Journal of
J. Neurol. 216, 181--188 (1977)
Neurology ~) by Springer-Verlag 1977
Changes of Sensory Conduction Velocity and Refractory Periods with Decreasing Tissue Temperature in Man* K. Lowitzsch, H. C. Hopf, and J. Galland Neurological Department, University of Mainz, Langenbeckstr. 1, D-6500 Mainz 1, Federal Republic of Germany
Summary. Changes with temperature of maximum sensory nerve conduction velocity as well as absolute and relative refractory periods were tested in 14 human subjects. Corresponding to previously published findings maximum conduction velocity decreased with cooling following a Q10 of + 1.4. The absolute and relative refractory periods were increased by cooling, the Q10 being --3.1 and - 3 . 3 5 respectively. There was a tendency showing a more pronounced temperature effect at low temperatures. The Q l0 and the steepness of the regressionline changed at the level of 26.9°C, but were significant for the relative refractory period only. Key words: Conduction velocity, sensory - Refractory period - Tissue temperature and conduction velocity - Electromyography Zusammenfassung. An 14 gesunden jugendlichen Probanden wurde die sensible Nervenleitgeschwindigkeit sowie die absolute und relative Refrakt~irperiode des N. ulnaris bei Temperaturen zwischen 35 ° C und 20 ° C bestimmt. Die Gewebstemperatur wurde durch eisgektihlte Gelkissen bis auf 20 ° C gesenkt und subkutan dicht am Nerven bestimmt. Fiir die Bereiche 35°C bis 25°C und 30°C bis 20°C wurden die Q~0-Werte fiir die sensible N L G mit 1,36 bzw. 1,44, ftir die absolute Refrakt~irperiode mit - 3 , 1 8 b zw. -3,01 und ftir die relative Refrakt~irperiode mit -3,21 bzw. - 3 , 4 9 bestimmt. Die Unterschiede der Q10-Werte ftir die N L G und die Refrakt~irperioden sowie die Zunahme des Q10 unterhalb einer Temperatur von 27°C werden anhand der bisher ver6ffentlichten Literaturbefunde diskutiert. Unter Beriicksichtigung dieser Befunde ergibt sich bei Extrapolation klinisch-neurophysiologischer Megwerte auf 35°C fiir die N L G eine Korrektur yon 1,3 m/s pro °C und far die relative Refrakt/irperiode yon 0,5 ms/° C. Dedicated to Prof. Fritz Buchthal on the occasion of his seventyth birthday
182
K. Lowitzsch et al.
A m o n g v a r i o u s c o n d i t i o n s influencing impulse c o n d u c t i o n tissue t e m p e r a t u r e is one o f the i m p o r t a n t factors slowing d o w n c o n d u c t i o n velocity ( D a w s o n , 1956; C a r p e n d a l e , 1956; J o h n s o n a n d Olsen, 1960; Paintal, 1965, 1973; M c L e o d , 1966; B u c h t h a l a n d R o s e n f a l c k , 1966, 1971). There is, however, slight d i s a g r e e m e n t as to the exact extent o f this effect at different t e m p e r a t u r e levels (De Jesus et al., 1973; Beyeler a n d Ludin, 1977). The refractory periods are k n o w n to react m o r e sensitively to c o o l i n g (Paintal, 1966). As there are very few o b s e r v a t i o n s in m a n , we again studied the t e m p e r a t u r e effects on c o n d u c t i o n velocity as well as on the a b s o l u t e a n d relative r e f r a c t o r y periods o f h u m a n sensory nerve fibers in situ.
Material and Methods The effect of temperature on maximum nerve conduction and refractory periods was tested in 14 normal subjects aged between 19 and 27 years (mean 23.4). Ulnar nerve sensory fibers were stimulated percutaneously at the fifth finger near the metacarpophalangeal joint using ring electrodes with an interelectrode distance of 35 mm. Stimulating shocks were square wave impulses of 0.1 ms duration and highly supramaximal intensity (95--100 volts, about 50 times threshold intensity) generated by a battery operated stimulation unit (Digitimer type 2533). Nerve action potentials were recorded unipolarly at the wrist. A thin steel needle, insulated except of the tip, was placed close to the nerve as the different electrode. According to Buchthal and Rosenfalck (1966) the needle position was changed until the threshold for activating motor fibers was lowest when using them as stimulating electrodes. The indifferent electrode was an uninsulated needle placed 50 mm apart. The electrode impeadance was 1--2 kohms at 1000--20000 cps and 2--10kohms at 50--500cps, the input impeadance 2 × 3 megohms. The noise level was 0.41~V peak to peak. Twenty to fifty single sweeps were averaged (Hewlett Packard Averager type 5480A). Operated at 2 channels with 512 addresses each, and an analysis time of 10ms, the shortest interval between two points was 20 ~ts. The stimulus artefact and the first positive peak of the compound nerve action potential served as reference points for latency measurements. The durations of the refractory periods were estimated by applying double shocks of variable intervals to the nerve. The stimulus intervals were controlled by a crystal clock and were adjusted in steps of 0. lms. For each interval the conduction time of the test potential was compared to that of the unconditioned potential by switching off the conditioning stimulus and superimposing both sweeps. The shortest interval at which the second (test) potential was conducted at "resting" velocity was taken as the relative refractory period. The longest interval at which the test potential could not be evoked by the second stimulus was taken as the absolute refractory period. The arm was cooled by putting cryogel coldpack bags around it. Measurements were performed only after the tissue temperature remained stable for about 10 minutes. The tissue temperature was measured close to the stimulating cathode by a thermocouple needle using the Disa unit type H + B3 3 545 547. The temperature was taken immediately before and after the testing procedure at each temperature level, the measurements being accepted only if temperatures changes were less than 0.1°C.
Results
Sensory Fiber Maximum Conduction Velocity. The m a x i m u m c o n d u c t i o n velocity decreases with decreasing t e m p e r a t u r e . The m e a n values were 49.26 m / s at 35°C and 2 9 . 6 5 m / s at 2 0 ° C as calculated f r o m 13 and 10 subjects respectively
Sensory Conduction Velocity
183
Table 1. Average values of conduction velocity, absolute and relative refractory periods of ulnar nerve sensory fibers at different temperatures Temperature (°C)
Q10
25
20
t-test
35
30
Conduction velocity (m/s) N
49.26 13
4 2 . 7 2 36.18 29.65 10 11 10
+1.36
+1.44
n.s.
Relative refractory period (ms) N
3.19 14
5.76 11
-3.21
-3.49
P 0.05). The steepness of the regression lines for both groups was not reliably different and no parallel deviation could by demonstrated (F-test).
Relative Refractory Period. The relative refractory period increases with decreasing temperature. At 35°C the average duration was 3.19 ms in 14 subjects and at 20°C, 20.09ms in 10 subjects (Table 1). The relative refractory period and the temperature are negatively correlated (Fig. 1 c). However, there was a significant difference in the steepness of the regression lines at low and high temperature ranges with the point of intersection at 26.9+ 2.5°C (P
J. Neurol. 216, 181--188 (1977)
Neurology ~) by Springer-Verlag 1977
Changes of Sensory Conduction Velocity and Refractory Periods with Decreasing Tissue Temperature in Man* K. Lowitzsch, H. C. Hopf, and J. Galland Neurological Department, University of Mainz, Langenbeckstr. 1, D-6500 Mainz 1, Federal Republic of Germany
Summary. Changes with temperature of maximum sensory nerve conduction velocity as well as absolute and relative refractory periods were tested in 14 human subjects. Corresponding to previously published findings maximum conduction velocity decreased with cooling following a Q10 of + 1.4. The absolute and relative refractory periods were increased by cooling, the Q10 being --3.1 and - 3 . 3 5 respectively. There was a tendency showing a more pronounced temperature effect at low temperatures. The Q l0 and the steepness of the regressionline changed at the level of 26.9°C, but were significant for the relative refractory period only. Key words: Conduction velocity, sensory - Refractory period - Tissue temperature and conduction velocity - Electromyography Zusammenfassung. An 14 gesunden jugendlichen Probanden wurde die sensible Nervenleitgeschwindigkeit sowie die absolute und relative Refrakt~irperiode des N. ulnaris bei Temperaturen zwischen 35 ° C und 20 ° C bestimmt. Die Gewebstemperatur wurde durch eisgektihlte Gelkissen bis auf 20 ° C gesenkt und subkutan dicht am Nerven bestimmt. Fiir die Bereiche 35°C bis 25°C und 30°C bis 20°C wurden die Q~0-Werte fiir die sensible N L G mit 1,36 bzw. 1,44, ftir die absolute Refrakt~irperiode mit - 3 , 1 8 b zw. -3,01 und ftir die relative Refrakt~irperiode mit -3,21 bzw. - 3 , 4 9 bestimmt. Die Unterschiede der Q10-Werte ftir die N L G und die Refrakt~irperioden sowie die Zunahme des Q10 unterhalb einer Temperatur von 27°C werden anhand der bisher ver6ffentlichten Literaturbefunde diskutiert. Unter Beriicksichtigung dieser Befunde ergibt sich bei Extrapolation klinisch-neurophysiologischer Megwerte auf 35°C fiir die N L G eine Korrektur yon 1,3 m/s pro °C und far die relative Refrakt/irperiode yon 0,5 ms/° C. Dedicated to Prof. Fritz Buchthal on the occasion of his seventyth birthday
182
K. Lowitzsch et al.
A m o n g v a r i o u s c o n d i t i o n s influencing impulse c o n d u c t i o n tissue t e m p e r a t u r e is one o f the i m p o r t a n t factors slowing d o w n c o n d u c t i o n velocity ( D a w s o n , 1956; C a r p e n d a l e , 1956; J o h n s o n a n d Olsen, 1960; Paintal, 1965, 1973; M c L e o d , 1966; B u c h t h a l a n d R o s e n f a l c k , 1966, 1971). There is, however, slight d i s a g r e e m e n t as to the exact extent o f this effect at different t e m p e r a t u r e levels (De Jesus et al., 1973; Beyeler a n d Ludin, 1977). The refractory periods are k n o w n to react m o r e sensitively to c o o l i n g (Paintal, 1966). As there are very few o b s e r v a t i o n s in m a n , we again studied the t e m p e r a t u r e effects on c o n d u c t i o n velocity as well as on the a b s o l u t e a n d relative r e f r a c t o r y periods o f h u m a n sensory nerve fibers in situ.
Material and Methods The effect of temperature on maximum nerve conduction and refractory periods was tested in 14 normal subjects aged between 19 and 27 years (mean 23.4). Ulnar nerve sensory fibers were stimulated percutaneously at the fifth finger near the metacarpophalangeal joint using ring electrodes with an interelectrode distance of 35 mm. Stimulating shocks were square wave impulses of 0.1 ms duration and highly supramaximal intensity (95--100 volts, about 50 times threshold intensity) generated by a battery operated stimulation unit (Digitimer type 2533). Nerve action potentials were recorded unipolarly at the wrist. A thin steel needle, insulated except of the tip, was placed close to the nerve as the different electrode. According to Buchthal and Rosenfalck (1966) the needle position was changed until the threshold for activating motor fibers was lowest when using them as stimulating electrodes. The indifferent electrode was an uninsulated needle placed 50 mm apart. The electrode impeadance was 1--2 kohms at 1000--20000 cps and 2--10kohms at 50--500cps, the input impeadance 2 × 3 megohms. The noise level was 0.41~V peak to peak. Twenty to fifty single sweeps were averaged (Hewlett Packard Averager type 5480A). Operated at 2 channels with 512 addresses each, and an analysis time of 10ms, the shortest interval between two points was 20 ~ts. The stimulus artefact and the first positive peak of the compound nerve action potential served as reference points for latency measurements. The durations of the refractory periods were estimated by applying double shocks of variable intervals to the nerve. The stimulus intervals were controlled by a crystal clock and were adjusted in steps of 0. lms. For each interval the conduction time of the test potential was compared to that of the unconditioned potential by switching off the conditioning stimulus and superimposing both sweeps. The shortest interval at which the second (test) potential was conducted at "resting" velocity was taken as the relative refractory period. The longest interval at which the test potential could not be evoked by the second stimulus was taken as the absolute refractory period. The arm was cooled by putting cryogel coldpack bags around it. Measurements were performed only after the tissue temperature remained stable for about 10 minutes. The tissue temperature was measured close to the stimulating cathode by a thermocouple needle using the Disa unit type H + B3 3 545 547. The temperature was taken immediately before and after the testing procedure at each temperature level, the measurements being accepted only if temperatures changes were less than 0.1°C.
Results
Sensory Fiber Maximum Conduction Velocity. The m a x i m u m c o n d u c t i o n velocity decreases with decreasing t e m p e r a t u r e . The m e a n values were 49.26 m / s at 35°C and 2 9 . 6 5 m / s at 2 0 ° C as calculated f r o m 13 and 10 subjects respectively
Sensory Conduction Velocity
183
Table 1. Average values of conduction velocity, absolute and relative refractory periods of ulnar nerve sensory fibers at different temperatures Temperature (°C)
Q10
25
20
t-test
35
30
Conduction velocity (m/s) N
49.26 13
4 2 . 7 2 36.18 29.65 10 11 10
+1.36
+1.44
n.s.
Relative refractory period (ms) N
3.19 14
5.76 11
-3.21
-3.49
P 0.05). The steepness of the regression lines for both groups was not reliably different and no parallel deviation could by demonstrated (F-test).
Relative Refractory Period. The relative refractory period increases with decreasing temperature. At 35°C the average duration was 3.19 ms in 14 subjects and at 20°C, 20.09ms in 10 subjects (Table 1). The relative refractory period and the temperature are negatively correlated (Fig. 1 c). However, there was a significant difference in the steepness of the regression lines at low and high temperature ranges with the point of intersection at 26.9+ 2.5°C (P
