CVR: Respiratory Flashcards
What two areas of the brain, not in the medulla oblongata, are involved in the control of breathing?
Pneumotaxic and apneustic centres in the pons.
What two areas of the brain, not in the pons, are involved in the control of breathing?
Dorsal respiratory group and ventral respiratory group, both in the medulla oblongata.
Which area of the medulla oblongata is predominantly active during inspiration?
The dorsal respiratory group (DRG).
What provides background ventilatory drive?
A neural network in the brainstem (central pattern generator).
Concentration of which gas predominantly influences breathing?
CO2
What do the central chemoreceptors in the brainstem detect to monitor breathing?
Hydrogen ion concentration.
How does an increase of PaCO2 cause the central chemoreceptors in the brainstem to detect increase in hydrogen ion concentration via the bicarbonate buffer system?
- CO2 crosses blood brain barrier.
- CO2 + H2O (catalysed by carbonic anhydrase) = H2CO3 (carbonic acid)
- H2CO3 dissociates = H+ + HCO3-
Where are the peripheral chemoreceptors?
Carotid bodies and aortic arch.
What do the peripheral chemoreceptors in the carotid bodies and aortic arch measure to monitor breathing?
Measure PaCO2 predominantly, but also measure PaO2 and pH.
What are the three types of mechanoreceptors in the lungs that send afferent information to the respiratory control centres via the vagus nerve?
JIS!
J receptors (juxtacapillary AKA pulmonary C-fiber receptors), irritant, and stretch.
Where are the receptors which prevent respiratory activity during swallowing?
The pharynx.
Why can x-rays be dangerous?
They are a form of ionising radiation, which can damage tissue, cells, and DNA (mutagen).
What colour are more dense structures on an x-ray? Give an example.
White. E.g. bones.
On a chest x-ray, why is the diaphragm higher on the right?
Due to the presence of the liver.
What anatomical landmark on a chest x-ray can be used to assess symmetry?
The clavicles.
Why aren’t the anterior aspects of the ribs easily visible on a chest x-ray?
They are cartilaginous.
Which view is most ideal for a chest x-ray and why; AP (anterior-posterior) or PA (posterior-anterior)?
PA (posterior-anterior); patient facing the detector, standing up.
This is because there will be a crisper image and accurate size of the heart than in AP view, and the scapulae can be protracted.
Which causes more ionising radiation for a patient, chest x-ray or abdominal x-ray?
Abdominal x-ray.
Where should you look to check for cyanosis?
Under the tongue at glossal artery.
Both Type 1 and Type 2 respiratory failure are characterised by hypoxaemia (low PaO2) due to an inability to maintain normal blood gases. What is the difference between Type 1 and Type 2 respiratory failure?
Type 1 = hypocapnia/normal PaCO2
Type 2 = hypercapnia (high PaCO2)
What causes Type 1 respiratory failure?
Many different causes, including infectious, congenital, and neoplasmic (tumour) causes.
What causes Type 2 respiratory failure?
Hypoventilation leading to hypercapnia. For example, in COPD.
Why might someone with anaemia not be cyanotic when severely hypoxic?
Cyanosis is caused by large amount of deoxygenated haemoglobin. Anaemic patient might not have enough haemoglobin to be cyanotic.
In chronic hypercapnia, such as in COPD, chemoreceptors are thought to reset. Breathing is no longer driven by increase in PaCO2 and instead driven by decrease in PaO2.
Why might giving supplementary O2 to a patient with COPD cause Type 2 respiratory failure?
If give supplementary O2 and raise PaO2, the patient might lose their ventilatory drive and hypoventilate, causing CO2 retention and hence Type 2 respiratory failure.
At the level of what rib is the optimal VQ ratio seen?
Rib 3
The total lung capacity is found by adding what two lung volumes?
Residual volume and vital capacity.
Laplace’s law states P = 2T / r
where P = pressure, T = tension, r = radius.
In relation to Laplace’s law, why do premature babies, who haven’t developed surfactant yet, struggle to inflate their lungs?
Surfactant reduces surface tension of alveoli, reducing the pressure needed to overcome to inflate alveoli.
Does the alveolar epithelium have a role other than gas exchange?
Yes! Also has a host defence function; can be triggered to produce certain defence proteins (e.g. anti-viral) when a pathogen is present.
Mucus and cilia in the respiratory epithelium are an important intrinsic (non-immunity) host defence mechanism. Why?
Mucus and cilia together form the mucociliary escalator (AKA mucociliary clearance); trapping pathogens and particles and wafting them up out of the respiratory tract.
What is airway mucus?
A viscoelastic gel produced by goblet cells and submucosal glands. Contains water, carbohydrates, proteins, and lipids.
Why is mucus important in the respiratory tract?
Protects the epithelium from foreign material/pathogens and reduces fluid loss.
What reflexes are an important part of intrinsic/non-immune host defence mechanisms?
Sneezing and coughing.
Name the four afferent nerves involved in the cough reflex.
Trigeminal, glossopharyngeal, superior laryngeal, vagus.
What two efferent nerves are involved in the cough reflex?
Recurrent laryngeal and spinal nerves.
Where are the sensory neurons which trigger the sneeze relfex?
In the nasal cavity.
Do motor neurons for sneeze or cough reflex trigger more effectors?
Sneeze.
Name the four steps involved in respiratory epithelium repair/regeneration following insult/injury.
- Spreading and de-differentiation (stop being cuboidal and ciliated).
- Cell migration.
- Cell proliferation (from basal cells).
- Re-differentiation (become ciliated epithelial cells again).
What feature of respiratory epithelium allows it to effect a complete repair?
Functional plasticity; they can change their phenotype.
What airway abnormality are most chronic pulmonary diseases associated with?
Respiratory epithelial abnormalities.
Poor mucociliary clearance function can cause potentially fatal obstructive mucus plugs. How do mucus plugs form?
Proteins in mucus polymerise to form large plugs.
Is asthma hereditary?
Not necessarily, very complex, does run in families but there is no direct Mendelian inheritance of asthma.
What is the most common lethal autosomal recessive genetic disorder in Caucasians?
Cystic fibrosis
Which chromosome and where on this chromosome is the variant which causes cystic fibrosis?
Long arm of chromosome 7
What causes cystic fibrosis?
Defect in code for CFTR (cystic fibrosis transmembrane regulator).
Approximately how common is cystic fibrosis?
1 in 2500 live births (1 in 25 people carry recessive gene).
What is measured in newborns to screen for cystic fibrosis?
Trypsin.
There are 6 classes of abnormality of cystic fibrosis genotypes. Which is the most common?
Class II (delta F508 mutation).
Alpha-1 antitrypsin deficiency (A1ATD) is an autosomal recessive/co-dominant genetic disorder. How does it cause emphysema and bronchiectasis?
Unable to produce enough antitrypsin so trypsin (serum protease) destroys lung tissue.
Name 4 common work exposures that cause asthma.
Latex, paints, shellfish, flour, isocyanate paint sprays.
What are the two categories of pneumoconioses (dust-related lung diseases)?
Fibrogenic or non-fibrogenic.
Give 2 examples of fibrogenic pneumoconioses.
Asbestosis and silicosis.
Which hypersensitivity reaction is IgE mediated, normally immediate and is seen in anaphylaxis, asthma, hay fever?
Type I
Which hypersensitivity reaction is also caused cytotoxic hypersensitivity, onset hours-days, seen in transfusion reactions and Goodpasture syndrome (Anti GBM disease), and is the underlying mechanism for several autoimmune disorders?
Type II
Which hypersensitivity reaction involves deposition (accumulation) of immune complexes, 7-21 days time course, and is seen in hypersensitivity pneumonitis?
Type III
Which hypersensitivity reaction is T-cell mediated, onset days-weeks/months, seen in tuberculosis, sarcoidosis, and Stevens-Johnson syndrome.
Type IV
In type I hypersensitivity reactions, what two types of mediators are released by antigen of allergen binding with IgE?
Soluble immediate mediators e.g. histamine, and granule delayed mediators e.g. proteases.
What causes Type II hypersensitivity reactions?
Antibodies (IgG or IgM) bind to the person’s own cell antigens, triggering different cell processes including complement activation.
Anti Glomerular Basement Membrane Disease (anti GMB) is a type II hypersensitivity reaction; an autoimmune process where antibodies to subunit on GBM (found in alveoli and kidneys) are developed.
What symptoms can Anti Glomerular Basement Membrane Disease (anti GBM) cause?
Haemoptysis and renal failure.
Describe the acute and chronic stages of hypersensitivity pneumonitis.
Acute: inflammation of alveoli within the lung caused by hypersensitivity to inhaled agents.
Chronic: causes scarring of alveoli.
Can be fibrotic/non-fibrotic.
What hobby/job is a common cause of hypersensitivity pneumonitis?
Having/working with birds (“bird fancier’s lung”).
Could also mention; farmer’s lung from working with mouldy hay. Saxophone player’s lung from bacteria inside instrument. etc.
In diving, at each 10m increase of depth how much does the atmospheric pressure increase by?
1 atm (1 atmospheric pressure, or 760mmHg)
What is the atmospheric pressure at sea level?
1 atm (1 atmospheric pressure, or 760mmHg)
What equation, based on Boyle’s Law, helps to calculate lung volume at a given depth when diving?
P1V1=P2V2
Pressure at sea level (1atm) * volume of lungs at sea level =
pressure at depth (e.g. 150m deep, will be 16ata) * volume of lungs at that depth.
Why can surfacing from a dive be fatal if you hold your breath when resurfacing?
Lung volume increases as depth decreases. This increases intra-thoracic pressure forcing air out of lungs into other spaces e.g pneumomediastinum, pneumothorax, pulmonary gas embolism.
Why do divers use low FiO2 gas mixes?
Because of the equation
PiO2 = FiO2 x Pressure (atmospheric).
If atmospheric pressure increases, PiO2 will increase with same FiO2.
At sea level PiO2 = 0.21 x 1 = 0.21.
Pulmonary oxygen toxicity, or the Lorrain Smith Effect, can occur if PiO2 is >0.5 ata (atmospheres absolute).
What are the three key symptoms?
Cough, chest tightness/pain, SOB.
What spirometry measured values can be used to diagnose airway obstructive disease (e.g. COPD)?
FEV1/FVC.
Obstruction is diagnosed when value <0.7
What spirometry measured value can be used to diagnose airway restrictive disease (e.g. asbestosis)?
FVC <80% of predicted.
In asthma, will MEF (mid expiratory flow) be low, normal, or high?
MEF will be low. This causes “scalloped” shape in the flow volume curve in spirometry.
In emphysema, will TLco (transfer estimate test with carbon monoxide) be low, normal, or high?
Low; reduced surface area of alveoli for gas exchange.
During increased minute volume, e.g. during exercise, a person with COPD might experience dynamic hyperinflation. What is dynamic hyperinflation?
Reduced elasticity means less recoil, which increases end expiratory volume. They are unable to return lung volume to normal and end up breathing at top of lung volume capacity.
What is orthopnoea?
Breathlessness on lying down.
Which immunoglobulin (Ig) is primarily secreted in breast milk?
IgA
Ignoring any relatively small contribution of inspired water vapour, what is the approximate partial pressure of inspired oxygen (PiO2) in KPa for a patient on 40% oxygen?
40KPa
Through what process does adrenaline cause bronchodilation?
Adrenaline binds to β 2-receptors in the smooth muscle of the bronchioles.
What two inter-related synchronous movements of the ribs allow inspiration/expiration?
Superior and anterior (the pump handle)
Lateral shaft elevation (the bucket handle)
Which pleura of the lung has pain sensation, visceral or parietal?
Parietal pleura.
Do the pleura of the lung run along the fissures between lobes, or just on the surface of the lung?
The visceral pleura continues along the fissures, the parietal is just on the surface.
How is respiration controlled by ventilation and perfusion?
Constriction/dilation of bronchioles (ventilation) and arterioles (perfusion).
How does the pressure of the pulmonary arteries differ from the pressure of the bronchial arteries?
Pulmonary artery pressure is similar to right ventricular pressure e.g. 25/8 (RV = 25/0)
Bronchial artery pressure is the same as systemic pressure e.g. 125/80 (LV = 125/0).
Activation of what receptors on respiratory smooth muscle causes bronchodilation?
Beta 2 receptors.
Some asthma and COPD treatments, such as ipratropium, block M3 muscarinic receptors on smooth muscle cells. Why would this treatment be effective?
Activation of muscarinic receptors stimulates smooth muscle constriction in parasympathetic stimulation. Blocking this pathway prevents bronchioles from constricting.
What is a typical minute volume in L?
5L/min
What is a typical physiological dead space in ml?
175ml.
What is the dead space?
Volume of air not contributing to ventilation.
What is the difference between the anatomical dead space and the alveolar dead space? Give typical volume amounts in ml.
Anatomical dead space: air in non-gas exchanging section of the airway, about 150ml.
Alveolar dead space: alveolar without capillary blood supply for gas exchange, about 25ml.
The systemic circulation aims to increase perfusion to tissues with higher O2 demand (e.g. hypoxic tissue) and so vasodilation occurs.
How does the pulmonary circulation respond to the same conditions?
Aim is to reduce perfusion to alveoli that are not well ventilated (hypoxic), to minimise ventilation/perfusion mismatch. Response is vasoconstriction.
In healthy people, what is the A-aDO2, or the alveolar arterial O2 difference (difference in PAO2 and PaO2) in KPa?
approx. 1KPa
Give four factors that when increased cause a right shift in the oxygen dissociation curve.
Acidity
2,3 DPG
Temperature
PaCO2
What equation is used by blood gas machines to estimate bicarbonate, and what two measured values are required for this calculation?
The Henderson-Hasselbach equation.
Uses pH and PaCO2.
Is FiO2 lower at high altitude?
No, FiO2 stays the same (21%).
PiO2 lowers because ambient pressure lowers.
PiO2 = FiO2 x ambient pressure.
Regional distribution of blood flow is affected more by gravity in pulmonary or systemic circulation?
Pulmonary
Describe the difference in vessel walls of the pulmonary and systemic circulations.
Pulmonary vessels have thinner walls with less smooth muscle than systemic vessels.
In Pouiseuille’s Law, resistance varies with the radius to the power of 4. What does this mean happens when there is a small change in the radius?
A small change in the radius will cause a large difference in resistance (wider radius = reduced resistance)
Which two mechanisms allow the pulmonary circulation to respond to an increased cardiac output in exercise to maintain a stable mean pulmonary arterial pressure?
Recruitment and distension/dilation of capillaries.
What is total lung capacity (TLC)?
The volume of air in the lungs upon the maximum effort of inspiration. Average = 6L.
What is residual lung volume?
The volume of air remaining in the lungs after maximum forceful expiration, keeps the alveoli open at all times.
What is the vital capacity of the lungs?
The maximum volume of air exhaled during a forced exhalation after a forced inhalation.
What is tidal volume?
The amount of air that moves in or out of the lungs with each respiratory cycle.
Males = 500ml average.
Females = 400ml average.
FEV1 and FVC are measured during spirometry. What do they stand for?
FEV1 = Forced Expiratory Volume in 1 second.
FVC = Forced Vital Capacity.
In the bicarbonate buffer system, what happens to CO2 + H2O if pH is high (alkalosis/not enough hydrogen ions)?
Carbonic anhydrase catalysis the combination of CO2 + H2O, to form carbonic acid (H2CO3), a weak acid that easily dissociates into hydrogen ions and bicarbonate.
Bicarbonate can then be secreted in the urine by the kidneys.
CO2 + H2O <-> H2CO3 <-> H + HCO3
In the bicarbonate buffer system, what happens to hydrogen ions and bicarbonate if pH is low (acidosis/too many hydrogen ions)?
Hydrogen ions and bicarbonate combine to form carbonic acid, which can then dissociate into carbon dioxide and water. Carbon dioxide can then be removed by the lungs.
CO2 + H2O <-> H2CO3 <-> H + HCO3
