GB2116850A

GB2116850A - Sweat collection device

Info

Publication number: GB2116850A
Application number: GB08307074A
Authority: GB
Inventors: Henry Lewis Webster; Wayne K Barlow
Original assignee: Wescor Inc
Current assignee: Wescor Inc
Priority date: 1982-03-15
Filing date: 1983-03-15
Publication date: 1983-10-05
Also published as: DE3309273C2; DE3309273A1; GB2116850B; GB8307074D0

Abstract

A sweat-collection device has a shallowly concave sweat-collecting surface (15) defining a concavity (13) with a rim (14) lying wholly within a common plane for placement over an iontophoresis-stimulated area of a person's skin to collect sweat from the skin and pass it through a bore (18). The concavity is so shallow that no dead space occurs between the collecting surface and the skin and flesh bulge into the concavity when the device is applied to a patient. The concavity may incorporate barriers for preventing soft skin and flesh from closing the bore. Flexible tubing (17) is secured to the axial bore (18) for receiving and storing the collected sweat, and a chamber (19) may be provided in the body of the device opposite the sweat- collecting surface for holding the tubing (17) in a flat coil. A strap is provided for securing the device to a patient. Provision may be made for retaining and discharging sweat after it has been collected. <IMAGE>

Description

SPECIFICATION Sweat collection device This invention relates to the collection of human sweat for medical evaluation and is particularly directed to the providing of a new sweat collection device.

For many years it has been known that the concentrations of sodium and chloride are considerably above normal. in the sweat of children suffering from cystic fibrosis of the pancreas.

In recent years, itshas been common to induce sweating in a localized area of a person's body by an iontophoretic application of a drug such as pilocarpine nitrate. Under one sweat-collection method, the stimulated skin area is covered by a pre-weighed, salt-free, gauze pad which is held in place by a sheet of plastic sealed to the patient such that the sweat produced in the covered area is collected in the gauze pad. After approximately 45 minutes or longer the pad is quickly removed and re-weighed, after which the sweat is eluted into an aqueous solution for analysis, taking care not to allow evaporation of any of the sweat, since sweat evaporation results in artificially high concentrations of sodium and chloride.

More recently, it has been discovered that electrical conductivity and osmolality measurements of sweat are also useful for determining increased sodium and chloride concentrations.

An advantage of these methods is that a much smaller volume of sweat can be used than is required by the gauze method, and it has been common practice sealingly to secure a small inverted cup over the pilocarpinetreated skin area for the collection of the secreted sweat. Sweat droplets form on the skin covered by the cup and are collected for analysis by tilting the cup and scraping the skin-contacting portions of the cup's rim across the skin to pool the droplets and force the pooled sweat into the cup. This method of collection has suffered, however, by reason of condensation on the interior of the cup, which introduces major error in the results of the analysis. Also, a large surface area of sweat is exposed when the cup is removed, thus making it necessary to work rapidly when collecting the sweat so that salt concentration will not be artificially high.

Use of a cup for sweat-collection also poses the problem of determining how much sweat will be collected, since some persons sweat much more than others. Thus, just prior to removing a cup, one is never sure whether or not a sufficient quantity of sweat has been collected.

A heat sweat cup as described in U.S.A.

Patent Specification 4,266,556 has eliminated the serious problem of error caused by condensation. It provides an error-free sample of the patient's sweat. However, as with any cup device for collecting sweat, and even though a practitioner can become very adept, with practice, it is difficult to avoid loss of sweat during scraping, and error may arise from inclusion of sweat, concentrated by evaporation, that borders the area by the cup.

Although the heated cup must be recognized as a major advance in sweat collection devices, there has been one other negative factor connected with its use. It should be realized that the patients who are tested for cystic fibrosis are generally quite young.The iontophoresis step requires the patient to be "attached" to an electrical power source for several minutes. Use of a heated cup extends this time by some fifteen minutes more, a length of time which may seem interminable to a child.

A A quite different sweat-collecting device was used early in the 1 960's for experimental purposes in simultaneously measuring the rate of sweating and the salt concentration of the sweat. It is described and schematically illustrated in the June 1963 issue of "The Journal of Pediatrics", pages 855-867, in an article entitled "Studies of Salt Excretion in Sweat" by Lewis E. Gibson and Paul A. di Sant' Agnese. This device comprised a shaped, cylindrical block of transparent ''Lu- cite" plastic, having a concave bottom surface bordered by an annular flat margin for direct application to the skin of a patient as a sweat collector. Sweat produced within the area covered by the concavity was forced into an elongate, transparent, measuring tube connected to an axial bore leading upwardly from the centre of the concavity.Salt concentration of the sweat was determined by means of two electrodes extending into the axial bore in spaced relationship lengthwise of the bore to measure electrical conductivity of the sweat in the bore. Periodically, sweat was removed from the device by means of a syringe connected to a so-called "puff-off" tube that intersected the bore below the electrodes. The total sweat sample obtained by the syringe was subjected to electrical conductivity measurement to determine average conductivity and was analyzed photometrically for salt content.

This device had what the experimenters termed "dead space", which included space between the skin of the person being tested and the concave sweat-collecting surface of the device. Although this was recognized as a source of possible error in test results obtained by experimental use of the device and was taken into consideration in test calculations made, it represents a loss of sweat volume which could be serious in the routine medical laboratory use of a device of this kind.

Thus, sweat loss due to dead space ranged from 8.8 to 42.1 microlitres and averaged 20.3 microlitres. Since the average patient normally produces a total volume of only 50-60 microlitres of sweat during an entire period of collection, losses of such magnitude cannot be regarded as insignficant. Moreover, the sweat collected under these circumstances is not representative, since the rate of sweat production decreases with time after pilocarpine stimulation, and salt concentration in the sweat depends upon the rate of sweat formation in the individual.

Although a device of this kind might seem to offer advantages over other sweat-collection devices, its limitations preclude practical application other than the experimental use de scribe.

The device of the present invention has structural similarities to that of the experimental Gibson et al sweat-collecting device. Thus, it comprises a sweat-collecting body having a concave undersurface which may or may not be bordered by a flat peripheral margin. Also, an axial bore is positioned at the centre of the concavity to provide for removal of sweat collected within the concavity. However, we have found that the amount of dead space within the concavity is related to the overall height of the concavity and that, by significantly decreasing this height, the dead space can be effectively eliminated. In addition, we have found that the collected sweat can be conveniently stored and removed for analysis in a length of flexible tubing connected with the axial bore externally of the concavity and compactly held by the body of the device while awaiting use.

The flexible tubing as so connected is preferably coiled in flat spiral formation for compactness, and provision is advantageously made for retaining the coiled tubing in a receiving recess formed on the back of the sweat-collecting body. Additionally, provision is made for securely attaching the device to a patient, as by a size-adjustable strap to be fastened around a limb of the patient.

A modification of the device for use on infants and adults having unusually soft skinned flesh resides in the provision, at the entrance of the bore leading from the concavity, of barrier means against skin and flesh intrusion into such entrance of the bore. The barrier means may take various forms, such as radial ribs protruding into the concavity and tapering outwardly a relatively short distance from the periphery of the bore, or corresponding recesses in the concave surface defining the concavity. Such means may even be a permeable paper disc covering the bore entrance, but this is not favoured since it involves placement of a separate item during application of the device to a patient. We have not been able to detect any dead space within the concavity in the use of these modifications.

In use of the device, after a desired amount of sweat has been collected in the coiled tubing, such tubing is detached from the bore, either by pulling it free of the bore in those instances in which the end of the tubing is merely inserted into and frictionally held by the bore, or by severing it with a sharp knife at the bore, the latter entailing only a very small loss of sweat contained within the tub ing over the length of the bore. Opposite ends of the tubing are closed, for example by forming the tubing into a closed loop and attaching its opposite ends to the opposite ends of a relatively short length of rigid tub ing, such as stainless steel. In this way the collected sweat is removed and held intact for carrying to the laboratory for determination of salt concentration at an appropriate time.

To transfer the collected sweat to a testing vessel, it is advantageous to attach an elas tomeric bulb to one end of a second length of rigid tubing and then to attach the other end of the rigid tube to the free end of the sweat collector tubing after it has been disconnected from the closed loop position. By carefully squeezing the elastomeric bulb, a required quantity of the collected sweat can be conve niently deposited into the testing vessel by way of the short rigid tube at the opposite end of such disconnected sweat-collector tubing.

A A better way of accomplishing this, how ever, is to form an elastomeric bulb by attach ing a short length of a relative large diameter, flexible plastic tubing to the hubs of two blunt hypodermic needles, close the passage through one of the needles, and attach oppo site ends of the sweat-filled collector tubing to the respective needle shanks. For discharge of the sweat, the tubing end attached to the closed needle is detached and used as the discharge end.

The accompanying drawings illustrate the nature and modes of use of preferred embodi ments of the invention. In these drawings: Figure 1 is a view in axial vertical section showing one embodiment of the device on a scale considerably larger than actual size, the diameter of the sweat-collector tubing shown as attached to the sweat-collecting body and the extent of concavity of the concave sweat collecting surface of the sweat-collecting body being exaggerated; Figure 2 is an inverted plan view of the device of Fig. 1 drawn to a much smaller scale, but still larger than would normally be actual size; Figure 3 is a very similar to that of Fig. 2 but in plan; Figure 4 is a fragmentary perspective view showing the device secured to the forearm of a apatient; ; Figure 5 is a fragmentary longitudinal sec tion showing how the collector tubing is formed into a closed loop for storage; Figure 6 is a similar view to Fig. 5 showing how sweat is transferred from the collector tubing to a testing vessel after disconnection of the closed loop; Figure 7 is a view corresponding to that of Fig. 2 but illustrating a somewhat different embodiment of the device; Figure 8 is a view corresponding to that of Fig. 2, but of the device of Fig. 7; Figure 9 is a view corresponding to that of Fig. 3, but again of the device of Fig. 7; Figure 10 is a fragmentary section view along line 10-10 of Fig. 8, showing radial ribs protruding into the concavity from the concave surface as barriers to skin and flesh intrusion into the bqre entrance;; Figure 11 is a similar view showing similarly formed recesses in the concave surface as barriers to skin and flesh intrusion into the bore entrance; and Figure 12 is a view corresponding to that of Fig. 5, but showing a preferred alternative arrangement.

In the form illustrated shown in Figs. 1-3, the device of the invention comprises a solid, sweat-collecting body advantageously moulded to shape from a suitable plastic material, such as polyethylene or polystyrene, and including a portion 10 of disc formation projecting integrally from a back portion formed as a backing plate 11 having slot-like openings 12 at its opposite ends for the reception of straps constituting means for attaching the device to a person.

The face of the sweat-collecting body portion has a shallow concavity 13 whose rim 14 lies wholly in a common plane and which is defined by a broad sweat-collecting, concave surface 15. Preferably, and as here illustrated, the concavity 13 is of squat conical formation, having a broad base and very low altitude.

The rim 14 is a flat annulus in this embodiment.

This concave face of the body portion 10 is adapted to be placed and held firmly against the surface of a patient's skin by a sizeadjustable strap 16, the ends of which are secured in slots 12. A coiled length of flexible, sweat-collector tubing 17 is shown as having one of its ends fitted into, or otherwise connected to a bore 18, which extends axially through the body portion 10 and communicates with the concavity 13 at the apex of its concave, sweat-collecting surface 15.

Provision is preferably made for retention of the sweat-collector tubing 17 in compactly coiled form at the back of the body by recessing the backing plate portion 11 in the form of a circular chamber 19 overlying the sweatcollecting surface 15. Tubing 17 is coiled in flat spiral formation and placed in the receiving chamber 19. This feature of the invention, it should be noted, may be advantageously utilized apart from other features explained herebelow.

Although the rim 14 of the concavity 13 is here shown as a flat annulus having substantial width between its inner and outer diameters, the width of the annulus can be reduced to an annular edge without affecting the efficacy of the invention.

As seen in Fig. 4, sweat is usually collected from the fleshy underside of a patient's forearm 20 or from the fleshy portion of the patient's inner thigh. For convenient application to the limb, the strap 16 is preferably made as two separate lengths provided with means for adjustment, such as by having the material "Velcro" applied to its overlapping ends.

When the device is in place on a person's skin, the skin and underlying flesh bulge into the concavity 13 provided by the surface 15, Fig. 1.

The outstanding feature of the present invention from an operative stand point, differentiating it from the earlier Gibson et al experimental device previously described, is the fact that the concavity backed by the concave, sweat-collecting surface is so shallow as to place the area of skin covered thereby in contact with the sweat-collecting surface over substantially the entire area of the latter, without leaving dead space. We have found that, in this way, sweat, under the pressure at which it is secreted from the seat glands, is able to travel rapidly across the interface of the skin and collecting surface 15 toward and into the bore 18, so that substantially all of the sweat is collected in the flexible tubing 17. Pressure of the collecting surface and rim of the device against the skin should be only that which will effect firm placement against the skin.Excessive tightening of the strap 16 is neither necessary nor desirable.

In this embodiment, a diameter of twentyseven millimetres for the open base of concavity 13, with a depth of one millimetre at the apex, i.e. for the altitude of the preferred squat cone formation, has been found to be very satisfactory, along with collector tubing 1 7 having an inside diameter of 0.86 millimetres. The cone measurements are regarded as optimum. However, the concavity could have a maximum depth or altitude substantially in the range of from 0.5 to 1.75 millimetres and a diameter substantially in the range of 20 to 35 millimetres. This depth or altitude is in contrast to a depth of 2.5 millimetres in the Gibson et al experimental device in which significant dead space was present between the sweat-collecting surface and bulged skin.

In use of the device having the optimum dimensions indicated above, it has been found that about one minute elapses from the time the device is strapped onto an area of the patient's skin that has been stimulated by iontroporetic application of pilocarpine, until sweat appears in the collector tubing 17.

Once sweat appears, it is possible to see the meniscus of sweat advance in the tubing. If desired, markings may be provided to indicate the volume of sweat collected Typically, a volume of about eight microlitres of sweat is required for analysis by osmolality or electrical conductivity methods.

However, it is desirable to collect an excess of sweat for ease in handling and to allow the analysis to be repeated so as to average out any deviation in salt concentration caused either by variations in the amount of salt contained in various portions of the excreted sweat or by external factors. The present device can easily collect fifty to sixty microlitres of sweat from most patients, in a collection time of fifteen minutes.

When a sufficient amount of sweat has been collected, the collector tubing 1 7 is disconnected from the axial bore 18, either by pulling it free or by severing it at its point of emergence from such bore. It should be noted that there is a tendency for a vacuum to form between the collection surface and the skin, so if the strap is loosened and the device removed with the tubing 17 still connected, sweat may be inadvertently withdrawn from the collector tubing and deposited back on the skin. Thus, it is important that the tubing 17 be removed first.

The sweat collected in the flexible tubing 1 7 may be expelled and tested in any convenient way. However, it is advantageous to provide for the closing of opposite ends of such tubing pending a convenient time for testing to avoid any loss by evaporation or otherwise while carrying the sweat sample to the testing location. For this purpose, a feature of the invention is to employ, as shown in Fig. 5, a relatively short length of rigid tubing such as stainless steel, to connect the opposite ends of the tubing 17.

One end of the tubing 17 is removed from the rigid tube 21 when the sweat is to be analysed.

A further feature of the invention, as shown in Fig. 6, is the attachment of one end of the tubing 17, after disconnection from the rigid tube 21, to an elastomer bulb 22 so that a desired quantity of the collected sweat can be conveniently expelled from the collector tubing 17 into a testing vessel. The elastomeric bulb 22 is conveniently attached to the tubing 17 by means of a second relative short length of rigid tubing 23, preferably stainless steel corresponding to the rigid tube 21.

Figs. 7-1 1 illustrate further embodiments of the invention developed to overcome the problems encountered with infants and adults having very soft skin and flesh.

When the device is in place on a patient, the patient's skin and underlying flesh bulge into the concavity 27, but are prevented from blocking sweat flow through the bore 31 by the ribs 32 serving as barriers.

The embodiment of Fig. 11 is similar to that of Figs. 7-10, except that, instead of ribs protruding into its concavity 33 as barrier means, similarly formed recesses 34 in concave surface 35 are provided for the purpose.

With the dimensionsof the device being the same as those indicated for the embodiment of Figs. 1-3, ribs 32 of the embodiment of Figs. 7-1 Q are approximately four millimetres in length and protrude approximately 0.33 millimetres from the sweat-collecting surface at the entrance of the bore 31, while the recesses are similarly approximately four millimetres in length and approximately 0.33 millimetres in depth at the entrance to the bore 36, which is also shown as being counterbored for the reception of tubing 37.

The closed loop tubing arrangement of Fig.

12 is presently preferred over that of Fig. 5, for it provides a pneumatic, elastomer bulb which eliminates the more cumbersome arrangement of Fig. 6. Thus, a relatively short length 38 (about 1 > inches in length) of relatively large diameter (about 5mm l.D.) flexible plastic tubing, such as a silicone type of plastic, provides the bulb by having its ends attached to respective blunt hypodermic needles 39, such as those marketed by Popper 8 Sons Inc., Hyde Park, New York, under part No. 7402 (Hose Hub 22 gauge by 3/8 blunt), by a close stretch fit over the hubs 39a thereof, leaving the shanks 39b free to receive respective opposite ends of the sweatfilled collector tubing 17 or 30. One of the needles has the opening therethrough closed, as by the application of a drop of epoxy glue to the shank end, and is colour-coded at its hub, so that the tubing end can be conveniently detached from its shank and used as the discharge spout for the sweat when the bulb 38 is pressed.

Whereas this invention is here illustrated and described with specific reference to embodiments presently contemplated as the best mode of performing such invention in actual practice, it is to be understood that various changes may be made in adapting the invention to other embodiments within the ambit of the appended claims.

Claims

1. A sweat-collection device, comprising a solid body having a shallow concavity at a face thereof defined by a sweat-collecting surface which gradually recedes from a rim lying wholly in a common plane to an axial bore that extends to the opposite face of said body, whereby skin and flesh of a person to whom the device is applied will bulge into contact with said surface over substantially its entire area when said rim is placed firmly against said skin, leaving substantially no dead space in the interface between the bulging skin and said surface; a length of flexible, sweat-collector tubing having one end connected to said bore at said opposite face of the body so as to receive sweat from said surface; and means for fastening said body against the area of skin from which sweat is tobe collected, so as to maintain firm placement of said rim and surface against the skin.

2. A sweat-collection device according to Claim 1, wherein the tubing is coiled in flat formation, and the said opposite face of the body is recessed as a chamber for receiving the coiled tubing, said coiled tubing being compactly positioned within the receiving recess.

3. A sweat-collection device according to Claim 1, wherein the body includes a portion of disc formation which projects integrally from a rectangular portion formed as a backing plate; and wherein the means for fastening the body to the skin of a person comprises means at opposite ends of said backing plate for removably receiving an attachment strap.

4. A sweat-collection device according to Claim 1, wherein the sweat-collecting surface is of squat conical formation.

5. A sweat-collection device according to Claim 4, wherein the altitude of the conical formation is within the range of 0.5 to 1.75 millimetres and the diameter of the base is within the range of 20 to 35 millimetres.

6. A sweat-collection device according to Claim 1, wherein the shallow concavity is of circular formation having a maximum depth within the range of from 0.5 to 1.75 millimetres and diameter within the range of from 20 to 35 millimetres.

7. A sweat-collection device according to Claim 1, wherein the device includes barrier means at the entrance of the bore for preventing unusually soft skin and flesh from protruding into the bore.

8. A sweat-collection device according to Claim 7, wherein the barrier means comprises symmetrically placed, outwardly tapered ribs protruding from the sweat-collecting surface into the concavity and radiating from the opening of the axial bore.

9. A sweat-collection device according to Claim 7, wherein the barrier means comprises symmetrically placed, outwardly tapered grooves in the sweat-collecting surface and radiating from the opening of the axial bore.

10. A method of collecting sweat from a person's skin for testing, comprising the steps of inducing sweating in an area of the person's skin; attaching a sweat-collection device in accordance with Claim 1 over said area of the person's skin, with the rim of the sweatcollecting surface placed firmly against said skin; detaching the sweat-collector tubing from the axial bore of the body of the device after sweat has been collected; and closing the ends thereof; and, at an appropriate time thereafter, expelling collected sweat from said tubing into a testing vessel.

11. A method according to Claim 10, wherein the ends of the sweat-collector tubing are closed by connecting them to opposite ends, respectively, of relatively short tubular means to form a closed loop.

12. A method according to Claim 11, wherein the short tubular means includes a pneumatic bulb intermediate its ends with one of said ends closed and one open; and wherein collected sweat is expelled from the sweat-collector tubing by disconnecting one end thereof from the closed end of the tubular means and pressing said bulb.

13. A sweat-collection device, comprising a solid body having a recessed, sweat-collecting surface at a face of said body with a rim that lies wholly in a common plane and having an axial bore extending from said surface to the opposite face of the body of the device, said surface being adapted for placement against a sweat-producing area of a person's skin for sweat-collection; a length of flexible, sweat-collector tubing having one end connected to said axial bore at said opposite face of the body, so as to receive sweat from said surface; and said opposite face of the body of the device being recessed for receiving the coiled tubing, said coiled tubing being compactly positioned in the receiving recess in flat, coiled formation.

14. A sweat-collection device, comprising a solid body having a shallow concavity at a face thereof defining a sweat-collecting surface which gradually recedes from a rim lying wholly in a common plane to an axial bore that extends to the opposite face of said body, so that said surface will substantially conform to the bulging of a person's skin and so the skin and surface will be in contact over substantially the entire area of said surface when said rim is placed firmly against said skin, leaving substantially no dead space in the interface between the bulging skin and said surface; and means for fastening said body against the area of skin from which sweat is to be collected, so as to maintain firm placement of said rim and surface against the skin.

1 5. A sweat-collection device in accordance with Claim 14, having the opposite face of the body recessed as a chamber for receiving flexible tubing when connected to the axial bore and coiled in flat formation.

1 6. A sweat-collection device in accordance with Claim 15, including a length of flexible tubing normally connected to the axial bore for collecting sweat therefrom and normally coiled in flat, spiral formation within the receiving chamber; and a pneumatic bulb arrangement comprising tubular shanks extending from sealed connection with respective opposite ends of a relatively short, relatively large diameter flexible tube and adapted to snugly receive opposite ends of said flexible tubing, one of said tubular shanks being closed.

17. A sweat-collection device substantially as hereinbefore described with reference to, and as shown in Figs. 1 to 6, 7 to 11 or Fig. 12 of the accompanying drawings.