Lung physiology Flashcards
What structures contribute to the respiratory pump?
Bones, muscles, pleura, peripheral nerves, airways
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.
True or False: the intercostals are the main muscles of respiration.
False - the diaphragm is the main muscle of respiration.
What is respiratory epithelium?
Pseudo-stratified, columnar, ciliated, interspersed with goblet cells.
What cell type lines most of the surface of an alveoli?
Type 1 pneumocytes.
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.
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.
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?
Internal intercostal muscles these muscles contract pulling the ribcage inwards and downwards.
abdominal wall muscles
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.
What does perfusion (Q) refer to?
refers to the flow of blood to alveolar capillaries
What is perfusion of pulmonary capillaries dependent on?
- Pulmonary artery pressure.
- Pulmonary venous pressure.
- Alveolar pressure.
What does ventilation (V) refer to?
Refers to the flow of air into and out of the alveoli
What is the relevance of ventilation and perfusion?
For effective gas exchange to occur, alveoli must be ventilated and perfused
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 - when a blood clot blocks a blood vessel within the lungs.
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 - fluid builds up in the lungs, making it difficult to breathe
Does the apex of the lung have a high or a low V/Q? Why?
The apex of the lung has a high V/Q (less perfusion) due to gravity
There is more perfusion at the base of the lung.
Nomenclature;
PaCO2
PACO2
PaO2
PAO2
PiO2
FiO2
VA
VCO2
PaCO2: arterial CO2
PACO2: alveolar CO2
PaO2: Arterial O2
PAO2: alveolar O2
PiO2: pressure of inspired O2
FiO2: fraction of inspired O2
VA: alveolar ventilation
VCO2: CO2 production
What is normal PCO2 level?
4-6KPa
PaCO2 equation?
PaCO2 = K VCO2 / VA
Carbon dioxide = K CO2 production / alveolar ventilation
What are the 7 layers for gas exchange?
- Alveolar epithelium.
- Interstitial fluid.
- Capillary endothelium.
- Plasma layer.
- RBC membrane.
- RBC cytoplasm.
- Hb binding sites.
What is the alveolar gas equation?
PAO2 = PiO2 - (PaCO2/R)
Alveolar gas = pressure of inspired O2 - (CO2/R)
What is hypoxia?
A state in which oxygen is not available in sufficient amounts at the tissue level to maintain adequate homeostasis
Name 4 causes of hypoxia.
- Hypoventilation.
- V/Q mismatch.
- Diffusion abnormality.
- Reduced PiO2.
What effect does hypoxia have on pulmonary vessels?
It vasoconstricts the vessels and so redirects blood to O2 rich alveoli.
What effect does hypoxia have on systemic vessels?
Vasodilation.
What is hypercapnia?
When you have too much carbon dioxide (CO2) in your blood.
Name 4 causes of hypercapnia.
- Increased dead space ventilation; rapid, shallow breathing.
- V/Q mismatch.
- Increased CO2 production.
- Reduced minute ventilation.
What is type 1 respiratory failure?
Hypoxia / hypoxyaemia
What is type 2 respiratory failure?
Hypoxia and hypercapnia
What if the difference between type 1 and 2 respiratory failure?
Type 1 respiratory failure occurs when the respiratory system cannot adequately provide oxygen to the body, leading to hypoxemia.
Type 2 respiratory failure occurs when the respiratory system cannot sufficiently remove carbon dioxide from the body, leading to hypercapnia.
What causes a shift in the oxygen dissociation curve and which way does it shift?
Shift right
Increasing temperature
Increasing 2,3 diphosphoglyceric acid
Increasing H+ concentration
Increasing CO2
Shift left
Decreasing temperature
Decreasing 2,3 diphosphoglyceric acid
Decreasing H+ concentration
Decreasing CO2
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.
What is Hb affinity for O2?
How readily Hb acquires and releases O2 at respiring tissues.
What does Boyles law describe?
How pressure of a gas increases as volume decreases.
What is Boyle’s law?
Pressure and Volume are inversely proportional;
P1V1 = P2V2
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 Henry’s law?
The solubility of a gas is proportional to the partial pressure of the gas.
S1/P1 = S2/P2.
What is Laplace’s law?
P = 2T/R.
Pressure = 2(surface tension)/ radius
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.
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.
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)
Describe the 4 main acid-base disorders…
Respiratory acidosis; increased PaCO2, decreased pH, mild increased HCO3-
Respiratory alkalosis; decreased PaCO2, increased pH, mild decreased HCO3-
Metabolic acidosis; reduced bicarbonate and decreased pH
Metabolic alkalosis; increased bicarbonate and increased 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 a cause of metabolic alkalosis?
Vomiting; loss of H+.
What is the respiratory compensation mechanism for metabolic alkalosis?
Chemoreceptors are inhibited, reduced respiration, PaCO2 increases.
Why can hypoxia cause respiratory alkalosis?
Hypoxia leads to hyperventilation as the person tries to inhale more O2. This means you lose a lot of CO2 resulting in alkalosis.
What is forced vital capacity?
Volume of air that can be forcibly exhaled after maximum inhalation.
How can you work out total lung capacity?
Add vital capacity to residual volume.
How could you diagnose a patient with having an obstructive lung disease?
The FEV1/FVC ratio would be less than 70% predicted value.
What is the normal range of FEV1 FVC ratio?
Equal to or > 70%
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.
Define FEV1…
FEV1: Forced expiratory volume in one second
The volume of air that can be forcibly exhaled in 1 second.
Define forced vital capacity (FVC)…
The maximum volume of air that can be forcibly exhaled after maximal inhalation. Usually in 6 seconds.
Equation for total lung capacity?
TLC = VC + RV.
Vital capacity + residual volume
Define total lung capacity…
The vital capacity plus the residual volume. It is the maximum amount the lungs can hold.
Define residual volume (RV)…
The volume of air remaining in the lungs after a maximal exhalation.
Define functional residual capacity (FRC)…
The volume of air remaining in the lungs after a tidal volume exhalation.
Define tidal volume (TV)…
The volume of air moved in and out of the lungs during a normal breath.
Define expiratory reserve volume (ERV)…
The additional volume of air that can be forcibly exhaled after a tidal volume expiration.
Define inspiratory reserve volume (IRV)…
The additional volume of air that can be forcibly inhaled after a tidal volume inspiration.
What is lung compliance?
A measure of the lung’s ability to stretch and expand. Compliance = ∆V/∆P.
What happens to the FEV1 and FVC in an elderly person?
They both decrease and the residual volume increases.
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.
Why do you see decreased elastic recoil in an ageing lung?
The elastin degenerates and ruptures.
Why do you see decreased muscle strength in an ageing lung?
There is a decrease in type 1, fatigue resistant fibres. And muscle mass also decreases.
Why do you see a decreased response to hypoxia and hypercapnia in an ageing lung?
The lung is more vulnerable and has a decreased awareness meaning these changes aren’t detected till late on.
Why do you see decreased immune function in an ageing lung?
There is less protective mucus and sputum clearance is less effective.
Why do you see impaired gaseous exchange in an ageing lung?
The SA for gaseous exchange decreases and there is increased V/Q mismatch.
Why does the residual volume increase in an ageing lung?
The chest wall changes shape. There is increased calcification and stiffness.
Define vital capacity…
The maximum volume of air that can be exhaled after a maximal inhalation.
What is the normal tidal volume in an adult?
500ml
What is the thickness of the air-blood barrier in nm?
200-800nm
Define peak expiratory flow (PEF)…
The greatest rate of airflow that can be obtained during forced exhalation.
Define airway obstruction…
Impediment to inspiratory and expiratory air flow.
Define airway restriction…
When the lungs are restricted from full expansion.
