An Improved Sweat Collector*

Vol. 53, No. 3

THE JOURNAL OP INVESTIGATIVE DERMATOLOGY

Copyright

P ,,ted in U.8.A

1969 by The Williams & Wilkins Co.

AN IMPROVED SWEAT COLLECTOR* KENZO SATO, M.D. AND RICHARD L. DOBSON, M.D.

A major attribute of normal sweat gland from the surrounding area, particularly when function is that the sodium content of sweat sweating has been thermally induced. A hypothetical example of this source of error is shown

varies directly with sweat rate. Because of this,

methods to evaluate sweat gland function in Figure 1. When the rate of sodium excretion must consider both electrolyte concentration is plotted against sweat rate, a linear function and sweat rate per unit area. This requires is produced at higher sweat rates. The slope of that sweat be collected from a precisely de- this line is equal to the sodium concentration marcated area using techniques which eliminate of the precursor fluid produced by the secreboth evaporation and contamination. Evapora- tory cells, An extrapolation of the straight tion is the most common source of error and is portion of the curve to the "x" axis is a measure of the maximum ability of the sweat duct to reabsorb sodium (free water clearance) (1). The solid line of Figure 1 depicts an accurately

measured representation of the relationship between sweat rate and the rate of sodium excretion. The dotted line depicts the curve

Rate of

Sodium

Sweat Rote

TOP

1. The rate of sodium excretion plotted against sweat rate gives a linear, function at Foe.

higher sweat rates. In this hypothetical example, the solid line represents the results of accurate measurement. The dotted line depicts the effects of sweat leakage giving spurious reductions in ductal and secretory function.

evident in the results of sweat testing in children with cystic fibrosis. Concentrations of sodium well in excess of 140 mEq/l are encountered which clearly represent an error in

I

technique due to evaporation of water, since the maximum possible sweat sodium concentration

is approximately 140 mEq/l, or isotonic to serum concentrations (1). Errors also occur due

to leakage of sweat into the collection area * From the Division of Dermatology, University of Oregon Medical School, Portland, Oregon

BOTTOM

97201.

This study was supported by the following:

U.S. Army Research and Development Command, Office of the Surgeon General, Contract DA-49-

unit rpm

193-MD 2176 and 2184, and the National Institutes of Health Grant AM-O5655 and Training Grant 5-TI-AM-5300. Received March 28, 1969; accepted for publica-

tion May 7, 1969.

PIG. 2. Sweat collecting apparatus. Top and

bottom views of base portion.

232

233

SWEAT COLLECTOR

which prevents both evaporation and con-

A

filter papers

tamination. The device is shown in Figures 2 and 3. The bottom portion is attached to the skin with Weldwood Contact Cement.® This adhesive must be applied to the skin and the base of the chamber and allowed to dry before

30.5

the chamber is put into position. Unlike

51

......_—rubber gasket ________ plate

earlier models of the chamber which had a flat base, the new model is equipped with drainage

B

grooves which allow sweat to drain away ________ knife edge

drainage grooves 49

Faa. 3. Sweat collecting apparatus assembled

from the collection area. The knife edge prevents leakage in either direction. The top of the chamber contains a rubber gasket sandwiched

between the base plate and a thumb screw. Tightening the screw compresses and expands

the gasket insuring an airtight seal. Sweat which would result if sweat leaked into the is collected on pre-weighed filter paper 2.4 cm collection area. A spurious reduction in both in diameter (Whatman No. 542). free water clearance and the sodium content of precursor fluid would be calculated. To circumvent these difficulties in technique, we have developed a sweat collecting apparatus

REFERENCE

1. Cage, G. M. and Dobson, R. L. Sodium secre—

tion and reabsorption in the human eccrine sweat gland. J. Clin. Invest., 44: 1270, 1965.