PFT

Pulmonary Diagnostics Performed by RT’s: Pulmonary Function Tests Arterial Blood Gases Other: V/Q scan Radiological studies

Pulmonary Function Tests: These are the four basic: Lung Volumes & Capacities Spirometry FRC Determination Diffusion Capacity

Lung Volumes & Capacities

Lung Volumes & Capacities IRV: Inspiratory Reserve Volume VT (VT): Tidal Volume FRC: Expiratory Reserve Volume RV: Residual Volume, can never be blown out!

Lung Volumes & Capacities Lung Capacities: IC: Inspiratory Capacity, Often done therapeutically VC: Vital Capacity, the useable amount of air in the lungs FRC: Functional Residual Capacity, the amount of air left in the lungs after a normal exhalation. TLC: Total lung capacity.

Terms to know: BTPS ATPS ATPD Q: What happens to air from BTPS to ATPS? A: It cools from body temp to room air. The effects volume (Charles’ Law).

CL= Volume/pressure Vital Capacity VC is decreased in restrictive component of disease. Restrictive (among other things) is a disease of low compliance. CL= Volume/pressure

Compliance Examples: 1000 ml / 20 cmH2O = 50 ml/cmH2O Okay Compliance 800 ml /40 cmH2O = 20 ml/cmH2O Bad compliance

Spirometry

Spirometry Definition Spirometry is a Forced Expiratory Vital Capacity Maximum effort in the first second is important. The FVC is timed and graphed. The values of importance in the test are…. (next slide)

Spirometry FVC To meet “ATS standards” one must blow out for 6 seconds or obvious plateau No coughs or starts-and-stops Good “start of test” (computer “back extrapolates” volume to tell) Three efforts with at least two efforts being 200 ml apart. Predicted value calculated from age, height, sex, race, weight.

GO! Start Normal Tidal breathing Back to Normal breathing FVC Tracing

FVC Tracing FVC FEV1 Volume (ml) 1 sec Time (Sec)

FEV1 First major timing mark: Measured in milliliters, (like FVC) represents the amount of air blown out in the first second of the FVC maneuver. By itself, is non-specific since it is low in both obstructive and restrictive categories.

FEV1/FVC The FEV1 divided by FVC is one of the most useful values in this diagnostic test. This value compares the amount blown out in one second to the total FVC and expresses this as a percentage. Generally, high percentages are good and low percentages are bad.

Example FVC = 4.0 L FEV1 = 3.8 L 3.8 = 95% 4.0 Is this good or bad?

FEF25-75% This value indicates flow in the small airways. Is derived by taking the slope of the line created by plotting 25% and 75% of actual FVC. This is the most sensitive indicator of mild or early obstructive component.

{ { { { { FEF 25-75% 100% 75% 50% 25% Slope = Y2-Y1 X2-X1 75% FVC We will not calculate this, or do this measurement manually, but it is nice to know how this value is derived. 50% { 25% FVC 25%

Peak Expiratory Flow Rate PEFR roughly indicates flow in the large airways. Easy to perform, and therefore a common diagnostic test to indicate airway obstruction. Calculated (or derived) much like the FEF25-75%

Others FEF200-1200 FEV2 FEV3

Classification of spirometry based on disease process

Classification Normal Early small airways disease (obstructive component) Obstructive Restrictive Combined

Obstructive Diseases Chronic Bronchitis Asthma Emphysema Combined Obstructive/Restrictive: Cystic Fibrosis (combined) Bronchiectasis (combined)

Restrictive (Wide category!) Acute Restrictive component Infectious diseases such as pneumonia Non-infectious disease processes such as pulmonary edema Chronic Restrictive component Infectious diseases such as fungal diseases Environmental diseases such as Asbestosis

Obstructive Spirometric classification Normal volumes FVC Reduced flows FEV1/FVC FEF25-75% FVC = 3.7 1.2 / 3.7 = 32% FEV1 = 1.2 1 sec

Percent of Predicted Actual / Predicted = % of Predicted Example: Based on my age, height, sex, race, and weight, I am predicted to have a Forced Vital Capacity of 4.7 Liters. I performed the test and only scored 3.6 L. What is my “percent of predicted”, and is this normal?

Percent of Predicted Although most people perform more than 82% of predicted, we call an FVC percent of predicted “abnormal” when it falls below 75%

Obstructive Spirometric classification Normal volumes FVC Reduced flows FEV1/FVC FEF25-75% FEF25-75%= 3.5 L/s FEF25-75%= 1.0 L/s 75% = 2.8 Notice the difference in slope for the obstructive (black) vs. the normal (green) 25% = .93 1 sec

Restrictive Spirometric classification Low Volumes Normal “flows” FEV1/FVC FEF25-75% 1.9 / 2.0 = 95% FVC = 2.0 FEV1 = 1.9

Also…. FEV1 FEF25-75% PEFR Can be compared to predicted normals and scored as “percent of predicted”

Flow Volume Loop

Flow volume loop We have been graphing spirometric data on Volume / Time scale, but you can also graph the data on Flow / Volume scale…

Discussion What is the difference between SVC and FVC Why does obstructive disease manifest itself as low flows on the expiratory curve. Why doesn’t restrictive disease affect flows?

Next time…. Diffusion Capacity FRC Determination