Effects of exogenous factors on spatial accuracy in neurosurgery

The study aimed to assess the effect of exogenous factors such as surgeon posture, surgical instrument length, fatigue after a night shift, exercise and caffeine consumption on the spatial accuracy of neurosurgical manipulations. For the evaluation and simulation of neurosurgical manipulations, a testing device developed by the authors was used. The experimental results were compared using nonparametric analysis (Wilcoxon test) and multivariate analysis, which was performed using mixed models. The results were considered statistically significant at p < 0.05. The study included 11 first-year neurosurgery residents who met the inclusion criteria. Hand support in the sitting position (Wilcoxon test p value = 0.0033), caffeine consumption (p = 0.0058) and the length of the microsurgical instrument (p = 0.0032) had statistically significant influences on the spatial accuracy of surgical manipulations (univariate analysis). The spatial accuracy did not significantly depend on the type of standing position (Wilcoxon test p value = 0.2860), whether the surgeon was standing/sitting (p = 0.1029), fatigue following a night shift (p = 0.3281), or physical exertion prior to surgery (p = 0.2845).When conducting the multivariate analysis, the spatial accuracy significantly depended on the test subject (p < 0.0001), the use of support during the test (p = 0.0001), and the length of the microsurgical instrument (p = 0.0397). To increase the spatial accuracy of microsurgical manipulations, hand support and shorter tools should be used. Caffeine consumption in high doses should also be avoided prior to surgery.     

枸橼酸咖啡因与氨茶碱对早产儿不同时相血糖值的影响比较

目的观察并比较枸橼酸咖啡因及氨茶碱对早产儿不同时相血糖的影响程度。方法选择新生儿监护室诊断为原发性呼吸暂停的出生胎龄＜34周的早产儿172例，采用随机数字表法分为咖啡因组与氨茶碱组各86例。比较两组早产儿用药前及用药后15、30min、1、1.5、2、4、6、12、12.5、24.5、36.5和48h血糖的变化。结果两组早产儿用药后除6、12和48h血糖值比较差异均无统计学意义（均P＞0.05），其他用药后时相比较差异均有统计学意义（均P＜0.05）。咖啡因组早产儿用药后30min血糖值上升，至1h达峰值，后逐渐回落；用药后30min、1、1.5、2及24.5h血糖值与用药前比较差异均有统计学意义（均P＜0.05）。氨茶碱组早产儿用药后血糖值上升，30min达峰值，后逐渐回落；用药后15、30min、1、1.5、2、4、6、12.5、24.5、36.5h血糖值与用药前比较差异均有统计学意义（均P＜0.05）。结论枸橼酸咖啡因可引起早产儿血糖升高，但升高幅度较氨茶碱小、持续时间也较短。     

一次采样测定人体咖啡因清除率的研究

咖啡因主要经肝细胞色素Ｐ４５０ＩＡ２代谢，测定其药代动国学参数可反映该Ｐ４５０亚型的活性。本研究显示咖啡因清除相为一级动力学；唾液和血浆的药代动力学参数有良好的相关性；含体重因素的清除率的变异系数比半减期小；用一次采样测定其清除率以８ｈ时点为宜。     

Caffeine and light effects on nighttime melatonin and temperature levels in sleep-deprived humans

The effects of caffeine ingestion and exposure to bright light, both separately and in combination, on salivary melatonin and tympanic temperature were assessed in humans. Four treatments during a 45.5 h sleep deprivation period were compared: Dim Light-Placebo, Dim Light-Caffeine, Bright Light-Placebo and Bright-Light Caffeine. The Dim Light-Caffeine condition (200 mg twice each night) relative to the Dim Light-Placebo condition suppressed nighttime melatonin levels and attenuated the normal decrease in temperature. Combining caffeine ingestion with bright light exposure (≥2000 lux) suppressed melatonin and attenuated the normal nighttime drop in temperature to a larger degree than either condition alone; i.e. effects were additive. Circadian effects were also observed in that the amplitude and phase of the temperature rhythm were altered during treatment. These findings establish that the human melatonin system is responsive to caffeine. Other evidence suggests that caffeine may influence melatonin and temperature levels through antagonism of the neuromodulator adenosine.     

Epileptogenic actions of xanthines in relation to their affinities for adenosine A1 receptors in CA3 neurons of hippocampal slices (guinea pig)

In order to analyze the epileptogenic mechanisms of caffaine and related xanthines, putative effects of these drugs were studied on adenosine receptors of CA3 neurons in hippocampal slices. Epileptogenic concentrations of different xanthine derivatives strongly correlated with their affinities for the inhibitory A₁ adenosine receptor subtype. The A₁ receptor agonists adenosine and R-PIA reversibly depressed xanthine-induced epileptic activity without effects on the resting membrane potential or on spontaneously occuring action potentials. These findings suggest that the epileptogenic potency of xanthines is primarily due to the blockade of the A₁ receptors through an abnormal rise of intracellular cAMP and to the excessive transmembrane calcium fluxes underlying paroxysmal depolarization shifts.     

THE ROLE OF P_1-PURINERGIC RECEPTORS IN THE SPINAL MECHANISMS OF ACUPUNCTURE ANALGESIA

It has been extensively proved that electro-acupuncture elicit analgesia in bothextensive areas and local region via supraspinal structures and spinal cord.The present investigationwas to study the role of P_1-purinergic receptors in the spinal mechanisms of weak electroacupuncture-induced analgesia.Leg withdrawal latency(LWL)to noxious radiant heat focused on the ankle regionwas used to assess the effects of acupuncture and that of P_1-purinergic(adenosine)receptor antago-nists,theophylline and caffeine on the electro-acupuncture(EA)analgesia.EA prolonged the LWLby 16.7%±20.3%,with an after-effect lasting about 15 min.Both theophylline and caffeineblocked the EA-induced prolongation of LWL in a dose-dependent manner at the doses of 1.6-16 mg/kg.These results suggest that P_1-purinegic receptor is involved in the spinal mechanisms of weak EAproduced analgesia in the rat.     

Suppression of sleepiness in drivers: Combination of caffeine with a short nap

Previous research has shown that caffeine and a<15-min nap effectively and separately reduce sleepiness in drivers for I hr. In the present study, we examined in 12 sleepy individuals the treatments combined, taken during a 30-min break, prior to a longer (2 hr) continuous monotonous afternoon drive in a car simulator. Nonnap comparisons were 200 mg caffeine only and placebo. For placebo, driving incidents. Subjective and electroencephalographic measures of sleepiness all reflected a mid-afternoon peak'. This peak was significantly reduced by caffeine and eliminated by the combined treatment, which reduced incidents to 9% of placebo levels versus 34% of placebo levels for caffeine alone. Naps comprising “nonsleep dozing” were still effective.     

Fulminant malignant hyperthermia associated with ketoacidotic diabetic coma

Malignant hyperthermia (MH) in humans is usually triggered by volatile anaesthetics and depolarizing muscle relaxants. However, other factors or drugs (e.g. cresol) are thought to induce MH. We report a case of fulminant MH associated with a ketoacidotic diabetic coma. After therapy for diabetic coma with insulin (containing the preservative cresol) and electrolyte solutions was started, the patient complained of increasing myalgia, developed a high fever and respiratory and metabolic acidosis and lost consciousness. MH was treated immediately with dantrolene; the patient recovered within 14 days. Five months later the patient was diagnosed as MH-susceptible by the in vitro caffeine and halothane contracture test. This case supports the assessment that MH and diabetes are associated diseases and that cresol could possibly trigger MH. Furthermore, therapy with dantrolene has been demonstrated to the beneficial in the treatment of MH associated with diabetic coma.     

The effects of a low dose of caffeine on cognitive performance

There is little evidence concerning the effects of caffeine in doses typical of one cup of tea. The present study investigated the effect of 60 mg caffeine, consumed in either tea or hot water, on performance on a subset of the CANTAB test battery. Eight males participated in a practice session and four test sessions. In each test session, the participant consumed a different hot beverage and then, over approximately 90 min, completed nine tests from the CANTAB battery. The four beverages were created by crossing beverage identity (tea or hot water) and caffeine dose (0 or 60 mg). Significant speeding of reaction time by caffeine consumption was found in pattern recognition, delayed match to sample, and match to sample visual search. The effect on reaction time of 60 mg caffeine can be detected, and may be evident within minutes of consumption. Received: 16 March 1998/Final version: 27 July 1998     

Multiple effects of caffeine on calcium current in rat ventricular myocytes

Caffeine exerts a number of different effects on L-type calcium current in rat ventricular myocytes. These include: (1) a slowing of inactivation that is comparable to, but not additive to, that produced by prior treatment of the cells with ryanodine (a selective sarcoplasmic reticulum Ca²⁺ releaser) or high concentrations of intracellular 1,2-bis[2-aminophenoxy]ethane-N,N,N,N-tetraacetic acid (BAPTA) (a fast Ca²⁺ chelator), (2) a stimulation of peak I _Ca that is comparable to, but not additive to that produced by prior treatment with isobutylmethylxanthine (a selective phosphodiesterase inhibitor), and (3) a dose-dependent decrease of peak I _Ca that is not prevented by pretreatment with any of these agents. None of the caffeine actions could be mimicked or prevented by administration of 8-phenyltheophylline, a specific adenosine receptor antagonist. We conclude that only the slowing of I _Ca inactivation is due to caffeine's ability to deplete the sarcoplasmic reticulum of calcium. The stimulatory effect of caffeine on peak I _Ca is probably due to phosphodiesterase inhibition, while caffeine's inhibitory effect on I _Ca is independent of these processes and could be a direct effect on the channel. The multiplicity of caffeine actions independent of its effects on the sarcoplasmic reticulum lead to the conclusion that ryanodine, though slower acting and essentially irreversible, is a more selective agent than caffeine for probing sarcoplasmic reticulum function and its effects on other processes.The experimental part of this work was published during the postdoctoral stay of I. Zahradník in the Department of Physiology and Biophysics, The University of Texas Medical Branch, Galveston, TX 77555, USA