Skip to Main Content

++

INTRODUCTION

++

Obstructive pulmonary disease is characterized by an increase in airflow resistance and the presence of air trapping. Work of breathing is increased in these conditions, and an increase in residual volume (RV) and total lung capacity (TLC) is common.

++

PULMONARY FUNCTION TESTS

++

In patients with early disease, pulmonary function tests characteristically demonstrate a reduction in maximum midexpiratory flow (MMEF), which is the forced expiratory flow between 25% and 75% of vital capacity (FEF25–75%). Normal MMEF is >2.0 L/s for adult males and >1.6 L/s for adult females. A reduction of MMEF to <70% of these values may be the only manifestation of early disease (Figure 45-1). This value is not technique- or effort-dependent.

++
FIGURE 45-1

Reduction in MMEF (FEF25–75%), FEV1 and FEV1/FVC in obstructive disease (volume vs. time). (Reproduced, with permission, from Fauci AS, Braunwald E, Kasper DL, et al. Harrison’s Principles of Internal Medicine. 17th ed. New York, NY: McGraw-Hill; 2008: Fig. 246-2, p. 1586.)

Graphic Jump Location
++

As obstructive disease becomes more severe, there is a reduction in both the measured forced expiratory volume in 1 second (FEV1) and the FEV1/FVC (forced vital capacity) ratio. A decrease of these values to below 75% of predicted is typical in obstructive disease. Additionally, the slow vital capacity (SVC) will be greater than the FVC when FVC is abnormally decreased secondary to obstruction.

++

Although less accurate and specific than spirometry, peak flow rates using peak flow meters can also be used to evaluate obstructive disease. They do not replace spirometry during the initial evaluation of chronic disease, but can be a helpful point-of-care tool to measure a patient’s response to therapy during an acute exacerbation. Normal peak flow values are based on age, sex, and height, and there are several online calculators available.

++

Flow volume loops graphically record maximal inspiratory and expiratory maneuvers with flow on the Y-axis and volume on the X-axis. Unlike the characteristic flow volume loops for restrictive disease, which are fairly consistent for the variable etiologies of restrictive disease, the flow volume loops of patients with obstructive disease can differ greatly and are able to distinguish between various types of obstructions: intra- and extra-thoracic obstruction, or fixed or variable obstruction (Figure 45-2).

++
FIGURE 45-2

A comparison of the effects of variable types of obstruction on flow volume loops. (Reproduced with permission from McKean SC, Ross JJ, Dressler DD, Brotman DJ, Ginsberg JS, eds. Principles and Practice of Hospital Medicine. New York, NY: McGraw-Hill Education, Inc.; 2012: Fig. 103-4.)

Graphic Jump Location
++

In patients with a fixed obstruction, the degree of obstruction is not altered by changes in pleural or airway pressures. There is a reduction of airflow during both inspiration ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessAnesthesiology Full Site: One-Year Subscription

Connect to the full suite of AccessAnesthesiology content and resources including procedural videos, interactive self-assessment, real-life cases, 20+ textbooks, and more

$995 USD
Buy Now

Pay Per View: Timed Access to all of AccessAnesthesiology

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.