Pulmonary function tests in clinical practice pdf


 

Pulmonary Function Tests in Clinical Practice is an unique book providing a simplified to interpreting most diagnostic tests in the field of respiratory medicine. PDF · Lung Volumes. Ali Altalag, Jeremy Road, Pearce Wilcox. Pages Complete review of pulmonary function tests in clinical practice, including ISBN ; Digitally watermarked, DRM-free; Included format: PDF. measurements, quality control and lung physiology that is used to generate the data. Adapted from Pulmonary Function Tests in Clinical practice. Figures

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Pulmonary Function Tests In Clinical Practice Pdf

your test. What is spirometry? Spirometry is one of the most commonly It can take practice to be able to do Pulmonary function tests (PFT's) are breathing. practice. Recommended reference sources are updated with data for spirometry and diffusing Keywords: pulmonary function testing; reporting spirometry; reference clinical application should be included. ∘ The normal. This revised and updated book provides a simplified approach to interpreting most diagnostic tests in the field of respiratory medicine. Easy to understand and .

Open in a separate window Patients with active respiratory infections such as tuberculosis are not precluded from having PFTS however the tests should ideally be deferred until the risk of cross contamination is negligible. If patients with infectious disease must undergo testing then extra precautions in addition to the standard decontamination of equipment may be necessary. A sitting position is typically used at the time of testing to prevent the risk of falling and injury in the event of a syncopal episode, although PFTS can be performed in the standing position. Patients are advised not to smoke for at least one hour before testing, not to eat a large meal two hours before testing and not to wear tight fitting clothing as under these circumstances results may be adversely effected 1. False teeth are left in place unless they prevent the patient from forming an effective seal around the mouth piece. Normal or predicted ranges of values are obtained from large population studies of healthy subjects. Values are taken for people matched for age, height, sex and where appropriate ethnicity. PFTS should be performed three times to ensure that the results are reproducible less than ml variation and accurate. Dynamic studies are performed first spirometry, flow volume curves, peak expiratory flow rates , followed by lung volumes, bronchodilator testing and finally diffusion capacity. Each of these aspects of PFTS will now be reviewed in more detail. Spirometry Spirometry is the most frequently used measure of lung function and is a measure of volume against time. It is a simple and quick procedure to perform: patients are asked to take a maximal inspiration and then to forcefully expel air for as long and as quickly as possible a forced vital capacity manoeuvre- Figure 1. Measurements that are made include.

There is increasing evidence that reduction in hyperinflation by various therapeutic modalities bronchodilators, surgery, et cetera may play a significant role in reducing dyspnea. The value of measuring lung volumes, especially RV, before and after bronchodilator, has yet to be fully defined but certainly merits consideration and further study.

Body plethysmography has emerged as the standard gold? The role of gas dilution techniques is still not completely resolved.

At least one recent investigation has suggested that good correspondence between helium dilution and volume measurement by CT scan, even in subjects who are obstructed, can be interpreted as evidence that body plethysmography systematically overestimates lung volume, and that the degree of overestimation correlates with the severity of obstruction. Imaging technologies may be able to provide an estimate of lung volume, but the cost and risk of radiation exposure make them less than ideal.

Pediatrics For more than 30 years there have been substantial efforts to standardize pulmonary function testing in adults. Because of the increased elastic recoil of the child's lungs, emptying occurs rapidly and the FEV1 may not be an ideal index of airway function.

Because the child's lung has greater elasticity and empties more rapidly, there is less variability in the FVC and in the forced expiratory time or FET. The acceptability and repeatability criteria used for adults are not entirely suitable for children.

An expiratory time of 3 seconds for patients less than 10 years old was included in the spirometry standards, but this may not be appropriate because most children exhale their VC and reach a plateau in less than 3 seconds. Computer displays or recorders need to be able to scale data appropriately to allow visual inspection of efforts when small volumes are measured. Use of a statistically valid lower limit of normal LLN z-scores is one area in which pediatric lung function testing has out-stripped adult testing, which still reports results as percents of predicted.

Airway Resistance The physiology of airway resistance has been well described, and the partitioning of resistance across the respiratory system corresponds to changes that occur with obstructive lung disease.

However, measurement of airway resistance and derived parameters has not always been viewed as a complement of spirometry. Because lung volume VTG can be measured in the same session, it is useful to express resistance and its reciprocal, conductance, as specific for the lung volume at which they are measured sRaw and sGaw, respectively. Because sRaw encompasses lung volume, it is not as useful as sGaw specific conductance , which represents Raw per unit of lung volume.

Airway resistance and specific conductance can be useful adjuncts to spirometry for both bronchodilator and bronchial challenges studies, in which the functional properties of various portions of the airways are changed. Specific conductance sGaw also has the advantage of not requiring a deep inspiration, which may affect bronchomotor tone during spirometric maneuvers.

The forced oscillation technique FOT offers an alternative means of measuring resistance in the pulmonary system. By applying a perturbed flow at the mouth and measuring the resulting pressures across a range of frequencies, the resistive characteristics of the airways, lung parenchyma, and of the chest wall can be measured.

Unlike Raw measured by plethysmography, resistance and the associated variables measured by FOT represents contributions from both the lung and chest wall. The measurements are relatively easy to perform, requiring only tidal breathing, and are applicable to a wide range of subjects, including children who are too young to perform spirometry.

Although the methodology for FOT is somewhat complex, it can be used for studying bronchodilator or bronchochallenge response, the viscoelastic properties of the lung, and distinguishing inspiratory from expiratory mechanics in obstructive lung disease.

Resistance can also be assessed using an interrupter technique Rint. This method uses airway occlusion during tidal breathing to estimate alveolar pressure, and then relate this to flow at the mouth. Rint requires careful attention to proper technique and repeated measurements, but has been demonstrated as useful in children suspected of having airway obstruction. Exercise Testing Spirometry, lung volumes, and diffusing capacity tests remain the standards for evaluating subjects whose chief complaint is dyspnea.

But static tests may not provide an explanation of the patient's symptoms or correlate with the individual's level of impairment. In these circumstances, some form of exercise evaluation is required. Stair climbing is a simple form of exercise dating back 50 years.

The number of stairs climbed has been shown to relate inversely to such things as postoperative complications, but the test is limited by variability and lack of standardization. Exercise challenge tests are commonly used to look for exercise-induced bronchospasm EIB. Shuttle walk tests have also been used in a variety of settings to evaluate exercise intolerance.

The incremental shuttle walk test ISWT sets a pace for the subject and then increases the pace at a fixed rate until the subject's symptoms occur; the distance walked is reported. The most commonly used test appears to be the 6-minute walk test, which has been standardized by the ATS.

The primary outcome variable is the distance covered in 6 min 6MWD on a closed course of at least 30 meters length.

The Lung. Clinical Physiology and Pulmonary Function Tests : Academic Medicine

The 6MWT is included in some multi-dimensional metrics such as the BODE body mass index, air-flow obstruction, dyspnea, exercise capacity index. Unfortunately, a reduced 6MWD is largely non-specific as to the etiology that might be causing exercise intolerance.

Cardiopulmonary exercise testing CPET with measurement of exhaled gases has numerous indications. Although it seldom is able to diagnose specific causes of exercise intolerance, it is useful in discriminating cardiovascular versus pulmonary limitations to work. Other indications include assessment of work capacity in various lung disease states, as well as in congestive heart failure or evaluation for heart transplant.

It is also widely used to assess perioperative risk in thoracic and abdominal surgery. The complexity of the testing as well as the expertise required to safely perform CPET has limited it to a certain extent. But when combined with blood gas sampling it provides a complete picture of cardiopulmonary and exercise physiology. Pulse oximetry before and after the 6MWT is suggested by the ATS guideline, but many clinicians monitor SpO2 during the test and thus compromise the design and end point of the walk.

In the future, exercise testing may include evolving parameters such as heart rate recovery HRR , which has been shown to correlate with overall cardiovascular status.

Technology will most likely also influence exercise testing with the ability to monitor physiologic parameters remotely eg, wireless, blue-tooth, et cetera and to assess such basic functions as cardiac output noninvasively via impedance cardiography.

In the realm of standardization, the technologist has received the least attention. The most important asset of the successful pulmonary function technologist is motivation. In the United States, pulmonary function technologists are quite often respiratory therapists, but a desire to do something other than the usual respiratory care duties does not equal motivation.

Upon transitioning to a position in a pulmonary function lab, the technologist or therapist has to be considered a student. In this role, those with a motivation to excel as a professional may be expected to perform better than someone who pursues sufficient mastery just to meet expectations.

Testing for cognitive aptitude ability to learn , conscientiousness, and critical thinking skills may be better than traditional methods of selecting someone to work in a pulmonary function laboratory.

Training of personnel in the laboratory setting typically requires a one-on-one type of mentoring in order for the individual to become proficient in the basic tests and procedures employed by the lab.

Key to this training is adequate and appropriate feedback. Computerized PFT systems provide much of the information needed to assess the quality of the data obtained, and as such serve in the feedback role.

More important, however, is for each laboratory to have a mechanism by which all technologists get continued feedback related to their performance. Several large studies have documented that performance tends to remain high when there is feedback, but may fall in its absence. Australia and New Zealand implemented a voluntary credentialing program that has had good success and has been used as a model in a few other countries.

Although there is not yet a mandate to credential individual laboratories, the benefits to the public, to third-party payers, and to those conducting research seem obvious.

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Office Spirometry During the last decade there has been a great deal of interest in the detection of COPD with spirometry as the primary tool.

Various organizations have proposed making spirometry widely available in primary care practice settings. Other countries have fared somewhat better, but there is still not widespread adoption of spirometry for making the diagnosis of airway obstruction.

National and international efforts to raise awareness of COPD have included spirometry workshops, testing sessions, and related initiatives. The spirometers themselves may or may not contribute to the problem. Although the ATS recommends daily calibration or calibration checks , very few spirometers are sold with the required 3 L syringe. Modern spirometers designed for physicians' offices use disposable flow sensors, but only a small number of these have been validated for accuracy over extended intervals.

The software accompanying these spirometers is often not user-friendly, and older systems may not provide the NHANES III reference equations recommended for interpretation. Because spirometry is an effort-dependent test, the patient's ability to cooperate sometimes becomes a limiting factor.

In order to get the best results, those performing the test need to know how to operate the spirometer correctly, as well as a certain level of skill in communicating the proper technique to the patient. Several studies have demonstrated that the training for those performing spirometry must be supported by ongoing feedback in order obtain acceptable measurements over a long interval.

These rules have been shown to misclassify elderly patients as having obstruction when they do not, and missing younger subjects who may have early onset of airway abnormality. Use of spirometry in primary care will continue to be problematic unless high quality testing to diagnose and treat COPD or asthma is tied to reimbursement. Predicted Values Reference Equations Reference equations are a key component of PFTs, because patients infrequently have serial tests for purposes of comparison.

Predicted values for TLC are often hampered by the fact that the reference populations are typically small and the techniques used may not be reflective of those in current practice. Over time some individuals about one third with the nonspecific pattern progress to frank obstruction or restriction. Restriction may even be present in patients who have asthma FEV1 and FVC are similarly reduced and both respond to bronchodilator therapy. However, they may not be comparable in black subjects from other ethnic backgrounds.

Similarly, reference values for Mexican-Americans are slightly higher than those of Hispanics of non-Mexican origin. The same study suggested that reference values for Chinese-Americans could be estimated as 0.

The Global Lungs Initiative GLI, sponsored by the ERS proposes to generate all-age equations for each of the major ethnic groups from a large pooled database of healthy subjects.

Pulmonary Function Tests in Clinical Practice

Unfortunately, various reference equations produce markedly different results in terms of identifying and quantifying gas exchange abnormality. The equations of Miller et al represent a large population living near sea level, with adjustments for current and former smokers available. Lower Limit of Normal Unlike most other laboratory tests in which the expected or normal values remain the same throughout life in adults , pulmonary function parameters vary with sex, age, height, and ethnicity.

As far back as , the ATS guidelines have recommended using a statistically valid LLN based on the lowest 5th percentile of a healthy non-smoking population.

Pulmonary Function Tests in Clinical Practice

For spirometry, very good reference sets are available for a limited number of ethnic groups, mainly whites. One of the strengths of this set, as well as for other recently published normals, is that LLN values can be readily calculated based on the lowest 5th percentile.

Using this approach prevents the age- or sex-related bias that is introduced when a fixed percentage is used to define normality. Almost all pulmonary function systems are computerized, so it is very easy to calculate predicted values, even if the regression equations are complex or require look-up tables. Modern statistical methods are providing more precise equations to estimate the limits of normal for pulmonary function variables. The lambda, mu, sigma LMS technique, which has been used to generate growth charts for children, can be applied to pulmonary function data in healthy subjects.

This method allows modeling of not only the predicted value, but of the changing variability and skewness of the data because of age and height. Although many guidelines for diagnosing COPD still rely on fixed cutoffs, many clinicians are now considering limits of normal that better differentiate not only the presence of disease, but its severity as well. COPD is the target disease, and it continues to be under-diagnosed and misclassified in many patients.

Lung Volumes. Gas Transfer. Bronchial Challenge Testing. Approach to PFT Interpretation. Illustrative Cases on PFT. Arterial Blood Gas Interpretation. Exercise Testing. Diagnostic Tests for Sleep Disorders. Back Matter Pages About this book Introduction Pulmonary Function Tests in Clinical Practice is an unique book providing a simplified approach to interpreting most diagnostic tests in the field of respiratory medicine.

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