Respiratory Flashcards
What is Charles’ law?
Pressure increases as temperature increases
What is the universal gas law?
How does alveoli maintain ventilation/perfusion ratio?
How does alveoli maintain ventilation/perfusion ratio?
Hypoxic pulmonary vasoconstriction - Diverts blood away from poorly ventilated areas Hypoxic alveoli vasoconstrict pulmonary vessels
What is boyle’s law?
Pressure inversely proportional to volume
What is the consequence of chronic hypoxic vasoconstiction?
Right ventricular failure Chronic increased resistance causes high after-load for right side of heart - cor pulmonale
What cells do alveoli contain and what are their function?
Type 1 pneumocytes - gas exchange Type 2 pneumocytes - produce surfactant to reduce surface tension
What is surface tension?
Elastic tension of liquids which makes them acquire the least surface area possible
What is the epithelial lining of the upper respiratory tract?
Pseudostratified ciliated epithelia with goblet cells
What are the muscles of inspiration?
Diaphragm External intercoastals
What are the muscles of expiration?
None - elastic recoil
What factors determine rate of diffusion?
Surface area Resistance - nature of barrier, nature of gas Gradient of partial pressure
What is the partial pressure of O2 and CO2 in lungs?
pO2 - 13.3kPa pCO2 - 5.3kPa
What are the muscles of forced inspiration?
Diaphragm External intercostals Scalene Serratus anterior Sternocleidomastoid Pectoralis minor
What are the muscles of forced expiration?
Internal intercostals Innermost intercostals Abdominal muscles
What is residual volume and how can it be measured?
Volume left in lungs after maximal expiration Measured via helium dilution test
What is anatomical dead space?
The air in the upper airways that is unavailable for gas exchange
What is physiological dead space?
Anatomical dead space + alveolar dead space Alveolar dead space is the alveoli that have insufficient blood supply as those that are damaged by accident or disese
How do you measure a patient’s anatomical dead space?
Nitrogen washout test
Explain nitrogen washout test
Patient takes breathe of 100% O2 The O2 reaches the alveoli and mixes with residual atmospheric air that contains nitrogen, but air in conducting airways remains 100% O2. Person exhales through one way valve and gas content is measured. Nitrogen concentration initially 0 as exhaling dead space 02 but then gradually rises
What is the alveolar ventilation rate and how is it calculated?
Amount of air that reaches the alveoli = pulmonary ventilation rate (tidal vol x RR) - dead space ventilation rate (dead space volume x RR)
What ribs are atypical?
1, 2, 10, 11, 12
What does the bucket-hand type movement of the external intercostals cause?
Expansion of anteroposterior and transverse diameters of chest
What is the innervation of intercostal muscles?
Intercostal nerves from anterior rami of T1-T12
What are the openings of the diaphragm and at what level do they occur?
T8 - vena cava T10- oesophagus T12- aorta (aortic hiatus)
What is the innervation of the diaphragm?
Phrenic nerve (C3, 4, 5)
Where do the neurovascular supply to intercostal muscles run? State in which order they lie
Intercostal groove of rib (lower border) Between internal and innermost intercostal muscles Vein, artery, nerve (VAN)
What do the intercostal nerves supply?
Intercostal muscles, parietal pleura, overlying skin
Describe course of intercostal arteries
Thoracic aorta - posterior intercostal artery Subclavian artery - internal thoracic artery - anterior intercostal artery Anterior and posterior intercostal arteries anastomose
Describe course of venous drainage from intercostal veins
Anterior veins - internal thoracic vein - subclavian vein Posterior vein - azygous vein on right and hemiazygous vein on left - superior vena cava
What is the role of the fluid produced by the parietal pleura?
Increases surface tension between pleura layers, therefore keeping lungs connected to thoracic wall Allows layers to slide over one another
What level is the carina, the hilum of lungs and sternal angle?
Carina = T5 Hilum = T5-T7 Sternal angle = T4-T5
Define compliance
Volume change per unit pressure change ‘Stretchiness’
What factors determine compliance?
Elastic tissues and surface tension
Lung compliance demonstrates hystresis, what does this mean?
Compliance is different on inspiration and expiration at identical lung volumes
What does surfactant do in terms of surface tension?
Reduces surface tension when lungs are deflated, but not fully inflated. Therefore little breaths are easy, big breaths are harder. Also prevents larger alveoli absorbing smaller ones (Laplace’s law of bubbles)
What is Laplace’s law? Why is it important in alveoli?
Pressure is inversely related to radius Bigger the radius the lower the pressure, so big alveoli would eat smaller alveoli to reduce pressure in small alveoli. However as alveoli get bigger the surface tension in the walls increases because surfactant becomes less effective.
What is Poiseulle’s law?
The resistance of a tube increases with falling radius R = 1/R4
Why do the small airways not have a high resistance?
Lots are connected in parallel over a branching structure
What will affect peak flow?
Resistance of large airways Severe obstruction of smaller airways
What is the purpose of measuring transfer factor? How is this done?
Measures diffusion capacity Rapid maximum inspiration of air containing small proportion of CO, breathe held for 10secs then small collected mid-expiration to see concentration of CO
Explain the Bohr effect
Decrease in pH, increase in CO2 causes a decrease in Hb’s affinity for O2, therefore it will be released. So at sites of high metabolism more O2 will be given up
What causes a shift in the oxygen dissociation curve to the right?
Decreased pH Increased 2,3-BPG Increased temperature
List the reactions of CO2 in the blood
Dissolves in water Reacts with water: CO2 + H2O -> H+ + HCO3- (requires carbonic anhydrase) Binds to proteins forming carbamino compounds
What is the normal CO2 content on the arterial and venous blood?
Arterial CO2 = 21.5mmol/L Venous CO2 = 23.5mmol/L
How does most CO2 travel in the blood?
80% as HCO3- 11% as carbamino compounds 8% dissolved CO2
How is HCO3- made from CO2 in the plasma?
In RBCs there are high quantities of carbonic anhydrase so CO2 rapidly reacts to form H+ and HCO3- H+ binds to Hb drawing the reaction towards HCO3- production Amount produced depends on Hb buffering effects
Define hyperventilation
Ventilation increases with no change in metabolism
Define hypoventilation
Ventilation decreases with no change in metabolism
How do you calculate plasma pH?
Henderson-Hesselbach using pCO2 and [HCO3-]
What are the consequences of respiratory acidosis?
Enzymes become lethally denatured
What pH defines respiratory alkalosis?
>pH 7.6
What are the consequences respiratory alkalosis?
Calcium only soluble in acid, so increase in acid causes decrease in free calcium causing nerves to become hyper-excitable (decreases gradient across membrane, so closer to threshold) Produces fatal tetany
Give some causes of respiratory acidosis
Hypoventilation - opioid supression of breathing centres Inability to ventilate adequately - neuromuscular diseases Airway obstruction - COPD, asthma
Give some causes of respiratory alkalosis
Hyperventilation - panic attack CNS - stroke, subarachnoid haemorrhage, meningitis Drugs - aspirin, caffeine High altitudes Fever
Give some causes for metabolic acidosis
Increased anion gap causes: Lactic acidosis, ketoacidosis, chronic renal failure, intoxication (alcohol, salicylates, metformin), Normal anion gap causes: Diarrhoea, renal tubular acidosis
Give some causes for metabolic alkalosis
Persistent vomiting, diuretic therapy, antacids/bicarbonate use, hyperaldosteronism
Where are peripheral chemoreceptors located? What do they detect?
Carotid and aortic bodies pO2 - decrease in O2 relative to their own supply pCO2 Fairly insensitive
Where are the central chemoreceptors located? What do they detect?
Medulla Detect changes in pH of CSF (determined by arterial pCO2)
How is the HCO3- concentration of CSF controlled?
By choroid plexus cells Determined by ratio of [HCO3-] to pCO2 Persistent changes in pCO2 are compensated by choroid plexus cells altering CSF [HCO3-]
What are the 5 things necessary to maintain arterial pO2 within range?
- pO2 in inspired air 2. Adequate ventilation 3. Adequate diffusion 4. Ventilation/perfusion ratio of 0.8 5. No presence of right to left cardiac shunt
Define type 1 and type 2 respiratory failure
Type 1 - normal pCO2 but low pO2 Type 2 - high pCO2 and low pO2
Give some causes of type 1 and type 2 respiratory failure
Type 1: Fibrosis, early asthma, early COPD, altitude, pulmonary oedema, emphysema, PE Type 2: Severe asthma, chronic COPD, neuromuscular problems, chest wall defects, airway obstruction
Define asthma
Increased responsiveness of bronchi to various stimuli, manifesting in widespread narrowing of small airways Characterised by airway inflammation and remodelling
Define pneumonia
Infection of the pulmonary parenchyma with consolidation (exudation of fluid)
How do you assess severity of pneumonia?
CURB-65 Confusion Urea >7mmol/L Respiratory rate >30mmol/L Blood pressure 65
Give the common causes of community-acquired pneumonia
Streptococcus pneumoniae Haemophilus influenzae Influenza A & B, adenovirus (viruses)
Give common causes of hospital acquired pneumonia
Gram -ve enteric bacteria (E. Coli) Staphlococcus aureus and MRSA
Give common causes of pneumonia in immunosuppressed hosts
Cytomegalovirus Aspergillus Pneumocystis jiroveci Crytosporidia
Give some causes of a transudate pleural effusion
Cardiac failure Hypoalbuinaemia Nephrotic syndrome Sepsis
Give some causes of exudate pleural effusions
Neoplasms Infection - TB, pneumonia Immune disease - RA, SLE Abdominal disease - pancreatitis causing diaphragmatic inflammation, ascites, subphrenic abscess
Give some causes of pleuritis
Infection - TB, pneumonia Autoimmune - RA, SLE Lung cancer Pneumothorax Pulmonary embolism
What pH defines respiratory acidosis?
pH
