Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Miniaturization”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,495 records · Page 83Linked to original sources
PubMed1996

Pediatric Transesophageal Echocardiography by Means of a Miniature 5-MHz Multiplane Transducer.

The development of a miniature multiplane transesophageal echocardiographic (TEE) transducer for pediatric use is the latest development in TEE. Horizontal, longitudinal, and all possible intermediate oblique planes can be obtained with minimal transducer manipulation. We studied 48 patients with an experimental 5-MHz transducer, which contains 48 transmitting elements. The dimensions of the tip are 27 x 10.6 x 7.9 mm. Patients ages ranged from 2 days to 16 years, their weights from 3.6-67 kg. Multiplane TEE proved to be complementary to the single horizontal plane in assessing the right ventricular outflow tract, the left ventricular outflow tract, ascending aorta, the atrial septum, the atrioventricular (AV) valves, especially in AV septal defects, and double inlet left ventricle (DILV). Moreover, multiplane TEE was extremely helpful in judging the outflow tracts and ventricular septal defects in more complex heart defects such as DILV, double outlet right ventricle, and hearts with discordant connections. Multiplane TEE offered superb monitoring of cardiac interventions. We conclude that multiplane TEE provides new imaging planes and enables visualization of every major structure of the heart by unlimited scan planes. Multiplane TEE is indispensable in congenital heart defects. Thus, multiplane TEE adds to diagnostic assurance and enhances decision making for surgery. (ECHOCARDIOGRAPHY, Volume 13, November 1996)

Journal Article↗
PubMedDate not supplied

Radiographic aspects of Pneumocystis carinii pneumonia in the miniature Dachshund.

The thoracic radiographic changes of Pneumocystis carinii in 7 miniature Dachshunds were reviewed. The dogs were 7-12 months old and presented with polypnea, exercise intolerance and clinical signs suggestive of immune-incompetence. P. carinii pneumonia was diagnosed in all the dogs using transtracheal aspirate cytology and confirmed at postmortem in 3 dogs that died. Radiographically, diffuse pulmonary changes were present and varied from a mild interstitial and bronchial pattern to an alveolar pattern. Radiographic evidence of cor pulmonale was present in 1 dog. The most severe radiographic changes were seen in 2 of the dogs that died.

Animals↗
PubMedDate not supplied

Miniaturization of the flowing fluid electric conductivity logging technique.

An understanding of the hydraulic properties of the aquifer and the depth distribution of salts is critical for evaluating the potential of ground water for conjunctive water use and for maintaining suitable ground water quality in agricultural regions where ground water is used extensively for irrigation and drinking water. The electrical conductivity profiles recorded in a well using the flowing fluid electric conductivity (FEC) logging method can be analyzed to estimate interval-specific hydraulic conductivity and estimates of the salinity concentration with depth. However, operating irrigation wells commonly allow limited access, and the traditional equipment used for FEC logging cannot fit through the small access pipe intersecting the well. A modified, miniaturized FEC logging technique was developed for use in wells with limited access. In addition, a new method for injecting water over the entire screened interval of the well reduces the time required to perform FEC logging.

Electric Conductivity↗
PubMed1999

Thrombosis of the portal vein in a miniature schnauzer.

A miniature schnauzer with a history of apathy, anorexia and jaundice was presented to the Utrecht University Clinic for Companion Animals. Abnormal laboratory findings included highly increased levels of total bile acids and alkaline phosphatase, and hyponatraemia. Abdominal ultrasonography revealed that the right side of the liver was enlarged and the left side was small, together with a thrombus in the portal vein. Biopsies from the right side of the liver demonstrated subacute to chronic active hepatitis, for which the dog was treated with prednisolone (1 mg/kg/day for four weeks). No improvement was observed and the owner requested euthanasia. At necropsy the left lobes of the liver were found to be small and firm, while the right lobes were large and soft. There were two thrombi in the portal vein. Microscopic examination revealed chronic active hepatitis and cirrhosis.

Animals↗
PubMed1983

Properties of miniature post-synaptic currents at the Torpedo marmorata nerve-electroplate junction.

The post-synaptic conductance changes induced by spontaneous release of neurotransmitter on the Torpedo marmorata electroplates were studied by focal extracellular recording methods. It was found that miniature post-synaptic currents (m.p.s.c.s) recorded on the innervated and non-innervated faces of the electrocyte are opposite in sense and the distribution of amplitudes is bimodal. The bimodal distribution could reflect the presence of two populations of m.p.s.c.s (smaller and giant m.p.s.c.s). In the smaller m.p.s.c.s the distribution of the ratio (amplitude/decay time constant) shows two populations that probably represent areas with different receptor densities. The value of the mean open-channel lifetime estimated from the decay time constant of the m.p.s.c. is 0.92 +/- 0.67 ms (n = 319, temperature 20 +/- 1 degree C). Prostigmine (10 microM) increases the amplitude, decay time constant and time to peak of the m.p.s.c. A decrease of temperature increases m.p.s.c. decay time, the activation energies found ranging from 8.0 to 12.6 kcal x mol-1. Increasing the external K+ concentration produces a decrease in the decay time constant. High concentrations of divalent ions, particularly Ca2+, increase the decay time constant of the m.p.s.c. Alkaline or acid bathing solution produces a decrease in the decay time constant. An almost total substitution of external Cl- by non-permeant SO42- does not modify the time course of the m.p.s.c.

Animals↗
PubMed1968

Miniature synaptic potentials at frog spinal neurones in the presence of tertodotoxin.

1. Spontaneous subthreshold potentials have been recorded with an intracellular electrode from neurones of the isolated spinal cord of the frog.2. Records of both depolarizing and hyperpolarizing potentials were obtained from cells in normal Ringer solution and also when impulse conduction in the cord had been abolished by tetrodotoxin (TTX).3. Comparisons of results before and after TTX show that the majority of the spontaneous potentials are analogous to miniature end-plate potentials.

Animals↗
PubMed1970

Miniature potentials in denervated slow muscle fibres of the frog.

1. Pyriformis and iliofibularis muscles of the frog were studied with micro-electrodes. Both muscles contain a mixture of fast and slow muscle fibres, which can be distinguished by differences in their miniature end-plate potentials (min.e.p.p.s).2. In addition, the membrane time constant of fast fibres is < 20 msec, while that of slow fibres is > 200 msec.3. The characteristic difference in time constant persisted after denervation and allowed the identification of fibre type.4. Denervated slow fibres had min.e.p.p.s of variable time courses and skew amplitude distributions. Their frequency was lower than in normally innervated fibres, and could be increased by hypotonic solutions.5. In analogy with similar observations made previously in fast muscle fibres, it is suggested that after nerve degeneration the Schwann cells of small motor nerve fibres release packages of transmitter which give rise to min.e.p.p.s.

Acetylcholine↗
PubMed1971

Tetanic and post-tetanic rise in frequency of miniature end-plate potentials in low-calcium solutions.

1. Miniature end-plate potentials (min.e.p.p.s) were recorded intracellularly from frog neuromuscular junctions.2. The ;phasic' release of transmitter which is directly related to nerve impulses was suppressed by withdrawal of Ca from the external medium plus addition of Mg.3. Under these conditions, min.e.p.p.s continued to be discharged even when EGTA was added, although in this case min.e.p.p. frequency appeared to decrease to about half the rate in normal Ringer.4. Tetanic stimulation of the nerve approximately doubled the rate of min.e.p.p.s even in Ca-free solutions with EGTA added.5. The tetanic increase in frequency was greater without EGTA and greater still with some Ca added. Therefore, it is concluded that the tetanic rise in min.e.p.p. frequency can occur even in the absence of the immediate ;phasic' release of transmitter normally induced by nerve impulses; and that the magnitude of the increase is related to Ca concentration.A possible relation between ;phasic' and ;residual' effects of nerve impulses is described.

Animals↗
PubMed1971

Effects of calcium and magnesium on the frequency of miniature end-plate potentials during prolonged tetanization.

1. End-plate potentials (e.p.p.s) and miniature end-plate potentials (min.e.p.p.s) were recorded intracellularly from the cutaneous pectoris nerve-muscle preparation of the frog during prolonged stimulation at low frequencies (5/sec-50/sec).2. When Ca was present in the bathing solution, the quantum content of the e.p.p. and the frequency of occurrence of the min.e.p.p.s gradually increased during the period of stimulation. During the first few minutes of stimulation, the min.e.p.p. frequency increased linearly with time, and the rate of increase was dependent on the Ca concentration of the bathing solution. However, Mg had no effect on this Ca-dependent increase in min.e.p.p. frequency.3. A large maintained increase in min.e.p.p. frequency also occurred during prolonged stimulation in solutions that contained no added Ca and 1-2 mM-EGTA. Under these conditions the increase in min.e.p.p. frequency was dependent on the Mg concentration of the bathing solution and was exponential in time.4. It is suggested that the rise in min.e.p.p. frequency is caused by an accumulation of Ca or Mg ions in the nerve terminal, and it is suggested that these ions enter the terminal at relatively non-specific sites distinct from the Ca-specific sites that trigger the ;phasic' release of transmitter.

Animals↗
PubMed1974

The intervals between miniature end-plate potentials in the frog are unlikely to be independently or exponentially distributed.

1. It has been suggested that spontaneous quantal release of transmitter at the neuromuscular junction is a Poisson process. One logical argument against accepting the Poisson hypothesis is that so far relatively few intervals between miniature end-plate potentials (min.e.p.p.s) have been studied in any single experiment. Release is known to occur from many sites on the nerve terminal, so many intervals must be studied before drawing any conclusions about the timing of release from the individual sites. Moreover, the statistical methods that have been used are relatively insensitive to deviations from Poisson predictions.2. The Poisson hypothesis is evaluated with respect to three major criteria:(a) The fit to the exponential distribution is analysed by five goodness of fit tests which were applied to eleven sets of data, showing that it is unlikely that the data sets were generated by an exponential distribution.(b) The independence of intervals is assessed in two ways. First, the autocorrelogram of intervals is constructed. This shows an excess of significant positive correlations beyond the 5% limits of the Poisson expectation. Secondly, the unsmoothed power spectrum is calculated, and compared to the Poisson prediction by means of the modified mean test. Again, most sets deviate significantly from the Poisson expectation. It is unlikely that the intervals are independent.(c) The possibility of simultaneous occurrences is evaluated by construction of the amplitude histogram of min.e.p.p.s. In all sets the Poisson prediction for the frequency of multiples of the unit height was exceeded by the empirical data sets. The over-all conclusion is that the process which generates spontaneous releases is unlikely to be Poisson.

Journal Article↗
PubMed1976

Sub-miniature end-plate potentials at untreated frog neuromuscular junctions.

1. Some properties of unusually small spontaneous miniature end-plate potentials (sub-min.e.p.p.s) at untreated end-plates of adult frogs have been examined. 2. These small potentials, which show a fast time course, add a highly skewed component to the normal Gaussian distribution of min.e.p.p. amplitudes. 3. Sub-min.e.p.p.s were not evoked by single nerve stimuli, though their frequency could be raised by tetanic nerve stimulation. 4. When min.e.p.p. rate was raised by addition of lanthanum, submin.e.p.p. frequency was also increased, though by a smaller factor than normal min.e.p.p.s. In contrast, sub-min.e.p.p. frequency was unchanged when min.e.p.p. rates were raised by either ethanol or hypertonic solutions.

Action Potentials↗
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↗
PubMed1977

On the effect of calcium on the frequency of miniature end-plate potentials at the frog neuromuscular junction.

1. The effect of the extracellular Ca concentration on the frequency of miniature end-plate potentials (min. e.p.p.s) at the frog neuromuscular junction was studied. 2. In saline containing elevated K (5 or 11 mM), the frequency of min. e.p.p.s increased as Ca concentration was increased from 0-1 to 1-3 mM. However, with further increases of Ca concentration up to 10 mM, min. E.P.P. frequency declined. 3. In saline containing the normal concentration of K (2 mM), increasing Ca concentration from 0-1 to 10 mM produced a slight, monotonic increase in min. e.p.p. frequency. 4. The non-monotonic effect of Ca on min. e.p.p. frequency in preparations depolarized by elevated K is consistent with the existence of two opposing effects of Ca on transmitter release. Firstly, raising the external concentration of Ca increases the electrochemical potential for Ca entry, which tends to increase Ca influx and transmitter release. Secondly, increasing external Ca concentration increases electrostatic screening of fixed negative charges on the outer surface of the nerve terminal membrane. Such an increase in screening of charges near voltage-sensitive Ca gates would produce a hyperpolarization across the gates and they would tend to close, an effect which would tend to decrease Ca influx. The monotonic increase in min. e.p.p. frequency with increasing Ca concentration in 2 mM-K is consistent with the voltage insensitivity of the Ca gates at potentials close to the normal resting potential.

Animals↗
PubMed1978

The role of calcium ions in tetanic and post-tetanic increase of miniature end-plate potential frequency.

1. The role of Ca ions in transmitter release changes, during and after high frequency stimulation of the motor nerve (10--100 Hz), was examined at the frog neuromuscular junction. 2. The stimulation-induced changes in miniature end-plate potential frequency (f) resembled the changes in end-plate potential amplitude recently described by Magleby and Zengel (1975, 1976). 3. The effects of tetanic stimulation on f under inward electrochemical gradient for Ca ions were compared with those under reversed gradient and four differences were found: (a) The increase in f during the tetanus under reversed Ca gradient conditions is much smaller than with an inward Ca gradient. (b) The increase in f under reversed Ca gradient is preceded by a small decrease in f, whereas with an inward Ca gradient an immediate increase in f is observed. (c) After the termination of the tetanus with a reversed Ca gradient, there is a further increase in f, compared to a decrease with an inward Ca gradient. (d) The augmentation phase of post-tetanic potentiation was practically abolished. 4. The experimental results are explained by assuming that high frequency nerve stimulation causes an increase in transmitter release by at least two distinct processes: influx of Ca ions through the presynaptic membrane and release of Ca ions from intracellular stores. It is suggested that Na ions couple nerve activity to intracellular release of Ca.

Action Potentials↗
PubMed1980

A study of tetanic and post-tetanic potentiation of miniature end-plate potentials at the frog neuromuscular junction.

1. The involvement of calcium sodium, potassium and magnesium in tetanic and post-tetanic potentiation of miniature end-plate potential frequency was examined at the frog neuromuscular junction using conventional electrophysiological techniques. 2. Tetanic potentiation is larger in calcium containing solutions, than in solutions which generate reversed electrochemical gradient for calcium during nerve activity. 3. Tetanic potentiation increases with stimulation frequency and duration, under both inward and reversed electrochemical gradient for calcium conditions. This indicates that factors, other than calcium entry, participate in tetanic potentiation. 4. Addition of the potassium conductance blocking agent, 3-aminopyridine (5 mM), increases tetanic potentiation in calcium containing media, while depressing it under reversed calcium gradient. 5. Electronic depolarization of the nerve terminal in tetrodotoxin-containing Ringer solution, produces tetanic potentiation under inward gradient, but fails to do so under reversed gradient. This indicates that the entry of sodium ions participates in the generation of tetanic potentiation. 6. Addition of magnesium ions suppresses tetanic potentiation in calcium containing solution, but increases tetanic potentiation under reversed gradient. 7. The results are explained by the hypothesis that calcium entry and intracellular calcium translocation participate in the generation of tetanic potentiation. 8. Both the fast and the slow components (augmentation and potentiation respectively) of post-tetanic potentiation increase in duration, with increase in the tetanic stimulation rate. 9. The decay of post-tetanic potentiation increases: when [Ca]o is elevated by ionophoretic application during the decay phase only, when ouabain is present in the medium or when [Mg]o is elevated. These finding suggest that calcium, sodium and possibly magnesium take part in post-tetanic potentiation.

Animals↗
PubMed1982

Properties of miniature excitatory junctional currents at the locust nerve-muscle junction.

1. Miniature excitatory junctional currents (m.e.j.c.s) were examined in conditions where inward current was carried mainly by Na(+) (i.e. in normal medium, Ca(2+)-free medium and Cl(-)-free medium). M.e.j.c.s were also examined in isotonic Ca(2+) where the inward post-synaptic current was carried mainly by Ca(2+).2. In normal medium, mean m.e.j.c. amplitude = 2.34+/-0.05 nA. The decay time constant of m.e.j.c.s (excluding a small percentage with abnormal shapes) was tau(m.e.j.c.) = 2.62+/-0.11 msec (V(m) = -80 mV, T = 22 degrees C). Decay-time was not markedly changed in Ca(2+)-free or Cl(-)-free medium. tau(m.e.j.c.) approaches the life-time of glutamate activated junctional channels.3. Excitatory junctional currents, evoked by nerve impulses, decayed slightly faster than m.e.j.c.s obtained in the same fibres. Extracellularly recorded m.e.j.c.s and voltage-clamped m.e.j.c.s were similar in time course.4. tau(m.e.j.c.) decreased exponentially with membrane hyperpolarization. An e-fold change was produced by 182.+/-24.8 mV change in V(m).5. The dependence of mean m.e.j.c. amplitude on clamp potential showed a slight non-linearity at hyperpolarized levels. The equilibrium potential for transmitter action was close to 0 mV in normal solution as well as in Ca(2+)-free and Cl(-)-free solutions.6. The kinetics of junctional channels are altered in isotonic Ca(2+). M.e.j.c. amplitude was reduced to about one-third normal size; mean m.e.j.c. = 0.74+/-0.03 nA. The decay time becomes markedly briefer, tau(m.e.j.c.) = 1.01+/-0.08 msec, indicating a reduction in mean channel life-time (V(m) = -80 mV, T = 22 degrees C).7. A population of slow time course and composite m.e.j.c.s appear when muscle fibres are hyperpolarized in isotonic Ca(2+), thus producing a prolongation in mean tau(m.e.j.c.). This results from an influence of post-synaptic membrane potential on presynaptic transmitter release. If such m.e.j.c.s are ignored the voltage dependence of tau(m.e.j.c.) of the remaining events is abolished or even reversed indicating that voltage sensitivity of channel life-time is altered in isotonic Ca(2+). The equilibrium potential for transmitter action may be slightly more positive than normal.8. We estimate that a single packet of neurally released transmitter normally opens, on average, 250 ion channels at these junctions.

Animals↗
PubMed1984

Bimodal miniature and evoked end-plate potentials in adult mouse neuromuscular junctions.

Intracellular recordings of spontaneous miniature end-plate potentials (m.e.p.p.s) in muscles from adult CBF-1 mice revealed a population of muscle fibres in which the amplitude distribution of m.e.p.p.s was bimodal. The large mode m.e.p.p.s were similar to those from fibres having unimodal amplitude distributions and the small mode m.e.p.p.s were about one-half to one-quarter the amplitude of the large mode. In five diverse muscle groups (extensor digitorum communis, gluteus maximus, diaphragm, extensor digitorum longus, and soleus) from mice 10-12 or 31 months of age, bimodal m.e.p.p. amplitude distributions were present in about 20% of fibres sampled. In the common bimodal distribution (type 1), the rise times of small mode m.e.p.p.s were similar to those of large mode m.e.p.p.s. A rare class of small mode m.e.p.p.s (type 2) having long rise times was also observed. Amplitudes and half-decay times of type 1 small mode m.e.p.p.s increased in the presence of an anticholinesterase (edrophonium). Increasing extracellular potassium concentration led to an increase in large mode m.e.p.p. frequency but had more variable effects on small mode frequency. In the few cases available for study, type 2 small mode m.e.p.p.s disappeared after addition of edrophonium or increased potassium. When the extracellular calcium/magnesium ratio was reduced, large mode but not small mode m.e.p.p. frequency decreased. In almost all muscle fibres in which end-plate potentials (e.p.p.s) were evoked by nerve stimulation at 20 Hz in low calcium/high magnesium solution, small mode e.p.p.s similar to small mode m.e.p.p.s appeared during 'failures' of large mode m.e.p.p.s. Also, in twelve out of fifteen fibres which had unimodal m.e.p.p. amplitude distributions, small mode e.p.p.s appeared which were similar in amplitude to small mode m.e.p.p.s in fibres with type 1 bimodal m.e.p.p.s. Thus, if both spontaneous and evoked potentials are included, small mode m.e.p.p.s are present at most CBF-1 mouse adult neuromuscular junctions independent of muscle type or animal age. Small and large mode m.e.p.p.s differ in certain responses but both are evoked by nerve stimulation at physiological frequencies and therefore participate in normal neuromuscular synaptic activity. The possible origin of small mode m.e.p.p.s is discussed.

Aging↗
PubMed1984

Changes in miniature end-plate potentials after brief nervous stimulation at the frog neuromuscular junction.

The amplitude of miniature end-plate potentials (m.e.p.p.s), recorded at the frog neuromuscular junction in a normal ionic environment and in absence of drugs, was examined following 10-450 nerve impulses using conventional electrophysiological techniques and on-line computational analysis. In both contracting preparations and non-contracting preparations pre-treated with glycerol, 100 or more nerve impulses resulted in a maximal fall in mean amplitude of about 20% with recovery apparent over the next 10-20 min. In an altered ionic environment with a lowered Ca and raised Mg concentration, 450 nerve impulses did not produce a decrease in mean amplitude but a similar reduction was seen following a larger number of impulses. The reduction in amplitude was estimated to follow the release of the order of 5000-10000 quanta at end-plates in a normal ionic environment and on average 17000 quanta in the presence of a lowered Ca and raised Mg concentration. Changes in the mean size of the spontaneous quantal response is considered to be a presynaptic event and to reflect the loss and slow recovery of larger packets of transmitter from a vesicular store that is readily released by nerve impulses.

Animals↗