Important Respiratory terms

Question 1

What is Dalton’s law?

Answer 1

In a mixture of non reacting gases Ptotal = Pa + Pb. (P total is the sum of the pressures of individual gases).

Question 2

What is Boyle’s law?

Answer 2

Pressure and Volume are inversely proportional:
P1V1 = P2V2.

Question 3

What is Henry’s law?

Answer 3

The solubility of a gas is proportional to the partial pressure of the gas. S1/P1 = S2/P2.

Question 4

What is the alveolar gas equation?

Answer 4

PAO2 = PiO2 - (PaCO2/R)

Question 5

What is the acid/base dissociation equation?

Answer 5

CO2 + H2O = H2CO3 = HCO3- + H+

Question 6

What enzyme catalyses the formation of bicarbonate and hydrogen ions from CO2 and H2O?

Answer 6

Carbonic anhydrase.

Question 7

What is the henderson hasselbalch equation?

Answer 7

pH = pKa + log (A-)/(HA)

Question 8

What is Laplace’s law?

Answer 8

P = 2T/R.

Question 9

What is the significance of Laplace’s law?

Answer 9

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).

Question 10

Define tidal volume (TV).

Answer 10

Volume of air moved into or out of the lungs during normal, quiet breathing.

Question 11

What is a normal tidal volume?

Answer 11

500ml.

Question 12

Define inspiratory reserve volume (IRV).

Answer 12

The additional volume of air that can be forcibly inhaled after a tidal volume inspiration.

Question 13

Define expiratory reserve volume (ERV).

Answer 13

The additional volume of air that can be forcibly exhaled after a tidal volume expiration.

Question 14

Define inspiratory capacity (IC).

Answer 14

Inspiratory capacity: the sum of IRV and TV.

Question 15

Define residual volume (RV).

Answer 15

The volume of air remaining in the lungs after a maximal exhalation.

Question 16

Define functional residual capacity (FRC).

Answer 16

The volume of air remaining in the lungs after a tidal volume exhalation.

Question 17

What equation can be used to work out FRC?

Answer 17

FRC = ERV + RV.

Question 18

Define vital capacity (VC).

Answer 18

Vital capacity: the volume of air breathed out after the deepest inhalation.

Approximately equal to Forced Vital Capacity (FVC)

Question 19

Define total lung capacity (TLC).

Answer 19

The vital capacity plus the residual volume. It is the maximum amount the lungs can hold.

Question 20

What 2 equations can be used to work out TLC?

Answer 20

1. TLC = VC + RV.
2. TLC = TV + FRC + IRV.

Question 21

Define forced expiratory volume in 1 second (FEV1).

Answer 21

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.

Question 22

Define forced vital capacity (FVC).

Answer 22

The maximum volume of air that can be forcibly exhaled after maximal inhalation. Usually in 6 seconds.

Question 23

Define peak expiratory flow (PEF).

Answer 23

The greatest rate of airflow that can be obtained during forced expiration. Age, sex and height can all affect PEF.

Question 24

What is the equation for trans-pulmonary pressure?

Answer 24

Transpulmonary pressure = alveolar pressure - pleural pressure. (TPP is always positive).

Question 25

What is lung compliance?

Answer 25

A measure of the lung’s ability to stretch and expand. Compliance = ∆V/∆P.

Question 26

What is the transfer coefficient?

Answer 26

The ability of O2 to diffuse across the alveolar membrane.

Question 27

How can you find the transfer coefficient?

Answer 27

Low dose CO is inspired, the patient is asked to hold their breath for 10s at TLC, the amount of gas transferred is measured.

Question 28

Main 3 spirometry measures.

Answer 28

1. FEV1
2. FVC
3. FEV1/FVC ratio

Question 29

Normal reference ranges for spirometry.

Answer 29

FEV1: >80% predicted
FVC: >80% predicted
FEV1/FVC ratio: >0.7

Question 30

Spirometry results for obstructive lung diseases.

Answer 30

1. Reduced FEV1 (<80% of the predicted normal)
2. Reduced/Normal FVC (but to a lesser extent than FEV1)
3. FEV1/FVC ratio reduced (<0.7)

Question 31

Explain obstructive lung diseases and their spirometry results.

Answer 31

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:

1. During normal breathing, the pressure volume relationship is no different from in a normal lung.

= FVC normal/reduced (less reduction than FEV1)

2. 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)

3. 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

Question 32

Spirometry results for restrictive lung diseases.

Answer 32

1. Reduced FEV1 (<80% of the predicted normal)
2. Reduced FVC (<80% of the predicted normal)
3. FEV1/FVC ratio normal/high (>0.7)

Question 33

Explain restrictive lung diseases and their spirometry results.

Answer 33

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)

2. 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.
3. 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