Spirometry and respiratory diseases

In a nutshell

There are various lung diseases that can affect lung function. Spirometry can be used to help diagnose and monitor the efficacy of the treatment of these diseases. This summary explores how lung function can be affected by different diseases and describes how lung disease data can be interpreted.

Spirometry 

Doctors can measure lung function using a spirometer which measures the volume of air breathed in and out. A graph is produced which can be interpreted and used to calculate the metrics explained in the table below. 

Note: $$1\ dm^3$$ is the same as $$1\ litre$$.​

These metrics can be shown on a spirogram which is shown below. 

Primary tuberculosis

Primary tuberculosis (TB) is caused by a bacterium and when the immune system detects the bacterium, the immune cells surround the bacteria and build up to form a small lump known as a tubercle.

The presence of tubercles results in the death of the lung tissue which reduces the surface area for gas exchange. This can reduce the tidal volume so less air is inhaled during each breath. To compensate for this, the ventilation rate increases to ensure enough oxygen is taken up. 

There are various symptoms of TB. These are listed below.

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Examples

• Coughing up blood
• High mucus production
• Shortness of breath
• Fatigue
  

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Fibrosis

Definition

Pulmonary fibrosis is a lung disease that results from lung tissue damage and scarring from exposure to asbestos or infection. The damaged lung tissue is thicker than healthy tissue which reduces its elasticity. As a result, the lungs can not expand as much and this decreases the tidal volume and $$FVC$$.​

Another consequence of the thicker scar tissue is an increased diffusion distance. This slows the rate of diffusion and therefore decreases the efficiency of gas exchange. 

In order to compensate for this, the ventilation rate increases to ensure sufficient oxygenation of the blood. 

There are various symptoms of fibrosis. These are listed below. 

Examples

• Shortness of breath 
• Dry cough 
• Fatigue
• Chest pain
• Weakness

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Emphysema

Definition

Emphysema is a lung disease caused by long-term smoking and exposure to high levels of air pollution for a prolonged duration of time. 

Alveoli are crucial for gas exchange and their walls are made with an elastin protein which helps them recoil to expel air when the individual is breathing. 

There are various symptoms of emphysema. These are listed below.

Examples

• Frequent coughing (especially coughs that produce a lot of mucus)
• Shortness of breath
• A whistling noise when breathing
• Chest tightness
  

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Asthma

Definition

Asthma is a chronic respiratory condition that results in the inflammation and irritation of the airways. 

Asthma can be caused by allergies to pollen and dust. An asthma attack is when symptoms of asthma worsen. During this time, the smooth muscle lining the bronchioles contract and excess mucus is produced. This makes it more difficult for the individual to breathe so there is a reduced air flow in and out of the lungs which results in a decreased $$FEV_1$$. ​

There are various symptoms of asthma. These are listed below. 

Examples

• ​Wheezing
  
• Chest tightness
• Shortness of breath

The symptoms above can be alleviated by drugs that are breathed in through inhalers. These drugs cause the bronchiole muscles to relax which increases the air flow. 

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Interpreting lung disease data

Data surrounding lung conditions can be collated and interpreted to identify risk factors for these diseases.

Correlation and causation

Correlation is a link between two variables. However, correlation does not imply causation because there may be other factors influencing the outcome. Causation is when one factor causes a change in another factor. 

Below are graphs showing positive, negative and no correlation. 

Relationship	Description	Example
Positive correlation	​When 'A' increases, 'B' also increases.
Negative correlation	When 'A' increases, 'B' decreases.
No correlation	There is no relationship between 'A' and 'B'.

Describing data 

In an exam, you may be asked to describe data. An easy way to do this is to follow the steps below.