The purpose of this packet is to briefly explain the content(s) of the various testing profiles as performed by this laboratory. They are as follows:
A. Complete Pulmonary Diagnostic Tests
Purpose: To verify and assess the presence of lung dysfunction
Includes: Spirometry (with Bronchodilator if indicated), Static Lung Volumes, Diffusing Capacity, Airway Mechanics, Arterial Blood Gases (includes Hemoximetry), Distribution of Ventilation (if other studies fall within the broad range of normal)
1. Spirometry: Maximal, forced expiration performed from total lung capacity (TLC) to residual volume (RV) with measurements of Forced Vital Capacity (FVC), Forced Expiratory Volume in One Second (FEV1) and the ratio between FEV1 / FVC. Also includes instantaneous flows from the FVC curve such as Peak Expiratory Flow (PEF), Forced Expiratory Flows (FEF) as a percentage of FVC curve (FEF25%, FEF50%, FEF75%, and FEF25-75%) and mean transit time (MTT). Note: Flow Volume Loop includes measurements of the Forced Inspiratory Vital Capacity (FIVC) obtained from RV to TLV, along with Peak Inspiratory Flow (PIF) and Forced Inspiratory Flow (FIF) at 50% of the FIVC. If there is evidence of airflow limitation (“obstruction”) and no medical contraindications present, then bronchodilator is administered (Isuprel via MDI, unless otherwise indicated) and spirometry is repeated in 10-15 minutes.
2. Lung Volumes: Includes Residual Volume (RV), Total Lung Capacity (TLC), and Functional Residual Capacity (FRC) &/or Volume of Thoracic Gas (VTG). Generally measured via two different methods (1) Total Body Plethysmography and (2) Multiple Breath Helium Dilution. The Plethysmographic method measures all thoracic gas (VTG), whereas Helium Dilution method (FRC) measures only the volume of ventilated lung. By employing these two methods, the volume of non-ventilated lung may be determined (if VTG/FRC > 109%), the result of which may be useful for assessing unventilated lung. Unless directed otherwise, static lung volumes will be determined by only one method, with preference given to Total Body Plethysmography. Post-bronchodilator static lung volumes are also performed to assess changes in RV/TLC ratio, primarily if, on baseline studies, there is evidence of airflow limitation on spirometry, or elevated RV/TLC ratio.
3. Diffusing Capacity: The measurement of diffusion gives information about the functioning capillary bed in contact with functioning alveoli and is also known as “transfer factor for carbon monoxide”. The single-breath (SB) method for Pulmonary Diffusion Capacity (DLCO) is employed by the Pulmonary Diagnostic Services. Other measurements include Specific Diffusing Capacity (DL/VA), which corrects the DLCO for the Lung Volume at which the procedure was performed, and hemoglobin correction for DLCO and DL/VA. The DL /VA is influenced by abnormalities of ventilation and perfusion that reduce potential surface area for gas exchange, thereby making it a useful tool for discriminating between obstructive lung disease types, e.g., emphysema vs. chronic bronchitis. DLCO may also be helpful when assessing possible intrapulmonic hemorrhage (i.e., DLCO > 140% predicted).
4. Airway Mechanics: This test, which includes airway resistance (Raw), along with their reciprocals: airway conductance (Gaw), and specific airway conductance (sGaw), provides an actual measurement of flow resistance through the airways, and therefore, a direct index of airway caliber. All other indices of flow resistance are determined by several factors of which airway caliber is only one. Therefore, airways mechanics is the only test which is specific for intrinsic airways disease. Furthermore, measurements of airway mechanics are much more sensitive than tests such as spirometry; while measurements such as FEV1 may remain normal long after the onset of airways disease, airway mechanics may detect such changes early on. Airway mechanics will also determine, in the presence of airways disease, the site of obstruction and/or the site of response to bronchodilators (i.e. central vs peripheral airways). Post-bronchodilator airway mechanics will be also be assessed if baseline data suggests abnormal airway mechanics indices (sGaw in particular).
5. Arterial Blood Gases: Anaerobically obtained arterial blood sample with measurement of pH, PCO2, PO2, Oxyhemoglobin Saturation (SaO2% or %HbO2), Carboxyhemoglobin Saturation (%HbCO) and Total Hemoglobin (Hgb). Calculated values are Plasma Bicarbonate (HCO3–), and Base Excess/Deficit.
6. Distribution of Ventilation: The Single Breath Nitrogen Washout Test (SBN2) provides an index of the topographic distribution of ventilation (“Slope of Phase III”) in that it reflects regional differences in lung mechanics rather than an aggregate measurement. SBN2 also provides measurements of anatomical dead space and “Closing Volume”, measurements which are no longer widely used. In order to reduce patient costs, this test is not commonly performed unless specifically requested.
B. Small Airway Disease Profile
Purpose: To detect the presence of covert peripheral airway dysfunction before it is apparent on routine tests.
Includes: Airway Mechanics, Closing Volume and Closing Capacity, He-O2 Flow Volume Loop, Dynamic Compliance (see Compliance below). There is currently technique controversy with He-O2 Flow Volume Loops. However, the remainder of the procedures can be performed, and the He-O2 Flow Volume Loops will only be performed after discussion with the Medical Director, Pulmonary Diagnostic Services.
C. Upper Airway Obstruction Profile
Purpose: Intended for subjects suspected of having central airway lesions; i.e., tracheal stenosis, laryngeal tumor.
Includes: Flow-Volume Loop, Airway Resistance, Intrapulmonic Gas Distribution (if other tests are normal)
D. Oncology Profile
Purpose: To be used to monitor pulmonary involvement from radio- and/or chemotherapy; i.e., fibrosis, pneumonitis. Note: Subject should be tested prior to commencement of therapy, periodically during course of therapy and approximately six months to a year after cessation of therapy.
Includes: Lung Volumes, Diffusing Capacity, Spirometry (if subject is being tested for the first time in this laboratory), Arterial Blood Gases, if other tests are abnormal.
E. Pre-op: Non-Thoracic Surgery
Purpose: To assess patient “Risk” for general anesthesia and possible postoperative pulmonary complications in patients without overt lung disease.
Includes: Spirometry (FVC), Maximum Voluntary Ventilation (MVV), Arterial Blood Gases
F. Pre-op: Thoracic Surgery
Purpose: To assess patient “Risk” for general anesthesia and possible postoperative pulmonary complications following thoracic surgery; i.e., lung resection, or in patients with overt lung disease.
Includes: Spirometry (FVC), MVV, Lung Volumes, Diffusing Capacity, Arterial Blood Gases
G. Neuromuscular Disease Profile
Purpose: To assess total (non-specific, aggregate) respiratory muscle strength by measuring maximal inspiratory and expiratory occluding pressures (“MIP and MEP”) at varying lung volumes. Note: Especially important profile to monitor respiratory muscle disease progression; i.e., ALS.
Includes: Flow-Volume Loop, MVV, Lung Volumes, Arterial Blood Gases, Respiratory Muscle Forces