11 :
Ph.H. QUAl\JER
PEF
12
17
such as may occur with concertina-hoses
during respiratory manoeuvres.
when handled
i
'I
10
-'"
3.5.1.4 Kymograph
The paper speed should be 3 cm/min for recording semistatic manoeuvres. and at least 120 cm/min for recording
dynamic lung volumes and ventilator:' flows.
::::. 8
:;;
,g
~
i
. .1
:i
11
6
"§
'6x
UJ 4
MEF:5~.FVC
2
FVC
0
r
0
I
1
!
2
!
3
i
-+
!
5
1
6
3.5.1.5 Pressure. leaks
The maximal pressure at the mouth during a forced expiratory ventilatory manoeuvre should not exceed 0.6 kPa.
The driving pressure required to achieve a volume
deflection should not exceed 0.03 kPa. The circuit should
be free from leaks. TI1ese are looked for by placing a
weight on the spirometer bell to raise the pressure by at
least 0.2 kPa: the recording should remain level over at
least a I min period. Tests for leaks should be performed
each week.
Expired volume (litre)
Fig. 5. - Using the «envelope method". a composite curve is oblaIned from a set of maximal expiratory
now-volume
curves by
oupenmposition
at the level of IOtal lung capacity and by r~portlng
,:1e largest now values at given percentages ot' the largest FVc.
"ot~ that the variability in maximal now ,hown here may arise
(mm different tlexion oj the neck at each FVC manoeuvre.
~.5.1.2 COI/S{rt/c{iOI/
.-\ long-cylinder spirometer bell is the simplest in conmuction and mechanically the least vulnerable.
For
the measurement of static lung volumes. a bell cross,ectional area of 300 to 400 cm~ and a moving mass of
maximally 600 g is acceptable.
A wide-cylinder bell
(cross-sectional area 2000 to 3000 cm:) has considerably
better dynamic properties for the same volume. weight
and material. Such a bell requires a specially constructed suspension and electrical amplification of the displacement signaL A larger surface without the problems of
suspension can be provided by a wedge-shaped spirometer.
3.5.1.6 Tel1lperafllre
The spirometer should be equipped with a thermometer
which should be carefully located. For correcting inspired
gas to BTPS conditions the temper..lture may be measured
at the inspiratory line near the mouthpiece. For expired
gas the situation is more complex since temperature
may rise considerably at the level of the soda lime when
CO, is adsorbed. In a water-seal spirometer the water
temPerature can be used for correcting inspiratory and expiratory gas volumes. In spirometers equipped with a gas
circulation pump the gas temperature at the outlet of the
spirometer. or under the spirometer bell. is an acceptable
compromise: in spirometers with a common gas inlet and
outlet the inspirator:' temperature should be measured at
that point: the site for expiratory tempemture corrections
should
be carefully
chosen
within
the spirometer
r106.
149).
111'11
,.i
3.5 .J..1..ff;/i brat iOI-:J
3.5.1.3 Connections
The gas connections of the spirometer serve the following purposes:
I. Oxygen supply to compensate for O,-consumption and
,tabilization of the oxygen concentration in the spirometer.
::. Supply of indicator gas (usually helium) for deterl1ining the functional residual capacity:
~. The connections for the subject are usually provided
~)ya two-way tap:
~. A connection to and from the spirometer should be
wailable. so that the tracer gas concentration in the spi'ometer (for example helium) can be measured.
Carbon dioxide should be adsorbed by soda lime
:ontained in a canister. The fractional CO- concentration
n the spirometer should be kept below 0.005. The
lOse connecting the patient to the spirometer should be
;ufficiently stiff to prevent spurious volume deflections.
I'
!,
The spirometer
calib
and recordin
e ui m
onths b
should be
means of an
accurate
displacement
shouldshould
be linear
al
il!ht 3within
~:tre~l.iItedI. Thesyrinfe'
the latter
be
over the entire volume range and capable of being recorded with an accuracy of i: 3% of the reading or :t
50 ml. whichever is greater. accounting for the potential
error in the volume displacement from the calibrated
syringe this implies that an error of up to 3.5% or 70
ml, whichever is greater. is acceptable. A change in volume of 25 ml should be detectable. Similarly the recorder speed should be checked at least quarterly with a
stopwatch. and be accurate within Ic~. In spirometers
where the time recording is initiated when the expired gas
exceeds a certain volume. the acceleration of the electric
motor is critical. TI1is is difficult to check. but can be
done with a calibrator based on explosive decompression
[150. 151] or equipment which delivers precisely known
flow patterns [152].