Biomedical subjects

W H Martin

Publications and source records attributed to W H Martin.

At least 37 records · Page 2Linked to original sources

PubMed1998

Fluorine-18-fluorodeoxyglucose cardiac imaging using a modified scintillation camera.

Conventional 201TI and hexakis 2-methoxy-2-isobutyl isonitrile studies are less accurate as compared to FDG PET in the prediction of functional recovery after revascularization in patients with injured but viable myocardium. The introduction of a dual-head variable-angle-geometry scintillation camera equipped with thicker crystals (5/8 in.) and high-resolution, ultrahigh-energy collimators capable of 511 keV imaging has permitted FDG SPECT to provide information equivalent to that of PET for the detection of injured but viable myocardium in patients with chronic ischemic heart disease. The development of standardized glucose-loading protocols, including glucose-insulin-potassium infusion and the potential use of nicotinic acid derivatives, has simplified the method of obtaining consistently good-to-excellent quality FDG SPECT cardiac studies. FDG SPECT may become the modality of choice for evaluating injured but viable myocardium because of enhanced availability of FDG, logistics, patient convenience, accuracy and cost-effectiveness compared to PET.

Equipment Design↗

PubMed1997

A simplified intravenous glucose loading protocol for fluorine-18 fluorodeoxyglucose cardiac single-photon emission tomography.

The myocardial uptake of fluorine-18 fluorodeoxyglucose (FDG) has emerged as the most sensitive and specific technique for the assessment of myocardial viability. With the development of FDG single-photon emission tomography (SPET) and dual head coincidence imaging, a hindrance to the widespread clinical use of FDG cardiac imaging is the complexity of the preinjection glucose loading necessary for obtaining interpretable myocardial FDG scans. In a population of 209 patients undergoing dual-isotope single acquisition (DISA) FDG/sestamibi (MIBI) SPET, we describe the improvements in both image quality and time efficiency using a new short, simple glucose/insulin/potassium (GIK) infusion protocol prior to FDG injection as compared to a conventional oral glucose loading protocol. DISA FDG/MIBI SPET scans were performed in 111 nondiabetic patients after oral loading with 50 g of glucose (group 1). Ninety-eight consecutive nondiabetic patients were subsequently scanned following preparation with a fixed-concentration GIK infusion administered at a standardized rate (group 2). A three-point grading scale was used to assess image quality. The time to FDG injection following glucose administration was significantly shorter for the group 2 patients (39.9+/-15.6 min; range 20-105 min) than for the group 1 patients (99.5+/-30.3 min; range 56-270 min) (P<0.0001), representing a 1-h decrease in patient preparation time. More of the group 1 patients (n=30; 27%) required supplemental intravenous boluses of regular insulin than did the group 2 patients (n=13; 13%) (P<0.02). There were more excellent and good quality graded images using the GIK method (group 2) than the more traditional oral loading protocol (group 1) (P<0.02). Nine of 111 scans (8%) in group 1 were uninterpretable, whereas only one of 98 scans (1%) in group 2 was uninterpretable. Standardized infusion of a fixed concentration of GIK prior to FDG administration and continued during myocardial FDG uptake is an effective yet simple method of obtaining consistently good to excellent quality FDG SPET cardiac scans. It is preferable to conventional oral glucose loading due to decreased patient preparation time and improved image quality. The technique is safe and should improve both the clinical use and the cost-effectiveness of FDG SPET imaging for the identification of injured but viable myocardium.

Case-Control Studies↗

PubMed1997

Effect of endurance training on fatty acid metabolism during whole body exercise.

Endurance exercise training increases fat oxidation during large muscle mass exercise. Although the source of this fat has been thought to be plasma free fatty acids (FFA) released from adipose tissue, the training-induced decrease in lipolytic hormonal responses to exercise is not consistent with this concept. The purpose of this communication is to review findings, from our laboratory indicating that, in young healthy subjects, endurance exercise training reduces plasma FFA turnover and oxidation during moderate intensity prolonged 2-leg cycling while simultaneously enhancing depletion of triglycerides from the active musculature. Evidence is presented that metabolism of intramuscular triglycerides can explain the increase in total fat oxidation observed in the trained state during large muscle mass exercise. However, these results may not be applicable to exercise involving small muscle groups, a distinction that is likely to be important in explaining the apparent conflict between our findings and those from other laboratories where experimental conditions were different. In summary, for large muscle mass exercise up to 2 h in duration, plasma FFA are a less important fuel source in the trained state, and intramuscular triglycerides supply the major portion of the increase in oxidized fatty acids.

Adult↗

PubMed1997

ABR and DPOAE detection of cochlear damage by gentamicin.

Auditory brainstem responses (ABR) and distortion product otoacoustic emissions (DPOAE) have been applied to the evaluation of peripheral auditory function. To date, no comparison of their relative sensitivities to aminoglycoside toxicity has been reported. The purpose of this study was to compare click evoked ABR testing and 2f1-f2 DPOAEs as detectors of cochlear damage induced by gentamicin treatment in guinea-pigs. ABR thresholds to click stimuli were recorded. DPOAE amplitude input/output functions were recorded using three different primary tone level conditions. In one condition, L1 was changed relative to a fixed L2. In the next condition, L2 was changed relative to a fixed L1. In the third condition, L1 and L2 were both changed while maintaining a consistent L1-L2 difference. Baseline L1-L2 differences were determined by adjusting L2 to produce the maximum DPOAE amplitude in each ear of each subject. Guinea-pigs were treated for a four week period with intramuscular injections of gentamicin. ABRs and DPOAEs were monitored and compared to baseline recordings or untreated control groups. DPOAE testing detected cochlear damage earlier than ABR testing. Changes in DPOAE input/output functions were noted after two weeks of treatment while changes in ABR threshold were not identified until after three weeks of treatment. The sensitivity of the DPOAE testing was related to the stimulus conditions utilized. L1-L2 differences were determined in the control group and for the initial test session by fixing L1 at 75 dB SPL and lowering L2 until the maximum DPOAE amplitude was obtained for each ear. All subsequent testing was begun using the optimal L1-L2 difference for each ear. The stimulus condition in which only L1 was changed and L2 was fixed resulted in the least sensitive DPOAE indicator of cochlear damage. The condition in which both L1 and L2 were changed, but the L1-L2 difference remained constant, resulted in the most sensitive indicator of damage. The onset and degree of cochlear damage secondary to gentamicin treatment was subject dependent. This study demonstrates that 2f1-f2 DPOAE testing is preferable to click evoked ABR testing for early detection of gentamicin toxicity of the cochlea. It also indicates that DPOAE stimulus parameters must be considered when developing test protocols. Specifically, recording the DPOAE amplitude input/output function while maintaining an effective L1-L2 difference is preferable to changing either L1 or L2 individually.

Acoustic Stimulation↗

PubMed1997

Sestamibi parathyroid scanning and preoperative localization studies for patients with recurrent/persistent hyperparathyroidism or significant comorbid conditions: development of an optimal localization strategy.

For patients with previous thyroid or parathyroid surgery and for those with significant comorbid conditions, noninvasive and invasive modalities exist for the preoperative localization of pathologic parathyroid tissue. Formal localization at our institution involves obtaining two studies that are independently positive for the same location. The studies utilized have included ultrasound, CT scans, MRI, technetium-99m/thallium-201 (Tc-Tl) imaging, and more recently, (99m)Tc-sestamibi (20-25 mCi) (MIBI) scans. These were followed by arteriography and/or venous sampling if necessary. From January 1992 through October 1995, 25 patients underwent preoperative parathyroid localization (10 reoperation, 3 grave hypercalcemia, 2 concurrent goiter, 2 cerebral vascular accident, 1 bleeding disorder, and 1 malignant ventricular arrhythmia) and were evaluated prospectively during the changeover from Tc-Tl to MIBI scanning at our institution. A total of 92 studies were obtained. All 25 patients were operated on by a single surgeon, and in each case the parathyroid adenoma was successfully resected with minimal morbidity (1 permanent hypoparathyroid and 1 temporary recurrent laryngeal nerve injury). True positives interpreted preoperatively: MIBI, 14 of 19 (74%); CT scan, 13 of 19 (68%); Tc-Tl, 4 of 8 (50%), ultrasound, 9 of 20 (45%); MRI, 8 of 14 (57%); arteriography, 3 of 7 (43%); venous sampling, 3 of 4 (75%); and positron emission tomography, 0 of 1. There were no false-positive MIBI scans. These results suggest that when formal parathyroid localization is needed in reoperative/complicated patients, 1) MIBI appears to be the most sensitive and specific study, and 2) the MIBI scan should be the initial study in any situation in which preoperative localization is needed. Ultrasound can be useful for patients with significant comorbidities who have not been previously explored. CT or MRI should then be used if further evaluation is needed. If the use of these noninvasive modalities does not produce positive gland localization, selective venous sampling should be utilized as the definitive procedure.

Adenoma↗

PubMed1996

Evoked and spontaneous electromyography to evaluate lumbosacral pedicle screw placement.

STUDY DESIGN: A prospective study was performed to evaluate the effectiveness of evoked and spontaneous electromyography in predicting pedicle wall breakthrough and subsequent lumbar radiculopathy occurring after placement of pedicle screw instrumentation of the lumbar spine. OBJECTIVES: To correlate cortical breakthrough of the pedicle wall with an electrically evoked electromyography threshold of stimulation, to assess the sensitivity of mechanically evoked electromyography for nerve root irritation, and to correlate postoperative nerve root irritation with intraoperative findings. SUMMARY OF BACKGROUND DATA: Pedicle wall breakthrough has been evaluated by radiographic means and found to be difficult to evaluate. Methods to perform both electrically evoked and mechanically evoked electromyography have been developed more sensitive tests for breakthrough. METHODS: Twenty-five patients receiving 112 pedicle screws were evaluated. RESULTS: Cortical breakthrough was associated with electrically evoked electromyography threshold of less than 11 milliAmps. Not all screws that had broken through the pedicle wall caused a postoperative radiculopathy. Electromyographic activity was sensitive to nerve root stimulation. CONCLUSIONS: Measuring the electrically evoked electromyography threshold of stimulation helps to assess pedicle screw placement. Mechanically evoked electromyography indicates intraoperative nerve root displacement. Postoperative radiculopathy correlated with pedicle wall breakthrough, but did not occur in every case.

Adolescent↗

PubMed1996

Detection of malignancies with SPECT versus PET, with 2-[fluorine-18]fluoro-2-deoxy-D-glucose.

PURPOSE: To compare single photon emission computed tomography (SPECT) with 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) and positron emission tomography (PET) with FDG to evaluate malignancies. MATERIALS AND METHODS: PET and SPECT, with fluorine-18 sodium fluoride, were performed sequentially in a cylindric phantom that contained different size spheres with activity ratios of 5:1, 10:1, and 15:1. PET and SPECT were also performed in 24 patients with known or suspected malignancies. RESULTS: Sensitivities of PET and SPECT were 2,238 cpm/microCi (82.8 cpm/MBq) and 129 cpm/microCi (4.8 cpm/MBq), respectively (reconstructed spatial resolution, 7 and 17 mm, respectively [13-cm radius of rotation]). In the phantom studies, lesions of 1.5 and 1.3 cm or more in diameter were detected with a ratio of 5:1 and 10:1, respectively, and an information density of 150 counts per square centimeter. At FDG PET, 46 hypermetabolic lesions consistent with tumor were depicted in patients; at FDG SPECT, 36 (78%) were depicted. Sensitivity of FDG SPECT was 92% for detection of malignancies 1.8 cm or more in diameter seen at FDG PET. CONCLUSION: Findings at FDG SPECT can help differentiate benign from malignant lesions.

Adult↗

PubMed1996

Effects of acute and chronic exercise on fat metabolism.

Fatty acids are an important source of energy for skeletal muscle contraction, particularly during exercise of mild-moderate intensity, prolonged duration, and in the fasting state. Plasma FFA transported from remote adipose tissue stores and triglycerides contained within skeletal muscle fibers are the major sources of these fatty acids. The relative contribution of each source is dependent on the mode, intensity, and duration of exercise and on training status. Plasma FFA oxidation is directly related to the rate of lipolysis in adiopose tissue. The most potent stimulants of the latter are the catecholamines, but a lower plasma insulin concentration during exercise also plays a contributory role. In contrast, intramuscular triglyceride hydrolysis appears to be mediated entirely by beta 2-adrenergic stimulation. Endurance training substantially enhances fatty acid oxidative capacity in skeletal muscle and increases the proportion of energy derived from fatty acid oxidation during exercise. In addition, the sympathoadrenal response to exercise is markedly blunted in the trained state. Studies conducted in our laboratory indicate that plasma FFA and glycerol concentrations and whole body FFA uptake and oxidation are all decreased during moderate-intensity exercise at the same absolute work rate after physical conditioning, probably because of the reduction of sympathoadrenal activity. However, the lipolytic response to catecholamines also is enhanced in trained subjects. Perhaps as a consequence, the magnitude of the decrease in lipolysis and plasma FFA oxidation is less than the decrement in sympathoadrenal activity in the same individuals during exercise in the trained state. Other investigations were conducted in our laboratory to determine the source of the additional fatty acids oxidized in physically conditioned subjects. These studies demonstrated that during moderate-intensity exercise at the same absolute work rate, depletion of triglycerides from within skeletal muscle fibers was twice as great after, as opposed to, before training. Regardless of training status, intramuscular triglyceride use accounted for about 90% of the oxidized fatty acids that were not supplied from adipose tissue via the plasma. Intramuscular triglycerides were the source of virtually all of the additional fatty acids oxidized in the trained state. Both before and after physical conditioning they explained the discrepancy between the rates of plasma FFA and total fat oxidation during moderate-intensity exercise of up to 2 hr in duration.

Adaptation, Physiological↗

PubMed1996

Localizing retrocochlear hearing loss.

PURPOSE: The origin of acute/sudden hearing loss is multifactorial. The association of vestibular symptoms does not necessarily isolate the pathologic condition to the inner ear. The audiogram provides a screen for differentiating conductive from sensorineural loss but often fails to provide more localizing information. METHODS: Three unusual patients with a variety of retrocochlear presentations of hearing loss are presented. Along with conventional auditory brainstem response (ABR) testing, newer auditory tests, including otoacoustic emissions and three-dimensional ABR analysis, can facilitate site-of-lesion testing. Magnetic resonance imaging (MRI) also provides graphic documentation for sources of retrocochlear hearing loss. RESULTS: One patient had gamma-knife treatment of an arteriovenous malformation, incurring a localised lesion to the inferior colliculus contralateral to the side of hearing loss. This effectively eliminated wave V, as confirmed by three-dimensional ABR analysis. A second patient with human immunodeficiency virus developed sudden complete hearing loss with retained otoacoustic emissions, confirming a retrocochlear lesion. A third patient with acute otitis media with sudden hearing loss and vertigo had an abnormal ABR and "mass lesion" on MRI. Hearing subsequently returned to normal, as did a repeated scan. CONCLUSIONS: The unique aspects of each case of retrocochlear hearing loss and the applied auditory electrophysiologic tests are reviewed.

Adult↗

PubMed1995

Short latency visual evoked potentials to flashes from light-emitting diodes.

Short latency visual evoked potentials (SVEPs) have been described in response to high-intensity, strobe flashes. High-intensity flashes can now be generated from goggle-mounted light emitting diodes (LEDs) and the SVEPs to such flashes have been shown to be reproducible across subjects, avoiding photic spread to the examination room and acoustical artifacts from the strobe stimulator. In this study, SVEPs from multichannel records are described in terms of normative latencies and amplitudes, as well as scalp distributions, to explore their generators. Potentials were recorded from 10 young male subjects, from 16 scalp locations, in response to flashes from goggle-mounted LEDs. Flashes were presented to each eye in turn, as well as binocularly. The latencies, scalp distributions and intersubject variabilities of the LED evoked SVEPs were similar to those obtained with strobe flashes. SVEP components were divided into 3 groups, according to their latency and the electrodes at which they were recorded with the largest amplitudes: periocular (under 40 msec latency), fronto-central (40-55 msec) and parieto-occipital (55-80 msec latency). The scalp distributions observed in this study suggest subcortical generators along the visual pathway, beginning at the retina. The use of goggle-mounted LEDs should promote routine evaluation of the integrity of the visual pathway between retina and cortex using SVEPs.

Adult↗

PubMed1995

The origin of the human auditory brain-stem response wave II.

Auditory brain-stem responses (ABRs) were recorded from human subjects undergoing neurosurgical procedures which exposed the auditory nerve. Scalp recordings indicated that the latency of the negativity between waves I and II (In) and the latency of positive peak II (IIp) were shorter when the nerve was suspended in air than when the nerve was submerged in cerebrospinal fluid or saline, while earlier and later waves remained unaffected. These results could not be attributed to changes in stimulus or recording parameters or conduction velocity. Computational and somatosensory experimental evidence of stationary potentials generated by physical properties of the volume conductor, including changes in conductivity or geometry, are presented to develop a model of wave IIp generation. The results of this study suggest that wave IIp (and probably In) are manifestations of current flux asymmetries across conductivity boundaries created by the temporal bone-cerebrospinal fluid intradural space-brain-stem interfaces. The current flux asymmetries are generated as the propagating auditory nerve action potential crosses the conductivity boundaries. These results also indicate that the physical characteristics of the volume conductor and neural pathways must be considered when interpreting surface recorded evoked potentials.

Action Potentials↗

PubMed1995

Evaluation of myocardial ischemia using a rest metabolism/stress perfusion protocol with fluorine-18 deoxyglucose/technetium-99m MIBI and dual-isotope simultaneous-acquisition single-photon emission computed tomography.

OBJECTIVES: This study sought to develop a dual-isotope single-acquisition single-photon emission computed tomographic (SPECT) protocol using a multihead SPECT camera equipped with an ultra-high energy collimator to evaluate rest metabolism/stress perfusion simultaneously with fluorine-18 (F-18) deoxyglucose/technetium-99m (Tc-99m) 2-hexakis-2-methoxy-2-methylpropyl isonitrile (MIBI). BACKGROUND: The most accurate and logistic method of identifying injured but viable myocardium remains a diagnostic challenge. METHODS: Sixty-five patients were given 25 to 50 g of glucose and, after approximately 60 min, an injection of 370 MBq (10 mCi) of F-18 fluorodeoxyglucose. After a 35-min distribution phase, patients underwent exercise or pharmacologic stress followed by administration of 925 MBq (25 mCi) of Tc-99m MIBI. Five patients underwent F-18 fluorodeoxyglucose position emission tomography before dual-isotope SPECT: RESULTS: With a window of 20% for both photopeaks and a technetium-99m/fluorine-18 concentration of 3.2:1, the "spillover" from fluorine-18 into the technetium-99m window is < 6% of the total counts in the window in patients with a normal distribution of both radiopharmaceuticals. Phantom images clearly demonstrated cardiac defects measuring 2 x 1 and 2 x 0.5 cm. There was no significant difference in the images of the five patients who underwent both positron emission tomography and SPECT: Fifty-seven patients (mean [+/- SD] age 55 +/- 15 years, range 25 to 83; 38 men, 19 women) had satisfactory images and were included in the study. Twenty-one patients had normal study results; 15 had mismatched defects; 14 had matched defects; and 7 had both matched and mismatched defects. Twenty-three patients (mean age 54 +/- 6 years, range 30 to 83; 14 men, 9 women) underwent coronary angiography within 3 months of dual-isotope SPECT: There were seven normal studies, eight with mismatched defects, one with a matched defect and seven with matched and mismatched defects. When stenosis > 70% was used as the criterion for a diagnosis of coronary artery disease, dual-isotope SPECT had a sensitivity of 100%, specificity of 88%, positive predictive value of 93%, negative predictive value of 100% and an accuracy of 96%. CONCLUSIONS: Dual-isotope SPECT may provide an alternative, accurate, cost-effective method to nitrogen-13 ammonia/F-18 fluorodeoxyglucose positron emission tomography or thallium-201 reinjection for identifying injured or dysfunctional but viable myocardium.

Coronary Angiography↗

PubMed1995

Rest myocardial perfusion/metabolism imaging using simultaneous dual-isotope acquisition SPECT with technetium-99m-MIBI/fluorine-18-FDG.

UNLABELLED: The purpose of this study was to develop a dual-isotope simultaneous acquisition (DISA) protocol using a multihead SPECT camera equipped with an ultrahigh-energy (UHE) collimator to evaluate simultaneously rest cardiac perfusion and metabolism with 99mTc-MIBI/18FDG. METHODS: Physical measurements were first performed with phantoms to develop the acquisition protocol. Fifteen patients underwent DISA-SPECT with 99mTc-MIBI/18FDG to validate the protocol. To evaluate the quality of the 99mTc-MIBI images acquired with the UHE collimator, four patients underwent a resting 99mTc-MIBI scan acquired with a high-resolution, low-energy collimator prior to DISA-SPECT. RESULTS: With a window of 20% for both photopeaks and a 99mTc/18F concentration ratio of 3.2:1, the spillover from 18F into the 99mTc window is 6% of the counts in the window for normal subjects. Phantom images clearly demonstrated defects measuring 2 x 1 and 2 x 0.5 cm. Technetium-99m-MIBI images obtained with the UHE and high-resolution collimators provided similar diagnostic information. Using a stenosis of > 70% as criteria to diagnose coronary artery disease, DISA-SPECT had a sensitivity of 100% and a positive predictive value of 93%. CONCLUSION: Simultaneous evaluation of rest myocardial perfusion/metabolism with a multihead SPECT camera equipped with an UHE collimator is possible using 99mTc-MIBI/18FDG with a dual-isotope simultaneous acquisition protocol.

Deoxyglucose↗

PubMed1995

FDG-SPECT: correlation with FDG-PET.

UNLABELLED: The clinical utility of FDG-PET imaging in the evaluation of patients with cardiac, oncologic and neurologic diseases is well documented. The major disadvantages of PET continue to be its high cost and limited availability. METHODS: With the goal of providing equivalent diagnostic information using a widely available, less expensive modality, we evaluated the clinical utility of FDG-SPECT imaging with a conventional dual-headed camera as compared to PET in 21 patients. RESULTS: To compare the image quality of the two modalities, major physical parameters and phantom determinations were obtained. By using the 511-keV collimators, we achieved resolution and system volume sensitivity that were less than those for PET by factors of 2.6 and 8, respectively. The SPECT system, on the other hand, could easily resolve 2 x 0.5-cm cold defects in the heart phantom and 2-cm hot lesions in a 22-cm cylindrical phantom with a target-to-background ratio of 5:1. FDG-SPECT imaging of nine patients with heart disease yielded similar diagnostic information of the amount of viable myocardium present when compared to PET. In seven of eight patients, malignant tissue visualized with FDG-PET was seen equally well with SPECT. The lesions not visualized with FDG-SPECT were either small (< or = 1.5 cm) or benign. SPECT imaging of four patients with cerebral lesions was inconclusive due to the small sample size but seemed promising. CONCLUSION: FDG-SPECT with 511-keV collimation is less expensive, more available and technically simpler than PET. We believe that FDG-SPECT has achieved sufficient sensitivity and resolution to detect myocardial viability and diagnose malignant tumors > or = 2 cm in diameter.

Adult↗

PubMed1994

Comparative aspects of Na+/K+ pump-mediated uncoupled Na+ efflux in red blood cells and kidney proteoliposomes.

Ouabain-sensitive uncoupled Na+ efflux has been studied in human, pig, and rat red cells and in vesicles containing reconstituted kidney Na+/K+ pumps obtained from these same species. The red cells from the different species gave qualitatively similar results; the uncoupled Na+ efflux was 15-30% of the Na+/K+ exchange rate, and this flux was inhibited at 5 mM extracellular Na+ (Na+o). At higher levels of Na+o there was a monotonic increase in the Na+ efflux. As has previously been observed in human red cells, the uncoupled efflux from pig red cells consists of Na+ and anion cotransport, suggesting that anion cotransport may be a general characteristic of uncoupled Na+ efflux in red cells. The uncoupled Na+ efflux carried out by pig and rat kidney Na+/K+ pumps differs from the red cell activity in that it represents no more than 2-4% of the Na+/K+ exchange rate and that 5 mM Na+o does not inhibit this efflux. Furthermore, the efflux does not appear to be dependent on anion cotransport. Vesicles containing human kidney Na+/K+ pumps differ from vesicles derived from pig or rat kidneys in that the Na+ efflux is not inhibited or stimulated by Na+ present on the opposite side; it thus appears that the Na+,K(+)-ATPase in these vesicles may be incapable of Na+/Na+ exchange. These results indicate that the ligand and kinetic properties of the uncoupled Na+ efflux mode of red cells are markedly different from kidney-derived Na+/K+ pumps reconstituted into proteoliposomes. The basis for these differences may be inherent in the Na+/K+ pumps themselves or represent differences between the two types of preparations studied.

Animals↗

PubMed1994

Brain-stem auditory evoked responses to hypercarbia in preterm infants.

To determine the effect of acute hypercarbia on brain-stem function in preterm neonates, we compared brain-stem auditory evoked responses (BAERs) during 8% CO2 breathing to those elicited during room air breathing in 12 healthy preterm infants during the first week of life. End-tidal CO2 (ETpCO2), respiratory rate and depth were monitored throughout the protocol. Absolute wave latencies and interpeak intervals of the BAERs were analyzed from duplicate trials. During 8% CO2 breathing, ETpCO2, respiratory rate and depth of respiration increased significantly (P < 0.05). The absolute latency of wave V was prolonged (P < 0.025) in the hypercarbic state as compared to baseline. Interpeak interval III-V was also prolonged (P < 0.025). Values of absolute peak latencies I and III were unaffected by the hypercarbic state. These data demonstrate that elevations in pCO2 which elicit ventilatory responses also effect the BAER. The specific effects on ventilatory pattern, peak V latency and interpeak interval III-V indicate brain-stem responsiveness and alterations in the more central components of the auditory pathway. These findings raise important considerations regarding the influence of hypercarbia on brain-stem function in preterm infants and the clinical management of such infants with abnormalities of gas exchange.

Administration, Inhalation↗

PubMed1994

A high-intensity, goggle-mounted flash stimulator for short-latency visual evoked potentials.

The few studies that have been done on short-latency, subcortical visual evoked potentials (SVEPs) have all used stroboscopic flashes as the evoking stimulus. The dimensions of the stimulator, the acoustical artifacts and the photic spread to the examination room limited the use of SVEPs to research laboratories. With the advent of high-efficiency light-emitting diodes (LEDs), high-intensity flashes can now be generated from goggle-mounted LEDs. In this study, a goggle-mounted high-intensity stimulator was constructed and its flashes used to evoke SVEPs. The reproducibility of SVEPs across subjects and the ease of using the high-intensity LED flash stimulator make them a promising candidate for testing subcortical visual pathway function in the operating room.

Cerebral Cortex↗

PubMed1994

3CLT ABR analyses in a human subject with unilateral extirpation of the inferior colliculus.

Reported are the results of analyses of three-channel Lissajous trajectories (3CLTs) of the auditory brain stem responses (ABRs) in a human subject in whom a focal lesion of the brain stem was caused by stereotactic radiosurgery, the 'gamma knife'. The surgery caused total destruction of the right inferior colliculus. The results, using multiple measures for defining ABR components, confirm findings from more conventional 2-channel recordings which, in turn, suggested the presence of an intact wave IV but a negligible, if not totally absent, wave V with stimulation of the left (contralateral) ear. The results thus support theories that wave V is generated by crossed pathways and that wave IV is an independent wave generated by the lateral lemniscus. Since magnetic resonance imaging suggested no destruction of tissue below the inferior colliculus, the findings also support theories of wave V generation at or rostral to the inferior colliculus. In practical terms, the results demonstrate the value of multichannel recordings of the ABR in component identification and in interpreting ABR abnormalities.

Adult↗