CBT2 Ventilation and gas exchange Flashcards
Define Tidal volume (TV or V small T)
The volume of air inspired and expired during regular breathing (i.e. gentle normal breathing not deep breathing)
Define Inspiratory reserve volume (IRV)
The volume of air that can be inspired after a tidal inspiration
Define Expiratory reserve volume (ERV)
The volume of air that can be expired after a tidal expiration
Define Residual volume (RV)
The volume of air that cannot be emptied from the lungs, no matter how hard you expire. This is fixed because of the lung-chest wall interface
How do you calculate the total lung capacity? (TLC)
RV + IRV + TV + ERV
How do you calculate the functional residual capacity (FRC)
RV + IRV. The volume of air in the lungs following a tidal expiration at rest. This capacity represents the “default” volume of the lungs, when the lung recoil (inwards) and chest recoil (outwards) are in equilibrium
How do you calculate inspiratory capacity (IC)
TV + IRV. The maximum volume of air the lungs can draw in from the equilibrium FRC point
How do you calculate vital capacity (VC)
TLC – RV; or, TV + IRV + ERV. The volume of air between the maximum and minimum achievable volumes (range)
What factors affect all the different breathing and lung volumes?
Height is the most influential, but others include:
- age
- genetics
- aerobic
- fitness
- disease
- developmental exposure to altitude
What does dead space describe? (V small D)
Generic term that describes parts of the airways that do not participate in gas exchange (e.g. conducting and respiratory airways)
What are the three types of dead space?
1) Anatomical dead space
2) Alveolar dead space
3) Physiological dead space
Describe Anatomical dead space
This includes the entirety of the conducting airways and the upper respiratory tract (oral/nasal cavity, pharynx and larynx). This value cannot be measured using standard spirometry. It requires a dilution test with a known volume of inert gas (e.g. helium)
Describe Alveolar dead space
This includes respiratory tissues unable to participate in gas exchange, usually due to an absent or inadequate blood flow. In healthy individuals, this volume is effectively zero
Describe Physiological dead space
This is the sum of anatomical and alveolar dead space volumes
How many generations are there in the conducting zone?
16 generations
Typically how many ml are there in the anatomical dead space?
150ml in adults at FRC
What are non-perfused parenchyma?
Alveoli without a blood supply
How many generations is the respiratory zone?
7 generations
How many ml is the respiratory zone in adults? (referred to as alveolar ventilation)
350ml
What is the amount of air moving in and out of the lungs per minute referred to?
pulmonary ventilation (V small E)
How is pulmonary ventilation calculated?
TV x breathing frequency
What is the primary function of breathing?
Ventilation of the alveolar tissue
What is alveolar ventilation?
The amount of air per minute reaching the gas exchange surface
How do you calculate alveolar ventilation during tidal breathing?
It is equal to the difference between tidal volume and dead space multiplied by breathing frequency (V small alv = ((VT - VD) x Rf).
Typically, for every generation further down the airway there is a divergence in the path associated with a _____ decrease in the pressure and velocity of airflow.
50%
At rest, how are the mechanical forces of the lungs balanced?
At equilibrium
How can the balance of mechanical forces be distorted, in order to stimulate ventilation?
Increasing pressure outside of the lung, or decreasing pressure inside the lung
What is positive-pressure breathing?
Increasing pressure outside of the lung (e.g. a patient on a ventilator)
Explain negative-pressure breathing, i.e. inhalation under normal conditions
The respiratory muscles decreases intrathoracic pressure (diaphragm contracts downward towards the abdomen and the external intercostal muscles pull the ribcage outwards and upwards) by creating a partial vacuum; the lung as an elastic expandable tissue stretches to fill the space which sucks air in from the outside the body to normalise the pressure.
At rest, with no activation of the respiratory muscles, the volume of the lungs is equal to the ________
functional residual capacity (FRC)
Explain exhalation
The fixed intrapleural volume must comply and hence the lung must expand. In this case, the force of the diaphragmatic contraction/chest wall expansion exceeds the recoil force of the lung tissue. At the end of inspiration, the chest wall force subsides and lung recoil passively empties the lungs.
Resistance in the lung is proportional to.. ?
Poiseuille’s Law
- The viscosity of a fluid (including air) x the length of the tube
- and is inversely proportional to the fourth power of the radius
Resistance = 8nl/pie(r^2)
n=viscosity
l=length
Explain why resistance doesn’t increase the deeper you get into the lungs
The constant generational divergence in the airways means that the cumulative cross-sectional area increases dramatically in the small airways (as you are dividing by the area in Poiseuille’s equation, as the area increases, the resistance decreases)
Explain the resistance from generation 0>23
Resistance is greatest in the fourth generation of the respiratory network, after which it decreases exponentially.
What is the nomenclature to describe partial pressure of water vapour in expired air?
italic P small E H small 2 O
What is the nomenclature to describe the carbon dioxide content in mixed venous blood?
Cv̄CO small 2
What is the nomenclature to describe the oxygen saturation of Hb in arterial blood?
SaO small 2
What do these prefixes describe?
- P (italic)
- F
- S
- C
- Hb
P (italic)= Partial pressure (kPa or mmHg) F= Fraction (% or decimal) S= Hb Saturation (%) C= Content (ml) Hb= Volume bound to hb (ml)
What do these subscript letters mean?
- I
- E
- A
- a
- v̄
- P
- D
- I = inspired
- E = expired
- A = alveolar
- a = arterial
- v̄ = mixed venous
- P = peripheral
- D = dissolved
Who else can italics P be used?
if you were discussing arterial oxygen you could simply refer to PO2
What is the purpose of breathe?
Fundamentally, the purpose of breathing is to maintain oxygen delivery to cells that are undertaking aerobic respiration (the process of releasing stored energy from food).
What is the basic equation for respiration?
C6H12O6 +6O2 -> 6CO2 + 6H2O + energy
What is fick’s law of diffusion?
Molecules diffuse from regions of high concentration to low concentration at a rate proportional to the concentration gradient (P1-P2) , the exchange surface area (A) and the diffusibility of the gas (D), and inversely proportional to the thickness (T) of the exchange surface.
What is the equation for fick’s law
V gas = (A/T) x D x [P1 -P2]
What is Henry’s law?
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the solubility (α) of the gas and the partial pressure (P) of the gas in equilibrium with that liquid.
What is the equation for Henry’s Law?
C small D = αgas x Pgas
What is the composition of atmospheric gas?
- 78.2% nitrogen
- 20.9% oxygen
- 0.9% argon
- 0.04% carbon dioxide
- 0.01% a number of inert gases (neon, xenon, helium, hydrogen)