L16 Flashcards
both Pulmonary Fibrosis and Pulmonary Hypertension increase dead space. which one increases functional dead space and which anatomical
Pulmonary Fibrosis = anatomical
Pulmonary Hypertension = functional
when you take fast shallow breaths what happens
We are breathing fast but we are reducing the tidal volume but the dead space will be the same therefore alveoli ventilation is significantly decreased
How does gas move from alveoli to capillary
Gases move across the alveolar capillary membrane
by Diffusion
what are different names from the barrier between the alveoli and the capillaries
- air-blood barrier
- blood-gas barrier
- alveocapillary membrane
what makes up the air blood barrier
airspace
- alveolar epithelial cell (type 1)
- basement membrane
- endothelial cell
blood
what does Ficks law of diffusion explain
Explains gas exchange through the membranes
what is the ficks law equation
F = (A/T) x D (P1-P2)
• Where: F = Flux (Amount flowing) A = surface area T = thickness D = Diffusion constant P1-P2 = pressure difference
what is the diffusion constant
how hard it is to get through the membrane
it is a constant therefore it is very constant across the membranes
what is Grahams Law
diffusion depends on gas solubility (S) and its molecular weight
what is more soluable O2 or CO2
• On a per-molecule basis, CO2 diffuses about 20x faster
than O2 due to CO2 higher solubility.
CO2 = 20x more soluable
what do you know about the surface area of the lungs
it is about 1/2 a tennis court
Usually area is huge so it doesn’t affect diffusion until you have obstructive lung disease
what is Emphysema
Emphysema is a disease characterized by dilation of the alveolar spaces and destruction of the alveolar walls.
There is a decrease in the surface area of the lung (A) in emphysema. what effect does this have on blood PO2
Fick’s law helps understand why patients with emphysema have
decreased PO2 in blood
decrease in A = decrease in F
in healthy lungs the Blood-gas barrier (air-blood barrier) in the lung is enormous, and the thin
how thin is it
0.3µm in many places
Therefore the thickness is not going to effects the diffusion in healthy individuals
what is Pulmonary fibrosis
involves thickening and scarring of the alveolar membranes
what causes Pulmonary fibrosis
– can arise from chronic inflammation, drugs,
industrial chemicals
Deposit of fibrotic tissue between alveolar and endothelial cells leads to thickening and scarring of the
alveolar membranes
what effect does this have on PO2 in the blood
T is inversely proportional to F therefore when T increases F decreases meaning decreased PO2 in the blood
what is a Pulmonary oedema
(water accumulation in alveoli)
what is the affect of a Pulmonary oedema on PO2
water in the lungs increases the diffusion distance (T) therefore decreasing the PO2 in the blood
in healthy individuals what is the most important factor for PO2 (ficks law)
The most important factor is the pressure difference
eg if there is more if PAO2 is higher than PaO2 then O2 will diffuse from the alveoli into the blood and vice versa
what is the normal value for PAO2
• 𝑷𝑨𝑶𝟐 ~100 mmHg – reduced from PB (159
mmHg) by water vapour in alveoli
what does PA)2 depend on
• 𝑷A𝑶𝟐 depends on:
- PIO2 of inspired air
- Alveolar ventilation (𝑽𝑨)
- Oxygen consumption ̇ (𝑽𝑶𝟐)
The atmospheric PO2 is usually constant,
so it is the balance between oxygen
consumption and alveolar ventilation that is most important.
what is PACO2 in a healthy human
• 𝑃A𝐶O2 is kept constant at 40 mmHg
what does PACO2 depend on
- Alveolar ventilation (𝑽𝑨)
- Carbon dioxide production (𝑽𝑪𝑶𝟐)
- 𝑃𝐼𝐶O2 of inspired air
what is Alveolar 𝑃𝐴𝐶O2 usually determined by
• Alveolar 𝑃𝐴𝐶O2 is usually determined
only by the balance between carbon
dioxide production and alveolar ventilation, because atmospheric PCO2 is negligible.
how do you measure partial pressures in arterial blood - PaO2 and PaCO2?
• Measure these from arterial blood sample
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
when the blood first comes into contact with the alveoli the PO2 will be low and the PCO2 will be high
what should it be when the capillary is leaving the alveoli
By the time the capillary leaves the alveoli the pressure of O2 in the capillary should be the same as it is in the alveoli
this is the same for CO2
Apply Fick’s law to understand diffusion during exercise
Exercise = more O2 burned in muscle
We increase inspiration rate and tidal volume which increases the alveoli ventilation (and alveoli surface area) = more gas exchange (lung diffusion capacity for O2)
Increased alveolar ventilation PAO2 increased
increased VO2 = decrease in PaO2
In the arteries it has decreased because of the metabolic demands
therefore O2 in the lungs has increased and O2 in the blood had decreased making a massive pressure greaident
More capillaries perfused = ↑ capillary surface area and
reduce diffusion distance for capillaries
• In a healthy lung what is the value for alveolar ventilation
• Alveolar ventilation (𝑽𝑨) = 4 L/min
what is the normal value (at rest) for pulmonary blood flow
• Pulmonary blood blow (𝑸) = 5 L/min
what is the normal V/Q ratio
the ratio of ventilation to perfusion
• normal 𝑉/𝑄̇ = 0.8
what happens if there is any change to the ratio of ventilation to perfusion (V/Q)
• Any change in the ratio impairs O2 and CO2 transfer
what are the 3 different things that can happen when there is a ratio of ventilation to perfusion missmatch
physiological shunt, anatomical shunt and low venteraltion/perfusion
what is physiological shunt
Hypoxia
One alveoli wont get as much O2 therefore the blood will be shunted past it and
PO2 is going to be low and the CO2 will be high
there is a decrease in alveolar ventilation
what is anatomical shunt
This is where we have an addition pulmonary artery or capillary which does not take part on picking up O2 as it is not close to the alveoli
Therefore it is a bypass and the PO2 is going to be low and the CO2 will be high
When they reach the lungs there is no balance reached and the V/Q ratio is going to be altered
