1. Field
The invention is in the field of sweat collection apparatus, whereby human sweat is collected for later medical evaluation and analysis.
2. State of the Art
It is desirable in some circumstances to collect samples of sweat from a human and perform tests on the sweat for medical purposes. For example, it was discovered in the 1950's that children with cystic fibrosis had elevated levels of chloride in their sweat. It has now become a routine way of screening children for cystic fibrosis to collect a sample of sweat for measurement of chloride ion levels. Such measurement may be accomplished by a chloride assay, electrical conductivity measurement, or by vapor-pressure osmolality measurements of the sweat sample.
Samples of sweat may be collected in various ways. The most common method used today is to introduce pilocarpine nitrate into the skin by means of an electrical current flowing through the skin between a pair of electrodes attached to the skin. This process is called Iontophoresis. Generally, current flow is continued for about 15 minutes, after which the electrodes are removed and a collection cup is placed over the area of the skin where the pilocarpine nitrate has been administered. After approximately 15 minutes, the sweat that has formed on the skin under the cup is collected into the cup by scraping the cup across the skin. Normally the collection cup is at room temperature which is a temperature below normal body and skin temperature.
The July, 1963 issue of Pediatrics contained an article by William R. Phillips, M.D. entitled "Electrical Conductivity of Sweat, A Simple, Home-Assembled Apparatus". In the section of the article entitled "Technique", Dr. Phillips says "A 75-watt lamp is placed 6 or 8 inches 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."
In the June 18, 1977 issue of the Medical Journal of Australia, an article by Lewis Webster, Ph.D. and Helen Lochlin entitled "Cystic Fibrosis Screening by Sweat Analysis, A Critical Review of Techniques", discusses the problem of condensate error which affects the reliability of sweat measurements and says "the condensate error, which has been noted elsewhere, could be minimized by arranging that the inverted cup be heated to a higher temperature than the skin surface throughout the collection period." The article goes on to say that the use of heat lamps is not practical on a large scale or for use with neonates, and then says "Extensive trials were undertaken to design the cup shown in FIG. 1, of convenient size and simple to construct, which could be preheated to a degree which maintained an optimal temperature differential during collection." The cup developed is then described. Basically, the cup has a heat reservoir of brass which is preheated before use and can maintain the cup at a temperature above skin temperature during time of collection, or about 15 minutes.
The cup developed by Webster and Lochlin has the inherent problem that only so much heat can be stored in the heat reservoir and that the cup at the beginning of the collection period has to be at a temperature which is uncomfortably high for many people in order that enough heat is stored so that the sweat collection is completed before the temperature of the cup falls below skin temperature. This gives a maximum collection time of about 15 minutes in most cases. Further, the temperature is not held constant or otherwise controlled during sweat collection. This is also true when heat lamps are used. There is no real temperature control. Thus, there remains much room for improving the collection cup.