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Biomedical subjects

J P Halonen

Publications and source records attributed to J P Halonen.

25 records · Page 2Linked to original sources
PubMed1978

Does transient blocking of axonal conduction occur in uraemic neuropathy?

In uraemic and other patients with neuropathies, motor unit spike intervals were analysed using a special computer program to detect prolonged intervals of twice the normal duration, so-called "double intervals." These may have different causes--trigger failure, double discharge, or a transient fall in the firing rate of coactive motor units. There was not sufficient evidence that transient conduction blockings will occur in the main axon in uraemic neuropathies.

Axons↗
PubMedDate not supplied

Conduction properties of epidurally recorded spinal cord potentials following lower limb stimulation in man.

Spinal somatosensory evoked potentials were recorded in 35 neurologically normal patients undergoing surgery for scoliosis. During posterior procedures the recording electrodes were placed in the dorsal epidural space and during anterior operations in the intervertebral discs. Stimulation was of the tibial nerve in the popliteal fossa and the posterior tibial and sural nerves at the ankle. At thoracic levels the response consisted of at least 3 components with different peripheral excitation thresholds and spinal conduction velocities (range 35-85 m/sec). All components were conducted mainly in tracts ipsilateral to the stimulus, component 1 being most laterally located. At low stimulus intensity only the fastest activity was recorded but this was markedly delayed over low thoracic segments and was recorded as a repetitive discharge rostrally. Higher intensities elicited additional components which were conducted at a slower but relatively uniform velocity; consequently they might overlap with or even overtake the fast activity at mid-to-low thoracic levels. Component 1 was much less prominent when the posterior tibial nerve was stimulated at the ankle and absent from the (cutaneous) sural nerve response; remaining potentials were conducted at velocities similar to those of components 2 and 3 following tibial nerve stimulation at the knee. Small 'stationary' potentials were recorded at all thoracic levels, probably due to the change in conductivity as the volley entered the spinal cord. Efferent activity was recorded at and below the thoraco-lumbar junction, possibly related to the H-reflex or F-wave. Similar, although smaller, afferent potentials were recorded from the anterior side of the vertebral column. Component 1 is likely to be due to the stimulation of group 1 muscle afferents which terminate in the dorsal horn and activate second order neurones, many of whose axons go to form the ipsilateral dorsal spinocerebellar tract. Components 2 and 3 are believed to be largely cutaneous in origin and to be conducted mainly in the dorsal columns.

Adolescent↗
PubMedDate not supplied

Contribution of cutaneous and muscle afferent fibres to cortical SEPs following median and radial nerve stimulation in man.

Somatosensory evoked potentials were recorded after stimulation of motor and cutaneous nerves in the upper limb. Stimulation of the thenar motor branch of the median nerve and the deep motor branch of the radial nerve produced only broad, ill-defined and small-amplitude scalp-recorded responses. In contrast, stimulation of purely cutaneous nerves (digital and the superficial radial) gave responses of large amplitude. The cortical responses following combined deep and superficial radial nerve stimulation were of smaller amplitude than the two individual responses combined. These findings suggest that, contrary to an earlier report (Gandevia et al. 1984), muscle afferents do not make a major positive contribution to the scalp-recorded cortical responses produced by electrical stimulation of mixed nerves in the upper limb.

Adult↗
PubMedDate not supplied

Centrifugal and centripetal mechanisms involved in the 'gating' of cortical SEPs during movement.

Pre- and post-central cortical SEPs were of reduced amplitude and altered wave form when the median nerve stimulus was delivered during active movement of the thumb. Peripheral, cervical and scalp far-field potentials were not significantly affected, apart from the positive wave following N13 at upper cervical level. The algebraic contribution of movement-related potentials was eliminated by wave form subtraction. Qualitatively similar effects were seen when the thumb was moved passively, suggesting that sensory input associated with the movement exerts a 'gating' effect which is at least as significant as that due to centrifugal influences. The effect was in some respects similar to that associated with interfering cutaneous stimulation, although an additional component was identifiable in the difference wave forms associated with active and passive movement. In contrast to passive movement, SEP gating during active movement was equally marked when the stimulus was delivered instantaneously with the first detectable displacement of the thumb. Thus the effect cannot have been entirely due to movement-related activity in distal cutaneous, muscle and joint receptors, since input from the latter could not have arrived at the CNS before the median nerve volley. Other centripetal mechanisms are not excluded, however, since arrival of the volley would be preceded by proprioceptive activity from proximal muscle receptors.

Adult↗
PubMedDate not supplied

Association of thermal perception thresholds with cardiovascular autonomic function in diabetes.

In order to study the association between warm thermal-perception thresholds (WPT), cold thermal-perception thresholds (CPT) and cardiovascular autonomic function, we examined 91 otherwise healthy patients with diabetes mellitus (69 with type I and 22 with type II). The covariance analysis revealed that WPT was associated with the deep-breathing E/I ratio and the Valsalva ratio (p = 0.004 and p = 0.008, respectively) whereas CPT was associated with the Valsalva ratio and the postural blood pressure decrement (p = 0.008 and p = 0.004, respectively). These associations possibly reflect histological similarities between the parasympathetic nerves and those mediating warm sensation, and between the sympathetic nerves and those mediating cold sensation.

Adolescent↗