Ventilation: Perfusion Relationship, Gas Transport in Blood, Additional Material on Oxygen Carriage in the Blood Flashcards
What does the ventilation (V) rate refer to?
Volume of gas inhaled and exhaled from the lungs in a given time period, usually a minute.
How can ventilation rate be calculated and what is the average?
Tidal volume X respiratory rate
In an average man, the ventilation rate is roughly 6L/min.
What is perfusion (Q)?
The total volume of blood reaching the pulmonary capillaries in a given time period.
Perfusion refers to blood flow through the pulmonary circulation.
What is a mismatch of V/Q at the base?
Ventilation<Perfusion ratio <1.0
What is a mismatch of V/Q at the apex?
Ventilation>Perfusion ratio >1.0
What can happen during V/Q mismatch?
When there is inadequate ventilation the V/Q reduces, and gas exchange within the affected alveoli is impaired.
As a result, the capillary partial pressure of oxygen (pO2) falls and the partial pressure of carbon dioxide (pCO2) rises.
What is shunt?
Shunt is a term used to describe the passage of blood through areas of the lung that are poorly ventilated. (ventilation«perfusion)
What is shunt the opposite of?
Alveolar dead space
What is alveolar dead space?
Volume of air in alveoli that are ventilated but not perfused
What are common causes of alveolar dead space?
Smoking
Bronchitis
Emphysema
Asthma
What is anatomical dead space?
Air in the conducting zone of the respiratory tract unable to participate in gas exchange as walls of airways are too thick
What is physiological dead space?
Anatomical DS + alveolar DS
What does haemoglobin get get from plasma?
Sequesters O2 from the plasma, thus maintaining a partial pressure gradient that continues to suck O2 out of the alveoli, until the haemoglobin becomes saturated with O2.
What is fundamental in determining how much O2 binds to haemoglobin?
Partial pressure of O2 in the plasma
What does blood transport?
O2 from lungs to tissues and the waste product of this process CO2 from tissues to lungs for removal.
How does O2 travel?
O2 travels in two forms in the blood:
In solution in plasma
Bound to haemoglobin protein in red blood cells
Bulk (77%) of CO2 is transported in solution in plasma, 23% is stored within haemoglobin
How much 02 is in per litre of plasma?
Only 3ml O2 dissolve per litre plasma
How much O2 is in per litre of blood?
200ml O2 per litre whole blood, 197m of which is bound to haemoglobin in red blood cells
What determines the degree of which haemoglobin binds to oxygen?
Partial pressure of oxygen in the blood.
What does the oxygen-haemoglobin dissociation curve describe?
Proportion of saturated haemoglobin plotted against partial pressure of oxygen
What determins the oxyhaemoglobin dissociation curve?
Haemoglobin binding affinity for oxygen
Rate haemoglobin acquires
What is the primary transporter of oxygen in blood?
Haemoglobin
What does P50 on the oxygen-haemoglobin dissociation curve describe?
Partial pressure of oxygen when haemoglobin is 50% saturated
What does a right shift in the oxygen-haemoglobin dissociation curve cause?
Raised p50, lower oxygen affinity
What causes a right shift in the oxygen-haemoglobin dissociation curve?
Increased pCO2
Increased temperature
Increased 2,3 DPG
Decreased pH (more acidic)
Haemoglobin affinity for O2 increases
What does a left shift in the oxygen-haemoglobin dissociation curve cause?
Lower p50, higher oxygen affinity
What causes a left shift in the oxygen-haemoglobin dissociation curve?
Decreased pCO2
Decreased temperature
Decreased 2,3 DPG
Increased pH (more basic)
HbF (haemoglobin F)
Haemoglobin affinity for 02 decreases
What does the sigmoidal shape of the oxygen-haemoglobin dissociation curve tell us?
Heamoglobin has an increasing affinity for O2 as the number of bound O2 molecules goes up.
Binding 4th O2 molecule is much easier than binding that first O2 molecule. This is called positive co-operativity.
What are the three means of CO2 transport in the blood from peripheral tissues and back to lungs?
- Dissolved gas (7%)
- Bicarbonate (70)
- Carbaminohemoglobin bound to hemoglobin (23%)
What happens when CO3 reacts with carbonic anhydrase?
Form carbonic acid that then immediately dissociates to bicarbonate ions and hydrogen ions.
What is the difference between partial pressure and gas content (Arterial O2c concentration)?
PaO2 refers to purely O2 in solution in the plasma and is determined by O2 solubility and the partial pressure of O2 in the gaseous phase that is driving O2 into solution.
Total oxygen content = the total amount ofoxygen carried in the blood; equal to the amount of oxygen carried by the hemoglobin in the red blood cells plus the amount of oxygen dissolved in the plasma.
What does 92% of haemoglobin in RBC in the form of?
Form HbA.
Remaining 8% is made up of HbA2, HbF and glycosylated Hb
What is myoglobin?
- Myoglobin is another oxygen carrier molecule found exclusively in cardiac and skeletal muscle
What has a higher affinity for oxygen?
Myoglobin and foetal haemoglobin both have a higher affinity for oxygen than normal adult haemoglobin.
Why is foetal haemoglobin greater?
The affinity of the foetal haemoglobin is greater than the maternal haemoglobin so the foetus can extract oxygen from that maternal haemoglobin and equally the muscle myoglobin can extract oxygen from that adult haemoglobin.
What side does the foetal oxygen-haemoglobin curve shift to?
To the left
What is hypoxia?
Inadequate supply of oxygen to tissues. Various causes.
What are the five types of hypoxia?
Hypoxaemic Hypoxia
Anaemic Hypoxia
Stagnant Hypoxia
Histotoxic Hypoxia
Metallic Hypoxia
What is the most common type of hypoxia?
Hypoxaemic Hypoxia
What is hypoxaemic hypoxia?
Reduction inO2 diffusion at lungs either due to decreased PO2 atoms or tissue pathology.
What is Anaemic Hypoxia?
Reduction in O2 carrying capacity of blood due to anaemia (red blood cell loss/deficiency.
What is stagnant hypoxia?
Heart disease results in inefficient pumping of blood to lungs/around the body.
What is histotoxic hypoxia?
Poising prevents cells from utilising oxygen delivering to them eg. carbon monoxide/cyanide
What is metallic hypoxia?
Oxygen delivery to the tissues does not meet increased oxygen demand by cells.
What does CO form when bound to haemoglobin?
Carboxyhaemoglobin with an affinity 250 times greater than O2- binds readily and diassosiates very slowly so very problematic once dissolved in circulatuon.
How much pCO is needed to cause progressive carboxyhaemoglobin?
0.4mmHm
What are the signs and symptoms of CO retention signs?
Characterised by hypoxia, headache, cherry red skin and mucous membranes.
Respiration rate unaffected
due to normal arterial PCO2.
Potential brain damage and death.
Treatment for CO retention?
100% oxygen to increase PaO2
What pathologies can cause hypoventilation?
Emphysema Fibrotic lung disease
When will haemoglobin pair with CO2?
When oxygen level decreases
What is the Bohr effect?
Shift of haemoglobin binding curve to the right
Higher PO2 needed for the same saturation
When temperature falls is it easier or harder for tissues to extract oxygen?
Harder
Is saturation of haemoglobin affected by partial pressure?
No
Does anaemia affect PaO2 (arterial)?
No - there is no change in the ability of the oxygen to reach the blood
What is the function of foetal haemoglobin?
Pulls oxygen from adult haemoglobin and delivers it to the foetus
What is the driving force of Oxygen in gas to the blood?
Partial pressure of the Oxygen in the gas mixture
What causes respiratory acidosis?
Hypoventilation, causing CO2 retention, leads to increased [H+] bringing about respiratory acidosis.
What causes respiratory alkalosis?
Hyperventilation, blowing off more CO2, lead to decreased [H+] bringing about respiratory alkalosis.
Why is pH normally stable?
All CO2 produced is eliminated in the air.
How can breathing influence PCO2?
Hypoventilation and hyperventilation Plasma H+ will vary accordingly
How can breathing influence PCO2?
Hypoventilation and hyperventilation Plasma H+ will vary accordingly
What influences alveolar ventilaiton?
Airway resistance
Lung compliance
Rate and depth of breathing
What synthesises DPG?
Erythrocytes
When does production of 2,3 - DPG increase?
When there is inadequate oxygen supply (heart or lung disease) and helps maintain oxygen release in the tissues.
What is oxygen dissolved in plasma influenced by? (PO2)
.
