Respiratory Flashcards
How much air do you normally inhale per breath?
500mL
12-15 breaths/minute= 6-8L/min total ventilation
How much O2 enters the body per minute?
250mL
How much CO2 is expired per minute?
200mL
How many times does the airway divide between the trachea and alveolar sacs?
23 times
What are the first 16 divisions of the airways?
The conducting zones- dead space = 150mL per breath
What are the last 7 divisions of the airways?
Transitional and respiratory zones- for gas exchange = 350mL per breath= alveolar ventilation
Is anatomical dead space = physiological dead space?
In a normal person, yes
How is gas moved in the alveolar region?
Chiefly by diffusion
Where do you find type I and type II pneumocytes?
They line the alveoli
What are type I pneumocytes?
They are flat, large cytoplasmic extensions and are the primary lining of the cells. Simple squamous epithelial cells
What are type II pneumocytes?
They are granular pneumocytes, thicker and have numerous lamellar inclusion bodies. They secrete surfactant
What are the other cells present in the lungs?
Macrophages, lymphocytes, plasma cells, APUD cells, mast cells
What is the volume of the conducting zone?
About 150mL
What is the volume of the lung excluding the conducting zone during resting conditions?
About 2.5-3L
How do you distinguish a respiratory from a terminal bronchiole?
Respiratory bronchioles have alveoli lining the walls
What is the predominant mode of gas flow in the respiratory bronchioles?
Diffusion rather than convection
How many alveoli are there and how big are they?
300million, 0.3mm
What makes the alveolar structure stable?
Surfactant- lowers the surface tension
How are large particles filtered out of the airways?
By the nose
How are particles that reach the airway removed?
By the mucus escalator which is propelled by millions of tiny cilia
Where does the mucus in the airway come from?
From mucous glands and goblet cells in the bronchial walls?
How are particles that reach the alveoli removed?
They are engulfed by macrophages and then material from the alveoli is removed from the lung via lymphatics
What is the blood supply to the lungs?
Mainly from RV- 5L/min
Additionally from bronchial circulation from aorta- this supplies conducting airways down to terminal bronchioles
What is the mean pressure in the pulmonary artery at rest
~15mmHg
What is the average diameter of the capillaries that cover the alveoli?
10 micrometers- just big enough for an RBC
What is the thickness of the blood-gas barrier?
<0.3 micrometer
How much time does blood spend in the capillaries?
3/4 of a sec
What is the total area of the B-G barrier?
50 square meters
What happens if the pressure in the capillaries rises to unphysiologically high levels?
The blood gas barrier can be damaged
What happens to venous return during inspiration?
It increases
What changes about the time that an RBC spends exposed to alveolar gas during exercise?
Spends less time
750ms at rest, 250ms during exercise
What are the 3 volumes that can’t be measured with simple spirometry
- Residual volume
- Functional residual capacity because it involves residual volume ERV+RV
- TLC for same reason
What is the pulmonary blood flow per minute?
5L/min
What decreases the functional residual capacity of the lung? (4)
- Supine position
- Term pregnancy
- Post-operative atelectasis
- Chronic bronchitis with sputum retention
How should you initially treat an acute fall in FRC?
With high flow mask oxygen
What can cause a restrictive defect in ventilatory function? (4)
- Fractured ribs
- Upper abdominal surgery
- Lobar pneumonia
- Old T6 spinal cord injury
What is the closing volume of the lung?
The lung volume when small airway closure begins to occur
What is the approx value of the closing volume of the lung?
Between the residual volume and the functional reserve capacity
What can increase the closing volume of the lung?
Age
Small airways disease
What is alveolar ventilation?
The volume of fresh gas entering the alveoli per minute (or volume of gas leaving)
What is the formula for alveolar ventilation?
Tidal volume-dead space = 500-150=350mL per breath
Thus can be increased by increasing tidal volume
What is the relationship between alveolar ventilation and respiratory rate?
Directly related to RR but when RR increases, TV gets compromised
What is the relationship between alveolar ventilation and alveolar PCO2?
Inverse
If alveolar ventilation increases (hyperventilation)x3 PACO2 decreases by 1/3
What are 3 factors contributing to alveolar PO2?
- Inspired oxygen concentration
- Alveolar ventilation
- Oxygen consumption of the body
What are the factors that contribute significantly to the oxygen tension difference between alveolar gas & systemic arterial blood (A-a PO2 diff)?
- Anatomical R) to L) shunt
2. Low ventilation/ perfusion ratio in regions of the lung
What is the difference of the effect of oxygen on the microcirculation of the pulmonary circulation vs the systemic circulation?
In pulmonary circulation, decreased O2 causes constriction of capillaries, in systemic, causes dilatation.
What happens when a healthy person hyperventilates before renal compensation kicks in? (4 things)
- PACO2 of about 20mmHg
- A decrease in plasma bicarb
- A decrease in ICP
- A PaO2 of about 120mmHg
When can the amount of anatomical dead space increase?
With a big inspiration because of traction or pull exerted on the bronchi by surrounding lung parenchyma
What is physiological dead space?
The volume of gas that does not eliminate CO2
May be the same as anatomical dead space in normal individuals
What can increase physiological dead space?
Lung disease due to inequality of blood flow and ventilation within the lung
How can you measure physiological dead space?
Using Bohr’s equation (PACO2-PECO2)/PACO2
What is physiological dead space the sum of?
Anatomical + alveolar dead space (alveolar dead space is negligible in health)
What is the ratio of physiological dead space to tidal volume?
0.3 I.e. 150/500mL
What is the role of pulmonary acini?
All oxygen uptake occurs in the acini
What changes in the acini during inspiration?
The percentage change in volume of the acini during inspiration exceeds that of the whole lung
What is the relationship of the volume of the acini to total volume of the lung at FRC?
It is greater than 90% of the total volume of the lung at FRC
What is Fick’s Law?
Law of diffusion of a gas through tissue slice
What is the diffusion rate of a gas through tissue slice proportional to? (Fick’s law of diffusion, 3 things)
- The surface area
- The partial pressure difference btw the 2 sides
- The solubility of the gas in the tissue
What is the diffusion rate of gas inversely proportional to?
The thickness of the tissue and to the square root of the molecular weight
Which diffuses more rapidly, CO2 or O2?
CO2, about 20 times more rapidly
How does the example of carbon monoxide exemplify diffusion limitation of Fick’s law?
- CO diffuses freely through B-G barrier
- Binds intimately with Hb therefore exerts no effect on pCO in blood
- More can diffuse through but only 3/4/ of a second to do so, there fore is diffusion limited
- Amount absorbed is entirely dependent on the surface area available
How does NO exemplify the perfusion limitation of Fick’s law?
- It does not bind with Hb after diffusing across the B-G barrier, partial pressure rises rapidly
- 3/4 second to diffuse, but no NO can be transferred after a while
- Thus the amount of gas taken up by blood depends entirely on amount of blood flow
What is oxygen uptake like compared to CO and NO?
The rate of uptake sits somewhere between CO and NO
How quickly does pO2 of blood equal that of the alveolar gas?
After 1/3 of its time in the capillary
How much time does the blood spend in the alveolar capillary at rest?
3/4 of a second
How much time does blood spend in an alveolar capillary during exercise?
Approx 1/4 of a second
What challenges the diffusion process of oxygen going across the blood gas barrier?
Exercise, alveolar hypoxia and thickening of the blood gas barrier
What’s the relationship between oxygen uptake by Hb in the lung capillaries and pH?
Directly related I.e. if blood more alkaline, oxygen is more easily taken up by Hb, more acidotic, harder to take up
What is the relationship between oxygen uptake by Hb in the lung capillaries and PACO2?
Varies inversely with PACO2, if too much CO2 in blood, less is taken up by Hb
Which direction does the dissociation curve move in after birth?
To the left
How does oxygen uptake by Hb in lung capillaries relate to 2,3DPG?
It varies inversely, so the more 2,3DPG, the harder it is to take up oxygen
Which gas is used to measure diffusion capacity?
CO (carbon monoxide)
What is the value of normal diffusion capacity?
25mL/min/mmHg
What happens to diffusion capacity during exercise?
Increases 2-3x
What is the definition of the diffusion capacity?
The volume of gas that will diffuse through the membrane each minute for a partial pressure difference of 1mmHg.
I.e. the ease with which gases can find themselves transported into alveolar capillary blood
What is the equation for measuring DC?
Net rate of gas transfer/ partial pressure gradient
I.e. for CO V(CO)/ PCO
In a normal person, what would happen if you doubled the DC?
Increase maximal oxygen uptake at high altitude
What can limit the diffusion of oxygen during exercise?
High altitude
How is DC affected when one lung is removed?
It is decreased
Is DC decreased or increased in pulmonary fibrosis?
Decreased as pulmonary fibrosis leads to thickening of the blood gas barrier
What are 4 things that reduce the DC of the lung for CO?
- Emphysema due to loss of the pulmonary capillaries
- Asbestosis- causes thickening of the blood gas barrier
- Pulmonary embolism as blood supply cut off to part of the lung
- Severe anaemia
What is the pressure within the right atrium?
~2mmHg
What is the pressure within the right ventricle?
25/0mmHg
What is the pressure in the pulmonary artery?
25/8mmHg- mean pulmonary pressure is 15mmHg
What is the pressure in the pulmonary capillary bed?
~8-12mmHg
What is the pressure returning to the Left Atrium?
~5mmHg
What can happen to the alveolar vessels if the alveolar pressure increases?
They can get compressed
What is the pressure in the extra-alveolar vessels?
How are the extra-alveolar vessels opened?
Pulled open by the radial traction of the surrounding parenchyma
What causes constriction of the alveolar arteries?
Alveolar hypoxia
What increases the caliber of the alveolar and extra-alveolar vessels?
Lung inflation
What is the equation for determining pulmonary vascular resistance?
Vascular resistance= (input pressure-output pressure)/blood flow (6L/min)
=15-5/6=1.7mmHg/Lmin
What is the relationship of pulmonary vascular resistance to systemic resistance?
PVR is normally v small, about 10% of the systemic vascular resistance
What controls pulmonary vascular resistance locally?
Oxygen tension in the adjacent alveoli
Name 3 things that increased PVR is associated with
- High and low lung volumes
- Alveolar hypoxia because of constriction of small pulmonary arteries
- Drugs that cause contraction of muscle e.g. serotonin, histamine, Noradrenaline
Name 2 things that are associated with decreased PVR?
- Exercise because of recruitment and distension of capillaries
- (Acutely) increasing venous pressure
What causes a fall in PVR during exercise? (4 things)
- Increased pulmonary arterial pressure
- Increased pulmonary venous pressure
- Recruitment of pulmonary capillaries
- Distension of pulmonary capillaries
What does the body’s blood vessels normally do in response to hypoxia?
Vasodilate
What happens to the vessels in the lungs when there is hypoxia and what does this do?
Constriction, this shunts blood to better ventilated regions
What does alveolar hypoxia do to small pulmonary arteries?
Causes constriction
Why does alveolar hypoxia cause constriction of the alveolar blood vessels?
Probably a direct effect of the low PO2 on the vascular smooth muscle
The mechanism involves K+ channels in the vascular smooth muscle
What is the role of hypoxia pulmonary vasoconstriction at birth?
It’s critical in the transition from placental to air breathing
How does hypoxic pulmonary vasoconstriction help in those with lung disease?
It directs blood flow away from poorly ventilated areas, thus it is going to areas where it is more likely to pick up lots of oxygen
What can reduce hypoxic pulmonary vasoconstriction?
Inhaling low concentrations of nitrous oxide
What are the 3 vascular functions of the lung?
- Gas exchange
- Storehouse for blood
- Filter for blood- clots get trapped in the lungs and don’t go to the brain
What are 5 metabolic functions of the lung?
- Converting angiotensin I-II by ACE
- Inactivating bradykinin
- Removing serotonin
- Removing leukotrienes
- Removes 30% of NA
What are biologically active substances metabolised by the lungs?
- Synthesised and used in the lungs- surfactant
- synthesised and stored or released into blood- PG’s, histamine, kallikrenin
- Partially removed from the blood- PG’s, bradykinins, adenine nucleotides, serotonin, NA, ACH
- Activated in the lungs- Angi-AngII
How is the accumulation of water in pulmonary alveoli prevented?
- Surfactant which maintains a low surface tension in alveoli
- A low hydrostatic pressure in the alveolar capillaries
What is the pO2 in air?
150mmHg
What is the pO2 by the time it reaches the alveoli?
100mmHg
What are the 3 factors that determine alveolar pO2?
- Alveolar ventilation (most important)
- FiO2
- How much O2 is taken up by the Hb
What are the 6 layers that O2 has to move through the B-G barrier to get from alveoli to RBC?
- Surfactant
- Epithelial cell
- Interstitium
- Endothelial cell
- Plasma
- RBC membrane
What are the systemic effects of arterial hypoxia? (List 4)
- An increased RR
- Dilatation of coronary arterioles
- Respiratory alkalosis
- Constriction of renal arterioles
Name four causes of hypoxaemia
- Hypoventilation
- Diffusion limitation
- Shunt
- Ventilation- perfusion inequality
What effect does hypoventilation have on alveolar and arterial PCO2 vs PO2?
- Always increases alveolar and arterial PCO2
- Always decreases alveolar and arterial PO2 unless additional O2 is inspired
Therefore hypoxaemia is easy to reverse by increasing FiO2
What are 4 causes of hypoventilation?
- Drugs that reduce respiratory drive e.g. morphine, barbiturates
- Damage to chest wall
- Paralysis of respiratory muscles
- High resistance to breathing e.g. diving in deep water
What is a shunt when talking about the lungs?
It refers to blood that enters the arterial system without going through ventilated areas of lung
What happens when you try to treat hypoxaemia from shunting with added inspired O2?
Not much, it responds poorly
When 100% O2 is inspired, the arterial PO2 does not rise to the expected level- a useful diagnostic test
What do regional difference of V/Q cause in the upright human lung?
A pattern of regional gas exchange
What is the V/Q pattern in the upright lung?
They decline in a linear fashion from bases to apices
What are the V/Q ratios like in the upper part of the lung?
They are high in the upper portion, high PO2 because perfusion is lower at apices
What does V/Q mismatch result in?
It impairs the uptake or elimination of all cases by the lung
Is the elimination of CO2 impaired by V/Q mismatch?
Yes, but it can be corrected by increasing the ventilation to the alveoli, by contrast, the hypoxaemia resulting from V/Q inequality cannot be eliminated by increases in ventilation.
The different behaviour of the 2 gases is due to the different shapes of their dissociation curves
How is O2 carried in the blood?
Combined with Hb- presence of Hb in blood increases O2 concentration by 70x
Dissolved
Why would dissolved O2 alone not be enough to meet tissue demands?
Because it obeys Henry’s law- amount dissolved is proportional to the partial pressure- this in itself is not enough to meet tissue demand
What is directly responsible for how much O2 tissues will get?
HbO2= saturation of O2 on Hb
The drive for HbO2 is the pO2 and relationship via sigmoid curve
What is the oxygen saturation of Hb for a pO2 of 100mmHg?
97.5%
What is the Hb saturation at a pO2 of 40mmHg (like in venous blood)?
75%
What is the p50?
The pO2 for 50% of O2 saturation
Normally about 27mmHg
What is the significance of the flat part of the O2 dissociation curve?
Even if the pO2 in alveolar gas falls somewhat, loading of O2 will be little affected
What is the significance of the steep part of the curve?
Means that even a small drop in pO2 affects significantly how much O2 will get on the Hb
What do you do if you want to get more O2 to the peripheries?
Pump up the pO2 with high flow O2, this ensures more O2 gets on the Hb and therefore gives more O2 for the tissue
What shifts the curve to the left (increased O2 affinity)?
CO HbF Hypothermia Decreased PCO2 Decreased 2,3-DPG
What shifts the curve to the right (decreased O2 affinity)?
Hyperthermia
Increased PCO2
Low pH
Increase 2,3-DPG
What happens to O2 offloading in exercise?
Exercising muscle is acid, hypercarbic and hot and thus benefits from increased unloading of O2 from its capillaries
What is associated with elevated levels of 2,3-DPG?
Associated with chronic hypoxia- high altitude, chronic lung disease
Does oxygen uptake by Hb in the lung capillaries vary directly or indirectly with blood pH?
Directly
How does oxygen uptake by Hb in the lung capillaries vary with increased PACO2?
It varies inversely
How does carbon monoxide interfere with O2 transport?
It binds closely with Hb
Has 240 times the affinity of O2 for Hb I.e. for the same partial pressure, CO will bind 240x more strongly than O2
Therefore Hb concentration in blood may be normal, but O2 conc greatly reduced
Does COHb shift the curve to the left of the right?
The left and thus interferes with the unloading of O2
What are 5 features of CO poisoning?
- Reduced O2 concentration of arterial blood
- Reduced O2 concentration of mixed venous blood
- O2 dissociation curve shifted to the left
- CO is colourless and odourless
- Normal arterial pO2
What are the physiological changes that occur at high altitude?
At high altitude, sympathetic activity, heart rate, and cardiac output, increase. Plasma volume is reduced leading to haemoconcentration. Hyperventilation leads to respiratory alkalosis and increases pulmonary arteriolar resistance that may lead to pulmonary hypertension.
What are the physiological changes that occur at high altitude?
At high altitude, sympathetic activity, heart rate, and cardiac output, increase. Plasma volume is reduced leading to haemoconcentration. Hyperventilation leads to respiratory alkalosis and increases pulmonary arteriolar resistance that may lead to pulmonary hypertension.
