Lecture 16 Flashcards
How does breathing pattern affect alveolar ventilation?
- fast and shallow breathing: the tidal volume decreases but the frequency increases so the total ventilation remains the same
alveolar ventilation decreases - slow and deep breathing: the frequency is a low slower but the volume is more so the total ventilation remains the same
alveolar ventilation increases
What is the effect of fast shallow breathing on alveolar ventilation?
There is a decrease in alveolar ventilation which causes hypoxia (decreased partial pressure of alveolar O2) and hypercapnia (increased partial pressure of alveolar CO2) and acidity.
From a gas exchange point of view, there is a decrease in the transfer of O2 from the alveoli into the capillaries and the CO2 is not being removed and so it wastes ventilation in the dead space. It is energetically costly for the respiratory muscles.
What is the effect of slow deep breathing on alveolar ventilation?
There is an increase in alveolar ventilation. This causes hyperoxia (increased partial pressure of O2 in the alveoli) and hypocapnia (decreased partial pressure of CO2 in the alveoli) and alkalinity. There is an increase on gas exchange but it is energetically costly for the respiratory muscles and so they are working harder to get air in.
The respiratory quotient (RQ) is: A. V̇ O2/V̇ CO2 B. a measure of cell metabolism. C. V̇ CO2/ ̇VO2 D. A and B are both correct. E. B and C are both correct.
E
We need to exchange _____ and ______ between alveolar air and ______ in lung ________ by ______
O2 CO2 blood capillaries diffusion
We need to exchange ________ and _______ between _________ in tissue _______ and cells in the __________ by _________
O2 CO2 blood capillaries tissues diffusion
Gases move across the alveolar capillary membrane by ____________
diffusion
What are three different names for the barrier between the lungs and the blood?
- air-blood barrier
- blood-gas barrier
- alveocapillary membrane
What three things make up the air blood barrier?
- alveolar epithelial cells (type 1)
- basement membrane
- endothelial cell
Which direction does O2 flow through the air-blood barrier?
from the type 1 epithelial cells, through the basement membrane and through the endothelial cell into the blood
What direction doesCO2 flow through the air-blood barrier?
From the blood endothelial layer, through the basement membrane then through the alveolar type 1 cell into the lungs
What does Fick’s Law of diffusion describe?
the gas exchange through the membranes
What is Fick’s Law of diffusion?
What do each of the components mean?
F = A/T D (P1-P2) F = flux (ie. amount flowing) A = surface area of the alveoli T = thickness of the membrane D = diffusion constant ie. how easy it is to move stuff across the membrane P1-P2 = pressure difference
What does the diffusion constant depend on?
the solubility of the gas, and the molecular weight (as described by Graham’s Law)
Which diffuses faster, CO2 or O2? Why is this?
CO2 diffuses about 20x faster than O2 due to CO2 having a higher solubility
What can we do to increase the area of the alveoli?
we can breathe in which increases the ventilation which increases the area
What is a disease that results in a decrease in the area of the alveoli?
Explain this
This is a disease characterised by dilation of the alveolar spaces and destruction of the alveolar walls. There is a decrease in the surface area of the lung. This means that patients have less air flow through the alveoli and therefore there is decreased PO2 in blood
What is the thickness of the air-blood barrier?
0.3μm
What is a condition that affects the thickness of the membranes?
Explain this
Pulmonary fibrosis this involves the thickening and scarring of the alveolar membrane.
Deposit of fibrotic tissue between alveolar and endothelial cells leads to thickening and scarring of the alveolar membranes.
This means there is an increase in the thickness in the alveoli and so patients have less air flow through the alveoli and therefore there is decreased PO2 in blood
What is pulmonary oedema and how does it affect diffusion capacity?
This is water accumulation in the alveoli. This increases the diffusion distance and so there is reduced diffusion capacity
What is the main factor affecting diffusion capacity/flow?
the pressure difference
What are the pressure differences that drive diffusion?
- Partial pressure of O2 in the alveoli vs partial pressure of O2 in the blood
- partial pressure of CO2 in the alveoli vs partial pressure of CO2 in the blood
If there is more O2 in the alveoli than in the blood, which way does O2 move?
there is movement of O2 from the alveoli into the capillaries
What is the approximate partial pressure of oxygen in the alveoli?
100mHg (it is reduced reduced from PB (159 mmHg) by water vapour in alveoli)
What three things does PAO2 depend on?
- PIO2 (partial pressure of oxygen in the inspired air)
- alveolar ventilation ie. how much O2 you are bringing into the alveoli
- oxygen consumption
The atmospheric PO2 is usually constant so it is the balance between oxygen ________ and alveolar _________ that is the most important
consumption
ventilation
What is the approximate partial pressure of CO2 in the alveoli?
it is kept constant at 40mmHg
What three things does PACO2 depend on?
- alveolar ventilation ie. how much CO2 we are breathing out
- carbon dioxide production
- PICO2 of inspired air
Alveolar PACO2 is usually determines only by the balance between _________ production and ________ ventilation, because __________ _________ is negligible
CO2
alveolar
atmospheric PCO2
Where do we measure partial pressures in arterial blood, PaO2 and PaCO2?
we measure these from arterial blood sample
What is the usual value for PaO2?
100 mmHg
What is the usual value for PaCO2?
40mmHg
The movement of oxygen by diffusion between the alveoli and the pulmonary capillary blood is:
A. inversely related to the area of the alveolar membrane. B. inversely related to the diffusion constant
C. directly related to the thickness of the alveolar membrane.
D. proportional to the partial pressure gradient between air-blood barrier.
D. proportional to the partial pressure gradient between air-blood barrier.
Describe the movement of O2 from the alveolus into the capillary
The partial O2 pressure in the alveolus is greater than that in the capillary so O2 flows in until the pressures are the same (and they are the same as the original PAO2)
Describe the movement of of CO2 from the capillary into the alveolus
The partial CO2 pressure in the capillary is greater than that in the alveolus so CO2 flows in until the pressures are the same (and they are the same as the original PACO2)
How is diffusion changed during exercise and how does this relate to Fick’s Law?
When you exercise, there is more O2 burned in the muscle. There is increase tidal volume and increased alveolar ventilation (rate) and so the alveolar surface increases. The lung diffusion capacity for O2 also increases.
Because of the increase in alveolar ventilation (rate), there is an increase in the partial pressure of alveolar O2. Because of the increased oxygen ventilation, there is a decrease in the partial pressure of arterial O2. This means that there is an increase in P1-P2
All these things mean that there is more gas exchanged. More capillaries are perfused and so there is increased capillary surface area and reduced diffusion distance for capillaries so O2 gets into the blood faster
What is the ratio of ventilation to perfusion? What are the normal values? What is the effect of a change in this ratio?
This is the ratio of how much air you are bringing in and how much blood is being brought close to the alveoli.
In a healthy lung, alveolar ventilation = 4L/min and pulmonary blood flow = 5L/min so the normal V/Q (both with dots as they are rates) = 0.8
Any change in the ratio impairs O2 and CO2 transfer
What are three examples of
Ventilation and perfusion mismatch?
- anatomical shunt
- physiological shunt
- low ventilation/perfusion
Describe an anatomical shunt and explain how it causes a mismatch of V and Q
This is when there is an additional pulmonary artery which may not take part in picking up O2. It bypasses the alveoli and goes to the pulmonary veins. When they reach the veins, no balance is reached ie. there is less O2 and more CO2
Describe a physiological shunt and explain how it causes a mismatch of V and Q
This is when there is an alveoli which is blocked so the O2 in that alveoli is less than the other one. The veins leaving the alveoli are not balanced so there is decreased ventilation
Describe low ventilation and explain how it causes a mismatch of V and Q
Ventilation decreases reducing PO2 in alveoli and so the ratio is altered
What are three lung diseases that leas to impaired ventilation?
- atelectasis (fibrosis)
- emphysema
- pulmonary oedema (fluid)
What are three vascular diseases cause impaired perfusion?
- pulmonary hypertension
- heart failure
- COPD
