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Simplified Understanding of Lung Capacity and Lung Conditions

Lung capacity refers to the total amount of air inside the lungs at certain phases of the respiratory cycle. The several components of lung capacity have different characteristics and may be altered by lung and airway conditions, age and lifestyle choices.

Lung Capacity and Lung Conditions

Several lung conditions can affect lung capacity and make breathing slowly become more difficult over time. These lung conditions may be classified as either obstructive lung disease or restrictive lung disease.

The average human respiratory rate is 30-60 breaths per minute at birth,[1] decreasing to 12-20 breaths per minute in adults. The average total lung capacity of an adult human male is about 6 litres of air.

The maximum amount of air an adult male can hold is 6 litres, and your lungs mature by the time you are about 20-25 years old. After about the age of 35, their function declines as you age, and as a result, breathing can slowly become more difficult over time.

Obstructive Lung Disease

People with obstructive lung disease have airflow limitation due to the inability to completely expel air from the lungs. Because of narrowing of the airways, an abnormally increased amount of air remains in the lungs at the end of full exhalation. Some conditions related to obstructive lung disease include:

In obstructive lung disease, the FEV1 is reduced due to an obstruction of air escaping from the lungs. Thus, the Index of Air Flow or Tiffeneau-Pinelli Index (FEV1/FVC ratio, see Index of Air Flow or Tiffeneau-Pinelli Index below) will be reduced. More specifically, according to the National Institute for Clinical Excellence, the diagnosis of COPD is made when the FEV1/FVC ratio is less than 0.7 or 70%, and the FEV1 is less than 80% of predicted; however, other authoritative bodies have different diagnostic cutoff points.

Restrictive Lung Disease

On the other hand, people with restrictive lung disease have difficulty expanding their lungs when they inhale. The difficulty filling lungs with air often results from stiffness in the lungs themselves and in other cases, chest wall stiffness, weak muscles or damaged nerves. Some conditions related to restrictive lung disease include:

  • Interstitial lung disease,
  • Sarcoidosis,
  • Neuromuscular disease,
  • Pulmonary fibrosis,
  • Asbestosis and Mesothelioma, and
  • Silicosis.

In restrictive lung disease, both forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) are reduced, however, the decline in FVC is more than that of FEV1, resulting in a higher than 80% the Index of Air Flow or Tiffeneau-Pinelli Index (FEV1/FVC ratio, see Index of Air Flow or Tiffeneau-Pinelli Index below).

Testing Methods

Spirometry is a common test used to measure lung capacity, specifically the amount and flow of air that can be inhaled and exhaled. This test is used to diagnose conditions that affect lung conditions, such as COPD and asthma, as well as to monitor the severity of these conditions and their response to treatment.

During the test, you are asked to take the deepest breath possible and exhale into the mouthpiece of the device as hard as possible and for as long as possible. A clip will be placed on your nose to prevent air from leaking out. You will need to do the test at least three times to make sure the results are relatively consistent.

The common measurements used are as follows:

1. Forced Vital Capacity (FVC) is the maximum volume of air which can be exhaled or inspired during either a maximally Forced Vital Capacity (FVC) or a Slow Vital Capacity (VC) manoeuvre. i.e. the amount of air which can be forcibly exhaled from the lungs after taking the deepest breath possible. FVC is used to help determine both the presence and severity of lung diseases. Unit of measurement is the volume of air measured in litres.

2. Vital Capacity (VC) is normally equal to Forced Vital Capacity (FVC) unless airflow obstruction is present, in which case VC is usually higher than FVC, i.e. is the maximum amount of air a person can expel from the lungs after a maximum inhalation. It is equal to the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume. Unit of measurement is the volume of air measured in litres.

A normal adult has a vital capacity between 3 and 5 litres. A human’s vital capacity depends on age, sex, height, mass, and ethnicity.

3. Forced Expired Volume (FEV) or Forced Expired Volume in 1 second (FEV1) is the volume expired in the first second of maximal expiration (exhaling air) after a maximal inspiration (deep breath) and is a useful measurement of how quickly full lungs can be emptied. Unit of measurement is the volume of air expired in 1 second, measured in litres in 1 second.

4. Index of Air Flow or Tiffeneau-Pinelli Index

Index of AirFlow or Tiffeneau-Pinelli Index is a calculated ratio used in the diagnosis of obstructive and restrictive lung disease. It represents the proportion of a person’s vital capacity that they can expire in the first second of forced expiration. Forced Expired Volume divided by Vital Capacity equals % Index of Airflow, as shown below.

Depending on whichever volume is higher out of VC or FVC, the result is expressed as a percentage of the VC or FVC and gives a clinically useful index of airflow limitation. Normal values are approximately 80%.

5. Peak Expiratory Flow (PEF) is the maximal expiratory flow rate achieved, and this occurs very early in the forced expiratory manoeuvre.

Normal spirogram showing the measurements of forced vital capacity (FVC), forced expired volume in one second (FEV1) and forced expiratory flow over the middle half of the FVC (FEF25-75%). The left panel is a typical recording from a water-sealed (or rolling seal) spirometer with inspired volume upward; the right panel is a spirogram from a dry wedge-bellows spirometer with expired volume upward.

Normal maximal expiratory and inspiratory flow-volume loop.
Source: Rob Pierce and David P. Johns, Spirometry – The Measurement and Interpretation of Ventilatory Function in Clinical Practice (Australia, 1995, 2004, 2008), 4.

Lung Capacity and Aging

Another factor affecting lung capacity is aging. Several changes happen to our body as we get older, and at about age 36, the function of the lungs starts to decline. As we get older, the diaphragm gets weaker, decreasing the ability to inhale and exhale. The ribcage changes shape and is less able to expand and contract with breathing. The lung tissue and airways lose elasticity, change shape and some close. The nervous system goes through natural changes with time, as well. The nerves in the airway become less sensitive to foreign particles, and the particle build-up in the lungs can damage the lung tissue and cause partial or full blockages in the airways.

Lung Capacity and Lifestyle Choices

Your lung capacity also improves with a healthy lifestyle, such as doing regular exercise and maintaining an active lifestyle. Studies show that aerobic activity leads to a larger lung capacity for both males and females, and a greater lung capacity leads to a more efficient respiratory system to distribute oxygen throughout the body. Physical inactivity and smoking have, of course, the opposite effect to the capacity of the lungs to expand and function. Most adults nowadays do not meet the current recommendation of at least 30 minutes of moderate physical activity on 5-7 days per week. Smoking and sedentary lifestyle both are negatively associated with healthy lungs, causing a person to have lower lung capacity.

Lung Capacity and AirPhysio® Device

In addition to regular exercise, an effective way of increasing lung capacity is the use of an all-natural, drug-free process called Oscillating Positive Expiratory Pressure (OPEP). The AirPhysio® device is an airway physiotherapy device that uses the OPEP process to open closed and semi-closed airways with positive expiratory pressure and improve airway clearance through the vibration of the airway. You can feel the device working as soon as you blow into the device.

AirPhysio comes in 3 different versions to accommodate for different lung capacities and conditions. These include the following:

1. AirPhysio Children/Low Lung Capacity – for children and people with a low lung capacity version who need airway physiotherapy for mucus clearance to help improve their lung capacity and clear obstructions.

2. AirPhysio CleanMyLungs – for people with average lung capacity who need airway physiotherapy for mucus clearance and improve lung capacity before their condition worsens.

3. AirPhysio Sports – for people with healthy lungs who need to open up their airways and give their airways a good clean out before a workout or an event.

AirPhysio® increases lung capacity, reduces breathlessness during exercise, increases exercise tolerance, and speeds up recovery times after working out or training. AirPhysio® also assists with clearing the airway for individuals suffering from cystic fibrosis, asthma, bronchiectasis, atelectasis, Chronic Obstructive Pulmonary Diseases (COPDs) such as chronic bronchitis and emphysema, or other conditions producing retained secretions.

AirPhysio® is a 100% Australian made and is proudly supporting Asthma Australia.

References:

The Difference Between Obstructive and Restrictive Lung Disease
Lung Capacity and Aging
http://cssf.usc.edu/History/2004/Projects/J1022.pdf
What Is Forced Vital Capacity (FVC)?
Vital capacity
FEV1/FVC ratio

Spirometry
Restrictive lung disease
Vital capacity
Lung volumes

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