Ventilation and gas exchange Flashcards
What is minute ventilation?
The volume of air expired in one minute or per minute
What is respiratory rate?
The frequency of breathing per minute
What is alveolar ventilation?
The volume of air reaching the respiratory tone per minute
What is respiration?
The process of generating ATP either with an excess of oxygen (aerobic) and a shortfall (anaerobic)
What is anatomical dead space?
The capacity of the airways incapable of undertaking gas exchange
What is alveolar dead space?
Capacity of the airways that should be able to undertake gas exchange but cannot (e.g. hypoperfused alveoli)
What is physiological dead space?
Equivalent to the sum of alveolar and anatomical dead space
What is hypoventilation?
Deficient ventilation of the lungs; unable to meet metabolic demand (increase PO2 - acidosis)
What is hyperventilation?
Excessive ventilation of the lungs atop of metabolic demands (results in reduced PCO2 - alkalosis)
What is hyperponea?
Increased depth of breathing (to meet metabolic demand)
What is hypopnea?
Decreased depth of breathing (inadequate to meet metabolic demand)
What is apnoea?
Cessation of breathing (no air movement)
What is dyspnoea?
Difficulty in breathing
What is bradypnoea?
Abnormally slow breathing rate
What is tachypnoea?
Abnormally fast breathing rate
What is orthopnoea?
Positional difficulty in breathing (when lying down)
How do you calculate minute ventilation? (L/min)
-gas entering and leaving the lungs tidal volume (L) x breathing frequency (breaths/min)
How do you calculate alveolar ventilation? (L/min)
-gas entering and leaving the alveoli tidal volume (L) - dead space (L)
What factors affect lung volumes and capacities?
- Body size (height, shape)
- Sex (male, female)
- Disease (pulmonary/neurological)
- Age (chronological, physical)
- Fitness (innate, training)
What is the conducting zone in dead space?
- 16 generations
- No gas exchange
- Typically 150 mL in adults at FRC
- Equivalent to anatomicaldead space
What is the respiraotey zone in dead space?
- 7 generations
- Gas exchange
- Typically 350 mL in adults
- Air reaching here is equivalent to alveolar ventilation
What is non-perfused parenchyma?
- Alveoli without a blood supply
- No gas exchange
- Typically 0 mL in adults
- Called alveolardead space
How does the chest wall and lungs act?
The chest wall has a tendency to spring outwards, and the lung has a tendency to recoil inwards
What happens at FRC?
These forces are in equilibrium at end-tidal expiration (functional residual capacity; FRC), which is the ‘neutral’ position of the intact chest.
What are the results in inspiration?
Inspiratory muscle effort + chest refill > lung recoil
What are the results in expiration?
Chest recoil < lung recoil + expiratory muscle efforts
What are the lungs surrounded by?
by a visceral pleural membrane
What is the inner surface of the chest wall covered by?
a parietal pleural membrane
Whats in the plural cavity?
- The pleural cavity (the gap between pleural membranes) is a fixed volume and contains protein-rich pleural fluid
- The chest wall and lungs have their own physical properties that in combination dictate the position, characteristics and behaviour of the intact chest wall
What is a heamo-thorax?
Intrapleural bleeding
What is a pneumothorax?
Perforated chest wall (could also be caused by a punctured lung)
What drives flow?
Pressure gradients
-Normal breathing is ‘negative pressure breathing’
What are negative and positive transmural pressures?
-Transmural pressures
(Pinside – Poutside)
-A negative transrespiratory pressure will lead to inspiration
-A positive transmural pressure leads to expiration
What are shorthands?
Patm = atmospheric pressure Ppl = intrapleural pressure Palv = alveolar pressure
PTT = Transthoracic pressure PTP = Transpulmonary pressure PRS = Transrespiratory System pressure
What is the inspiratory muscle forces?
- The effect of the diaphragm is like a syringe
- A pulling force in one direction - The effect of the other respiratory muscles is like a bucket handle
- An upwards and outwards swinging force
What is dalton law?
Pressure of a gas mixture is equal to the sum (Σ) of the partial pressures (P) of gases in that mixture
What is fick law?
Molecules diffuse from regions of high concentration to low concentration at a rate proportional to the concentration gradient (P1-P2), the exchange surface area (A) and the diffusion capacity (D) of the gas, and inversely proportional to the thickness of the exchange surface (T)
What is Henry law?
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid
What is boyle law?
At a constant temperature, the volume of a gas is inversely proportional to the pressure of that gas
What is Charles law?
At a constant pressure, the volume of a gas is proportional to the temperature of that gas
What happens as air passes down respiratory tract?
WARMED, HUMIDIFIED, SLOWED and MIXED as air passes down the respiratory tree
What is total O2 delivery at rest?
16mL-min-1
What is resting VO2?
Resting V̇O2 is approx. 250 mL·min-1 so obviously relying on dissolved oxygen alone is not conducive with life.
What do haemoglobin monomers consist of?
Haemoglobin monomers consist of a ferrous iron ion (Fe2+; haem- ) at the centre of a tetrapyyrole porphyrin ring connected to a protein chain (-globin); covalently bonded at the proximal histamine residue
What type of proteins is Hb?
Allosteric
What is cooperatively?
As one O2 joins to haemoglobin becomes easier for other O2 to join
(from tense low affinity to relaxed high affinity)
What happens with foetal haemoglobin?
Greater affinity than adult HbA to ‘extract’ oxygen from mothers blood in placenta
What happens for myoglobin?
Much much greater affinity than adult HbA to ‘extract’ oxygen from circulating blood and store it.
How is O2 transported?
O2 transported in solution (~2%) or bound to Hb (~98%)
How is CO2 transported?
CO2 transported in solution, as bicarbonate (HCO3-) and as carbamino compounds (e.g. HbCO2)
What shape is Oxygen dissociate curve?
sigmoid shaped
What shape is carbon dioxide dissociated curve?
is almost linear
What causes downward shift?
anaemia
What causes Left shift?
- Decrease temp
- Alkalosis
- Hypocapnia
- Decrease 2,3 DPG
↑pH, ↓PCO2, ↓temp and ↓2,3-DPG
(= Increased affinity as O2 binds at a lower pO2)
What causes right shift?
- Increased temperature
- Acidosis
- Hypercapnia
- Higher 2,3 DPG
↓pH, ↑PCO2, ↑temp and ↑2,3-DPG
(Bohr effect)
What causes upward shift?
polycythaemia
What is the affinity of myoglobin?
VVVV greater affinity than adult haemoglobin to extract oxygen from circulating blood and store it
Describe the oxygen dissociation curve
- When the PO2 is low is when O2 is off-loaded and when Hb has a lower affinity of the O2
- But once the first O2 binds then the others bind easier
- When the PO2 is high is when O2 is taken up by Hb