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Biomedical subjects

B Venkatesh

Publications and source records attributed to B Venkatesh.

At least 55 records · Page 3Linked to original sources
PubMed1999

Inter observer variability of the transcranial Doppler ultrasound technique: impact of lack of practice on the accuracy of measurement.

OBJECTIVE: Published data on the observer variability with the transcranial doppler (TCD) ultrasound are limited by the use of the product moment correlation coefficient. This study was designed to quantify the intra and inter observer variability with the TCD in terms of the intra class correlation coefficient (ICC) and to assess the impact of lack of practice on the observer variability and the accuracy of data generated. METHODS: The study was performed in two phases. In phase I, three observers insonated the middle cerebral artery in 10 healthy volunteers and measured peak systolic and end diastolic cerebral blood flow velocities. In phase II, the same observers repeated the experiment on five healthy volunteers after an eight week break during which none of the observers were allowed to use the TCD system. The observers were blinded to the measurements obtained. RESULTS: The ICC for peak velocity measurement was 0.9 (0.81-0.99) in phase I and 0.85 (0.66-1.00) in phase II (p < 0.05). The ICCs for end diastolic velocity measurements for phase I and II were 0.8 (0.64-0.96) and 0.67 (0.33-1.00) respectively (p < 0.01). CONCLUSIONS: A high level of observer agreement is possible with the TCD for measurement of cerebral blood flow velocities. Lack of regular practice with the system reduces the accuracy of measurements and impacts on both measured and calculated indices.

Adult↗
PubMed1999

Accuracy of pleural fluid pH and PCO2 measurement in a blood gas analyser. Analysis of bias and precision.

Pleural fluid pH measurements are used in the management of parapneumonic effusions. This study evaluated the accuracy of the pleural fluid pH and PCO2 measurement in a blood gas analyser (BGA) and the error induced by altering the aerobic environment and temperature of sample storage prior to analysis. The pH electrodes in a pH meter and a BGA were initially evaluated using aqueous reference solutions. The accuracy of pH and PCO2 electrodes was then assessed in pleural fluid tonometered to a known PCO2. The effects of aerobic compared to anaerobic storage and storage temperature, 0 degrees C vs 37 degrees C of pleural fluid were evaluated for errors in pH and PCO2 measurement. The BGA and the pH meter measured pleural pH with negligible bias and imprecision (0.01+/-0.01 pH units). The PCO2 measurement bias and imprecision of the BGA was small: 1.8+/-0.57 torr (0.2+/-0.08 kPa) at 2% CO2, 0.1+/-0.93 torr (-0.01+/-0.1 kPa) at 5% CO2 and -3.77+/-0.81 (-0.5+/-0.1 kPa) torr at 10% CO2 level. Aerobic storage resulted in a clinically important overestimation of pleural fluid pH by both the pH meter and the BGA of 0.14-0.16 pH units (p<0.05). No significant differences were detected when storage at 0 degrees C was compared to that at 37 degrees C. A BGA is reliable for pleural fluid pH measurements. Pleural fluid PCO2 measurements in a BGA have a concentration-dependent bias and imprecision. Anaerobic storage of specimens for pleural pH and PCO2 analysis is mandatory.

Biosensing Techniques↗
PubMed1999

Does splanchnic ischemia occur in isolated neurotrauma? A prospective observational study.

OBJECTIVE: To characterize the incidence and severity of splanchnic ischemia, as defined by gastric tonometry, in patients with isolated severe head injury and to examine the relationship between cerebral hemodynamics and splanchnic ischemia. DESIGN: Prospective observational study. SETTING: Neurosurgical intensive care unit in a tertiary referral center. PATIENTS: Ten patients with severe neurotrauma. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The mean arterial pressure, intracranial pressure, and gastric mucosal P(CO2) measurements were recorded at 15-min intervals. Intramucosal pH was calculated every 3 hrs. All patients received stress ulcer prophylaxis. Nine patients received noradrenaline infusions to maintain a target cerebral perfusion pressure of 70 mm Hg. The mean baseline gastric mucosal P(CO2) and intramucosal pH were 38+/-10 torr and 7.38+/-0.1 pH units, respectively. Nine patients manifested low intramucosal pH during the study period. Gastric mucosal P(CO2) values ranged from 36 to 132 torr. Intramucosal pH measurements ranged from 6.9 to 7.47. The mucosal gap ranged from -12 to +93 torr (mean +/- SD, 17+/-17 torr). The pH gap ranged from -0.1 to +0.54 pH units (mean +/- SD, 0.14+/-0.11 pH units). There was no statistically significant relationship between cerebral hemodynamics, the use of inotropes, and gastric mucosal P(CO2), or intramucosal pH. CONCLUSIONS: Splanchnic ischemia (intramucosal pH, <7.3) occurs commonly in isolated neurotrauma, with a statistically nonsignificant trend toward development of mucosal ischemia with decreased cerebral perfusion.

Acidosis↗
PubMed1999

Accuracy of intramucosal pH calculated from arterial bicarbonate and the Henderson-Hasselbalch equation: assessment using simulated ischemia.

OBJECTIVES: To determine the accuracy of intramucosal pH (pHi) calculated using arterial bicarbonate instead of mucosal capillary bicarbonate in the Henderson-Hasselbalch equation. DESIGN: Simulation of progressive ischemia in mucosal capillary blood. SETTING: University research laboratory. SUBJECTS: Normal human blood diluted with plasma. INTERVENTIONS: Three venous blood specimens were heparinized and diluted to a mean hemoglobin concentration of 5.0 (+/-0.9) g/dL by addition of plasma (2:1, vol:vol). Mucosal capillary aerobic flow stagnation was simulated by multiple exposures of each cooled specimen to a gas mixture containing 90% nitrogen and 10% CO2. When PCO2 measured at 37 degrees C (98.6 degrees F) was approximately 120 torr (16 kPa), the assigned anaerobic threshold, subsequent anaerobic flow stagnation was simulated by mixing the hypercapnic specimens in sealed syringes with five to six successive small aliquots (<100 microL) of lactic acid (10 g/L). MEASUREMENTS AND MAIN RESULTS: The relationship between Pco2 and pH in the specimens was compared with the relationship between the same PCO2 values and pHi calculated by substituting bicarbonate concentrations of 22 and 26 mmol/L in the Henderson-Hasselbalch equation. As PCO2 rose from 50 torr (8 kPa), conventionally calculated pHi increasingly underestimated simulated mucosal capillary pH, with bias >0.1 pH unit at the simulated anaerobic threshold of 120 torr (16 kPa). As PCO2 rose further the values converged, becoming equivalent at PCO2 approximately 150 torr (20 kPa). From PCO2 > or =200 torr (26.7 kPa), conventional pHi progressively overestimated simulated mucosal pH. The difference was >0.3 pH units at PCO2 = 250 torr (33.3 kPa). CONCLUSIONS: In the mucosal PCO2 range usually encountered clinically, the arterial bicarbonate substitution causes underestimation of mucosal capillary pH. With moderate mucosal capillary lactic acidosis the error becomes small, and in severe regional ischemia there is significant overestimation of mucosal capillary pH.

Anaerobic Threshold↗
PubMed1999

Continuous Intra-arterial Blood Gas Monitoring.

OBJECTIVE: To review the technology and the role of continuous intra-arterial blood gas monitoring in critical illness. DATA SOURCES: Articles and published peer review abstracts on continuous intra-arterial blood gas monitoring. SUMMARY OF REVIEW: The history of intermittent and continuous blood gas analysis and the development of technology of continuous blood gas monitoring are reviewed. A summary of the various clinical trials on the evaluation of continuous blood gas monitoring systems, and the various factors which might affect the performance characteristics in the clinical setting is also presented. The potential role and future applications of this technology in critical illness are described. CONCLUSIONS: Over the last 10 years, a number of continuous intra-arterial blood gas monitoring systems have been developed. Only a few have reached commercial availability. While the performance characteristics of these systems are comparable, the levels of accuracy of these systems obtained in vitro are not consistently obtained in clinical trials. Arterial blood flow, wrist movement, wall effect and variability of blood gas analysers are some of the factors which determine the accuracy and reproducibility of these systems. Evidence to support the clinical usefulness of these monitors exists only in the form of case studies. Controlled studies demonstrating an improvement in outcome with the use of these monitors are lacking.

Journal Article↗
PubMed1998

Genomic structure and sequence of the pufferfish (Fugu rubripes) gene encoding an actin-related protein.

Using a polymerase chain reaction (PCR)-generated gene fragment as a probe, we isolated and sequenced a gene encoding an actin-related protein belonging to the Arp3 family from the pufferfish, Fugu rubripes. The Fugu Arp3 gene spans 3.7kb from the transcription start site to the polyadenylation signal. This is the first report of the genomic sequence of a vertebrate Arp3 gene. The Fugu Arp3 gene consists of 12 exons and 11 introns compared to Drosophila homologue, which has six exons and five introns. The protein sequence encoded by the Fugu gene is 97% and 80% identical to bovine and Drosophila homologues, respectively. The Fugu Arp3 gene is expressed in a wide range of tissues, with higher levels detected in the gills, kidney, ovary, skin and testis. Three different size transcripts of the Arp3 gene (1.4kb, 1.8kb and 2.2kb) were identified in various tissues.

Actin-Related Protein 3↗
PubMed1998

Something fishy in the rat brain: molecular genetics of the hypothalamo-neurohypophysial system.

The brain peptides vasopressin and oxytocin play crucial roles in the regulation of salt and water balance. The genes encoding these neurohormones are regulated by cell-specific and physiological cues, but the molecular mechanisms remain obscure. New strategies, involving the introduction of rat transgenes into rats, are being used to address these issues, but the complexity of the rat genome has hampered progress. By contrast, the pufferfish, Fugu rubripes, has a "junk-free" genome. The oxytocin homologue from Fugu, isotocin, has been introduced into rats and is expressed in oxytocin neurons, where it is upregulated by physiological perturbations that upregulate the oxytocin gene. The Fugu and rat lineages separated 400 million years ago, yet the mechanisms that regulate the isotocin and oxytocin genes have been conserved. Fugu genome analysis and transgenesis in the physiologically tractable rat host are a powerful combination that will enable the identification of fundamental components of the neural systems that control homeostasis.

Animals↗
PubMed1998

Transfer and expression of a multiple antibiotic resistance plasmid in marine bacteria.

Conjugal transfer of a multiresistance plasmid from Pseudomonas fluorescens to halophilic and halotolerant bacteria was studied under in vitro and in situ conditions. Mating conducted in broth as well as on plates yielded a plasmid transfer frequency of as high as 10(-3). Among these two, plate mating facilitated conjugal transfer of plasmid, because the cell-to-cell contact is more in plate mating. When P. fluorescens was incubated in seawater, the organism progressively lost its colony forming activity within 15 days. Microscopic examination revealed the presence of very short rods, indicating that the cells have become viable but nonculturable (VNC). Mating conducted in natural seawater without any added nutrients revealed that the conjugal transfer is influenced by the physical state of the donor and the recipients as well as the availability of nutrients. But a plasmid transfer frequency of 10(-7) was obtained even after the donor cells have become VNC suggesting that the nonculturable state and nutrient deprived condition may not limit plasmid transfer. The results suggest that the terrestrial bacteria entering into the seawaters with antibiotic resistance plasmids may be responsible for the prevalence of resistance genes in the marine environment.

Anti-Bacterial Agents↗
PubMed1998

Validation of air as an equilibration medium in gastric tonometry: an in vitro evaluation of two techniques for measuring air PCO2.

This laboratory-based bench study was undertaken to evaluate the accuracy and equilibration characteristics of air and saline respectively as CO2 equilibrating media in the silicone balloon of a gastric tonometer and to compare two methods of measuring air PCO2. Two gastric tonometers were suspended in a bath containing 0.9% saline maintained at 37 degrees C. Certified calibration gases at three different CO2 concentrations were bubbled into the bath. When the bath PCO2 measurement was stable the tonometers were primed with 5 ml of air and 2.5 ml normal saline respectively and allowed to equilibrate for 30 and 90 minutes. Following equilibration, samples were aspirated and analysed in duplicate in a blood gas analyser. Bias and precision were calculated from the measured and expected PCO2 values. A consistent negative bias (21-23%) was seen with air at all three CO2 concentrations at 30 and 90 minutes with a coefficient of variation between 2.7 and 3.3%. Imprecise data were obtained with saline at different levels of CO2. A similar experimental set-up was used to compare air PCO2 measurement by a blood gas analyser and an infra-red analyser (Tonocap). Similar bias was obtained with the blood gas analyser with respect to air PCO2 measurement as in experiment 1. The infra-red analyser measurement was highly precise with negligible bias. Air appears to be a better CO2 equilibration medium during bench testing of tonometry producing a systematic negative offset and requiring a uniform correction factor of 1.25. This correction factor is independent of equilibration time and equilibrating CO2 concentration. The use of the infra-red analyser eliminates any bias in the measurement of air PCO2 and obviates the need for a correction factor.

Air↗
PubMed1998

Hepatic portal venous gas in a critically ill patient.

A case of hepatic portal venous gas following intestinal ileus in a critically ill patient in the intensive care unit, who went on to have a successful outcome, is described. Although hepatic portal venous gas (HPVG) is usually associated with an abdominal catastrophe and portends a poor clinical outcome, there are a number of benign causes of HPVG. The pathophysiological processes such as gut bacterial translocation and altered intestinal permeability that may occur as a paraphenomenon in the setting of HPVG are discussed.

Aged↗
PubMed1997

Transgenic rats reveal functional conservation of regulatory controls between the Fugu isotocin and rat oxytocin genes.

We have asked whether comparative genome analysis and rat transgenesis can be used to identify functional regulatory domains in the gene locus encoding the hypothalamic neuropeptides oxytocin (OT) and vasopressin. Isotocin (IT) and vasotocin (VT) are the teleost homologues of these genes. A contiguous stretch of 46 kb spanning the Fugu IT-VT locus has been sequenced, and nine putative genes were found. Unlike the OT and vasopressin genes, which are closely linked in the mammalian genome in a tail-to-tail orientation, Fugu IT and VT genes are linked head to tail and are separated by five genes. When a cosmid containing the Fugu IT-VT locus was introduced into the rat genome, we found that the Fugu IT gene was specifically expressed in rat hypothalamic oxytocinergic neurons and mimicked the response of the endogenous OT gene to an osmotic stimulus. These data show that cis-acting elements and trans-acting factors mediating the cell-specific and physiological regulation of the OT and IT genes are conserved between mammals and fish. The combination of Fugu genome analysis and transgenesis in a mammal is a powerful tool for identifying and analyzing conserved vertebrate regulatory elements.

Animals↗
PubMed1997

Carbon dioxide and oxygen partial pressure measurements in the cerebrospinal fluid in a conventional blood gas analyzer: analysis of bias and precision.

Cerebrospinal fluid (CSF) gas tension measurements have been used as a marker of cerebral oxygenation in animal models and in human studies. Discrepancies in the measurement of PCO2 and PO2 in non-blood solutions by standard blood gas analyzers have been described. The CSF is a physiological non-blood fluid with an ability to carry only dissolved O2 or CO2. The aim of this experiment was to determine the bias and precision of CSF pCO2 and pO2 measurements of a contemporary blood gas analyzer and a continuous gas sensor. CSF from human patients was tonometered to known PCO2 and PO2 using standard calibration gases in a bubble tonometer. Following equilibration, a continuous measurement of the partial pressure of gases in the CSF in the tonometer solution was made using a calibrated Paratrend 7 gas sensor (Biomedical Sensors, Bucks., UK) inserted into the equilibration chamber of the tonometer and continuous CSF pH, PCO2 and PO2 measurements recorded at 1-min intervals. After equilibration, a 3-ml CSF sample was aspirated anaerobically from the tonometer and analysed in duplicate using an ABL 620 (Radiometer, Copenhagen) blood gas analyser. The measured pCO2 and pO2 from the ABL 620 blood gas analyser and the Paratrend 7 sensor were paired with the expected values to calculate bias and precision. Small offsets in PCO2 and large offsets in PO2 measurement were seen with the ABL 620 blood gas analyser. This study brings into question clinical decisions based on CSF PO2 measurements. The implications for calibrating CSF sensors against CSF gas measurements are discussed.

Blood Gas Analysis↗
PubMed1997

Genomic structure and sequence of the pufferfish (Fugu rubripes) growth hormone-encoding gene: a comparative analysis of teleost growth hormone genes.

A nested polymerase chain reaction (PCR) technique for amplifying a fragment of the gene (GH) encoding teleost growth hormone has been developed. Using this technique, a fragment of the pufferfish, Fugu rubripes and Arothron maculatus, dwarf gourami, Colisa lalia; guppy, Poecilia reticulata; and goldfish, Carassius auratus GH genes were cloned. The Fugu rubripes (Fugu) gene fragment was used to isolate the GH gene from a Fugu genomic library. The complete nucleotide sequence of a 8.5-kb SacI genomic fragment containing the Fugu GH gene has been determined. The GH gene spans 2.5 kb from the first codon to polyadenylation signal, and contains six exons and five introns similar to the GH genes of salmonids, tilapia, barramundi, flounder and yellowtail. The GH introns contain microsatellite and satellite sequences. The microsatellites found in the fifth intron of the GH gene are also present in the corresponding introns of tilapia, barramundi and flounder GH genes. Southern analysis revealed that the GH gene is a single-copy gene in the Fugu. The promoter region of the Fugu GH gene contains conserved sequences that are likely to be involved in the pituitary-specific expression of the gene. A phylogenetic tree of nucleotide (nt) sequences of all known teleost GH genes has been inferred using the distance matrix method. The topology of this tree reflects the major phylogenetic groupings of teleosts. The intron patterns and repetitive sequences of GH genes can serve as useful natural markers for the classification and phylogenetic studies of teleosts.

Amino Acid Sequence↗
PubMed1997

Organization of the Fugu rubripes Hox clusters: evidence for continuing evolution of vertebrate Hox complexes.

The clustered organization of Hox genes provides a powerful opportunity to examine gene gain and loss in evolution because physical linkage is a key diagnostic feature which allows homology to be established unambiguously. Furthermore, Hox genes play a key role in determination of axial and appendicular skeletal morphology and may be a key component of the evolution of diverse metazoan body forms. Despite suggestions that changes in Hox gene number played a role in evolution of metazoan body plans, there has been a general lack of evidence for such variation amongst gnathostomes (or indeed any vertebrate) and it has therefore been widely assumed that differential regulation may be the key element in all vertebrate Hox evolution. We have studied the Hox gene clusters of a teleost fish, Fugu rubripes, to test the possibility that Hox organization may have varied since the origin of jawed vertebrates. We have identified four Hox complexes in Fugu and found an unprecedented degree of variation when compared with tetrapod clusters. Our data show that: Fugu clusters are widely variant with respect to length; at least nine genes have been lost; there is a new group-2 paralogue; and pseudo-gene remnants of group-1 and group-3 paralogues were found in the Hoxc complex, when compared with the present mammalian clusters. We show that gene loss after duplication of the prototypical vertebrate Hox clusters is a key feature of both tetrapod and fish evolution.

Amino Acid Sequence↗
PubMed1997

Continuous measurement of gut luminal PCO2 in the rat: responses to transient episodes of graded aortic hypotension.

OBJECTIVES: To test the rapidity of a continuous PCO2 measurement system response to brief reductions in gut perfusion from transient episodes of graded aortic hypotension, and to investigate the relationship between the increase in ileal luminal PCO2 and mean aortic pressure during the episodes. DESIGN: Prospective, experimental animal study. SETTING: University research laboratory. SUBJECTS: Adult male Sprague-Dawley rats, weighing 430 to 510 g. INTERVENTIONS: Five Sprague-Dawley rats were anesthetized with intraperitoneal sodium phenobarbital and ventilated with 100% oxygen via tracheostomy to a PaCO2 of 30 to 50 torr (4.0 to 6.7 kPa). Distal aortic pressure was monitored invasively, and a sensor was inserted into the ileal lumen. Luminal PCO2 measurements were recorded every 2 secs. Normal saline was infused at 3 mL/hr, and isoflurane was titrated to a mean aortic pressure of 80 to 100 mm Hg. In each rat, paired 2-min inductions of distal aortic hypotension were induced by digital elevation of an aortic silk sling above the celiac artery to as many as possible of the following pressures (mm Hg): 60, 50, 40, 30, 20, and 10. The experiment was stopped if instability of luminal PCO2 or hypotension persisted through the intervening 8-min recovery periods. MEASUREMENTS AND MAIN RESULTS: One rat completed paired inductions of all six goal aortic pressures. Two rats completed five inductions. One rat completed four inductions, and one rat completed three inductions. The times to onset of luminal hypercapnia and to peak luminal hypercapnia were highly consistent and independent of the degree of hypotension. Onset of hypercapnia was usually detected < 1 min after aortic elevation, but peak luminal hypercapnia occurred approximately 1 min after release of the aortic sling. Regression analysis showed an inverse linear relationship between the maximum increase in luminal PCO2 above baseline and mean aortic pressure during induced hypotension (r2 = .6; p < .001). CONCLUSIONS: Continuous ileal luminal PCO2 measurement by the sensor is rapidly responsive to brief reductions in aortic pressure in a rat model. Maximum luminal PCO2 increase during such perturbations is inversely related to mean aortic pressure.

Animals↗
PubMed1997

Hypoglossal neuropraxia following endotracheal intubation.

A case of hypoglossal nerve neuropraxia following elective drainage of bilateral chronic subdural haematomas is described. We postulate that the cause of neuropraxia was inadvertent extubation of the trachea with the cuff inflated, leading to compression and stretch of the nerve against the greater horn of the hyoid bone. The literature on cranial nerve palsies following endotracheal intubation is reviewed.

Aged↗