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Biomedical subjects

R L Ruff

Publications and source records attributed to R L Ruff.

100 records · Page 6Linked to original sources
PubMed1977

A quantitative analysis of local anaesthetic alteration of miniature end-plate currents and end-plate current fluctuations.

1. The effect of the local anaesthetic QX222 on the kinetics of miniature end-plate currents (m.e.p.c.s) and acetylcholine (ACh) induced end-plate current (e.p.c) fluctuations was studied in voltage-clamped frog cutaneous pectoris neuromuscular junctions made visible with Nomarski differential interference contrast optics. 2. In Ringer solution the m.e.p.c.s decayed with a single exponential time course and the e.p.c. fluctuation spectra were characterized by single Lorentzian functions, with the spectral cut-off frequency well predicted by the m.e.p.c. decay rate. 3. In the presence of 0-1-0-5 mm QX222 at-50 to -100 mV holding potential both the e.p.c. fluctuation spectrum and the m.e.p.c. decay consisted of a fast and a slow component, with the cut-off frequency of each spectral component predicted by the decay rate of the corresponding constituent of the m.e.p.c. 4. Hyperpolarization increased the decay rate and relative amplitude of the fast component of the m.e.p.c. and decreased the decay rate of the slow m.e.p.c. component. 5. With 0-05 mm QX222 and -70 mV holding potential the m.e.p.c.s. and e.p.c. fluctuation spectra consisted of three components. The third component of the m.e.p.c. and e.p.c. spectra had nearly the same decay rate and cut-off frequency as was found at the same end-plate under equivalent conditions before drug exposure. 6. The kinetic predictions of four different schemes for local anaesthetic action were compared with observed m.e.p.c.s. and e.p.c. fluctuations. 7. Schemes in which the local anaesthetic acted by creating two kinetically distinct populations of acetylcholine receptors or by interacting with ACh receptor to produce a biphasic exponential decay of the end-plate channel conductance did not accurately predict the e.p.c. fluctuation spectrum. 8. The variance of the e.p.c. fluctuations vanished at the reversal potential indicating that local anaesthetic action was not due to the presence of different ion selective end-plate channels. 9. QX222 action could be explained by alteration of the ACh receptors such that they sequentially c-hanged from one conductance state to another. A specific case in which QX222 binds to the ACh receptors in its open state creating a partially blocked state, was found to be the most parisimonious. 10. The conductance, gamma, of a single end-plate channel was estimated from e.p.c. fluctuations. In Ringer's solution gama = 24-4 +/- 1-2 (s.d.) pmho. In the presence of 0-1 mm to 0-5 mm QX222 the effective single channel conductance, gamma, varied from 14-2 to 1-39 pmho. 11. gamma decreased with increased local anesthetic concentration, hyperpolarization, or decreased temperature. The variation in gamma is thought to reflect the dependence on the experimental conditions of the relative probability that the ACh receptors is in an open vs a partially blocked state.

Acetylcholine↗
PubMed1976

Local anesthetic alteration of miniature endplate currents and endplate current fluctuations.

The effect of the local anesthetic QX222 on the kinetics of miniature endplate currents and acetylcholine induced endplate current fluctuations was studied in voltage clamped cutaneous pectoris muscle of Rana pipiens. Both the endplate current fluctuation spectra and the miniature endplate current decay consisted of two or three components depending upon the holding potential and local anesthetic concentration. The cutoff frequency of each spectral component was equal to the decay rate of its corresponding constituent of the miniature endplate current. Comparison of the relative amplitudes of the spectral and miniature endplate components indicated that QX222 did not act by creating two kinetically distinct populations of acetylcholine receptors. QX222 action could be explained by alteration of the acetylcholine receptors such that they sequentially change conformation form one open state to another. A specific case in which QX222 binds to the open state of the acetyl-choline receptor creating a blocked state, was found to account for the observed relationship between the relative amplitudes of the miniature endplate current and spectral components, as well as the previously observed voltage and concentration sensitivity of the decay rates of endplate current components.

Anesthetics, Local↗
PubMedDate not supplied

Ionic channels: II. Voltage- and agonist-gated and agonist-modified channel properties and structure.

This article reviews the different forms of ionic channels: voltage-gated, agonist-gated, and agonist- and second messenger-modified channels. The recent advances in our knowledge of the amino acid sequence of the sodium channel and the nicotinic acetylcholine receptor and the relationship of the primary structure to the channels' quarternary structure and function are discussed.

Animals↗
PubMedDate not supplied

Electrically induced recovery of gait components for older patients with chronic stroke.

OBJECTIVE: To compare the gains for chronic stroke patients in volitional gait pattern attained from treatment with functional neuromuscular stimulation (FNS) and intramuscular electrodes (IM) with gains attained using conventional therapy, including treatment with FNS using surface electrodes (surface-stim). DESIGN: This single-subject research design consisted of a series of two subjects. Three months of conventional therapy and surface-stim were followed by treatment using the FNS-IM system. Two stroke patients had cerebrovascular accident 1 or 4 yr before the study and ambulated with a cane. Interventions consisted of 3 months of conventional exercise and gait training including surface-stim, followed by 7-14 months of treatment with the FNS-IM system. Treatments occurred up to 3 times/wk for 1-hr sessions and a home program. Outcome measures consisted of six kinematic gait components, as measured by a six-camera video-based data-acquisition system. Coordination of isolated joint movement was measured according to the Fugl-Meyer scale. RESULTS: Both subjects improved during conventional therapy to some degree. During FNS-IM treatment, gains were made beyond those attained during conventional therapy. Statistically significant differences were found between conventional and FNS-IM therapy. CONCLUSIONS: For these two subjects, gains in volitional control of gait were made during conventional treatment (including surface-stim); for these two subjects during FNS-IM treatment, additional gains were made in volitional gait pattern, beyond those attained during conventional therapy.

Aged↗
PubMedDate not supplied

Transient ischemic attacks associated with hypotension in hypertensive patients with carotid artery stenosis.

In a group of 132 patients with transient ischemic attacks ((TIAs) 7 patients (4 men, 3 women, ages 64 to 81) had TIAs preceded by hypotension. The average fall of mean blood pressure during an attack was 26.4 +/- 5.5 mm Hg (SD). Only one of these patients had a TIA which was not preceded by hypotension. This episode occurred during a paroxysm of coughing. All 7 of these patients had hypertension, and cerebral arteriography performed in 4 of the 7 revealed hemodynamically significant carotid artery stenosis. Each of the 4 patients developed hypotension and a TIA after the procedure. Twenty of the other patients had hypotensive episodes but did not develop focal neurological deficits. None of these patients had carotid artery stenosis. This study suggests that hypertensive patients with carotid artery stenosis may be at risk to develop focal cerebral ischemia during acute hypotensive episodes.

Aged↗
PubMedDate not supplied

Complications of lumbar puncture followed by anticoagulation.

The complications associated with lumbar puncture (LP) were compared in 2 groups of 342 patients. The first group of patients was anticoagulated after the LP, and the second was not. The incidence of minor headache or back pain was similar in the 2 groups (Group 1--62%, Group 2--64%). The anticoagulated patients had a higher incidence of paraparesis (Group 1, 5 patients, Group 2, No patients; p less than .05) and severe back or lumbosacral radicular pain lasting more than 48 hours (Group 1, 18 patients, Group 2, 6 patients; p less than .025). Seven of the anticoagulated patients developed spinal hematomas (5 with paraparesis, 2 with severe back pain). Among the anticoagulated patients the risk of a major complication was increased by a traumatic LP (p less than .001), starting anticoagulation within one hour of the LP (p less than .001), or aspirin treatment at the time of the LP (p less than .001). This study suggests that if LP is done, delaying anticoagulation for at least one hour and avoiding concurrent aspirin therapy may decrease the risk of developing an extraparenchymal spinal hematoma.

Anticoagulants↗
PubMedDate not supplied

Performance of an intramuscular electrode during functional neuromuscular stimulation for gait training post stroke.

The goal of rehabilitation for stroke patients in this research was to improve the volitional coordination of the swing phase and stance phases of gait. Functional neuromuscular stimulation (FNS) is a promising rehabilitation tool for restoring motor control. For our gait training protocols, FNS systems with surface electrodes were impractical. For the rehabilitation protocols that we defined, available implantable electrode designs did not meet desired criteria regarding fracture rate, invasiveness of placement procedures, and maintenance of position at the motor point. The criteria for the new intramuscular (IM) electrode design included minimally invasive electrode placement technique, accurate placement of electrodes, good muscle selectivity, consistency of muscle activation, good position maintenance of the electrode at the motor point, comfortable stimulus, and practical donning time for the system. A percutaneous electrode was designed for placement beneath the skin at the motor point of seven paralyzed or paretic muscles in the lower limb. A single-helical coil lead, a double-helical coil electrode, and fine wire barbs were design features that enhanced the anchoring capability of the electrode. A polypropylene core enhanced electrode durability. Implantation tools were custom-designed to enable accurate electrode placement without incision. We studied 17 subjects with a total of 124 electrodes. With the use of IM electrodes, FNS was provided for 1,413.8 electrode months. During this time, no instances of infection occurred. The measure of electrode integrity showed a 99% electrode survival rate. Throughout the treatment protocols, 93% of the electrodes delivered a good muscle response; 7% (nine electrodes) moved from the motor point and delivered a poor muscle response during the treatment protocol. Anchoring performance was higher for electrodes implanted in muscles that moved the hip (96.0%) and ankle joints (97.45%) compared with electrodes implanted in muscles that moved the knee joint (88.5%). Ninety-seven percent of the electrodes delivered a comfortable stimulus. Three percent delivered a stimulus that was uncomfortable at therapeutic levels and therefore were not used. We achieved gains in subject impairment and disability measures. The system proved to be practical for use in both clinical and home environments.

Aged↗