week 5 Flashcards
What is the purpose of respiration?
Remove oxygen from the air for use at the body tissues
remove carbon dioxide from body tissues and eliminate it in expiration
What happens in external respiration?
exchange of oxygen at alveoli
exchange of carbon dioxide at alveoli
What happens in internal respiration?
exchange of oxygen and carbon dioxide at the tissue
What does atmospheric air consist of?
nitrogen
oxygen
water
carbon dioxide
What is Dalton’s Law of partial pressures?
the total pressure in a gas mixture is the sum of the partial pressures of each individual gas
What is the partial pressure of a gas?
The pressure contributed by a single gas in a mixture of gases
What do English texts use as units for gas pressure?
KPa
How do you work out Kpa from mmHg?
Kpa = mmHg / 7.5
What unit do paediatrics use to measure gas pressure?
mmHg
What is Henry’s law?
The amount of gas in solution depends on the partial pressure of the gas and its solubility
What does oxygen move along the conducting zone by?
Bulk flow
What does oxygen move by in the respiratory zone?
diffusion
Name some factors controlling the rate of diffusion
area of the barrier
diffusing ability of the gas
inversely proportional to the thickness of the barrier
partial pressure difference
What is Fick’s Law?
diffusion is proportional to (surface area x difference in concentration)/diffusion distance
Name some influencing factors to diffusion
temperature
movement of molecules
partial pressure of the gas in the 2 areas
What is the partial pressure of oxygen in mixed venous blood?
40mmHg
What is the partial pressure of oxygen in alveoli air?
104mmHg
How long does equilibration take between venous blood and alveoli air?
about 0.25 seconds
Does oxygen combined with haemoglobin contribute to the partial pressure within the capillary blood?
NO
What happens to oxygen once haemoglobin is saturated?
Oxygen collects in the plasma
What limits transfer of oxygen at the alveoli?
It is perfusion limited i.e. by lack of blood supply
What is the partial pressure of carbon dioxide in mixed venous blood?
45mmHg
What is the alveolar partial pressure of carbon dioxide?
40mmHg
Why does carbon dioxide reach equilibrium in the same time as oxygen despite a small gradient?
Carbon dioxide is more soluble
Describe the shape of a red blood cell
Biconcave disc shaped
What cellular structures does a red blood cell lack?
nuclei, mitochondria and ribosomes
In what two ways is oxygen carried in the blood?
majority of oxygen is combined with haemoglobin
Once all available haemoglobin has been saturated with oxygen, the remaining oxygen is dissolved in plasma
Describe the structure of haemoglobin
2 alpha polypeptide chains
2 beta polypeptide chains
each chain forms a protein subunit with single haem group
How much oxygen does each haem group combine with?
1 molecule of oxygen
How many oxygen molecules can 1 haemoglobin combine with?
4
What is a saturated/fully loaded haemoglobin molecule called?
oxyhaemoglobin
What is a haem group that is not combined with oxygen called?
deoxyhaemoglobin
What happens to haemoglobin once the first oxygen molecule binds to a haem group?
Haemoglobin molecule begins to change shape, this increases the affinity of haemoglobin for oxygen and oxygen molecules 2,3 and 4 easily bind
How do you work out the percentage of haemoglobin saturation?
(oxygen bound to Hb) / (Oxygen capacity of Hb) x 100
What is the Henderson Hasselback equation?
water + carbon dioxide <- -> carbonic acid <- -> hydrogen ion + bicarbonate ion
How does bicarbonate maintain the pH of blood?
Acts as a buffer
What is the Bohr effect?
High levels of CO2 produce more hydrogen when converted to bicarbonate
An excess of hydrogen ions leads to a low pH causing the blood to become more acidic
In acidic environments Hb dissociates from oxygen
This shifts the oxygen dissociation curve to the right
What type of relationship do Hb and oxygen have?
reversible relationship
What is carbon dioxide transported mainly as?
bicarbonate ions
What is PaO2?
The partial pressure of oxygen dissolved in the blood and is measured in mmHg or Kpa
What is pH?
An expression of the hydrogen ion concentration. A scale used to define whether a liquid is acidic or alkaline
What is the pH of the body?
7.35-7.45
What does SaO2 represent?
The percentage of available haemoglobin which is combined with oxygen
What can SaO2 be analysed and measured from?
Directly from an arterial blood sample
What is spO2?
The percentage of available haemoglobin which is saturates, but measure non invasively using a pulse oximeter
How does a pulse oximeter measure SpO2?
Haemoglobin changes shape when bound to oxygen so absorbs and reflects light differently
The finger probe can detect the change in the way oxyhaemoglobin and deoxyhaemoglobin absorbs and reflects light
it then quantifies this
What percentage of haemoglobin are normally saturated with oxygen in arterial blood?
97.5%
What is the normal value of PaO2?
11-14 Kpa
What is the normal value of SaO2?
> 94%
What is the normal value of SpO2?
> 94%
What are the advantages/purpose of pulse oximetry?
non invasive/painless
used for continuous monitoring during treatment or exercise
as an outcome measure post treatment
aid exercise prescription
identify the need for additional/supplementary oxygen
What are the limitations of saturation probes?
limited usefulness if patient has low blood pressure, cold peripheries, hypothermia, PVD, anaemia
may be low in the elderly, during sleep and with COPD
the sensor is affected by movement, nicotine stains, clubbing, bruising, nail polish
What are ABG’s?
A diagnostic test performed on blood taken from an artery - most commonly from the wrist or the ear with some anaesthetic cream. Tested in a machine which produces the results in minutes
What do ABG’s give accurate information on?
pH, PaO2, SaO2 and the partial pressure of carbon dioxide in arterial blood
What changes can result in a change to the normal levels of oxygen and carbon dioxide in the blood?
changes in respiratory mechanics (disorders of ventilation) and changes in the respiratory system that impedes diffusion (disorders of oxygenation) result in a change to the normal levels of oxygen and carbon dioxide in the blood
What are some of the complications of ABG’s?
Arteriospasm
Haematoma
nerve damage
fainting or vasovagal response
decreased blood pressure
sweating
Where do they collect arterial blood from?
radial (1st choice)
brachial
femoral
