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J L Ochoa

Publications and source records attributed to J L Ochoa.

At least 55 records · Page 3Linked to original sources
PubMed1993

Vasomotor innervation of the skin of the hand: a contribution to the study of human anatomy.

The sympathetic vasomotor innervation of the skin of the human hand was studied in 47 subjects who underwent local anaesthetic block of ulnar, median or radial nerves at elbow or wrist levels. Areas of cutaneous anaesthesia were compared with cutaneous territories of paralytic vasodilatation delineated by infrared telethermography. It was found that: (1) during ulnar nerve block the area of vasodilatation matched the area of anaesthesia in all 15 cases; (2) median nerve block induced paralytic vasodilatation which, in 14 of 15 cases, matched the area of cutaneous anaesthesia in median territory, but also extended to the unanaesthetised lateral part of the dorsum of the hand; (3) no vasodilatation developed during radial nerve block in 17 of 18 cases, whereas areas of sympathetic sudomotor paralysis matched the area of radial sensory loss in all 5 subjects in whom sweating function was studied. It is concluded that: (1) the ulnar nerve supplies vasomotor fibres to its cutaneous sensory territory, no less and no more; (2) the median nerve normally provides supplementary vasomotor innervation to the skin of the radial aspect of the dorsum of the hand; (3) the radial nerve supplies sudomotor innervation for the lateral aspect of the dorsum of the hand, but (4) does not normally contribute vasomotor sympathetic fibres to the skin of the hand.

Adult↗
PubMed1992

Quantitative somatosensory thermotest. A key method for functional evaluation of small calibre afferent channels.

The quantitative somatosensory thermotest (QST) assesses the function of afferent channels concerned with sensory submodalities served by small calibre fibres. Measured ramps of ascending or descending temperature are applied to the skin through a Peltier contact thermode, and detection thresholds are recorded as the subject signals the onset of a particular sensation. The present study describes underlying principles, methodological aspects and normal reference values for the QST. In patients, measurement of thresholds for cold sensation, warm sensation, cold-induced pain and heat-induced pain, applied to 465 individuals, yielded 13 abnormal patterns segregated into three main groups: (i) thermal (cold or warm) hypoaesthesia; (ii) thermal hyperalgesia (abnormally reduced threshold for cold and/or heat induced pain); (iii) thermal hypoaesthesia combined with thermal hyperalgesia. Critical analysis of these results yielded a number of observations of general relevance: (i) thermal specific (warm or cold) hypoaesthesia and thermal (heat or cold) hyperalgesia may occur in the absence of hypoaesthesia for tactile submodalities served by large calibre afferents; (ii) cold hypoaesthesia and warm hypoaesthesia may dissociate from each other; (iii) thermal pain hyperalgesias may occur in the absence of hypoaesthesias for specific cold or warm sensations; (iv) cold hyperalgesia and heat hyperalgesia may dissociate from each other. Thus, a negative routine sensory examination and unimpaired sensory nerve action potentials do not exclude possible somatosensory dysfunction. Furthermore, while most methods of sensory testing only document normality or deficit, the QST permits additional documentation of hyperalgesia, a positive sensory phenomenon that implies unusual pathophysiologies such as sensitization of receptors, central hyperexcitability, disinhibition or, possibly, ectopic nerve impulse discharge. This psychophysical test does not specify the level within afferent channels, between skin and brainmind, where the abnormality resides. It is recommended that the QST for all four thermal specific and thermal pain functions be incorporated in routine neurological assessment.

Adolescent↗
PubMed1992

Single C nociceptor responses and psychophysical parameters of evoked pain: effect of rate of rise of heat stimuli in humans.

1. Effects of rate of rise of temperature stimuli applied to skin on (i) unitary receptor threshold and frequency response often single C nociceptors, and (ii) on magnitude and reaction times of evoked pain were studied in fifteen healthy human volunteers. 2. Temperature ramps of 32 to 45 or 47 degrees C were applied at three consistent rates of rise to receptive fields of C nociceptors in dorsum of foot (n = 9) or hand (n = 1). For rates of rise of 0.3, 2.0 and 6.0 degrees C/s, mean receptor threshold for heat was remarkably uniform: 41.5 +/- 0.57, 41.5 +/- 0.61 and 41.9 +/- 0.71 degrees C respectively. 3. The mean discharge rate of the ten cutaneous C nociceptors increased with rate of rise of temperature stimuli: 1.22 +/- 0.13, 4.57 +/- 0.49 and 13.45 +/- 0.71 impulses/s, respectively, for stimulus temperature rates of 0.3, 2.0 and 6.0 degrees C/s. 4. Magnitude estimates of pain for thirteen subjects also increased with rate of rise of temperature stimuli. Mean normalized magnitude estimates of heat pain were: 11.8 +/- 1.55, 15.1 +/- 0.84 and 28.0 +/- 1.87 for stimulus rates of rise of 0.3, 2.0 and 6.0 degrees C/s, respectively. 5. Results of simultaneous recordings of reaction time for pain and of C nociceptor responses to heat ramps given at 2.0 degrees C/s, in three subjects, indicate that under those circumstances heat pain messages are exclusively mediated by C nociceptors.

Adult↗
PubMed1991

Differential effect of compression-ischaemia block on warm sensation and heat-induced pain.

The effect of compression-ischaemia nerve block on psychophysical thresholds for warm sensation and heat-induced pain was studied on 19 normal human volunteers. Although those two sensory submodalities should be predicted to block simultaneously, based on the fact that both are served by unmyelinated primary afferents, it was actually found that warm sensation was much more vulnerable to compression-ischaemia than heat-induced pain. This is interpreted as resulting from different summation requirements for each of the two sensory modalities; sensation of warmth depends on spatial summation to a larger extent than heat-induced pain. Such differential vulnerability is in line with recent clinical studies reporting deterioration of warm sensation associated with preservation of heat pain in peripheral nerve disorders caused by diabetes, ageing and other neuropathic processes.

Afferent Pathways↗
PubMed1991

Warm and cold specific somatosensory systems. Psychophysical thresholds, reaction times and peripheral conduction velocities.

Perception thresholds for warm and cold sensation were measured by two methods, the method of levels and the method of limits, at various rates of temperature change. The following findings were obtained. (1) The threshold value is critically dependent upon the method through which it is obtained, being higher for the method that includes reaction time in the measurement. (2) When using a method that includes participation of reaction time, threshold increases with increasing rate of temperature change. (3) The artefactual threshold elevation recorded through the method of limits corresponds precisely to the reaction time. (4) Conduction velocities for the primary afferents mediating the sensations of warm and cold, calculated on the basis of reaction time and conduction distance are in keeping with the mediation of warm sensation by unmyelinated primary afferents and of cold sensation by small myelinated afferents. (5) Measurement of threshold by the method of levels and direct measurement of reaction time enables calculation of conduction velocity for the specific sensory submodality tested from a single stimulation site.

Adolescent↗
PubMed1991

Pathophysiology of injured axons.

In this article we have touched briefly upon certain changes in peripheral axonal physiology which may, in part, explain the mechanisms of painful nerve injury. The next article discusses surgical approaches to these disorders and how they may relate to the known pathophysiology of injured axons.

Animals↗
PubMed1991

Surgical management of post-traumatic neuropathic pain.

The optimum management strategies for painful neuromas and neuromas-incontinuity are still unknown. Basic research and clinical development in this area is potentially rewarding and exciting. Neurosurgeons have the necessary basic and clinical neuroscience background to contribute significantly to this field and are trained in the requisite microsurgical techniques. Only by careful and thoughtful approach to individual cases can we hope to make future progress in these extraordinarily difficult pathologic conditions.

Humans↗
PubMed1990

New method to identify nociceptor units innervating glabrous skin of the human hand.

A new technique is described for detecting nociceptor activity in microelectrode recordings from cutaneous fascicles of the human median nerve. The search strategy involves combined intraneural microstimulation and microneurographic recording in intrafascicular sites, where a critically low electrical stimulus amplitude evokes a threshold sensation of pain. From the subject's projection of pain to a small area of skin, the experimenter is guided to receptive fields of recordable nociceptor units. This technique has allowed, for the first time, to identify and study receptive properties of very high threshold nociceptors with A and C fibers in the glabrous skin of the human hand.

Adult↗
PubMed1990

Release of cold-induced burning pain by block of cold-specific afferent input.

While the pure sensation of cold is evoked by activation of a specific set of afferent channels, an additional set is believed to be activated by noxious low-temperature stimuli evoking cold pain. At primary afferent level, the channels concerned with the cold fraction of cold pain are served by myelinated A delta cold-specific fibres, whereas those concerned with the pain fraction are served by unmyelinated C nociceptors. In the present study, interaction between the two types of afferent input underlying cold pain was investigated by selectively blocking conduction in myelinated fibres. When doing so to the point of abolishing cold sensation, ramps of low-temperature stimuli eventually evoked a first sensation of burning pain. In addition to, and contemporaneous with, this change in quality, a significant decrease in pain threshold (reduction in required stimulus energy) was recorded when applying a noxious low-temperature stimulus. Such exaggeration in magnitude of low temperature-induced pain and the unmasking of its burning quality by A fibre block imply release of central sensory transmission due to removal of inhibitory primary afferent input. Myelinated fibres transmitting either tactile, cold sensations or both could exert this inhibition. Previous evidence of suppression of pain by low-temperature stimuli indicates that it is the cold-specific input that normally exerts this central gating on nociceptor input. The present results may also offer an explanation for the occurrence of a syndrome of burning pain on cold exposure in neuropathic patients with impaired ability to perceive cold.

Adult↗
PubMed1990

Innervation territories for touch and pain afferents of single fascicles of the human ulnar nerve. Mapping through intraneural microrecording and microstimulation.

The peripheral distribution of the fibre content of individual ulnar nerve fascicles supplying skin and muscles of the hand in human volunteers was indirectly mapped by tracing the fields of projected sensation evoked by intraneural electrical microstimulation (INMS) and by tracing receptive fields delineated through intraneural recording of afferent impulse activity elicited by natural stimulation of end organs. Moderate intensity suprathreshold INMS, delivered in cutaneous fascicles, induced nonpainful sensations projecting to stereotyped and coherent areas of skin, the fascicular projected fields (FPFs). Fascicular receptive fields (FRFs) were mapped during microneurographic recording by determining the area of skin which, when activated by light tactile stimuli, elicited afferent neural discharges recorded intraneurally. It was found that at a given electrode position in a skin nerve fascicle, moderate intensity INMS induced nonpainful sensations projecting to a cutaneous field (FPF) that coincides with the FRF, while high intensity INMS induced painful sensations projecting within the cutaneous field of nonpainful sensations. Pain induced by INMS in muscle nerve fascicles was projected to the muscles innervated by that fascicle and, in most instances, to areas beyond the muscular receptive field. The study demonstrates that individual ulnar nerve fascicles, at wrist levels, subserve well-defined cutaneous territories in the hand, and that the area of skin covered by the sum of all ulnar fascicular receptive or projected fields matches the maximal possible cutaneous distribution of the ulnar nerve. Insights of practical relevance regarding clinical expression of fascicular nerve injuries are also brought up by this study.

Adult↗
PubMed1987

Intraneural microstimulation in man. Its relation to specificity of tactile sensations.

Recent advances in knowledge, and controversy, concerning cutaneous mechanoreception are reviewed. In particular, the question of perceptive specificity is discussed in the light of new experimental approaches, namely microneurography and microstimulation of identified tactile units from the glabrous skin of the human hand. Additional data are also presented. It is concluded that the human brain has an exquisite capacity to detect, localize, delineate, and classify sensations from the input of individual tactile units in the glabrous skin of the hand. The physiological specificity of low-threshold mechanoreceptors in the hand, which has been well documented in previous studies, can now be linked to distinct attributes of very simple tactile sensations which subjects report when a single afferent is stimulated electrically through an intraneural microelectrode. This conclusion does not conflict with the concept that the brain normally makes use of temporal and spatial patterns of impulses from a large number of receptors of various types to form more complex tactile percepts, such as in the recognition of texture, but the microstimulation data demonstrate that particular patterns of nerve impulses are not a necessary determinant of the subjective quality attribute of a simple tactile sensation. On the contrary, the sensations elicited by a train of impulses in a single afferent unit are remarkably distinct and well characterized in a number of respects. A further conclusion is that the afferent inputs are processed differently in tactile subsystems. This observation warrants caution in generalizing results from one system into a common theory of the origin of sensory modality.

Electric Stimulation↗
PubMed1984

Referred pain from intraneural stimulation of muscle fascicles in the median nerve.

Microelectrode recordings were obtained from 118 cutaneous and 26 muscle fascicles in the intact median nerves of healthy human subjects. The exploring electrodes were also used for painful electrical stimulation of the identified fascicles. Cutaneous pain was accurately projected to fields within the median innervation territory. Deep pain was projected to muscles innervated by the median nerve, but in 7 experiments it was also segmentally referred to muscles in the ipsilateral upper arm, axilla or chest. Reaction time measurements indicated that referred pain was conveyed by afferent group III fibres from muscle, but did not exclude a possible contribution by group IV fibres. Referred pain was influenced by temporal and spatial summation of the afferent inflow. The magnitude of referred pain was positively correlated to the stimulation frequency of deep nociceptive fibres. The results from this study on experimentally induced pain confirm clinical observations of proximal referral of pain in patients with median nerve entrapment, and prompt consideration of possible involvement of nerve fascicles supplying deep structures in the forearm or hand in the differential diagnosis of pain in the chest and upper arm.

Adult↗
PubMed1984

A new method for demonstration of central effects of analgesic agents in man.

A new method of eliciting experimental pain in man is described. Microelectrodes are inserted percutaneously into the peripheral nerves of awake subjects, and are positioned close to nociceptive fibres in order to elicit pain during intraneural electrical stimulation. Under fixed stimulation conditions the estimated magnitude of evoked pain remains relatively stable, unless a high stimulus frequency is used, which may lead to excitation failure of nociceptive fibres. This method can be employed to test for possible central modulation of pain, for instance by analgesic agents, since peripheral receptors are bypassed.

Adult↗
PubMed1984

Mechanical injury of peripheral nerves. Fine structure and dysfunction.

In summary we have examined the morphology of the normal peripheral nerve, presented the types of mechanical nerve injury and associated histopathology, and discussed possible mechanisms responsible for symptoms of pain, paresthesiae, and weakness associated with these lesions. Neurapraxia consists of intussusception of axon and myelin through the nodes of Ranvier resulting in prolonged nerve conduction block. Axonotmesis and neurotmesis describe more severe disruptions of nerve fiber architecture, are difficult to distinguish electrophysiologically, and have poorer prognoses for functional regenerative repair. Chronic entrapment lesions consist of telescoping myelin internodes and tapering of the sheaths with bulbous polarization of internodes away from the site of injury. Both acute and chronic lesions chiefly involve large myelinated fibers and both may create neuralgia, although the mechanism by which this occurs is poorly understood. Presently, increasing evidence suggests ectopic impulse generators and ephaptic transmission may be responsible for sensorimotor phenomena in these lesions.

Humans↗
PubMed1983

Peripheral projections of nerve fibres in the human median nerve.

Elementary sensations of definable quality were evoked by intraneural electrical stimulation of sensory units through tungsten microelectrodes inserted in the median nerve of awake human subjects. The most commonly reported sensations were tapping, pressure, dull pain and sharp pain, which correlated with recording from RA units, SA I units, C nociceptors and A delta nociceptors, respectively. All sensations were projected more often to the fingertips than to the palm. The multifocal projections of sensations recruited by excitation of small groups of neighbouring nerve fibres were significantly more scattered in space than anticipated if these fibres had preserved an orderly intraneural map, implying lack of somatotopy in the nerve. Mean projected field sizes were 3.4 mm2 for sharp pain, 9.2 mm2 for tapping/vibration, 29.3 mm2 for pressure and 35.4 mm2 for dull pain, and in addition the latter two showed a rising size gradient from fingertip to palm. Consideration of projected field size as a variable in discriminative touch suggests that input from RA units and A delta nociceptors may be of importance in stimulus localization, while SA I units may play an additional role in two point discrimination.

Adult↗