Respiration - Weeks 1 to 4 Flashcards
What is the function of the respiratory system?
To ensure that tissues are supplied with adequate O2
To remove CO2 from the lungs produced in metabolism
It does this via gas exchange and blood transport
What is tidal volume?
The volume which is taken in in one breath at rest (quiet respiration)
Define ventilation
The mechanical system which allow to lunds to expand and supply air to the lungs
Define the inspiratory reserve volume
The extra air breathed in, when we breathe deeper at rest
The opposite of the expiratory reserve volume
What creates pressure exerted by gases?
Gas molecules move about and collide, the more frequent or harder the collision, the more pressure a gas can exert
What is partial pressure?
The pressure exerted by a single gas in a mixture. Usually is equal to its percentage in the mixture.
Gases diffuse down partial pressure gradients
Boyle’s Law?
States that pressure is inversely proportional to volume
If constant temperature and constant amount of gas
As more collisions if higher volume in same space
Is a measure for O2 availability
How does Boyle’s Law apply to respiration?
As in inspiration, we are making the lung volume bigger which decreases the pressure in the lungs, so air flows into the lungs (as lower pressure to outside air)
Also, at altitude, air is at a lower pressure so the molecules are further away, so the amount of O2 received in one breath is lower at higher altitude.
Charles’ Law?
States that gases have more energy at higher temperatures, which increases pressure, due to more collisions
Pressure is proportional to Temperature
How do gases interact with fluid?
Dynamic- water can evaporate and gases can dissolve
Water exerts vapour pressure (saturated vapour pressure) when at equilibrium and at a constant temperature
Why is saturated vapour pressure important in respiration?
As gases mix with water in the airways, so SVP contributes to the pressure in the lungs
What is tension?
Equal to the partial pressure, exerted by gases when dissolved in fluid
NOT equal to the amount dissolved, cause gas can react with components
How do you work out how much gas is in fluid?
Amount of gas dissolved in a fluid= tension x solubility
What are the branches after the terminal bronchioles?
The respiratory bronchioles
The alveolar ducts
Alveolar sacs (surrounded by pulmonary capillary network)
Give some features of the pulmonary circulation
Low resistance
Low pressure
Receives the whole cardiac output
Matched by ventilation via hypoxic vasoconstriction
How is the thoracic cavity volume increased (for quiet inspiration)?
Requires work to increase space
Diaphragm contracts
External Intercostal Muscles
Breathing out is passive recoil
What muscles are used in forced expiration?
Internal Intercostal Muscles
Abdominal Muscles
Why would we have forced expiration?
Obstruction
Exercise
Disease States
Define compliance
The stretchiness of the lungs, higher compliance is higher stretch
= volume change/ unit pressure change
What disease increases lung compliance?
Emphysema
What disease decreases compliance?
Lung Fibrosis
How do the lungs reduce surface tension?
Surfactants
They prevent the alveoli from collapsing and one well perfused one becoming enlarged
As lungs expand surfactants get further from each other which keeps the surface tension the same
Describe Respiratory Distress syndrome
Babies born Premature
Lungs are stiff as don’t have enough surfactants
They have few, large alveoli
Breathing and GE is compromised
Can also occur post-trauma
What is resistance?
The opposition to flow through the airways
How do we work out resistance?
Pressure/Rate of Flow
8 x Viscosity x Length / Pi r^4
How does resistance change?
Most comes from upper tract (smaller ones have lower pressure as in parallel)
Higher Resistance in forced expiration harder as lung is compressed
Describe Obstructive Airway Disease
Small airways are narrowed by disease e.g. Asthma, Chronic Bronchitis
Resistance increases earlier in expiration
Breathing out can be difficult
Define Fick’s 1st Law
Law of diffusion
Movement of molecules across a barrier is proportional to permeability x surface area x gradient
What are the values of pO2 and pCO2?
pO2 13.3kPa
pCO2 5.6kPa
How are alveolar and arterial partial pressures related?
In a normal patient, the values are the same
What 2 Factors does diffusion resistance depend on?
The nature of the barrier - thickness, distance, surface area
The nature of the gas - diffusion co-efficient
The Permeability of the Barrier equation =
(Diffusion Co-efficient x Solubility) / Thickness
Diseases associated with Resistance
Fibrotic Lung Disease - Increase thickness
Pulmonary Oedema - Increase distance
What is AVR?
The alveolar ventilation rate
(The Total Volume - Anatomical Dead Space) x Respitation Rate
Define Serial Dead Space
Anatomical DS aka Volume of the Airways
about 150ml
Measure: Nitrogen Washout
Define Distributive Dead Space
Dead/Damaged Alveoli, Alveoli with poor Perfusion
Don’t support gas exchange
Add to Serial DS
What is Physiological Dead Space?
Serial + Distributive Dead Space
Alveolar Ventilation Rate equation
AVR = Pulmonary Ventilation Rate - (Physiological Dead Space x Resp Rate)
Look up Lung Function Tests
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