Important Respiratory terms Flashcards
What is Dalton’s law?
In a mixture of non reacting gases Ptotal = Pa + Pb. (P total is the sum of the pressures of individual gases).
What is Boyle’s law?
Pressure and Volume are inversely proportional:
P1V1 = P2V2.
What is Henry’s law?
The solubility of a gas is proportional to the partial pressure of the gas. S1/P1 = S2/P2.
What is the alveolar gas equation?
PAO2 = PiO2 - (PaCO2/R)
What is the acid/base dissociation equation?
CO2 + H2O = H2CO3 = HCO3- + H+
What enzyme catalyses the formation of bicarbonate and hydrogen ions from CO2 and H2O?
Carbonic anhydrase.
What is the henderson hasselbalch equation?
pH = pKa + log (A-)/(HA)
What is Laplace’s law?
P = 2T/R.
What is the significance of Laplace’s law?
It tells us that small alveoli have a greater pressure and so air will move from small alveoli to larger alveoli; uneven aeration. (Surfactant can prevent this).
Define tidal volume (TV).
Volume of air moved into or out of the lungs during normal, quiet breathing.
What is a normal tidal volume?
500ml.
Define inspiratory reserve volume (IRV).
The additional volume of air that can be forcibly inhaled after a tidal volume inspiration.
Define expiratory reserve volume (ERV).
The additional volume of air that can be forcibly exhaled after a tidal volume expiration.
Define inspiratory capacity (IC).
Inspiratory capacity: the sum of IRV and TV.
Define residual volume (RV).
The volume of air remaining in the lungs after a maximal exhalation.
Define functional residual capacity (FRC).
The volume of air remaining in the lungs after a tidal volume exhalation.
What equation can be used to work out FRC?
FRC = ERV + RV.
Define vital capacity (VC).
Vital capacity: the volume of air breathed out after the deepest inhalation.
Approximately equal to Forced Vital Capacity (FVC)
Define total lung capacity (TLC).
The vital capacity plus the residual volume. It is the maximum amount the lungs can hold.
What 2 equations can be used to work out TLC?
- TLC = VC + RV.
- TLC = TV + FRC + IRV.
Define forced expiratory volume in 1 second (FEV1).
Forced expiratory volume in 1 second:
-> The volume of air that can be forcibly exhaled in 1 second of maximal forced expiration from a position of full inspiration.
-> A fraction of the FVC.
Define forced vital capacity (FVC).
The maximum volume of air that can be forcibly exhaled after maximal inhalation. Usually in 6 seconds.
Define peak expiratory flow (PEF).
The greatest rate of airflow that can be obtained during forced expiration. Age, sex and height can all affect PEF.
What is the equation for trans-pulmonary pressure?
Transpulmonary pressure = alveolar pressure - pleural pressure. (TPP is always positive).
What is lung compliance?
A measure of the lung’s ability to stretch and expand. Compliance = ∆V/∆P.
What is the transfer coefficient?
The ability of O2 to diffuse across the alveolar membrane.
How can you find the transfer coefficient?
Low dose CO is inspired, the patient is asked to hold their breath for 10s at TLC, the amount of gas transferred is measured.
Main 3 spirometry measures.
- FEV1
- FVC
- FEV1/FVC ratio
Normal reference ranges for spirometry.
FEV1: >80% predicted
FVC: >80% predicted
FEV1/FVC ratio: >0.7
Spirometry results for obstructive lung diseases.
- Reduced FEV1 (<80% of the predicted normal)
- Reduced/Normal FVC (but to a lesser extent than FEV1)
- FEV1/FVC ratio reduced (<0.7)
Explain obstructive lung diseases and their spirometry results.
Cause:
- Airway obstruction causes an increase in resistance, causing a reduction in airflow
- Increased pulmonary compliance
-> So, shortness of breath -> hard to exhale air
= breathing-out problem
(the air stays in the lung after full expiration)
Explain spirometry results:
- During normal breathing, the pressure volume relationship is no different from in a normal lung.
= FVC normal/reduced (less reduction than FEV1)
- However, when breathing rapidly, greater pressure is needed to overcome the resistance to flow, and the volume of each breath gets smaller.
= FEV1 reduced (more reduction than FVC)
- It is very difficult for a person with an obstructive disease to exhale quickly due to the increase in airway resistance. As a result, the FEV1/FVC ratio will be much lower than normal, for example 40% as opposed to 80%.
= FE1/FVC reduced
Examples:
1. COPD
2. Asthma
3. Emphysema
4. Bronchitis
5. Bronchiectasis
6. Cystic fibrosis
Spirometry results for restrictive lung diseases.
- Reduced FEV1 (<80% of the predicted normal)
- Reduced FVC (<80% of the predicted normal)
- FEV1/FVC ratio normal/high (>0.7)
Explain restrictive lung diseases and their spirometry results.
Cause:
- Reduced lung compliance (‘stretchiness’)
- Increases stiffness inside lung tissue / chest wall cavity
- Reduction in lung volume + lung expansion
-> difficulty in taking air into the lungs
= breathing-in problem
Explain spirometry results:
1. FEV1 reduced (larger than FVC though)
- FVC reduced
- If you can’t breathe in as much, then you won’t be able to breathe out as much, so will be less than normal values. - FE1/FVC ratio normal/high (above 0.7)
- It’s easy for a person with a restricted lung to breathe out quickly, because of the high elastic recoil of the stiff lungs.
- E.G. 90% rather than 80%
Examples:
1. Interstitial lung disease (e.g. pulmonary fibrosis, pneumoconiosis, sarcoidosis)
2. Neurological (i.e. motor neurone disease)
3. Scoliosis or chest deformity
4. Obesity
