Respiratory Flashcards
What is the kinetic theory of gases?
Gases are a collection of molecules moving around a space, generating pressure by colliding with the walls of the space.
As collisions become more frequent, and harder, pressure goes up.
Explain the broad functions of the respiratory system in health?
The respiratory system works to ensure that all tissues receive the oxygen that they need and can dispose of the CO2 they produce.
Blood carries gases to and from tissues, where the lungs exchange them with the atmosphere.
What is Boyles law?
If a given amount of gas is compressed into a smaller volume, the molecules will hit the wall more often. Therefore pressure will rise.
If temperature is constant, Pressure is Inversely Proportional to Volume
What is Charles law?
The kinetic energy of molecules Increases with Temperature.
As temperature increases, the molecules hit the walls more often, so pressure increases.
Pressure is Proportional to Absolute Temperature (scale starts at absolute zero)
What is the universal gas law?
The universal gas law allows the calculation of how volume will change as pressure and temperature changes.
Pressure x Volume = Gas Constant x Temperature (0K)
What is partial pressure?
In a mixture of gases molecules of each type behave independently. So each gas exerts its own pressure, which is a portion of the total pressure (a partial pressure).
It is calculated as the same fraction of the total pressure as the volume fraction of the gas in the mixture.
What is vapour pressure?
In biological systems gas mixtures are always in contact with water.
So gas molecules dissolve, and water molecules evaporate, and then exert their own partial pressure. This partial pressure is known as vapour pressure.
What is saturated vapour pressure?
When the rate of molecules entering and leaving water at the same time is equal, this is the Saturated Vapour Pressure.
When gases enter our body, they are completely saturated with water vapour, so they don’t dry out our lungs.
What is tension?
Gas tension in liquids indicates how readily gas will leave the liquid, not (at least directly) how much gas is in the liquid. At equilibrium (achieved very quickly in the body), Tension = Partial Pressure.
How is the content of a gas in a liquid determined?
The amount of Gas that enters a liquid to establish a particular tension is determined by Solubility.
Content = Solubility x Tension
(How easily gas will dissolve x How readily it will leave)
If the gas reacts with a component of the liquid however, this reaction must be complete before tension, and therefore content can be established.
Total Content = Reacted Gas + Dissolved Gas
E.g.
Plasma just dissolves O2
A pO2 of 13.3kPa (ppO2 in the lungs), gives a blood content of 0.13 mmol/L of O2
Whole blood contains Haemoglobin, which reacts chemically with Oxygen.
At pO2 of 13.3kPa, Haemoglobin binds 8.8mmol/L of O2
Total Content = O2 Bound to Haemoglobin + O2 dissolved in Plasma
= 8.8 + 0.13
= 8.93 mmol/L
What is tidal volume?
The lung volume that represents the amount of air that is displaced between normal inspiration and expiration, when extra effort is not applied
What is respiratory rate/ pulmonary ventilation rate?
The number of breaths taken in a set time, usually 60 seconds
What is the difference between the bronchial and pulmonary circulation?
The lungs have two circulations – pulmonary and bronchial.
The bronchial circulation is part of the systemic circulation, and meets the metabolic requirements of the lungs. The pulmonary circulation is the blood supply to the alveoli, required for gas exchange.
What is ventilation perfusion matching?
For efficient oxygenation, ventilation of the alveoli needs to be matched with perfusion. The optimal Ventilation/Perfusion ratio is 0.8. Maintaining this means diverting blood from alveoli that are not well ventilated.
This is achieved by hypoxic pulmonary vasoconstriction. Alveolar hypoxia results in vasoconstriction of pulmonary vessels, and the increased resistance means less flow to the poorly ventilated areas and greater flow to well ventilated areas.
Chronic hypoxic vasoconstriction can lead to right ventricular failure. The chronic increase in vascular resistance puts a high afterload on the right ventricle, leading to its failure.
Define the upper respiratory tract
Upper Respiratory Tract The parts of the respiratory system lying outside the thorax o Nasal Cavity o Pharynx o Larynx
Define the lower respiratory tract
The parts of the respiratory system lying inside the thorax o Trachea o Main/Primary bronchi o Lobar Bronchi • Three on right • Two on left • Bronchi have cartilage in their walls o Segmental Bronchi o Sub-segmental Bronchi o Bronchioles • No Cartilage in the walls • More smooth muscle than Bronchi o Terminal Bronchioles • ~200,000 o Respiratory Bronchioles o Alveolar Ducts o Alveoli • ~300,000,000
What are the broad functions of different parts of the respiratory tract?
The lungs are a means of getting air to one side, and blood to the other of a very thin membrane, with a large surface area.
The trachea and bronchi have cartilaginous rings in order to hold them open and provide a path for air to travel to the alveoli.
Bronchioles draw air into the lungs by increasing their volume, using the smooth muscle in their walls.
Alveoli provide the single cell thickness membrane for diffusion (Type I cells, Simple Squamous epithelia). They also produce surfactant (Type II cells) to reduce the surface tension of the alveoli.
Describe the structure and function of the nose
The nose is part of the respiratory tract, superior to the hard palate. It is comprised of the external nose and nasal cavity, which is divided into the right and left cavities by the nasal septum.
The functions of the nose include smelling, respiration, filtration of dust, humidification of inspired air, and reception and elimination of secretions from the paranasal sinuses and nasolacrimal ducts.
Air passing over the respiratory area of the nose is warmed and moistened before it passes through the rest of the upper respiratory tract to the lungs.
The olfactory area contains the peripheral organ of smell.
Describe the structure and function of the conchae (turbinates)
The superior, middle and inferior Nasal Conchae (or turbinates) curve inferiormedially, hanging like short curtains from the lateral wall of the nasal cavity.
The conchae are scroll-like structures that offer a vast surface area for heat exchange.
The inferior concha is the longest and broadest and is formed by an independent bone (the Inferior Concha).
The middle and superior conchae are the medial processes of the Ethmoid Bone.
A recess or nasal meatus underlies each of the turbinates, dividing the nasal cavity into four passages.
The Sphenoethmoidal Recess, lying superoposterior to the superior conca, receives the opening of the sphenoidal sinus
Describe the structure and function of the para nasal sinuses
The paranasal sinuses are air-filled extensions of the respiratory part of the nasal cavity into cranial bones (Frontal, Ethmoid, Sphenoid and Maxilla).
The sinuses are named according to the bones in which they are located.
What are the frontal sinuses?
The Right and Left Frontal Sinuses are between the outer and inner tables of the frontal bone, posterior to the superciliary arches and the root of the nose. They are usually detectable in children by 7 years of age.
They each drain through a Frontonasal Duct into the ethmoidal infundibulum, which opens into the semilunar hiatus of the Middle Nasal Recess.
What are the ethmoidal cell sinuses?
The Ethmoidal cells (Sinuses) are small invaginations of the mucous membrane of the middle and superior nasal recesses into the Ethmoid bone.
The Ethmoidal cells usually are not visible in plain radiographs before 2 years of age.
The Anterior Ethmoidal Cells drain directly or indirectly into the middle nasal recess through the ethmoidal infundibulum.
The Middle Ethmoidal Cells open directly into the middle nasal recess.
The Posterior Ethmoidal Cells open directly into the superior nasal recess.
What are the sphenoidal sinuses?
The Sphenoidal Sinuses are located in the body of the sphenoid and may extend into the wings of the bone.
The body of the sphenoid is fragile, and only thin plates of bone separate the sinuses from several important structures (Optic nerves and chiasm, the pituitary gland, internal carotid arteries).
They drain directly into the Sphenoethmoidal Recess.
What are the maxillary sinuses?
The Maxillary Sinuses are the largest of the paranasal sinuses. They occupy the bodies of the Maxillae.
They drain by one or more openings, the Maxillary Ostium (ostia), into the middle nasal recess by way of the semilunar hiatus.
Describe generally the structure and location of the pharynx
The Pharynx is the superior, expanded part of the Alimentary System, posterior to the nasal and oral cavities and extending inferiorly past the larynx.
The Pharynx extends from the Cranial Base to the Inferior Border of the Cricoid Cartilage Anteriorly and the Inferior Border of C6 Vertebra Posteriorly.
It is widest (Approximately 5cm) opposite the hyoid and narrowest (approximately 1.5cm) at its inferior end, where it is continuous with the oesophagus.
What are the 3 divisions of the pharynx?
The Pharynx is divided into Three Parts:
o Nasopharynx
• Posterior to the nose and superior to the soft palate
• Respiratory Function as it is the posterior extension of the nasal cavities
• Lymphoid tissue forms a tonsillar ring around the superior part of the pharynx, which aggregates to form Tonsils
o Oropharynx
• Posterior to the mouth
• Extends from the soft palate to the superior border of the epiglottis
• Digestive Function
• Involved in swallowing (GI LO 2.7)
o Laryngopharynx
• Posterior to the Larynx
• Ends from the superior border of the epiglottis to the inferior border of the cricoid cartilage, where it becomes continuous with the oesophagus.
What is the larynx?
The Larynx connects the inferior Oropharynx to the Trachea. It also contains the complex organ of voice production (The ‘voice box’).
It extends from the Laryngeal Inlet, through which it communicates with the Laryngopharynx to the level of the inferior border of the cricoid cartilage. Here the laryngeal cavity is continuous with the Trachea.
The Larynx’s most vital function is to guard the air passages, especially during swallowing when it serves as the sphincter/valve of the lower respiratory tract, thus maintaining the airway.
The voice box controls sound production. It is composed of nine cartilages, connected by membranes and ligaments containing the vocal folds.
What is the middle ear?
The cavity of the middle ear, or tympanic cavity is the narrow air-filled chamber in the petrous part of the temporal bone. The Tympanic cavity is connected with: o Nasopharynx • Anteromedially • Pharyngotympanic (Eustachian)Tube o Mastoid cells • Posterosuperiorly • Mastoid Antrum
What type of membranes does the respiratory system contain?
The respiratory system contains:
Mucous Membranes, which line the conducting portion of the respiratory tract, bearing mucus-secreting cells to varying degrees
Serous Membranes, which line the pleural sacs that envelop each lung
What areas of the respiratory tract have Pseudostratified, ciliated epithelia with Goblet Cells?
Nasal Cavity Pharynx Larynx Trachea Primary / Secondary Bronchi
Which areas of the respiratory system have simple columnar ciliated epithelia with Clara cells (dome shaped with microvilli- some secretions)?
Bronchioles and terminal bronchioles
Which areas of the respiratory system have simple cuboidal sparsely ciliated epithelia with Clara cells?
Respiratory bronchioles
Alveolar ducts
Which areas of the respiratory system have simple squamous epithelia?
Alveoli
Histologically describe the non olfactory region of the nasal cavity
Non-Olfactory regions
o Pseudostratified ciliated epithelium.
o Mucous glands and venous sinuses in lamina propria.
o Venous plexuses swell every 20-30 minutes, alternating air flow from side to side to prevent over-drying.
o Arterial blood flow warms inspired air
o Held open by surrounding cartilage or bone.
Histologically describe the olfactory region of the nasal cavity
o Particularly thick Pseudostratified epithelium
o No goblet cells
• No mucus
o Located in posterior, superior region of each nasal fossa
o Contains olfactory cells (bipolar neurons)
o Bowman’s Glands
• Serous glands flush odorants from the epithelial surface
Histologically describe the larynx
o Ventricular folds are lined by Pseudostratified epithelium
• Ventricles and their folds give resonance to the voice
o Vocal cords lined by Stratified Squamous Epithelium
• Can stop foreign objects from reaching the lungs
• Close to build up pressure when coughing is required
Histologically describe the trachea
Pseudostratified ciliated epithelium o Lamina propria (many elastin fibres) o Seromucus glands o C-Shaped Cartilage Ring
Histologically describe primary bronchi
o Similar to trachea
o Cartilage rings completely encircle the lumen
Histologically describe lobar and segmental bronchi
o Similar to primary bronchi
o Cartilage in crescent shapes, not Ring or Completely encircling lumen
Histologically describe the bronchus
o Small diameter
o Cartilage reduced to small islands
o Glands in Submucosa
Histologically describe the bronchiole
o No cartilage or glands
o Surrounding alveoli keep the lumen
As bronchioles get smaller, goblet cells give way to Clara cells, interspersed between ciliated cuboidal cells.
Clara cells secrete a surfactant lipoprotein, which prevents the walls sticking together during expiration.
They also secrete Protein CC16. This is a measurable marker in bronchoalveolar damage or leakage across the air-blood barrier.
o CC16 Lowered = Lung Damage
o CC16 Raised = Leakage across barrier
Histologically describe a terminal bronchiole
o Absence of goblet cells in these very narrow airways is important to prevent individuals ‘drowning’ in their own mucus
What is the difference between terminal bronchiole, respiratory bronchiole, alveolar duct, alveolus and alveolar sac
The presence of lack of cartilage, glands and differing diameters distinguishes Bronchi from Bronchioles.
Terminal Bronchiole
o No alveolar openings
Respiratory bronchiole
o Bronchiole wall opens onto some alveoli
Alveolar Duct
o Duct wall has openings everywhere onto alveoli
Alveolus
o A single alveoli
Alveolar Sac
o Composite air space onto which many alveoli open
Describe the structure of alveoli
o Abundant capillaries
o Supported by a basketwork of elastic and reticular fibres
o Covering composed chiefly of Type I pneumocytes
o Simple Squamous
o Cover 90% of surface area
o Permit gas exchange with capillaries
o Scattering of intervening Type II pneumocytes
o Simple Cuboidal
o Cover 10% of surface area
o Produce surfactant
o Macrophages line alveolar surface to phagocytose particles.
New alveoli continue to develop up to the age of 8 years, when there are approximately 300,000,000.
Alveoli can open into a respiratory bronchiole, an alveolar duct or sac or another alveolus (via an alveolar pore).
In quiet breathing what muscles are involved in inhalation and exhalation?
Quiet Breathing o Inhalation • Diaphragm • External Intercostals o Exhalation • None
In forced breathing what muscles and structures are involved in inhalation and exhalation?
Forced Breathing o Inhalation • Diaphragm • External Intercostals • Scalene • Pectoralis Minor • Sternocleidomastoid • Serratus Anterior o Exhalation • Internal Intercostals • Innermost Intercostals • Abdominal Muscles
The rate at which gas exchange occurs across the alveoli depends on which 3 factors?
o Area available for the exchange
o Resistance to diffusion
o Gradient of partial pressure
How does area affect gas exchange in the alveoli?
The greater the surface area, the greater the amount of gas exchange occurring.
The area of the alveolar surface is large because there are a huge number of alveoli, generating in a normal lung an exchange area of around 80m2. In normal lungs, the area available is not a limiting factor on gas exchange.
How does resistance to diffusion affect gas exchange in the alveoli?
The diffusion pathway from alveolar gas to alveolar capillary blood is short, but there are several structures between the two. First gas must diffuse through the gas in the alveoli, then through:
o The alveolar epithelial cell
o Interstitial fluid
o Capillary endothelial cell
o Plasma
o RBC membrane
This means gases have to diffuse through 5 cell membranes, 3 layers of intra cellular fluid and 2 layers of extra cellular fluid. Despite this the overall barrier is less than 1 micron.
Two gases have to diffuse, oxygen into the blood and carbon dioxide out of it. The resistance is not the same for the two gases. For most of the barrier (the cells, membranes and fluid) the rate of diffusion is affected by the solubility of the gas in water, and carbon dioxide diffuses much faster, because it is more soluble.
Overall, Carbon Dioxide diffuses 21 times as fast as oxygen for a given gradient. This means that anything affecting diffusion will only change oxygen transport, as that is limiting (If there is a problem affecting the exchange of gases, O2 will be affected first)
How does partial pressure affect gas exchange?
The partial pressure of oxygen and carbon dioxide in the alveolar gas must be kept very close to their normal values (O2 – 13.3kPa/CO2 – 5.3kPa) if the tissues of the body are to be properly supplied with oxygen and lose their carbon dioxide. This is achieved by exchange of gas between alveolar gas and atmospheric air brought close to it through the airways of the lung by the process of ventilation.
Air is driven through the airways of the lungs by the pressure changes produced by increases and decreases in the volume of the air spaces next to the alveoli. The movement of breathing lowers pressure in the terminal and respiratory bronchioles during inspiration, so air flows down the airways to them and then increased pressure during expiration so air flows back out again.
Fresh atmospheric air does not enter the alveoli, and exchange of oxygen and carbon dioxide occurs by diffusion between alveolar gas and atmospheric air in the terminal and respiratory bronchioles.
How is respiration measured?
The movement of air during breathing can be measured with Spirometry.
Define tidal volume
The lung volume that represents the amount of air that is displaced between normal inspiration and expiration, when extra effort is not applied
Define inspiratory reserve volume
The extra volume that can be breathed in when extra effort is applied
Define expiratory reserve volume
The extra volume that can be breathed out when extra effort is applied
Define residual volume
The volume left in the lungs at maximal expiration. This cannot be measured with a spirometer; it must be measured by helium dilution
What’s the difference between lung volumes and capacities?
Lung volumes change with breathing pattern. Capacities do not, as they are measured from fixed points in the breathing cycle.
Define vital capacity
The biggest breath that can be taken in, measured from the max inspiration to max expiration. It often changes in disease, and is about 5L in a typical adult.
Define functional residual capacity
The volume of air in the lungs at resting expiratory level (Expiratory reserve volume + residual volume). It is typically about 2L.
Define inspiratory capacity
The biggest breath that can be taken from resting expiratory level (lung volume at the end of quiet expiration). It is typically about 3L.
What is serial (anatomical) dead space?
Air enters and leaves the lungs by the same airways. So the last air in is the first air out, does not reach the alveoli and is therefore unavailable for gas exchange. The volume of the conducting airways is known as the Anatomical or Serial Dead Space and is normally about 150ml.
What is alveolar (distributive) dead space?
The volume of air in alveoli not taking part in gas exchange is known as the Alveolar (or Distributive) Dead Space. i.e. Due to disease etc.
The air contained in the conducting airways is not the only air that fails to equilibrate with alveolar capillary blood. Some alveoli receive an insufficient blood supply; others are damaged by accident or disease, so that even in the air that reaches the alveolar boundary, there is a proportion that fails to exchange.
What is physiological dead space?
Anatomical Dead Space + Alveolar Dead Space = Physiological Dead Space
How is physiological dead space measured?
Physiological Dead space is determined by measuring pCO2 (or pO2) of expired alveolar air. The alveolar air is diluted by dead space air to form the expired air, and the degree of dilution is a measurement of a physiological dead space.
How is serial dead space determined?
Nitrogen washout test
Describe the nitrogen washout test
Serial (Anatomical) Dead Space is measured by the Nitrogen Washout Test.
o The patient takes a maximum inspiration of 100% oxygen.
o The oxygen that reaches the alveoli will mix with alveolar air, and the resulting mix will contain Nitrogen (there is 79% Nitrogen in air)
o However, the air in the conducting airways (dead space) will still be filled with pure oxygen.
o The person exhales through a one way valve that measures the percentage of Nitrogen in it and volume of air expired
o Nitrogen concentration is initially zero as the patient exhales the dead space oxygen.
o As alveolar air begins to move out and mix with dead space air, nitrogen concentration gradually climbs, until it reaches a plateau where only alveolar gas is being expired
o A graph can be drawn to determine the dead space, plotting Nitrogen % against Expired Volume.
How do you calculate alveolar ventilation rate? (The amount of air that actually reaches the alveoli)
Alveolar Ventilation Rate = Pulmonary Ventilation Rate – Dead Space Ventilation Rate
Alveolar Ventilation Rate =(Tidal Volume x RR) – (Dead Space Volume x RR)
How do the lungs and thorax contribute mechanically to respiration?
Air is drawn into the lungs by expanding the volume of the thoracic cavity. Work is done during breathing to move the structures of the lungs and thorax and to overcome the resistance to flow of air through the airways.
The space between the lungs and thoracic wall, the pleural space, is normally filled with a few millilitres of fluid, the surface tension of which forms a pleural seal holding the outer surface of the lungs to the inner surface of the thoracic wall. Therefore the volume of the lungs changes with the volume of the thoracic cage.
What is pneumothorax?
If the integrity of the pleural seal is broken, the lungs will tend to collapse.
E.g. If air gets in between the two layers of the pleura, fluid surface tension is lost and the lungs collapse.
What is lung compliance?
The ‘stretchiness’ of the lungs is known as compliance.
It is defined as volume change per unit pressure change.
High Compliance means that the Lungs are Easy to Stretch.
How is compliance measured and calculated?
Compliance is measured by measuring the change in lung volume for a given pressure. The greater the lung volume the greater the compliance and vice versa. However, even with the constant elasticity of lung structures, compliance will also depend on the starting volume from which it is measured, so it is more usual to calculate Specific Compliance, which is:
Volume Change Per Unit Pressure Change / Starting Volume of Lungs
What are the 3 main factors that affect the compliance of the lungs?
Surfactant
Surface tension
Bubbles
Where do the elastic properties of the lungs arise from?
The elastic properties of the lungs arise from two sources, Elastic Tissues in the lungs and Surface Tension forces of the fluid lining the alveoli.
What is surface tension and how does it affect compliance?
Surface tension is interactions between molecules at the surface of a liquid, making the surface resist stretching. The higher the surface tension, the harder the lungs are to stretch (lowers compliance).
What is surfactant? What produces surfactant? And how is surfactant related to surface tension and thus compliance?
At low lung volumes, the surface tension of the lungs is much lower than expected. This is due to the disruption of interactions between surface molecules by Surfactant, produced by Type 2 Alveolar Cells.
Surfactant is a complex mixture of phospholipids and proteins, with detergent properties. The hydrophilic ends of these molecules lies in the alveolar fluid and the hydrophobic end projects into the alveolar gas. As a result they float on the surface of the lining fluid, disrupting interaction between surface molecules.
Surfactant reduces surface tension when the lungs are deflated, but not when fully inflated. So little breaths are easy, and big breaths are hard, and it takes less force to expand small alveoli than it does large ones.
How do the ‘bubbles’ in the lung affect surface tension and compliance?
Alveoli form an interconnecting set of bubbles. If Laplace’s law is applied (Pressure is inversely related to the radius of a bubble), large alveoli would ‘eat’ small ones.
As alveoli get bigger, the surface tension in their walls increases, as surfactant is less effective. So pressure stays high and stops them from ‘eating’ the smaller alveoli.
Describe resistance in airways and Poisseulles law
In addition to work done against the elastic nature of the lungs, energy must be expended to force air through the airways. The resistance of an airway to flow is determined by Poiseulle’s Law when flow is laminar, which is true of most of the airways of the lungs.
Poiseulle’s Law:
The resistance of a tube increases sharply with a falling radius.
However, the combined resistance of the small airways is normally low, because they are connected in parallel over a branching structure, where the total resistance to flow in the downstream branches is less than the resistance of the upstream branch.
Most of the resistance to breathing therefore resides in the upper respiratory tract.
Overall, work is done against:
o The elastic recoil of the lungs and thorax
o Elastic properties of the lungs
o Surface tension forces in the alveoli
o Resistance to flow through airways
o Of little significance in health, but often affected by disease
At rest the work of breathing consumes only 0.1% of total oxygen consumption, so it is efficient.
How does resistance change in the breathing cycle?
During inspiration, the bronchioles use their smooth muscle to increase their radius. This decreases their resistance (Poiseulle’s Law), allowing air to be drawn easily through them into the alveoli.
Describe spirometry
The patient fills their lungs from the atmosphere, and breathes out as far and fast as possible through a Spirometer.
Simple Spirometry allows measurement of many lung volumes and capacities. Vital capacity is particularly significant. Tables can be used to predict the vital capacity of an individual of known age, sex and height.
Why may vital capacity be less than normal?
Vital Capacity may be less than normal because the lungs are not:
- Filled normally in inspiration- due to altered compliance of lungs and force of inspiratory muscles
- Emptied normally in expiration- due to increase in airway resistance or compression of the lungs
- Or Both
In what conditions is compliance increased?
Emphysema
Break down of elastic makes walls more stretchy
In what conditions is compliance decreased?
Lung fibrosis
Thickening and fibrosis of elastic makes wall stiff
What is Forced Vital Capacity?
FVC is the maximum volume that can be expired from full lungs.
What is the Forced Expiratory Volume in One Second (FEV1)?
FEV1 is the volume expired in the first second of expiration from full lungs. (>70% FVC)
It is affected by how quickly air flow slows down, so is low if the airwards are narrowed (obstructive deficit)
What is a vitalograph?
Plot of volume expired (y) against time (x)
A type of spirometry which records the volume exhaled following a vital capacity breath.
Initial rapid rise which tails into a plateau
Helps differentiate between restrictive and obstructive deficit
How is a vitalograph obtained?
Restrictive and obstructive deficits can be separated by asking the patient to breathe out rapidly from maximal inspiration through a single breath spirometer, which plots volume expired against time
What is a restrictive deficit and how does it come about?
Maximal filling of the lungs is determined by balance between maximum inspiratory effort and the force of recoil of the lungs
- if the lungs are unusually stiff, or if inspiratory effort is compromised by muscle weakness, injury or deformity, then a RESTRICTIVE DEFICIT is formed
Affects air coming in/ INSPIRATION
How does a restrictive deficit affect FVC and FEV1?
FVC is reduced
FEV1 >70% of FVC (as both FEV1 and FVC decrease proportionally)
So ratio of FEV1:FVC is the same
Give an example of a condition where a restrictive deficit occurs
Muscle weakness
Lung fibrosis
What is an obstructive deficit and how does it come about?
During expiration, particularly when forced, the small airways are compressed - increases flow resistance eventually to a point where no more air can be driven out of the alveoli
- if the airways are narrowed, then excitatory flow is compromised much earlier in expiration producing an OBSTRUCTIVE DEFICIT
Affects air going out/EXPIRATION
How does an obstructive deficit affect FVC and FEV1?
FEV1 reduced
FVC relatively normal
So FEV1: FVC ratio is decreased
Give an example of a condition where an obstructive deficit occurs
Asthma
COPD
What is a flow volume curve and how is it produced?
Plot of volume expired (x) against flow rate (y) - derived from a vitalograph trace (tangents)
Sharp increase followed by more gradual decrease
Why is a flow volume curve more informative than a vitalograph?
A flow volume curve is a much more sensitive indicator of airway narrowing
Can also discriminate large and small airway narrowing
How is a flow volume curve broken down into 4 categories? Describe each (A-D and A has a special name)
A- when the lungs are full, airways are stretched so resistance is at a minimum, flow is therefore at a maximum (PEAK EXPIRATORY FLOW RATE)
B-D- when lungs are compressed, more air is expired and the airways begin to narrow, so resistance increases and flow rate decreases
What is PEFR and how is it determined?
Peak EXPIRATORY flow rate
From a flow volume curve - peak flow
Can be measured with a simple cheap device, so often used as a screening test for airway narrowing but it’s very insensitive
PEFR is affected most by the resistance of which airways? How does this affect the flow volume curve?
In normal individuals, peak flow is affected most by the resistance of large airways, but will also be affected by the severe obstruction of the smaller airways (e.g. Asthma)
Mild obstruction of airways produces a scooped out EXPIRATORY curve- more severe obstruction will also produce PEFR
What does the helium dilution test measure?
Measurement of residual volume by measuring functional residual capacity (FRC)- which can’t be measured by spirometry
Why is helium used to measure residual volume in the helium dilution test?
Helium- inert, colourless, odourless, tasteless, non toxic gas
Helium cannot transfer across the alveolar capillary membrane and so is contained within the lungs
How is the helium dilution test carried out?
At end of the normal tidal expiration the patient is connected to a circuit which is connected to a circuit, which is connected to a container containing a gas mixture with a known helium concentration (C1) and volume (V1)
- end of tidal expiration
- lung volume - FRC = ERV + RV
Patient continues to rebreathe into container until quilibrium occurs (4-7mins)
New concentration of helium (C2)
- C1 x V1 = C2 x V2
- V2 = V1 + FRC
Since C1, V1 and C2 are all known, (V2 and then) FRC can be calculated
Therefore RV = FRC - ERV (measured by spirometry)
What is Transfer factor?
CO transfer factor- measures rate of transfer of CO from alveoli to blood in ml per minute per kPa (ml/min/kPa)
Way of measuring the DIFFUSION CAPACITY of the lungs because amount transferred will depend on how well gas diffusion takes place
Why is CO used to calculate transfer factor and thus diffusion capacity?
Inhaled CO used because of its very high affinity for haemoglobin - since all CO entering the blood binds to H, very little remains in plasma so we can assume free plasma ppCO is zero
So concentration gradient between alveolar ppCO and capillary ppCO is maintained
As a result the amount of CO transferred from alveoli to blood is limited only by the diffusion capacity of the lungs
What is the process for measuring transfer factor?
Patient performs full expiration, followed by maximum inspiration of a gas mixture composed of air, a tiny fraction of CO and fraction of inert gas such as helium (tiny fraction of CO as it’s toxic, fraction of inert gas to make an estimate of total lung volume)
Breath held for 10 seconds
Patient exhales - gas held mid expiration - to gain a an alveolar sample
Concentration of CO and inert gas
From these measurements CO Transfer factor is calculated
What measurements are usually shown in a lung function report?
Vital capacity FEV1 (before and after bronchodilator) Ratio FEV1/FVC Peak EXPIRATORY Flow rate (FRC, RV, TLC, RV/TLC) Transfer factor CO conductance
How soluble is oxygen?
Oxygen is not sufficiently soluble in body fluids for adequate gas transport in simple solution- 21 times less soluble than CO2
What is the solubility coefficient of oxygen at a partial pressure of 13.3kPa and temp of 37C?
0.01mmol/L/kPa
How much oxygen does plasma contain at partial pressure of 13.3 kPa and temp of 37C?
= 0.01 (Oxygen solubility coefficient) x 13.3
= 0.13 mmol/L of dissolved oxygen
What protein in the blood helps with the transport of oxygen around the body, despite its low solubility?
Haemaglobin
What’s the concentration of Hb in the blood?
2.2mmol/L
How much Oxygen is carried in the blood, when it’s fully saturated?
8.8mmol/L
What is Hb like at the lungs?
Blood leaves the lungs with the Hb almost saturated with oxygen
R state
Will an increase in oxygen in all parts of the lungs increase the content of oxygen in the blood?
No as most Hb is usually saturated already
What maintains the composition of alveolar gas?
Ventilation and perfusion
What is the alveolar pO2?
13.3kPa
What is the mixed venous blood pO2?
5.3kPa
What is the alveolar pCO2?
5.2kPa
What is the mixed venous blood pCO2?
6.6kPa
Does CO2 or O2 diffuse more rapidly in a gas phase?
O2
Does CO2 or O2 diffuse more rapidly in a liquid phase?
CO2
21 times more that O2
How long does it usually take for sufficient gas exchange to occur at the alveolar capillary membrane?
500ms (half the time blood spends in the capillaries=1000ms/1s)
Under normal conditions, what’s the difference between the composition of alveolar air and alveolar capillaries?
Alveolar capillaries have the same gaseous composition as alveolar air - therefore arterial gas tensions are determined by alveolar gas composition
- and so respiration has to be controlled to keep alveolar pCO2 at 5.3kPa and alveolar pO2 at 13.3kPa
What is Hb like at the tissues?
Unloading of oxygen depends on fall of pO2 in capillaries
Changes in Hb brought about by different conditions in the tissues
T state
The extent that capillary pO2 can fall without compromising diffusion of O2 into cells depends on what?
Capillary density -
Higher capillary density means that O2 is spread more sparsely
So pO2 can fall a lot before it affects the diffusion of O2 into the tissues
E.g. Myocardium -capillary pO2 can fall further due to their being lots of capillaries and so there will be large amounts of oxygen about
What is the Bohr shift? And what causes it?
Shift of O2 Hb curve to the right due to
Low pH in tissues
High temp in tissues
Increased 2,3 DOG Low O2 tension
Conditions favour the T low affinity state for oxygen
Why is CO2 in the blood important?
Essential part of BUFFER systems - controls pH of ECF
Why is a large amount of CO2 found in the arterial blood? (Even though it’s til now been known as ‘waste’ and thus has been transported from tissues to lungs to be expired)
Lots of CO2 is found in arterial blood too (as well as that found in the venous blood as ‘waste’ because it is required for ACID BASE BALANCE
How does CO2 react with H2O?
CO2 dissolves in H2O H+ + HCO3-
What enzyme catalyses (CO2 dissolves in H2O H+ + HCO3-) reaction?
Carbonic anhydrase
How much carbonic anhydrase is found in the plasma and how does affect the reactions of CO2 in plasma?
Little found
Makes reactions slower
How much carbonic anhydrase is found in the red blood cells and how does affect the reactions of CO2 in RBCs?
Lots found
Faster reactions
What pushes this reaction forward?
CO2 dissolves in H2O H+ + HCO3-
An increase in dissolved CO2 which is proportional to pCO2
ventilation related
What opposes the forward direction of this reaction?
CO2 dissolves in H2O H+ + HCO3-
An increase in HCO3-
Metabolism related
What ratio does plasma pH depend on?
pCO2 : [HCO3-]
1:20
If pCO2 of plasma is high (ie. pCO2 : [HCO3-] is high), is pH high or low?
Low
If [HCO3-] of plasma is high (ie. pCO2 : [HCO3-] is low), is pH high or low?
High
Why does the pCO2: [HCO3-] buffer work far from its pK (dissociation constant)?
Because of excess HCO3-
What is the Henderson Hasselbach equation?
pH = pKa + log ( [HCO3-]/pCO2 x 0.23)
Where does most HCO3- come from in the plasma?
NaHCO3
Negligible HCO3- is formed from the dissolution of CO2
In body fluids with few or no other buffer systems (plasma CSF) concentration of HCO3- is not significantly affected by changes in pCO2 and remains effectively constant over all physiological values of pCO2 unless changed by other mechanisms
In this reaction CO2 dissolves in H2O H+ + HCO3 in RBCs where does the H+ produced bind to?
Haemoglobin which has a large buffering capacity
This is enhanced further when haemoglobin is deoxygenated at the tissues and H+ is high
The binding of H+ to Hb in this reaction (CO2 dissolves in H2O H+ + HCO3) in RBCs has what affect on the equilibrium of the reaction?
Reaction is pushed to the right
More HCO3- is produced
The amount produced depends primarily on the buffering effects if haemoglobin with only minor effects of changes in pCO2
How is HCO3- exported from the red blood cell during this reaction? (CO2 dissolves in H2O H+ + HCO3)
HCO3- which is being produced in large quantities in the red blood cell due to the constant removal of H+ by Hb, is exported from the red cell in exchange for the inward movement of Cl-
Used elsewhere in body- liver (check with LMSRS)
The pH of overall body fluids is dependent on the relationship between what 2 molecules in the plasma and Red cell?
Amount of CO2 dissolved in the PLASMA AND
Amount of HCO3- formed from CO2 in the RED CELL by reaction involving Hb
What are carbonamino compounds?
Protein part of Hb to which CO2 binds to
Contributes to CO2 transport but not acid base balance
Describe the overall contents of arterial blood
Plasma dissolves 0.7mmol CO2/litre of blood (plasma only 60% of total volume)
Plasma contains 15.2mmol HCO3-/litre of blood
Cells dissolve 0.3mmol HCO3-/litre
Cells contain 4.3mmol HCO3-/litre
Blood has 1mmol carbaminos/litre
Contains 21.5mmol CO2/litre
Describe the overall contents of venous blood
Plasma dissolves 0.8mmol CO2/litre of blood (plasma only 60% of total volume)
Plasma contains 16.3mmol HCO3-/litre of blood
Cells dissolve 0.4mmol HCO3-/litre
Cells contain 4.8mmol HCO3-/litre
Blood has 1.2mmol carbaminos/litre
Contains 23.5mmol CO2/litre
