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Biomedical subjects

C D Martin

Publications and source records attributed to C D Martin.

10 recordsLinked to original sources
PubMed2001

Improved incidental memory with nicotine after semantic processing, but not after phonological processing.

RATIONALE: A number of lines of evidence suggest that a nicotinic cholinergic system is mediating attentional processing. However, the evidence is less clear for a nicotinic system being involved in mnemonic processing. OBJECTIVES: The present study investigated the effects of nicotine on memory using a depth of processing paradigm. METHODS: A double-blind design was used with participants (n = 40) smoking either a nicotine containing cigarette (n = 20) and a denicotinized cigarette (n = 20). After smoking, each set of these participants was further subdivided into two groups (n = 10 for each). One group were presented with a series of trials each beginning with the presentation of a "decision word" which they had to say whether it represented something which was living or non-living (semantic-orienting). The second group had to say whether the word had one syllable or two syllables (phonological or non-semantic orienting condition). This decision was followed by a word in coloured ink whose colour participants were required to name as quickly as possible. On completion of the whole task the participants were given an unexpected free recall test. RESULTS: The nicotine-containing cigarette reduced the latencies for decision-making and colour naming in comparison with the denicotinized cigarette. The free recall test showed that nicotine-containing cigarette increased the number of words remembered, but only for the semantic-orienting condition and not the non-semantic condition. CONCLUSIONS: There is a nicotinic cholinergic system that mediates effortful processing. It can be deployed for attentional processing, including the associative processing required for memory encoding.

Adolescent↗
PubMed1999

Stress-induced cortisol, mood, and fat distribution in men.

OBJECTIVE: A previous study in our laboratory (Moyer et al., Obes Res. 1994;2:255-62 found that, in response to uncontrollable laboratory stress, women with a high waist-to-hip ratio (WHR) had higher cortisol reactivity, poorer coping skills, and lower anger responses than women with low WHR. We aimed to compare high WHR men's stress responses to these women. RESEARCH METHODS AND PROCEDURES: The current study examined cortisol reactivity and psychological data of 27 healthy high WHR men exposed to the same laboratory challenges as the women from our previous study. Men's data are discussed in relation to that of the high and low WHR women. RESULTS: Men responded to the stress with increases in both cortisol and blood pressure. In comparison with the high and low WHR women, men had significantly higher total cortisol on the stress day. However, when comparing a sub-sample of men and women matched in WHR's, differences in cortisol secretion were greatly diminished and no longer significant. In addition, men had higher desire for control than both high and low WHR women, and lower mood reactivity than low WHR women. Despite the lower mood reactivity of high WHR groups, the high mood reactors among the high WHR women, and to a lesser extent, men, tended to have higher cortisol reactivity. DISCUSSION: These results suggest that the psychological differences and greater exposure to cortisol observed among the high WHR men and women may have played a role in contributing to their greater abdominal fat depots.

Adolescent↗
PubMed1998

Comparing two heat and moisture exchangers, one hydrophobic and one hygroscopic, on humidifying efficacy and the rate of nosocomial pneumonia.

OBJECTIVE: Many heat and moisture exchangers with filter (HMEF) have been developed. In-house data from companies provide some information about their performances; unfortunately, to our knowledge, no comparative evaluation in clinical conditions has been undertaken of these newer products. The aim of this study was to compare the efficiency of two HMEFs, one hydrophobic and one hygroscopic, on humidifying capacity and the rate of bronchial colonization and ventilator-associated pneumonia in ICU patients. DESIGN: Prospective, randomized study. SETTING: ICU of a university hospital. PATIENTS: All patients who required mechanical ventilation for > or = 24 h during the study period. INTERVENTIONS: On admission to the ICU, patients were randomly assigned to one of two groups. In one group, the patients were ventilated with a hygroscopic device (Humid-Vent Filter Light HMEF; Gibeck; Upplands Vaesby, Sweden). The condensation surface was made of paper (Microwell) impregnated with CaCl2. The filter membrane was made of polypropylene. In the other group, the patients were ventilated with a hydrophobic device (Pall BB100 HMEF). The condensation surface was made of a hydrophobic resin with a hydrophylic layer. The filter membrane was made of ceramic fibers. In both groups, HMEFs were changed daily. MEASUREMENTS AND RESULTS: Both groups of patients were similar for the tested characteristics, including parameters of mechanical ventilation. Sixty-six patients were ventilated for 11.7+/-11 days with the Humid-Vent Filter Light HMEF and 70 patients for 12.2+/-12 days with the Pall BB 100. Patients ventilated with the Humid-Vent Filter Light underwent 6.0+/-3.0 tracheal aspirations and 1.7+/-2.0 instillations per day, and those with the Pall BB 100, 6.0+/-3.0 and 1.6+/-2.0 per day, respectively (not significant [NS]). Abundance of tracheal secretions, presence of blood, and viscosity, evaluated by semiquantitative scales, were similar in both groups. No difference in the rate of atelectasis was observed between the two groups (7.5% and 7.1%, NS). One episode of tracheal tube occlusion was observed with the Humid-Vent Filter Light HMEF, and one with the other HMEF (NS). One patient in each group (NS) was switched to an active heated humidifier because of very tenacious bronchial secretions despite repeated instillations. Tracheal colonization was observed at a rate of 67% with the Humid-Vent Filter Light and 58% with the Pall BB 100 (NS). A small, but NS difference was observed in the rate of ventilator-associated pneumonia: Humid-Vent Filter Light, 32% (27.1 per 1000 ventilator days); and Pall BB 100, 37% (30.4 per 1000 ventilator days). Bacteria responsible for tracheal colonization and pneumonia were similar in both groups. Three patients in each group died from their nosocomial pneumonia. CONCLUSION: Despite differences in their components, the two HMEFs tested achieved similar performances in terms of humidification and heating of inspired gases. Only one episode of endotracheal tube occlusion was detected and very few patients (one in each group) had to be switched to an active heated humidifier. No difference was observed either in the rate of tracheal colonization or of ventilator-associated pneumonia. These data show that the hygroscopic HME (Humid-Vent Filter Light) and the hydrophobic HME (Pall BB 100) are suited for use in ICU patients.

Adult↗
PubMed1993

Ketamine inhibition of cytoplasmic calcium signalling in rat pheochromocytoma (PC-12) cells.

This study examines the mechanism of action of ketamine, a dissociative anesthetic, with a specific focus on its ability to inhibit changes in the concentration of intracellular free calcium, [Ca2+]i, in PC-12 cells. The resting [Ca2+]i as measured with the fluorescent probe Fura-2 AM in control cells is 184.8 +/- 8.6 nM (mean +/- SEM, n = 15). Changes in [Ca2+]i via influx through voltage-gated calcium channels after membrane depolarization with potassium chloride were monitored in the absence and presence of various concentrations of ketamine. Potassium-depolarization caused a dose-dependent rapid increase in [Ca2+]i, averaging 62 +/- 5%, 33 +/- 2% and 18 +/- 3% (n = 10 each) above control levels for 70 mM, 50 mM and 35 mM KCl, respectively. Ketamine, in the dosage range studied (5-500 microM), inhibited the increase in [Ca2+]i stimulated by potassium-depolarization in a dose-dependent manner. The computer-fitted dose-response curve of the pooled data yielded a half maximal suppression concentration, ED50, of 33 microM. In conclusion, this study demonstrates that ketamine inhibits Ca2+ influx through voltage-gated Ca2+ channels in PC-12 cells at clinically relevant doses, and may play a role in ketamine's action as a general anesthetic agent.

Animals↗
PubMed1987

An analysis of naltrexone precipitated abstinence in morphine-dependent chronic spinal dogs.

Graded doses of naltrexone (0.31, 1.125, 5.0, 20.0 and 80.0 micrograms/kg) were administered to five beagle-type dogs dependent on increasingly large stabilization doses of morphine (0.5, 1.0, 2.0, 4.0, 8.0, 16.0 and 24.0 mg/kg/day) and the intensity of precipitated abstinence (PAS) was determined by a previously developed scoring system. A complete crossover design was executed with all dogs receiving all doses of both naltrexone and morphine. The data were analyzed using a two-way analysis of variance (dogs and treatments). Treatment variance was partitioned into a regression and residual component. A mathematical model for relating the intensity of abstinence (PAS) to the concentrations of morphine and naltrexone was developed using the law of mass action and assuming that the degree of morphine physical dependence is related directly to the number of mu receptors occupied by morphine and the intensity of PAS is proportional to the number of receptors from which morphine is displaced by the antagonist. Using the mathematical model the deviations of the observed values from the calculated values were minimized using an iterative curve-fitting procedure which varied the values of the dissociation constants of morphine (KA) and naltrexone (KB) and the activity coefficient for morphine (alpha). The analysis of variance showed that the treatment effect was significant and that the regression accounted for most of this variance. The values which provided the best fit were: KA, 1.58 mg/kg; KB, 0.95 microgram/kg; and alpha, 245.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

The infusion of catecholamines in dogs under general anaesthesia with fentanyl. The effects on intrapulmonary shunt.

The pulmonary venous admixture, PaO2, and pulmonary and systemic haemodynamics were studied in six mongrel dogs during infusion of dobutamine (infusion rate 7.5 micrograms . kg-1 . min-1), dopamine (7.5 micrograms . kg-1 . min-1) and isoproterenol (0.1 microgram . kg-1 . min-1). Anaesthesia was performed by a single injection of Fentanyl (0.35 mg/kg). The carbon dioxide tension and body temperature were strictly maintained within limits. Only isoproterenol produced a significant change in pulmonary arterial pressure from an average of 1.2 +/- 0.4 kPa to 1.6 +/- 0.2 kPa (P less 0.05). There was no significant change in systemic haemodynamics with any of the three drugs. The use of catecholamines in dogs with healthy lungs does not induce any development in pulmonary venous admixture when haemodynamics are unchanged. Changes in these variables are dependent upon changes in pulmonary blood flow rather than being direct effects of the catecholamine.

Anesthesia, General↗
PubMedDate not supplied

Identification of a new phencyclidine analog, 1-(1-phenylcyclohexyl)-4-methylpiperidine, as a drug of abuse.

A previously unreported phencyclidine (PCP) analog. 1-(1-phenylcyclohexyl)-4-methylpiperidine (I) in which the piperidine ring has been substituted with 4-methylpiperidine, has been observed to be an abused drug in Virginia. The I was obtained coated over parsley in an approximate concentration of 1.7% (w/w). I . HCl was isolated, purified, and compared to authentic I . HCl (sample obtained from DEA and synthesized in the laboratory) using melting point, IR, 1H-NMR, GC and GC/MS. Unequivocal identification of I . HCl was based on its 13C-NMR. The intraperitoneal LD50 of I . HCl in male mice was 301.1 mumoles/kg (267.1--339.2, 95% confidence limits) and the ED50 was 43.0 mumoles/kg (37.3--54.3). The therapeutic index, LD50/ED50, for I . HCl was 7.0 and is much lower than that observed with phencyclidine, 38.0.

Animals↗