4Where do the lungs sit?Lungs: Mid-clavicular line: 6th rib, Mid axillary line: 8th rib and Scapular line 10th ribTip: For pleural location, add 2 to each of the above!
5Describe the respiratory system Divide it neatly into two parts:Upper respiratory tract (what parts does this involve?) has a rich blood supply and its epithelium is covered by a mucus secretion.. It’s function it to warm, moisten and filter so the air is suitable for gases exchange.Lower RT (what parts?) Two main bronchi divide into smaller airways until the end respiratory portion is reached distally.
6An overview of the Respiratory tree ContractileAre lined by?TracheaResp. EpitheliumBronchi 1,2 and 3 (B-receptors here!)✔BronchioleSimple ciliated cuboidal + clara cellsRespiratory BronchioleAlveolar DuctFlat non-ciliated epithelium, no glandsAlveolusPneumocytes 1 and 2Question: What three layers must the gas diffuse across to reach the red blood cell at the Alveolus?Answer:The type 1 pneumocyte, the basement membrane and the endothelium
7Bohr and Haldane effects This is a good mnemonic for remembering what causes the Haemoglobin to disassociate with O2:CADET face right, and release!Question: what do the letters in CADET stand for?Bohrs effect is to do Acid, Haldane = CO2Answer: CO2, Acid, 2,3-DPG, Exercise and Temperature
8What three key steps are involved in gas exchange? Ventilation (The amount of air reaching the respiratory portion = V)Perfusion (The amount of blood reaching the respiratory potion = Q)Diffusion (The process of gas transport across the separating barrier)Question: What do the following V/Q ratio mean?V/Q = 0V/Q = 1V/Q = infinityTotal block in the airway/alveolarVentilation/perfusion are matched, ideal!Lung unit is ventilated, but not perfused (apex)Clearly shunting and dead space ventilation are the extremes of ventilation:perfusion mismatch and less extreme forms of mismatch exist. Indeed acute respiratory failure is characterised by increase in the spread of ventilation perfusion ratios as opposed the normal situation where ratios are closely clustered around 1Can we help the patient with oxygen therapy?What is the V/Q ratio in a normal, healthy lung?
9ComplianceCompliance is the change in alveoli volume you get for a change in pressure (C=V/P)It goes down in lung fibrosis (More effort needed to inflate the lungs)Up in emphysema (Lungs inflate easily, but with a loss of surface area)Surfactant prevents alveolar collapse because it lowers surface tension. This increases lung compliance.Question: Why might a runner or patient with COPD purse their lips toIncrease the resistance to breathing out?
10Sensory control of breathing Describe the chemical feedback mechanism we use in breathing?Chemoreceptors are located on the brainstem (80% of drive – vital!) medulla region which respond to Hydrogen Ions (although it is CO2 which crosses the BBB, this increases the number of H+ ions)Peripheral chemoreceptors are located in the carotid sinus and aortic arch – these respond to PaO2, PaCO2, pH, Blood flow, TemperatureTip- Don’t confuse these with Baroreceptors, also located in the Carotid Sinus and Aortic Arch!CSF doesn’t have as much protein in it as blood, therefore the buffering ability is lower and hence a rise in PaCO2 has a larger effect on pH of the CSF than in the blood
11MCQs Which of the following is not true? Lung expansion is greatest inferiorlyPresence of hysteresis demonstrates lung compliancePulmonary fibrosis and emphysema both result in low lung complianceThe main function of surfactant is to reduce surface tension
12Regarding the dorsal respiratory group, which would increase inspiratory rate? Low O2 at the central chemoreceptorsStretching of airways (Hering-Brewer reflex)Metabolic acidosisIncreased breathing intensity (from ventral respiratory group)
13Case 1Santa Claus visits his local GP complaining of shortness of breath. On questioning he reveals that he has had a productive cough for at least 4 months every year since forever. What microscopic changes are seen in chronic bronchitis? (2)Hypersecretion of mucusGoblet cell hyperplasiaYou realise this has affected his ability to transport gas (and presents). What is the rate of diffusion dependent on?Area/thickness x concentration difference
14What else can shift the O2 curve? You discover that Mr Claus lives in a very cold environment and wonder whether that could be also be affecting his oxygen dissociation curve. Does it?Yes, low temp results in a shift to the leftWhat else can shift the O2 curve?pH and 2,3 BPG.Is this the Bohr or the Haldane effect?Bohr
15Mr Claus tells you that he is planning a trip that will involve travelling at altitude for significant periods of time. Which type of respiratory failure would you be most worried about?Type 1 – (hypoxaemic without hypercapnia) as very low PIO2.Mr Claus wants antibiotics to help him get better. Which of the following is the most appropriate response?Tell santa he’s on your naughty list for inhaling so many irritants so he can’t get what he wants.Given that santa is a people pleaser you endeavour to copy and set him up for CT, CXR, FBC, PET scan etc.Carry out a FEV1/FVC test and spirometry to help diagnose.Tell santa that you know best and give him COPD meds
16Case 2Santa’s little helper walks through the door (imagine he’s human). He is breathing very quickly and his lips look blue. He says he has just inhaled a peanut. Where is it likely to have gone?Right lung as right bronchus is more verticalWhat condition is He likely to be experiencing (remember it’s acute)Atelectasis (partial collapse of the lung)What will happen to the alveoli distal to the peanut?All their air will be taken into the blood and they will collapse
17Does surfactant have any other roles? Santa’s little helper wonders why your alveoli don’t collapse all the time. Can you help him out? (2)Surfactant released from type II pneumocytes interact with fluid in the lung to reduce surface tension and so reduces the likelihood of collapse.Does surfactant have any other roles?Antioxidant effectImmune functionAtelectasis will also result in changes to the V/Q ratio. How will it change?V/Q = 0
18Can you explain why 100% O2 won’t help him? Regardless of how much O2 he receives, no air is reaching the collapsed part and so there will be no improvement.The peanut is removed via bronchoscopy but his stats stay <88%. What treatment could you use to open his alveoli?CPAP (continuous positive airway pressure)
20Carl is experiencing the bends due to several problems: After a long scuba diving session on a Caribbean reef, Carl boards a plane to Coventry. He begins to feel pain in his elbow on the flight back. What is happening to him?Carl is experiencing the bends due to several problems:Applying Boyle's law, a lot of gas was forced into Carl's bloodstream during the dive to prevent his lung’s from collapsing and there was not sufficient time to decompress the excess before he boarded the plane.The plane is not pressurized to sea level, which further reduced atmospheric pressure holding the gases in suspension (Henry's law). Carl will have to be transported to a hyperbaric chamber to be repressurized. This will reduce the volume of the gas bubbles in his arm so that normal circulation can resume.