Irving H. Wagman

Nerve Conduction Velocity During Hypothermia in Man

Alterations in peripheral nerve impulse conduction during cooling were investigated in 7 surgical patients. A significant association between maximum conduction velocity and mean nerve temperature was found for peroneal nerve. Conduction velocity fell from 49.6 m./second at 35.5° C to one-half (25.9 m./second) at 23.5° C. and to one-fourth (12.1 m./second) at 21.5° C Conduction velocity decreased linearly at a rate of 1.84 m./second/degree centigrade between 36° and 23° C. (P < 0.001). Below 23° C. nerve threshold rose rapidly and conduction velocity fell sharply. Results obtained in this investigation are in good agreement with findings obtained from other species over a comparable temperature range.

Effect of carbon dioxide on the cortical seizure threshold to lidocaine

Abstract The purpose of this experiment was to determine the effect of CO 2 on the threshold of cortical seizures produced by a local anesthetic (lidocaine). Apneic cats were mechanically ventilated at constant minute volume and oxygen tension, with only inspired CO 2 concentration being altered. Arterial CO 2 tension, measured just prior to lidocaine injection, ranged from 20 to 100 mm Hg. Spontaneous electrical activity from cortical and subcortical areas, which always included amygdala, was continuously recorded. Increasing the arterial CO 2 tension reduces the dose of lidocaine which will just produce an electrical seizure. Thus, the cortical threshold to lidocaine-induced electrical seizures is lowered when the arterial CO 2 tension is increased and, conversely, is heightened if the tension is reduced. The seizure is not related to the transient hypotension produced by rapidly injected lidocaine. Two mechanisms, separately or together, are postulated to explain this: CO 2 increases cerebral blood flow, thereby delivering more lidocaine per unit time to the brain; and CO 2 itself has an excitatory effect on subcortical structures (presumably amygdala and related limbic elements). A third possible mechanism may be that CO 2 increases the relative intraneuronal concentration of pharmacologically active lidocaine cation.

Measurement of a Spinal Reflex Response (H-Reflex) During General Anesthesia in Man: Association Between Reflex Depression and Muscular Relaxation

An electrically evoked monosynaptic reflex (the H-reflex) was studied during general anesthesia, in 25 surgical patients. Different levels of muscular relaxation were obtained by varying inspired anesthetic concentrations of halothane or methoxyflurane. At each level, the ratio of maximum reflex response during anesthesia to maximum response when awake (the H-ratio), was calculated. Poor relaxation, during light anesthesia, was accompanied by a large reflex response and a high H-ratio. As relaxation improved, reflex amplitude fell, and H-ratio decreased. With profound relaxation of jaw and abdominal muscles, the H-ratio approached zero. The relation between H-ratio and muscular relaxation was statistically significant. Thus, muscular relaxation during general anesthesia is associated with decreased reflex excitability of the spinal motoneuron pool. This presumably is the result of direct or indirect anesthetic action at the spinal synapse. With increasing anesthetic concentrations, synaptic transmission is depressed, the reflex decreases in amplitude and muscular relaxation becomes more profound.

Neural limitations of visual excitability V. Cerebral after-activity evoked by photic stimulation

Abstract In locally anesthetized and in lightly anesthetized cats, a 5-msec flash of light to the eye evokes from the visual cortex a “primary” potential, followed by a train of after-discharges which may last 300 msec or longer. The duration, frequency and amplitude of after-discharges are variable, but it is clear that the total duration becomes longer with increasing intensity or duration of the photic stimulus. These after-discharges can be disrupted by the response to a subsequent longer flash when the onset of the second flash occurs before the total response to the first flash is over (i.e. within 300 msec). If one plots, on the ordinate, the reduction in the duration of the after-discharges elicited by a preceding test flash and, on the abscissa, the conditioning flash-test flash interval, the curve is similar to those obtained in previous studies of the psychophysical threshold in the human subject. These findings suggest that the perception of a single flash of light is related to the whole complex of waves elicited by a light flash and not just to the “primary” response.

Use of halothane anesthesia for surgical preparation of the experimental animal.

Halothane (2-bromo-2-chloro-l,l,l-trifluoroethane) is a potent, nonirritating inhalation agent;fi induction is rapid and (on the basis of human experience) without discomfort. The striking absence of salivation makes anesthesia with halothane safer than with ether as a procedure in the laboratory animal, and a drying agent such as atropine may be omitted.? Since its vapors are nonexplosive, it can be safely used in the presence of electronic equipment. A mechanical respirator may also be employed without concern about explosion hazards.

Does oxygen protect against local anesthetic toxicity

The use of barbiturates to prevent or treat toxic reactions to local anesthetic agents was proposed almost 50 years ago by Tatum and associates.2 Though still cited in standard pharmacology texts,3 the use of barbiturates to treat drug-induced seizures is discouraged by some workers.4,5 Moore and Bridenbaugh5 believe that ventilation with oxygen (0,) is of primary importance in the treatment of systemic toxic reactions due to local anesthetics. These authors have stated that administration of O2 will often prevent such a reaction from progressing to the stage of seizures.