A Low FVC With a Normal Ratio: Interpreting Spirometry in a 54-Year-Old With Breathlessness, and Why Restriction Cannot Be Diagnosed Without Lung Volumes
[Student Name]
University of Phoenix
NRP/571: Advanced Health Assessment II and Clinical Procedures
Week 3 Assignment
[Instructor Name]
[Date]
The patient is a composite written for a model paper.
Mr. V., a 54-year-old former drywall installer, has had increasing breathlessness on exertion for a year and a dry cough. He smoked for 10 years in his twenties. His BMI is 29. Listening at the bases, I hear fine, dry crackles late in inspiration on both sides, like hook-and-loop fastener being pulled apart. Office spirometry was performed. This paper interprets it.
Step 1: Is the Test Acceptable and Repeatable?
Before interpreting numbers, quality must be confirmed. The ATS/ERS standardization of spirometry describes acceptability criteria, including a good start without hesitation, maximal effort and adequate duration or plateau, and repeatability criteria, with the two largest FVC and FEV1 values within 150 mL of each other (Graham et al., 2019). Mr. V. produced three acceptable maneuvers, with the two best FVC values 90 mL apart. The test is valid.
Step 2: Which Reference Values?
Results are compared with predicted values for age, height and sex. The Global Lung Function Initiative developed reference equations from large multi-ethnic populations covering ages 3 to 95 (Quanjer et al., 2012), and more recent recommendations move away from race-specific equations. The 2022 ERS/ATS interpretive strategy recommends expressing results as z-scores and using the lower limit of normal, a z-score of -1.645, rather than fixed percentages of predicted (Stanojevic et al., 2022).
Step 3: The Results
FEV1: 2.30 L, z-score -2.2.
FVC: 2.85 L, z-score -2.4.
FEV1/FVC: 0.81, z-score +0.6, normal.
No significant bronchodilator response.
Step 4: The Pattern
The FEV1/FVC ratio is above its lower limit, so there is no obstruction. The FVC is below its lower limit. A reduced FVC with a normal ratio is a pattern that suggests restriction, but spirometry cannot confirm it (Stanojevic et al., 2022). A low FVC can also result from air trapping in obstructive disease, poor effort, obesity or neuromuscular weakness. Only measurement of total lung capacity can confirm a restrictive ventilatory defect.
Spirometry measures the air that comes out, not the air that stays in; restriction is a statement about both.
Step 5: Severity
The 2022 interpretive strategy grades severity by z-score rather than percent predicted; a z-score between -2.5 and -4 is moderate (Stanojevic et al., 2022). His FEV1 z-score of -2.2 indicates mild impairment by this scheme.
Why the Pattern Concerns Me
His crackles, dry cough and occupational exposure raise concern for interstitial lung disease, which causes true restriction. Drywall work can involve exposure to silica and other dusts. Obesity can also reduce FVC, but his BMI of 29 is unlikely to explain it alone.
Step 6: The Next Tests
I order full pulmonary function tests with lung volumes, to measure total lung capacity, and diffusing capacity for carbon monoxide, which is reduced in interstitial lung disease because thickened tissue impairs gas transfer. I also order a high-resolution CT of the chest and refer him to pulmonology. A six-minute walk test with oxygen saturation will assess exertional desaturation.
Results
Total lung capacity is below the lower limit of normal, confirming restriction, and diffusing capacity is reduced. High-resolution CT shows reticular changes at the lung bases, and he is referred for evaluation of interstitial lung disease.
The Flow-Volume Loop
The shape of the flow-volume loop adds information that numbers alone do not. In obstruction, the expiratory limb is scooped, or concave. In restriction, the loop is narrow but of normal shape, reflecting a small lung volume with preserved or even increased flow. Mr. V.'s loop was narrow with a normal shape, consistent with a restrictive process and not with air trapping, which supports ordering lung volumes rather than assuming obstruction.
Why Fixed Cutoffs Mislead
If I had used the older rule of an FVC below 80% of predicted, the result might have been similar in his case, but fixed cutoffs misclassify many patients: they overdiagnose abnormality in older adults and underdiagnose it in younger ones. The 2022 strategy's use of z-scores and lower limits of normal applies the same statistical definition of abnormal across ages and sizes (Stanojevic et al., 2022).
Quality Problems That Mimic Restriction
A submaximal effort or early termination of exhalation can reduce FVC and create a false restrictive pattern. This is why the acceptability and repeatability checks in Step 1 matter. His test met the standards (Graham et al., 2019), so the low FVC is likely real.
What Diffusing Capacity Adds
A reduced diffusing capacity with restriction points to disease of the lung tissue itself, such as interstitial lung disease, whereas restriction from obesity or chest wall problems usually preserves diffusing capacity. This distinction guides the rest of the evaluation.
Why Office Spirometry Still Matters
Even though office spirometry cannot confirm restriction, it was the test that first showed something was wrong. Mr. V. had attributed his breathlessness to weight and deconditioning. An objective, inexpensive test in primary care turned a vague symptom into a measurable abnormality that justified further evaluation.
Explaining the Results
I show Mr. V. his results and explain that his lungs hold less air than expected, that the next tests will measure exactly how much and whether oxygen passes normally into his blood and that his work history may be relevant. He is worried; I explain that finding the cause early gives more treatment options.
Smoking History
His 10 years of smoking decades ago make obstructive disease less likely given his normal ratio, but smoking history remains relevant to some interstitial diseases and to lung cancer screening eligibility, which I review separately.
Oxygen Saturation
His resting oxygen saturation is 95%. A walk test will show whether it falls with exertion, which would support home oxygen evaluation and indicate more significant gas exchange impairment.
Medication Review
Some drugs, such as amiodarone, methotrexate and nitrofurantoin, can cause lung scarring. Mr. V. takes none of these, which I record, since drug-induced lung disease is part of the differential for new restriction.
Follow-Up
I will review the full results with him and coordinate the pulmonology visit, ensuring he does not wait months between tests.
Vaccinations
I update his influenza and pneumococcal vaccines, since lung disease raises the stakes of respiratory infections.
Referral Letter
The referral letter includes the spirometry values with z-scores, the flow-volume loop description, his exposures and the examination findings, so the pulmonologist can plan the visit and order any further tests in advance.
Occupational History
I document his occupational exposures in detail, including years, materials and protective equipment, since they may bear on diagnosis and compensation.
Conclusion
Mr. V.'s acceptable, repeatable spirometry showed a reduced FVC with a normal FEV1/FVC ratio, interpreted with z-scores and lower limits of normal as the 2022 strategy recommends. The pattern suggested but could not confirm restriction; lung volumes confirmed it, and a reduced diffusing capacity with CT changes pointed toward interstitial lung disease. Knowing what spirometry cannot show led directly to the tests that could.
References
Graham, B. L., Steenbruggen, I., Miller, M. R., Barjaktarevic, I. Z., Cooper, B. G., Hall, G. L., Hallstrand, T. S., Kaminsky, D. A., McCarthy, K., McCormack, M. C., Oropez, C. E., Rosenfeld, M., Stanojevic, S., Swanney, M. P., & Thompson, B. R. (2019). Standardization of spirometry 2019 update: An official American Thoracic Society and European Respiratory Society technical statement. American Journal of Respiratory and Critical Care Medicine, 200(8), e70-e88. https://doi.org/10.1164/rccm.201908-1590ST
Quanjer, P. H., Stanojevic, S., Cole, T. J., Baur, X., Hall, G. L., Culver, B. H., Enright, P. L., Hankinson, J. L., Ip, M. S. M., Zheng, J., & Stocks, J. (2012). Multi-ethnic reference values for spirometry for the 3-95-yr age range: The global lung function 2012 equations. European Respiratory Journal, 40(6), 1324-1343. https://doi.org/10.1183/09031936.00080312
Stanojevic, S., Kaminsky, D. A., Miller, M. R., Thompson, B., Aliverti, A., Barjaktarevic, I., Cooper, B. G., Culver, B., Derom, E., Hall, G. L., Hallstrand, T. S., Leuppi, J. D., MacIntyre, N., McCormack, M., Rosenfeld, M., & Swenson, E. R. (2022). ERS/ATS technical standard on interpretive strategies for routine lung function tests. European Respiratory Journal, 60(1), Article 2101499. https://doi.org/10.1183/13993003.01499-2021
How this NRP 571 Week 3 example is structured
The NRP/571 Week 3 work usually addresses spirometry and pulmonary function testing. This paper follows interpretation in order, quality, reference values, pattern, severity and next test, and shows why a common pattern needs confirmation before it becomes a diagnosis. Students search this week as NRP 571 Week 3, NRP571 Wk 3 or NRP/571 Wk 3; all three are the same assignment.
NRP/571 Week 3 questions, answered
What does NRP/571 Week 3 usually ask for?
Many sections ask students to interpret spirometry, identify obstructive or restrictive patterns and state the next steps.
What is a restrictive pattern on spirometry?
A reduced FVC with a normal or high FEV1/FVC ratio. It suggests restriction, but only measurement of total lung capacity confirms it, because a low FVC can also result from air trapping or poor effort.
Why use the lower limit of normal instead of fixed cutoffs?
Fixed cutoffs, such as 80% of predicted or a ratio of 0.70, misclassify people depending on age, height and sex. The lower limit of normal, the 5th percentile of a healthy reference population, adjusts for these factors.
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