Lung Functioning And Its Medical Diagnosis

As air quality is an increasingly concern for many people, especially in urban cities, I wanted to discuss the how doctors diagnosis a person with asthma using the most common technique in the North America, a procedure called spirometry1.

Spirometry is a breathing test that uses a spirometer to measure lung volume and how well your lungs are able to move air in and out. It is a quick and simple method used to assess lung function and can help diagnose, or test for and identify a variety of conditions, such as asthma2. The procedure of a common spirometry test is shown below:

Similar to a doctor providing diagnosis pulmonary lung diseases, we need to understand what the results indicate. Below is a screenshot of a graph with labels. The y-axis represents the volume of air in the lungs and the x-axis represents time. Therefore, this graph shows how the volume of air in our lungs changes with time. The first section of the graph represents the tidal volume. The tidal volume represents the volume of air that moves in and out of your lungs during normal breathing or passive breathing. This part of breathing is happening involuntarily. Moving onto the next section of the graph, where the patient was asked to take a deep breath, the volume of air has increased beyond the normal breath, called active breathing. This extra volume of air is known as the inspiratory reserve volume. Together with the tidal volume, the inspiratory reserve volume is the maximal amount of air we breathe in. For last section of the graph. The individual is asked to breathe out more than their normal breath. This extra volume of air that is exhaled is known as the expiratory reserve volume, which makes maximal expiratory volume when combined with tidal volume.

blog lung

Know that we know the meaning of results, how do doctors diagnose patients with asthma? The answer is: what are their lung volume during active breathing. When comparing total lung volumes between an athlete, a normal person and an asthmatic person, they all have the same total lung volume. What changes is the amount of air that can move in and out of the lungs during a breath. Athletes tend to have greater volume of air that can be inhaled and exhaled during active inspiration and expiration3. This is also shown during competition as they have more oxygen that will enhance their performance. Their chest muscles are stronger allowing them to expand their chests more in order to increase the air intake and to contract the chests more to exhale more air. Thus, it’s the increase in efficiency of the lungs, rather than changes in the size of the lungs.

On the other hand, a person with asthma will have the opposite results than an athlete. Asthma is a very prevalent lung condition that makes it difficult to breathe for those who have it. When we compare the lung volume graph of someone who suffers asthma and compare it a normal graph, we will see that the amount of air that is blown out by an asthmatic is much less than a normal person in the same amount of time4. This is because the airways are narrower in those who suffer asthma so there is more resistance and difficulty in exhalation resulting in less air being blown out.

From a single spirometry test, we can already see the power of technology when combined with scientific knowledge. Just one single graph tells some much useful information that vastly increases the efficiency of health care and thus quality of life. In the end, I hope the advancement in technology will further increase the efficiency by targeting on curing disease than diagnosing them.


  1. Ferguson, G. T., Enright, P. L., Buist, A. S., & Higgins, M. W. (2000). Office spirometry for lung health assessment in adults: a consensus statement from the National Lung Health Education Program. Chest Journal117(4), 1146-1161.
  2. White, P., Wong, W., Fleming, T., & Gray, B. (2007). Primary care spirometry: test quality and the feasibility and usefulness of specialist reporting. British Journal of General Practice57(542), 701-705.
  3. Caillaud, C. F., Anselme, F. M., & Prefaut, C. G. (1996). Effects of two successive maximal exercise tests on pulmonary gas exchange in athletes.European journal of applied physiology and occupational physiology74(1-2), 141-147.
  4. Smith, A. D., Cowan, J. O., Filsell, S., McLachlan, C., Monti-Sheehan, G., Jackson, P., & Taylor, D. R. (2004). Diagnosing asthma: comparisons between exhaled nitric oxide measurements and conventional tests.American journal of respiratory and critical care medicine169(4), 473-478.


Tiffany is a graduated student in biochemistry and economics who is passionate about research and medicine. She hopes to become a clinical medical researcher in the future. Throughout her undergraduate degree, Tiffany has gained extensive research in both web lab and clinical medicine. She has 2.5 years of wet lab research in which yielded 3 publications, and 1 year of clinical research experience in which she led a group of undergraduate and medical students. She loves to answer any questions, whether it is research, academic or extra curricular related.


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