Measurement Chronaxie

1 measurement

1.1 values
1.2 stimulation
1.3 motor vs sensory

measurement

an electrode inserted muscle of interest, stimulated using surface current. chronaxie values increase resulting hyperventilation can ascribed change in skin impedance, physiological factors responsible change being under influence of autonomic nervous system. example of preponderating influence condition of skin , underlying tissues may exert compels caution in judging results of chronaxie measurements percutaneous stimulation. fresh , normal sartorius placed straight in ringer solution , stimulated through solution without direct contact electrodes subject give 2 distinct strength-duration curves, 1 of them being spread on several hundredths of second.

values

the chronaxie values mammalian ventricles @ body temperature range 0.5 ms (human) 2.0 4.1 ms (dog); 8.2/1 ratio. has been reported large-diameter myelinated axons have chronaxie times ranging 50 100 µs , 30 200 µs, , neuronal cell bodies , dendrites have chronaxie times ranging 1 10 ms or 30 ms. chronaxie times of grey matter reported being 380 +/- 191 ms , 200±700 ms. interpretations of chronaxie times further confounded additional factors. chronaxie times reported soma , dendrites have been established using intracellular pulses cannot readily extrapolated extra- cellular stimuli. data reported in literature use either motor response physiological threshold in humans or action potential generation in animals. these largely based on stimulation through macro-electrode, in case of humans 1.5 Â 1.2-mm dbs electrode. data derived micro-electrode stimulation , physiological mapping of sensory thalamus scarce. 2 stimulation methods may result in different results. few studies have attempted correlate chronaxie times sensory perception, although understanding neural elements involved in subjective percept, such tingling, has important physiological implications. measurements taken different types of electrodes , stimulators having unknown output impedances. chronaxie values human arm sensory nerves range 0.35 1.17 ms, ratio of 3.3. values obtained insufficient information establish cause of variability. chronaxie values human denervated skeletal muscle ranges 9.5 30 ms @ body temperature, representing ratio of 3.16. reduction in chronaxie occurs during reinnervation. published values chronaxie have wide range. if chronaxie best descriptor of tissue excitability in homogeneous tissue specimen, @ known temperature, should determined constant-current stimulator providing rectangular cathodal stimulus waveform. chronaxie derived strength-duration curve current , shows if stimulus duration shorter chronaxie, more current required stimulate, type or location of electrodes stimulator of known or unknown output impedance. in addition, chronaxie value, determined, identifies pulse duration minimum energy. in addition, charge delivered @ chronaxie, determined, 2, twice minimum charge. therefore, if minimum charge delivery sought prolong life of battery in implanted stimulator, pulse duration of less measured chronaxie should selected; duration of one-tenth chronaxie provides charge 10% above minimum charge.

stimulation

electric , magnetic stimulation produced different sensations. electric stimulation, sensation typically described localized directly below electrodes on surface of skin. magnetic stimulation, sensation typically described distributed throughout palm , digits of hand. in particular, subjects reported sensations in either medial or lateral digits. these observations suggest electrical stimulation may preferentially activate cutaneous afferent nerve fibers whereas magnetic stimulation may preferentially activate deeper nerves, such ulnar or median nerve.

motor vs sensory

other studies have compared activation of sensory , motor fibers using electric , magnetic stimulation demonstrated through stimulation of nerve , muscle tissue magnetic activation of intramuscular nerve fibers in arm , leg occurs @ lower threshold electric stimulation. also, sensory fibers shown have lower threshold electric stimulation. electric stimulation of wrist determined when short pulses used (less 200 μs), motor fibers more readily excitable, whereas long pulse durations (greater 1000 μs), sensory fibers more prone depolarization. related observation electric stimulation preferentially activates sensory fibers compared motor fibers long pulse durations, , inverse short pulse durations. magnetic stimulation, motor fiber threshold lower

than sensory fibers.