Patient information on phantom limb pain: a focus group study of patient experiences, perceptions and opinions.

Educating patients about their condition is regarded as a fundamental step in pain management. This study used focus groups with patients to explore their experiences and perceptions of the information on phantom pain that they received before and after amputation, and their views on improving this information. Thirty-one patients with a lower limb amputation attended one of seven focus groups. The majority reported phantom pain although there were individual variations in character, severity and persistence. There were wide variations in what people were told from occasional reports of good information to instances of people reporting little or no information from professionals. There were strong feelings that information should be given before or soon after amputation with a preference for verbal one-to-one explanations. Professionals, particularly nurses and surgeons, were regarded as the best source of information, although peer support was seen to be important. These findings indicate that people require timely up-to-date information on phantom pain which sensitively addresses the variability of the experience and provides the foundation for ongoing pain management. We propose that the information process could be improved by ensuring that professionals use standard information for patients derived from purposefully written sections in national guidelines.

C- and Adelta-fibre mediated thermal perception: response to rate of temperature change using method of limits.

Studies investigating the effect of rate of temperature change on thermal thresholds have used a variety of different methods and threshold combinations, and many display incomplete reporting of statistical analyses. It has been suggested that C- and Adelta-fibre mediated thresholds differ in their reaction to different rates of temperature change. Ten healthy female volunteers (aged 18-26 years; mean 21 +/- S.D. 2.53) undertook cold sensation (CS), warm sensation (WS), cold pain (CP) and heat pain (HP) threshold determinations on the thenar eminence of the dominant hand. Rates of temperature change of 0.5, 1, 2.5 and 4 degrees C/s were used, with a modified method of limits. Adaptation temperature was 32 degrees C and thermode size 3 cm x 3 cm. Results showed a significant increase in WS, HP and CP thresholds with increased rates of temperature change (all p < 0.001), but no significant change for CS (p = 0.653). These results suggest that thresholds with a C-fibre component (WS, HP and CP) and those that are Adelta-fibre mediated (CS) behave differently. A traditional explanation of measurement artefact alone is insufficient in rationalizing these results, with additional factors potentially involved. Slow rates of temperature change were shown to reduce mean intra-individual differences in recorded threshold values, and also to abolish ceiling effects with HP threshold determinations. Clinically, therefore, using slow rates of temperature change with method of limits has a range of benefits over and above simply minimizing measurement artefact.

Alteration of interferential current and transcutaneous electrical nerve stimulation frequency: effects on nerve excitation.

OBJECTIVES: To investigate the effects of different interferential current (IC) and transcutaneous electrical nerve stimulation (TENS) frequencies on sensory, motor, and pain thresholds. STUDY DESIGN: Single blind, repeated measures design. SETTING: Laboratory. PARTICIPANTS: Women students 18 to 30 years old (n = 24). INTERVENTIONS: Premodulated IC and square-wave TENS pulses (125micros phase duration) were applied over the median nerve at a range of frequencies in all subjects. MAIN OUTCOME MEASURES: The peak current (in milliamperes) was recorded twice at each threshold for each frequency, and averaged. RESULTS: Both IC and TENS displayed a statistically significant effect of frequency for each threshold. However, frequency effects with IC were not well defined and were of small magnitude. Pure 4kHz current (0Hz amplitude modulated frequency) with IC did not produce effects different from those produced when an amplitude modulated frequency was included. With TENS, frequency effects were very clearly observed, with a distinct increase in the current intensity at each threshold as frequency decreased. CONCLUSIONS: It is postulated that the medium frequency component of IC is the main parameter in stimulation, contrary to traditional claims of the amplitude modulated frequency being important. TENS was shown to be a more adaptable method of stimulating these nerve pathways than IC.

Characteristics of background and evoked discharges of multireceptive neurons in lumbar spinal cord of cat.

1. Intracellular recordings were made in laminae III-V of the dorsal horn of the cat spinal cord from a group of multireceptive neurons that exhibited similar physiological properties. The background discharge contained irregular and occasional clusters of action potentials, each arising from a complex excitatory postsynaptic potential (EPSP); brushing elicited more frequent clusters containing more action potentials, whereas noxious heating elicited more regular firing, with action potentials arising singly. The distribution of interspike intervals (ISIs) was measured for the background and heat-evoked discharges and revealed characteristic differences in pattern between the two states. 2. Statistical tests were applied to the point process of times of occurrence of spikes within a discharge to establish stationary, to identify renewal instants, and to describe the process between renewal instants. In each case, the statistical description of the discharge was related to the physiological state of the neuron as revealed by recording of synaptic potentials and analysis of the different activating inputs. 3. Background discharge was stationary, and spikes occurred singly or occasionally in clusters. The data were therefore analyzed as a series of "bursts," where a burst could be made up of one or more spikes. Examination of the pattern of serial dependence led to the conclusion that the point process renewed itself after each burst. This, together with the distribution of the intervals between bursts, suggested that bursts were triggered by single, distinct events, which occurred randomly at a slightly and randomly varying average rate. The variation in the number of spikes in a burst suggested random variation in the strength of the physiological trigger. 4. Clusters of action potentials arising from a complex EPSP could be produced by simultaneous stimulation of a number of fast-conducting A beta fibers in the periphery and gentle mechanical stimulation, whereas stimulation of slow C fibers and noxious heat evoked discrete EPSPs from which action potentials arose singly. It was, therefore, concluded that background activity was, at least in part, the result of random activity in a randomly varying number of A beta primary afferent fibers, which could arise from operative procedures. 5. The discharge evoked by heat was stationary, and the absence of serial dependence established that the point process renewed itself after every spike and was, therefore, a simple renewal process. The distribution of the ISIs suggested that each spike was triggered by a randomly occurring physiological event.(ABSTRACT TRUNCATED AT 400 WORDS)

Membrane properties of nociceptive neurones in lamina II of lumbar spinal cord in the cat.

1. Intracellular recordings were made from neurones in lamina II of the dorsal horn of the lumbar spinal cord of the cat, and the electrotonic responses to brief rectangular current pulses of up to 0.5 nA passed through the recording microelectrode measured. 2. The majority of penetrations were associated with input resistances lower than 70 M omega, low resting potentials (-25 to -45 mV) and frequent firing of action potentials. Stable resting potentials of -50 to -75 mV were recorded in twenty neurones which exhibited continuous ongoing synaptic activity without action potentials. The threshold for action potential initiation was around -42 mV. The current-voltage relationships were linear over most of the range of currents used; with depolarizing currents rectification became apparent close to the firing threshold. Input resistances ranged from 80 to 150 M omega. 3. The time course of the decay of the electrotonic response was exponential with a time constant of 0.8-2.0 ms. The morphology of the cells--small soma with a small number of fine processes--and these short time constants suggest that axial current flow is limited and that the charge is dissipated locally within the soma through the membrane capacitance. 4. Effective membrane capacities were calculated from the estimated soma surface area of typical neurones in lamina II stained with HRP, and assuming a specific membrane conductance of 1.0 microF cm-2 they ranged from 3.1 to 15.7 pF. Membrane capacities were calculated for the twenty neurones in this study from measurement of input resistance and time constants (6.4-15.0 pF) and lay within this range. 5. Three neurones which had their electrical properties measured were also stained with horseradish peroxidase (HRP). Their specific membrane capacitances (1.1-1.2 microF cm-2) and specific resistances (0.9-1.1 k omega cm2) were within the range of values measured for other neurones in the CNS. 6. The short time constants found for these neurones suggests that temporal summation of postsynaptic potentials evoked by short-acting neurotransmitters will be limited. This may help to explain why action potentials arise singly from discrete, short-lived EPSPs. There is anatomical evidence for multiple connections from terminal branches of A delta and C afferent fibres within the superficial dorsal horn; this suggests that spatial summation of EPSPs is a major factor in synaptic integration of some of the primary afferent inputs to these neurones.

Spinal processing: anatomy and physiology of spinal nociceptive mechanisms.

The processing of nociceptive input that occurs at the spinal level represents the first stage of effective control over its access to higher regions of the central nervous system. Recent developments in both the anatomy and physiology of nociceptive processing pathways at this level are beginning to yield an integrated understanding of structure and function. Most small afferent axons terminate in the more superficial laminae of dorsal horn, but technical difficulties have, until recently, prevented analysis of the functional properties of identified small fibres. A direct input of nociceptive afferents on to particular dorsal horn neurons is difficult to establish in view of the slow impulse conduction in these fibres and the small size of target neurons in the substantia gelatinosa. The small cells themselves are being analysed for relations between structure and function, using physiological, intracellular staining and immunocytochemical techniques to characterize their properties. They appear to be a highly heterogeneous population with many sub-classes, whether typed according to the transmitter they contain, e.g. enkephalin, to their physiological responses: whether excitatory or inhibitory to nociceptive and other inputs, or to both. The multireceptive neurons that project out of the dorsal horn toward supraspinal regions are, in general, located in deeper laminae and are likely to receive nociceptive information through polysynaptic pathways. The nocireceptive neurons in lamina I, which receive exclusively nociceptive inputs from myelinated and non-myelinated afferents project, at least in part, to thalamic and brain stem regions. Polysynaptic nociceptive pathways in dorsal horn may be subject to different controls from neurons in laminae I and II. Tonic descending inhibition is operative on the former and it is becoming clearly established that descending systems such as those containing noradrenaline, can regulate the access of nociceptive information to higher levels. The mechanisms of such descending controls and the importance of their interaction with segmental control systems, such as those involving the dynorphin opioids, are just beginning to be understood. Many somatosensory neurons in dorsal horn, both the large cells, some of which project supraspinally, and the small cells of superficial laminae, receive convergent nociceptive and non-nociceptive inputs. Although solely nociresponsive neurons are clearly likely to fill a role in the processing and signalling of pain in the conscious central nervous system, the way in which such useful specificity could be conveyed by multireceptive neurons is difficult to appreciate.(ABSTRACT TRUNCATED AT 400 WORDS)

Nociceptive neurones in the superficial dorsal horn of cat lumbar spinal cord and their primary afferent inputs.

The morphology, background activity and responses to stimulation of primary afferent inputs of small neurones in the superficial dorsal horn which could only be excited from the skin by noxious stimulation were investigated by intracellular recording and ionophoresis of HRP. Neurons which gave similar responses to afferent stimulation were morphologically heterogeneous with respect to dendritic tree geometry and axonal projection, but were located around the lamina I/II border. Cutaneous excitatory receptive fields responding to noxious stimulation were generally small; most neurones had more extensive inhibitory fields responding to innocuous mechanical stimulation, in many cases overlapping the excitatory fields. Generally, stimulation of the excitatory field resulted in depolarization of the neurone and increased action potential firing, and stimulation of the inhibitory field resulted in hyperpolarization. Electrical stimulation of peripheral nerves revealed the existence of converging excitatory inputs carried by different fibre groups, and all neurones received an inhibitory input activated at low threshold. Excitatory responses were short-lived and occurred consistently in response to repeated stimulation. Central delay measurements gave evidence of a number of A delta monosynaptic inputs but only one A beta monosynaptic input; inhibitory inputs along A beta fibres were polysynaptic. The constant latency and regularity of the C response suggested monosynaptic connections. Low intensity stimulation of inhibitory inputs elicited a short-lived i.p.s.p. which increased in amplitude with increasing stimulus strength until it disappeared into a more prolonged hyperpolarization. This was associated with inhibition of background action potentials, and increased in duration with increasing stimulus strength up to C levels, indicating an A delta and C component. It is suggested that the level of excitability of these neurones depends on the relative amounts of concurrent noxious and innocuous stimulation, and that the resultant output, which is conveyed mainly to other neurones within the spinal cord, could modulate reflex action at the spinal level as well as affecting components of ascending sensory pathways.

Statistical analysis of ongoing activity of neurones in the substantia gelatinosa and in lamina III of cat spinal cord.

Intracellular recordings from substantia gelatinosa (s.g.) neurones in chloralose-anaesthetized cats and in decerebrate preparations revealed the existence of ongoing synaptic activity. 59% of s.g. neurones showed ongoing spiking activity at rates of more than one per second. The ongoing activity of twenty s.g. neurones was subjected to statistical analysis. Stationarity was established for the activity of each neurone, the interspike interval (i.s.i.) distributions were bell-shaped, and no evidence of dependency of the length of an interval on the one preceding it was found. The mechanism of spike generation in these neurones is therefore an example of a renewal stochastic process. The pattern of ongoing discharge of twelve neurones recorded in lamina III was markedly different, and generated in each case a unimodal asymmetric i.s.i. histogram with a sharp rise to mode after a short dead time and a slow decay. The activity was stationary only in the long term, and there was strong evidence of dependency of intervals. The spike generating mechanism was therefore an example of a non-renewal stochastic process. The different patterns of activity are discussed in relation to differences in cutaneous input, and it is suggested that the pattern of activity in the s.g. neurones is the result of convergence on the neurones of a large number of small independent excitatory influences, whereas that of the neurones in lamina III is the result of excitation by powerful synchronous synaptic inputs. It is re-emphasized that statistical analysis of neural impulse sequences is a valuable technique in investigation of the function of a neurone within its network.

Intracellular marking of identified neurones in the superficial dorsal horn of the cat spinal cord.

Intracellular iontophoresis of horseradish peroxidase has been used to mark identified neurones in the superficial dorsal horn of cats. The cats were anaesthetized with alpha-chloralose and paralysed with gallamine triethodide. Four specific nocireceptive neurones in the marginal zone and seven neurones in the substantia gelatinosa were recovered. One of the former and four of the latter are described in detail and are illustrated as reconstructions from serial sections. The results confirm previous conclusions that the substantia gelatinosa contains neurones classified as 'inverse' and that the nocireceptive neurones of lamina I are Waldeyer Cells.

Micro-electrode studies on mammalian vascular muscle.

1. Transmembrane potentials were measured in smooth muscle cells in the walls of small arteries in the frog tongue and skin of the lateral abdomen. Resting potentials had mean values of 64.7 and 43.6 mV respectively, and action potentials of up to 60 mV amplitude and 100-200 msec duration could be elicited by electrical stimulation in the tongue vessels.2. Micro-electrodes were inserted into smooth muscle cells in the walls of small arteries and arterioles of the rat mesenteric circulation. Intracellular potentials varied continually and maximum polarization averaged 39.4 mV.3. Rhythmic slow waves with a period varying from 4.5 to 7.8 sec were observed, and their amplitude but not their frequency was affected by the level of anaesthesia.4. Spike potentials were recorded, amplitude up to 35 mV, with occasional overshoot, and duration 40-50 msec; these were followed by a positive after-potential, 100-150 msec duration and amplitude up to 8 mV.5. Experiments using chemical and surgical means of interfering with the autonomic nervous system showed that the amplitude, but not the frequency, of the slow waves and the occurrence of action potentials were markedly affected by nervous influences.6. Stimulation of the smooth muscle by asphyxia, electrical stimulation of the splanchnic nerves, and local application of adrenaline, noradrenaline and vasopressin increased the frequency of action potentials and the amplitude of the slow waves, and inhibiting agents such as acetylcholine and removal of the nerve supply depressed the electrical activity.