WO2013057470A1

WO2013057470A1 - Heat acclimatisation monitoring

Info

Publication number: WO2013057470A1
Application number: PCT/GB2012/000800
Authority: WO
Inventors: Craig John ROXBURGH; Daniel George ROIZ DE SA; Simon Keith DELVES; Joanne Louise FALLOWFIELD; Adrian John ALSOPP
Original assignee: The Secretary Of State For Defence
Priority date: 2011-10-19
Filing date: 2012-10-19
Publication date: 2013-04-25
Also published as: GB201118015D0; GB2495851A; GB201218812D0

Abstract

A patch for assessing heat acclimatisation comprising a detectable marker for determining acclimatisation status. The marker is usually a chemical marker that responds to sweat, or other bodily fluids and indicates through measurable changes such as conductivity or colour for example that the body has reached a state of heat acclimatisation.

Description

Heat Acclimatisation Monitoring

This invention relates to a device which can be placed onto the skin to be used as an indicator of whether a human has reached a state of heat acclimatisation or not.

Anyone who needs to be deployed to an environment of elevated tempe rature, such as military personnel and professional athletes, need to undergo a period of physiological adjustment before they become heat acclimatised, thus reaching the optimal physical conditions tor their required task.

Current assessment of heat acclimatisation often requires analysis of an individual^'s bodily fluids, such as sweat or blood , to identify specific biomarkers as an indication tha t an acclimatised physiological state has been reached. Chemical sweat analysis is currently a tedious and lengthy process involving initial transportation of samples to a laboratory, introducing potential for evaporation, contamination and decomposition, followed by time consuming laboratory analysis.

Eccrine sweat glands are found mostly in the hairless skin areas of the body and produce larger and more practically useable quantities of sweat compared to apocrine sweat glands; apocrine glands tend to end in hair follicles rather than pores. Significant changes in the concentration of the molecular and ionic species are known to occur with changes in physiological state. At low rates of sweating the pH of eccrine sweat is slightly acidic ( ~pH 5) due to increased lactic acid secretion, whilst at increased flow rates the pH becomes alkaline (~pH 7.5) due to increased bicarbonate levels. Thus on attaining the heat acclimatised physiological state, where sweat flow-rate increases by approximately 50%, the pH would be expected to be more alkaline.

Changes in inorganic sweat compositions and/or constituents such as sodium , chloride , calcium, zinc and bicarbonate are also known to occur with changes in physiological state .

Studies such as the paper by Harker, Coulson, Fairweather, Taylor and Daykin in Metabolomics, Volume 2, Number 3, 1 05- 1 1 2, have shown that concentration of certain sweat constitue nts vary significantly between individuals. Factors such as age , sex , race, diet and heat acclimatisation procedures used all have a conside rable effect on concentration. Further to this, variations in the sweat constituent concentrations may also arise from the type and position of sweat collection system and from the analytical technique used . These specific chemical changes in concentration , conductivity and/or pH can be measured using indicators in the form of a device attached lo the skin as detailed m the prior art described below;

US patent no. US3635213 describes minimising the exposure of a sweat sample to air, reducing risks of evaporation and contamination . A method is described whereby a sweat collecting receptacle is strapped to a patient to collect sweat, stimulated by iontophoresis. This is then measured by analysing the conductivity of the collected sweat. The collecting receptacle is formed into the shape of a funnel and in the base there are located two electrodes. This system is then connected to a measuring device . It is primarily used as a system for diagnosis of cystic fibrosis.

The major problem with this method is that the subject excretes sweat into a funnel. This would not be practical for an individual undertaking significant physical activity as the test would have to be done when the patient(s) were stationary. Further, the sweat sample is exposed to air, which is not ideal as it could lead to evaporation of the sample thus rendering the results erroneous. A further problem associated with this method is the analysing device used. The results must be read from an analytical scale and this could be time consuming and erroneous.

Canadian patent no. CA1 21 7698 describes a process utilising sweat analysis as a personal screen for cystic fibrosis. It describes a quantitative test whereby sweat is in contact with an absorbed flat patch. When placed on the skin of the subject the patch collects a fixed volume of sweat and, by measuring chloride ion levels, provides a visual indication in the form of a colour change when the level is in excess of a predetermined concentration.

A problem with this patch is that the whole patch is in continuous contact with the skin . The chemicals which trigger the colour change may mleract with the skin thus presenting the risk of not correctly identifying and/or quantifying the ions of interest due to undesired side reactions causing the colour change to be disrupted Additionally the patent fails to appreciate that the sweat patch produced may cause transdermal effects or a change of pH at the skin surface due to general toxicity. Several variables of the utilised chemicals need to be taken into account such as degree of ionisation, lipophilicity and duration ot contact element.

Further, it is known that during heat acclimatisation, the sweat produced by a n individual changes in composition. This has not been taken into consideration in CA 121 7698 and only deals with a comparison of chloride ions produced in someone with cystic fibrosis compared to a person who does not have the disease.

The present invention seeks to overcome these problems by providing a device for rapidly and efficiently analysing sweat samples quicker and giving an obvious indicator of the result.

Further the invention greatly reduces decomposition in air and contamination and adverse reaction when the device is brought into contact with the skin.

Accordingly, the present invention provides a device in the form of a patch which acts as an indicator that the heat acclimatised physiological state has, or has not, been attained.

In a first embodiment of the invention, the patch will indicate whether an individual is heat acclimatised or not by a visible colour indication.

The basic structure of the patch according to this embodiment itself comprises a semipermeable membrane through which sweat can pass from the skin and is retained in the patch; or a simple absorbent materia! such as gauze. The patch may be constructed from known materials such as those used for waterproof sticking plasters or wound dressings which allow for the passage of a fluid from one side but not ihe other. When a bodily fluid is absorbed and or/adsorbed into the patch it is retained and may be used as described below to determine whether an individual is heat acclimatised .

During heat acclimatisation there is a stepwise reduction in sodium chloride concentration indicating that a similar loss for both species (sodium ions and chloride ions) occurs. I t is expected that non-heat acclimatised individuals have chloride concentration levels of ~ 55 mmol L ¹ and heat acclimatised individuals have chloride concentration levels ol - 36 mmol L^'1 , subject to dietary control. These concentrations are dependent upon the individual and one might observe a range of (± 20%) for both the higher and lower limit. This would not lead to overlapping ranges as one would expect a human with a non acclimatised chloride concentration at the bottom end of the range to show a correspondingly low concentration in the acclimatised range.

In a patch according to this embodiment of the invention may contain fluorescein as an indicator. Silver nitrate is utilised as the 'controlling' chemical and reacts with chloride ions to give silver chloride. By incorporating silver nitrate at a concentration capable of reacting with all the present chloride ions, the concentration level of silver nitrate is set slightly above that of chloride ion concentration levels expected for heat acclimatised individuals; hence when the individual is heat acclimatised no chloride ions will remain and the indicator patch will turn red/pink. The red/pink colour is caused by the reaction of the carboxylic acid group of the fluorescein with the silver ions, forming the silver carboxylate, indicating that heat acclimatisation has been reached.

By incorporating silver nitrate at a lower concentration than chloride ions expected in the sweat of a heat acclimatised person the indicator patch will remain yellow, indicating that physiological heat acclimatisation has not yet been reached.

AgN0₃ + CI ^' -> AgCI + N0₃ ^" ( Equa tion 1)

Silver nitrate preferentially reacts with chloride ions in the presence of fluorescein to form silver chloride. When the concentration of silver nitrate is greater than that of chloride the excess silver ions react wtih fluorescein to produce the pink/red-coloured fluorescein silver-carboxylate. Thus by incorporating silver nitrate at a concentration slightly higher than that of the chloride-ion levels - expected in the heat acclimatised state - the excess silver nitrate will react with the fluorescein producing a pink/red-coloured complex - acting as a visual indictor that the heat acclimatised slate is reached.

Considering the non-heat acclimatised state, in which the chloride concentration is much higher than that of the silver nitrate, all the silver nitrate will preferentially react with the chloride and thus there will be no remaining free silver ions to form a pink/red-coioured fluorescein silver carboxylate: thus no colour change will occur. Typical silver nitrate concentration levels would be set at approximately 40 mmol/L Overall, this results in a device/system which turns red/pink when the heat-acclimatised sta te is reached, remaining yellow in a non-heat acclimatised state) .

Another chemical detection test which can be used to detect presence of chloride ions is mercuric nitrate and 1 ,5-diphenylcarbazone as the indicator. The concentration of mercuric nitrate can be set at a concentration to colourimetrically distinguish between the diffe rent chloride concentrations in the non-heat acclimatised and heat-acclimatised physiological states A range of 1 7.5-20 would be a typical concentration for the mercuric nitrate. This produces a violet coloured complex in heat acclimatised states. In the non-heat acclimatised state it remains colourless.

A further chemical detection test, for detecting chloride ions is the use of mercuric nitrate, ferric nitrate and mercuric thiocyanate (Equations 2-4). Mercuric nitrate effective ly acts as the chloride controlling species; any excess chloride ions subsequently react with mercuric thiocyanate to form a mixture of mercuric chloride and thiocyanate ions. The thiocyanate reacts with ferric nitrate to produce ferric thiocyanate which is red in colour, hence indicating non-heat acclimatisation due to the excess of chloride ions.

The concentration of the mercuric nitrate can be set at such a concentration to differentiate the non-heat acclimatised and heat acclimatised physiological states . Typical concentrations of mercuric nitrate to colourimetrically differentiate the two states would be A range of 1 7.5-20.

Hg(N0₃)₂ + 2 CI - -> HgCI₂ + 2 N0₃ [ Equation

2)

Hg(SCN)₂ + 2 CI ^' -> HgCI₂ + 2 NCS ^" ( Equation ³)

Fe(N0₃)₃ + 3 NCS ^' -> 3 N0₃ ^" + Fe(SCN)₃ red-coloured (Equation 4)

Another colourimetric chemical detection system can also be used for distinguishing different chloride ion concentrations. Silver nitrate , set at a typical concentration level of 40 mmol/, in the presence of indicator amounts of potassium chromate , can be used to visually differentiate the non-heat acclimatised and heat acclimatised physiological states. When the concentration of sweat chloride is greater than that of silver nitrate an indicating white colour will result. When the sweat chloride concentration is less than that of the silver nitrate the red colour of the potassium dichromate will remain. Thus, by setting the silver nitrate concentration at typically 40 mmol/L we can differentiate the non-heat acclimatised and heat acclimatised states: i.e. in the non heat acclimatised state the typical chloride concentrations are -55 mmol/L ; thus there will be an excess of chloride ions present causing a white colourisation. When the heat acclimatised state is reached i.e. typically 35 mmol/L chloride, there will be no excess chloride present (as it will preferentially react with the silver nitrate) thus the red colourisation will remain. Ove rall, this test represents a colourimetric differentiation between the non heat acclimatised and heat acclimatised physiological states. An excess of chloride ions will result in a white colour indicating that the individual is not heat acclimatised whereas when the individual is heat acclimatised a red/brown colour will remain.

More reliable and accurate results for all of the aforementioned colourimetric test systems would be achieved when the dietary sodium chloride intake is controlled

In yet another embodiment, colourimetric detection chemicals can be used to detect a change in the concentration of sodium ions, which are known to significantly reduce in concentration during attainment of heat acclimatisation. A yellow solution of sodium zmc uranyl acetate is formed on exposure of zinc uranyl acetate to sodium ions. As with chloride, the excess of sodium ions shows that the individual is not yet heat acclimatised. Here the dietary sodium intake needs to be controlled and maintained at a relatively constant level in order to ensure consistent and reliable results.

In a further embodiment, colourimetric detection chemicals can be used to detect a cha nge in the concentration of zinc ions. Potassium ferrocyanide is the 'controlling^' chemical, in the presence of a trace of potassium feme cya nide, and an indicator, which is preferably a diphenylamine, diphenylbenzidine or an analogue or derivative thereof; the indicator undergoes a colour change to bright blue when exposed to divalent zinc ions (equation 5) .

3Zr>2» ₊ 2K₄Fe (CN ₆ - =~— ^ί———^► Κ,Ζπ, Fe CN_fi) , + 6K^÷ Equa on 5

° trace ol potassium lernc cyanide « ⁱ <" '« '

( blue coloured with addition of indicator) Alternatively 8-hydroxyquinoline is used as the detection chemical for zinc ions as it forms a zinc complex which fluoresces under UV light. This patch can be used in conjunction with a small portable UV light-source to detect fluorescence. The magnitude of the fluorescence is related to the concentration of zinc ions.

Calcium ion concentrations reduce by approximately 30% to 50% post attainment of heat acclimatisation . Colourimetric tests based on the use of chemicals such as . ((0₃PC( R, R^' )P0₃)4^'), specifically methylene diphosphonate (MDP, R=R^' =H) and hydroxyethylidene diphosphate (HE DP, R=OH, R^' =Me) have been used to identify calcium ions through the formation of a yellow colour. Thus attainment of the heat acclimatised physiological state could be measured and predicted through a reduction in the intensity of the yellow colourisation - associated with the known drop in calcium ion concentration. The advantage of using calcium ions is that they are relatively diet independent .

In a second embodiment of the invention orga nic constituents are used as biomarkers to produce a colour or other metric change to demonstrate whether or not an individual is heat acclimatised.

Lactic acid can be used as a biomarker as it is known that lactic acid concentrations decrease with sweat flow rate which increases (by approximately 50%) during attainment of heat acclimatisation . A colourimetric test is used to detect the presence of lactic acid over a predefined concentration range. Typical concentration reductions a re approximately 40 mmol/L to 20 mmol/L.

Another biomarker which can be used is urea . This is advantageous over other named organic biomarkers in that it possesses a lower inter-group concentration va riation. At low sweat flow rates the urea concentration is approximately four times higher than at high sweat flow rates. As sweat flow rates increase significantly during acclimatisation the associated drop in urea concentration may be utilised as an indicator of heal acclimatisation.

In the first and second embodiments described above the colourimetric detection chemicals are already present in the patch . This ensures that the patch doesn't have to be moved or transported for analysis, thereby overcoming the problems of the prior ah . The colourimetric chemicals may be in (he body of the patch attached to the skin or they may be in a part of the patch which is not directly applied to the skin, as is. described in UK patent application no. GB 1022018.

Certain ions decrease in concentration during heat acclimatisation therefore creating a drop in electrical, or ionic, conductivity of sweat. Therefore , a third embodiment of the invention measures changes in pH to determine whether and individual is heat acclimatised.

Concentration levels of bicarbonate increase with increasing rates of sweat secretion. As sweat flow rates increase during the heat acclimatisation process the concentration of bicarbonate also increases, thus measurement of bicarbonate concentration gives an indication of physiological heat acclimatisation attainment.

The invention comprises a personal heat acclimatisation status monitor based on any type of indication such as pH (measured either electronically or colourimetrically) or an audible response . For example , an LED can illuminate to show thai the pH has risen above a certain level giving a simple visual indication, or an alarm could sound to indicate the increase. The monitor is directly linked to the patch to analyse the sweat which has been absorbed and/or adsorbed in (he patch. Alternatively, an electronic patch attached directly to the skin using 'skin sensors', or pads, as is used in a polygraph, could act as heat acclimatisation status monitor. Further, the monitor may be slightly remote to the 'skin sensors' e.g. it does not have to be directly attached to the skin. This could be achieved via an electrical connection. Alternatively, the skin sensors, and the remainder of the overall heat acclimatisation predicting device (either attached directly to the skin , or remote) could be constructed in the form of a 'wrist-watch' like system, with measurement data transmitted to a 'processing unit' via an electrical connection, or an electromagnetic transmitting/signal, to a data processing/ handling unit.

In a fourth embodiment a device comprising a patch, is used to measure heat acclimatisation by analysing sweat samples by making use of a conductivity measuring device. A polygraph or any similarly acting device can be used to analyse the skins sweat conductivity changes. An LED will illuminate when gross sweat salt concentration (and hence conductivity) falls to below a certain level. This device can be worn at all times or B2012/000800

9 intermittently and can be configured to trigger an alarm when heat acclimatisation is achieved.

Variations of the electrical device, and/or including transmission of data(simiiar to those described for the pH measuring device) can be used.

The invention will now be described with reference to the accompanying drawings.

Figure 1 is a side view of a first embodiment of the invention

Figure 2 is a perspective view of a first embodiment of the invention.

Figure 3 is a side view of an alternative first embodiment of the invention

Figure 4 is a side view of a second embodiment of the invention.

Figures 5 a and 5b show two embodiments where the indicator is mixed with the sweat after removal

Figure 6 shows a reaction scheme of silver and chloride ions using fluorescein as a colourimetric indicator.

Figure 7 shows a reaction scheme of mercuric nitrate and chloride ions using 1 ,5- diphenylcarbazone as a colourimetric indicator.

Figure 8a-c show - capillary action electrodes.

Figure 1 shows a first, embodiment of the invention, a two-part patch ( 10). The patch comprises a two-part system having a chemical recognition system having a first part ( 12) configured to collect sweat from the skin, and a second part ( 1 3) remote from the skin, in use, containing colourimetric detection chemicals ( 14). The first part ( 12) has a permeable base ( 15) to permit sweat to penetrate it, In use, the first part ( 12) is placed on the skin to collect seat. After sweat collection the patch (10) is removed from the skin , and the two parts ( 12, 13) are brought together so that the upper surfaces (2, 3) contact each other so that the sweat contacts with the detection system ( 14). Although not shown, either or both of the upper surfaces (2,3) can have a removable impermeab)9 barrier to prevent inadvertent contact of the surfaces before sufficient sweat has been collected.

Figure 2 is a perspective view of the embodiment shown in figure 1 .

Figure 3 is a side view of an alternative first embodiment of the invention. A two-part patch (10^' ) is shown comprising a two-part system having a chemical recognition system having a first part (12) configured to collect sweat from skin and a second part ( 13') containing colourimetric detection chemicals (14). The first part ( 12) has a permeable base ( 1 5) to permit sweat to penetrate it in use . The second part ( 1 3') has an impermeable base ( 16) to prevent sweat from entering the second part. There is an adhesive layer ( 1 7) on the permeable base ( 1 5) and impermeable base ( 1 6) for attaching the patch to the skin. The adhesive layer is permeable to allow the passage of sweat from the skin to the first part ( 12).

Figure 4 is a side view of a second embodiment of the invention. The patch ( 10') comprises one part ( 1 8) .containing a colourimetnc detection system ( 14) and has a permeable base ( 15) to permit sweat to pass from the skin of the wearer to collect sweat . When the patch is brought in to contact with sweat it retains the sweat. The sweat is in contact with the detection chemicals ( 14) and a visible colourimetric indication of acclimatisation is the result. Although not shown in the figure, this embodiment can have a permeable adhesive layer on the lower pa rt for attachment to the skin of a wearer.

Fig . 5 has two separate embodiments. In fig 5a the are two separate parts to the device: a first ( 1 2) in contact with the skin which collects sweat, and a second part containing the reagent 1 3. The reagent is contained behind an impermeable layer ( 1 9) . When required , the impermeable layer is removed so that the two halves ca n be brought together to mix the reagent with the sweat.

In Fig. 5b the impermeable layer is be tween the two compartments in a single device ( 1 8 ) and is removed by pulling out the impermeable layer ( 1 9) from the middle of the device to enable the sweat and the indicator to mix.

The patch 10' or second part ( 13) is impregnated with, or contains, colourimetnc detection chemicals. The detection chemicals are fluoroscein and silver nitrate with fluorescein as the colourimetric indicator. Figure 6 shows a reaction scheme of fluorescein and chloride ions. When the person whose sweat is being monitored is not heat acclimatised there will be an excess of chloride ions present which results in no colour change; the patch or second part remains yellow. When the subject is heat acclimatised there is a greater concentration of unreacted silver nitrate present and the patch or second part turns a red- pink colour.

Figure 7 shows a reaction scheme of an alternative colourimetric chlonde detection system is depicted in the reaction scheme shown in Figure 7. This comprises of mercuric dinitrate with 1 ,5-diphenylcarbazone acting as the colourimetric indicator. In the non-heat acclimatised state there is an excess of chloride ions resulting in no colour change. In the heat acclimatised state there are less chloride ions resulting in an excess of unreacted mercuric ions which are able to complex with the diphenylcarbazone indicator, producing a deep blue colouration.

Figures 8a-c - show a capillary action electrode. The electrode(20) is designed possessing a corrugated, channelled or rippled effect (22) as depicted in the diagrams. The corrugations, channels or ripples (22) are of optimised dimensions (radii or effective semicircular diameter) to maximally enable sweat to 'capillary-flow' or channel along the corrugations, channels or ripples towards the outer edges of a sensor: this enables freshly generated 'free flowing sweat' to contact the sensor. The sensor may additionally comprise of micro-pores (26) enabling the sweat to capillary-flow between the inner and outer surface of the sensor, also allowing constant replenishment with freshly generated sweat. The sensors are contained within a non-conductive (insulating) thin film (such as a polyimide polymer) and separated by a suitable distance to allow formation of a 'conductance cell' which enables measurement of the sweat conductuctivity. The thin film insulating material may itself contain channels that are parallel to those of the sensors (see diagram 8b), allowing the flow of sweat between the sensors and hence conductivity to be realised (a natural sweat flow towards the outer edges of the sensor will be generated) . The realisation of 'free-flowing' sweat contacting the sensor represents a more accurate real-time value of sweat conductance through constant replenishment. Overall, the attainment of free flowing sweat across the skin sensor avoids the accumulation of sweat salts, and hence falsely high real-time sweat conductivity values. This enables the device to be worn either constantly, or intermittently, throughout the attainment of heat acclimatisation") . The sensor contacting the skin (29) is made of a suitably stable material such as platinised electrodes and/or those using in polygraphs.

When a subject is to be monitored or assessed to determine whether or not they have become heat acclimatised patch, according to any one of the embodiments is attached to the skin of the subject. The sweat will be absorbed and/or adsorbed through a membrane (semi-permeable or otherwise) when the wearer is subjected to exercise and/or heat. The device and/or patch can be worn for a predetermined time based upon the requirements of the acclimatisation tests and/or saturation of the patch with sweat. The two-part patch is advantageous over the prior art as the chemical detection system is remotely contained from the skin eliminating potential skin toxicological problems; including transdermal effects etc. Further, this two-part patch nega tes detrimental decomposition of the chemicals by undesi rable reactions with elements or chemicals in the skin of the user.

A further advantage of the present invention is that the sample does not come into contact with air (or only briefly) , therefore minimising the possibility of evapora tion , decomposition or contamination.

The colour indication in the form of either an LED, similar light indicating device or a chemical reaction gives an advantage over prior art as it is a quicker way of assessing physiological acclimatisation to heat, The visual indication gives an advantage over prior art as the physiological status of the individual being tested can be easily seen without the need for laboratory analysis The pH working range of the detection chemicals is 4-8 so as not to cause genera) toxic or transdermal, physical andJor chemical damage to the skin should inadvertent contact occur, thus overcoming the problems of the prior art. Where the colourimetric detection system is remote from the skin all chemical contact toxicology problems are eliminated allowing the use of chemical detection systems which would otherwise be precluded. Overall, the methodology of this system greatly enhances its usefulness to this application since a far wider range of potential chemical agents can be utilised.

The patch may be attached to the skin by any suitable means such as a commercially used sticking plaster adhesive . The adhesive may be protected by a suitable impermeable and physically robust covering when the patch is not in use.

The basic structure of the patch itself comprises a semi-permeable membrane throug which sweat can pass f rom the skin, and is retained in the patch; or a simple absorbent material such as e. g. medical grade gauze (the material will need to be analytically free from the target analytes). The patch may be constructed from known ma terials such as those used for waterproof sticking plasters, or wound dressings, which allow for the passage of a fluid from one side but not the other. When a bodily fluid is absorbed and or/adsorbed into the patch it is retained and may be used as described below to determine whether an individual is heat acclimatised.

If pH, conductivity or potential difference (voltage) are used as the metric to determine heat acclimatisation then the device (see Fig 8b) can contain, for example, Iwo electrodes, and take the form of a 'wrist-watch' based system.

During the physiological attainment of heat acclimatisation there are overall changes in the chemical and/or physical parameters of sweat: these properties can be utilised as alternative metrics in producing a diagnostic test for heat acclimatisation, examples include ; light absorbance / transmission ; UV absorbance / transmission; refractive index; viscosity; density; vapour pressure ; ion-selective electrode detection ; liquid ion- chromatography; and osmotic pressure (micro-differences across a semi-permeable membrane, or similar).

Claims

1 . A patch for assessing heat acclimatisation comprising a detectable marker for determining acclimatisation status.

2. A patch according to claim 1 wherein the detectable marker is a chemical

detection system.

3. A patch according to claim 2 wherein the chemical detection system is configured to detect the presence of chloride ions in sweat.

4. A patch according to claim 3 wherein the chemical detection system comprises fluorescein and silver nitrate.

5. A patch according to claim 3 wherein the wherein the chemical detection system comprises 1 ,5-diphenylcarbazone and mercuric nitrate.

6. A patch according to claim 3 wherein the chemical detection system comprises ferric nitrate, mercuric nitrate and mercuric thiocyanate.

7. A patch according to claim 2 wherein the chemical detection system is configured to detect the presence of sodium ions in sweat.

8. A patch according to claim 7 wherein the chemical detection system comprises zinc uranyl acetate.

9. A patch according to claim 2 wherein the chemical detection system is configured to detect the presence of zinc ions in sweat.

1 0. A patch according to claim 9 wherein the chemical detection system comprises potassium hexacyanoferrate as a controlling chemical, in the presence of a trace of potassium ferric cyanide and a colourimetric indicator

.

1 1. A patch, according to any of claims 1 to 10 wherein the patch comprises a first part configured to contact skin, and a second part containing the chemical detection system.

12. A patch according to claim 10 wherein the colourimetnc indicator is

diphenylamine, diphenylbenzidine or analogues thereof.

13. A patch, according to claim 9 wherein the chemical detection system comprises 8- hydroxyquinoline.

14. A patch according to claim 2 wherein the chemical detection system is configured to detect the presence of lactic acid in sweat.

15. A patch according to claim 2 wherein the chemical detection system is configured to detect the presence of urea in sweat.

16. A patch according to claim 1 wherein the detectable marker is a changes in pH.

17. ,A patch according to claim 16 wherein the change in pH is measured

electronically or colourimetrically.

18. A patch according to claim 16 or 1 7 wherein changes in bicarbonate

concentration are measured.

19. A patch according to claim 1 wherein the detection system is configured to

measure changes in electrical conductivity.

20. A patch, according to any of claims 1 to 19 having a pH in range of 4 to 8

21 . A patch and/or device according to claim 1 wherein the detectable marker

comprises an LED.

22. A method for assessing heat acclimatisation status, comprising the steps of : a. Contacting the first part of the patch according to claim 11 with skin to collect sweat and

b. Contacting the first part of the patch with the second part containing the

chemical detection system.

23. A method for assessing heat acclimatisation status comprising the steps of:

a. Contacting the patch according to any of claims 1 to 21 with skin to collect sweat.

24. A method according to either claim 22 or 23 further comprising the step of

removing the patch from the skin.

25. A method according to any of claims 22, 23 or 24 wherein a change in the

detectable marker is assessed.