“5 A5 ‘H’
11L1
Ftc. 1. Schematic diagram of the conductivit unit.
(Submitted for 1)ublication September 25, 1962; accepted March 12, 1963.)
ADDRESS: 719 \Vest Water Street, Elmira, New York.
PEDIATRIcs, July 1963
89
A
Simple,
Home-assem
bled
Apparatus
William R. Phillips, M.D.
I
N THIS ARTICLE we d!escribe a metllOdlof d!eterlllining the electrical
cond!uctiv-ity of sweat. Tile instrument described!
(Fig. 1) andl the technique used is basically
tile same as tilat used by Shwadllman et
a!. in the preceding artidle.l Tile
instru-ment silo\Vfl in Figure 2 differs only in
tluat the iontophoresis equipment is built
into the same cabinet with the
collductiv-ity unit.
The instrumeiut described! in this article
measures tile electrical cond!uctance of
cm-(!iluted sweat. Because tilere is no \Veiglling
and! dilution of the sample, and! because iuo
chemical analysis is done, several sources
of error are removed. The results of the test
are known immediately.
The method was conceived ill 1959 fol-lowing publication of Gibson and Cooke’s2
article on iontopluoresis of pilocarpule and
of Bloxam’s irticle descril)ing all
illstrfl-ment for measuring tile electrical
con-ductance of hod!y fluids. An electrical
iia-gram u5Cdl for the iontopiloresis of
pilo-carpme has alread!y been publislled.2 Our
only change in tins electrical circuit as
I)resentedl by Gibson and Cooke was tue
insertion of a 1/100-watt fuse in the skin
electrodle circuit. Tluis fuse blows at 16
milleamperes. We also use a small
22%-volt “B” battery andl omit the pilot ligiut. A built-in timing d!evice is addled! for
dOll-venience.
The electrical d!iagranl for tile
cOildiuc-tivity part of tiue instrument is Silown in
Figure 1. The wheatstone bridge is dlriven
with 6 volts alternating current. This avoids
significant polarization of tiue sample. An
“electric eye” is used instead of a meter.
The conductivity chamber for Ilolding tiuc
sample of sweat is a 5-cm section of a Kato
nhicro-sedlinlelltatioll rate IPettd’ The
chamber electrodes are two 5-inch lengths
of 30-gauge 14-carat wluite-gold ‘ire. These
wires are illserted! illtO the ends of tile
Kato pil)ette containing sweat, andi
ad!-vancedi until their tips are 2 cm apart. Tiue
other endis of tlleSe wires are collllected!
to tile bridige circuit by two bindling posts.
The instrument is caiibratec! by using
soltt-tions of SOd!iulll dilloridle of known strengtil
expressed in meq/i. Tile strength of the
various calibratillg solutiomis used is
mdi-cated OIl the conductivity mdlicatOr as shown in Figure 2. There are no
provi-SiOl1S for temperature conil)ellsatiOll. Tiue
instrument is sufficiently accurate at any
comfortable room temperature. No part of tile instrument is custom built. Each
90 SWEAT CONDUCTIVITY
Fic. 2. 1, interval timer for iontophoresis; 2, con-eluctivity indicator; :3, switch for conductivity unit; 4, pilot light for the conductivity unit (there is no pilot light for the iontophoresis section of the
instrument); 5, “electric eye”; 6, conductivity
chamber; 7, combination switch and regulator for
the iontophoresis current; 8, jacks for the skin
electrodes; 9, Milleammeter for indicating the
ionto-phoresis current; and 10, 1/100 watt fuse in the
skin electrode circuit.
commercially. The total cost of parts is $40.
For construction of the conductivity unit
alone the cost of parts is $20.
TECHNIQUE
The iontophoresis is done with the
in-strument disconnected from the 115-volt
house current. A 0.1% solution of
pilo-carpine chloride is iontophoresed into a
3-by-6-cm area on the forearm at a current
flow of 4 milleamperes for a period of 6
minutes. In infants or emaciated children
whose forearms are too small, an area on
the back is used. After washing and
dry-ing, the iontophoresed area is covered
with a shallow plastic cup (Fig. 3). The
edges of the cup must effectively seal the
area to prevent escape of sweat, as well
as to prevent evaporation. The cup is
fastened to the skin with a small strip of
adhesive and then bandaged snugly but
comfortably against the arm or back with
several turns of elastic bandage. A 75-watt
lamp is placed 6 or 8 in. from the cup to
keep it warm during the collection period.
This heat prevents condensation of salt free
moisture on the walls of the cup. It also
increases the yield.
After a collection period of 25 minutes
the bandage and the cup are removed. The
sweat on the skin is immediately scooped
up with a sharp edged spoon (Fig. 4).
With a mouthpiece and rubber tube
suffi-cient sample is drawn into the Kato pipette
from the pool of sweat in the spoon. The
pipette is mounted into its mounting clip
on the instrument. The gold wires are
in-serted in each end of the pipette and
ad-vanced until their ends are 2 cm apart,
using the etchings on the pipette for exact
positioning. It is only necessary that tilere
be enough sweat in the pipette to allow
the tips of the wires to be embedded in
the sweat and their tips still be 2 cm
apart. There must be no intervening
bub-bles. As each wire is positioned its
corre-sponding binding post is tightened.
The instrument is now plugged into the
house current and the switch of the
con-ductivity unit is turned on. After the
“elec-tric eye” begins to glow green, the knob
of the conductivity indicator is adjusted to
that point wilich gives the widest opening of the “eye.” The pointer now indicates
that strength of sodium chloride solution
(in meq/l) wilose conductance equals tile
Normal’ Cy8tic Fibrosis*
Age Nv mber
(yr) !l.eadincjf
Age
Number (yr) Readingf
.lge
Number (yr) Iteadingt
12 ‘2 15)7 3 1)7 4 17 5 ‘2 6 ‘2 7 ‘2 8 3 9 5 10 6 11 6 12 8 13 10 14 15 15 15 16 15 17 ‘24 >150 135 >150 >150 150 125 135 125 >150 140 150 120 150 125 130 125 >150 57 60 40 70 30 35 25 40 30 20 30 28 30 25 50 22 50 70 30 50 30 30 25 33 35 50 30 30 50 40 30 30 50 60 45 65 45 60 35 35 32 30
C Normal range 20 to 80, average 44; cystic fibrosis range 120 to > 150.
t
The instrument reading indicates the strength of sodium chloride solution in meq/l that equals in conductancethe sample of sweat.
TABLE I
THE ELECTRICAL CONDUCTANCE OF SWEAT: NORMAL AND ABNORMAL (CYSTIC Fimcosts)
1 (1 wk)
‘2 3 4 5 6 7 547 8 9 5)7 11 5 i-I 11 1 5 13 557 14 15 16 17 18 517 19 ‘20 ‘21 15)7 ‘23 1557 ‘24 ‘25 ‘26 15)7 27 ‘28 15)7 ‘29 15)7 30 81 ‘2 ‘2 33 ‘2 34 ‘2 35 ‘2 36 ‘2 37 ‘2 38 ‘2 39 3 40 4 41 4 42 4
43 4 30
44 5 ‘25
45 5 35
46 5 65
47 5 40
48 6 25
49 6 50
50 6 50
51 6 40
52 6 70
53 6 40
54 7 50
55 7 35
56 8 75
57 8 45
58 8 30
59 9 30
60 9 50
61 9 35
62 10 40
63 10 40
64 11 50
65 11 30
66 11 50
67 11 30
68 11 43
69 15 60
70 18 48
71 25 55
72 28 55
73 30 50
74 36 65
75 36 70
76 37 80
77 38 40
78 38 55
79 40 40
80 46 65
81 50 60
82 54 55
92 SWEAT CONDUCTIViTY
emphasized that this reading is not the
level of tile sodium cilloride in the sweat. It is rather an indication of the total
elec-trolyte content as reflected by its ability to
conduct electricity. It is true that sodium
and chloride ions are the most influential
iOflS 011 this condluctance because of their
numerical superiority in sweat.
Accord-ingly sweat samples showing abnormally
high conductivity rates will also have
aT)-normally higlu sOdliunl andl chloridle
con-tent.
RESULTS
A large series of \vell-colltrOlled tests has
1)eefl presented in an earlier article.1 The
following results were obtained in a pedi-atric practice located in an area where
Cilemical analysis of sweat was not readily
available.
In 104 attempts we were unable to
oh-tam sufficient sweat for testing in four
subjects. Three of these failures were in
infants and OllC was in an adult. The yield
of sweat was usually between 0.2 and 0.5
ml. Only a fraction of this amount is
needed. Of tile 100 successfully completed
tests, 8:3 were made 011 normal subjects.
or n patients with illnesses other than
cystic fibrosis. In tilis nollcystic fibrosis
group tile lowest readhng was 20, while
the Ilighest was 80; the average was 44. Tile remaining 17 tests were done on 17
patiellts known to have cystic fibrosis. In
this group the lowest reading was 120,
while five of the group gave readings
higher than 150, whicil is beyond the
ac-curate range of the instrument
(
Table I).SUMMARY AND CONCLUSIONS
All apparatus for determining the
elec-trical conductivity of undiluted sweat has
been described. The technique used and
the results obtained have been presented.
The results indicate that the instrument,
\vllen used with the technique described,
is of value in the diagnosis of cystic
fi-brosis ill children.
ADDENDUM
Since this ork \VdS completed the instrument
has l)eell improve(l l the’ addition of a control
for calibration. This is accomplished b simply
sui)stituting I variable 70K-ohm resistor for the
50K-ohm 6xei resistor in the wheatstone bridge
(Fig. 1). At the beginning of a test, a standard
solution containing 100 med1 of saline solution is
Plt1e(l in the conductivity pip:tte. The
conduc-tivitv indicator is set at 100. The calibration
con-trol is tlse’n adjusted until the eye is at its widest opening. This automatically compensate’s for
van-ations in ambient temperature, as well as other intrinsic variations from the original calibration.
REFERENCES
1. Shvachmin, H., Dunham, R., and Phillips, IV.
Fl. : Electrical conductivity of sveat : a simple
diagnostic test ill children. PEDIATHICS, 32:85,
1963.
2. Cil)SOl1, L. E., and Cooke, B. E. : A test for
concentration of electrolyte in swe’at in cystic
fll)rosis of tl#{236}epancreas utilizing pilocarpine
iOfltO1)horeSis. PEDIATRICs, 23:545, 1959.
:3. Bloxam, A. P.: A new instrument for the
measurement of electrical conductivity of
