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Biomedical subjects

B Venkatesh

Publications and source records attributed to B Venkatesh.

At least 91 records · Page 5Linked to original sources
PubMed1994

A multiparameter sensor for continuous intra-arterial blood gas monitoring: a prospective evaluation.

OBJECTIVE: To compare measurements of arterial blood gases made by a new continuous intra-arterial blood gas monitor with measurements in a standard blood gas analyzer in patients in the general and cardiac intensive care units. DESIGN: Criterion standard study. SETTING: The cardiac surgical and the general medical intensive care units of a tertiary referral center. PATIENTS: Thirteen consecutive patients requiring mechanical ventilation and blood gas monitoring. INTERVENTIONS: All patients had a blood gas sensor placed through a 20-gauge cannula inserted into the radial artery. The duration of monitoring ranged from 9.42 to 117.45 hrs. MEASUREMENTS AND MAIN RESULTS: A total of 158 simultaneous measurements of pH, PCO2, and PO2 were made from the sensor and the blood gas analyzer, and the bias and precision were calculated on all measured parameters. The overall bias +/- precision values were 0.01 +/- 0.06 for pH, 1.4 +/- 4.8 torr (0.2 +/- 0.7 kPa) for PCO2, and 2.8 +/- 25.6 torr (0.4 +/- 3.4 kPa) for PO2. The bias and precision for PO2 measurements that were < 150 torr (< 20 kPa) were 0.45 +/- 20.7 torr (0.1 +/- 2.8 kPa). The bias and precision for values of PO2 that were > 150 torr (> 20 kPa) were -8.1 +/- 28 torr (-1.1 +/- 3.8 kPa). The mean in vitro 90% response times of pH, PCO2, and PO2 sensors were found to be 78, 143, and 70 secs, respectively. There were no instances of any complications attributable to the sensor. CONCLUSIONS: The continuous intra-arterial blood gas monitor tested in this study measures and trends arterial blood gases with an acceptable level of clinical accuracy. Longevity and safety of sensor function have also been demonstrated.

Aged↗
PubMed1993

Characterization of the pufferfish (Fugu) genome as a compact model vertebrate genome.

Cloning and sequencing techniques now allow us to characterize genes directly instead of having to deduce their properties from their effects. This new genetics reaches its apotheosis in the plan to obtain the complete DNA sequence of the human genome, but this is far beyond the capacity of present sequencing methods. Small 'model' genomes, 'such as those of Escherichia coli (4.7 megabases (Mb) and yeast (14 Mb), or even those of Caenorhabditis elegans (100 Mb) and Drosophila (165 Mb), are better scaled to existing technology. The yeast genome will contain genes with functions common to all eukaryotic cells, and those of simple multicellular organisms may throw light on the genetic specification of more complex functions. However, vertebrates differ in their morphology and development, so the ideal model would be a vertebrate genome of minimum size and complexity but with maximum homology to the human genome. Here we report the characterization of the small genome (400 Mb) of the tetraodontoid fish, Fugu rubripes. A random sequencing approach supported by gene probing shows that the haploid genome contains 400 Mb of DNA, of which more that 90% is unique. This genome is 7.5 times smaller than the human genome and because it has a similar gene repertoire it is the best model genome for the discovery of human genes.

Animals↗
PubMed1992

Steroid metabolism by ovarian follicles and extrafollicular tissue of the guppy (Poecilia reticulata) during oocyte growth and gestation.

In the viviparous guppy, fertilization and gestation are intrafollicular. Fully developed embryos are ovulated at the end of gestation just prior to parturition. The metabolism in vitro of various radiolabeled steroid precursors by isolated ovarian follicles at various stages of the reproductive cycle and extrafollicular (EF) tissue of the guppy was investigated. While estradiol-17 beta was one of the end products of metabolism in vitellogenic follicles, 17 alpha, 20 beta-P and several 5-reduced metabolites were synthesized by postvitellogenic follicles. The yield of 17 alpha, 20 beta-P, however, was much lower than some 5 beta-reduced metabolites synthesized by postvitellogenic follicles. Gestation stage follicles rapidly converted the precursors into 5-reduced and polar 7-hydroxylated steroids, and their glucuronides. Although postpartum follicles showed very poor potential for steroid metabolism, they synthesized estradiol-17 beta from testosterone. These results demonstrate distinct changes occurring in the steroidogenic potential of the follicles during the reproductive cycle. Unlike in other viviparous vertebrates, no particular steroid seems to be involved in maintaining gestation in the guppy; all the steroid precursors are converted into highly polar metabolites and their conjugates during gestation, thereby facilitating their excretion. The EF ovarian tissue also synthesized 7-hydroxylated steroids and their glucuronides, providing evidence for the first time that the teleost ovarian EF tissue plays a role in steroidogenesis. The possible physiological significance of the synthesis of the novel polar steroids by the follicles and the EF tissue is discussed.

17-alpha-Hydroxyprogesterone↗
PubMed1992

Steroid production by ovarian follicles of the viviparous guppy (Poecilia reticulata) and its regulation by precursor substrates, dibutyryl cAMP and forskolin.

Production in vitro of estradiol-17 beta, testosterone, 17 alpha-20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta-P), 17 alpha-hydroxyprogesterone, and progesterone by follicles of the guppy at various stages of oocyte growth and gestation was investigated. Basal production of estradiol-17 beta was highest in 0.8- and 1.2-mm follicles, whereas that of testosterone and 17 alpha,20 beta-P was highest in 1.6-mm (postvitellogenic) follicles. Levels of these steroids declined after fertilization and were undetectable in late gestation and postpartum follicles. 17 alpha-Hydroxyprogesterone and progesterone levels were low at all stages. Thus, none of these steroids appears to be involved in maintaining gestation. Regulation of estradiol-17 beta and 17 alpha,20 beta-P secretion by vitellogenic (1.0 mm) and postvitellogenic follicles by precursor substrates, dbcAMP (0.1 to 10 mM) and forskolin (1 to 100 microM), was also investigated. Vitellogenic follicles synthesized increased quantities of estradiol-17 beta in the presence of exogenous testosterone, whereas estradiol-17 beta production by postvitellogenic follicles was not altered by testosterone. These results suggest decreased aromatase activity in the postvitellogenic follicles. Dibutyryl cAMP and/or forskolin stimulated testosterone and estradiol-17 beta production by vitellogenic follicles but did not stimulate conversion of testosterone to estradiol-17 beta, suggesting that the adenylate cyclase system stimulates estradiol-17 beta production by stimulating testosterone production but does not mediate conversion of testosterone to estradiol-17 beta. Postvitellogenic follicles synthesized increased quantities of 17 alpha,20 beta-P in response to 17 alpha-hydroxyprogesterone in a dose-dependent manner. Although 1 microM of forskolin stimulated 17 alpha,20 beta-P production by postvitellogenic follicles in the absence of exogenous 17 alpha-hydroxyprogesterone, 100 microM of forskolin inhibited 17 alpha,20 beta-P production. Dibutyryl cAMP, however, did not affect 17 alpha,20 beta-P production. In the presence of 50 ng of 17 alpha-hydroxyprogesterone, dbcAMP (10 mM) and forskolin (1 to 100 microM) suppressed 17 alpha,20 beta-P production. It is suggested that cAMP mediates 17 alpha,20 beta-P production up to a certain threshold level, beyond which it inhibits 17 alpha,20 beta-P production.

17-alpha-Hydroxyprogesterone↗
PubMed1992

Effects of neurohypophyseal and adenohypophyseal hormones, steroids, eicosanoids, and extrafollicular tissue on ovulation in vitro of guppy (Poecilia reticulata) embryos.

In the viviparous guppy, oocyte maturation is followed by intrafollicular fertilization and gestation. The fully developed embryos are ovulated at term just prior to parturition. Various agents were tested in vitro for their effects on ovulation of embryos in isolated follicles of the guppy. Arachidonic acid (10 and 100 microM), PGE2, PGF2 alpha, and 6-keto-PGF1 alpha (0.1 microgram/ml) induced ovulation, while PGE1, 15-keto-PGF2 alpha, leukotriene B4, 5-, 12-, and 15-HETEs (0.01 to 0.1 microgram/ml), cortisol, 11-deoxycortisol (25 and 250 ng/ml), estradiol-17 beta, testosterone, 17 alpha,20 beta-P, progesterone (5 and 50 ng/ml), isotocin, vasotocin (0.02 to 2 microgram/ml), and guppy pituitary extract (one and two glands per fish) did not. Extrafollicular (EF) ovarian tissue cocultured with isolated follicles induced ovulation, and the medium levels of PGE and PGF in such incubations were higher than those in the control. Indomethacin, the cyclooxygenase inhibitor, did not inhibit ovulation induced by arachidonic acid and EF tissue, although it inhibited PGE and PGF production. NDGA, the lipoxygenase inhibitor, did not inhibit ovulation induced by arachidonic acid or EF tissue. A combination of eicosanoids synthesized by follicles and EF tissue may be involved in the induction of ovulation. Dibutyryl cAMP inhibited ovulation induced by PGE2, PGF2 alpha, 6-keto-PGF1 alpha, and EF tissue suggesting that a low level of cAMP may be associated with ovulation in the guppy.

Animals↗
PubMed1992

Prostaglandins and teleost neurohypophyseal hormones induce premature parturition in the guppy, Poecilia reticulata.

Administration of PGE2, PGF2 alpha, isotocin, and vasotocin to pregnant guppies during late gestation induced premature parturition. Indomethacin (10 micrograms/g body wt), the cyclooxygenase inhibitor, did not inhibit parturition at term, suggesting that some lipoxygenase metabolites may be involved in the induction of parturition. Pituitary extract, as well as LH-RH, did not induce premature parturition. It may be that in the guppy, in which ovulation occurs at the end of gestation just prior to parturition, gonadotropin is not involved in the induction of ovulation and parturition.

Animals↗
PubMed1992

Steroid metabolism in teleost gonads: purification and identification of metabolites by high-performance liquid chromatography.

A simple, efficient, and comprehensive technique for the purification, identification, and quantitation of the common steroid metabolites synthesized by the gonads of teleosts involving five systems of high-performance liquid chromatography (HPLC) was developed. Steroid standards were identified in HPLC by UV absorption at 254 nm or 280 nm, by differential refractive index, or by using radioactive standards. Metabolites that do not absorb UV light and are not resolved in the isocratic HPLC systems were identified in thin-layer chromatography following purification by HPLC. By using this technique, most of the steroid metabolites, including some polar metabolites, synthesized by the gonadal tissues of the teleosts can be purified within three steps of chromatography. The HPLC systems reported here are also useful in identifying the chromium trioxide oxidized products of metabolites, such as triols and tetrols, which considerably narrows down the number of probable metabolites.

Animals↗
PubMed1991

Progestins and cortisol delay while estradiol-17 beta induces early parturition in the guppy, Poecilia reticulata.

Fertilization and gestation are intrafollicular in the guppy (Poecilia reticulata), and ovulation occurs at the end of gestation prior to parturition. In this study, the effects in vivo of the ovarian steroids, progesterone, 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta-P), cortisol and estradiol-17 beta, the antiprogestin RU 486, and aromatase inhibitor, 4-hydroxyandrost-4-ene-3,17-dione (4-HAD), on gestation and parturition were studied in the guppy. Progesterone (0.05 and 0.10 micrograms/ml of water), 17 alpha,20 beta-P (0.01 micrograms/ml and greater), cortisol (0.10 micrograms/ml) and 4-HAD (0.10 micrograms/ml) all prolonged gestation presumably by inhibiting ovulation. 17 alpha,20 beta-P was most effective in inhibiting ovulation and parturition for up to 36 days postpartum. This inhibition was reversed when fish were transferred to steroid-free water. Besides extending gestation, 17 alpha,20 beta-P and 4-HAD also inhibited development of vitellogenic oocytes. Estradiol-17 beta (0.05 and 0.10 micrograms/ml) and RU 486 (10 micrograms/g body weight) both induced premature parturition presumably by accelerating onset of ovulation. These results, together with our previous observations on the steroid profile in the guppy, strongly suggest roles for estradiol-17 beta and cortisol in regulating ovulation and parturition.

Animals↗
PubMed1990

Steroid hormone profile during gestation and parturition of the guppy (Poecilia reticulata).

The guppy is an ovoviviparous teleost with fertilization and gestation occurring intrafollicularly, and ovulation and hatching at around parturition. The levels of estradiol-17 beta (E), testosterone (T), cortisol (F), 17 alpha-hydroxyprogesterone (17-OHP), 17 alpha-20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P), and progesterone (P) in the guppy at different stages of gestation were measured in 60 microliters of serum with a highly specific, sensitive, precise, and accurate procedure involving high-performance liquid chromatography and radioimmunoassay. Levels of E and T increased during vitellogenic growth of oocytes and declined sharply after fertilization, increasing again gradually during late gestation to reach prefertilization levels at periparturition. F levels decreased significantly during fertilization followed by an increase during gestation and a sharp decline again at periparturition. The level of 17-OHP was significantly lower at periparturition than at other stages, while that of 17,20 beta-P was significantly higher in periparturition than in late gestation. There was no significant change in the levels of P at all stages of gestation, suggesting that, unlike mammals, P may not be involved in maintaining gestation in this fish. Changes in the levels of E and T seem to be related to oocyte growth rather than gestation. The role of F in gestation is uncertain since the effect of stress could not be discounted or defined in this study. Thus, on the present results, the role of any particular steroid in maintaining gestation of the guppy is not obvious. The elevated levels of E at term may facilitate parturition in addition to its role in vitellogenesis during oocyte growth.

Animals↗
PubMed1989

Blood steroid levels in the goldfish: measurement of six ovarian steroids in small volumes of serum by reverse-phase high-performance liquid chromatography and radioimmunoassay.

A reliable and rapid technique for the measurement of estradiol-17 beta, testosterone, progesterone, 17 alpha-hydroxyprogesterone, 17 alpha,20 beta-dihydroxy-4-pregnen-3-one, and cortisol by reverse-phase high-performance liquid chromatography and radioimmunoassay in single female goldfish serum samples of 50 microliters was developed. The steroids were extracted with Sep-Pak C18 cartridges after heat treatment. While estradiol-17 beta was assayed directly after extraction, the other steroids were separated on a mu Bondapak C18 stainless-steel column with acetonitrile:water (53:47, v/v) in 17 min under isocratic conditions, and then quantitated by specific radioimmunoassays. The technique was validated and was shown to be highly accurate, precise, sensitive, and specific for measuring those particular ovarian steroids in goldfish serum. The steroid levels measured in this way were not significantly different from those measured after separation on a Nova-Pak C18 column with methanol:water (56:44, v/v), where all the individual steroids could be completely resolved during a 40-min run. With this technique, the steroid levels in the serum of the goldfish during the secondary yolk stage, the tertiary yolk stage, and at 0 hr after ovulation were determined. While estradiol-17 beta was found to be significantly higher in the tertiary yolk stage, testosterone was significantly higher in the secondary yolk stage than in the other two stages. There was no significant difference in the levels of cortisol, 17 alpha-hydroxyprogesterone,17 alpha,20 beta-dihydroxy-4-pregnen-3-one, and progesterone among the three stages. We conclude that the technique is particularly useful for assaying multiple steroids in very small volumes of biological fluids.

Animals↗
PubMed1978

Nerve conduction velocity in hypertensive patients.

Due to conflicting reports in the literature regarding nerve conduction velocities (NCVs) in hypertensives, peroneal and sural NCVs and facial nerve conduction latencies were studied in 30 hypertensives and in 30 controls. An improved technique of NCV measurement was used. Twenty-one of the hypertensives were retested after five weeks, and five of them were tested for motor and sensory NCVs of the median nerve during a short period of partial occlusion of blood flow in the arm. No changes were found that could be related to blood pressure, duration of hypertension, eyeground changes, or partial restriction of blood flow.

Adult↗
PubMed1978

Gastrocnemius muscle belly and tendon length in stroke patients and able-bodied persons.

Length changes of gastrocnemius muscle belly and tendon at different passive tensions and ranges of motion (ROM) were measured in 31 healthy persons and 15 hemiplegic patients with clinically demonstrated ankle joint plantar flexion (PF) contractures. Preliminary studies were done to obtain accurate determination of gastrocnemius muscle insertion and origin points on x-ray films, to calculate the magnification factor due to x-ray beam divergence and to measure the length changes in muscle belly by the use of a wire hook placed at the muscle-tendon junction. Our results revealed: (1) change in length at different passive tensions is in the muscle belly, not in the tendon, (2) in hemiplegic patients no statistical difference in elongational characteristics of affected gastrocnemius muscle bellies with clinically demonstrated ankle PF contractures and of the contralateral nonaffected muscle bellies, (3) spastic and flaccid gastrocnemius muscle bellies are not statistically different in respect to passive elongations, (4) gastrocnemius muscle bellies of both affected and nonaffected legs of hemiplegic patients were statistically different from the muscle bellies of healthy persons in regard to maximal ROM and maxinum muscle belly length changes, (5) there was approximately .5 mm change in the belly length for each degree of ankle ROM, (6) age is not a factor influencing passive elongation of muscle belly, (7) average muscle belly lengths were consistently shorter in hemiplegic muscles while their tendon lengths did not change. The enumerated findings suggest that the limitation of ankle ROM in spastic hemiplegic legs obtained by the standard clinical measurements technique represents a change in muscle belly rest length without a structural contracture of the muscle fibers.

Adult↗
PubMed1976

Nerve conduction velocity measurements: improved accuracy using superimposed response waves.

A new procedure of serial motor nerve conduction velocity (NCV) measurements with the use of "superimposed response waves" technique (or double stimulus technique) was performed on 29 normal subjects. Six peripheral nerves were tested once a week for four to six weeks. A total of 760 NCV measurements were thus obtained to try to assess the magnitude of error in serial NCV testings. With the double stimulus technique employed, a significant reduction in variations of serial NCV measurements was found. The overall standard deviation of four to six consecutive NCV measurements in the 34 subjects was 1.3 meters per second with a coefficient of variation of 2.4%. These findings obtained with the double stimulus technique have proven to be approximately three times more accurate than results obtained by investigators who studied nerve conduction velocity measurement variation with single stimulus standard NCV testing techniques.

Electric Stimulation↗
PubMedDate not supplied

Continuous measurement of blood gases using a combined electrochemical and spectrophotometric sensor.

The use of a combined electrochemical and fibreoptic continuous intra-arterial blood gas sensor is described. The purpose of the study was to evaluate the performance of the sensor in 10 patients in the intensive therapy unit following insertion through a femoral arterial cannula. To our knowledge this is the first published study on the valuation of an intravascular blood gas sensor through a femoral arterial cannula. A total of 71 sets of data comparing the sensor with the blood gas analyser were obtained. The bias and precision for pH, PCO2 and PO2 were 0.006 and 0.07 pH units, 0.2 and 1.65 kPa (4.6% and 29%) and 0.8 and 2.7 kPa (5.1% and 14.3%) respectively. There was a degree of imprecision of the PCO2 sensor, the reasons for which are discussed. In summary, the intra-arterial sensor functioned well when inserted into the femoral artery in post-cardiopulmonary bypass patients. There were no complications attributable to sensor placement.

Blood Gas Analysis↗