Clinical Science ( 1 990) 79,43-50
43
Cutaneous vascular responses evoked in the hand by the cold pressor test and by mental arithmetic I. MARFUOTT, JANICE M. MARSHALL
AND
E. J. JOHNS
Department of Physiology,The Medical School, University of Birmingham,Birmingham, U.K.
(Received 22 December 1989/2 March 1990; accepted 13 March 1990)
SUMMARY
1. Laser Doppler flowmetry has been used to study changes in cutaneous erythrocyte flux produced in the hand (i) on successive immersion of the contralateral hand in water at 20°C (cold test) and then in water at 0-4°C (cold pressor test), and (ii)by mental arithmetic. 2. In 11 subjects, placing the right hand in water at 20°C for 2 min induced a significant decrease in cutaneous erythrocyte flux in the contralateral hand and a significant fall in mean arterial pressure. Cutaneous vascular resistance, calculated as arterial pressure/ cutaneous erythrocyte flux, showed no significant change. Thus, the decrease in erythrocyte flux was apparently due to a fall in perfusion pressure. 3. Subsequent immersion of the right hand in water at 0-4°C for 2 min caused a significant decrease in erythrocyte flux in the contralateral hand and a significant rise in mean arterial pressure. It is concluded that the cold pressor response evoked from one hand elicited a substantial reflex vasoconstriction in the skin of the other hand; accordingly, calculated cutaneous vascular resistance increased significantly. 4. Eight subjects performed mental arithmetic for two periods of 2 min separated by a rest period of 2 min. By the end of the second minute of each period of mental arithmetic there was a significant decrease in erythrocyte flux. Mean arterial pressure increased significantly in the first period only, but calculated cutaneous vascular resistance increased in both periods, consistent with cutaneous vasoconstriction. 5. The cold pressor test and mental arithmetic are aversive stimuli that evoke the characteristic pattern of the alerting or defence response which includes splanchnic vasoconstriction and muscle vasodilatation. Previous studies on the cutaneous vascular component of this response have yielded equivocal results. The present study provides firm evidence that it includes cutaneous vasoconstriction, at least in the hand. Correspondence: Dr J. M. Marshall, Department of Physiology, The Medical School, University of Birmingham, Birmingham B15 2TJ, U.K.
Key words: defence response, emotional stress, laser Doppler flowmetry, skin blood flow, thermoregulation. Abbreviation: pu, perfusion units.
INTRODUCTION It is well established that in man, as in other mammals, novel, noxious or aversive stimuli evoke a characteristic pattern of cardiovascular response which has been termed the alerting or defence response [ 11. In man, this response can be evoked by a variety of stimuli including the ‘cold pressor test’ and mental arithmetic when carried out under some duress [2, 3). The response includes tachycardia and a redistribution of cardiac output away from the splanchnic regions towards skeletal muscle, due to vasoconstriction in splanchnic circulation and vasodilatation in muscle. However, exactly what happens in the cutaneous circulation of man during the alerting response has remained an open question. Brod et al. [2] used the temperature of the skin of the forearm as a means of assessing cutaneous blood flow and simultaneously used plethysmography to record total blood flow to the contralateral arm, i.e. skin and muscle. They reported that in eight normotensive subjects, mental arithmetic produced no change in forearm skin temperature in three and a decrease in the other five, even though total forearm blood flow increased consistently and forearm vascular resistance, calculated by division using the measurement of arterial blood pressure, decreased in all eight subjects. The changes in skin temperature recorded in hypertensive subjects were just as inconsistent. Thus, they reached the unsatisfactory conclusion that the net vasodilatation in the forearm mainly reflected the behaviour of resistance vessels of muscle and that there ‘were no signs of vasodilatation in the skin’. In a second study, Brod et al. [4] used a ‘heat-conductivity meter’ placed on the forearm and estimated skin blood flow in ml min-’ 100 ml-’ of skin. Again, mental arithmetic consistently evoked an increase in total forearm blood flow in both normotensive and hypertensive subjects, whereas estimated skin blood flow increased
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in 13 subjects, did not change in three and fell in six. In five subjects, all of whom were hypertensive, arterial pressure was measured so that vascular resistance could be calculated. Total forearm vascular resistance decreased in all five. However, calculated cutaneous vascular resistance increased in three subjects, indicating vasoconstriction, but decreased in the other two, suggesting vasodilatation. Since both skin temperature and changes in thermal conductivity provide only indirect estimates of skin blood flow, it is not clear whether the variability of the results obtained reflects the technique used, or the variability of the responses of cutaneous resistance vessels. The study of Blair et al. [S], using hand plethysmography as a means of estimating cutaneous blood flow, did not resolve the issue. They found that acute emotional stress induced by leading the subject to believe that he/ she had suffered a major loss of blood, had little effect on hand blood flow. From this they drew the tentative conclusion that the cutaneous circulation plays little part in the alerting response. However, plethysmography, when applied to the hand, inevitably includes the muscles of the hand as well as skin and other tissues and therefore cannot give a pure estimate of cutaneous blood flow. In view of these uncertainties, we have used a laser Doppler flowmeter to investigate responses evoked in the cutaneous circulation by the cold pressor test and by mental arithmetic. The principles of the laser Doppler technique have been fully described by others [6,7]. Some of our results have already been reported in brief [8].
METHODS Subjects The experiments were performed on healthy volunteers who comprised members of the academic and technical staff and postgraduate and undergraduate students of the Department of Physiology. None had a history of any cardiovascular disorder. Approval for the experiments was obtained from the Local Ethical Committee. For each experiment the subject sat in a comfortable chair with both forearms and hands resting on a table such that they were approximately at heart level. The cuff of a semi-automatic sphygmomanometer (Bosomat 11) was placed on the right upper arm and was used to measure arterial blood pressure at intervals (see below). Erythrocyte flux was recorded continuously from the thenar eminence of the left hand using a Doppler flowmeter (Periflux PF3) via a PF 308 probe which was contained in a thermostatically controlled holder set at 34°C. The output of the laser Doppler flowmeter was displayed on a pen recorder (Grass model 7). Sample measurements of erythrocyte flux which were used for analysis were taken just before measurement of arterial blood pressure, since Roddie [9] demonstrated that inflation of a sphygmomanometer cuff on one arm could include a substantial, though short-lasting, decrease in the
blood flow of the contralateral hand. Experiments were begun when the subject had been sitting quietly for at least 30 min. By this time, in each subject, the recording of erythrocyte flux had achieved stability and measurements of systolic and diastolic pressure were consistent. Distractions in the room, both visual and auditory, were kept to a minimum. Throughout, the room was maintained at a temperature of 22-23°C. Protocol 1: immersion of contralateral hand in water at 20°Cand at 0-4°C These experiments were performed on 11 male and female subjects aged 26 f 2 years (mean fSEM). After a 2 min control period with the right hand in air, the right hand was placed successively in water at 20°C for 2 min, in water containing crushed ice at a temperature of 0-4°C for 2 min and then back to water at 20°C. Systolic and diastolic pressures were recorded from the right arm during the last 0.5 min of each 2 min period. A sample measurement of erythrocyte flux was made immediately before each occasion on which the sphygmomanometer cuff was inflated (see above). Finally, the right hand was moved from the water at 20°C to the bench so that it was in air again and then systolic and diastolic pressures were recorded once more from the right arm. Protocol 2: mental arithmetic These experiments were performed on eight male and female subjects aged 30 f 3 years. After a 2 min control period (see Fig. 2), the subject was repeatedly urged, for a period of 2 min, to subtract a two-digit prime number, e.g. 17, from a large three-digit number, e.g. 973, then from the remainder and so on. The subtractions were carried out to the beat of a metronome set at 60 beats/&. If the subject failed to provide an answer in the required time, the correct answer was supplied and he/she was urged to continue. For subjects who were able to complete the subtractions within the required time, the frequency of the metronome was gradually increased. This test period was followed by a 2 min rest period, then mental arithmetic was carried out as before except that a different prime number and starting number were used. Arterial blood pressure was recorded at the end of each 2 min period, sample measurements of erythrocyte flux being taken immediately before (see above). All results reported are taken from the first experiment of either type carried out by the subject. Thus the results reflect the response to a 'novel' stimulus. Data are presented as means SEM. Arterial pressure measurements are presented in mmHg, mean arterial pressure being calculated as diastolic pressure plus onethird (systolic minus diastolic pressure). Values of erythrocyte flux are given in perfusion units (pu) where 1 pu represents a signal of 1 mV as recorded by the laser Doppler meter. In most subjects the recording of erythrocyte flux showed rhythmic oscillations at between two and six per min, the value taken for analysis was the mean of the peaks and troughs of the oscillation around the time of
*
Skin blood flow during stress measurement. To gain an indication of whether any changes in cutaneous erythrocyte flux were due to changes in arterial pressure and therefore perfusion pressure to the skin, or to constriction or dilatation of the cutaneous blood vessels, cutaneous vascular resistance was calculated as mean arterial pressure divided by erythrocyte flux. Values for calculated cutaneous vascular resistance are expressed in mmHg/pu. Statistical analyses were carried out by using Student's paired t-test except when otherwise stated. P < 0.05 was taken as significant.
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RESULTS Protocol 1 All subjects reported that the right hand felt cool when it was placed in water at 20"C, but none reported any discomfort. By contrast, all subjects expressed discomfort when the right hand was placed in the water and crushed ice at 0-4°C. In fact, by the end of the second minute of this stimulus, all subjects reported pain from the right hand. On these criteria we have designated the first part of this test a 'cold test' and the second as a 'cold pressor test'; this distinction is consistent with the arterial pressure measurements. Cold test. As can be seen from the individual results (Fig. l ) , by the end of the second minute of hand immersion at 20°C, mean arterial pressure had decreased in all but two subjects, this change being significant (Fig. 2). This fall was largely due to a decrease in diastolic pressure which fell significantly from 71.6f 13.2 to 62.5 8.9 mmHg, while systolic pressure showed no significant change (112.5 f 15.4 vs 1 1 0 f 15.2 mmHg). Control values for erythrocyte flux in the left hand varied considerably between individuals (Fig. 1). However, erythrocyte flux decreased in all but three subjects when the right hand was placed in water at 20"C, such that by the end of the second minute of the cold test the fall was significant. Concomitant with the fall in the mean level of erythrocyte flux in each individual there was a tendency for the amplitude of the rhythmic oscillations to decrease. Of the three individuals who did not show a fall in erythrocyte flux, two showed no change and one a small increase. As a consequence of these changes in arterial pressure and erythrocyte flux, calculated cutaneous vascular resistance for the left hand tended to increase although this did not reach significance(Figs. 1 and 2). Cold pressor test. The changes seen during the cold pressor test were far more striking. By the end of the second minute after the right hand had been transferred to ice-cold water, mean arterial pressure had risen in all subjects to a level that was significantly higher than both the original control level and that attained during the cold test. This reflected a significant increase in systolic pressure to 126.6 f 20.0 mmHg and in diastolic pressure to 77.0f 18.1 mmHg. Simultaneously, in all but one subject, cutaneous erythrocyte flux in the left hand decreased to below the level reached during the cold test, the mean level being significantly lower both than the control level and the level attained during the cold test
*
U
Air
20°C
Fig. 1. Responses evoked in 11 individuals on transferring the right hand from air (control) to water at 20"C, to water plus ice and to water at 20°C. ( a )Mean arterial blood pressure (MAP). ( b ) Cutaneous erythrocyte flux in the left hand (LCEF). (c) Cutaneous vascular resistance in the left hand (LCVR), calculated as mean arterial blood pressure divided by erythrocyte flux. Measurements were taken at the end of the second minute of each stimulus, these being indicated by the vertical broken lines.
(Fig. 2). Simultaneously, the amplitude of the oscillations in erythrocyte flux decreased to the extent that by the end of the second minute of the cold pressor test, they had generally disappeared. The net result of these changes was that by the end of the cold pressor test, calculated cutaneous vascular resistance had increased in all subjects and to mean levels that were more than twofold greater than in the control period (Fig. 2). After transfer of the right hand from the ice-cold water to water at 20°C again, mean arterial pressure, cutaneous erythrocyte flux in the left hand and calculated vascular resistance all returned towards or even beyond control
46
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-**
**
I
100
90
levels (Figs. 1 and 2). Thereafter, when the right hand was transferred to air again, the mean arterial pressure returned to 82.9 k 4.1 mmHg. This was not significantly different from the value recorded at the beginning of the experiment when the right hand was in air (86.9f3.8 mmHg), but was significantly higher than the values recorded during the two periods of cooling at 20°C ( P < 0.05 in each case). Protocol 2: mental arithmetic
80
70
(4
-**
**
*
18° 1
I
All subjects found these tests stressful. They showed facial and behavioural signs of anxiety hen attempting the subtraction, embarrassment when they made mistakes and/or admitted after the test that they had felt under stress. These signs and feelings did not lessen during the second period of testing. As can be seen from Figs. 3 and 4, there were no obvious differences between the cardiovascular changes recorded in the first and second periods of mental arithmetic. Mean arterial pressure had generally increased by the end of the second minute of mental arithmetic. The difference between the mean arterial pressure recorded during the control period and during the subsequent period of mental arithmetic reached statistical significance for the first test. There were no significant differences between the systolic pressures, nor between the diastolic pressures, recorded during the control period and the subsequent period of mental arithmetic. Cutaneous erythrocyte flux in the left hand fell substantially in all subjects by the end of the second minute of mental arithmetic, but returned to control levels between the tests. The differences between the values recorded during the control periods and during mental arithmetic were significant. As during the cold pressor test, the oscillations in erythrocyte flux decreased in amplitude and finally disappeared during mental arithmetic. As a consequence of these changes, calculated cutaneous vascular resistance in the left hand was, without exception, higher during each period of mental arithmetic than during the control periods, the increases being statistically significant. DISCUSSION
Fig. 2. Histograms showing means of the data presented ~ ,~ . in Fig. 1. Each column represents the m e a n k ~ 0 Control values; El, right hand in water at 20°C; 83, right hand in water at 0-4°C.( a )Mean arterial blood pressure (MAP). ( b ) Cutaneous erythrocyte flux in the left hand (LCEF).( c ) Cutaneous vascular resistance in the left hand (LCVR), calculated as mean arterial pressure divided by erythrocyte flux. Statistical significance (paired r-test): *P
2t-a---, 0
Fig. 4. Histograms showing means of the data presented in Fig. 3. Each column represents mean It SEM. 0,Control values; m, mental arithmetic. ( a ) Mean arterial pressure (MAP). ( 6 )Cutaneous erythrocyte flux in the left hand (LCEF).(c)Cutaneous vascular resistance in the left hand (LCVR), calculated as mean arterial pressure divided by erythrocyte flux. Statistical significance (paired f-test): *P
43
Cutaneous vascular responses evoked in the hand by the cold pressor test and by mental arithmetic I. MARFUOTT, JANICE M. MARSHALL
AND
E. J. JOHNS
Department of Physiology,The Medical School, University of Birmingham,Birmingham, U.K.
(Received 22 December 1989/2 March 1990; accepted 13 March 1990)
SUMMARY
1. Laser Doppler flowmetry has been used to study changes in cutaneous erythrocyte flux produced in the hand (i) on successive immersion of the contralateral hand in water at 20°C (cold test) and then in water at 0-4°C (cold pressor test), and (ii)by mental arithmetic. 2. In 11 subjects, placing the right hand in water at 20°C for 2 min induced a significant decrease in cutaneous erythrocyte flux in the contralateral hand and a significant fall in mean arterial pressure. Cutaneous vascular resistance, calculated as arterial pressure/ cutaneous erythrocyte flux, showed no significant change. Thus, the decrease in erythrocyte flux was apparently due to a fall in perfusion pressure. 3. Subsequent immersion of the right hand in water at 0-4°C for 2 min caused a significant decrease in erythrocyte flux in the contralateral hand and a significant rise in mean arterial pressure. It is concluded that the cold pressor response evoked from one hand elicited a substantial reflex vasoconstriction in the skin of the other hand; accordingly, calculated cutaneous vascular resistance increased significantly. 4. Eight subjects performed mental arithmetic for two periods of 2 min separated by a rest period of 2 min. By the end of the second minute of each period of mental arithmetic there was a significant decrease in erythrocyte flux. Mean arterial pressure increased significantly in the first period only, but calculated cutaneous vascular resistance increased in both periods, consistent with cutaneous vasoconstriction. 5. The cold pressor test and mental arithmetic are aversive stimuli that evoke the characteristic pattern of the alerting or defence response which includes splanchnic vasoconstriction and muscle vasodilatation. Previous studies on the cutaneous vascular component of this response have yielded equivocal results. The present study provides firm evidence that it includes cutaneous vasoconstriction, at least in the hand. Correspondence: Dr J. M. Marshall, Department of Physiology, The Medical School, University of Birmingham, Birmingham B15 2TJ, U.K.
Key words: defence response, emotional stress, laser Doppler flowmetry, skin blood flow, thermoregulation. Abbreviation: pu, perfusion units.
INTRODUCTION It is well established that in man, as in other mammals, novel, noxious or aversive stimuli evoke a characteristic pattern of cardiovascular response which has been termed the alerting or defence response [ 11. In man, this response can be evoked by a variety of stimuli including the ‘cold pressor test’ and mental arithmetic when carried out under some duress [2, 3). The response includes tachycardia and a redistribution of cardiac output away from the splanchnic regions towards skeletal muscle, due to vasoconstriction in splanchnic circulation and vasodilatation in muscle. However, exactly what happens in the cutaneous circulation of man during the alerting response has remained an open question. Brod et al. [2] used the temperature of the skin of the forearm as a means of assessing cutaneous blood flow and simultaneously used plethysmography to record total blood flow to the contralateral arm, i.e. skin and muscle. They reported that in eight normotensive subjects, mental arithmetic produced no change in forearm skin temperature in three and a decrease in the other five, even though total forearm blood flow increased consistently and forearm vascular resistance, calculated by division using the measurement of arterial blood pressure, decreased in all eight subjects. The changes in skin temperature recorded in hypertensive subjects were just as inconsistent. Thus, they reached the unsatisfactory conclusion that the net vasodilatation in the forearm mainly reflected the behaviour of resistance vessels of muscle and that there ‘were no signs of vasodilatation in the skin’. In a second study, Brod et al. [4] used a ‘heat-conductivity meter’ placed on the forearm and estimated skin blood flow in ml min-’ 100 ml-’ of skin. Again, mental arithmetic consistently evoked an increase in total forearm blood flow in both normotensive and hypertensive subjects, whereas estimated skin blood flow increased
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in 13 subjects, did not change in three and fell in six. In five subjects, all of whom were hypertensive, arterial pressure was measured so that vascular resistance could be calculated. Total forearm vascular resistance decreased in all five. However, calculated cutaneous vascular resistance increased in three subjects, indicating vasoconstriction, but decreased in the other two, suggesting vasodilatation. Since both skin temperature and changes in thermal conductivity provide only indirect estimates of skin blood flow, it is not clear whether the variability of the results obtained reflects the technique used, or the variability of the responses of cutaneous resistance vessels. The study of Blair et al. [S], using hand plethysmography as a means of estimating cutaneous blood flow, did not resolve the issue. They found that acute emotional stress induced by leading the subject to believe that he/ she had suffered a major loss of blood, had little effect on hand blood flow. From this they drew the tentative conclusion that the cutaneous circulation plays little part in the alerting response. However, plethysmography, when applied to the hand, inevitably includes the muscles of the hand as well as skin and other tissues and therefore cannot give a pure estimate of cutaneous blood flow. In view of these uncertainties, we have used a laser Doppler flowmeter to investigate responses evoked in the cutaneous circulation by the cold pressor test and by mental arithmetic. The principles of the laser Doppler technique have been fully described by others [6,7]. Some of our results have already been reported in brief [8].
METHODS Subjects The experiments were performed on healthy volunteers who comprised members of the academic and technical staff and postgraduate and undergraduate students of the Department of Physiology. None had a history of any cardiovascular disorder. Approval for the experiments was obtained from the Local Ethical Committee. For each experiment the subject sat in a comfortable chair with both forearms and hands resting on a table such that they were approximately at heart level. The cuff of a semi-automatic sphygmomanometer (Bosomat 11) was placed on the right upper arm and was used to measure arterial blood pressure at intervals (see below). Erythrocyte flux was recorded continuously from the thenar eminence of the left hand using a Doppler flowmeter (Periflux PF3) via a PF 308 probe which was contained in a thermostatically controlled holder set at 34°C. The output of the laser Doppler flowmeter was displayed on a pen recorder (Grass model 7). Sample measurements of erythrocyte flux which were used for analysis were taken just before measurement of arterial blood pressure, since Roddie [9] demonstrated that inflation of a sphygmomanometer cuff on one arm could include a substantial, though short-lasting, decrease in the
blood flow of the contralateral hand. Experiments were begun when the subject had been sitting quietly for at least 30 min. By this time, in each subject, the recording of erythrocyte flux had achieved stability and measurements of systolic and diastolic pressure were consistent. Distractions in the room, both visual and auditory, were kept to a minimum. Throughout, the room was maintained at a temperature of 22-23°C. Protocol 1: immersion of contralateral hand in water at 20°Cand at 0-4°C These experiments were performed on 11 male and female subjects aged 26 f 2 years (mean fSEM). After a 2 min control period with the right hand in air, the right hand was placed successively in water at 20°C for 2 min, in water containing crushed ice at a temperature of 0-4°C for 2 min and then back to water at 20°C. Systolic and diastolic pressures were recorded from the right arm during the last 0.5 min of each 2 min period. A sample measurement of erythrocyte flux was made immediately before each occasion on which the sphygmomanometer cuff was inflated (see above). Finally, the right hand was moved from the water at 20°C to the bench so that it was in air again and then systolic and diastolic pressures were recorded once more from the right arm. Protocol 2: mental arithmetic These experiments were performed on eight male and female subjects aged 30 f 3 years. After a 2 min control period (see Fig. 2), the subject was repeatedly urged, for a period of 2 min, to subtract a two-digit prime number, e.g. 17, from a large three-digit number, e.g. 973, then from the remainder and so on. The subtractions were carried out to the beat of a metronome set at 60 beats/&. If the subject failed to provide an answer in the required time, the correct answer was supplied and he/she was urged to continue. For subjects who were able to complete the subtractions within the required time, the frequency of the metronome was gradually increased. This test period was followed by a 2 min rest period, then mental arithmetic was carried out as before except that a different prime number and starting number were used. Arterial blood pressure was recorded at the end of each 2 min period, sample measurements of erythrocyte flux being taken immediately before (see above). All results reported are taken from the first experiment of either type carried out by the subject. Thus the results reflect the response to a 'novel' stimulus. Data are presented as means SEM. Arterial pressure measurements are presented in mmHg, mean arterial pressure being calculated as diastolic pressure plus onethird (systolic minus diastolic pressure). Values of erythrocyte flux are given in perfusion units (pu) where 1 pu represents a signal of 1 mV as recorded by the laser Doppler meter. In most subjects the recording of erythrocyte flux showed rhythmic oscillations at between two and six per min, the value taken for analysis was the mean of the peaks and troughs of the oscillation around the time of
*
Skin blood flow during stress measurement. To gain an indication of whether any changes in cutaneous erythrocyte flux were due to changes in arterial pressure and therefore perfusion pressure to the skin, or to constriction or dilatation of the cutaneous blood vessels, cutaneous vascular resistance was calculated as mean arterial pressure divided by erythrocyte flux. Values for calculated cutaneous vascular resistance are expressed in mmHg/pu. Statistical analyses were carried out by using Student's paired t-test except when otherwise stated. P < 0.05 was taken as significant.
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RESULTS Protocol 1 All subjects reported that the right hand felt cool when it was placed in water at 20"C, but none reported any discomfort. By contrast, all subjects expressed discomfort when the right hand was placed in the water and crushed ice at 0-4°C. In fact, by the end of the second minute of this stimulus, all subjects reported pain from the right hand. On these criteria we have designated the first part of this test a 'cold test' and the second as a 'cold pressor test'; this distinction is consistent with the arterial pressure measurements. Cold test. As can be seen from the individual results (Fig. l ) , by the end of the second minute of hand immersion at 20°C, mean arterial pressure had decreased in all but two subjects, this change being significant (Fig. 2). This fall was largely due to a decrease in diastolic pressure which fell significantly from 71.6f 13.2 to 62.5 8.9 mmHg, while systolic pressure showed no significant change (112.5 f 15.4 vs 1 1 0 f 15.2 mmHg). Control values for erythrocyte flux in the left hand varied considerably between individuals (Fig. 1). However, erythrocyte flux decreased in all but three subjects when the right hand was placed in water at 20"C, such that by the end of the second minute of the cold test the fall was significant. Concomitant with the fall in the mean level of erythrocyte flux in each individual there was a tendency for the amplitude of the rhythmic oscillations to decrease. Of the three individuals who did not show a fall in erythrocyte flux, two showed no change and one a small increase. As a consequence of these changes in arterial pressure and erythrocyte flux, calculated cutaneous vascular resistance for the left hand tended to increase although this did not reach significance(Figs. 1 and 2). Cold pressor test. The changes seen during the cold pressor test were far more striking. By the end of the second minute after the right hand had been transferred to ice-cold water, mean arterial pressure had risen in all subjects to a level that was significantly higher than both the original control level and that attained during the cold test. This reflected a significant increase in systolic pressure to 126.6 f 20.0 mmHg and in diastolic pressure to 77.0f 18.1 mmHg. Simultaneously, in all but one subject, cutaneous erythrocyte flux in the left hand decreased to below the level reached during the cold test, the mean level being significantly lower both than the control level and the level attained during the cold test
*
U
Air
20°C
Fig. 1. Responses evoked in 11 individuals on transferring the right hand from air (control) to water at 20"C, to water plus ice and to water at 20°C. ( a )Mean arterial blood pressure (MAP). ( b ) Cutaneous erythrocyte flux in the left hand (LCEF). (c) Cutaneous vascular resistance in the left hand (LCVR), calculated as mean arterial blood pressure divided by erythrocyte flux. Measurements were taken at the end of the second minute of each stimulus, these being indicated by the vertical broken lines.
(Fig. 2). Simultaneously, the amplitude of the oscillations in erythrocyte flux decreased to the extent that by the end of the second minute of the cold pressor test, they had generally disappeared. The net result of these changes was that by the end of the cold pressor test, calculated cutaneous vascular resistance had increased in all subjects and to mean levels that were more than twofold greater than in the control period (Fig. 2). After transfer of the right hand from the ice-cold water to water at 20°C again, mean arterial pressure, cutaneous erythrocyte flux in the left hand and calculated vascular resistance all returned towards or even beyond control
46
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-**
**
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100
90
levels (Figs. 1 and 2). Thereafter, when the right hand was transferred to air again, the mean arterial pressure returned to 82.9 k 4.1 mmHg. This was not significantly different from the value recorded at the beginning of the experiment when the right hand was in air (86.9f3.8 mmHg), but was significantly higher than the values recorded during the two periods of cooling at 20°C ( P < 0.05 in each case). Protocol 2: mental arithmetic
80
70
(4
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**
*
18° 1
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All subjects found these tests stressful. They showed facial and behavioural signs of anxiety hen attempting the subtraction, embarrassment when they made mistakes and/or admitted after the test that they had felt under stress. These signs and feelings did not lessen during the second period of testing. As can be seen from Figs. 3 and 4, there were no obvious differences between the cardiovascular changes recorded in the first and second periods of mental arithmetic. Mean arterial pressure had generally increased by the end of the second minute of mental arithmetic. The difference between the mean arterial pressure recorded during the control period and during the subsequent period of mental arithmetic reached statistical significance for the first test. There were no significant differences between the systolic pressures, nor between the diastolic pressures, recorded during the control period and the subsequent period of mental arithmetic. Cutaneous erythrocyte flux in the left hand fell substantially in all subjects by the end of the second minute of mental arithmetic, but returned to control levels between the tests. The differences between the values recorded during the control periods and during mental arithmetic were significant. As during the cold pressor test, the oscillations in erythrocyte flux decreased in amplitude and finally disappeared during mental arithmetic. As a consequence of these changes, calculated cutaneous vascular resistance in the left hand was, without exception, higher during each period of mental arithmetic than during the control periods, the increases being statistically significant. DISCUSSION
Fig. 2. Histograms showing means of the data presented ~ ,~ . in Fig. 1. Each column represents the m e a n k ~ 0 Control values; El, right hand in water at 20°C; 83, right hand in water at 0-4°C.( a )Mean arterial blood pressure (MAP). ( b ) Cutaneous erythrocyte flux in the left hand (LCEF).( c ) Cutaneous vascular resistance in the left hand (LCVR), calculated as mean arterial pressure divided by erythrocyte flux. Statistical significance (paired r-test): *P
2t-a---, 0
Fig. 4. Histograms showing means of the data presented in Fig. 3. Each column represents mean It SEM. 0,Control values; m, mental arithmetic. ( a ) Mean arterial pressure (MAP). ( 6 )Cutaneous erythrocyte flux in the left hand (LCEF).(c)Cutaneous vascular resistance in the left hand (LCVR), calculated as mean arterial pressure divided by erythrocyte flux. Statistical significance (paired f-test): *P
