Lung volumes notes PDF

Preview

Summary

07.LUNG VOLUMES1. RANGE OF PULMONARY FUNCTION TESTSi. Assessment of airways resistance ii. Lung volumes (spirometry) iii. Pulmonary diffusing capacity iv. Arterial blood gases v. Exercise capacity vi. Lung/chest compliance2. WHEN WOULD WE ASSESS LUNG FUNCTION?i. Screening for the presence of obstruc...

Description

07.12.18

LUNG VOLUMES 1. RANGE OF PULMONARY FUNCTION TESTS i.

Assessment of airways resistance

ii.

Lung volumes (spirometry)

iii.

Pulmonary diffusing capacity

iv.

Arterial blood gases

v.

Exercise capacity

vi.

Lung/chest compliance

2. WHEN WOULD WE ASSESS LUNG FUNCTION? i.

Screening for the presence of obstructive and restrictive diseases

ii.

Evaluating the patient prior to surgery

iii.

Evaluating the patient's condition for weaning from a ventilator. If the patient on a ventilator can demonstrate a vital capacity (VC) of 10 - 15 ml/Kg of body weight, it is generally thought that there is enough ventilatory reserve to permit (try) weaning and extubating.

iv.

Documenting the progression of pulmonary disease - restrictive or obstructive

v.

Documenting the effectiveness of therapeutic intervention

3. LUNG VOLUMES AND CAPACITIES The total volume in the lungs is subdivided into named volumes and capacities A. Volumes i.

Do not overlap

ii.

Cannot be further divided

iii.

When added together, equal total lung capacity

B.

Capacities i.

Subdivisions of the total volume that include two or more of the 4 basic lung volumes

4. S P I R O M E T R Y

2

i.

Spirometers vary widely - the ones we use look like this

ii.

The general principal is that as air is blown through the turbine, the flow rate is measured and used to calculate the volume

iii.

If the details of the participant are entered (age, sex, race, height, weight) then they can be used to calculate the percentage of a normative value

5. SLOW VITAL CAPACITY (SVC OR VC) MANOEUVRE (STATIC) These measurements are useful because they are not limited by constriction of the airways (there is no time restriction for inhalation or exhalation) and do not require a lot of motivation and effort from the patient A. Put on nose clip B. Inhale maximally C. Put mouthpiece into mouth D. Blow out fully, stopping only at maximal exhalation E. Remove mouthpiece without inhaling through monitor

6. FORCED VITAL CAPACITY (FVC) MANOEUVRE (DYNAMIC) To get started right away, just tap any placeholder text (such as this) and start typing. A. This is the same as the SVC except that the patient needs to BLOW as HARD and FAST as possible during the exhalation stage B. You would normally repeat the measure three times, and take the best of the three C. It is not a comfortable procedure and the patient may need a rest between each attempt D. A disadvantage of this procedure is that it requires a lot of effort and motivation from the patient; if they are in pain or feel unwell, they may not fully inhale or exhale, or may make little effort. E. You would normally perform a slow VC in addition to this, if you wanted to assess static volumes and capacities

3

7. FORCED EXPIRATORY VOLUME IN 1 SECOND (FEV 1 AND FORCED EXPIRATORY RATIO (FER) (DYNAMIC) A. In this procedure, the patient is asked to take a deep breath in and blow out as fast and as far as possible B. The FEV1 (Forced Expiratory Volume in 1 second) is a measure of the rate of air flow – the higher the value, the faster the flow C. The FVC (Forced Vital Capacity) is the total volume the patient can exhale forcibly D. The ratio of FEV1 to FVC (FER) is a measure of the patency of the airway –f the value is below 80% it suggests that the airway is constricted

8. RESPIRATORY DISORDERS A. Restrictive disorder i.

A disorder which restricts the expansion of the lungs

ii.

May be caused by stiffness of the lungs or chest wall, weakness of the muscles or damaged nerves

iii.

Examples:

B.

4

-

Pulmonary fibrosis

-

Sarcoidosis (an autoimmune immune disease)

-

Obesity

-

Muscular dystrophy

Obstructive disorder i.

A disorder in which the airways are narrowed

ii.

Air is exhaled more slowly than normal

iii.

Residual volume may be higher than normal

iv.

Examples:

-

Chronic obstructive lung disease (COPD) including chronic bronchitis and emphysema

-

Asthma

-

Cystic fibrosis

C. Restrictive respiratory diseases i.

Makes it more difficult to get air into the lungs.

ii.

They “restrict” inspiration.

iii.

Decreased VC; decreased TLC, RV, FRC

D.

5

Obstructive respiratory diseases i.

Makes it more difficult to get air out of the lungs.

ii.

Decrease FVC; increased TLC, RV, and FRC

9. WHOLE BODY PLETHYSMOGRAPHY

6

i.

The patient sits in a sealed box, breathing from the outside air

ii.

The changes in thoracic volume during breathing cause changes in the box pressure

iii.

This can be used to measure any of the lung volumes, but is particularly useful for measuring airways resistance, TLC and RV

10.

PEAK EXPIRATORY FLOW RATE (PEFR) (DYNAMIC) This test can be affected by motivation and effort e.g. someone who is tired or in pain may not get a representative result i. 7

Take a deep breath in

11.

ii.

BLOW as fast and as hard as possible

iii.

It is not necessary to exhale fully

iv.

This gives you the maximum flow rate that the person can generate

v.

It is dependent upon the diameter of the airway, so can be used to detect airway obstruction

HELIUM DILUTION Used to measure residual volume

8

i.

Helium does not cross the barrier between the alveoli and the blood

ii.

The patient inhales gas of a known concentration from a container of known volume

iii.

After breathing for several minutes, the concentration of helium in the lungs + container stabilises

iv.

The concentration of helium can then be used to calculate the volume of the lungs + container (and therefore the TLC)

v.

The residual volume can be calculated by subtracting the VC from TLC

12.

FLOW-VOLUME LOOPS (DYNAMIC)

9

i.

The patient inhales and exhales through a spirometer

ii.

Inhalation on the graph starts at the righthand side, and the volume trace goes downwards!

iii.

Exhalation goes upwards and from left to right

iv.

Diagnosis is supported by the combination of peak flow, lung volumes and overall shape of the loop (which shows anomalies in airways resistance)...