Ashley Trattner

When I was 13, I had my first love … no just kidding (for those who didn’t connect that I was quoting Justin Beiber’s “Baby” … anyway!). At 13, I started getting serious about basketball. I was practicing for hours on end super hard and trying to get into the best shape possible for my team! Though I was running into a problem: sports induced asthma. Every time my heart rate would reach a certain intensity, I felt a huge constriction in my ability to breathe properly and get enough oxygen. It wasn’t fun! So my parents and I went to a Pulmonologist (doctors who specialize in treating respiratory issues) to figure out what was going on. In my appointment, they had me do a Spirometry test before and after running on a treadmill (pretty cool right).

A Spirometry test consists of taking a big breath in and exhaling for as long and as hard as possible into a tube that’s connected to an analyzer (like blowing out birthday cake candles). This analyzer measures the volume of air you exhale as a function of time, and converts this information into multiple graphs that represent your lung’s capacity for inhalation, exhalation, and your speed of exhalation. For example, this analyzer can create a volume-time curve graph (see Figure 4.122)⁴ which shows the time course of exhalation starting from a baseline of zero volume.¹ This allows physicians to evaluate the completeness of the end of the test, or when the patient cannot exhale any more.¹ General guidelines recommend that patients try to exhale for at least 6 seconds. If after about 15 seconds the patient is still exhaling, this may be indicative of obstructive impairment (common in obese patients or those with lung diseases).¹

VC represents a patient’s forced vital capacity, or the largest amount of air that they can forcefully exhale after breathing in. The slope of the curve represents the rate at which the patient exhales, first steeply and then leveling off. The slope of this curve will always increase sharply (the patient’s initial hard exhale), approach the maximum volume of air that the patient can push out, and then decrease constantly (the patient’s slow decline of exhalation effort as they run out of air). The X-axis represents the passage of time in seconds as the patient exhales and the Y-axis represents the volume of air in liters that the patient exhales. To evaluate the graph to decipher normality, you need to check the ratio between the forced-out air volume in the first second and the total forced capacity of the lungs. The normal value of this ratio is above 0.75-85.² Values less than 0.70 suggest airflow limitations and ratios higher than 0.85 suggest restrictive lung disease.²

Another graph this test creates would be a flow-volume curve graph, which shows the flow rate of air as a function of volume (in liters per second) (see Figure 4.123).⁴ This graph highlights the patient’s effort in exhaling and is characterized by an immediate vertical rise, a sharp peak, and a smooth descent that returns to zero flow.¹ The slope of this graph represents the change in air flow / the change in time. The area under this curve, or its integral from 0 to 1, represents the net volume of air flow / the FEV1 value (which stands for “forced expiratory volume in 1 second”).³ This area can also be used to relate the flow volume curve to the volume time curve.

The patient exhales hard in the first few seconds and this forcefulness peaks and then decreases.

Based on FEV1 values and other results, doctors can make informed decisions about a patient’s treatment plan and/or the state of their lung health. Physicians start by looking at the FVC parameter to see if it falls within normal range, next the FEV1 parameter is checked; if the FEV1/FVC ratio value is at 69% or less, there is a strong likelihood that there is some form of obstructive lung disease. Generally, it is accepted that predicted percentages for FVC and FEV1 should be above 80% and one’s FEV1/FVC ratio percentage should be above 70% to be normal.⁷ Doctors can then take this information and implement treatments. For instance, one standard intervention to alleviate airflow obstruction is inhaled medicines that reduce swelling in airways.⁸ For me, after running, my ability to exhale was hindered as compared to my pre-run breathing test. Physicians also compare results to large data pools that construct general guidelines for what “good lung health” looks like. My doctor prescribed me an inhaler to take before playing sports and it helped with my breathing immensely!

References

1. CDC. Spirometry Quality Assurance: Common Errors and Their Impact on Test Results. 2012.
2. FEV1 / FVC Ratio – General Practice Notebook. gpnotebook.com/simplepage.cfm?ID=-254803957.
3. “Flow Volume Loops: A Critical Analysis – Stepwards.” Stepwards, 6 Mar. 2018.
4. Hughes-Hallett, Deborah, et al. Applied Calculus. Available from: Yuzu, (5th Edition). Wiley Global Education US, 2013.
5. Mayo Clinic. “Spirometry – Mayo Clinic.” Mayoclinic.org, 17 Aug. 2017.
6. Moore, V.C. “Spirometry: Step by Step.” Breathe, vol. 8, no. 3, 1 Mar. 2012, pp. 232–240.
7. NuvoAir. “Do You Know How to Interpret the Results of Your Spirometry Test?” Nuvoair.com, 2018.
8. World Health Organization: WHO and World Health Organization: WHO. “Chronic Obstructive Pulmonary Disease (COPD).”