ISO 9360-1 Anaesthetic and respiratory equipment –Heat and
moisture exchangers (HMEs) for humidifying respired gases in
humans –Part 1: HMEs for use with minimum tidal volumes of 250 ml
Measurement of moisture loss- HME
6.2 Measurement of moisture loss
6.2.1 Principle
The performance of an HME shall be measured by recording the mass
of water lost from the test apparatus specified in 6.2.2.
6.2.2 Test apparatus
The test apparatus (Figure 1 ) shall comprise the following
components.
6.2.2.1 Bidirectional flow generator.
This is a mechanically-driven piston used to produce a flow having
sinusoidal waveform.
6.2.2.2 Humidity generator (HG), consisting of
a) a heated water bath (Figure 2) through which air is bubbled in
both directions;
b) a rigid cylindrical reservoir (Figure 3) with a maximum volume
of 7 l and a diameter of approximately 1 50 mm,containing a 2 l
reservoir bag;
c) a thermally insulated chamber (Figure 4), which contains the
water bath, the reservoir and a heat source.
6.2.2.3 Air delivery system (Figure 5), consisting of a T-piece with an internal diameter
greater than 1 5 mm, and an exhaust tube at least 200 mm in
length.
6.2.2.4 Weighing equipment, with an accuracy of ±0,1 g or better in the range of the
mass to be measured.
6.2.2.5 Flowrate measuring equipment, with an accuracy of at least 5 % of the reading.
6.2.2.6 Calibration HME (Figure 6) consisting of a housing containing 81 polyvinyl
chloride (PVC) tubes arranged in a 9 * 9 array, each with
an internal diameter of 2 mm, an external diameter of 4 mm, and a
length of 50 mm.
When the apparatus has been constructed and operated as specified
in 6.2.2, the moisture loss from the humidity generator with
the calibration HME will be as shown in Table 3.
Key
1 to 1 9 see annex A
20 Sinewave generator inlet
21 Air outlet
22 Dry air supply (23 ±1 ) °C, < 1 mg H 2 O per litre air
23 Weighing equipment
Figure 1 — Test apparatus side view
6.2.3 Test conditions
6.2.3.1 The air delivered to the HME machine port by the air
delivery system shall be at a temperature of 23±1℃ and
shall have a humidity not exceeding 1 mg.l -1
6.2.3.2 The HME shall be tested at those conditions specified in
Table 2 which are within the range specified for the HME by
the manufacturer, at the maximum tidal volume recommended by the
manufacturer if this value is greater than 1 l, at a frequency
of 1 0 breaths.min -1 , and an I:E ratio of 1 :1 .
6.2.4 Procedure
6.2.4.1 Connect the HG to the bidirectional flow generator.
6.2.4.2 Adjust the bidirectional flow generator to give one of the
test conditions in Table 2, measured at the machine port of
the HME, within the operating range of the HME as specified by the
manufacturer. Adjust the flowrate of air delivered by the air
delivery system to be between >1 and <1 ,5 times the peak
flowrate of air drawn into the machine port of the HME. The
peak flowrate is stated in Table 2.
6.2.4.3 Operate the test apparatus with an HME of the same type
that is to be tested for a minimum of 1 h,with the water bath at a
temperature of 37 ±0.5℃ , and the air within the insulated
chamber at temperature of 37 ±1℃ . Maintain this temperature
for the duration of the test procedure.
6.2.4.4 Confirm that the volume of air leaving the machine port of
the HME is that required for the test condition chosen from
Table 2.
6.2.4.5 Record the mass of the HG only (i.e. not including the HME)
(m 0 ).
6.2.4.6 Replace the HME with the one to be tested and operate the
test apparatus for (60 ? 5) min.
6.2.4.7 Record the mass of the HG only (i.e. not including the HME)
(m 1 ).
6.2.4.8 Continue to operate the test apparatus up to the maximum
time of use recommended by the
manufacturer.
6.2.4.9 Record the mass of the HG only (i.e. not including the HME)
(m 2 ).
6.2.4.10 Confirm that the volume of air leaving the machine port of
the HME is that required for the test condition chosen from
Table 2.
6.2.4.11 Calculate the HME moisture loss for the first hour, M 1 ,
using the formula
M 1 = (m 0 -m 1 ) /V 1
where
m 0 is the initial mass of the HG;
m 1 is the mass of the HG after 1 h;
V 1 is the total volume of air leaving the HME machine port
during the first hour of the test.
6.2.4.12 Calculate the HME moisture loss for the entire duration, M
max , using the formula
M max = (m 0 - m 2 ) /V 2
where
m 0 is the initial mass of the HG;
m 2 is the mass of the HG after the maximum time of use as
recommended by the manufacturer;
V 2 is the total volume of air leaving the HME machine port
during the entire test period.
6.2.4.13 Repeat the procedures in 6.2.4.2 to 6.2.4.1 2 for all the
test conditions given in Table 2 which are within
the operating range of the HME as specified by the manufacturer.
When the apparatus has been constructed and operated as specified
in 6.2.4, the moisture loss from the humidity generator with
the calibration HME attached should be as shown in Table 3. This
shall be confirmed for the specific test apparatus by
conditioning the test apparatus for at least 2 h (see 6.2.4.3), and
then operating the test apparatus for a period of 2 h with the
calibration HME, and measuring the mass loss over that period (all
mass measurements shall be made without the HME attached to
the test apparatus).