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Biomedical subjects

M K Chakrabarti

Publications and source records attributed to M K Chakrabarti.

At least 19 recordsLinked to original sources
PubMed1995

The uptake of enflurane during anaesthesia.

The uptake of enflurane at a constant end-expired concentration of 2% in oxygen was studied in 38 patients, ASA 1 or 2, undergoing elective orthopaedic procedures. The anaesthetic was administered using a computer-controlled closed circle system. Following an initial 4 min period during which the expired concentration of enflurane was established, the rate of uptake of enflurane showed a triexponential decline. The mean cumulative use of enflurane after 60 min was 10.7 ml, and after 120 min was 18.4 ml.

Adult↗
PubMed1995

The estimation of inspired isoflurane concentration in a low-flow system.

We have examined the predictability of inspired isoflurane concentration during low-flow anaesthesia using a to-and-fro breathing system. Twenty one adult patients requiring mechanical ventilation of the lungs during surgery took part in this study. Using a fresh gas flow of 2 l.min-1, the ratio of inspired isoflurane concentration to isoflurane vaporizer setting was found to be approximately 4/5th after 5 min of anaesthesia. The ratio was maintained throughout the procedure, except for a few minutes following each change in vaporizer setting.

Adult↗
PubMed1994

Ventilation techniques to minimize circulatory depression in rabbits with surfactant deficient lungs.

Changes in aortic blood flow were measured in rabbits with both normal and surfactant depleted lungs in order to elucidate the effect of different modes of ventilation on the circulation while optimizing arterial oxygenation (PaO2). Conventional mechanical ventilation (CMV), reversed inspiratory to expiratory ratio of CMV (IRV), high frequency positive pressure ventilation (HFV), and high frequency oscillation (HFO) were used. Normocapnia was maintained throughout during different modes of ventilation. In normal lungs the aortic blood flow during IRV was significantly lower with similar levels of PaCO2 compared with CMV, HFV, and HFO. In lavaged lungs, without positive end-expiratory pressure (PEEP), the aortic blood flow during CMV was significantly higher than with other modes of ventilation. When 10 cm H2O of PEEP was applied, the PaO2 increased maximally to normal values at all modes of ventilation, but the aortic blood flow was significantly reduced (P < 0.05) during CMV and IRV compared to HFV and HFO. The aortic blood flows at 5 cm H2O of PEEP were very similar during CMV, HFV, and HFO but significantly reduced during IRV. This study showed that at an optimal arterial oxygenation with higher PEEP levels, maintenance of aortic blood flow was maximal during HFV and HFO.

Animals↗
PubMed1994

Antigenicity and antigenic cross-reactivity of outer membrane proteins of Vibrio parahaemolyticus.

Antigenicity of outer membrane proteins was studied and compared between Kanagawa positive (clinical) and negative (environmental) strains of Vibrio parahaemolyticus. Murine antibodies recognized a wide range of outer membrane proteins of Kanagawa negative strains as antigens with molecular masses ranging between 102 kDa to 14 kDa. However, only a few of the total outer membrane proteins of clinical isolates were antigenic and comprised a 55kDa protein as the major antigen. Although a marked difference in antigenicity was found, molecular masses of outer membrane proteins of Kanagawa positive and negative strains migrated similarly in SDS-PAGE. Several outer membrane proteins of Kanagawa-positive strains were found to be antigenic and ubiquitous in a cross-reactivity study indicating that the ubiquitous proteins which could not be recognized by anti-KP antibodies were buried in the outer membrane.

Bacterial Outer Membrane Proteins↗
PubMed1994

Comparison of clonidine with fentanyl on phrenic nerve activity and their interaction in anaesthetized rabbits.

We have compared the effects of clonidine and fentanyl on phrenic nerve activity in anaesthetized rabbits during artificial ventilation. Both drugs caused dose-dependent inhibition of phrenic nerve activity and complete abolition in all experiments. The calculated ED50 values were 3.7 micrograms kg-1 for clonidine and 3.9 micrograms kg-1 for fentanyl. Pretreatment with clonidine 1 microgram kg-1 i.v. depressed phrenic nerve activity to 81.8% of control values. This effect was additive with subsequent doses of fentanyl which was confirmed with an ED50 isobologram. We conclude that clonidine has the potential for deleterious respiratory effects at doses similar to those of fentanyl, but the interaction between the two drugs is additive and hence differs from their known synergistic antinociceptive interaction.

Anesthesia, General↗
PubMed1994

Clonidine has comparable effects on spontaneous sympathetic activity and afferent A delta and C-fiber-mediated somatosympathetic reflexes in dogs.

BACKGROUND: Clonidine, an alpha 2-adrenergic agonist, has been studied as an adjunct or alternative to spinal opioids in the management of moderate to severe pain. This study examined the relative effects of clonidine on efferent spontaneous sympathetic activity and afferent A delta and C fiber-mediated somatosympathetic responses. METHODS: Spontaneous and evoked sympathetic activity in renal sympathetic nerves, mediated by A delta and C fibers by means of supramaximal electrical stimulation of the radial and tibial nerves, were observed in anesthetized dogs. Incremental doses of clonidine were administered intrathecally or intravenously in each of five preparations followed by intravenous naloxone 2 mg and yohimbine 5 mg. RESULTS: Both spontaneous sympathetic outflow and afferent A delta- and C fiber-mediated somatosympathetic responses evoked by tibial nerve stimulation were depressed in a similar dose dependent manner by clonidine administered intrathecally or intravenously in a dose ratio of approximately 1:4. Intrathecal clonidine inhibited and eliminated both local spontaneous sympathetic outflow and tibial nerve evoked sympathetic responses but had no significant depressant effect on the radial nerve evoked sympathetic reflexes. When administered intravenously clonidine had a similar depressant effect on both radial and tibial nerve elicited reflexes and spontaneous sympathetic activity. CONCLUSIONS: Clonidine, administered intrathecally or intravenously, has a similar depressant effect on both spontaneous sympathetic outflow and afferent A delta- and C fiber-mediated somatosympathetic reflexes. When administered intrathecally it has little effect on reflexes evoked via the descending pathway by radial nerve stimulation.

Animals↗
PubMed1994

The Ohmeda Rascal II. A new gas analyser for anaesthetic use.

The Ohmeda Rascal II is a multigas analyser and pulse oximeter for dedicated anaesthetic.use. It uses the Raman scattering of laser light to identify and quantify oxygen, nitrogen, carbon dioxide, nitrous oxide and three volatile anaesthetic agents. Its response times equal or better the published response times of infrared or photo-acoustic devices. It is linear within the clinical ranges of all gases and vapours, simple to use, requires no maintenance, holds its calibration well, and is a suitable monitor for clinical and research use.

Alcohols↗
PubMed1993

Effect of ICI197067, a kappa-opioid receptor agonist, spinally on A delta and C reflexes and intracerebrally on respiration.

Intrathecal (i.t.) injection of a kappa-opioid receptor agonist, ICI197067, caused a similar dose dependent depression of A delta and C fibre mediated nociceptive reflexes in renal sympathetic nerves due to supramaximal electrical stimulation of tibial nerves in anaesthetized dogs. A total dose of 8 mg i.t. abolished these reflexes. When administered into the 4th ventricle (i.c.v.) in a total dose range from 0.1-2.5 mg ICI197067 caused no respiratory depression; a total dose of 10 mg i.c.v. abolished both phrenic nerve activity and spontaneous respiration. The ED50 ratio of ICI197067 for depression of respiration (i.c.v.) and somatosympathetic reflexes (i.t.) is approximately 1.5:1 compared with 0.3:1 for fentanyl. ICI197067 i.c.v. caused a similar reduction in arterial pressure compare to fentanyl without comparable changes in heart rate. Thus in terms of cardiorespiratory depression and blockade of A delta and C fibre pathways kappa-opioid receptor agonists may be safer and more effective for producing spinal analgesia than mu-opioid receptor agonists.

Animals↗
PubMed1993

Cardiorespiratory effects of conventional and high frequency ventilation in rabbits with bilateral pneumothoraces and surfactant depleted lungs.

We compared high frequency ventilation (HFV) to conventional mechanical ventilation (CMV) under normoxic and normocapnic condition in surfactant depleted rabbits with bilateral pneumothoraces. We hypothesized that lower airway pressures would be required with HFV under these conditions. We applied CMV and HFV in 8 anaesthetized rabbits with a prototype ventilator at frequencies of 30, 100, 200, and 300 cycles/min. A positive end-expiratory pressure (PEEP) just below the pressure sufficient to open the air leak from the pneumothoraces was applied at all frequencies. Airway pressures, gas exchange, heart rate, and mean arterial pressure were recorded. Peak airway pressure decreased significantly from 2.50 to 2.10 kPa when the frequency of ventilation was increased from 30 to 300 cycles/min. There were no significant changes in mean airway pressure, PaO2, arterial pH, heart rate, and mean arterial pressure when HFV was compared to CMV. In conclusion, during HFV peak airway pressures measured at the mouth were decreased. Our ability to maintain adequate gas exchange in the face of ongoing pulmonary air leaks may reflect lower alveolar pressures.

Animals↗
PubMed1993

Synergism between the antinociceptive effects of intrathecal midazolam and fentanyl on both A delta and C somatosympathetic reflexes.

The interaction between the antinociceptive effects of fentanyl and midazolam, administered intrathecally (i.t.), was examined in dogs. Midazolam 1 mg (i.t) depressed the A delta and C fibre mediated somatosympathetic reflexes to 68.3 and 85.2% of control values and then reduced the subsequent doses of fentanyl (i.t.) required to abolish these reflexes by 50%. After midazolam (1 mg, i.t.) the ED values for fentanyl were markedly less than the theoretical predicted additive values. This indicates synergism between the effects of fentanyl and midazolam.

Analgesics↗
PubMed1993

Evaluation of the efficacy of different antibiotics in inhibiting colonisation of Vibrio cholerae O1 in the rabbit intestine.

The efficacy of ciprofloxacin, norfloxacin and tetracycline in prevention of colonisation of V. cholerae O1 in the rabbit intestine were tested. V. cholerae O1 highly colonised the gut of rabbits which did not receive any antibiotic. All antibiotics tested inhibited the colonisation of V. cholerae O1 within the rabbit intestine. Moreover, ciprofloxacin and norfloxacin were found to be as effective as tetracycline suggesting that these drugs should be subjected to clinical trials for the treatment of cholera in comparison with tetracycline.

Animals↗
PubMed1993

Differential effects of alfentanil, fentanyl, pethidine and lignocaine administered intrathecally on nociceptive responses evoked by low and high frequency stimulation of somatic nerves.

We have studied in anaesthetized dogs the effects of alfentanil, fentanyl, pethidine and lignocaine administered intrathecally on nociceptive responses evoked by low and high frequency supramaximal electrical stimulation of the tibial and radial nerves. Doses were selected to abolish both A delta and C fibre somatosympathetic reflexes to single stimuli. Pethidine and lignocaine eliminated reflex pressor and heart rate responses to repeated single stimuli and almost completely abolished responses to train stimulation. The pressor response to single stimuli was abolished by fentanyl and reduced by alfentanil, but these drugs did not reduce significantly this response to train stimulation, suggesting a stimulation rate-dependent effect. Of the opioids, only pethidine had an effect comparable to that of lignocaine. The absence of sympathetic block and antagonism by naloxone imply a lack of significant local anaesthetic effect. We suggest that the greater analgesic efficacy of pethidine is a result of endogenous synergism between a minor local anaesthetic and a major opioid effect.

Alfentanil↗
PubMed1993

Lack of a ceiling effect for intrathecal buprenorphine on C fibre mediated somatosympathetic reflexes.

We observed that buprenorphine 20 micrograms kg-1 i.v. in dogs caused an initial significant reduction in both A delta and C fibre mediated somatosympathetic reflexes evoked by tibial and radial nerve stimulation, to approximately 75% and 70% of control values. Larger doses (up to 100 micrograms kg-1 i.v.) had progressively less effect and the mean responses were depressed to only approximately 65% and 55% of control, indicating a ceiling effect. Buprenorphine 450 micrograms intrathecally (i.t.) completely abolished tibial C fibre reflexes, but 20% of A delta responses could not be eliminated with doses up to 1050 micrograms i.t. Fentanyl 100 micrograms kg-1 i.v. or 150 micrograms i.t. after buprenorphine i.v. or i.t., respectively, had little additional effect. This study confirms the limited ceiling effect of buprenorphine on nociceptive reflexes when administered systemically, and provides evidence that when administered i.t. in sufficient doses it abolishes the C responses (lack of ceiling effect for C responses), but the A delta responses show a plateau or ceiling effect.

Animals↗
PubMed1993

Specific enhancement by fentanyl of the effects of intrathecal bupivacaine on nociceptive afferent but not on sympathetic efferent pathways in dogs.

BACKGROUND: Bupivacaine alone, or in combination with opioids, has been shown to provide adequate pain relief without motor paralysis. This study examined the effects of bupivacaine administered intrathecally on sympathetic efferent and A delta- and C-fiber-mediated afferent pathways in dogs and the interactions with intrathecal fentanyl. METHODS: Spontaneous activity in renal sympathetic nerves was observed, as were reflex somatosympathetic responses mediated by A delta and C fibers evoked by supramaximal electrical stimulation of the tibial and radial nerve. Bupivacaine was administered intrathecally in doses of 0.5, 1, 2, and 3.5 mg, each in 0.5 ml, and 7 mg in 1 ml with or without pretreatment with 5.4 mg intrathecal fentanyl (ED25 for depression of C tibial reflexes) in each of five preparations. RESULTS: Bupivacaine caused a dose-dependent inhibition of both A delta- and C-fiber-mediated somatosympathetic responses evoked by tibial nerve stimulation. The depression of radial and tibial nerve reflexes and spontaneous renal sympathetic activity was similar. Pretreatment with fentanyl (5.4 micrograms, intrathecally) depressed tibial C-fiber reflexes by only 23.8% without any significant effect on either tibial A delta or radial A delta and C fiber responses. Fentanyl markedly enhanced the effect of subsequent doses of bupivacaine on tibial A delta and C reflexes without any additional effect on either spontaneous sympathetic activity or radial responses. CONCLUSIONS: Intrathecal bupivacaine has no selectivity for the afferent and efferent pathways, and intrathecal fentanyl acts synergistically to enhance the effect of bupivacaine on the afferent pathway without a measurable effect on sympathetic outflow.

Adrenergic Fibers↗
PubMed1993

An evaluation of anaesthetic loss from a closed breathing system.

We present the results of a laboratory study of the loss of isoflurane from a to-and-fro system, ventilated with oxygen, using a standard ventilator connected to the system via a long corrugated tube (the trunk) in place of the reservoir bag. No conventional fresh gas supply is used and isoflurane is injected as a liquid directly into the soda lime canister. The loss of isoflurane from the system due to mixing in the trunk was generally less than that lost by absorption into rubber and plastic system components. Glass syringes used for injection of liquid isoflurane were found to be a potential source of much greater leaks. The results showed that a to-and-fro system ventilated with oxygen via an open trunk functions as a virtually completely closed anaesthetic breathing system.

Anesthesia, Closed-Circuit↗
PubMed1993

A computer-controlled closed anaesthetic breathing system.

We describe the design and working of a computer-controlled, closed anaesthetic breathing system which rapidly achieves and maintains a prescribed end-tidal concentration of isoflurane in oxygen. The system is simple to set up and not expensive; the only nonstandard component is a modified glass syringe. We have demonstrated that gas analysers may contribute as much as the patient to the accumulation of nitrogen within the breathing system. Details of our clinical experience with the system are presented in an accompanying article.

Algorithms↗
PubMed1993

The uptake of isoflurane during anaesthesia.

The uptake of isoflurane at a constant end-expired concentration of 1.5% in oxygen was studied in 15 women, ASA 1 or 2, undergoing elective total abdominal hysterectomy. The anaesthetic was administered by a simple computer-controlled to-and-fro closed system. After an initial period of wash-in to the system, the rate of uptake of isoflurane decreased bi-exponentially with a rapid reduction during the first 15 min. Perturbations from this bi-exponential decline reflect changes in cardiac output. The mean (SD) cumulative use of isoflurane was 4.5 (0.43) ml after 30 min and 7.3 (0.79) ml after 60 min.

Adult↗