Showing papers by "David Burke published in 1974"

Sensory conduction of the sural nerve in polyneuropathy.

Abstract: Using surface electrodes, sensory nerve action potentials (SAP) have been recorded in the proximal segment (mid-calf to lateral malleolus) and the distal segment (lateral malleolus to toe 5) of the sural nerve and in the median nerve in 79 control subjects. The values obtained for the distal segment of the sural nerve varied widely and in seven apparently normal subjects no SAP could be distinguished. In the proximal segment conduction velocities were over 40 m/s and there was no significant change with age, unlike the median nerve in which a highly significant slowing occurred with age. Comparison of the results of sural and median sensory conduction studies in 300 consecutive patients screened for sensory polyneuropathy confirms the value of sural nerve sensory studies as a routine screening test, and confirms the belief that the changes in polyneuropathy are usually more prominent in lower limb nerves. It is therefore suggested that studies of sural sensory conduction form the single most useful test in the diagnosis of sensory polyneuropathy.

Isometric contraction of the abductor digiti minimi muscle in man

Abstract: Isometric contraction of the abductor digiti minimi muscle (ADM) has been studied in six normal subjects. Twitch contraction times of ADM ranged from 60 to 68 ms and twitch torque ranged from 2·33 to 6·24 × 10-3 Nm. In three subjects torque declined by an average of 31% after tetanization at 50 Hz for 30 seconds but there was no similar diminution in the evoked muscle action potential suggesting that the fatigue arose from intrinsic muscular mechanisms. A marked decline in tetanic torque occurred with continued tetanization in two subjects for a total of five minutes, but this change was accompanied by a decrease in the muscle action potential. In six subjects threshold stimulation to the ulnar nerve at the wrist and to various sites over the motor point of ADM allowed 55 threshold twitch contractions to be identified after averaging. A unimodal range of contraction times ranging from 40-100 ms was found and this was confirmed by additional experiments in two subjects in whom 30 threshold twitch contractions were identified using a needle electrode to stimulate various sites in the motor point. Tetanization at 50 Hz was performed using threshold stimulus levels. Nine threshold tetanic contractions were evoked in two subjects. In eight tetanic torque progressively fatigued to between 14 and 20% within 60-90 seconds, but, in one tetanic contraction, torque proved relatively fatigue resistant. These results suggest that there is a homogeneous group of motor units in ADM (with respect to contraction time) and that this group contains what are probable fast twitch fatigue sensitive and fatigue resistant motor units. No evidence of a distinct group of slow twitch units was found.

Contractile properties of the abductor digiti minimi muscle in paramyotonia congenita

Abstract: In two subjects with paramyotonia congenita the isometric torque generated by the abductor digiti minimi and the surface EMG recorded over ADM decreased during prolonged or repetitive contractions, whether these were voluntarily or electrically induced. Isometric twitch times did not alter significantly during this muscle fatigue. Cooling greatly accelerated the fatiguing process. It is suggested that this local muscle weakness is due to a progressive decrease in excitability of the muscle cell membrane.

An analysis of myotonia in paramyotonia congenita

Abstract: In two subjects with paramyotonia congenita myotonic delay in muscle relaxation, recorded electromyographically and with a displacement transducer, was found to increase with repeated forceful contractions. Myotonia was elicited readily in warm temperatures, was initially aggravated by cooling, but was invariably lost as muscle fatigue developed. The EMG evidence of myotonia usually subsided before complete muscle relaxation had occurred, suggesting that a defect of the contractile mechanism was present over and above any defect at membrane level.

Contractile properties oftheabductor digiti minimi muscle inparamyotonia congenita

Abstract: SYNOPSIS Intwosubjects withparamyotonia congenita theisometric torquegenerated bythe abductor digiti minimi andthesurface EMG recorded overADM decreased during prolonged or repetitive contractions, whether these were voluntarily or electrically induced. Isometric twitch times didnotalter significantly during this muscle fatigue. Cooling greatly accelerated thefatiguingprocess.Itissuggested thatthislocal muscle weakness isduetoa progressive decrease in excitability ofthemuscle cell membrane. Muscular weakness isnowrecognized toplay a major role inthesymptomatology ofparamyotonia congenita. Episodes ofgeneralized paresis similar tohyperkalaemic periodic paralysis, or, rarely, hypokalaemic periodic paralysis, arewell documented insomefamilies withotherwise classical paramyotonia. Forthese reasons, the right ofparamyotonia congenita toexist asa nosological entity distinct ontheonehandfrom myotonia congenita andontheother fromthe periodic paralyses hasbeendebated. A wellrecognized butless well-studied formofweaknessinparamyotonia isthat whichdevelops in theexercised muscle andaccompanies butoutlasts themyotonia. Thispaperanalyses theproperties ofthe abductor digiti minimi muscle (ADM)intwo subjects withparamyotonia congenita toelucidateaspects ofthis local formofweakness that develops withmuscle use.Features ofmyotonia willbeanalysed ina subsequent paper (Burke etal., 1974b). METHODS Twobrothers, aged 24and19years, withparamyotonia congenita werestudied. Thesubjects presented withtheclassical clinical syndrome anda family history ofadominantly inherited condition which

Isometric contraction oftheabductor digiti minimimuscleinman

Abstract: SYNOPSIS Isometric contraction oftheabductor digiti minimi muscle (ADM)hasbeenstudied in sixnormalsubjects. Twitchcontraction timesofADM ranged from60to68ms andtwitch torque ranged from2-33to6-24 x 10-3Nm.Inthree subjects torque declined byan averageof310% after tetanization at50Hzfor30seconds butthere was nosimilar diminution intheevoked muscle action potential suggesting thatthefatigue arosefromintrinsic muscular mechanisms. A markeddecline in tetanic torqueoccurred withcontinued tetanization intwosubjects foratotal offive minutes, but this change was accompanied byadecrease inthemuscle action potential. Insixsubjects threshold stimulation totheulnarnerveatthewrist andtovarious sites overthemotorpointofADM allowed 55threshold twitch contractions tobeidentified after averaging. A unimodal rangeofcontraction times ranging from40-100 ms wasfoundandthis wasconfirmed byadditional experiments intwosubjects inwhom 30threshold twitch contractions wereidentified using aneedle electrode to stimulate various sites inthemotorpoint. Tetanization at50Hz was performed using threshold stimulus levels. Ninethreshold tetanic contractions wereevokedintwosubjects. Ineight tetanic torqueprogressively fatigued tobetween14and20%within 60-90seconds, but,inone tetanic contraction, torqueproved relatively fatigue resistant. Theseresults suggest thatthere isa homogeneousgroupofmotorunits inADM (with respect tocontraction time) andthat this groupcontains whatareprobable fasttwitch fatigue sensitive andfatigue resistant motorunits. No evidence ofa distinct groupofslowtwitch units was found.