Respiratory Module 1 Flashcards
What is ventilation and how is it measured
the removal of CO2 from the lungs. measured by PaCO2 or PvCO2
What is oxygenation and how is it measured
The movement of oxygen through the blood. Depends on the integrity of the exchange interface and the surface area available. Measured through PaO2
What is partial pressure
This is the pressure exerted by a gas dissolved in a liquid
What is compliance, what is the compliance of a normal lung?
The distensibility of lungs. The normal lung has high compliance meaning it distends easily with minimal pressure
What compromises the ventilatory apparatus and what does it do
chest wall, diaphragm, nerve and blood supplies. Moves the air in and out of the lungs
Pulmonary parenchyma is made up of…
Alveoli, lymphatics, blood supply and interstitium
What is the conducting zone
regions of the lower respiratory tract that conduct air and take no part in gas exchange. This area holds a fixed amount of air and is referred to as the anatomic dead space
What is the respiratory zone
after the terminal bronchioles the respiratory bronchioles start and they take part in gas exchange. Gas movement occurs through diffusion as there is no velocity present due to the large surface area
How is the lung ventilation and perfusion spread
Ventilation: alveoli dorsally are larger than those ventrally as the weight of the lung compresses the more ventral alveoli. Ventral alveoli have a greater capacity to expand.
Perfusion: there is greater perfusion ventrally due to gravity pulling blood
What cells are the alveolar epithelium made of
Alveolar epithelium is made of Type 1 and Type 2 pneumocytes. Type 1 cells are large flat epithelial cells and make up 95% and Type 2 cells are taller and bigger cells that produce surfactant
What stimulates breathing
- Hypercarbia - very tightly managed
- Central Chemoreceptors: located in the ventral medulla, sensitive to changes with pH and will increase ventilation to decrease this. CO2 –> BBB –> reacts with H2O to form H+ and HCO3 in CSF and alters pH
- Pulmonary stretch receptors: mechano-receptors located in the airway of smooth muscle - slow respiration in response to pulmonary distention
- Peripheral chemoreceptors: Located in the carotid bodies and aortic bodies - activated by low PO2 (hypoxaemia) and decreased pH - PaO2 has to be quite bad to trigger - O2 sensitive k+ channels
Explain the normal respiratory cycle
Normal cycle has active inspiration and passive expiration. External intercostal muscles contract to pull out rib cage and the diaphragm contracts and flattens to allow expansion. All this causes the chest cavity to expand causing an increase in negative pressure that pulls air in through the nostrils
Expiration occurs passively due to natural recoil of the lungs when the external intercostal muscles and diaphragm relax in to resting
Explain residual volume and its role
the amount of air left in the lungs after maximum expiration. This prevents alveoli from completely collapsing and would lead to shear injury of the alveoli
what makes up the total lung capacity
Residual volume and the vital capacity
Explain the ventilation perfusion zones that are possible within the lungs
Three zones.
Zone 1: highest V/Q - the capillaries are squashed by the alveolar pressure so there is minimal to no blood flow with good ventilation - not present in healthy animals
Zone 2: Central region of lungs - pressure in the arterial capillaries are higher than alveolar pressure allowing perfusion to occur but is dependent on the arterial-alveolar pressure gradient (finger on hose pipe)
Zone 3: Blood flow exceeds the ventilation. the most dependant part of the lung
Mechanisms of O2 carriage
O2 can be dissolved in plasma or bound to Hb
What is Ficks law and what is it used to explain
used to explain diffusion of gasses through tissue. the rate of diffusion is proportional to the area which diffusion is occurring to the solubility of the molecule dissolving to the pressure difference across the tissue undergoing diffusion. It is inversely proportional to the thickness of the tissue where diffusion is taking place and the molecular weight of the molecules
CO2 diffuses 20X faster than O2 due to greater solubility though the molecular weight is similar
Animals become hypoxic before they are hypercarbic because so easy for CO2 to diffuse out
What is the law of mass action
Whichever substance is in greatest quantity will displace other substances from haemoglobin
How is oxygen dispersed in the system
98% of O2 is transported with Hb and 2% is dissolved in the blood - this two percent is crucial as creates the diffusion gradient allow O2 to flow from areas of high to low concentration
Oxygen dissociation curve
The oxygen dissociation curve is a sigmoid curve and discribes the relationship between SPO2 and PaO2. The binding of one O2 molecule to Hb increases the speed of other O2 binding causing the steep rise. Once most Hb are saturated it takes increased levels of O2 to find free binding sites - causing a plateau.
What causes Left Shift
Left shift - The left shift means that saturation of the curve is higher at any given O2, retains more O2. Haldane effect: O2 decreases affinity of Hb to CO2. This is caused by: increased pH, decreased CO2, decreased temperature, decreased 2-3 DPG, increased carbonmonoxide and methaemoglobin
What causes Right Shift
Right shift - means saturation of the curve is lower at any given O2, it releases more O2 to its surroundings. Bohr effect: high levels of CO2 causing reduced affinity of Hb to O2. Caused by: an increase in CO2, decrease in pH, increased temperature and 2, 3DPG (by product of red cell metabolism - accumulate with chronic hypoxia)
Explain the carriage of CO2
30% bound to proteins: Hb, albumin, plasma proteins
60% reacts with H20 - happens in RBC, catalysed by carbonic anhydrase and turns in to bicarb and h+ ion. Bicarb moves into plasma (hamburger effect - exchanged with cl- to retain electroneutrality)
- in lungs due to high O2 drives bicarb and H+ to combine to form water and CO2 which is released in lungs to be expelled
10% dissolved in plasma
CO2 dissociation curve
There is a consistent difference of 5mmHg between oxy and deoxy blood. Steep curve so small changes in PCO2 will result in large changes in PaCO2
What are causes of inadequate oxygen within tissues
Normally there is low O2 within tissues which allows O2 to readily flow into tissues due to difference in gradients
Decreased PaO2 - hypoxaemia, pulmonary disease
Decreased Hb - haemorrhage, anaemia, carboxy, methaem
Decreased tissue perfusion: hypovolaemia, shock
Tissues unable to use O2 - cyanide toxicity, toxic hypoxia
When does hypoxaemia require O2 supplementation
PaO2 <80mmHg, SpO2 <95%
Lifethreatening at <90%, 60mmHg
What are the causes of reduced PaO2
- V/Q mismatch
- Diffusion impairment
- Hypoventilation
- Decreased FiO2
- Shunting
Explain low, high and zero V/Q mismatch areas
Low V/Q - Poor ventilated area with good perfusion - O2 responsive
High V/Q - Well ventilated aera with poor perfusion
Zero V/Q - No ventilation despite perfusion - positive pressure ventilation responsive
What are causes of diffusion impairement within the lungs
Severe pulmonary disease
Inhalation injury
ARDs
Interstitial fibrosis
Caused by - generalised thickening of blood:gas interface - type 2 pneumocytes proliferate over type 1 in response to inflammation, fluid build up within the alveolar interstitium
Causes of hypoventilation
Caused by anything that disrupts the bellows (chest wall, diaphragm, nerves and vessels)
-Trauma to chest wall
-LMN disease
-Phrenic nerve damage
-Abdominal distension affect diaphragm movement
-Pleural space disease
-Airway obstruction
-CNS depression and resp fatigue
