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.

Metric	Description
Tidal volume	The tidal volume is the volume of air in each breath. A healthy tidal volume for an adult is $0.4\ dm^3 - 0.5\ dm^3$ .
Ventilation rate	The ventilation rate is the number of breaths per minute. A healthy ventilation rate for an adult is $15$ breaths per minute.
Forced expiratory volume ( $FEV_1$ )	The forced expiratory volume is the maximum volume of air that can be expelled from the lungs in one second.
Forced vital capacity ( $FVC$ )	The forced vital capacity is the maximum volume of air that can be expelled forcefully following a deep breath.

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

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

Biology; Substance exchange; KS5 Year 12; Spirometry and respiratory diseases — 1. Tidal volume, 2. Forced vital capacity, 3. Ventilation rate

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.

Examples

Coughing up blood
High mucus production
Shortness of breath
Fatigue

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

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.

1.	Particles from cigarette smoke or in polluted air will become trapped in the alveoli.
2.	These particles cause inflammation of the alveoli which alerts the immune cells, such as phagocytes, that there are foreign particles present.
3.	The phagocytes produce an enzyme that breaks down the elastin in the alveoli walls which reduces their ability to expel air by reducing their ability to recoil.
4.	The enzyme will eventually break down the walls of the alveoli which reduces the surface area available for gas exchange.
5,	To compensate, the individual's ventilation rate will increase.

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

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.

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.

1.	Identify if there is an increase, decrease, plateau or no pattern at all.
2.	Draw a conclusion and state any correlation.
3.	Consider any influencing variables that may not have been mentioned or limitations of current data.

Learn with Basics

Length:

Unit 1

Structure and function of the human gas exchange system

Unit 2

The respiratory system and breathing rate

Jump Ahead

Optional

Unit 3