Respiratory Physiology Flashcards
Issues with respiratory physiology in aviation
Toxic gases and fumes Hypoxia Life support systems Accident investigation Vibration G Lung diseases Trapped gases
Partial pressure of gas at sea level
Nitrogen 593mmHg
Oxygen 160 mmHg
Other 7mmHg
Total 760mmHg
Partial pressure of the gases in Tracheal and why there is a difference
Nitrogen 538mmHg
Oxygen 149mmHg
CO2 26mmHg
Water vapour 47 mmHg
Change is due too water vapour
Partial pressure of gas at the Aveolar and why the change
Oxygen 103mmHg
Due to metabolic effect (CO2 dilutes gases)
Describe Oxygen Cascade
Atmosphere to trachea - Humidification (47mmHg water vapour. O2 149mmHg
Trachea to alveolus - Alveolar gas equation
- metabolic effect = O2 103mmHg, CO2 40mmHg
Alveolus to pulmonary capillary - Difusion - O2 95 mmHg?
Pulmonary capillary to artery - physiological shunt
Function of respiratory system
Gas exchange Heat exchange Blood reservior Immunological functions Hormonal/enzyme function
Function of Upper respiratory tract
Warming
Humidification
Filtration
Mechanics of respiration
Inspiration is active - overcome both elastic recoil and viscous forces
Expiration is passive at rest - Accessory muscle use when exercising. Utilise stored energy to overcome airways resistance
What is the work of breathing and what compounds can increase or decrease it
Respiratory work 1-2% of BMR
Component
- Resistance
— airways
— Inertial load of gas - related to density
- Compliance
—Parenchyma - effected by eg oedema
— Chest wall - effected by eg obesity or kidneys
Vital importance of surfactant - hold aveola open
Control of minute ventilation
Central - in brain stem. Centres in medulla, inputs from other centres to pons. Higher control eg emotional and pain.
Chemoreceptors - homeostatic control
- central - predominantly CO2
—- located in medulla on floor of 4th ventricle detect H+ in CSF
- peripheral: in aorta and carotid bulb. PaO2 threshold in <55mmHg. Results in sympathy-adrenal activation
Lung receptors
- irritant receptors - initiate cough response
- stretch receptors- prevents over inflation
- J receptors - responds to Pul HTN
Peripheral receptors
- muscle spindles - signal = increase resp rate
- pain, temperature
Hormonal
Describe hypoxic ventilators response
Peripheral chemoreceptors cause an increase in minute ventilation irrespective of PaCO2
Hyperventilation always occurs with hypoxia
The law of gaseous diffusion
A gas will move down a pressure gradient from an area of higher pressure to an area of lower pressure.
It’s a passive process with no transporters
No carriers/receptors
Moves based on concentration and solubility
Oxygen is very insoluble and needs high pressure gradient to move it.
Explain Fick’s law of diffusion
Diffusion is proportion to SA and Pressure. Inversely to thickness.
Describe the A-a gradient and what it means and what effects it
A-a Gap = PAO2-PaO2
Is a marker of oxygen exchange
Measure V/Q scatter
Occurs due to - Shunts - pathological (eg pneumonia) and anatomical - Dead space - air without blood - Diffusion limitation V/Q mismatch
A-a gradient 5-15mmHg with mean ~8. Increases with age.
Hypoxemia with normal gradient = hyperventilation
Hypoxemia with widened gradient = V/Q mismatch, diffusion limitation (response to O2) or shunt (poor response to O2)
Vascular tone in response to O2
Skeletal - reduced O2 = vasodilation
Lung - reduce O2 = vasoconstriction (about 50%) can result in pul HTN if enough
Explain V/Q mismatching and west zones
V/Q mismatching is a difference between vascular flow and air flow.
Zone 1: PA>Pa>Pv
Zone 2. Pa>PA>Pv. Ideal
Zone 3: Pa>Pv>PA
Majority are zone 2.
More alveolus in the bases of the lung and gravity means more blood in the bases as well.
Effects of VQ mismatch on gas exchange
PaCO2 - no effect. Increased ventilation due to increasing PaCO2 dissociation curve
PaO2 - hypoxemia with widen A-a gap. Inability to compensate with increase ventilation as blood already saturated. Need supplemental oxygen
Explained diffusion limitation vs perfusion limited
At rest at sea level movement of Oxygen from aveolar to blood is limited by perfusion due to high concentration gradient of O2 from aveolar of 103 to blood at 40mmHg that the 02 moves in to blood and saturation is affect at 1/3 of the distance across capillary. This means the rate of O2 saturation is based on the speed of perfusion through the capillaries. Curve is steep and then plateaus
At Altitude the concentration of the alveolar O2 is reduced = reduced pressure gradient from alveolar to blood which reduces the movement of Oxygen combined with the insolubility of 02. This means that oxygen becomes diffusion limited and requires more time to diffuse into the blood which flattens the curve.
Explain the oxygen- haemoglobin Dissociation curve
Hb bind 4x02
- the first is bound tight and the last is bound loose
At the tissue there is low partial pressure of 02 which causes disassociation for 02 from Hb.
In certain conditions eg increase H+, ^ temp, ^2,3 DPG, increase CO2, increase Altitude = right shift due to the increase in O2 offloading = lower saturation at tissues
In certain conditions eg reduce H+, reduced CO2, reduced temp, reduced 2,3 DPG, reduce altitude, HbF and Met Hb. Shifts the curve Left as less O2 is unloaded at tissues.
Called the Bohr effect is the right shift
How is CO2 carried in the blood
Dissolved, 5% in arterial
Bicarbonate 90%
carb amino 5%
Haldane effect
Describes how with offloading of O2 a the tissues, deoxygenated blood is a better carrier of CO2 as deoxygenated-haemoglobin.
Has increase affinity for CO2
Is a better a buffer
Partial pressure of O2 at tissue and mitochondria
Tissue ~30mmHg
Mitochondria ~1-3mmHg (5mmHg)
Pasteur point
Is the cellular PO2 below which aerobic metabolism cannot occur.
~ 1mmHg
