Respiratory physiology Flashcards
what is the main function of the lungs
involved in gas exchange
- Enables O2 delivery to the cells for oxidative phosphorylation
- Eliminates CO2
when does expiration become active (2)
- during forced expiration
- if airway or tissue resistance is increased
what are other functions of the lungs (6)
- Synthesis for e.g. surfactant, ACE
- Metabolism of different compounds e.g. vasoactive substances like bradykinin
- component of the immune system
- Clearance of Inhaled Particles
- Drug delivery and Elimination
- Reservoir for blood(500-900ml)
central chemoreceptors are not responsive to what
to changes in PaO2
inspiration is what
active breathing
what do muscles of inspiration do
pull the chest up and out
what stimulates the central chemoreceptors(2)
by CO2 and H ions.
These CO2 and H ions are from CSF not blood
what is expiration
is passive with quite breathing
what are the muscles of inspiration (2)
- diaphragm
- external intercostal muscles
what are the muscles of forced expiration (2)
- Internal intercostal
- the abdominal wall muscles
where are the peripheral chemoreceptors located (2)
- carotid bodies
- aortic bodies
activation of central chemoreceptors does what
stimulates ventilation
what controls ventilation (2)
- central chemoreceptors
- peripheral chemoreceptors
where are central chemoreceptors located
in the medulla on the brain side of the BBB
what do peripheral chemoreceptors do
monitor arterial blood gases
what are the afferent neurons for peripheral chemoreceptors (2)
- CN9- carotid bodies
- CN 10- aortic bodies
what are the 4 lung capacities
- FRC
- IC
- VC
- TLC
what do central chemoreceptors adapt to
chronic CO2 elevation like in COPD
what do peripheral chemoreceptors not do
they do not adapt
what stimulates peripheral chemoreceptors (3)
- increase in PaCO2
- increase in arterial H ions
- decrease in paO2
what drugs have depressant effects on ventilation (2)
- anesthetic agents
- opioids
what makes up IC
IRV + TV
what makes up FRC
ERV + RV
what are the 4 lung volumes
- VT
- IRV
- ERV
- RV
what makes up VC
IRV + TV+ ERV
what makes up TLC
IRV + TV + ERV + RV
what is tidal volume
Amount of air that enters or leaves the lung in a single respiratory cycle at rest(~500ml or 6-8ml/kg)
what is IRV
Additional amount of air that can be inhaled after a normal tidal inspiration
what is ERV
Additional volume that can be expired after a passive expiration
what is RV
amount of air left in the lung after a maximal expiration
In mechanically ventilated patients, ventilator-associated lung injury can occur as a result of (2)
- Volutrauma – diffuse alveolar damage caused by overdistension of the lung.
- Barotrauma – damage to the lung as a result of high airway pressure.
what is FRC
Amount of gas in the lungs at the end of a passive expiration
what is TLC
amount of air in the lung after a maximal inspiration
what is IC
maximal volume of gas that can be inspired from FRC
what is VC
maximal volume that can be expired after a maximal inspiration
why is FRC so important in anesthesia
because with preoxygenation, the FRC is denitrogenated.
why is preoxygenation important
It acts as an O2 reservoir at times of apnoea e.g. at induction of general anesthesia
why is FRC physiologically important (3)
- O2 buffer
- prevention of alveolar collapse
- optimal lung compliance
how does FRC act as an O2 buffer
O2 continuously diffuses from the alveoli to the pulmonary capillaries.
how does FRC prevent alveolar collapse
If FRC did not exist (i.e. expiration to RV) alveoli would collapse.
how does FRC provide optimal lung compliance (2)
- Conveniently, lung compliance is at its lowest at FRC.
- Pulmonary vascular resistance (PVR) is also at its lowest
FRC is reduced by what (5)
- Position
- FRC falls by 1000 mL just by lying supine. - Raised intra-abdominal pressure
- e.g. obesity, pregnancy, acute abdomen, laparoscopic surgery. - Anesthesia
- The cause is not known, but is thought to be related to decreased thoracic cage muscle tone. - Decreasing age
- that is, neonates, infants and young children. - Lung disease
- e.g. pulmonary fibrosis, pulmonary oedema, atelectasis, ARDS
FRC is the balance point between what
the tendency of the chest wall to spring outwards and the tendency of the lung to collapse inwards
FRC is increased by what (4)
- PEEP
-which is commonly used to maintain FRC intraoperatively, especially in pediatric anesthesia and following intubation - Emphysema
-Lung elastic tissue is destroyed, resulting in reduced inward elastic recoil. - Increased height
- Change from supine to erect position
what is intrapleural pressure (2)
- The fluid pressure within the pleural cavity
- It is the outside pressure for the alveoli, airways and vessels
why is intrapleural pressure normally negative
Lungs tend to collapse inwards and chest wall tends to spring outwards
what is the intrapleural pressure at the apices and bases
–10 cmH2O at the apices and –2.5 cmH2O at the bases
what is intramural pressure
- It is the pressure difference that drives air in and out of the lungs during breathing
- It is the pressure gradient across the wall of any tube or sphere
- PTM=Pi-Po
what happens for inspiration to take place (3)
- Intrapleural pressure falls because of the activity of the inspiratory muscles expanding the chest wall.
- This is transmitted across the lung, and alveolar pressure falls towards −1 cmH2O, and as this is less than atmospheric pressure at the mouth, air flows into the lung.
- At the end of inspiration, intrapleural pressure is −8 cmH2O, alveolar pressure is again zero (atmospheric), gas flow into the lungs has ceased and the lung volume has increased by about 500 mL (tidal volume).
what happens for expiration to take place (3)
- When the activity of inspiratory muscles stops, the lung and chest wall reduce in volume as the equilibrium between the expanding chest wall and the elasticity of the lung moves back down to the resting volume.
- Intrapleural pressure increases (becomes less negative) and alveolar pressure becomes positive (equal to +1 cmH2O), and, as this is more than the mouth pressure, gas flows out of the airways and is exhaled.
- At the end of expiration, intrapleural pressure is again −5 cmH2O, alveolar pressure is zero, expiratory flow has ceased and the lung has returned to the resting volume (FRC).
how is O2 carried from the lungs to the tissues (2)
- Bound to Hb, accounting for 98%.
- Dissolved in plasma, accounting for 2%.
the O2 tension of the blood is determined from what
the amount of O2 dissolved in plasma
what does Fick’s law of diffusion state
states that diffusion occurs along a pressure gradient, so O2 diffuses to the tissues from the dissolved portion in the plasma, not from Hb itself.
- O2 then dissociates from Hb as plasma PO2 falls, replenishing the O2 dissolved in the plasma.
what shifts the oxyhemoglobin dissociation curve to the right (6)
- increase in temp
- increase in PaCO2
- increase in 2.3-BPG
- increase in H+
- exercise
- sickle cell
what shifts the oxyhemoglobin dissociation curve to the left (8)
- fetal Hb
- Methemoglobinemia HB
- carbon monoxide poisoning
- stored bank blood
- decrease in temperature
- decrease in PaCO2
- decrease in 2.3- BPG
- decrease in H+
what oxidizing agents can oxidize the Fe2+ in Hb to Fe3+ resulting in Hb called methemoglobin (3)
- nitrates
- prilocaine
- sulphonamides
what does anemia do
decreases the oxygen-carrying capacity of blood without independently altering the P50 of blood
what does polycythemia do
Polycythemia increases the oxygen-carrying capacity of blood without altering the P50 of blood
