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Biomedical subjects

G Farrell

Publications and source records attributed to G Farrell.

At least 37 records · Page 2Linked to original sources
PubMed1991

Isochronic mapping: a preliminary report of a new technique.

A new technique which we have named 'isochronic mapping' is described. The conventional technique of plotting isopotential maps shows little or no contrast for far-field potentials such as the auditory brainstem response (ABR). However, by modifications to the mapping software, the latency values of a peak can be plotted and lines of equal time or isochronic maps can be produced. Data from a normal subject has been obtained for both the compound and derived ABRs and are described in detail. The data are clear but the time delays between earliest and latest projections of a peak are hard to interpret. For monaural click stimulation, wave JV of the ABR projects first to the contralateral side of the head then moves towards the stimulated ear arriving some 0.3 ms later. Possible interpretations of this finding are discussed but further experimentation is needed to develop our understanding of these data.

Acoustic Stimulation↗
PubMed1989

Verification of a new test of endolymphatic hydrops.

A new objective test of endolymphatic hydrops has been described previously. The test uses auditory brain-stem response (ABR) techniques to estimate the basilar membrane travelling wave velocity (TWV). The underlying hypothesis is that raised pressure in the scala media will lead to an increase in the stiffness of the basilar membrane and that this will give rise to a travelling wave velocity that is greater than normal. It was considered that verification of the technique could be obtained by carrying out the new test before and during a glycerol dehydration procedure. Patients who required this procedure for verification of the diagnosis or as a prognostic indicator for sacculotomy, underwent the following tests. Prior to dehydration an audiogram, the ABR TWV test and a blood sample (for plasma osmolality) were taken. The patient was then given the appropriate amount of glycerol mixed with lemon juice and laid on a bed in a test room. The audiogram and a blood sample were repeated every hour and the ABR TWV test was repeatedly carried out every twenty minutes between the other tests. Six of these procedures have been carried out. In five of them the 0.5 and 1 kHz average threshold improved by at least 10dB and in all those cases the ABR TWV test showed an abnormal pre-dehydration result which moved towards the normal value following dehydration. One patient gave ABR TWV results that were within normal limits before and during the procedure and gave an audiometric change of only 5dB.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Clinical methods for the objective estimation of loudness discomfort level (LDL) using auditory brainstem responses in patients.

Our previous work showed that the slope of the JV latency/intensity function can be used to estimate the loudness discomfort level (LDL). In this study, the previous work was repeated using normal subjects and patients whose LDL was unknown at the time of test. The results showed that the original model still applied. Further measures were taken to evaluate clinical methods of applying this technique. Four basic approaches were used, a 'correction factor' model and a 'curve-fitting' model and these were applied to data obtained from measurements taken in both 5 dB and 10 dB increments. The results showed that the 'correction factor' models were better than the 'curve-fit' approach. The prediction of LDL based upon the 5 dB increment data gave the greater accuracy but the 10 dB increment data gave predictions that were sufficiently accurate for clinical use (95% confidence limits of +/- 8 dB). Thus this ABR estimator has wide application and good accuracy in estimating subjective LDL. A clinical protocol for applying this technique is described.

Adolescent↗
PubMed1988

Hepatic testosterone metabolism in male rats with portal bypass.

This study was performed to ascertain whether testosterone metabolism is altered in male rats with portal bypass, and whether such changes could contribute to the reduction in serum testosterone concentration and raised serum estrogen levels that are observed in this situation. The metabolic clearance rate of testosterone was determined by a prime-dose constant-infusion technique in male rats subjected to complete portal vein ligation and in sham-operated controls. Testosterone clearance was similar in rats with portal vein ligation and control rats (9.01 +/- 2.29 and 8.26 +/- 2.83 ml/min, respectively) but the clearance per gram of liver was greater in rats with portal vein ligation than in controls (1.18 +/- 0.18 versus 0.68 +/- 0.24 ml/min.g liver, p less than 0.0001). After 180 min of [3H]testosterone infusion, [3H]estradiol comprised 1.2% of plasma total radioactivity in male controls but was increased to 11% in rats with portal vein ligation (p less than 0.005). Similarly, biliary excretion of [3H]estradiol was eightfold greater in male rats with portal vein ligation compared with controls (p less than 0.001). In control male rats, the major metabolites of testosterone present in bile were 2 alpha-hydroxytestosterone, 16 alpha-hydroxytestosterone, and 7 alpha-hydroxytestosterone. Portal bypass was associated with reduced biliary excretion of 2 alpha-hydroxytestosterone and 16 alpha-hydroxytestosterone to approximately 50% of control, but there was no change in the excretion of 7 alpha-hydroxytestosterone. Conversely, portal bypass was associated with increased formation of dihydrotestosterone, indicating stimulated activity of testosterone 5 alpha-reductase. It is concluded that portal bypass in male rats is associated with altered pathways of testosterone metabolism and, in particular, with increased aromatization of testosterone to estradiol. The site of such estradiol formation has not been determined by this in vivo study. However, selective changes occurred in the regiospecific and stereospecific hydroxylation pathways of testosterone and in 5 alpha-reductase activity after portal bypass in male rats. It is concluded that portal bypass, in the absence of parenchymal liver damage, results in demasculinization and feminization of C19 steroid metabolism in the male rat liver. These metabolic changes could be revelant to the pathogenesis of changes in sexual characteristics in cirrhosis.

Animals↗
PubMed1987

The objective estimation of loudness discomfort level using auditory brainstem evoked responses.

The loudness discomfort level (LDL) is of importance in the fitting of hearing aids, but very young children are unable to provide a subjective judgement of LDL. Therefore the relationship between Jewett wave V latency and subjective loudness was investigated to ascertain if objective estimation of LDL is possible. ABR recordings were taken from 8 normally hearing subjects at the stimulus intensity corresponding to their LDL and at stimulus levels from 10 to 30 dB below this. The wave V latency/intensity function did not correlate well with the LDL. However, the slope of this function did correlate to a high degree and a predictive model of LDL was derived. Identical measurements were then taken from a sample of 12 cochlear-impaired subjects with a range of audiometric profiles. Their subjective LDLs could be predicted from the wave V latency function to an accuracy of +/- 5 dB, using the model derived from the normally-hearing subjects. This model appeared to be equally valid for all the degrees and profiles of hearing loss included in the sample and showed a closer relationship to LDL than did absolute wave V latency or estimates derived from the acoustic reflex.

Adult↗
PubMed1986

Myocutaneous fenestration in sleep apnea patients.

We present a patient with severe obstructive sleep apnea syndrome (OSAS), including O2 desaturations to 11%, who was successfully managed with myocutaneous fenestration tracheostomy. The myocutaneous fenestration technique employs bilateral horizontal skin-platysma advancement flaps sutured directly to a tracheal fenestra created between rings two to four. It conforms ideally to the unique physical and psychological demands of the sleep apnea patient. Rapid healing time and minimal granulation tissue, combined with a permanently functional, yet reversible and minimally disfigurative stoma, highlight the advantages of the technique over standard tracheostomy. The myocutaneous fenestration tracheostomy is uniquely applicable to the surgical treatment of patients with moderate to severe obstructive sleep apnea.

Humans↗
PubMed1985

Halothane hepatitis. Detection of a constitutional susceptibility factor.

We studied susceptibility to halothane hepatitis with an in vitro test that detects cell damage from electrophilic drug intermediates. Metabolites of phenytoin were generated by incubation of phenytoin with rat hepatic microsomes in the presence of the epoxide hydrolase inhibitor 1,1,1-trichloropropene oxide (TCPO), which prevents the further metabolism of phenytoin to an inert metabolite. In lymphocytes exposed to this system, cytotoxicity was measured by trypan blue dye exclusion and was expressed as the percentage increase in trypan blue-positive cells after the addition of TCPO. In the presence of TCPO, lymphocytes from 11 patients with halothane hepatitis exhibited an increase in cytotoxicity at 0.06 mM phenytoin that was eight times greater than the increase in healthy controls (54 +/- 10 per cent [mean +/- S.E.M.] vs. 7.1 +/- 2.2 per cent, P less than 0.0001). Patients with other liver diseases and persons recently exposed to halothane without adverse effects did not differ from healthy controls. In three patients with halothane hepatitis who were studied serially, the lymphocyte abnormality was still present after 13 months. Family studies revealed abnormal results on 10 cytotoxicity tests among 19 members of four families. We propose that there is a familial, constitutional susceptibility factor that predisposes persons to halothane hepatitis.

Adult↗
PubMed1984

Visual evoked response changes following intrathecal injection of water-soluble contrast media: a possible method of assessing neurotoxicity and a comparison of metrizamide and iopamidol.

An investigation was carried out to ascertain if there was a change in visual evoked responses following the intrathecal injection of water-soluble contrast media for myeloradiculography and if this change provided an indication of neurotoxicity as assessed by the onset of headache during a period of 20 h following the radiological examination. The patients were unselected and examined, when facilities for measuring the visual evoked response were available, immediately before and at 1 and 20 h after the examination. Control readings were carried out before, 1 h and 20 h after lumbar puncture in patients who did not have an injection of contrast medium. The first 25 patients in the series received metrizamide; when iopamidol became available a change to the newer medium was made and iopamidol was used on all subsequent patients. All the injections were carried out by the same radiologist and the patients were kept in hospital overnight and interviewed the next morning, avoiding a specific reference to headache unless the patient denied all symptoms. It was found that the latency of the visual evoked response was affected in some cases by the presence of contrast medium in the cerebrospinal fluid and that there was a correlation between the severity of headaches and the delay in the visual evoked response at the 20 h post-myelogram measurement, but not at 1 h after the examination. It would appear, therefore, that the visual evoked response measurement is a valid method of assessing, in the short term, the neurotoxicity of intrathecal water-soluble contrast media and that, on this evidence, iopamidol is less neurotoxic than metrizamide. We are not aware of any long-term complications resulting from the use of either contrast medium.

Contrast Media↗
PubMed1983

[5 years' experience with revascularization of the corpus cavernosum by a new microsurgical technic in the treatment of vascular sexual impotence].

Treatment of 138 patients with sexual impotence of vascular origin involved revascularization of the dorsal and/or cavernous arteries of the penis by means of a venous auto or homograft branched on the external iliac or femoral arteries. Arteries requiring revascularization can be clearly detected by peroperative arteriography. Two or three shunts are usually necessary. The branches of the venous graft are firstly anastomosed microsurgically (under a 25 to 30 magnification) to the dorsal and/or cavernous arteries of the penis after their microsurgical dissection. The origin of the graft is then joined to the femoral or terminal iliac arteries. Results were generally excellent and there were very few complications: thrombosis during the first 30 postoperative days in 9 cases, hemorrhage in only one case during the last 3 years, frequent but rapidly regressing edema of the foreskin, and obturation of the shunt after the first month (between the 6th and 32nd months) in 4 patients. Postoperative priapism was never noted. This technique, in contrast to that employing direct implantation of the epigastric arteries into the corpus cavernosum, ensures the return of normal physiological erections. Follow-up after a minimum of 6 months showed that recovery was total in 78.6%, the condition being made worse in only 8.8%.

Angiography↗
PubMed1980

Toilet hygiene: clean round the bend.

Toilet cleaning is now so complex, writes Geoff Farrell, that it seems a graduate in chemistry and biology is the only person likely to make an efficient toilet cleaner. Mr. Farrell stresses the need to get in to all the nooks and crannies and discusses the dangers of mixing cleaning compounds as though you were pouring a Bacardi and Coke.

Housekeeping, Hospital↗
PubMed1979

Symptomatic lower esophageal ring: treatment of 24 patients.

The lower esophageal ring, or Schatzki's ring, consists of a thin, submucosal, circumferential scar which forms a thin incomplete diaphragm in the lower esophageal lumen. The symptoms may be either episodic aphagia or progressive dysphagia, and the severity of symptoms is related to the diameter of the ring. Between 1970 and 1978, we saw 24 patients with lower esophageal rings and complaints of episodic aphagia or progressive dysphagia. Symptoms of esophagitis were present in 20 of the 24. Twenty were treated surgically by interrupting the rings and repairing the sliding hiatal hernias. Two were treated by dilatation and two received no treatment to the ring. Hiatal hernias have recurred in two patients. In one, there is a recurrent ring and in the other, an acid peptic stricture. The ring has responded to dilatation and the peptic stricture to dilatation and repair of the recurrent hernia. Two patients without symptoms of esophagitis, treated by dilatation, are doing well but the follow-up period is so far too short to draw any conclusion.

Aged↗
PubMed1978

Response bias in category and magnitude estimation of difference and similarity for loudness and pitch.

Interval scales of sensory magnitude were derived from magnitude and category estimates of loudness differences, loudness similarities, pitch differences, and pitch similarities. In each of the four loudness experiments, a loudness scale was constructed from a nonmetric analysis of the rank order of the judgments. The four loudness scales so constructed were found to be equivalent to one another and indicated that loudness was a power function of sound pressure with an exponent of .29. A similar analysis for the four pitch experiments found the pitch scales derived in each case to be equivalent to one another and linear with the mel scale of pitch. Thus the same sensory and similarities for two distinct perceptual continua. For both pitch and loudness, these sensory scales were used to generate scales of sensory differences. A comparison of the category and magnitude estimates of sensory differences with the scale of sensory differences derived from the nonmetric analyses indicated the presence of significant response biases in both category and magnitude estimation procedures.

Acoustic Stimulation↗