RESP 330
Cardiopulmonary Diagnostics
Class Notes
Unit #4
Spirometry
Spirometry
describes those pulmonary function tests that cam be performed by measurement
of air moved into and out of the lungs.
These tests do not require the use of special gasses or the analysis of
gas concentrations. In the dark ages,
they were performed using water seal or other types of displacement
spirometers. The basic tests to
determine the Tidal Volume and Minute Ventilation, Vital Capacity and the
components of it along with the Maximum Voluntary Ventilation and the flowrates
during the performance of a Forced Vital Capacity Exhalation and Inhalation
fall within the definition of spirometry.
Resting
Ventilation
is a test to determine three basic parameters of ventilation. The patient is attached to a device in such a
way that all their ventilation passes through it and asked to breathe
normally. After a period of
accommodation to the device, the technologist initiates recording of the
ventilation for at least one minute. During
the minute, the total volume inhaled and exhaled is recorded along with the
number of breaths. The Average Tidal
Volume is calculated by dividing the Minute Ventilation by the number of
breaths. This maneuver is graphically
represented with a plot of volume versus time.
Volume
Time
Lung
Subdivisions
are those lung volumes that comprise the Vital Capacity. The specific volumes are the Tidal Volume,
Inspiratory Reserve Volume and the Expiratory Reserve Volume. These are determined by a combination of the
Slow Vital Capacity and Resting Ventilation tests. A person is asked to breathe normally for a
few breaths. This portion of the test is
to determine the normal Functional Residual Capacity for the person. This is the amount of air left in the lungs
at the end of a normal exhalation. This
resting end-expiratory level is determined by the interaction of the thorax
desiring a larger resting volume and the lung wanting a smaller restive
volume. The point at which these two
forces are equal determines the FRC. Once the FRC for that person is determined, the individual is asked
to perform a sow inhalation to full lung volume (TLC) and then to exhale slowly
to the point their lungs are empty (RV).
By determining the volume they inhale above their FRC, the Inspiratory
Capacity is measured. Subtracting the
average Tidal Volume from the IC, the Inspiratory Reserve Volume is
determined. The volume the person
exhales beyond their normal FRC, the Expiratory Reserve Volume is determined. The Vital Capacity is the Sum of the IRV, TV
and ERV. The IC plus the ERV is another
way to determine the VC. This maneuver
is normally graphed as volume vs. time.
A
person with significant air trapping from a
obstructive problem will have a Slow Vital Capacity significantly (15%) larger
than their Forced Vital Capacity. This
is due to less compression of the airways with the slow exhalation and less air
being trapped in alveoli distal to airways that have been compressed to the
point of collapsing. Expiratory
pressures are much less during the slow exhalation compared to the forced
exhalation. With a restrictive problem,
all these lung volumes/capacities (IRV, ERV, VC and to a lesser extent TV) will
be reduced from predicted and they will be reduced in the same proportions. With an obstructive problem, the VC will be
reduced by a decrease in both the IRV and the ERV. It is not really possible to use the specific
volumes to differentiate between obstruction and restriction. To differentiate between these problems, one
must look at the SVC and FVC to see if there is a significant difference.
Timed Vital Capacity (Forced Vital Capacity) is a test in which the
expiratory and inspiratory flowrates are evaluated along with the volume the
person can voluntarily inhale and exhale.
This test is similar to the SVC except there is no need to establish the
normal resting FRC and the person is instructed to inhale maximally, then exhale maximally, as rapidly as possible. The exhalation must last at least 6 seconds
and assure that all the VC is exhaled.
The maximal forced exhalation is followed immediately with a forced,
maximal inhalation if the desire is to perform a flow-volume loop. The loop indicates both the exhalation and
inhalation portions are performed. The
test may be done only on the expiratory portion of the maneuver as well. This test is one of the best methods for the
diagnosis of airway obstruction. The
flowrates determined during the test will be reduced in persons with
obstructive lung disease. The results of
this test are normally graphed as volume vs. time and flow vs. volume. These two plots will enable the determination
of all the needed information.
Volume
Time
Inspiratory
Flow
Volume
Expiratory
Maximum
Voluntary Ventilation is a test that will determine the ventilatory reserve of a
person. This test is a measure of the
greatest amount of breathing a person can sustain for a short period of
time. The person is instructed to inhale
and exhale rapidly and deeply for a period of 12 – 15 seconds. Patients cannot sustain this level of
ventilation for very long, as they will become hypocapnic. The individual is to achieve a balance
between rate and depth that has them ventilating at a rate that permits them to
breathe at a tidal volume greater than their TV but less than their VC. The MVV should be about 35 times their actual
FEV1.0. If it is
significantly less, one should question the instruction and effort of the
patient. Breathing rates greater than
about 110 BPM generally are associated with panting at low tidal volumes and
rates below 80 BRP are generally associated with too large tidal volumes. Either of these situations will result in an
MVV lower than the actual for the person.
The results from this test are very dependant on the effort of the
person being tested so it is important to assure the person provides a good
effort. The total volume exhaled in the
12 or 15 seconds is multiplied by 60 seconds / accumulation time to determine
the total ventilation the person would have achieved if they had breathed at
the same rate and volume for the entire minute.
Derivation of Specific Values and Their Significance
.
. .
V
or Minute Ventilation is the total amount of air a person inhales (VI) or exhales
(VE) each minute. The patient
breathes normally for one minute and all the air inhaled or exhaled during that
time is accumulated. Minute ventilation
will increase with increased production of CO2 or with increased
consumption of O2 so long as the person has the ability to do
so. With chronic obstructive disease,
the minute ventilation can not be increased due to limitations of airflow. The body generally increased minute
ventilation by first increasing rate and later by increasing volume. Increased volume is more efficient at the
dead space is ventilated each breath. AS
more breaths are taken, a part of each additional breath is used just to
ventilate dead space. When tidal volume
is increased at the same rate, every additional milliliter of ventilation is
involved in gas exchange as the breath has already ventilated the dead
space. Minute ventilation will decrease
with a decreased production of CO2 or with decreased consumption of
O2.
Breathing
Rate (BPM)
is the number of breaths taken during the minute of volume accumulation. It is important to realize the rate of
breathing may be changed by fact that the person has a very large mouthpiece in
their mouth, a nose clip obstructing their nasal passages and a therapist
watching their breathing. This may
affect the minute ventilation. Repeated
trials and sufficient time for the person to become accustomed to the equipment
should be used to obtain the most accurate data.
Average
Tidal Volume (VT or TV) is the average volume of the breaths taken during
the accumulation of the ventilation. It
is calculated by dividing the minute ventilation by the breaths per
minute. Tidal volume will remain
relatively the same in the presence of mild restrictive or obstructive lung
disease. Only with moderate and severe
problems is the tidal volume significantly altered.
Slow
Vital Capacity
is described above. SVC will be
decreased in restrictive lung diseases.
It will also be reduced when the RV (FRC) increases in persons with
obstructive disease, the VC must decrease a similar amount.
Inspiratory
Capacity (IC)
is the largest volume a person can inhale from the end of a normal exhalation
(FRC). It is a measure of the
inspiratory reserve a person has. The IC
will be about three times the ERV in normal lungs. The IC is about 75% of the VC and the ERV is
about 25%. The IC will be decreased with
any problem that decreases the VC.
Inspiratory
Reserve Volume (IRV) is the additional volume a person can inhale beyond the normal tidal
volume. It is a reserve of volume the
lungs can hold. It is determined by
subtracting the average TV form the IC.
Expiratory
Reserve Volume (ERV) is the additional volume a person can exhale after a normal
exhalation. It is that part of the FRC
that the person can voluntarily exhale.
The other portion that cannot be exhaled is the RV. This volume is normally part of the air that
enables gas exchange to occur during exhalation.
Forced
Vital Capacity
is the largest volume of air a person can inhale or inhale with the maximum
effort. It is generally measured as a
Forced Expiratory Vital Capacity (FEVC) by having the person inhale as deeply
as they can (to TLC) then exhaling as rapidly and fully as possible. The Forced Inspiratory Vital Capacity (FIVC)
is measured by having the person exhale as far as they can (to RV) then
inhaling as rapidly and fully as possible.
In most new PFT devices, the person first performs a FEVC and then
immediately performs an FIVC. This
sequence of maneuvers is called a flow-volume loop. Ideally the FIVC and the FEVC should be the
same. With obstructive problems, the FIVC
may be greater than the FEVC.
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Tined
Expiratory Volumes (FEVT) are measured from a volume
versus time graph of a forced exhalation.
The most common times at which the volumes are measured are one-half
second, one second and three seconds after the beginning of the
exhalation. These are volumes and will
be reduced with either obstructive or restrictive abnormalities. When these volumes are compared to the Vital
Capacity of the person as a percentage of the total volume exhaled, the
percentage exhaled at specific times will provide information about the expiratory
flowrates. In persons with obstructive
diseases, the percentages will be reduced from normals as indicated below.
Forced
Expiratory Volume in ½ Second (FEV0.5) is the volume that a person
can exhale in the first half second of a forced exhalation. Normally a person should be able to exhale
between 50 and 60% of their vital capacity in the first half second. With obstructive abnormalities, the
percentage of the vital capacity exhaled will decrease as the collapsing
airways will not permit sufficient flow to allow this much air to be exhaled so
rapidly. With restrictive abnormalities,
the percentage will stay the same or may slightly increase, though it will remain
below 120% of predicted.
Forced Expiratory Volume in 1 Second (FEV1.0) is the volume that a person can exhale in the first second of a forced exhalation. Normally a person should be able to exhale between 75 and 85% of their vital capacity in the first second. With obstructive abnormalities, the percentage of the vital capacity exhaled will decrease as the collapsing airways will not permit sufficient flow to allow this much air to be exhaled so rapidly. With restrictive abnormalities, the percentage will stay the same or may slightly increase, though it will remain below 120% of predicted.
Forced
Expiratory Volume in 3 Second (FEV3.0) is the volume that a person can exhale in the first three seconds of a
forced exhalation. Normally a person
should be able to exhale between 95 and 98% of their vital capacity in the
first three seconds. With obstructive
abnormalities, the percentage of the vital capacity exhaled will decrease as
the collapsing airways will not permit sufficient flow to allow this much air
to be exhaled so rapidly. With
restrictive abnormalities, the percentage will stay the same or may slightly
increase, though it will remain below 120% of predicted.
Peak
Expiratory Flowrate (PEF or PEFR) is the highest flowrate that a person achieves
during a FEVC maneuver. This occurs very
early in the exhalation. The flow-volume
curves above indicate that restrictive problems generally do not affect the
PEFR but obstructive problems do. Most
of the airway resistance comes from the large airways, so problems with small
airways will only make a difference that can be seen when the degree of
obstruction in these airways is very large.
Forced
Expiratory Flowrate between 200 and 1200 ml of expiratory volume (FEF
Forced
Expiratory Flowrate between 25 and 75% of the FEVC (FEF25-75) is a determination of the
average flowrate at which the middle half of the FEVC is exhaled. This provides some information about the
conditions of the small airways. The
flow in this portion of the exhalation is less dependent on effort than the
peak flowrate. This flow is more related
to the condition of the airways than to the effort the patient provides during
the forced exhalation. This value is
determined by integration of the electronic information with modern pulmonary
function machines and was based on calculating the slope of a line connecting
the points at which 25% and 75% of the forced vital capacity was exhaled by the
person. The limitation of the test is
that so little of the total airway resistance occurs in the bronchioles.
Forced
Expiratory Flowrate between 75 and 85% of the FEVC (FEF75-85) is a value representing the
average flowrate between the point the person has exhaled 75 and 85% of their
vital capacity. In the continuing
attempt to identify that pulmonary function parameter that will identify obstruction
at a point that the obstruction is still reversible, this flow is even less
dependent on patient effort than the FEF25-75 and provides
information on smaller, more distal airways than the tests described so
far. Many of these flow rates that are
averages are again due to the fact instantaneous flows can not be determined
reliably from volume – time graphs.
Forced
Expiratory Flowrate at 50% of the FEVC (FEF50) is the instantaneous flow
rate at the point a person has exhaled exactly half of their vital
capacity. It provides similar
information to the FEF25-75 and is easier to determine from the more
common flow – volume plot used today.
Forced
Expiratory Flowrate at 75% of the FEVC (FEF75) is the instantaneous flow
at the point the person has exhaled exactly ¾ of their vital capacity.
.
Volume
of Isoflow (VISOV) is a special test in which the
dependence of expiratory flowrate on the density of the gas is determined. A person performs a forced exhalation
maneuver and the information in plotted as flow versus volume. The gas in the lungs of the person is replaced
by a mixture of 80% helium and 20% oxygen and the forced exhalation maneuver is
repeated. The two curves are plotted on
the same paper or computer screen with the volume aligned at Residual
Volume. The percentage of the Vital
Capacity where the two curves are the same is calculated as a percentage of the
Vital Capacity.
Resting Ventilation
Patient becomes accustomed to
machine
Nose Clip on - Mouthpiece in
Normal, quiet breathing
Continue at least 60 seconds
Graph Volume vs Time .
Total breathed in or out = V Minute Ventilation
Minute Ventilation =
____________
Breathing Rate Tidal Volume (average or mean)
Normals : VT
400 - 1000 ml
Breathing Rate 6 - 16 / minute
Minute
Ventilation 4.0 -8.0 L/min.
With obstruction or restriction
VT decreases
As VT decreases
breathing rate increases
Vmin
increase with increased metabolism
Vmin
increases with hypoxemia
Vmin
increases with hypercapnea
Less energy to increase rate
rather than volume
Rate and Volume Effects on Alveolar Ventilation
VA = (VT
- VDS) x BR
Vmin
= 500 x 12 = 6.0 L/Min
VA = (500 - 150)
Vmin
= 1000 x 12 = 12.0 L/Min
VA = (1000 - 150)
Vmin
= 500 x 24 = 12.0 L/Min
VA = (500 - 150)
VT increase affects
VA more than Rate increase
Vital Capacity (VC or SVC)
Noseclip
and mouthpiece
Several quiet breaths on
machine
Establish baseline FRC
Inhale fully followed by slow,
full exhalation
Exhale slow, full followed by
full inhalation
Do not force exhalation - keep
airways open
Forced Vital Capacity (FVC)
Noseclip
and mouthpiece
Inhale fully
Immediately exhale all air as
fast and as far as possible
Try to get out air as fast as
possible
Try to get all air out (3 Sec
minimum)
Often follow with Forced
Inspiration
Graph Volume vs Time or Flow vs Volume
Vital Capacity
Depends on Compliance and
resistance
FVC and SVC should be same
(±5%)
Airway obstruction decrease FVC
not SVC
Volume may be normal but takes
much longer to exhale (4 - 6 Sec
Normally)
Spirometer needs to accommodate
long enough time (20 seconds)
Restriction reduces SVC and FVC
same
FVC < 80% Predicted abnormal
both obstruction and Restriction
TLC decreased proportionally =
restrict
FEVT
FEVT Normals
FEVT compared to FVC
for evaluation of obstruction
FEV0.5 / FVC % = 50
- 60 %
FEV1.0 / FVC % = 75
- 80%
FEV3.0 / FVC % = 97%
FEVT
Forced Expiratory Flowrates
FEF50 and FIF50
PEFR FEF
PEFR very effort dependent most
affected by large airway problems, severe obstruction in peripherals will
decrease
FEF
May be increased with
restriction
FEF25-75 Mid
expiratory flowrate
FEF75-85 More
peripheral airways
FEF50 instantaneous
flow at 50% of FVC
FIF50 instantaneous
flow at 50% of IVC
FEF50 / FIF50 should
be <1.0
Further into volume looks at
more peripheral airways
Want to see changes in smallest
airways
Maximum Voluntary Ventilation
(MVV)
Maximum amount of breathing
Patient breathes fast and deep
for 10-15 seconds
Record total volume moved in
that time
Calculate out to one minute
Need correct combination of
rate and volume
Too fast or too deep will
decrease MVV
.
Volume of Isoflow (V iso V)
Best test we currently have to
look at reversible obstruction
Perform flow-volume loop as
usual
Replace air in lungs with He /
O2
VC x 3 or tidal for 6 minutes
Repeat Flow-volume loop
Superimpose curves at RV
Determine volume exhaled where
flow is independent of gas density
Pulmonary Compliance (CL+T)
Ease with which lung is
distended
Change in volume / change in
Pressure
Measured under static
conditions 10 sec+
For most accuracy patient is
paralyzed
Should measure at variety of
volumes
Normal is 100 ml / cm H2O
Restrictive disease decreases
Emphysema increases
Airway Resistance (RAW)
Difficulty of moving air
through airways
Pressure needed at given
flowrate
Change in pressure / flow (cmH2O/l/sec)
Obstructive disease increases
Resistance and flowrate will
move in opposite directions
As resistance increases, work
of breathing increases, use accessory muscles of exhalation
Maximum Inspiratory /
Expiratory Pressures (MIP / MEP)
Measurement of muscular
strength
MIP - occlude inspiratory valve
Allow exhalation, request
inhalation
Observe maximum pressure
Maximum of 20 seconds
MEP - Occlude expiratory valve
Allow inhalation, request
Exhalation
Observe maximum pressure
Normals for Adults
Minute
Ventilation?
4 - 10 Liter / minute
Breathing rate?
6 - 16 / minute
Tidal Volume?
400 - 1000 ml / breath
Vital
Capacity?
2.5 - 6.0 Liter
Total Lung
Capacity?
4.0 - 8.0 Liter
Functional
Residual Capacity?
2.3 - 4.6 Liter
Inspiratory
Capacity?
2.0 - 3.4 Liter
Inspiratory
Reserve Volume?
1.6 - 2.4 Liter
Expiratory
Reserve Volume?
1.1 - 2.4 Liter
Peak Expiratory Flowrate?
6.0 - 13.5 Liter / Second
FEF 200-1200?
3.5 - 10.0 Liter / Second
FEF 25-75?
2.0 - 5.5 Liter / Second
FEF 75-85?
1.0 - 2.5 Liter / Second
FEF 50?
3.5 - 6.7 Liter / Second
FEF50
/ FIF50?
< 1.0
Maximum
Voluntary Ventilation?
90 - 160 Liter / Minute
Volume of
Isoflow?
10 - 20 % of Vital Capacity
Pulmonary
Compliance?
100 ml / cm H2O
Airway Resistance
0.6 - 2.4 cm H2O /
Liter / Second
MIP?
> 60 cm H2O
MEP?
80 - 100 cm H2O
Spirometry Before and After
Bronchodilator
Assure no bronchodilators on
board at least 1.5 times duration of action
Perform spirometry as usual
If see indication of
obstruction
Aerosol with fast acting
bronchodilator
Repeat spirometry
Determine if response to
bronchodilator
Response is increase of 20% or
more in flows (volumes)