Usually the modification of sweating was maintained throughout the. However, in 1950, Takagi and Sakurai, also working in Japan, reported

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1 THE EFFECT ON SWEATING OF PRESSURE ON THE BODY SURFACE. By E. S. WATKINS. From the Hot Climate Physiological Research Unit, Oshodi, Lagos, Nigeria. (Received for publication 25th October 1955) KuNO [1934] drew attention to a "hemihidrotic reflex" phenomenon which occurred when lying down on one side of the body. This reflex consisted of an increase of sweating over the upper side of the body and a coincident decrease of sweating of the lower side. Ogata and Ichihashi [1935, 1936] concluded that this reflex was initiated by posture and consequent vasodilatory changes in the dependent part of the body. However, in 1950, Takagi and Sakurai, also working in Japan, reported a " hemihidrotic reflex" in which, in response to pressure on one side of the body, decrease of sweating occurred on that half of the body with concurrent increase of sweating on the contralateral half. This response could be elicited by pushing the chest or one side of the body against a wall or post, or against the side of a chair. Pressure by smaller objects such as a box (10 cm. x 8 cm.) was also effective in modifying sweating, and even very small areas of pressure, such as the end of a pencil 1 cm. in diameter, could initiate the reflex. The distribution of effective pressure points was described, and the areas most sensitive to pressure stimulation were found to be the axillary and pectoral regions; in these regions the reflex was evoked within 5 minutes of pressure being applied, while in less sensitive areas a latent period of over 5 minutes was found. Usually the modification of sweating was maintained throughout the periods of pressure, which were up to 20 minutes in duration. Somewhat paradoxically, pressure on both sides of the body caused increase of sweating over the whole body in the Japanese winter and a decrease of sweating in the Japanese summer. From this evidence and from sweat rate observations during postural changes Takagi and Sakurai conclude that the sweating reflexes described by Kuno, Ogata and Ichihashi and previously ascribed to postural changes are, in fact, reflexes caused by pressure on the body surfaces. If this reflex response to pressure is consistent and sufficiently large, then it must be considered in the design of equipment and seating for industrial and military purposes in hot climates, where uneconomic sweating or inhibition of sweating are of importance. It was decided, therefore, to repeat the Japanese experiments to see if the reflex could be demonstrated in the West African under controlled climatic conditions, and to observe, in addition, its relation to total sweat loss and change in body temperature. VOL. xli, NO

2 264 Watkins METHODS Nine male West Africans acted as subjects and 27 experiments were performed. These included 5 control experiments in which no pressure was applied to the subject to observe the changes in sweating on the two sides of the body without any stimulus. In 20 of the experiments, pressure was applied to the pectoral region or axilla by leaning against a wall, or by leaning with the arm over a projecting board, with the chest and axilla in contact with the board (area of contact 200 cm.2). In the remaining two tests a cork (diameter 2-5 cm.) was used to apply pressure to the pectoral region. Sweat rate was measured throughout each experiment simultaneously, on both sides of the body from similar areas of the scapular regions of the subject, using a refined filter-paper weighing technique. The scapular regions were chosen for comparison as they present a flat surface, and consequently were convenient for the collecting technique employed. The same areas were used throughout each experiment to avoid the differences of sweating from area to area, within an anatomical region, which are known to exist [Weiner, 1945]. Filter-paper discs (area 8 cm.2) were weighed in weighing bottles before and after contact with the skin, and were handled at all times in the climatic chamber with dry dissecting forceps, to prevent contamination with sweat from the observers. The areas of the subject's skin, from which sweat was being collected, were gently dried with blotting-paper before the filterpapers were applied. The papers were held in contact with the skin for two minutes by a movable diaphragm-lid of perspex in a shallow cylindrical perspex container, similar to that described by Thomson [1951]. This prevented contamination of the filter-paper by sweat running from other skin areas. The discs were then returned to the weighing bottles which were closed by tight-fitting glass lids, and bottle plus contents were weighed immediately. The increase in weight gives sweat rate in mg./8 cm.2/2 min. To check the accuracy of this technique, 3 experiments were conducted in which the hourly sweat rates of two subjects were estimated by measuring weight loss. At the same time the filter-paper technique was used for measuring the sweat rates of the head, arm, trunk and leg areas, and the total hourly sweat rate was calculated as the sum of the sweat rates of each anatomical region. For the six exposures, the mean sweat rate was 557 g./hr. by weight loss and 527 g./hr. by calculation from regional sweating. This represented a difference of 0 5 mg./8 cm.2/2 min. Similar validation of this type of technique of sweat collection, as a means of estimating total body sweat loss as compared with weight loss measurements, was demonstrated by Weiner [1945]. In the main series the subjects stood in the climatic chamber in still

3 Sweating Responses to Pressure 265 air at a climate of F. (400 C.) dry bulb, and F. (320 C.) wet bulb to induce sweating without working. The men were weighed nude and their rectal temperatures were taken at the beginning and end of each exposure. Sweat rates were observed as soon as visible sweating was established, and thereafter every 10 minutes over a period of 70 minutes. ci12 E 9g C F Left ~~~~~~~~~~~~~Scapular FIG# TIME (MINUTES) 1.-Spontaneous changes in a control exrperiment. In order not to miss a very rapid reflex response, 3 experiments were performed measuring the sweat rate at five-minute intervals, before pressure (0, 5, 10), during pressure (15, 20, 25) and after pressure (30, 35). In the remaining 17 pressure experiments for the first 20 minutes no pressure was applied; there was then a period of pressure of 30 minutes, followed by a final recovery period of 20 minutes after pressure was removed. Thus three measurements of sweat rate were obtained before pressure (0, 10, 20), three during pressure (30, 40, 50) and two (60, 70) after pressure. RESULTS In the control experiments marked decrease of sweating often occurred spontaneously on one side of the body with concurrent increase of sweating on the other side (fig. 1); this was the case sometimes in the pressure experiments in the period before pressure was applied (fig. 2). If these periods of observation are considered together, it was found that in 740 minutes of observation spontaneous changes similar to the supposed reflex occurred fifteen times when no pressure had been applied. The changes in sweating of both scapular regions during all the pressure experiments are summarized in Table I. The immediate

4 266- Watkins TABLE I.-CCHANGES IN SWEAT RATE IN ScAPuLAR REGGIONS DURING INITIAL TEN MINUTES OF PRESSuRE APPLICATION Pressure side Opposite side Decreased Unchanged Increased Total Decreased Unchanged Increased Total * * Expected response according to Takagi and Sakurai. changes of sweating in the first 10 minutes of pressure were considered to be the response, for according to Takagi and Sakurai some pressure points have latent periods of j-2 min., some of 2-5 min., while others have latent periods of even longer. By this reckoning, however, response from the axillo-pectoral pressure points should have been apparent and maintained during the first 10 minutes of pressure Pressure to Left Side Applied 15 ~~~~~During Five-Minute Samplingal _S C4 u lo S Scapular FIG. 5 I10 IS 20O TIME (MINUTES) 2.-Similar changes of sweating on both sides during pressure. In 12 of 22 pressure experiments (Table I) changes of sweating on both sides of the body took place in the same direction during the period of pressure applied to one side of the chest. Fig. 2 shows an example of this response. In 3 experiments increase of sweating on the side pressed upon occurred associated with a decrease, or no change of sweating, on the other side (fig. 3). No reflex changes were found when a small area of the pectoral

5 Sweating Responses to Pressure region was pressed upon with a cork of 2-5 cm. diameter. From these results it is clear that the effect of pressure on the axillo-pectoral region was variable and unpredictable both in sign and quantity. In only 7 out of 22 experiments did changes occur during the first 10 minutes of pressure similar to those described as the "hemihidrotic reflex". During all the time of observation while pressure was applied, which totalled 595 minutes, the reflex occurred only 11 times-no more frequently than the spontaneous changes during no pressure. 13 Left 2 pular 12 Pressure to Right Side Applied 267 co 1-6 ight 6 capular FIa TIME (MINUTES) 3.-An example of increased sweating on the side pressed. However, in case a period of 10 minutes was too long to detect a rapid reflex response, in 3 experiments the exposure was reduced to 35 min. and the sweat rate recorded every 5 minutes. No reflexes were observed during the first 5 minutes ofpressure, and all 3 experiments failed to reveal a hemihidrotic response throughout pressure; in fact, in all 3 experiments, increased sweating on both sides of the body occurred during the pressure period. The results of one rapid sampling experiment are shown in fig. 2. Although these results showed that there was no immediate modification of sweating, as would have been expected if the supposed reflex existed, it was thought that one-sided pressure might result in an overall decrease of sweating on the same side, and an overall increase on the opposite side during the whole period of pressure. The mean sweat rates for the scapulae on the two sides before and during pressure have been calculated and compared, and the direction of change considered the response. The calculated mean sweat rates are shown in Table II. The results are also summarized in Table II (a change in the mean of 0-5 mg. being taken as significant, each mean was the mean of three sweat collections). Of these 20 experiments, in only 6 did the mean sweat rate increase on the opposite side and decrease on the side pressed upon during the I period of pressure.

6 268 Watkins TABLE II.-THE DIRECTIONAL CHANGES AND VALTUES OF MEAN SWEAT RATES (MG./8 cm.2/2 MIN.) BEFORE AND DURING PRESSURE Similar changes on both sides One side unchanged *Side pressed on decreased Opposite side increased Before * * I Side pressed During * *8 8* * Difference * * * *2-5* Before 5*8 6* * * Opposite side During * * Expected response according to Takagi and Sakurai. Difference ' The overall bodily changes and climates for the "pressure", "no pressure" and "rapid sampling" experiments are shown in Table III. Experiments. Type and number Pressure (17) No pressure (5) Rapid sampling (3) TABLE III.-BODILY CHANGES AND CLIMATES Length of exposure (min.) Mean rise rectal temp. (OF.) per exposure 0-92 (0.510 C.) 098 (0Q54 C.) 0-86 (0.480 C.) Mean sweat loss (kg.) per exposure *366 Mean dry bulb ('F.) (39.80 C.) (39.60 C.) (40Q90 C.) Mean wet bulb ('F.) 90-8 (32.70 C.) 90-6 (32-60 C.) 91-8 (33.20 C.) DIsCIUsSION As variations in sweating, similar to those which are held to constitute the supposed reflex, occurred at times when no pressure stimulus had been applied to the body, it is difficult to accept that the responses which did occur during pressure stimulation were other than chance effects.

7 Sweating Responses to Pressure 26g Statistical analysis of Table I and Table II by the chi-square (x2) test confirms that the frequency of the appearance of the "expected" response could have arisen entirely by chance. For Table I. X2=7X823 P= < 0.1 and > 0*05. Not significant. For Table II. X2=4-83 P=0.3. Not significant. The "expected" response was only seen seven times out of twentytwo attempts judging the results simply by the directional change of sweating, or six times out of twenty when the mean sweat rates for the periods are used as the index of response. Pressure over a small area was likewise ineffective, and thus no confirmation of the Japanese work can be found in these experiments. It is difficult in any case to accept the claims of Takagi and Sakurai, for in their paper few actual results are given and no real analysis is possible, and it would appear that no control experiments have been carried out. In addition, it is surprising to note that it is stated that the outer surfaces of the arms and legs have no receptors for pressure stimulation, yet it is presumably, according to the Japanese thesis, upon these regions that the pressure is brought to bear, when lying down on one side, which initiates the "hemihidrotic reflex'" of Kuno! Takagi and Sakurai mention that they were unable to demonstrate the reflex when the subject was fatigued, or in intensely sweating conditions. Similarly, the reflex was absent in minimally sweating conditions, or when the sensitivity of the subject was reduced by standing in a cold environment; the exact definition of these terms was not, however, made clear. But in this series of experiments, as can be seen from Table III, the subjects were not fatigued, nor were they at either the upper or lower limit of sweating. It should be pointed out that the present experiments were performed at dry bulb temperatures of F. (400 C.), while those of Takagi and Sakurai were done at F. ( C.), but nevertheless, in both series, the rates of sweating on the scapulae covered the same range of activity. However, as the pressure stimulus used in the experiments was that said by the Japanese to be adequate to initiate the reflex, the failure to elicit the expected response might possibly be attributed to the sweat glands becoming refractory to pressure influences when the heat load of the climate is sufficiently great. In West African subjects at least, it must be concluded that the reflex does not occur, or if it is does occur in some circumstances, it is certainly not physiologically significant in conditions where its operation might be of detriment to the organism.

8 270 Watkins SUMMARY 1. Simultaneous collections of sweat from both scapular regions of West Africans, using a filter-paper weighing technique, have been made to observe the changes in sweating during the application of pressure to one side of the body. 2. When no pressure was applied, it was found that sweating on the two sides of the body may be changing in opposite directions at any one time. 3. The hemihidrotic response to pressure, described by Takagi and Sakurai [1950] was only occasionally demonstrated, and its validity is suspect in view of the changes in sweating found when no stimulus was applied. ACKNOWLEDGMENTS Acknowledgments are due to Dr. W. S. S. Ladell and Dr. 0. G. Edholm for their advice and criticism of this work, and to Staff-Sgt. R. Byers, R.A.M.C., Mr. P. G. Phillips and Mr. E. A. Oshinyemi for their assistance in carrying out the experiments. I am grateful to the Director of Army Health for permission to publish this paper. REFERENCES KUNO, Y. (1934). Physiology of Human Perspiration, pp London: Churchill. OGATA, K. and ICEIHASHI, T. (1935). "Sweat reflexes due to changes in the posture of human body", J. Orient. Med. 23, OGATA, K. and ICHIHASHI, T. (1936). "Sweat reflexes due to changes in posture of human; changes in sweating on lying and standing", J. Orient Med. (Abstr. Sect.), 25, TAKAGI, K. and SAKURAI, T. (1950). "A sweat reflex due to pressure on the body surface". Jap. J. Phy8iol. (N.S.), 1, THOMSON, M. L. (1951). "Dyshidrosis produced by general and regional ultra. violet radiation in man", J. Phy8iol. 112, WEINER, J. S. (1945). "The regional distribution of sweating", J. Physiol. 104,