EMPHYSEMA AND SPIROMETRY Paul R Earl Facultad de Ciencias Biológicas Universidad Autónoma de Nuevo León San Nicolás, NL. Mexico Emphysema pathogenesis most often results from tobacco-induced inflammation and chronic elastase-induced destruction of alveolar septas (walls). This tissue destruction reduces the pulmonary surface area available for gas exchange and reduces elastic recoil, possibly leading to hyperinflation, airflow limitation, ventilation/perfusion mismatching, impaired oxygen transfer, increased pulmonary vascular resistance, and right heart dysfunction. Emphysema results from progressive destruction of alveolar septas. The adult lung does not spontaneously regenerate itself. Then of course the destructive effects of emphysema are considered progressive and irreversible. In the absence of a cure, therapies have focused on preserving the remaining lung, reducing complications and ameliorating symptoms. Emphysema is a devastating disease caused by destruction of lung tissue. The usual cause is cigarette smoking. As air sacs are destroyed in the lungs, large airspaces or holes appear in the lung. The elastic properties of the lung are decreased and the airways become narrower, resulting in overinflation of the lungs which are thus too large. This decreases the subject’s ability to move air in and out of the lungs, and lowers the passage of oxygen into the blood from the lungs. Then the percent of oxygen saturation in arterial blood might be 88% instead of say 95%. No available treatment for humans has been tried in the hope of regenerating functional lung tissue. However, all-transretinoic acid (ATRA; Vesanoid ® ; Roche Laboratories, Nutley, NJ) was shown to reverse anatomic and physiologic signs of emphysema in a rat model. Retinoids such as vitamin A and ATRA are known to activate genes involved in lung development. ATRA promotes alveolar septation and growth in the rat. Treatments. Is diet involved? The severity of emphysema sometimes correlates well with low vitamin A (retinol) intake. In emphysema, some of the alveoli and bronchiole tubes of the lungs are destroyed, and the lungs become enlarged and less efficient. Although treatments exist, such as antibiotics and inhalers, none of these are curative. The vitamin A derivatives work by actually helping the lung regrow in areas destroyed by disease. Retinoids are able to do this by turning on the genes that signal the growth of lung tissue. Suggestions. 1/ Do not smoke, because smoking leads to emphysema and also makes emphysema worse. 2/ Get regular exercise and eat a balanced nutritious diet. 3/ If you (or anyone in your family) are alpha-1-antitrypsin deficient, consult your doctor. 4/ Avoid industrial pollutants, second-hand tobacco smoke, grain dust and other air pollutants. 5/ High-potency vitamins are suggested. Histological section of normal lung tissue Many spaces and very few alveoli resulting from emphysema. Pathogenesis of emphysema. The lungs have a system of elastic fibers. The fibers allow the lungs to expand and contract. The normal lung has a remarkable balance between 2 classes of chemicals with opposing action. When the enzymatic balance is altered, the lungs lose the ability to protect themselves against the destruction of these elastic fibers. This is what happens in emphysema. Smoking is responsible for 82 % of chronic lung disease, including emphysema. Exposure to air pollution is a suspected cause. Irritating fumes, exhausts and dusts are typtcal of air pollution. Chronic obstructive pulmonary disease (COPD) is a growing problem. COPD is a term that usually applies to both chronic bronchitis and emphysema,and it has increased by 57 % between 1982 and 1993. Today, chronic bronchitis and emphysema combined constitute the most common chronic lung disease, affecting 15.8 million people in the US. The number of lives claimed by chronic lung disease has increased sharply, too. In 1979, it accounted for about US 50,000 deaths. In 1982, the number rose to 59,000 and by 1992 reached 86,974. SPIROMETRY Measuring lung functions. Spirometry is the system of measurement of pulmonary functions. It is outlined here largely following Esther Lum and Thomas Gross of Iowa University. The American Thoracic Society (ATS) has published guidelines for the standardization of spirometry equipment and performance. Spirometry with flow volume loops assesses the mechanical properties of the respiratory system by measuring expiratory volumes and flow rates. This test requires the patient to make a maximal inspiratory and a expiratory effort. The patient in a sitting position breathes into a mouthpiece. Nose clips are placed to prevent air leaks. Reversibility of airways obstruction can be assessed with the use of bronchodilators. After spirometry is completed, the patient is given an inhalation bronchodilator and the test is repeated. The purpose of this is to assess whether a patient's pulmonary process is bronchodilator responsive by looking for improvement in the expired volumes and flow rates. In general, a >12% increase in the FEV1 (an absolute improvement in FEV1 of at least 200 ml) or the FVC after inhaling a beta antagonist is considered a significant response. Definitions and Terms. 1/ FEV1 - forced expiratory volume 1 - the volume of air that is forcefully exhaled in one second, 2/ FVC - forced vital capacity - the volume of air that can be maximally forcefully exhaled, 3/ FEV1/FVC - ratio of FEV1 to FVC, expressed as a percentage, 4/ FEF 25 - 75 - forced expiratory flow - the average forced expiratory flow during the mid (25-75 %) portion of the FVC and 5/ PEF - peak expiratory flow rate - the peak flow rate during expiration Absolute and percentage values. Spirometry is typically reported in both absolute values and as a predicted percentage of normal. Normal values vary depending on sex, race, age and height. There is no single set of standard reference values, however and normal varies with the reference value used in each laboratory. It is therefore important to ensure that the reference formulas in the spirometry lab are applicable to the patient population that is being tested. Requirements for good pulmonary function tests (PFTs). Criteria for acceptability include: 1/ lack of artifact induced by coughing, glottic closure, or equipment problems (primarily leak), 2/ satisfactory start to the test without hesitation, 3/ satisfactory exhalation with 6 seconds of smooth continuous exhalation and a plateau in the volume time curve of at least one second, or a reasonable duration of exhalation with a plateau Normal spirogram Variable efforts by the patient Early glottic closure Cough Interpreting Spirometry a) Normal, b) Obstructive Lung Disease, c) Restrictive Lung Disease, d) Upper Airway Obstruction e) Interpretation Algorithm are examined. Normal. Spirometry should be interpreted using the flow volume and volume time curves as well as the absolute values for flows and volumes. The flow volume loop and volume time curve are often overlooked but provide valuable information. Certain disease states have characteristically shaped loops, so it is important to be able to recognize the different patterns. Normal spirogram Normal flow volume loop Obstructive lung disease. The primary abnormality detected by spirometry is airways obstruction. In obstructive lung diseases such as emphysema or chronic bronchitis, the FEV1 is reduced disproportionately more than the FVC resulting in an FEV1/FVC ratio less than 70 - 80%. This reduced ratio is the primary criteria for diagnosing obstructive lung disease by spirometry. The following scale grades the severity of obstruction: FEV1 > 80% predicted 65 - 80% 50 - 65% < 50% normal mild moderate severe Example of spirometry results demonstrating mild obstruction: Measure FVC FEV1 FEV1/FVC FEF25-75 PEF 2.63 1.58 60 0.59 4.90 Pred 3.11 84 2.28 73 2.56 5.78 %Pred 69 23 85 Mild Obstruction Flow Volume Severe Obstruction Flow Volume Mild Obstruction Volume Time Curve Restrictive lung disease. In restrictive lung disease, both the FEV1 and FVC are reduced proportionately. By affecting both the FEV1 and the FVC, restrictive lung disease presents with a normal or even elevated FEV1/FVC ratio. FVC FEV1 FEV1/FVC FEF25-75 PEF Meas 0.96 0.94 98 2.25 2.98 Pred %Pred 2.75 35 1.90 49 69 2.11 107 5.40 55 Restriction Flow Volume Restriction Volume Time Upper Airway Obstruction. Upper airway obstruction is less common than lower airway obstruction; however it can be suggested by spirometry. Upper airway obstruction includes variable extrathoracic obstruction, variable intrathoracic obstruction, and fixed intraor extrathoracic obstruction. These are best seen on the flow volume loops, where both inspiration and expiration can be viewed. Variable Extrathoracic Upper Airway Obstruction Fixed Upper Airway Obstruction In summary, spirometry is a most valuable system for the assessment of lung disease. By ensuring proper calibration of equipment and performance of test maneuvers, one can differentiate among several different disease processes. Many other tecniques like CT (computerized tomographic) scans contribute to the progressively better understanding of lung functions and tests. Perhaps the most important single test is for the percent of saturated oxygen in the arterial blood. EMPHYSEMA REVISITED Traveling. People who regularly need need to plan for mobility -- how to get from one place to another between refills. However, when traveling by plane, even people with lung disease who don't necessarily use oxygen at home may require inflight oxygen, because the air pressure in an airplane cabin is lower during flight than on the ground. Of course in your own car, there is no problem. Oxygen supplementation. The use of supplemental low-flow oxygen in patients with advanced COPD provides benefits include improvements in hemodynamic status, improved cognitive functioning, a decrease in hospitalizations and hospital days, increased survival and improved quality of life. Arterial blood gases or oxygen saturation should be monitored periodically in order to justify continued oxygen supply. Pacients are carefully selected. Also, some oxygen use may be temporary. Overview. In emphysema, lung tissue loses its elasticity, leading to collapse of the airways. On a CT scan, spaces in the lung with destruction appear. The pathogenesis may involve an imbalance between protease enzymes that break down proteins and protease inhibitors, which subsequently break down the protease enzymes. The 3 etiologic factors of 1/ cigarette smoking, 2/ atmospheric pollution and 3/ infection play their usual roles. More studies of alpha-1-antitrypsin (AAT) deficiency can provide some understanding of the role of protease enzymes. STOP SMOKING ! JUST DO IT ! Avoid irritants and noxious substances and possibly change your life style, including avoidance of passive smoke inhalation and in some cases even undergo a change of employment. Reducing pulmonary risks through modification of the patient’s life style, as the data on patient adherence clearly show, requires a major commitment of time and effort from the physician.
© Copyright 2018