of oxygen in alveolar air?

A
  • 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)
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16
Q

What contributes to shape of the oxygen dissociation curve?

A
  • 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
17
Q

What is the significance of the sigmoid curve?

A
  • 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
18
Q

What is the Bohr effect and what causes it?

A
  • Shift of dissociation curve to right i.e increased release of O2 to tissues
  • Caused by raised [H+], temperature, 2,3 BPG and hypercapnia
19
Q

What can cause the oxygen dissociation curve to be shifted to the left?

A
  • ALKALOSIS
  • Increased cardiac output
20
Q

What are the effects of shifts of the curve to left/right?

A
  • LEFT - greater oxygen affinity of Hb. Reduced release to tissues.
  • OPPOSITE for RIGHT
21
Q

Describe myoglobin.

A
  • 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
22
Q

What does myoglobin presence in blood indicate?

A

Muscle damage

23
Q

What makes respiration less effective?

A
  • Mitochondrial disease
  • Fewer mitochondria
  • Genetic abnormalities
24
Q

What is the effect of low haemoglobin levels?

A
  • Less oxygen can be carried
  • OPPOSITE FOR WHEN Hb LEVELS ARE RAISED - example during acclimitisation
25
Q

Describe what occurs to CO2 during oxygen carriage. PART 1

A
  • Produced in tissues
  • Converted to H+ and HCO3- by carbonic anhydrase
  • Can be carried dissolved in blood or bound to proteins
26
Q

Describe what occurs to CO2 during oxygen carriage. PART 2

A
  • Ions reconverted back to CO2
  • CO2 readily transferred across alveolar membrane - CO2 exchange rarely a problem unless severe lung disease

Karan - MBBS Year 1: Respiratory Week 1 (10 decks)

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