5. Pulmonary blood flow and gas exchange 1 Flashcards
Is the volume change greater for a given change in pressure greater at the apex or base of the lung?
At the base (volume change is greater)
What 2 thing decline with height from base to apex of the lung?
- alveolar ventilation
2. compliance
Why does compliance decrease with height from base to apex of the lung?
- due to alveoli being more inflated at FRC (functional residual capacity= volume of air in lungs after expiration)
- at base, the lungs are slightly compressed
What is the base of the lung compressed by hence more compliant lungs on inspiration?
compressed by the diaphragm (and lung structure above it)
What does any given change in intrapleural pressure bring about?
it brings about a larger change in volume at the base compared with the apex of the lung
In what direction in relation to heart does the pulmonary artery travel in?
AWAY from the heart
In what direction in relation to heart does the pulmonary vein travel in?
TOWARDS the heart
What blood is carried in pulmonary artery?
deoxygenated blood
What blood is carried in pulmonary vein?
oxygenated blood
Is pulmonary circulation opposite from systemic circulation in function?
Yes
What does pulmonary circulation do?
-delivers CO2 to the lungs and picks up O2
What are the 3 types of gas exchanges that occur when O2 enters the lungs?
- between atmosphere and lungs
- between lung (in alveoli) and blood
- between blood and cells
What circulation supplies airway smooth muscle, nerves and lung tissue with nutrients, oxygen and glucose?
Bronchial circulation (nutritive) supplied via bronchial arteries
What does bronchial circulation arise from?
from systemic circulation
What main vessels does pulmonary circulation consist of? (2)
- left pulmonary arteries
- right pulmonary arteries
Where do pulmonary arteries arise from?
from right ventricle (pulmonary circulation)
What do pulmonary arteries carry in terms of outputs?
entire cardiac output (from the right ventricle)
Describe the pathway of blood and vessels involved starting from deoxygenated blood flowing from Superior Vena Cava into right atrium.
- deoxygenated blood flows through superior vena cava into r. atrium and ventricle
- pulmonary arteries then carry deoxygenated blood to the lungs to pick up oxygen
- once O2 is picked up at the lungs, the oxygenated blood flows through pulmonary vein to the heart
- oxygenated blood flows through l.atrium and ventricle and is then pumped to the rest of the body through the aorta to supply body tissues
What is the flow and pressure of pulmonary circulation?
- high flow and low pressure system
What is the approximate systolic pressure? (when heart contracts, pressure is higher than at diastole)
~25mmHg
What is the approximate cardiac function pressure in systemic circulation?
~120mmHg
How much blood is circulating through the body’s systemic and pulmonary circulation?
5L/min
but can range from 4.7-5.5L
What is the pressure difference between pressure in arteries and veins?
only around 10mmHg, not very much (pressure gradient is very small)
Do arteries or veins have a higher partial pressure?
arteries
In what direction does air diffuse in? (gradient-wise)
down partial pressure gradient (from high to low partial pressure) until equilibrium is reached
O2 diffuses from what which partial pressure values down a partial pressure gradient?
from 100mmHg to 40mmHg
CO2 diffuses from which partial pressure values down a partial pressure gradient?
from 46mmHg to 40mmHg
What partial pressure values do clinicians use in hospital workplace?
kPa (textbooks use mmHg)
What is the general rule while looking at alveolar, arterial and venous partial pressure values of O2 and CO2?
- alveolar and arterial blood reflects what’s going on in lungs (values for both alveolar and arterial blood should be the same)
- venous blood reflects what’s going on in the tissues
What are the 5 rules for rate of gas diffusion across membrane
- directly proportional to partial pressure gradient
- directly proportional to gas solubility
- directly proportional to the available surface area
- inversely proportional to the thickness of the membrane
- most rapid over short distances
Is the larger partial pressure gradient for O2 or CO2 compartments?
O2 compartments
Why is diffusion of O2 slower than diffusion of CO2?
Because O2 is not soluble in water whereas CO2 is. O2 has to go from gaseous state to liquid since plasma is 90% water and fill up haemoglobin which takes more time
What does PP in alveoli correspond to?
corresponds with PP in systemic arterial blood
What does PP in pulmonary arterial blood (deoxygenated) correspond to?
corresponds with PP at tissues
What is the diffusion rate of oxygen travelling from 100mmHg to 40mmHg? (in ml/min)
250ml/min
What is the diffusion rate of CO2 travelling from 46mmHg to 40mmHg? (in ml/min)
200ml/min
What type of pneumocytes are directly in contact with epithelial capillary cell?
Type 1 pneumocyte (for gas exchange)
What never sits between capillary and a type 1 cell?
elastic fibres (to allow quicker gas exchange)
What are the main layers of the thin exchange surface of alveoli? (allows short diffusion distance)
ALVEOLAR SPACE (with type 1 pneumocytes) surfactant alveolar epithelium fused basement membranes endothelium CAPILLARY
What 4 lung diseases have a great effect on gas exchange?
- emphysema
- fibrotic lung disease
- pulmonary oedema
- asthma
What effect does emphysema have on gas exchange?
- destruction of alveoli REDUCES surface area for gas exchange
- poorer ventilation
What effect does fibrotic lung disease have on gas exchange?
- thickened alveolar membrane SLOWS gas exchange as fibre tissues push alveoli cells away from capillaries impairing diffusion
- loss of lung compliance may decrease alveolar ventilation
What effect does pulmonary oedema have on gas exchange?
- fluid in interstitial space increases diffusion distance, SLOWING down gas exchange
- arterial CO2 may be normal due to higher CO2 solubility in water
- particularly impedes movement of O2 because of its poor water solubility
What effect does asthma have on gas exchange?
- increased airway resistance
- decreases airway ventilation (PO2 low in alveoli and arterial blood ) since bronchioles are constricted
What does fibrosis look like on an x ray?
- thick black marks often found near the base of the lung
- prevents expansion of chest as elasticity faces resistance
- impedes air getting in and CO2 out
What is the primary cause of emphysema?
smoking
What does an emphysemic lung look like?
- has many large holes in it due to destruction of alveoli
- large holes impedes breathing causing shortness of breath (common symptom)
Do ventilation and perfusion compliment and ideally match each other?
Yes
What is perfusion?
local blood flow
What units are used to measure both ventilation and perfusion?
L/min
What is the optimum condition involving ventilation and blood flow?
ventilation = blood flow
What 2 pressures influence the distribution of blood flow in the lungs?
- hydrostatic (blood) pressure (Pa)
2. alveolar pressure
What is blood flow proportional to?
vascular resistance
declines with height of lung from base to apex
Which part of the lung is supplied with the most blood?
base of the lung
Why does the base of the lung have a high blood flow? (in terms of pressure and resistance)
because arterial pressure (in blood vessel) exceeds alveolar pressure and vascular resistance is low (decreased)
Which part of the lung is supplied with the least blood?
apex of the lung
Why does the apex of the lung have a low blood flow? (in terms of pressure and resistance)
because arterial pressure is less than alveolar pressure; this compresses the arterioles and vascular resistance is high (increased)
Is ventilation uniform across the lung?
No (more at the base)
Are both ventilation and blood flow greater at the base of the lung?
Yes
At which level is blood flow/perfusion greater than ventilation?
at the base of lung (bottom of thoracic cage)
At which level is ventilation greater than blood flow/perfusion?
at the apex of lung (top of thoracic cage)
At which rib level are ventilation and perfusion matched?
approx. rib 3
Why does the ratio of ventilation: perfusion change within the lung from base to apex in the upright position?
due to effect of gravity
What is the perfectly matched ratio of ventilation and perfusion?
ventilation:perfusion ration = 1
What are the 2 mismatches ratios of ventilation and perfusion?
- ventilation >perfusion>1
2. ventilation
What percentage of the height of a healthy lung performs quite well in matching blood and air? (perfusion and ventilation- right y axis)
over 75%
Where does the majority of the mismatch of ventilation:perfusion take place in the lung?
at the apex
How does the ventilation:perfusion ratio remain close to 1 at all times?
it’s auto-regulated
(when ventilation>blood flow or ventilation
What happens in terms of gases in alveoli when ventilation
- PCO2 increases and PO2 decreases
- more CO2 is being delivered to alveoli than is being removed by ventilation
- blood is not oxygenated and is not removing CO2 which may cause CO2 build up
What does it mean when blood is “shunted”?
- blood shift from one side of the heart to the other (poorly oxygenated blood is redirected to better ventilated areas (alveoli)
What is hypoxia?
lower partial pressure of O2 than normal
During hypoxia, what happens to PULMONARY vessels?
they constrict arterioles which directs blood to better ventilated areas (when tissue PO2 is low around underventilated alveoli)
During hypoxia, what happens to SYSTEMIC vessels?
they dilate; to deliver as much oxygen to tissues as possible to keep them alive
In what patients can ventilation
often in lung cancer patients
In what patients can ventilation>blood flow/perfusion?
often in patients with blood clots
What is the term that describes when ventilation>blood flow/perfusion?
alveolar dead space
What is alveolar dead space in terms of gas exchange?
air in alveoli that cannot be part of the gas exchange as excess O2 is delivered to alveoli than is being extracted by blood leading to O2 accumulation
What happens during shunt (ventilation
pulmonary vasoconstrict
systemic vasodilate
What happens when ventilation>perfusion to pulmonary and systemic vessels?
Oposite to shunt:
-pulmonary vasodilate
-bronchial vasoconstriction
(brings ratio back towards 1 by increasing perfusion)
What is a shunt?
-passage of blood through areas of lung that are poorly ventilated (ventilation«
What is the shut opposite of?
alveolar dead space
What is alveolar dead space?
alveoli that are ventilated but NOT perfused
What is anatomical dead space?
air in the conducting zone of the respiratory tract unable to participate in gas exchange as wall of airways in the region are too thick ( nasal cavities, trachea, bronchi, upper bronchioles)
What is physiological dead space?
Alveolar dead space + anatomical dead space (ALL dead space that can’t participate in gas exchange at all)
What 2 circulations supply the lungs?
- pulmonary (gas exchange)
- bronchial (supply nutrients to lungs)
Which side of the heart does the bronchial supply arise from?
left side (as oxygenated blood)
The pulmonary circuit receives the OUPUT from which side of the heart?
right side of the heart
Is pulmonary arterial pressure low or high?
low
What is the approximate systolic arterial pressure in mmHg?
~25mmHg
What is the approximate diastolic arterial pressure in mmHg?
~8mmHg
What is low pressure circuit more susceptible to?what does this cause?
to the effects of gravity; which gives rise to a great degree of variability in blood flow within the lung
Is base or apex more highly perfused and has more ventilation?
base
Changes in what cause the ventilation and perfusion to be greatest at the base of the lung?
changes in compliance across the lung
What happens to the ventilation:perfusion ratio from base to apex of the lung?
it increases (in the upright position)
The inequality in the ventilation:perfusion ratio is compensated by what?
compensated by local regulation of blood flow (controlled by local PO2)
Why are the overall rates of equilibrium between O2 and CO2 similar despite CO2 being more water soluble?
because of the greater pressure difference for O2
Does the diffusion of gases between the alveoli and the blood obey the rules of simple diffusion?
yes, they do (from high to low conc.)
