L4 Principles of Gas Exchange Flashcards
what is ECMO?
Extracorporeal membrane oxygenation (ECMO) is a treatment that uses a pump to circulate blood through an artificial lung back into the bloodstream of a very ill baby. This system provides heart-lung bypass support outside of the baby’s body.
what is the calculation for rate of diffusion?
Rate of diffusion = A x ΔP
A = surface area ΔP = pressure gradient
what is the universal gas equation?
PV = nRT
what is partial pressure of a gas in a mixture of gases?
the pressure that it would exert if it was the only gas in the container
what is dalton’s law (equation)?
the partial pressure of a gas in a gas mixture = total pressure x fractional concentration of the gas
what is 1 atm in: kPa, bar, mmHg and cmH2O?
1 atm = 101.3 kPa 1.013 bar 760 mmHg 1033 cmH20
what are the partial pressures of O2, CO2 and N2 at fractional concentration, at sea level and at an altitude of 5000m?
Oxygen:
21 %
21.3 kPa at sea level
11.8 kPa at 5000m
CO2:
0, 0, and 0
N2:
79 %
80 kPa sea
44.2 kPa 5000m
total % = 100, sea level = 101.3, 5000m = 56
why is partial pressure of oxygen lower in alveoli than room air?
- inspired air is humidified in upper airway
- in alveoli o2 is taken up while co2 is added
- body consumes more o2 molecules than it produces co2 molecules (1.25x)
why do we consume more o2 than we produce co2?
to do with the respiratory quotient which is dependent on diet. carbohydrate diet = respiratory quotient of 1, so for every o2 consumed, one co2 is produced. western diet as a quotient of 0.8 = so for every co2 produced, 1.2 molecules of o2 are consumed (less fat in fat)
what is the saturated vapour pressure of water at 37*C?
6.3 kPa
what is the partial pressure of oxygen at 37*C in fully humidified air?
saturated water vapour pressure = 6.3 kPa
oxygen saturation = 21%
sea level = 101.3 kPa
(101.3 - 6.3) x 0.21 = 19.95 kPa
what is the typical value of alveolar partial pressure of co2?
5 kPa
what is henry’s law?
solution in equilibrium with gas on top of it, the partial pressure of gas in solution is equal to the pp of gas above its surface
how does a partial pressure of a gas in solution relate to its solubility?
partial pressure of a gas in solution is inversely proportional to its solubility
greater the solubility, the more molecules can be accommodated for a given pp
(anaesthetic is given as a low solubility gas so it when it gets to brain it comes out of solution faster)
which one is more soluble, co2 or o2?
co2 is approx. 24 times more soluble in water than is oxygen
therefore co2 exerts a less pp than o2 for given number of molecules in solution
what is the relative density, relative water solubility, relative diffusing capacity and pp gradient (kPa) of o2 and co2?
relative density: o2 = 1.00, co2 = 1.37
relative water solubility: o2 = 1.00, co2 = 24.0
relative diffusing capacity: o2 = 1.00, co2 = 20.5
pp gradient: 02 = 8.3 kPa, 6.1 kPa
(co2 diffuses quicker than o2)
what is the difference between type I and type II respiratory failure?
Type I respiratory failure involves low oxygen, and normal or low carbon dioxide levels. Type II respiratory failure involves low oxygen, with high carbon dioxide.
how do you measure oxygen diffusing capacity?
oxygen uptake / (alveolar pO2 - mean pulmonary capillary PO2)
how do you measure carbon monoxide diffusing capacity and why is this used more than oxygen diffusing capacity?
carbon monoxide uptake - alveolar PCO (effectively 0 bc of very high affinity of CO for haemoglobin)
used more often as alveolar PO2 is very hard to measure
what is alveolar fibrosis?
thickening of the alveolar wall
leads to decreased rate of diffusion and inc time for diffusion
blood is not fully oxygenated, can lead to type I respiratory failure
what is pneumonia?
alveolar consolidation
bacterial infection fills lung
alveolus is blocked
blood goes around alveolus and is not oxygenated, is not participating in gas exchange
what is pulmonary edema?
frothy secretions
mismatch of left and right sides of heart. left supplies body, right supplies lungs. mismatch means right keeps pushing into lungs but left does not pull out of lungs (if non functional). need to offload left side of heart
what is interstitial edema?
systemic inflammatory response.
what is emphysema?
alveolar-capillary destruction
easy to ventilate as has no tissue inside the lungs. lungs damaged by smoking. alveolus destroyed. also by vit deficiency. insufficient gas exchange.
what is atelectasis?
alveolar collapse
older or larger patient who has lost elasticity in lungs. lung collapse.
what is compliance?
ability of us to expand our lungs, the amount of gas we remove for each change in pressure/force in lungs.
opposite of elasticity
= 1/elasticity
