TTT TTT TT

A, THERMOREGULATORY SWEATING:
1.8

mgm / min mgm/min | ¢
1.2

1,0
8

4 END EXERCISE

6
4

2

°

BEGIN EXERCISE

i | ] i | 1 1 i]

B. PSYCHOGENIC SWEATING |

CARD

TTT TTT TTT dt

1 1 L J

7 8 $s 0
TIME-MINUTES

8
TIME-MINUTES

9

oOo HW 12 7 «18

Ficure 9, These tracings represent recorded changes in evaporative water loss in A: from
the forearm during 2 brief period of exercise, and B: from the palm of the hand
when the subject was shown a card on which was printed a profane word.

—12—


of information are obtainable from these rec-
ords: 1. instaftaneous rate (ordinate), 2. ac-
celeration (slope of tracing at any part of the
curve), of water vapor production, and 3. total
amount of water produced (area under curve
for any time interval). A rate of air flow of
200 cc/min was adequate to keep the skin free
of accumulated sweat during both of these meas-
urements. Drying room air (or air from the
compressed air tank) befove it is presented to
the skin provides a reproducible sample for the
reference side of the cell and further. insures
complete evaporation of sweat by providing a
steep vapor pressure gradient.

Photographs of the control panel, cell hous-
ing, and the unit in operation are shown in Fig-
ures 10, 11 and 12 respectively.

This report has presented a method for the
measurement of evaporative water loss from
small skin areas. The same detection system
could be readily applied to measurements in-
volving larger skin areas, including whole body,
by drawing an aliquot through the thermal con-
ductivity cell from a faster flowing air stream
directed through a container enclosing a larger
body area. In this application, the measurement
of the amount of water passing through the
main air stream, plus the amount extracted by
the sampling circuit, would provide the required
calibration units as a function of cell imbalance.
Since other gas species are detectable by this
system, it is important that respiratory gases
not be allowed to mix with air used for evapo-
rative water measurements.

This method provides an indirect measure-
ment of evaporative water loss with a stable
reference and adequate precision for most tests.
The attachment of the sampling capsule need
not interfere with the free movements of the
subject and could be worn for extended periods
of time during most performance tests. Using
dry air as a carrier gas, the difficulties associ-
ated with using other gases or gas mixtures is
avoided (8). Although the calibration proce-
dures require meticulously precise techniques,
the actual operation of the system is relatively
simple.

—3—

BIBLIOGRAPHY

. Rodahl, K. and D. W. Rennie. Comparative

Sweat Rates of Eskimoes and Caucasians un-
der Controlled Conditions. Proj. No. 8-7951,
Rep. No. 7, AAL, Ladd AFB, Alaska, 1957.

. Belding, H. S. and B. A. Hertig. Sweating

and Body Temperatures Following Abrupt
Changes in Environmental Temperature. J.
Appl. Physiol., 17:103-106, 1962.

. Webb, P., L. N. Garlington and M. J.

Schwarz. Insensible Weight Loss at High Skin
Temperatures. J. Appl. Physiol., 11:41-44,
1957.

. Brebner, D. F. and D. McKersiake. The Ef-

fect of Cyclical Heating of the Front of the
Trunk on Forearm Sweat Rate. J. Physiol.
(Lond.) 158:144-153, 1961.

. Palmes, E. D. An Apparatus and Method for

the Continuous Measurement of Evanorative
Water Loss from Human Subjects. Rev. Sci.
Instr., 19:711-717, 1948.

. Bullard, R. W. Continuous Recording of

Sweating Rate by Resistance Hygrometry. J.
Appl. Physiol., 17:745-757, 1962.

. Custance, A. C. Cycling of Sweat Gland Ac-

tivity Recorded by a New Technique. J. Appl.
Physiol., 17:741-742, 1962.

. Wilcott, R. C. The Continuous Measurement

of Palmar Sweating. Am. J. Psychoi., 74:
619-624, 1961.

. Ratcliffe, J. S. A Thermistor Temperature

Controller with Increased Sensitivity, J.
Chem. Education, 39:637, 1962.


FLOW METER
( 200cc/ min)

i=
> Y o£ >
CALIBRATION
FLOW BOTTLES
REGULATOR
DRYING 4
UNIT
TE
THERMAL
CDNDUCTIVITY TEMP,
COMPRESSED CELL SENSOR
AIR
e TEMP.
J CONTROL
A HEATER (50° ¢)
o¢
CONNECTIONS { 0 5 — ii
To fou}
BRIDGE | o2
o3
os

Ficure 5. This design differs from that shown in Figure 4 in that a tank of compressed
air is used to maintain air flow through the system. Operating the differential
pressure-flow regulator at an inlet pressure of 12 psi was adequate to establish a
uniformly controlled air flow of 200 ce/min. The flow regulator was housed in
the control panel ezbinee.

—s—



CURRENT

VOLT ADy.

ADy. COURSE FINE
soa 2K S000
weed WW We

4) t 4

av 7 (NOTE 1) Ci)
oe 7, (NOTE 2) Oo 4
0-10
> ° CE nan
10 mA LL J
SENS. ar re §
'e ne
ADJ. Ps tors
BK J Lrre 2
00T) ew
) Wr Oo 3
Pape
Ww—t-O 6
NOTE:
-——____—_.6
. ADJUST TO 12.0 Vv.
2. ADJUST TO 6.0 mA. a } ve

Ficure 1. This circuit is a slightly modified form of the bridge suggested by the manufacturer

732-436 O-64--2

of the thermal conductivity cell. The numbered connections to the cell are specific
to the model, The mV. recorder used in these tests was a Varian, graphic recorder,
model G-14. A 12 V. wet cell battery was used as a DC voltage source in initial
studies. Two 6 V Ni-Cd batteries were used in later experiments; these units
provided a more stable, smaller voltage source. All electrical connections to the
thermal conductivity cell should be shielded throughout the circuit.

—5—

CONNECTIONS
TO THERMAL
CONDUCTIVITY
CELL

~ TO RECORDER

(0-10 mv)


10.
11.
12.
13.

14.
15.

. Thermoregulator

Parts List for Thermal Conductivity

Cell Circuit and Accessory Components:

- Model AEL 9677 Thermistor Thermal Con-

ductivity Cell, GOW-MAC Instrument Co.,
100 Kings Road, Madison, New Jersey. (1)

. 0-10 (with alternate 0-1.0) mv, DC record-

er (type used: Varian, graphic model G-
14) (1)

. Variable transformer (type used: “Adjust-

a-Volt”, type 100 BU, Standard Electric
Products Co., Dayton, Ohio) (1)

. Small air cirbulating fan (recomm. 4”

blade, 110v AC) (1)

(type used: Cat. No.
55260, thermoregulator with set point at
50.0°C (specify), Chicago Apparatus Co.,
1827 McGee Street, Kansas City 8, Mis-
souri) (1)

. Thermoregulator Relay (type used: Cat.

No. 55275 thermoregulator Buffer relay,
Chicago Apparatus Co., see above address)
(1)

. 12 V DC supply (recomm. N. - Cd, wet cell

or other suitable, rechargeable battery) (1)

. Rotametric type air flowmeter, 0-300 cc/

min range (1)

. Compressed air tank with two stage pres-

sure regulator and indicating air pressure
gauges (1) (if air flow is maintained by
drawing the air through the cell circuit, re-
quire suitable pump and vacuum gauge)

0-15 V DC panel meter (1)
0-10 MADC panel meter (1)
0-50 MICROAMPS, DC pane! meter (1)

Flow Controller (type used: Differential
Flow Controller, (Moore), Cat. No. PC-
103-6 for 1609, with needle valve) (1)
Three position stopcocks (3)

NE 51 panel lights with mounts (5)

16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.

27.

28.
29.
30.

31.

32.

1 amp. fuse with holder (1)
10 MA fuse with holder (1)
DPDT switch (4)

150 ohm flexible heater wire (1)
500 ohm, 2 watt pot. (3)

2K, 2 watt pot. (1)

5K, ten turn pot. (1)

100 ohm, ten turn pot. (1)
14 v (nom.) Hg. battery (2)
3 deck, 3 pos. switch (1)

1/2 watt resistors:

. 50 ohm w. w. (2)
. 150 ohm (1)

. 1.5 meg. (1)

. 220 k (1)

3.3 k (3)

. 250 ohm (1)

. 2.2 k (2)

| 2.7k (1)

Drierite Containers (type used: Cat. No.
20885, Drying Tower, Drierite, Chicago
Apparatus Co. (see above address} (2).

Pe ho AO oe

Shielded, single connector, stranded wire
Shielded, double connector, stranded wire

Mounting cabinet and panel for meters and
controls (1)

Insulated box (5) for constant temp. con-
tainer for TCC.

MISC.:

a. Solder, “hook-up” wire, banana plugs
and jacks, multiple terminal cable con-
nectors, grommets, terminal strips and
connectors, misc. hardware.

. P. E. tubing with connectors

Tygon tubing

|. 2.5K (nom.) thermistor probe.

Roo

ACKNOWLEDGEMENT

The authors would like to express their appreciation to Mr. J. Hildebrandt,
Department of Physiology and Biophysics, University of Washington,
School of Medicine, Seattle 5, Washington, who suggested the thermal
conductivity cell as a possible humidity sensor.

—4—


150.0
M

1.5V

4I|}-—-

Ficure 3. A separate indication of the temperature in the thermal conductivity cell housing
was provided with this circuit. Although this measurement of temperature was not
precise enough to provide an indication of cell temperature changes during operation
(heater contro) cycling), it served as a valuable aid in adjusting heater voltage
during cell warm-up.

ROOM TUBING REEDLE
‘AIR CONNECTOR VALVE

‘

FLOW
METER

(200¢e/min}

PLASTIC
CAPSULE Git

TEMP.
CONTROL
(50° ¢)

CONNECTIONS t ]

To pear:
BRIDGE INSULATION 2 Ae
B
os | +
DRYING
UNIT

Ficure 4. The numbered connections to the bridge circuit are supplied with the ceil. Pulsatile
variations in bridge output due to pressure and flow changes caused by pump action
can be damped by interposing a large air capacitance in series with the pump.
without adversely affecting the operating characteristics of the system.



bos fo &

A METHOD FOR THE MEASUREMENT OF
PHYSIOLOGIC EVAPORATIVE WATER LOSS

THOMAS ADAMS
Chief, Thermal Section
Environmental Physiology Branch

GORDON E. FUNKHOUSER
Environmental Physiology Branch

WARREN W. KENDALL

Department of Zoology
University of Oklahoma

lbp a

63-25

FEDERAL AVIATION AGENCY
CIVIL AEROMEDICAL RESEARCH INSTITUTE
AERONAUTICAL CENTER
OKLAHOMA CITY, OKLAHOMA
OCTOBER 1963


gms/5 min,

mv,

FLOW: 200 cc/ min

CELL
TEMP: 50°C
BRIDGE
CURRENT: 6.1 mA
mgm / min,
t ' i A 4 } 4 4 n 1 A 1 ,

2 4 6 8 410 #12 #14 #%16 18 20 2.2 24 26

Ficure 7. Bridge imbalance is shown as a function of the rate of water vapor production at
a bridge sensitivity setting of 4500 ohms. Increased or decreased cell sensitivity
would allow for measurements of other ranges of rates of water vapor production,
with the upper limit being defined by the saturation of air at the embient temperature
in which the unit is operated. The calibration points for this curve were obtained
on different days, reproducing operating values of the system at each different test.

—10—


\TION

TUBING

CONNECTOR
ROOM TO THERMAL
AIR —> DRYING > > => CONDUCTIVITY
UNIT CELL
RUBBER
STOPPER
vit
TI T AWWW
RS Gasset 4
=Ki AIR Vt
a | Nov
rl & Ac
Pa Pa ~
Ea b==
Mt dl
Fees, BRASS, ee)
| thst 6 cm mai
INSULATION

Ficure 6. A cross section of the device required to obtain steady rates of water vapor pro-

duction for calibration, During calibration. the tubing connector joined the air flow
circuits as shown in Figures 4 and 5 at the points indicated, replacing the plastic
capsule. An electrically insulated heater should te used which will allow a controlled
change in block temperature.

—9o—


(REGULATE
temp (LINE) CIRC.)
° —oV\» S / hig. SWITCH
NOV AC | RELAY
* ?

ry

ba” mf —
NO NC
CoRRENT) yor jem

(D¢ voLTS) (HEATER ADJUST)
VAR. TRANS.

Ficure 2. This diagram indicates the arrangement of the controls for the temperature stable
enclosure for the thermal conductivity cell and the remainder of the unit. The
mercury thermostat and regulator (see appendix A) may he replaced by a thermistor
driven relay similar to that suggested by Ratcliffe (9). Rapid heating of the cell
enclosure at the beginning of a test period may be obtained by applying a large
voltage to the heater; better temperature control is attained with the heater operating
at a lower wattage after the enclosure and components have reached thermal stability
at 50°C. A warm-up period of approximately 30 minutes is required with the de-
scribed design.

—6—


controlled housing by a small pump, is shown
in Figure 4; another, using a compressed air
tank to supply the kinetic energy required to
maintain air flow, is shown in Figure 5. Both
systems provided stalle cell responses with es-
sentially the same calibration characteristics;
the specific arrangement chosen should he dic-
tated by the application of the system. In both
arrangements, the thermal conductivity cell
(model 9677, GOW-MAC Instrument Co., New
Jersey) was housed in an insulated container
with a small fan and a temperature control
system to maintain the unit at 50°C (see Figure
11). The drying units shown in Figures 4 and
5 were tubes filled with “Drierite”.

Reproducible calibration is a difficulty com-
mon to all relative humidity or water vapor
pressure sensing elements, arising in part from
the detection characteristics of the individual
unit, but largely related to difficulties in ob-
taining stable, predictable, low levels of water
vapor. Calibration of the unit described here
required first, stability in air flow through, and
temperature of, the thermal conductivity cell,
and second, stability and reproducibility of
characteristics in the circuit driving the cell. An
additional problem was to provide a stable
source for different rates of water vapor pro-
duction.

The first problem was overcome by the de-
signs shown in Figures 4 and 5 discussed above.
The second, by monitoring both voltage across
and current flow through the thermal conduc-
tivity cell, as shown in Figure 1. The problem
of obtaining stable and controlled rates of evap-
orative water loss for calibration was met by
using the device described in Figure 6. It was
possible to obtain extremely stable rates of wa-
ter vapor production over the required calibra-
tion range by adjusting the surface area of the
water (filling one or more of the concentric
holes in the brass block) and/or water tempera-
ture (bringing the block to a desired tempera-
ture with the electric heater).

Calibration procedures consisted of running
dry air through the brass block shown in Figure
6, and into the thermal conductivity cell circuit.
As shown in Figure 1, one side of the cell is

exposed to the air sample and the balancing
thermistor continuously responds to dry air. For
calibration, a carefully weighed, small (approx.
50 gms) hottle filled with “Drierite” was con-
nected into the circuit at points A and B in
Figure 4, temporarily replacing the drying unit
interposed hetween the two sides of the cell, or
attached as indicated in Figure 5. A change in
weight of the calibration sample bottle in a pre-
scribed time interval reflected the amount of
water passing through the unit at a steady rate.

Imbalance in the bridge circuit (mV), plotted
as a function of the steady state rate of water
vapor traversing the unit, provided the calibra-
tion curve shown in Figure 7. Since the system
is shown to respond to very small rates of water
vapor production, it is of course, important that
fresh “Drierite” be used in each drying cylin-
der. Calibration botties were weighed to the
nearest 0.1 mgm. No changes in the calibration
curve were noted on successive days of measure-
ment, a characteristic not shared by an infra-
red analyzer technique (5).

Latency and time constant of response of the
unit depends on the size of the sampling cap-
sule, the length and diameter of the tubing con-
necting to the cell, and the air flow rate through
the system. Using a 2 cm. (diameter) by 1.5
em. plastic capsule for sampling and approxi-
mately 60 cm of PE 240 tubing with an air flow
rate of 200 cc/min, resulted in a response la-
tency and time constant in the order of 2 sec-
onds and 10 seconds respectively; using the
smaller capsules shown in Figure 8 shortened
these characteristics considerably. In any
combination of these factors, these characteris-
tics can be determined empirically and records
appropriately interpreted.

The design of two capsules used for the as-
sessment of physiologic sweating are shown in
Figure 8; A., for the measurement from ] cm?
skin surface and B., for air circulation over a
smaller skin area.

Two physiologic applications of the technique
are reported in Figure 9. In A., the plastic cap-
sule was sealed to the lateral surface of the
forearm during a brief bout of exercise (“run-
ning in place”); in B., the capsule was sealed
to the palmar surface of the hand. Three types

—2—


Tape tome ne

Ficure 10. This photograph shows the front of the panel used to control the unit. The three
meters (left to right) indicate DC voltage and current (DC mA) in the thermal
conductivity cell circuit, and temperature (calibrated in DC uA) within the cell
housing, respectively. The rotametric flow meter is shown on top of the panel
cabinet. The cable connecting the control panel and the cell enclosure, the 12 V DC
source and air connections were attached at the rear of the cabinet.

—13—


[
!
}

\
i
+
}

Ficure 12. This photograph indicates the general arrangement of the unit during operation.
The compressed air ‘tank is shown on the left. A 10 foot cable connects the control
panel to the cell enclosure. The recorder is shown to the left of the control panel

—15—

U.S. GOVERNMENT PRINTING OFFICE : 1964 072-436


A METHOD FOR THE MEASUREMENT OF
PHYSIOLOGIC EVAPORATIVE WATER LOSS

Thomas Adams, Ph.D.
Gordon E. Funkhouser
Warren W. Kendall

ABSTRACT

The precise measurement of evaporative water loss is essential to an accurate
evaluation of this avenue of heat loss in acute and chronic exposures to heat. In
psychological studies, the quantitative measurement of palmar sweating plays an equally

important role in establishing an index of emotional stress and anxiety. This

report

describes a technique for measuring local sweat response which is relatively inexpensive,
highly stable and accurate. Basically, the system uses a thermal conductivity cell for
the detection of water vapor in an air stream passing over the skin. A method for
calibration of the unit and examples of its application in physiological and psychological

testing are described.

A number of techniques have been used to
measure sweat gland activity in thermoregula-
tory and exercise physiology, and in experimen-
tal psychology (palmar sweating). The most
direct method, measurements of body weight
changes in time, lacks the precision demanded
in most studies, and is applicable only under
conditions of sizable sweat production (1-3).
Infra-red analyzers (4,5), resistance hygromet-
ric elements (6,7) and “coulometric cells” (8)
supply the desired sensitivity, but are too ex-
pensive or cumbersome for must applications.
Limited experiments by the present authors have
indicated that resistance hygrometric systems
are adequately sensitive in response to small
changes in water vapor, but are too difficult to
calibrate due to a large time constant associated
with the desorbtion of water from the hygro-
scopic mass. The characteristics of the hystere-
sis loops occurring in the calibration curves de-
pended on the calibration procedures.

This paper describes a sensitive, inexpensive
system for the measurement of evaporative
water loss. The technique is based upon the
varying thermal conductivity due to density
changes caused by fluctuations in the water va-
por content of air flowing through a thermal
conductivity cell.

Stability of the measuring system is critically
dependent upon a controlled flow of air through
the cell. Monitoring air flow with a rotametric
type flow meter, controlled by a precision nee-
dle valve (B4M, Nupro-fine valve with microm-
eter handie) and a differential flow controller
(Moore) in series in the air circuit, allowed for
measured baseline stability for several hours of
determinations. An air flow of 200 cc/min, al-
though in excess of the flow rates recommended
by the manufacturer, was found to be conven-
ient for control and sensitivity of the unit, and
met the requirements of the physiologic tests
(see below).

The bridge circuit driving the cell and indi-
cating resistance imbalance in the housed ther-
mistor elements, is shown in Figure 1. This cir-
cuit is basically that suggested by the thermal
conductivity cell manufacturer (GOW-MAC) ;
slight modifications (as shown) were necessary
to meet the specific recording scheme. The cir-
cuit providing control for the remainder of the
unit is shown in Figure 2. Figure 3 shows the
circuit used to indicate temperature in the cell
enclosure.

Two methods for directing air flow through
the unit have been used: one, in which the dry
carrier air is drawn through the temperature

—i—


FOREWORD

This instrument and method provides a system for the quantification of
evaporative water loss from the skin. Since humans have been demonstrated
to increase palmar sweating with emotional stress, this system can serve
as an adjunct to an accurate estimation of central nervous system activity,
paralleling other less precise observations of behavioral performance in
providing a measurement of anxiety in chronic and acute stress testing.
This procedure also allows for an accurate determination of heat loss by
evaporation of sweat during thermal stress. Since sweating is the only ave-
nue of heat loss operating under conditions in which environmental temper-
ature is greater than skin temperature, a quantitative measurement of
sweating is essential to the completion of a thermoregulatory balance sheet
in protection against hyperthermia.



A:

PLASTIC
|+——!9 mm —>|

OUTLET BLOCK

I3g., MALE

SYRINGE <a

NEEDLE HUBS 20mm

I3g., MALE ;
SYRINGE ——>

NEEDLE Huss jf | /SOLDERED

BRASS
TUBE

Ficus 8. A. This capsule was used in most tests, sampling from a skin surface area of 1 cm?.
The needle hubs were prese-fitted into holes drilled into the plastic bluxk. The
plastic shield at the end of the inlet tube inside the capsule insured uniform
dry air distribution over the skin surface.

For measurements of sweating activity from smaller skin areas this capsule
was attached to the skin with tape over the plastic holder.

- —u—


Ficure 11, The covers for the inner and outer metal boxes and the intervening top layer of
insulation have been removed to show the arrangement of components in the constant
temperature enclosure. The mercury switch, heater and thermistor for indicating cell

temperature are arranged immediately in front of the fan. The conductivity
cell and its connections are on the left. The cable connection to the control

panel is shown on the right of the outer box. The connections on the facing panel
are for the attachment of the skin capsule.

—14—