PFT PTF is one of the most important and most frequently utilized investigations in our field. Why do we do PFTs?
Clinical indications for PFT 1- evaluate signs and symptoms or abnormal finding. 2-assess and monitor the effect of disease, intervention, exposure on respiratory system. 3- assess and minimize preoperative risk. 4- objectively assess impairment. 5- understand severity and prognosis
Elements of PFT Spirometry Lung volumes Diffusing capacity, Exercise testing, Bronchial challenges Pulmonary function laboratories in the near future.
Important considerations The patient PFT will be less meaningful in patient who is not physically capable of providing constant and optimal effort. It is recommended the test should not be done within one month of acute coronary syndrome.
Similarly in patients with acute chest pain, abdominal pain, confusion, significant dementia. Accurate measurement of patient height Any abnormality should be mentioned like khyphoscoliosis, lower limb amputation, in these case arm span is measured instead of height.
Other considerations The laboratory and equipment. The laboratory personnel.
Reference values PFT interpretation is based on comparisons of patient own numbers with reference values derived from a representative population of healthy subjects. Values of PFT varies with 1-age 2-height 3-gender 4-race.
spirometry Measures exhaled volume of air vs time, and is the most commonly performed PFT. Volume or flow may be directly measured. The variables of interest are the FVC and the FEV1.
Spirogram It distinguishes obstructive pulmonary disorders from restrictive disorders. It measures the volumes in certain time: - Forced vital capacity (FVC ) - Forced expiratory volume in 1 second (FEV1) - FEV1/FVC ratio (FEV1%) - FEF 25-75%
Lung volumes Is the gold standard for establishing a restrictive abnormality. Techniques 1 – body plethesmography 2- nitrogen N2 washout 3- inhaled inert gas dilution.
Lung Volumes Unlike spirometry and diffusing capacity, the indications for performing lung volume measurements are limited. It includes patients who have reduced FVC values but are not overtly obstructed. A normal FVC excludes restrictive disease in almost every instance. When FVC is low, TLC may be useful to determine whether a true restrictive ventilatory pattern is present
Lung volumes (TLC, RV) tend to be increased in obstruction. Air-trapping and hyperinflation are poorly defined. Air-trapping is usually associated with an increased RV. Body plethysmography has emerged as the standard (gold?) for measurement of lung volumes. The role of gas dilution techniques is still not completely resolved. 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.
Definitions of Volumes and Capacities. TLC can be divided into several subdivisions grouped as volumes and capacities. 2 or more volumes make up a capacity.
Lung Volumes Tidal Volume (TV): volume of air inhaled or exhaled with each breath during quiet breathing Inspiratory Reserve Volume (IRV): maximum volume of air inhaled from the end-inspiratory tidal position Expiratory Reserve Volume (ERV): maximum volume of air that can be exhaled from resting end- expiratory tidal position
Lung Volumes Residual Volume (RV): – Volume of air remaining in lungs after maximum exhalation – Indirectly measured (FRC-ERV) not by spirometry
Lung Capacities Total Lung Capacity (TLC): Sum of all volume compartments or volume of air in lungs after maximum inspiration Vital Capacity (VC): TLC minus RV or maximum volume of air exhaled from maximal inspiratory level Inspiratory Capacity (IC): Sum of IRV and TV or the maximum volume of air that can be inhaled from the end-expiratory tidal position
Lung Capacities (cont.) Functional Residual Capacity (FRC): – Sum of RV and ERV or the volume of air in the lungs at end-expiratory tidal position – Measured with multiple- breath closed-circuit helium dilution, multiple-breath open-circuit nitrogen washout, or body plethysmography (not by spirometry)
Exercise challenge tests are commonly used to look for exercise- induced bronchospasm (EIB). Patients walk or jog at a high heart rate or ventilatory level for 6–8 min, followed by spirometry to assess airway narrowing. A fall of 10–15% in FEV1 is considered diagnostic of EIB.
6-minute walk test The most commonly used Exercise test. The primary outcome variable is the distance covered in 6 min (6MWD) on a closed course of at least 30 meters length. It is a self paced (constant work load) effort in which the subjects typically do not reach their peak V˙O2.
DLCO (diffusing capacity) indications To diagnose restrictive and obstructive diseases. To differentiate between restrictive and Obstructive diseases. Lung transplant candidacy. Disability assessment. Evaluating medication toxicity. Predicting exertional hypoxemia.
Interpretation of diffusing capacity tests should include appropriate adjustments for factors such as: 1. Hemoglobin (Hb). 2.Carboxyhemoglobin (COHb). 3.The population being tested. 4.Reference values use body weight as a variable. 5.Recent evidence suggests that a clinically important change to be as large as 20–25% under typical laboratory conditions.