Learning outcomes Flashcards
Compare pulmonary and systemic blood flow
Pulmonary blood flow refers to the flow of deoxygenated blood from the right side of the heart to the lungs, and the oxygenated blood from the lungs being pumped into the left side of the heart and is pumped around the body. Systemic blood flow refers to oxygen being deposited into the tissue and carbon dioxide being transported back to the lungs, the opposite of pulmonary circulation.
Describe the main anatomical features of the airways and gross anatomical features of the lung
air can enter through the nose or the mouth, then through the nasopharynx through the larynx which is where the vocal cords are located and marks the end of the upper respiratory system. Here the channel splits into the trachea which consists of stiff cartilage, guarded by a flap called the epiglottis, and the oesophagus. Through the trachea the airways split between the two lungs into the bronchus which further divide into secondary bronchus, which then divide into bronchioles which finally end as alveoli. Surrounding the lungs is the pleural cavity, diaphragm a dome shaped muscle, ribs and muscles.
Identify the different classes of airways and pneumocytes
Type 1 alveoli cells – thin for diffusion
type 2 alveoli cells surfactant – secrete surfactant, easing tension making breathing easier
macrophages
For the airways we have: Lymphocytes glands blood vessels epithelium mucus
as we progress from nose to lungs we lose cilia, mucous is lost and the epithelium become more squamous.
State the mechanical factors that affect respiratory minute volume.
pressure (boyle’s law) temperature volume solubility resistance and the radii of airways the stretch of the lungs trans pulmonary pressure
Explain why intrapleural pressure is always less than alveolar pressure.
intrapleural space is always being pulled at by the elastic pull of either the lungs or the ribs, however due to the tension of the fluid between the two membranes doesn’t separate. The alveolar pressure is always higher because it’s adhered to the ribs the pleural cavity allowing it to expand and compress.
Be able to describe the anatomy of the pleural cavity
it consists of a visceral membrane binding it to the lungs, and a parietal membrane binding it to the ribs, with about 3ml of fluid in between the two membranes which encompass the lungs.
Understand the relationship between the parietal and visceral pleura and why this is important for inflation of the lung
the small amount of fluid enables gliding but doesn’t allow for separation of the two membranes. They keep the lung adhered to the ribs through the membranes.
Be able to describe how the muscles of respiration act to increase and decrease thoracic volume
the muscles such as the diaphragm contracts, and the external intercostal muscles, scalene muscles, sternocleidomastoid muscles pull on the ribs increasing thoracic space allowing for the lungs to increase in volume for inspiration, where as if the diaphragm relaxes, and the internal intercostal muscles contract pulling on the ribs and the abdominal muscles contract, the thoracic space decreases, decreasing lung volume increasing pressure triggering expiration.
Relate Boyle’s law to the mechanics of breathing, inspiration and expiration
Boyle’s law dictates that as volume decreases, the pressure increases meaning there is an inverse relationship between the two. As someone inspires, the volume of the lungs increases and pressure decreases, so air can move from a place of high pressure to low pressure. As they expire, the volume decreases, and pressure increases so the gases move from an area of high pressure to low pressure.
Define the various lung volumes and capacities and, provide approximate normal values for them.
tidal volume – volume of either a inspiration or expiration – 500ml
total lung volume – 6000ml
expiratory reserve volume – 1100ml
residual volume – 1200ml
inspiratory reserve volume – 3000ml
air from dead space – 150ml
vital capacity – tidal volume + expiratory reserve volume + inspiratory reserve volume – 4600ml
functional residual capacity – expiratory reserve volume + residual volume – 2300ml
inspiratory capacity – tidal capacity + inspiratory reserve volume – 3500ml
State the role of pulmonary surfactant and the Law of Laplace
The role of pulmonary surfactant is to ease the fluid tension required for the absorption of oxygen to prevent the collapse of the alveoli. The law of Laplace (P=2T/r) is that increasing the volume of fluid within the alveoli increases the pressure, especially within smaller alveoli which is problematic as we need smaller alveoli instead of larger ones for increased surface area. Surfactant overcomes this as in a smaller space the concentration is increased and obstructs the affinity water molecules have for one another. This makes breathing easier, reduces recoil and increases lung compliance.
Summarise the basic characteristics of obstructive and restrictive lung disease.
obstructive lung disease has a massive effect of air exhaled and slightly reduces the vital capacity. An example of this is COPD as its major effect is on the airways, this reduces the ratio between FEV1/FVC (forced expiratory volume 1 second/forced vital capacity).
restrictive lung disease reduces the amount of air exhaled and the vital capacity dramatically, such as pulmonary fibrosis as this limit the lung expansion. This doesn’t reduce the ratio and often requires a comparison of forced expiratory flow (average of a forced expiration) to recognise.
Describe the tests used to identify abnormal lung function.
spirometry, it can be dynamic where the time taken to exhale a certain volume is measured or it can be static where only the volume is considered. It can measure tidal volume, expiratory reserve volume, inspiratory reserve volume, vital capacity and inspiratory capacity.
Know the normal values for alveolar and arterial gas partial pressures
Pa oxygen - 100 mm hg
Pa carbon dioxide – 40 mm hg
PA oxygen – 40 mm hg
PA carbon dioxide – 46 mm hg
Describe the difference between pulmonary and alveolar ventilation
pulmonary ventilation involves the tidal volume of each breath, then the number of breath per minute this tells us the total air getting into and out of the lungs. The alveolar ventilation refers to the fresh air for exchange reaching the alveolar, taking into account the dead air.
Describe the factors that affect the oxyhaemoglobin dissociation curve.
Factors that affect the oxyhaemoglobin dissociation curve are temperature, and increase in temperature will shift the curve to the right, resulting less affinity between haemoglobin and oxygen, and a decrease will shift it to the left meaning during severe hypothermia oxygen isn’t being diffused to the tissues. Increasing pH will also shift the curve to the right, as well as increasing the partial pressure of carbon dioxide and 2,3-DPG which is a chemical released during hypoxia to encourage oxygen diffusion.
State the factors that affect gas exchange
the partial pressure gradient
gas solubility
surface area
thickness of membrane
state the differences between partial pressure and gas content.
partial pressure determines the pressure of which the gaseous form is pushing the gas into solution, it doesn’t equal gas content which refers purely to the gas in solution, which is partly determined by solubility and partial pressure.
Compare oxyhaemoglobin dissociation for adult haemoglobin with that of foetal haemoglobin and myoglobin in relation to their physiological roles
myoglobin has the highest affinity for oxygen as it’s located in the muscles, then foetal haemoglobin as they both require the taking the oxygen from oxyhaemoglobin in order to meet energy demand.
Identify the forms in which CO2 is carried in the blood.
7% of CO2 dissolves directly into the plasma, 23% can bind to haemoglobin to form deoxyhaemoglobin and 70% forms HC03- bicarbonate ions in solution.
Identify the factors which favour CO2 unloading to the alveoli at the lungs.
the increase partial pressure of oxygen favours oxygen loading at the haemoglobin. On top of that carbon dioxide is being constantly removed at the lungs from plasma, meaning that the forms of CO2 transport are converted back into CO2 to try and from equilibrium, as well as the difference in partial pressure meaning that carbon dioxide will follow the gradient into the alveoli. Other factors like pH also favour oxygen loading which subsequently means carbon dioxide unloading.
Explain the relationship between ventilation and perfusion and its significance in health.
ventilation and perfusion should ideally match each other in rate of flow per L/min. conditions like emphysema, fibrotic lung disease, pulmonary oedema and asthma can all reduce the amount of oxygen being absorbed this results in deoxygenated blood being reabsorbed and mixed with oxygenated blood causing hypoxia.
Describe the term ‘shunt’.
shunt refers to the flow of blood through poorly ventilated areas, it when the rate of ventilation is less than perfusion, which is the opposite of alveolar dead space. Results in diverted blood flow as the systemic vessel around the effected alveoli is constricted and the bronchiole dilates.
Describe the role of haemoglobin in the transport of O2 in the blood.
only 3ml of oxygen can dissolve into plasma which isn’t enough to meet demands. As a result, haemoglobin can take absorb much more oxygen (1g of Hg can absorb 1.34g of oxygen), maintaining the partial pressure gradient of oxygen from the alveoli to the blood. Its cooperative binding works in that the more oxygen it has the easier it is for oxygen to bind, and as it begins to unload it’s easier to lose its oxygen. It’s ideal for the factors that affect dissociation are the ones found in the tissues where oxygen is needed most, whist these factors aren’t found in the lungs meaning it can readily pick up oxygen.
Explain why the shape of the oxyhaemoglobin dissociation curve is important to O2 loading in the lungs and unloading in the tissues.
the sigmoid shape of the oxyhaemoglobin curve means that a large decrease in oxygen partial pressure translates only to a small decrease in oxygen saturation of oxyhaemoglobin. Even at partial pressure of 40mmHg, oxygen saturation is still at 75% leaving a large reserve.
Explain the action of carbonic anhydrase in CO2 transport
carbonic anhydrase (H20) helps convert the carbon dioxide into carbonic acid which then dissociates into bicarbonate and hydrogen ions, the excess hydrogen ions bind to deoxyhaemoglobin whilst the bicarbonate is pumped out the erythrocyte through a chloride channel into plasma.
Know the difference between anatomical, alveolar and physiologic dead space
alveolar dead space shouldn’t really be present in a healthy human, it occurs once a alveolar is no longer participating in gas exchange. Anatomical dead space is the air present in the airways that is unable to participate in gas exchange, it equates to roughly 150ml and is regularly replaced with fresh air or stale air from the alveoli. Physiological dead space is calculated by adding together the anatomical and alveolar dead space.
State the factors that determine arterial PO2
oxygen bound to haemoglobin saturation of haemoglobin (temp, pH, PCO2, DPG) total number of binding sites oxygen dissolved in plasma alveolar ventilation perfusion of alveolar composition of air diffusion of oxygen
explain how respiratory motor movements are affected by the central nervous system
the diaphragm is innervated by the phrenic nerve, since the diaphragm is responsible for 70% of the work required for breathing it highlights how heavily influential the central nervous system is for control of breathing, if there is damage to the vertebrae C3,4,5 breathing ceases and results in death, this demonstrates that it is entirely dependent on the brain and it is not autonomous. The intercostal muscles that aid in breathing also are innervated and thus controlled by the intercostal nerves that stem from the spinal cord which their impulses originate from the brain stem.
List the factors involved in changing ‘respiratory drive’, rate and depth of breathing.
respiratory drive is controlled involuntary by the medulla and the pons, specifically the dorsal respiratory group (DRG) which controls the inspiratory muscles and the ventral respiratory group (vRG) which influences the expiratory and inspiratory muscles such as the pharynx, larynx and tongue. These centres are influenced by primarily chemoreceptors; however, they can also be influenced by chemoreceptors in the peripheral carotid and aorta. The further can be influenced by the limbic system through emotions, mechanoreceptors in the chest wall, or voluntarily by the higher centres of the brain but these can override by the brainstem.
Explain how, by monitoring the pH of CSF, the central chemoreceptors serve to regulate the arterial Pco2.
carbon dioxide and other gases can diffuse across the blood brain barrier whilst hydrogen ions cannot. These can then bind to carbon dioxide to form bicarbonate ions, these then bind to the central chemoreceptors, specifically the bound hydrogen ions then stimulate the DRG and VRG to increase the rate of ventilation, and if the concentration drops, the rate of ventilation reduces. This is known as hypercapnia as it is driven by the arterial partial pressure of carbon dioxide.
Explain how the peripheral chemoreceptors become important during hypoxia and acid-base imbalance.
during hypoxia the peripheral chemoreceptors in the carotid and aorta are sensitive to a singnifcant fall in arterial partial pressure changes for oxygen or acid base Imbalance, this is due to long term exposure of carbon dioxide to the central chemoreceptor rending it insensitive to changes. This makes what would normally be a secondary receptor essential for altering ventilation.
Outline the role of the respiratory system in acid-base disturbances
when the peripheral chemoreceptors detect a change in blood pH, where the concentration of hydrogen ions increase and the pH decreases known as acidosis, this can trigger an increase in ventilation known as hypoventilation to reduce the concentration of carbon dioxide. However, if the concentration of hydrogen ions decreases it can induce a decrease in the rate of ventilation known as hyperventilation in order to produce more hydrogen ions and can also trigger vomiting and retention of carbon dioxide.
Explain the basis of rhythm in respiration
we don’t consciously think about breathing, instead it’s a form of homeostatic control the rhythm of breathing trying to maintain respiratory acid base balance, partial pressure of carbon dioxide and oxygen. This is achieved through the brain stem and chemoreceptors which involuntarily regulate our breathing in response to stimuli. Co-ordinated by the firing of smooth and repetitive bursts of action potentials in the DRG to inspiratory muscles.
Identify the sites of chemoreceptors and identify the stimuli which activate them
chemoreceptors are located in the peripheral carotid and aorta, and the central medulla. They can be stimulated by changes in pH, carbon dioxide partial pressure and oxygen partial pressure.
strategies for management of COPD.
smoking cessation is key, but for management of COPD is a multi disciplinary team is required. Inhalers for relief, vaccines and pulmonary rehabilitation, long term oxygen therapy and lung volume reduction. This as well as psychological support, physiotherapy and nutritional assessment.
Describe the classes of drugs and modes of delivery available in the management of obstructive lung diseases, both asthma and COPD.
inhalers or nebulizers are the forms of delivery available
short acting bronchodilators
SABA – salbutamol
SAMA – ipratropium
long acting bronchodilators
LAMA – long acting anti-muscarinic agents
LABA long acting beta 2 agonist
high dose corticosteroids
however antibiotics or Long Term oxygen may be necessary
Define the role of patient education in the management of asthma and COPD.
patient education in the management of asthma and COPD is essential because asthma unlike COPD is reversible to an extent whilst COPD is progressive, persistent and productive. Whilst asthma can occur at any age but for COPD is more likely to occur after the age of 35. With COPD things like nocturnal hypoxia and family history is uncommon, with a possible allergy reaction. Whereas asthma is more familial, with nocturnal hypoxia being common and commonly linked to allergies. This biggest important aspect Is that smoking is often the biggest cause behind to COPD where as smoking can exacerbate asthma but is not responsible.
Describe the clinical management of acute, exacerbated COPD
the clinical management acute exacerbated asthma requires antibiotics if necessary for the bacterial infection, corticosteroids, oxygen at 70-80% saturation, nebulizer bronchodilators and perhaps hospital admission with investigations such as X-rays, ECG and blood cultures to rule out other possibilities.
Describe the defining features and epidemiology of asthma, its proven and putative aetiological factors.
asthma’s defining features is chronic but variable wheezing, shortness of breath and cough with response to asthma treatment. With one million UK being afflicted with it there are many causes resulting in the multiple hits aetiology with factors like genes, lung function, atopy and later exposures to stimulants like rhinovirus, exercise or smoking.
Differentiate the main causes of wheezing illness.
wheezing illnesses are causes by bronchoconstriction with airway wall thickening and increased luminal secretions making the airways smaller increasing the chance of a wheezing sound. This could mean it’s asthma but however this doesn’t rule out other conditions such as a foreign body presence, cystic fibrosis, immune deficiency, trachea-bronchomalacia or ciliary dyskinesia.
Discuss possible reasons for the changing prevalence and severity of respiratory disease with child’s age and possible links with respiratory disease in adult life.
more awareness now about the harmful effects of smoking, and youthful exposure to potential allergens such as mould and dust and their influence on children.
Describe the symptoms and clinical patterns of asthma.
asthma can have various severities, and different ages of onset and heterogeneity in response with different triggers. It fluctuates and is variable. Making it difficult to diagnose.
Define the specific features to be included in the clinical history of asthma.
wheezing, shortness of breath at rest, parental asthma and response to treatment. Recent viral infections that induce a wheeze and ideally over the age of 5 but not essential. More than one trigger is ideal as well. Cough variant asthma doesn’t exist, cough predominant asthma however is not uncommon.
Define the investigations used to diagnose asthma.
examination and spirometry not effective forms of diagnosis. The key part of the investigation is taking a proper history and waiting to see the response to treatment to either salbutomal or ICS.
Be aware of the term remodelling.
remodelling refers to the structural changes the lung can undergo when exposed to infection of insult at an early age that triggers structural changes such as excessive luminal secretions, and tissue overgrowth or chronic inflammation that results in restricted airways. Such conditions include asthma
Understand the relationship between respiratory illness in childhood and adulthood.
respiratory illness developed early on in childhood impedes the development of the lungs and thus determines the severity of future respiratory illnesses through-out adulthood and also sets the peak for the inevitable respiratory decline.
Understand the “tracking” of pulmonary function from early life into adulthood and factors which influence tracking
tracking of pulmonary function from early life into adulthood enables us to make predictions regarding the anticipated decline of respiratory function. This enables us to make the necessary precautions or give advice regarding whether or not they are in the risk zone of serious respiratory diseases such as COPD. Factors that influence tracking is whether the child was born prematurely, smoking, nutrition, ETS (alpha1 AT deficiency), low birth weight, maternal infection, chemical exposure pre-natal and post-natal, serious lung infections. As this can drastically alter the time of deuteriation and can potentially put the individual into the danger zone for developing serious lung diseases and thus reduce their quality of life and expectancy.
state the common upper respiratory tract infections
common cold (coryza) sore throat syndrome croup laryngitis sinusitis acute epiglottitis – caused by group A beta haemolytic streptococci
Describe the clinical features of a lung abscess
lung abscesses are the result of necrotic tissue being encapsulated to prevent further spread. It can be caused by tumours, aspiration, certain organisms such as staph aureus, pneumococci and klebsiella, or a metastatic in pyaemia (bacterial blood infection of the lung)
Describe the pathogenesis of bronchopneumonia and lobar pneumonia and the complications and consequences of lower respiratory tract infection
bronchopneumonia is often bilateral resulting in a patchy opacification. This is the result of inflammation of the bronchioles leading to the consolidation of pus within the alveoli. This is due to the failure of the macrophage mucociliary escalator system, perhaps being previously ulcerated or damaged by a virus such as influenza. Lobar pneumonia whilst having the same aetiology is different in that it is confined to one lobe of the lung. This is due to the nature of the bacteria causing the secondary infection being for more potent in stimulating the immune system to over act, causing consolidation of fluid. As a whole section of the lung is inflicted it spreading to the pleural membrane is far more likely. Failure of organisation of the inflammation may result in pleurisy, fibrosis of the lung known as an emphysema, necrosis of lung tissue leading to an abscess or even death.
Be aware of causes of recurrent pneumonia.
recurrent lung infections are often a warning sign of an organic cause to the problem. It may be a local bronchial obstruction such as a tumour, or local pulmonary damage as with bronchiectasis, generalised lung disease with COPD and cystic fibrosis or a non-respiratory disease such as aspiration or they may be immunocompromised.
Be aware of the different spectrum of hospital acquired (nosocomial) pneumonia compared with community acquired pneumonia
the different spectrum of pneumonia is classified in regards to understanding the aetiology of the infection. As community acquired Pneumonia will likely be a different strain in comparison to a hospital acquired pneumonia, with the hospital one being more likely to be antibiotic resistant. There is also pneumonia in the immunocompromised, atypical pneumonia, aspiration pneumonia and recurrent pneumonia.
Contrast the management of asthma with strategies for management of COPD.
bronchial asthma is considered to be reversible condition whether it be spontaneously or as a result of medical intervention, the smooth muscle contraction and inflammation can be modified by drugs.
COPD was considered non-reversible but this is changing. By pharmacologically targeting the smooth muscle tone and inflammation of the small airways the condition can be improved. With emphysema the loss of alveolar attachments is the most important aspect.
Describe the major pathological features of the common obstructive lung disease emphysema and their complications
chronic bronchitis and emphysema results from smoking, pollution, age and genetic susceptibly, or rarely an alpha 1 antiprotease deficiency.
emphysema is the increasing size of airspaces distal to the terminal bronchiole arising from dilation or the destruction of their walls without fibrosis. It can be centriacinar, in which the it’s isolated mainly to bronchiolar dilation and then alveolar tissue is lost and is counted by number. Pan-acinar, are is more uniform and is measured by area, it’s associated with a alpha 1 antitrypsin deficiency. Peri-acinar/scar bullous emphysema, a bulla is an emphysematous space greater than 1cm, if just underneath the pleura it’s referred to as a bleb. It results from an abundance of elastase protease enzymes this is triggered by the presence of a foreign body stimulating neutrophils and macrophages such as smoking, which also inhibits elastin synthesis and leads to uncontrolled tissue mdestruction.
Describe the defining features and epidemiology of COPD.
COPD is a progressive chronic disease, with airflow obstruction that doesn’t have a significant change over the timeframe of months, lung impairment is fixed with some minor reversibility.
In the U.K 1.2 million people are diagnosed with COPD meaning likely prevalence is 2 million. Globally it’s more than 300 million people with COPD with it being more common in men with basic education in a low income household
