EMPHYSEMA AND SPIROMETRY Paul R Earl Facultad de Ciencias Biológicas

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.