Control of Breathing Flashcards
What respiratory control centres of the brainstem control breathing?
- Inspiratory centre (medulla)
- Expiratory centre (medulla)
- Pneumotaxic centre (pons)
- Apneuristic centre (pons)
What (3) factors control breathing?
- Cerebral cortex: can exert voluntary control over breathing as well as centres involved in emotion and pain
- Peripheral chemoreceptors (in vascular system) & central chemoreceptors (in brain): detect changes to O2 and CO2
- Stretch receptors (in lungs) & activity receptors (in muscles and joints)
What are (4) airway characteristics?
- Rich blood supply
- Large surface area
- Tissues have intrinsic elastic properties
- Fluid lubrication (ensure rapid diffusion + counteract physical forces like surface tension)
Pontine Centres.
influence output from the medullary respiratory centres
Medullary Respiration Centres.
provide output to respiratory muscles
How does high levels of CO2 affect the body?
changes the body’s pH = toxic
What is partial pressure measured in?
kilopascals (kPa) or millimetres of mercury (mmHg)
E.g.: (0.133kPa = 1mmHg)
What is PaPO2?
Partial pressure of oxygen dissolved in plasma of arterial blood
What is PO2/PCO2?
Partial pressure of oxygen / carbon dioxide in the air
What is PvCO2?
Partial pressure of carbon dioxide dissolved in plasma of venous blood
What is partial pressure?
the concentration of each gas in the body
What are (3) factors affecting gas solubility?
- Partial pressure of gas
- Partial pressure of gas in liquid phase
- Solubility of a gas
How does partial pressure of gas affect gas solubility?
The greater the partial pressure the faster it will dissolve into the liquid phase
How does partial pressure of gas in liquid phase affect gas solubility?
If the partial pressure of a gas in the liquid phase becomes higher than its partial pressure in the gas phase, some of the dissolved gas will re-enter the gas phase
What (3) key factors will influence gaseous exchange?
- Gas partial pressure and gas solubility
- Matching of alveolar ventilation with pulmonary blood perfusion
- Structural characteristics of the respiratory membrane
What is ventilation (V)?
volume of air entering the alveoli
What is perfusion (Q)?
volume of blood flowing through the lungs
What is the ventilation/perfusion mismatch?
inadequacy of V or Q will significantly impact the oxygenation of the blood and the removal of CO₂
When side lying should the patient’s ‘bad’ lung be faced up or down (in terms of VQ)?
Up (so not lying on the bad side)
Where (in a healthy adult) is self-ventilating lung ventilation optimal?
lower 1/3 of lung (dependent region)
Which regions of the lung have a greater initial volume?
non-dependent (upper) lung
Which regions of the lung are partially expanded?
dependent (lower) lung
Why are the dependent (lower) lung regions partially expanded?
so they still have the capacity of further expansion + volume change
What is perfusion influenced & affected by?
- Gravity
- The interaction of alveolar, arterial + tissue pressure
What is perfusion?
the passage of blood, a blood substitute, or other fluid through the blood vessels or other natural channels in an organ or tissue
Does the distribution of perfusion increase up/down the lung?
Down
What (2) ways can Oxygen be carried in?
- Bound to haemoglobin (Hb) in red blood cells (RBCs) (98.5%)
- Dissolved in plasma (1.5% … this is how we measure PaO₂)
What does oxygen bind to in the blood?
Haem molecules in haemoglobin
How much O2 is reversible bound or released is determined by what?
- Partial pressure of oxygen in blood (PO2)
- Temperature
- Blood pH
- The partial pressure of carbon dioxide (PCO2) + therefore concentration of H+ ions
- Blood concentration of BPG (2,3-Biophosglycerate) produced by RBC
How much CO2 do respiring cells produce per minute?
200ml
What (3) ways does blood carry CO2 in the lungs?
- Dissolved as CO2 in blood plasma (7-10%)
- Chemically bound to Hb in RBC’s as carbaminohaemoglobin (20%)
- Bicarbonate ions in plasma (~70%)
What is carbaminohaemoglobin?
CO2 binds to globin portion of molecule
What happens when CO2 diffuses into red blood cells?
It combines with water to form carbonic acid.
Which enzyme speeds up the reaction between CO2 and water in RBCs?
carbonic anhydrase
Why is carbonic acid in red blood cells considered unstable?
It quickly dissociates into hydrogen ions and bicarbonate ions
What role do hydrogen ions play after being released from carbonic acid in RBCs?
They bind to haemoglobin and facilitate the release of oxygen
What is the normal pH of arterial blood?
7.35-7.45 pH
What is the normal pH of venous blood?
7.31-7.41 pH
How does blood become more acidic?
increased CO2 = increased H+ = decreased pH
How does blood become more alkali?
decreased CO2 = decreased H+ = increased pH
Tidal Volume (Vt)
Volume of air inhaled or exhaled during a single normal breath
What is Tidal Volume (Vt) in men vs women?
Men: 500ml
Women: 50ml
Inspiratory reserve Volume (IRV)
Maximum amount of air that can be inspired on top of a normal tidal inspiration
What is Inspiratory Reserve Volume (IRV) in men vs women?
Men: 3000ml
Women: 1900ml
What is Expiratory reserve volume (ERV) in men vs women?
Men: 1100ml
Women: 700ml
Expiratory reserve volume (ERV)
Maximum amount of air that can be exhaled following a normal tidal expiration
Residual volume (RV)
Volume of air remaining in the lung after a maximal expiration
What is Residual volume (RV) in men vs women?
Men: 1200ml
Women: 1100ml
What is Minimal Volume (MV) in men vs women?
Men & Women: 30-120ml
Minimal volume (MV)
Amount of air that would remain if the lungs collapsed
Total Lung Capacity (TLC)?
Total volume of the lungs at the end of a max inspiration
TLC=VT+IRV+ERV+RV
Vital Capacity (VC)
Maximum amount of air that can be inspired and expired in a single breath
VC=VT+IRV+ERV
Inspiratory Capacity (IC)
Maximum volume of air that can be inspired after a normal tidal expiration
IC=VT+IRV
Functional Residual capacity (FRC)
Volume of air remaining in the lungs at the end of normal tidal expiration
FRC=ERV+RV
What is total lung capacity (TLC) in men vs women?
Men: 5800ml
Women: 4200ml
What is vital capacity (VC) in men vs women?
Men: 4600ml
Women: 3100ml
What is inspiratory capacity (IC) in men vs women?
Men: 3500ml
Women: 2400ml
What is functional residual capacity (FRC) in men vs women?
Men: 2300ml
Women: 1800ml
If airways are blocked, what allows air to move (in order to minimise airway collapse)?
Collateral Ventilation
What is Pendelluft?
The movement of air between areas of differing compliance or resistance
(If one area of lung has greater resistance than the other it will take longer to fill, e.g. asthma, ARDS)
What does oscillation do?
- Improve mucus rheology (i.e. flow)
- Improve expiratory airflow bias
- Create shearing forces which move mucus off the airway walls
How does airway clearance work?
- Collateral ventilation
- Interdependence
- Pendelluft
- Expiratory flow bias
- Enhances oscillatory effect
What is interdependence?
If tidal volume is increased during inspiration expanding alveoli will exert a traction force on the surrounding alveoli
How does interdependence help?
Helps to re-expand surrounding alveoli that have collapsed surrounding alveoli that have collapsed