Ventilation and gas exchange Flashcards
What is minute ventilation and how do you calculate it?
Gas leaving and entering the lungs Minute ventilation (L/min)= Tidal volume (L) x Breathing freq. (breaths/min)
What is alveolar ventilation and how do you calculate it?
Gas entering and leaving the alveoli Alveolar ventilation (L/min) = (Tidal volume (L) - Dead space (L)) x breathing freq. (breaths/min)
What factors affect lung volume and capacity?
Body size (more height than weight) Fitness Age Disease (pulmonary, neurological) Sex
What is anatomical dead space?
Conducting zone of lungs with no gas exchange
Includes 16 generations of bronchiol bifurcations.
Typically 150ml in adults at FRC (functional residual capacity)
What is alveolar dead space?
Non-perfused parenchyma (part that carries out the function) with no gas exchange
Alveoli have no blood supply
Typically 0ml in adults
What is the respiratory zone?
Aka. alveolar ventilation
7 generations of bronchiol bifurcations
Typically 350ml in adults
What can increase dead space?
Anaesthesia circuit
Snorkelling
What decreases dead space?
Tracheostomy
Cricothyrotomy
What is the chest wall relationship?
Chest wall has tendency to spring outward and lung has tendency to recoil inwards
These forces are in equilibrium at end- tidal expiration (FRC) which is ‘neutral’ position of intact chest
Chest recoil = lung recoil
Inspiratory muscle effort + chest recoil >lung recoil
Expiratory muscle effort + lung recoil > chest recoil
What is the importance of pressure gradients?
Pressure gradients drive airflow
Normal breathing is called negative pressure breathing as Palv < Patm
What happens to air as it goes through our lungs?
As air enters our lungs its warmed, humidified and slowed down meaning pressure changes as you move from conducting zone to respiratory airways
What is transmural pressure?
Pinside - Poutside = transmural Pa
Same as transpulmonary pressure (Palv - Ppl)
What is transthroacic pressure?
PTT= Ppl- Patm
Difference between pressure in pleural cavity and atmosphere
What is trasresipratory pressure?
PRS= Palv - Patm
Difference between alveolar pressure and atmospheric pressure
What is transpulmonary pressure?
PTP = Palv- Ppl
Difference in pressure between alveoli and pleural cavity
What are the different gas laws?
Dalton Fick Henry Boyle Charles
What does Dalton’s gas law state?
Pressure of a mixture is equal to the sum of partial pressures in that mixture
What does Fick’s gas law state?
Molecules diffuse from region of high conc. to low conc. at a rate proportional to the conc. gradient (P1-P2), the exchange SA (A) and the diffusion capacity (D) of the gas and inversely proportional to the thickness (T) of the exchange surface:
Vgas = (A/T) D [P1-P2]
What does Henry’s gas law state?
At constant temp., amount of gas that dissolves in a given type and volume of liquid is directly proportional to PP. of that gas in equilibrium with that liquid
C = Agas Pgas
C= conc. of dissolved gas
Agas= henrys constant/ diffusion constant
Pgas= pressure of gas
What does Boyle’s law state?
At constant temp. volume of gas is inversely proportional to pressure of that gas
Pgas ∝ 1/Vgas
What does Charle’s law state?
At constant pressure, volume of gas is proportional to temp. of gas
Vgas ∝ Tgas
How do we calculate oxygen solubility?
Foe this we use henrys law C= KPgas Where C= solubility of gas K= henry's constant Pgas= Partial pressure of gas
For oxygen:
CO2 = 0.024 (constant) x 13.5
CO2= 0.32mLdL^-1
CO2= 0.32 x 10 (dL^-1 to L^-1) x 5L (L of blood) = 16mLmin^-1
Is dissolved O2 enough?
Dissolved O2 is only 16mLmin^-1 and we require 250mLmin^-1 therefore dissolves O2 alone is not enough so we need haemoglobin
How is haemoglobin structured?
Hb monomers consist of ferrous iron ion (Fe2+) at centre of a tetrapyrrole porphyrin ring connected to a protein chain- covalently bonded at proximal histamine reside
