NR 507 Pulmonary System & Function

Visit this site for case examples on Pulmonary Function Testing Case Questions and Answers Abbreviations: -FVC / Forced Vital Capacity -FEV1 / Forced Expiratory Volume in One Second -TLC / Total Lung Capacity -RV / Residual Volume -DLCO / Diffusion Capacity for Carbon Monoxide -BD / Bronchodilator Mechanics of Respiration: Pulmonary Function Tests Pulmonary function tests (PFTs) are non-invasive tests that provide information about lung function. PFTs alone cannot differentiate among the causes of respiratory abnormalities. Therefore, the patient's history, physical exam and other diagnostics must be considered when making a diagnosis. The PFT can help the NP determine the patient's respiratory pattern, specifically if the abnormality is due to an obstructive or restrictive problem. Once the pattern is identified, PFTs allow the NP to determine the severity of the disease. This data combined with other patient findings, leads to a diagnosis. There are some indications to help the NP to determine when to order PFTs: 1. When signs and symptoms of a respiratory problem require evaluation (cough, dyspnea, cyanosis, wheezing, hypoxemia, hypercapnia, and lung hyperinflation). 2. When disease progression needs to be determined. 3. When monitoring the effectiveness of drug therapy. 4. When monitoring for potential toxic effects of certain drugs. Components of a Pulmonary Function Tests Spirometry Spirometry: This measures air movement in and out of the lungs during various respiratory maneuvers. The NP can also determine how much air the patient is breathing in and out and how fast the patient is doing it. Think about the respiratory cycle in terms of lung volume and lung capacities. The capacity is just simply the sum of one of more volumes. There are three important measures on which the NP focuses when reviewing spirometry results: There are three important measures on which the NP focuses when reviewing spirometry results: 1.) FVC Measure Forced Vital Capacity (FVC); Normal 80-120% Definition The FVC measures the volume of air in the lungs that can be exhaled. Maneuver Patient inhales as deep as possible and then exhales as long and as forcefully as possible. There are three important measures on which the NP focuses when reviewing spirometry results: 2.) FEV1 Measure Forced Expiratory Volume in 1 second (FEV1); Normal 80-120% Definition Amount of air forcefully exhaled from the lungs in the first second. Maneuver The patient inhales and forcefully exhales as fast as possible. There are three important measures on which the NP focuses when reviewing spirometry results: 3.) FEV1/FVC ratio Measure FEV1/FVC ratio Definition Determines if the pattern is obstructive, restrictive or normal Maneuver This is a calculated ratio that represents the proportion of a person's vital capacity that they are able to expire in the first second of forced expiration to the full, forced vital capacity. Components of a Pulmonary Function Tests: Diffusing capacity The diffusing capacity is simply how well the lungs are able to exchange gas. Gas exchange is most efficient in a lung that has high surface area because it's easier for the blood to pick up the gas that's being exchange. An example of a condition that decreases the patient's diffusing capacity because of a loss of surface area is emphysema. Conditions that increase the lungs thickness can also decrease diffusing capacity as in the case of pulmonary fibrosis. Components of a Pulmonary Function Tests: Residual volume (RV) and Total Lung Capacity (TLC) RV + FVC = TLC RV is the amount of air that remains in the lungs after a forceful exhalation. RV + FVC = TLC. Note that the RV cannot be measured by spirometry. Other methods are used that require the patient to inhale an inert gas (helium) or sit in an airtight booth where the pressure is measured during breathing. These measurements are also called static lung volumes. The values add to the information obtained from spirometry. If the patient has an obstructive disease, RV and TLC results will be elevated which reveals air trapping and hyperinflation. In restrictive disease, the TLC is needed to confirm true restriction. It can also help in quantifying the degree of restriction. Steps to Analyze Pulmonary Function Tests (PFTs) First, the NP must understand how the results of the PFT is delivered. The results will yield measured values and percentages of predicted values. Predicted values and lower limits of normal have been standardized by population studies using individuals without lung disease. Each patient's predicted values depend on the age, height, and gender. This information is entered into a computer prior to the PFT. Once the results have been received, the NP looks at two factors: 1) the pattern of the condition; 2) severity of the condition. Step 1 - Determine the pattern In order to classify the respiratory issue as either obstructive, restrictive or normal., the NP starts by looking at the FEV1/FVC ratio. Obstructive pattern: If the FEV1/FVC ratio is "less than 70%" or less than the lower limit of normal for the patient. FEV1 also falls to a greater degree than the FVC. Restrictive pattern: If the FEV1/FVC ratio is "greater than 70%" or greater than the lower limit of normal, then the spirometry test is either normal, or a restrictive respiratory abnormality is present. To make this distinction, the NP must look at the TLC. In restrictive disorders, the percent predicted of TLC is 80%, where 80-120% represents a normal range. Measurement: Forced vital capacity (FVC) Obstructive -Decreased or normal Restrictive- Decreased Measurement: Forced vital capacity (FVC)Forced expiratory volume in 1 second (FEV1): Normal is 80% Obstructive - Decreased Restrictive - Decreased Measurement: FEV1/FVC ratio: Normal is 70% or less than the lower limit of normal for the patient Obstructive - Less than 70% Restrictive - Normal or 70% Measurement: Total lung capacity (TLC): Normal range is 80-120% of predicted Obstructive - 120% (represents hyperinflation) Restrictive - 80% Step 2 Determine the Severity The American Thoracic Society (ATS) system for grading the severity of pulmonary function test abnormality according to the FEV1 percent predicted, where normal is greater than 80% Severity & FEV1 % Predicted Mild 70% Moderate 60-70% Moderately Severe 50-60% Severe 35-50% Very Severe 35% Step 3 Bronchodialator Response One other aspect of spirometry is that it may be repeated after the patient receives a bronchodilator. If either the FEV1 or the FEV increases by at least 12% and by at least 200 mL from the pre-bronchodilator values, then the patient has had a significant bronchodilator response. The NP must consider the degree of severity of the respiratory abnormality. Characteristics of Obstructive and Restrictive Lung Disease Before comparing obstructive and restrictive lung disease, remember that we are keying in on how much air the patient can forcefully expire. FEV1 is the amount of air that the patient can forcefully expire in 1 minute. The normal range is between 80% - 120%. Also keep in mind the FVC, which is the amount of air that the patient can forcefully inspire and expire. The normal range is between 3-5 liters. These values can be altered in obstructive and restrictive pulmonary disease. Obstructive Disorders Obstructive disorders are characterized by obstruction to airflow during expiration. This can be related to conditions that increase mucus production leading to mucus plugs as in the case of chronic bronchitis or the loss of surface area of the lung that decreases areas of gas exchange as a result in inflammatory processes that destroys the lung's elastic resulting in decreased recoil. Regardless of the cause of the obstruction, there is an increased work of breathing (WOB), which requires more energy and effort to create airflow. This eventually results in a ventilation-mismatch where not enough CO2 is being expelled and not enough oxygen being brought in for gas exchange. In using emphysema as an example, the defect is destruction of the lung's elastic tissue caused by inflammation after the person has been exposed to smoking and other irritants over a long period of time. The lung is infiltrated with inflammatory cells that release cytokines that contribute to airway damage and mucus production. When elastin is destroyed, the lung loses its recoil ability that is necessary to expel air out. This leads to air trapping and enlarged alveoli that results in increased lung compliance and decreased elasticity. Ultimately, the lungs become overstretched without the ability to recoil. Individuals with an obstructive disorder will have less than 70% on their PFT. Both the FEV1 and FVC will be decreased.