接触性热痛诱发电位检测方法的建立

目的 建立接触性热痛诱发电位(CHEP)的检测方法,估测介导此诱发电位的外周神经传导速度.方法 受试者取卧位,应用CHEP刺激器,于两个强度水平(49.5℃和54.5℃)应用可调节脉冲,刺激部位为鱼际肌、手背、前臂的掌侧面.受试者在每次刺激后,按照视觉模拟评分标准对刺激强度分级.以Keypoint仪器记录,记录点为Cz和Pz.测定刺激强度和疼痛分级的关系、诱发电位的主要成分及外周神经传导速度.结果 刺激强度和疼痛分级的关系为:49.5℃和54.5℃刺激鱼际肌皮肤,疼痛分级分别为(3.2±0.3)、(4.4±0.5)级;54.5℃刺激手背和前臂掌侧面皮肤,疼痛分级分别为(6.3±0.8)、(7.2±0.5)级.于记录点记录到3个主要成分:Cz/N550、Cz/P750和Pz/P1000.介导此诱发电位的外周神经传导速度分别为(12.9±7.5)、(1.7±0.4)m/s,分别与Aδ纤维和C纤维的传导速度相对应.结论 CHEP能较为稳定、可靠地引出,介导此诱发电位的外周神经为Aδ纤维和C纤维.     

Hypohydration effects on thermoregulation during moderate exercise in the cold

Hyperosmotic hypovolemia impairs vasoconstriction during sedentary cold exposure. The purpose of this study was to determine whether hypohydration alters thermoregulation and cardiovascular responses to exercise in cold air. On four occasions, eight males [35.1 (2.7) years, 175.5 (3.1) cm, 73.3 (2.6) kg, 57.2 (2.6) ml kg^–1 min^–1 maximal oxygen uptake (O_2max), 19.6 (2.4)% fat] walked, in t-shirt, shorts, and shoes, at 50% O_2max, for 60 min in either a 4°C (Cold) or a 25°C (Temperate) environment in both hypohydrated state (HYPO, –4% body mass) and euhydrated state (EU). During exercise–cold stress, rectal temperature (T_re), mean weighted skin temperature, heart rate (HR), cardiac output (CO), and stroke volume (SV) were measured every 20 min. Mean weighted skin temperature values were not different between HYPO and EU but were lower (P<0.05) in Cold versus Temperate trials. T_re was not different (P>0.05) between HYPO–Cold and EU–Cold. CO and SV were not different within hydration states and were not different between Cold and Temperate trials (P<0.05). HR was not different between HYPO–Cold and EU–Cold. These data demonstrate that moderate intensity exercise in the cold while hypohydrated does not alter metabolic heat production, skin temperatures and heat loss, nor does it increase thermoregulatory and cardiovascular strain.     

Prediction of mean skin temperature in warm environments

Summary The data collected by the authors in four experimental series have been analysed together with data from the literature, to study the relationship between mean skin temperature and climatic parameters, subject metabolic rate and clothing insulation. The subjects involved in the various studies were young male subjects, unacclimatized to heat. The range of conditions examined involved mean skin temperatures between 33‡ C and 38‡ C, air temperatures (T_a) between 23‡ C and 50‡ C, ambient water vapour pressures (P_a) between 1 and 4.8 kPa, air velocities (V_a) between 0.2 and 0.9 m · s⁻¹, metabolic rates (M) between 50 and 270 W · m⁻², and Clo values between 0.1 and 0.6. In 95% of the data, mean radiant temperature was within ±3‡ C of air temperature. Based on 190 data averaged over individual values, the following equation was derived by a multiple linear regression technique: ˉT_sk=30.0+0.138T_a+0.254P_a−0.57V_a+1.28 · 10⁻³ M−0.553 Clo. This equation was used to predict mean skin temperature from 629 individual data. The difference between observed and predicted values was within ±0.6‡ C in 70% of the cases and within ±1‡ C in 90% of the cases. It is concluded that the proposed formula may be used to predict mean skin temperature with satisfactory accuracy in nude to lightly clad subjects exposed to warm ambient conditions with no significant radiant heat load.     

Seasonal variation in sweating responses of older and younger men

Eight older (60–65 years) and six younger (20–25 years) men were exposed to a standard heat stress for 60 min in summer, autumn, winter, and spring. The test consisted of placing the lower legs and feet in a 42°C water bath while sitting in constant environmental conditions (30°C and 45% relative humidity). The increase of rectal temperature (T _re) was significantly greater (P < 0.05) in autumn, winter, and spring than in summer for the older group, but significantly greater only in winter than in summer for the younger group (P < 0.05). The T _re was greater for the older group in all seasons, but of significance only in autumn and spring (P < 0.01). There were no significant season-related differences for metabolic heat production (m) and mean skin temperature ( _sk) during the heat test in the respective groups, although the m and _sk were lower for the older group in all seasons (P < 0.01). In the older group total body sweating rate (m_sw) divided by T _re (total m_sw/T _re) decreased from summer to winter (P < 0.02) and did not differ between winter and spring, whereas total m_sw/T _re in the younger group increased in spring after decreasing from autumn to winter (P < 0.03). The variations of the value, local sweating rate on the back and thigh divided by T _re (back m_sw/T _re and thigh m_sw/T _re), were similar to those of the total m_sw/T _re in each group, except for back m_sw/T _re in the younger group, which did not increase from winter to spring. The total m_sw/T _re, back m_sw/T _re and thigh m_sw/T _re were significantly less for the older group in summer, autumn and spring (P < 0.05). The range of seasonal variations was significantly less for the older group (P < 0.001). The results indicated that, compared with younger men in older men, the enhancement of sweating function toward summer occurred later and its reduction toward winter occurred earlier despite a smaller range of seasonal variation and that older men had a somewhat lesser capability to maintainT _re when challenged by heat stress in all seasons.     

Central and peripheral contributions to control of heart rate during heat acclimation

The contributions of the autonomic nervous system and the cardiac pacing cells in the development of heat-acclimation-induced bradycardia were analyzed, and the effect of heat acclimation on the chronotropic response of the heart to heat stress (40° C) was studied. Rats were acclimated at 34° C for 0, 5, 14, 30 and 60 days. Heart rate (HR) was measured in conscious animals, using chronic subcutaneous electrodes. Sympathetic and parasympathetic influences were studied by IP administration of 0.1 and 1 mg/100 g body weight atropine and propranolol respectively, while intrinsic HR (HR_i) was measured following administration of both drugs simultaneously. The effects of carbamylcholine and norepinephrine on the beating rate of isolated rat atria were investigated to study pacemaker responsiveness to neutrotransmitters. Up to day 14 of heat acclimation, bradycardia was attained by tonic parasympathetic acceleration (18%) and temporal sympathetic withdrawal (0.8% on day 14), to compensate for the gradually augmented HR_i (2.5% and 8% on days 5 and 14, respectively). Following long-term acclimation HR_i declined below pre-acclimation rate. This was associated with resumed sympathetic activity (16% and 10% on days 30 and 60 respectively) while parasympathetic activity continued to be high (18%). Tachycardia, known to occur with severe uncontrolled body hyperthermia, was attenuated following heat acclimation by 42%. It was concluded that during the initial phase of heat acclimation bradycardia is achieved primarily by changes in autonomic influences, while following long-term acclimation, changes in the intrinsic properties of the pacing cells (HR_i) and the autonomic system both play a role.     

Elongated peptides,not the predicted nonapeptide stimulate a major histocompatibility complex class I-restricted cytotoxic T lymphocyte clone with specificity for a bacterial heat shock protein

The peptides recognized by an H-2D^b-restricted CD8 cytotoxic T lymphocyte (CTL) clone which is specific for the 60-kDa mycobacterial heat shock protein (hsp) and cross-reacts with stressed host cells were characterized. None of the nonapeptides from hsp60 conforming to the H-2D^b binding motif were able to sensitize target cells for lysis by this CTL clone. Sequence analysis of the stimulatory fraction from a trypsin digest of hsp60, together with synthetic peptide studies, defined a cluster of overlapping epitopes. Carboxy-terminal extension by at least one amino acid of the nonamer predicted to bind best to H-2D^b was essential for CTL recognition. Two such elongated peptides, a 10-mer and a 12-mer stimulated the clone at similarly low concentrations in the 100 pM range. We assume that these two peptides comply best with the natural epitope. In contrast, the 11-mer was inactive. The stimulatory 10-mer bound to H-2D^b with an efficacy similar to that of the nonapeptide corresponding to the H-2D^b motif, as revealed by peptide induced major histocompatibility complex (MHC) surface expression on RMA-S cells and competitive blocking of epitope recognition by the nonamer. Binding of these carboxy-terminally extended peptides to the MHC groove can be explained by anchoring through the amino acid residue Asn in position 5 of the peptide and by intrusion of the hydrophobic carboxy-terminal Ala (10-mer) or Leu (12-mer), but not Gly (11-mer), into the hydrophobic pocket of the H-2D^b cleft. Because the carboxy-terminal part is thus larger than predicted this region of the peptide may arch up from the binding groove. We assume that recognition of steric components of the MHC/peptide complex broaden the range of epitope specificity for a single T cell receptor. This flexibility not only promotes recognition of several overlapping peptides from a single antigen, but may also increase the chance of cross-reaction with similar peptides from unrelated proteins, including autoantigens. Consistent with this latter assumption, the T cell clone cross-recognizes mycobacterial hsp60 and stressed host cells.     

Diurnal changes of thermoregulatory functions in pigeons

In pigeons, we studied the diurnal variation of body temperatures and its dependence on the diurnal variations of shivering, vasomotor activity and panting in light-dark (LD) — conditions (1212 h, 1001 Lux) and in different, but for at least 24 h constant ambient temperatures.In low ambient temperatures (below thermoneutrality) shivering was reduced shortly after lights off (early dark phase), and it increased again some hours before lights on (late dark phase); the lower the ambient temperature, the larger the reduction of shivering and the shorter the time of reduction.Within thermoneutrality, the decrease ofT _b in the early dark phase was associated with an increase of foot skin temperature, probably due to vasodilatation. Later-on foot skin temperature decreased again (vasoconstriction). The feet remained constricted even in the late dark phase, whenT _b already increased.At higher ambient temperature (above thermoneutrality) vasodilatation persisted all over the 24 h, while in these conditions respiratory rate increased significantly after lights off.The described diurnal variations of thermoregulatory effector mechanisms are in agreement with the concept of an active adjustment of the body temperature rhythm.Supported by the Deutsche Forschungsgemeinschaft (SBF 114)     

牙用遮色瓷热处理制度的研究

首次选用双相成核剂CaF2 和TiO2 为制备遮色瓷的成核剂 ,以SiO2 —Al2 O3 —K2 O—Na2 O系统为其基质成分 ,采用差热分析仪、扫描电镜和x衍射分析仪等实验手段来探讨本体系遮色瓷制备的热处理制度。结果表明阶梯制度的热处理方式适用于本体系的遮色瓷。瓷粉经过如下的热处理制度 :从室温以 8℃ /min的加热速度升温至 75 0℃保温 1h ,然后再以4℃ /min的升温速度升至 96 0℃ ,保温 2h后冷淬 ,其白榴石晶体的析晶行为良好 ,且晶体尺寸较小 (约 1μm左右 )。该热处理制度的确定为改善遮色瓷与金属的热匹配性和提高遮色瓷的理化性能提供了基础     

Mechanical and energy characteristics during shortening in isolated type-1 muscle fibres from Xenopus laevis studied at maximal and submaximal activation

 The mechanical and energy characteristics of isolated fast-twitch muscle fibres (type 1) of Xenopus laevis in isometric- and isovelocity contractions were measured at 20°C. The fibres were stimulated at either 60 Hz or 20 Hz to produce contractions at different levels of activation. The high stimulation frequency gave fused contractions, while at the low stimulation frequency tension fluctuated. When maximum isometric force had been reached, the fibres were shortened by 10% of the fibre length at different velocities. At 60 Hz stimulation during shortening the rate of heat production increased above the isometric rate of heat production. At 20 Hz stimulation during shortening, however, the rate of heat production was not different from the isometric rate of heat production. Mechanical efficiency was the same at the high and low level of activation. The actomyosin efficiency (i.e. the mechanical efficiency corrected for ”activation heat”) was highest at the low level of activation. We conclude that in fast-twitch muscle fibres from X. laevis, actomyosin efficiency is highest for partially activated muscle. From a comparison of the present results with those obtained from a study of slow-twitch muscle fibres presented earlier, it is concluded that fast-twitch muscle fibres are less efficient than slow-twitch muscle fibres. Received after revision: 13 May 1997 / Accepted: 1 July 1997