Respiratory Physiology 4 Flashcards
Define ‘perfusion’
Blood flow through pulmonary circulation
What value is the ideal ratio for ventilation to perfusion?
Close to 1 as possible
What ensured the ventilation perfusion remains as close to 1 as possible?
RSA - respiratory sinus arrhythmia
Occurs mainly due to increased vagal activity during expiratory phase
Both blood flow and ventilation _______ with height across the lung
Decrease
Is blood flow or ventilation higher at the base of the lungs?
Base
Why is blood flow higher at the base of the lungs than ventilation?
As arterial pressure exceeds alveolar pressure
Describe the state of blood flow at the apex of the lungs and explain why this is?
Blood flow is low as arterial pressure is less than alveolar pressure
While both decline, blood flow _____ faster than ventilation, meaning blood flow is ____ than ventilation at the base and ventilation is _____ than blood flow at the apex
While both in decline, blood flow declines faster than ventilation meaning blood flow is more that ventilation at the base and ventilation is more than blood flow at the apex
Where does the largest ventilation perfusion mismatch occur?
At the apex
Define ‘shunt’
Where blood is moved from the right side of the heart to the left side of the heart without underground gas exchange
When do shunts take place?
When blood flows through area of lung which has been restricted in some way which reduces gas exchange
Describe what happens to blood flow where there is tissue hypoxia within the lungs
The smooth muscle in the blood vessels going to that area constrict -> reducing amount of blood to poorly ventilated area and increasing amount of blood going to well ventilated area
Describe what happens to blood flow when there is tissue hypoxia within the systemic circulation
The smooth muscle in the blood vessels going to that area dilate -> increase the amount of blood to the poorly ventilated area and decreasing amount of blood going to well ventilated area
Describe the effect of an increase in PCO2 in relation to bronchial smooth muscle
Bronchiole smooth muscle dilated which helps to improve the ventilation in the poorly ventilated area of the lung
What causes ventilation to be higher than blood flow
Alveolar dead space
Where in the lung is it typical for ventilation > perfusion
- Occurs to small extent at apex of normal lung.
- Occurs pathologically in pulmonary embolus
Describe what happens to the smooth muscle within the blood vessels and the bronchioles when ventilation > perfusion
Opposite of shunt:
- Alveolar PO2 rises, PCO2 falls
- Pulmonary vasodilation
- Bronchial constriction
How much oxygen dissolves per litre of plasma?
3ml
What is the majority of oxygen bound to in the blood?
Iron within the haemoglobin
How much oxygen is present per litre of blood?
200ml per litre of whole blood
How much oxygen per litre of blood is carried within haemoglobin
197ml per litre of whole blood
Describe the two transport methods of carbon dioxide and state the amount of carbon dioxide which travels each way
77% of Carbon dioxide is transported in solution in plasma
23% is stored within the haemoglobin
What is the oxygen demand of resting tissues per min
250ml per min
What % of arterial oxygen is extracted by peripheral tissues at rest?
25%
Each haemoglobin contains how many:
- Haeme groups
- Iron groups
Which allows haemoglobin to carry how much oxygen per haemoglobin?
4 haeme groups
4 iron groups
Allows haemoglobin to carry 4 molecules of oxygen per haemoglobin
What is the major determinant of the degree to which haemoglobin is fully saturated
Partial pressure of oxygen in blood
When oxygen starts to bind to haemoglobin it makes it _____ for more oxygen to bind via ________ _______ and vice versa when oxygen is leaving, which is called __-_________ _______
Easier
Complimentary conformation
Co-operative binding
What does partial pressure of oxgygen refer to?
Oxygen in solution in plasma - not in rbc’s
What is the effect of haemoglobin sequestering oxygen from the plasma?
- Maintains a partial pressure gradient which sucks oxygen out of alveoli until the Hb becomes saturated with oxygen
How long does it take for haemoglobin to become fully saturated with oxygen after coming into contact with alveoli?
0.25s
What is the total contact time for blood with the alveoli?
~0.75s
You can have a large fall in partial pressure with a _____ impact on oxygen content of blood as long as the partial pressure of oxygen is above ___%
- Small
- 60%
What is an effect of the PaO2 being below 60%?
Decreases the affinity oxygen has for haem groups on haemoglobin
in venous blood haemoglobin is only __% saturated as it has given __% needed for peripheral tissues
- 75%
- 25%
What are the 4 factos which affect the oxygen dissociation curve
- Change in pH
- Change in PCO2
- Change in Temperature
- Change in [DPG]
Describe the effect on the oxygen dissociation curve for a change in pH
- Lower pH shifts graph to right. I.e higher PO2 needed for saturation of haemoglobin
- Higher pH shifts graph to left. i.e less PO2 needed for saturation of hemoglobin
Describe the effect on the oxygen dissociation curve for a change in PCO2
- Higher PCO2 shifts graph to right. I.e higher PO2 needed for saturation of haemoglobin
- Lower PCO2 shifts graph to left. I.e less PO2 needed for saturation of haemoglobin
Describe the effect on the oxygen dissociation curve for a change in temperature
- Higher temperature shifts graph to right. I.e higher PO2 needed for saturation of haemoglobin
- Lower temperature shifts graph to left. i.e less PO2 needed for saturation of haemoglobin
Describe the effect that a higher [DPG] has on the oxygen dissociation curve
- Higher [DPG] shifts graph to right. i.e Higher PO2 needed for saturation of haemoglobin
- Lower [DPG] shifts graph to left. i.e less PO2 needed for saturation of haemoglobin
Define ‘anemia’
Any condition where the oxygen capacity of blood is compromised
Why does PO2 stay normal within aneamia despite blood oxygen content being low?
- Possible as partial pressure does not reflect the total oxygen content of blood, only oxygen content of plasma
- Not possible to have low plasma PO2 and normal total blood O2 levels
Is it possible for someone with anaemia to have red blood cells which are fully saturated with oxygen as PO2 is normal?
- Yes
(only caveat is iron deficiency where number of oxygen binding sites will be reduced, but those present will still be saturated)
How does carbon monoxide form?
From incomplete combustion of carbon fuel. eg car fuel
Describe the affinity CO has for haemoglobin
Has an affinity for haemoglobin 250 greater than oxygen to form carboxyhaemoglobin. Binds readily and dissociated very slowly
Describe the typical characteristics of carbon monoxide consumption
- Hypoxia
- Anaemia
- Nausea
- Headache
- Cherry red skin and mucous membranes
- Resp rate unaffected
- potential brain damage and death
Describe the treatment for carbon monoxide consumption?
Provide 100% oxygen to increase PaO2
Describe what happens to carbon dioxide molecules when they diffuse from tissues into the blood?
- 7% remains dissolved in plasma
- 23% combines with erythrocytes with deoxyhaemoglobin to from carbamino compounds
- 70% combines in the erythrocytes to form carbonic acid
- This this dissociates to yield biocarbonate and hydrogen ions
- Most of the bicarbonate then moves out of the erythrocytes into the plasma in exchange for chlorine ions and the excess hydrogen ions bind to deoxyhemoglobin
- The reverse occurs in the pulmonary capillaries and CO2 moves down its conc gradient from blood to alveoli
Explain why arterial partial pressure of oxygen is not the same as arterial oxygen conc.
PaO2 refers purely to oxygen in solution in the plasma and is determined by oxygen solubility and is the partial pressure of oxygen in the gaseous phase that is driving oxygen into solution
Values assinged to the partial pressure of a gas in solution are ____ to the partial pressure in gaseous phase that is driving that gas into solution at _______
- Equal
- Equilibrium
(in other words, the point when the number of ox molecules moving from the gaseous phase to the liquid phase equals the number of oxygen molecules moving in the opposite direction
How much oxygen binds to each gram of Hb
1.34ml
Describe what is myoglobin?
- another oxygen carrier molecule
- Found exclusively in cardiac and skeletal muscle
- Has only 1 haem group instead of 4
- Oxygen is more tightly bound than to haemoglobin
Describe the effect of foetal haemoglobin on the oxygen dissociation curve
- Shifts graph to right. ie a higher PO2 is needed for saturation
Describe the effect of myoglobin on the oxygen dissociation curve
- Shifts graph to the left .ie a lower PO2 is needed for saturation
What is a use of glycosylated haemoglobin
Can be used to monitor glucose control in diabetes
What are the 5 types of hypoxia?
- Hypoxaemic hypoxia
- Anaemic Hypoxia
- Stagnant Hypoxia
- Histotoxic hypoxia
- Metabolic hypoxia
Describe Hypoxaemic hypoxia
Most common of all hypoxias
- Reduction in oxygen diffusion at lungs either due to decreased PO2atmos or tissue pathology
Describe Anaemic hypoxia
Reduction in oxygen carrying capacity of blood due to anaemia
Describe stagnant hypoxia
When heart disease results in inefficient pumping of blood to lungs/around the body
Describe histotoxic hypoxia
When poisioning prevents cells utilising oxygen delivered to them. eg carbon monoxide/cyanide
Describe metabolic hypoxia
When oxygen delivery to the tissues does not meet increased oxygen demand by cells
