Pulmonary Function Testing

Pulmonary function test can identify and quantify respiratory system abnormalities and indicate other disorders outside the respiratory system, including neuromuscular weakness and cardiovascular processes.

Pulmonary function test allow for long-term monitoring of disease progression and response to therapy.

Spirometry measures the volume of air exhaled or inhaled by a patients as a function of time.

Spirometry screening is not recommended, rather it should be obtained from patients who describe chronic respiratory symptoms, and a history of exposures.

Irreversible or partially reversible airflow limitation, measured by spirometry prior to and after the administration of inhaled bronchodilator is the characteristic physiologic feature of COPD

The degree of air flow limitation is measured using a spirometer: can determine the severity of COPD, assays the response to medications, and follow the progression of the disease.

Spirometry is recommended as an essential test for persons with suspected COPD to confirm the diagnosis, measure severity of airflow obstruction, and assess progression of the disease.

Abnormal spirometry results can be separated into two classes of disorders: obstructive and restrictive.

FEV1 reaches a peak at about 20 years of age, followed by a relatively short plateau and a steady decline thereafter.

Between 4 and 12% of persons in the general population do not have an FEVI one peak in the predicted normal range, and identifies a group of high-risk persons with disordered development of lung function.

Obstructive disorders are suggested by a low FEV1/FVC ratio, whereas restrictive disorders are suggested by a normal FEV1/FVC ratio with a low FVC.

An obstructive process is defined as a FEV1/FVC ratio below the 5th percentile of the predictive value, often called the lower limit of normal.

Some define obstructive disease as an abnormal FEV1/FVC ratio as below 70%: this is controversial because the FEV1/FVC ratio is dependent on age and in older patients overestimates the disease and it underestimates it in younger patients.

A maximal forced expiratory flow time that exceeds six seconds has a sensitivity of 81% and specificity of 100% for identifying and FEV1/FVC of less than 0.65.

In obstructive disorders the FEV1/FVEC ratio is reduced.

The severity of obstruction is quantified by the degree of reduction in FEV1 which is derived from a population of normal individuals and calculated using height, age, sex, and ethnicity or race.

Includes several different studies: spirometry with flow-volume loop, lung volumes, and diffusing capacity of the lung for carbon monoxide.

Flow-volume loop provides clues about the quality, acceptability, reproducibility of the testing, determined by national standards.

Flow-volume loop can indicate abnormalities such as obstructive lesions of central airways.

Flow-volume loop Inspiratory flow’s are disproportionately reduced by lesions of the upper, extrathoracic, airway.

Inspiratory flows are disproportionately reduced by lesions of the opera, extrathoracic, airway.

Lesions in the lower trachea and mainstem bronchi primarily affect exploratory flows whereas the plateau on both the inspiratory and expiratory curves suggests a fixed lesion.

Spirometry should be offered to define objective evidence of lung disease prompted by dyspnea and or cough, or exercise intolerance.

Spirometry is utilized to confirm the presence of an obstructive a restrictive pattern of breathing.

Spirometry can provide index of lung disease severity and disease progression and prognosis over time.

Spirometry can lead to overdiagnosis of COPD in never smokers greater than 70 years of age, but produces fewer false positive results in younger adults.

Measures the mechanical function of the lung, the chest wall and the respiratory muscles by the assessment of the total volume of air exhaled from a full lung to an empty lung.

Spirometry provides objective assessment for the response and need for bronchodilator therapy.

A broncodilator can be administered during spirometry so that airway responsiveness can be assessed.

Spirometry establishes baseline lung function, detects pulmonary diseases, evaluates complaints of dyspnea, monitors effects of respiratory therapy, evaluates risk of surgical procedures, and can provide surveillance of occupational lung diseases.

Use of spirometry among patients with COPD is inconsistent with the percentage ranging from 6 to 68% in primary care clinics.

In patients with a clinical diagnosis of COPD who undergo spirometry, 32-42% do not have airflow obstruction.

PFT results may indicate both respiratory and non-respiratory disorders including helping in the diagnosis of cardiac or neuromuscular diseases.

Physicians underestimate COPD severity of approximately half of their patients compared with objective assessment by spirometry.

Vital Capacity (VC)-amount of air displaced by a maximal exhalation or inhalation maneuver.

The average vital lung capacity is 6 l for males and 4 l for females.

Total Lung Capacity (TLC)-point of maximal inspiration: it measures the total amount of air in the lungs.

Residual Volume (RV)-point of maximal expiration.

Forced Expiratory Vital Capacity FEVC-forced expiration from a point of maximal inspiration to a point of maximal expiration.

Forced expiratory volume in the first second of the FVC maneuver is the FEV1.

The ratio of FEV1 and FVC is used as an indicator of obstruction.

The forced expiratory flow at 25-75% of the pulmonary volume is an indicator of small airway disease, however nonspecific.

The forced vital capacity FVC and the forced expiratory volume in the first second of forceful exhalation, the FEV1, are usually reproducible to within 0.15 L.

A reduced FEV1 may reflect a decrease in the TLC, airway obstruction, loss of lung elastic recoil or respiratory muscle weakness.

The maximal voluntary ventilation (MVV) is a measure of the patient’s ability to breathe in and out as deeply and rapidly as possible: a normal value is approximately 40 times the FEV1 and the lower limit is about 30 times the FEV1.

A decrease in MVV may be due to upper airway obstruction, neural muscular weakness, or poor test performance.

FEV1 most commonly related to the presence of airway obstruction.

3 key parameters are FVC, FEV1, and FEV1-FVC ratio.

Normal values and lower limits of normal defined by the National Health and Nutrition Examination Survey (NHAAMES) III.

Pulmonary function testing-the NHANES III predicts values for white individuals, African-Americans and Mexican Americans.

Reduction in the FEV1 as compared to the FVC, the FEV1-FVC ratio (FEV1%) is the hallmark of obstructive lung disease.

Obstructive defects include asthma, chronic bronchitis, emphysema, bronchiectasis, cystic fibrosis, pneumonia, alpha-1-antitypic deficiency and bronchiolitis.

Obstructive airflow may be related to bronchial spasm, airway inflammation, increased bronchial secretions, and reduced parenchyma support of the airways due to loss of lung elastic recoil.

Checking the changes in FEV1 with the use of bronchodilators help indicate the degree of reversibility of airway obstruction.

Cornerstone, particularly FEV1, for preoperative selection of patients for thoracic surgery for lung cancer.

FEV1 pulmonary function tests have a value in predicting overall survival of patients resected for NSCLC.

FEV1 alone is not sufficient to predict quantitative outcomes for postoperative mortality and morbidity after thoracic surgery for NSCLC.

Poorly related to postoperative health related quality of life for patients undergoing thoracic surgery for NSCLC.

Spirometry cannot differentiate asthma from COPD.

Relative contraindications include: the presence of hemostasis, pneumothorax, unstable cardiac condition, aneurysms of the thoracic aorta, abdomen or brain, presence of increased ocular pressure, presence of recent abdominal or thoracic surgery and history of syncope associated with forced exhalation.

The graphic display from spirometric testing is called a flow-volume curve if that includes only expiratory flow or a flow-volume look if it includes both expiratory and inspiratory maneuvers.

Measurement of lung volumes is helpful in patients whose spirometry suggest restriction: reduced FVC, but normal FEV1/FVC ratio.

A restrictive disorder is characterized by a total lung capacity below the lower limits of normal and seen in patients with interstitial lung disease, neuromuscular weakness, or chest wall limitation.

The severity of restriction may be based on the decrease in TLC or FVC if no lung volumes are performed.

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