Ventilation and gas exchange (29) Flashcards
What is minute ventilation?
the volume of air expired in 1 minute/ per minute
What is respiratory rate?
the frequency of breathing per minute
What is alveolar ventilation?
the volume of air reaching the respiratory zone per minute
What is respiration?
the process of generating ATP either aerobically or anaerobically
What is anatomical dead space?
- the capacity of airways incapable of undertaking gas exchange (nose/mouth to terminal bronchioles)
- ‘conducting zone’ (16 generations)
What is alveolar dead space?
- the capacity of the airways that should be able to undertake gas exchange but cannot (e.g. alveoli w/out blood supply)
- ‘non perfused parenchyma’
What is physiological dead space?
the sum of alveolar and anatomical dead space
What is hypoventilation?
deficient ventilation of the lungs- unable to meet metabolic demand
What is hyperventilation?
excessive ventilation of the lungs above metabolic demand
What is hyperpnoea?
increased depth of breathing (to meet metabolic demand)
What is hypopnoea?
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)
What distinguishes lung volumes and capacities?
- volumes are discrete sections of the graph and DON’T overlap
- whereas capacities are the SUM of 2 or more volumes
What is inspiratory reserve volume?
the additional amount of air that can be inhaled after a normal inspiration (tidal volume)
What is tidal volume?
the lung volume representing the normal volume of air displaced between normal inhalation and exhalation w/ no extra effort
What is expiratory reserve volume?
the amount of extra air exhaled during a forceful breath out
What is residual volume?
the amount of air that remains in a person’s lungs after fully exhaling
What is functional residual capacity?
the amount of gas left in the lungs after normal expiration
What is inspiratory capacity?
the volume of air that can be inspired following a normal, quiet expiration (tidal volume+inspiratory reserve volume)
What is vital capacity?
the maximum amount of air a person can expel from their lungs after a maximum inhalation (inspiratory reserve + tidal volume + expiratory reserve)
What is the equation for minute ventilation?
tidal volume X breathing frequency
L/min
What is the equation for alveolar ventilation?
(tidal volume - dead space) X breathing frequency
What factors affect lung volumes and capacities?
- body size (height, shape)
- sex
- fitness
- age
- disease
What is non-perfused parenchyma?
- alveoli without a blood supply
- no gas exchange
- alveolar dead space
What reversibly increases anatomical dead space?
- ventilator
- snorkel
What reversibly decreases anatomical dead space?
- tracheostomy
- cricothyrocotomy
How is inspired gas modified in the airways?
warmed, humidified, slowed and mixed w/ air already in there
What are the different types of haemoglobin?
- Hb A (98%): Hb a + Hb b
- Hb A2 (2%): Hb a + Hb d
- Hb F (fetal): Hb a + Hb y
What is the allosteric behaviour of haemoglobin (cooperative binding)?
- Hb without oxygen has v. low affinity for oxygen
- when oxygen binds–> conformational change in protein structure–> greater affinity for oxygen
- inc. each time an oxygen binds
- tense–> relaxed (as O2 binds), opens up a binding site for 2,3-DPG–> pushes Hb into tense state, causing some O2 to be ejected
What is the P50?
the partial pressure at 50% HbO2 saturation
What causes a rightwards shift of the oxygen dissociation curve?
- metabolic activity- inc. in temperature
- acidosis (Bohr effect)
- hypercapnia (inc. CO2)
- inc. 2,3-DPG
rightwards shift causes inc. release of oxygen (unloading) e.g. in muscles, or placenta
What causes a leftwards shift of the oxygen dissociation curve?
- low temperature
- alkalosis
- hypocapnia (dec. CO2)
- dec. 2,3-DPG
- fetal haemoglobin (bc needs greater affinity for oxygen than adult HbA to ‘extract’ it)
- myoglobin (v. steep bc oxygen store)
inc. affinity/loading e.g. in lungs
What causes a downwards shift of the oxygen dissociation curve?
less Hb, so less total O2 in blood, but HbO2 saturation still high
e.g. anaemia–> impaired oxygen-carrying capacity
What causes an upwards shift of the oxygen dissociation curve?
polycythaemia, so inc. Hb in blood–> inc. oxygen-carrying capacity
How does carbon monoxide affect the oxygen dissociation curve?
- downwards and leftwards shift
- bc dec. capacity and inc. affinity
How is carbon dioxide transported (3 ways)?
- CO2 from respiration moves into blood from tissues
- reacts (non-enzymatically) w/ water to form carbonic acid (H2CO3)
- H2CO3 dissociates into H+ and HCO3- (most transported as bicarbonate)
- also CO2 moves into erythrocyte and combines w/ water using carbonic anhydrase enzyme–> inc. rxn rate
- HCO3- moved out of erythrocyte and Cl- moved in
- also CO2 binds to Hb (amine ends of globin chains)–> HbCO2
- protons in RBC bind to Hb
What is the Haldane effect?
- property of Hb
- deoxygenated blood can carry more CO2 at any given pressure i.e. veins
- and oxygenated blood has. a reduced capacity for CO2 i.e. arteries
What is pulmonary transit time?
amount of time that the blood is in contact w/ respiratory exchange surface
0.75s- how long it takes for O2 to equilibrate between plasma and alveoli
Why will increased tidal volume increase the concentration of dissolved oxygen in blood?
deeper breathing will increase the ‘refresh rate’ of air at the gas exchange surface
Why will uncontrolled type 1 diabetes shift the oxygen dissociation curve to the right?
may lead to diabetic ketoacidosis–> acidity shifts curve to right
Why is there greater of ventilation the lungs at the bottom?
alveoli are completely contracted so not much needed for them to expand
How do pressure gradients drive flow?
- high pressure–> low pressure
- inspiratory effort expands alveoli, decreasing its pressure, so air flows in until pressures equilibriate
- removing inspiratory effort, pressure inc., pushing air out
What is transmural pressure?
Pinside - Poutside
N.B. +ve transmural pressure leads to expiration
What is the chest wall relationship?
- lung tissue naturally recoils inwards and ribcage naturally recoils outwards
- chest recoil= lung recoil
- inspiratory muscle effort + chest recoil > lung recoil–> results in inspiration
- expiratory muscle effort + lung recoil > chest recoil–> results in expiration
What is a haemothorax?
vessel bleeding inside pleural cavity–> compresses lung- less space for lung to expand
What is a pneumothorax?
puncture of chest wall or lung, allowing air into intrapleural space
What is negative pressure breathing?
lowering Palv below Patm to create -ve pressure gradient
e.g. normal breathing
What is positive pressure breathing?
increasing Patm above Palv, forcing air into lungs
e.g. ventilator, mouth to mouth
What is transrespiratory system pressure?
Prs= Ralv - Patm
N.B. a -ve transrespiratory pressure will lead to inspiration
