Respiratory Flashcards
What structures contribute to the respiratory pump?
Bones (ribs and sternum), muscles (diaphragm and intercostals), pleura, nerves.
What structures make up the conducting airways?
Nose, pharynx, larynx, trachea, bronchi, bronchioles, terminal bronchioles.
What is the function of the conducting airways?
To filter, warm, humidify and conduct air to the lungs.
What is respiratory epithelium?
Pseudo-stratified, columnar, ciliated, interspersed with goblet cells.
Where is the resistance greatest in the airway?
In the trachea - the trachea is longer (length adds resistance) and there is only one of it (branching decreases resistance).
What equation can be used to demonstrate resistance of an airway?
Poiseuille’s law: R = 8ƞl / πr^4.
ƞ = viscosity, l = length
Briefly describe inspiration.
Inspiration is an active process. The external intercostal muscles and diaphragm contract. The volume of the thoracic cavity increases and you get a negative intra-thoracic pressure; air is drawn in.
What is the ‘pump handle’ representing?
The movement of the sternum. In inspiration the sternum moves anteriorly and superiorly.
What is the ‘bucket handle’ representing?
The movement of the rib cage. In inspiration the rib cage moves upwards and outwards.
Briefly describe expiration.
Expiration is usually passive. The ribs move down and in, the diaphragm relaxes. The intra-thoracic volume decreases and the pressure increases. Air is forced out.
Which muscles are involved in active expiration?
The internal intercostals; these muscles contract pulling the ribcage inwards and downwards.
What is V/Q mismatch?
When the perfusion of blood in capillaries isn’t matching the ventilation of the alveoli.
What is it called when you have a high V/Q ratio?
Dead space. Lots of ventilation but no perfusion.
What is a cause of a high V/Q ratio (dead space)?
Pulmonary embolism.
What is it called when you have a low V/Q ratio?
Shunt. Lots of perfusion but no ventilation.
What is a cause of a low V/Q ratio (shunt)?
Pulmonary oedema.
What is perfusion of pulmonary capillaries dependent on?
- Pulmonary artery pressure.
- Pulmonary venous pressure.
- Alveolar pressure.
Does the apex of the lung have a high or a low V/Q? Why?
High - effect of gravity, far more perfusion at the base of the lung.
What are the 7 layers for gas exchange?
- Alveolar epithelium.
- Interstitial fluid.
- Capillary endothelium.
- Plasma layer.
- RBC membrane.
- RBC cytoplasm.
- Hb binding sites.
Name 4 causes of hypoxia.
- Hypoventilation.
- V/Q mismatch.
- Diffusion abnormality.
- Reduced PiO2.
Name 4 causes of hypercapnia.
- Increased dead space ventilation; rapid, shallow breathing.
- V/Q mismatch.
- Increased CO2 production.
- Reduced minute ventilation.
What is the alveolar gas equation?
PAO2 = PiO2 - (PaCO2/R)
What is Dalton’s law?
In a mixture of non reacting gases Ptotal = Pa + Pb. (P total is the sum of the pressures of individual gases).
What is Boyle’s law?
Pressure and Volume are inversely proportional:
P1V1 = P2V2.
What is Henry’s law?
The solubility of a gas is proportional to the partial pressure of the gas. S1/P1 = S2/P2.
What is the acid/base dissociation equation?
CO2 + H2O = H2CO3 = HCO3- + H+
What enzyme catalyses the formation of bicarbonate and hydrogen ions from CO2 and H2O?
Carbonic anhydrase.
What is the henderson hasselbalch equation?
pH = pKa + log (A-)/(HA)
What is Laplace’s law?
P = 2T/R.
What is the significance of Laplace’s law?
It tells us that small alveoli have a greater pressure and so air will move from small alveoli to larger alveoli; uneven aeration. (Surfactant can prevent this).
Where is surfactant produced?
It is produced by type 2 pneumocytes in the alveoli.
When is surfactant produced?
It starts being produced from 34 weeks gestation and production increases rapidly 2 weeks before birth.
List 4 functions of surfactant.
- Prevents alveoli collapse.
- Allows homogenous aeration.
- Reduces surface tension.
- Maintains functional residual capacity.
Premature babies may have surfactant deficiency. What are the consequences of this?
- Respiratory distress syndrome.
- Non-compliant lungs.
- Unequal aeration.
- Reduced lung volume.
How can you treat surfactant deficiency?
Ensure the patient is warm and is receiving O2 and fluids. Begin surfactant replacement.
Briefly describe the controller-effector-sensor loop.
The sensor detects a change (hypoxia), sends signals along the afferent pathway to the controller. The controller then sends signals along the efferent pathway to the effector. The effector responds.
What does the pneumotaxic area do and where is it located?
It switches off inspiratory neurones and so allows expiration. It is located in the upper pons.
What does the apneustic centre do and where is it located?
It inhibits expiration by activation inspiratory neurones. It is located in the lower pons.
Where are SASR (slow adapting stretch receptors) located?
Found in smooth muscle around airways.
What activates SASR?
Lung distension.
How do SASR respond to activation?
They inhibit inspiration and so promote expiration.
Where are RASR (rapidly adapting stretch receptors) located?
Between airway epithelial cells.
What activates RASR?
Lung distension and irritants.
How do RASR respond to activation?
Bronchoconstriction.
What activates C fibres J receptors?
Increased interstitial fluid volume.
How do C fibres J receptors respond to activation?
They cause rapid, shallowing breathing. Bronchoconstriction and cardiovascular depression.
Where are central chemoreceptors located?
Medulla oblangata.
What stimulates central chemoreceptors?
An increase in H+ concentration in the ECF.
Where are peripheral chemoreceptors located?
Carotid and aortic bodies.
What stimulates peripheral chemoreceptors?
A decrease in PaCO2.
What is the respiratory drive more senstitive to, CO2 or O2?
It is very sensitive to CO2 and so CO2 is a greater drive. A small change in PaCO2 results in a large ventilatory change.
Oxygen dissociation curve: what causes the curve to shift to the right?
An increase in temperature and a decrease in pH.
Oxygen dissociation curve: what does it mean when the curve shifts to the right?
There is increased O2 unloading. Hb’s affinity for oxygen has decreased.
Oxygen dissociation curve: what causes the curve to shift to the left?
A decrease in temperature and an increase in pH.
What is a cause of respiratory acidosis?
Inadequate ventilation; could be due to obstruction e.g. COPD.
What is the renal compensation mechanism for respiratory acidosis?
Increased ammonia formation. H+ secretion increases and there is increased HCO3- reabsorption.
What can cause respiratory alkalosis?
Hyperventilation in response to hypoxia.
What is the renal compensation mechanism for respiratory alkalosis?
H+ secretion decreases; more H+ is retained. HCO3- secretion.
What is a cause of metabolic acidosis?
Renal failure; loss of HCO3-, excess H+ production.
What is the respiratory compensation mechanism for metabolic acidosis?
Chemoreceptors stimulated, enhancing respiration, PaCO2 decreases.
What is the respiratory compensation mechanism for metabolic alkalosis?
Chemoreceptors are inhibited, reduced respiration, PaCO2 increases.
What is a cause of metabolic alkalosis?
Vomiting; loss of H+.
Is respiratory compensation fast or slow?
FAST!
What is type 1 respiratory failure and what are its causes?
Hypoxemia.
Causes: V/Q mismatch due to alveolar hypoventilation, high altitude, shunt, diffusion problem.
What is type 2 respiratory failure and what are its causes?
Hypoxemia and hypercapnia.
Causes: inadequate alveolar ventilation due to reduced breathing effort, decreased SA, neuromuscular problems.
What is forced vital capacity?
Volume of air that can be forcibly exhaled after maximum inhalation.
How could you diagnose a patient with having an obstructive lung disease?
The FEV1/FVC ratio would be less than 70% predicted value.
How could you diagnose a patient with having an restrictive lung disease?
The FEV1/FVC ratio would be normal but their FVC value would be very low.
How can you work out total lung capacity?
Add vital capacity to residual volume.
What is tidal volume?
The volume of air moved into or out of the lungs during normal, quiet breathing.
What changes are seen in an aging lung?
Decreased compliance, muscle strength, elastic recoil, immune function. Decreased response to hypoxia and hypercapnia. Impaired gaseous exchange.
What happens to the FEV1 and FVC in an elderly person?
They both decrease and the residual volume increases.
What effect does hypoxia have on pulmonary vessels?
It vasoconstricts the vessels and so redirects blood to O2 rich alveoli.
What is hypersensitivity?
Undesirable reaction produced by the immune system.
Hypersensitivity: What is the mechanism of a type 1 reaction?
Antigens interact with IgE bound to mast cells. Histamine is released. This can cause hayfever, asthma, acute anaphylaxis etc. (Antihistamines are often given as treatment).