Which of the following measures and evaluates a patients lung capacity and volume?

Airflow

Quantitative measures of inspiratory and expiratory flow are obtained by forced spirometry. Nose clips are used to occlude the nares.

In expiratory flow assessments, patients inhale as deeply as possible, seal their lips around a mouthpiece, and exhale as forcefully and completely as possible into an apparatus that records the exhaled volume (forced vital capacity [FVC]) and the volume exhaled in the first second (the forced expiratory volume in 1 second [FEV1]—see figure ). Most currently used devices measure only airflow and integrate time to estimate the expired volume.

In inspiratory flow and volume assessments, patients exhale as completely as possible, then forcibly inhale.

These maneuvers provide several measures:

• FVC: Maximal amount of air that the patient can forcibly exhale after taking a maximal inhalation

• FEV1: Volume exhaled in the first second

• Peak expiratory flow (PEF): Maximal speed of airflow as the patient exhales

FEV1 is the most reproducible flow parameter and is especially useful in diagnosing and monitoring patients with obstructive pulmonary disorders (eg, asthma Asthma Asthma is a disease of diffuse airway inflammation caused by a variety of triggering stimuli resulting in partially or completely reversible bronchoconstriction. Symptoms and signs include dyspnea... read more , COPD Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease (COPD) is airflow limitation caused by an inflammatory response to inhaled toxins, often cigarette smoke. Alpha-1 antitrypsin deficiency and various occupational... read more

FEV1 and FVC help differentiate obstructive and restrictive lung disorders. A normal FEV1 makes irreversible obstructive lung disease unlikely whereas a normal FVC makes restrictive disease unlikely.

Normal spirogram

FEF25–75% = forced expiratory flow during expiration of 25 to 75% of the FVC; FEV1 = forced expiratory volume in the first second of forced vital capacity maneuver; FVC = forced vital capacity (the maximum amount of air forcibly expired after maximum inspiration).

The forced expiratory flow averaged over the time during which 25 to 75% of the FVC is exhaled may be a more sensitive marker of mild, small airway airflow limitation than the FEV1, but the reproducibility of this variable is poor.

The peak expiratory flow (PEF) is the peak flow occurring during exhalation. This variable is used primarily for home monitoring of patients with asthma Asthma Asthma is a disease of diffuse airway inflammation caused by a variety of triggering stimuli resulting in partially or completely reversible bronchoconstriction. Symptoms and signs include dyspnea... read more and for determining diurnal variations in airflow.

Interpretation of these measures depends on good patient effort, which is often improved by coaching during the actual maneuver. Acceptable spirograms demonstrate

• Good test initiation (eg, a quick and forceful onset of exhalation)

• No coughing

• Smooth curves

• Absence of early termination of expiration (eg, minimum exhalation time of 6 seconds with no change in volume for the last 1 second)

Reproducible efforts agree within 5% or 100 mL with other efforts. Results not meeting these minimum acceptable criteria should be interpreted with caution.

Lung volume

Lung volumes are measured by determining functional residual capacity (FRC). FRC is the amount of air remaining in the lungs after normal exhalation. The total lung capacity (TLC) is the volume of gas that is contained in the lungs at the end of maximal inspiration.

Normal lung volumes

ERV = expiratory reserve volume; FRC = functional residual capacity; IC = inspiratory capacity; IRV = inspiratory reserve volume; RV = residual volume; TLC = total lung capacity; VC = vital capacity; VT= tidal volume.

FRC = RV + ERV; IC = VT + IRV; VC = VT+ IRV + ERV.

FRC is measured using gas dilution techniques or a plethysmograph (which is more accurate in patients who have airflow limitation and trapped gas).

Gas dilution techniques include

• Nitrogen washout

• Helium equilibration

With nitrogen washout, the patient exhales to FRC and then breathes from a spirometer containing 100% oxygen. The test ends when the exhaled nitrogen concentration is zero. The collected volume of exhaled nitrogen is equal to 81% of the initial FRC.

With helium equilibration, the patient exhales to FRC and then is connected to a closed system containing known volumes of helium and oxygen. Helium concentration is measured until it is the same on inhalation and exhalation, indicating it has equilibrated with the volume of gas in the lung, which can then be estimated from the change in helium concentration that has occurred.

Both of these techniques may underestimate FRC because they measure only the lung volume that communicates with the airways. In patients with severe airflow limitation, a considerable volume of trapped gas may communicate very poorly or not at all.

Body plethysmography uses Boyle’s law to measure the compressible gas volume within the thorax and is more accurate than gas dilution techniques. While sitting in an airtight box, the patient tries to inhale against a closed mouthpiece from FRC. As the chest wall expands, the pressure in the closed box rises. Knowing the pre-inspiratory box volume and the pressure in the box before and after the inspiratory effort allows for calculation of the change in box volume, which must equal the change in lung volume.

Knowing FRC allows the lungs to be divided into subvolumes that are either measured with spirometry or calculated (see figure ). Normally the FRC represents about 40% of TLC.

Flow-volume loop

In contrast to the spirogram, which displays airflow (in L) over time (in seconds), the flow-volume loop displays airflow (in L/second) as it relates to lung volume (in L) during maximal inspiration from complete exhalation (residual volume [RV]) and during maximum expiration from complete inhalation (TLC). The principal advantage of the flow-volume loop is that it can show whether airflow is appropriate for a particular lung volume. For example, airflow is normally slower at low lung volumes because elastic recoil is lower at lower lung volumes. Patients with pulmonary fibrosis have low lung volumes and their airflow appears to be decreased if measured alone. However, when airflow is presented as a function of lung volume, it becomes apparent that airflow is actually higher than normal (as a result of the increased elastic recoil characteristic of fibrotic lungs).

Flow-volume loops

(A) Normal. Inspiratory limb of loop is symmetric and convex. Expiratory limb is linear. Airflow at the midpoint of inspiratory capacity and airflow at the midpoint of expiratory capacity are often measured and compared. Maximal inspiratory airflow at 50% of forced vital capacity (MIF 50% FVC) is greater than maximal expiratory airflow at 50% FVC (MEF 50% FVC) because dynamic compression of the airways occurs during exhalation.

(B) Obstructive disorder (eg, emphysema, asthma). Although all airflow is diminished, expiratory prolongation predominates, and MEF < MIF. Peak expiratory flow is sometimes used to estimate degree of airway obstruction but depends on patient effort.

(C) Restrictive disorder (eg, interstitial lung disease, kyphoscoliosis). The loop is narrowed because of diminished lung volumes. Airflow is greater than normal at comparable lung volumes because the increased elastic recoil of lungs holds the airways open.

(D) Fixed obstruction of the upper airway (eg, tracheal stenosis, goiter). The top and bottom of the loops are flattened so that the configuration approaches that of a rectangle. Fixed obstruction limits flow equally during inspiration and expiration, and MEF = MIF.

(E) Variable extrathoracic obstruction (eg, unilateral vocal cord paralysis, vocal cord dysfunction). When a single vocal cord is paralyzed, it moves passively with pressure gradients across the glottis. During forced inspiration, it is drawn inward, resulting in a plateau of decreased inspiratory flow. During forced expiration, it is passively blown aside, and expiratory flow is unimpaired. Therefore, MIF 50% FVC < MEF 50% FVC.

(F) Variable intrathoracic obstruction (eg, tracheomalacia). During a forced inspiration, negative pleural pressure holds the floppy trachea open. With forced expiration, loss of structural support results in tracheal narrowing and a plateau of diminished flow. Airflow is maintained briefly before airway compression occurs.

FVC = forced vital capacity; MEF = maximal expiratory flow; MIF = maximal inspiratory flow; PEF = peak expiratory flow; RV = residual volume; TLC = total lung capacity.

Flow-volume loops require that absolute lung volumes be measured. Unfortunately, many laboratories simply plot airflow against the FVC; the flow-FVC loop does not have an inspiratory limb and therefore does not provide as much information.

Patterns of Abnormalities

Most common respiratory disorders can be categorized as obstructive or restrictive on the basis of airflow and lung volumes (see table ).

Table

Obstructive disorders

Obstructive disorders are characterized by a reduction in airflow, particularly the FEV1 and the FEV1 expressed as a percentage of the FVC (FEV1/FVC). The degree of reduction in FEV1 compared with predicted values determines the degree of the obstructive defect (see table ). Obstructive defects are caused by

• Increased resistance to airflow due to abnormalities within the airway lumen (eg, tumors, secretions, mucosal thickening)

• Changes in the wall of the airway (eg, contraction of smooth muscle, edema)

• Decreased elastic recoil (eg, the parenchymal destruction that occurs in emphysema)

With decreased airflow, expiratory times are longer than usual, and air may become trapped in the lungs due to incomplete emptying, thereby increasing lung volumes (eg, TLC, RV).

Table

Improvement of FEV1 and/or FVC ≥ 12% and 200 mL with the administration of a bronchodilator confirms the diagnosis of asthma Asthma Asthma is a disease of diffuse airway inflammation caused by a variety of triggering stimuli resulting in partially or completely reversible bronchoconstriction. Symptoms and signs include dyspnea... read more or airway hyperresponsiveness. However, some patients with asthma can have normal pulmonary function and normal spirometric parameters between exacerbations. When suspicion of asthma remains high despite normal spirometry results, with methacholine, a synthetic analog of acetylcholine that is a nonspecific bronchial irritant, is indicated to detect or exclude bronchoconstriction. In a methacholine challenge test, spirometric parameters are measured at baseline and after inhalation of increasing concentrations of methacholine. The concentration of methacholine that causes a 20% drop in FEV1 is called the PC20. Laboratories have different definitions of airway hyperreactivity, but in general patients showing at least a 20% drop in FEV1 from baseline (PC20) when the concentration of inhaled methacholine is < 1 mg/mL is considered diagnostic of increased bronchial reactivity, whereas a PC20 > 16 mg/mL excludes the diagnosis. PC20 values between 1 and 16 mg/mL are inconclusive.

Exercise testing Exercise Testing The two most common forms of exercise testing used to evaluate pulmonary disorders are the 6-minute walk test Cardiopulmonary exercise testing This simple test measures the maximal distance... read more may be used to detect exercise-induced bronchoconstriction but is less sensitive than methacholine challenge testing for detecting general airway hyperresponsiveness. The patient does a constant level of work on a treadmill or cycle ergometer for 6 to 8 minutes at an intensity selected to produce a heart rate of 80% of predicted maximum heart rate. The FEV1 and FVC are measured before and 5, 15, and 30 minutes after exercise. Exercise-induced bronchospasm reduces FEV1 or FVC ≥ 15% after exercise.

Eucapnic voluntary hyperventilation (EVH) may also be used to diagnose exercised-induced bronchoconstriction. EVH involves hyperventilation of a gas mixture of 5% carbon dioxide and 21% oxygen at 85% of maximum voluntary ventilation for 6 minutes. FEV1 is then measured at specified intervals after the test. As with other bronchial provocation tests, the drop in FEV1 that is diagnostic of exercise-induced bronchospasm varies by laboratory.

What measures and evaluates a patients lung capacity and volume?

Spirometry measures airflow. By measuring how much air you exhale, and how quickly you exhale, spirometry can evaluate a broad range of lung diseases. In a spirometry test, while you are sitting, you breathe into a mouthpiece that is connected to an instrument called a spirometer.

Which of the following would you include in patient preparation for a pulmonary function test?

To prepare for your pulmonary function test, follow these instructions:.

No bronchodilator medication for four hours..

No smoking for four hours before the test..

No heavy meals..

Do not wear any tight clothing..

The complete pulmonary function test takes around one and a half hours..

Which of the following measures the patient's response to a constant or increasing workload?

TEST 4 study guide and toward FINAL.

Which of the following diagnostic test is most likely to be performed if a patient is experiencing shortness of breath?

Spirometry is used to diagnose asthma, chronic obstructive pulmonary disease (COPD) and other conditions that affect breathing.