J. therm. BWl. Vol. 9. No. 3. pp. 171-176. 1984 0306-4565'84 S3.00 + 0.00 Pnnted in Great Britain. All rights reserved Copyright (' 1984 Pergamon Press Ltd

THERMAL SENSATION, SKIN BLOOD FLOW AND FREQUENCY ANALYSIS OF CUTANEOUS

VASOMOTOR RHYTHMS

K. ISSING, E. FUHR, F. Kosslvt and H. HENSELt)Iq Department of Physiology, University of Marburg. Deutschhausstral3e 2, 3550 Marburg. F.R.G.

(Received 7 July 1983; accepted in revised form 5 November 1983)

Abstract--I. In a climatic chamber, the air temperature of which (ambient or room temperature) was increased from 12 to 45~C, I 1 human subjects estimated their local thermal sensations at forehead, both hands and foot. Corresponding local skin blood flows were measured.

2. The subjects perceived local temperature sensation (LTS) and local thermal comfort (LTC). LTS was a linear function of local skin temperature ( T ~ ) and only slightly dependent on mean skin temperature (7,~). LTC was an inverted U-shaped function of Tk~,~ and also dependent on 7 ' , .

3. l 'he skin blood flow at forehead, both hands and foot as a function of increasing room temperature (Ta) showed that vasomotor oscillations began at different T,~,~ and 7¢, values, while rectal temperature was almost constant. There was no correlation between skin blood flow and LTS or LTC.

4. Frequency analysis of skin blood flow, measured at four skin locations, always showed long time rhythms with periods of some minutes. With the increase of Tk~,~ further blood flow rhythms of higher frequencies with periods of 10-20 s occurred. The amplitudes of the occurring frequencies rose to their maximum with the increase of Tas between 39 and 41C.

Key Word Index- -Local temperature sensation (LTS); local thermal comfort (LTC): thresholds of rhythmic skin blood flow; frequency analysis; Homo sapiens.

INTRODUCTION

Earl ier experiments , in which the skin t empera tu re at var ious sites of the body was locally changed, show tha t local t empera tu re sensat ion (LTS) expressed as cold or warm depends mainly on local skin tem- pera ture (Tk~.,J and slightly on mean skin tem- pera ture (7',k) or core temperature . Local thermal comfor t (LTC), the accompany ing c o m p o n e n t of t empera tu re sensat ion, expressed as p leasant or un- p leasant (Cabanac , 1969) depends bo th on Tk~j and T,k (Marks and Gonzalez , 1974: Mower, 1976; Beste, 1977; Hensel, 1977; H i ldeb rand t et al., 1981; Issing and Hensei, 1982). Local thermal d iscomfor t can be induced by asymmetr ic the rmal rad ia t ion (Olesen et al., 1973), d r augh t (Os tergaard et al., 1974; Fanger , 1977, 1979; Mcln ty re , 1979) and cold or warm floors (Oiesen, 1977). The main purpose of our exper iments was to s tudy LTS and LTC at several par t s of the body when no definite the rmode stimuli were locally applied to the skin. To study au tonomic cu taneous vascular responses and their possible corre la t ion with LTS and LTC, local skin b lood flow was measured. One supposes tha t b lood flow depends on the central drive f rom internal or external the rmorecep tors and on a direct effect of T~o,j on the b lood vessels of the skin. In h u m a n subjects, the interference of central and local effects o f t empera tu re on the v e n o m o t o r tone was confirmed. V e n o m o t o r responses were in- duced by changes in core t empera tu re or in average skin t empera tu re and influenced by the local tem- pera ture of the veins (Shepherd and Webb-Peploe , 1970; Rowell et al., 1971a, b; Zi tnik et al., 1971).

@Died in January 1983.

Therefore, the beginning of va somoto r oscillations of the arterioles in the skin and their character is t ic waves were of interest.

MATERIALS AND METHODS

Eleven human subjects (2 male, 9 female; age 20-30 yr) wearing bathing suits (clothing value: 0.05 clo) sat in a climatic chamber at a room and wall temperature of 12°C. Floor and ceiling temperatures could not be regulated. The relative air humidity was 45% and the air velocity 0.2-0.3 ms- ~. The right arm of the subjects was thermally insulated from the ambient (room) temperature (TR) by a water circulated, plastic cylinder maintained at 3YC. The temperatures of forehead, both hands, foot, rectum, upper arm. breast, thigh and calf were continuously measured with thermocouples. In addition, the heat transport index 2, which is proportional to cutaneous blood flow (Golenhofen et al.. 1963), was measured at forehead, both hands and foot with a Fluvograph (Hensel and Priebe, 1970; Hensel and Brandt. 1977). After a 30min adaptation period we oc- cluded the cutaneous blood flow of the subjects (the mea- sured 2) for 3 min. The TR was then linearly increased within 45 rain to a final temperature of 45°C and we occluded the skin blood flow again. While the T R rose and the relative air humidity and air velocity were kept constant, the subjects estimated their LTS and LTC at forehead, both hands and foot at voluntarily chosen time intervals. LTS was estimated on a 20-point magnitude scale between warm and cold, and LTC, at the same body parts, on an 8-point scale between pleasant and unpleasant.

From the skin temperature of upper arm, breast, thigh and calf, we calculated mean skin temperature (T.~; Rama- nathan, 1964). The changes (A2) of the heat transport index (skin blood flow) of forehead, both hands and foot were determined by the difference of the occlusion values at the beginning and the end of the experiments. At the thresholds, when skin blood flow of the various body parts became

171

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Fig. I. LTC as a function of T~,~ at forehead, right hand, left hand and foot at a 7~, between 28 and 37~C (left panel). LTS as a function of T~,~ at a T~, between 28 and 37~C: mean values from 11 subjects:

bars indicate SEM (right panel).

rhythmic (this is when vasomotion of the arterioles in the skin starts), we calculated the Tk~,~ and T,~.

To analyse the blood flow waves with a desk-top com- puter, we transformed the analogue data into a digital form by sampling the blood flow curves at constant time intervals (At) within a total measuring time (T). After removing linear trends in the measured curve (only the blood flow waves were of interest), we used these data points to calculate the amplitude spectra (amplitudes of the rhythms vs the frequencies) by the Fast Fourier Transformation method (Cooley and Tukey. 1965) and determined the frequencies of the blood flow rhythms. This analysis depends on the measuring time (T). because every frequency ca in the spectrum is a multiple of the basis frequency to o = 2Tt/T.

R E S U L T S

The subjects perceived LTS weakly at the various parts o f the body, but could distinguish it from LTC. Figure l, right-hand side, shows that LTS at fore- head, right hand, left hand and foot can be described

by linear functions (0.96 < r < 0.99; least squares) of T,~, at increasing T~k from 28 to 37°C. At the same time rectal temperature (T,,) fell from 37.07 to 36.55°C. The T~.,, ranges at the various parts o f the body were quite different: forehead, 33-38°C; right hand, 32-36°C; left hand, 22-36"C; and foot, 21-33°C. LTC (Fig. I, left-hand side) as a function of T,~,~ can be described as a polynomia; of the fourth power. Furthermore, LTC is correlated with T,k.

Original skin blood flow records of forehead, right hand, left hand and foot as a function of increasing Ta are shown in Fig. 2. Occlusion of cutaneous blood flow at a TR of approx. 12~C showed a moderate skin blood flow in the forehead, whereas the arterioles in the right hand (although thermally isolated from Ta), left hand and foot remained totally vasoconstricted. The difference o f blood flow by occlusion at 12 and 45°C Ta yielded the blood flow increase (A,;.) during the experiment. The amplitudes of cutaneous vaso- mot ion in the forehead were very small whereas in the

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Fig. 2. Original skin blood flow records (heat transport index 2) at forehead, left hand, right hand and foot as a function of increasing T R for 12 to 45°C.

173

extremities the waves were larger and also syn- chronized over the whole body. The blood flow records showed the different thresholds of the rhyth- mic skin blood flow. The comparison of the LTS or LTC with the autonomic vascular responses in the skin showed no correlation.

Figure 3 shows the increase of skin blood flow (A).) in forehead, right hand, left hand and foot as a function of T~,=j at increasing ~Psk as well as the corresponding thresholds of skin blood flow, where the rhythmic vasomotion began. A). of the forehead increased only moderately (0.9 units). A;. at the right and left hands were almost the same (approx. !.6 units), in spite of very different Tk,~s. A;. of the foot was the lowest (approx. 0.7 units). The thresholds of rhythmic skin blood flow of forehead and right hand occurred at high T~.j (32.9 and 32.6'C) and low J",~

(28.6 and 29.6°C). Whereas, at the left hand and foot, they occurred at low T ~ (27.4 and 25.2°C) and high T,k (34.9 and 31.2¢C).

Frequency analysis of skin blood flow rhythms at right hand, left hand, forehead, and foot showed that during low TRs between 11.5 and 15.2°C there were no blood flow rhythms. By increasing the TR to 32°C several rhythms with periods in the range of several minutes were found and the amplitudes of the rhythms rose with increasing temperature. At TRs higher than 32°C, additional rhythms of higher frequencies with periods of approx. 10-20 s occurred.

The maximal amplitudes of all rhythms were found at Tas between 39 and 41°C. The T ~ of both hands and forehead ranged between 36 and 37°C and that of the foot was approx. 28°C. When TR was higher than 41~C, the amplitudes of higher frequency

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Fig. 3. Increase of heat transport index A~. (increase of blood flow) at forehead (Z~), left hand (O), fight hand (A ) and foot (I-1) as a function of T~,l al a T,k between 28 and 37~C. Arrows indicate the corresponding beginnings (mean thresholds) of rhythmic cutaneous vasomotion. Mean va)ues of 11

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Local temperature sensation and thermal comfort 175

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Fig. 5. LTC as a function of T ~ , To, and T R, respectively. This LTC curve is qualitatively valid for all body parts.

rhythms decreased and only the rhythms with periods in the minutes range remained (see Fig. 4).

To study the intensity of vasomotion at the different skin locations, we compared the amplitude height of the blood flow rhythms, We found that the amplitude height in both hands were similar to those in the foot, but at the forehead they were approx. 90% smaller.

DISCUSSION

Our results show that the subjects can perceive LTS and LTC also without definite local thermode stimuli application. They compare their changing T~o~js at the forehead, both hands and foot with the simultaneously increasing T,k of their body. This thermal perception, however, is weaker than that with definite local thermode stimuli because of the lack of very distinct local temperature differences between the T ~ s and the T,k.

Earlier thermal comfort investigations with definite local thermode application at the palm of the hand had shown that it is possible to construct linear LTC regression curves as a function of definite thermode stimuli [Beste (1977), quoted by Hensel (1981)]. This means that, for example, at a low constant 7"sk and Tx, respectively, LTC increases linearly (see linear regression curves in Fig. 5). In our recent experi- ments, however, we did not apply definite local thermode stimuli nor was the T,k constant over the whole session. Nevertheless we can construct another LTC curve (polynomial of the fourth power, see Fig. 5) with the aid of the above-mentioned linear LTC regression curves. Due to the increase of Tk~ and T,A the points of the LTC curve have to go to the fight on the abscissa and to jump simultaneously on the ordinate to that linear regression curve that belongs to the corresponding T,A. The LTC curve constructed in this way as a function T~,~ and T,k is qualitatively valid for all body parts.

The Tk,~j ranges were quite different due to the different thermal conditions at various parts of the body. Therefore, the change of the heat transport

index (A;.) had many different values; e.g., it was lowest at the foot because of the strong cooling of this extremity by vasoconstriction at a T~ of approx. 12°C and a local foot temperature of approx. 21°C at the beginning of the experiment.

The lack of correlation between LTS and LTC and skin blood flow increase does not support the hypoth- esis (Hardy, 1970) that vasomotor influences other than changes in tissue temperature may be involved in local thermal comfort or discomfort. The mean blood flow increases A2 at forehead, right hand, left hand and foot as a function of T~o~t at increasing T,k had very different values. The rhythmic vasomotor thresholds of right hand and forehead occurred at high Tk,~j and low T,A. Whereas, they occur at the left hand and foot already at low T~o~ but high T,k. We suppose that cutaneous vasomotion, and particularly its rhythmic vasomotor thresholds, are directly de- pendent on T~z and indirectly on T,k, acting via afferent pathways on central nervous structures that influence efferently the arterioles. Although the T= was almost constant, it is known that cutaneous vascular responses depend on both core and skin temperature (Benzinger, 1969; Wyss et al., 1974, 1975; Wenger et at., 1975a, b; Johnson and Park, 1979). Therefore, one could postulate a particular set point for rhythmic vasomotor thresholds in the skin depending on special combinations of Tk~,~, 7',k and T= and thus partly influencing and controlling the thermoregulatory system.

The results of the frequency analysis of blood flow rhythms could be explained by vasomotion: at low TR, there are no rhythms due to the strong vaso- constriction of the vessels. With increasing tem- perature the vasoconstriction becomes weaker and thus the first, long-time rhythmic components occur. In the T R range between 39 and 41°C we suppose maximal rhythmic vasomotion and therefore we find a maximum of frequencies and the highest ampli- tudes. When the TR is above 41°C vasodilation increases and most of the short-time rhythms vanish and only frequencies with long periods remain. The small amplitude of the blood flow rhythms at the forehead is an indication of slight marked rhythmic vasomotion at this location.

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