Clinical Lecture Problem 1 - Respiratory problems

Question 1

What is TLC?

Answer 1

Total lung capacity - volume of air in the lungs at maximal inflation (TLC = VC + RV).

Question 2

What is TV/VT?

Answer 2

Tidal volume - volume of air moved into or out of the lungs during quiet breathing.

Question 3

What is RV?

Answer 3

Residual volume - volume of air remaining in the lungs after maximal exhalation.

Question 4

What is ERV?

Answer 4

Expiratory reserve volume - maximal volume of air that can be exhaled from the end-expiratory position.

Question 5

What is IRV?

Answer 5

Inspiratory reserve volume - maximal volume of air that can be inhaled from end-inspiratory level.

Question 6

What is IC?

Answer 6

Inspiratory capacity - IC = IRV + TV.

Question 7

What is VC?

Answer 7

Vital capacity - volume of air breathed out after deepest inhalation.

Question 8

What is FVC?

Answer 8

Forced vital capacity - the determination of the vital capacity from a maximally forced expiratory effort.

Question 9

What is FEV1?

Answer 9

Forced expiratory volume 1 - the volume that has been exhaled in one second after full inspiration.

Question 10

What is PEF?

Answer 10

Peak expiratory flow - highest forced expiratory flow measured with a peak flow meter.

Question 11

What is FEV1/FVC ratio?

Answer 11

It is a ratio used in the diagnosis of obstructive and restrictive lung disease. In normal people FEV1/FVC should be around 75-80%.

Question 12

What is FEV1/FVC ratio in obstructive diseases?

Answer 12

In obstructive diseases such as COPD, asthma, emphysema FEV1 is diminished due to an increase in airway resistance to expiratory flow, this will cause the ratio to decrease to <80% and usually around 45%.

Question 13

What is FEV1/FVC ratio in restrictive diseases?

Answer 13

In restrictive diseases such as pulmonary fibrosis FEV1 and FVC are reduced proportionally (both reduce). This can result in a normal or even increased ratio.

Question 14

What is the pathophysiology of obstructive lung diseases?

Answer 14

There is reduced flow at all lung volumes but flow is disproportionately reduced over mid and low lung volumes. There is an increase in RV, therefore increase in FRC so the pt will breathe at higher lung volumes - this is uncomfortable because at higher lung volumes the lung is less compliant. You will also see a major decrease in FEV1 hence a decrease in FEV1/FVC ratio.

Question 15

What happens with work of breathing in obstructive lung diseases?

Answer 15

There is more resistive work of breathing as the pt is breathing through a narrow tube. In order to optimise total respiratory work (in order to decrease total work of breathing) they breathe the same amount of air at higher lung volumes with slower frequency )deep and slow breaths). This means the pt will increase their elastic work of breathing since the lung is less compliant at high lung volumes (increase in elastic pressure) - C=V/P

Question 16

What is the pathophysiology of restrictive lung diseases?

Answer 16

There is markedly reduced TLC and reduced RV. There is a proportional decrease in FVC and FEV1 therefore normal ratio. At same absolute lung volume, flows are increased due to more elastic recoil.

Question 17

What is the pathophysiology of late inspiratory crackles?

Answer 17

When a person has interstitial lung disease (restrictive) there is basal airway closure with abnormal stiff small airways (the airways are non-compliant). In early inspiration the pt cannot generate enough negative pleural pressure to open the airways. In late inspiration the pt can generate enough negative pressure to open the non-compliant airways, so they snap open (crackle sound).

N.B. normal tidal breathing has no basal airway closure.

Question 18

What is the pattern of breathing with restrictive lung diseases?

Answer 18

In a pt with restrictive lung diseases they have decreased compliance.

1. Rest - normal tidal breathing requires more respiratory work (more elastic work) than a healthy individual.
2. Exercise - pt is SOB (rapid and shallow breathing) due to increased total respiratory work, there is more elastic work of breathing. In order to optimise total respiratory work they breath smaller volumes (Vt) with increased frequency, this means more resistant work of breathing when breathing rapid and shallow.

Question 19

What is the pattern of breathing for a normal healthy person?

Answer 19

1. Rest - normal tidal breathing requires some respiratory work.
2. Exercise - there is an increase in frequency and volume of tidal breathing, thus increased respiratory work (more elastic work).