Effects of Creep and Cyclic Loading on the Mechanical Properties and Failure of Human Achilles Tendons

The Achilles tendon is one of the most frequently injured tendons in humans, and yet the mechanisms underlying its injury are not well understood. This study examines the ex vivo mechanical behavior of excised human Achilles tendons to elucidate the relationships between mechanical loading and Achilles tendon injury. Eighteen tendons underwent creep testing at constant stresses from 35 to 75 MPa. Another 25 tendons underwent sinusoidal cyclic loading at 1 Hz between a minimum stress of 10 MPa and maximum stresses of 30–80 MPa. For the creep specimens, there was no significant relationship between applied stress and time to failure, but time to failure decreased exponentially with increasing initial strain (strain when target stress is first reached) and decreasing failure strain. For the cyclically loaded specimens, secant modulus decreased and cyclic energy dissipation increased over time. Time and cycles to failure decreased exponentially with increasing applied stress, increasing initial strain (peak strain from first loading cycle), and decreasing failure strain. For both creep and cyclic loading, initial strain was the best predictor of time or cycles to failure, supporting the hypothesis that strain is the primary mechanical parameter governing tendon damage accumulation and injury. The cyclically loaded specimens failed faster than would be expected if only time-dependent damage occurred, suggesting that repetitive loading also contributes to Achilles tendon injuries. © 2003 Biomedical Engineering Society. PAC2003: 8719Rr     

一种测量牙松动度的新方法

本文是出了一种客观确定牙松动的新方法。用瞬态碰撞激震测定牙固有振动半周期Ｔ／２和减幅系数η。以Ｔ／２为主，η为辅，度量牙齿的松动度。对依据的原理从牙周动力学模型出发进行了严密的数学推导；讨论了测试方案；介绍了牙模型测试实验；最后给出实际状态下测试的初步结果。     

Sensitivity to mechanical stimuli and the role of general sensory and perceptual processes in heartbeat detection

Sensitivity to heartbeat sensations is commonly assessed using tasks that require individuals to judge the simultaneity of heartbeats and tones. In two experiments, we investigated the suitability of this paradigm for examining cardioception. In the first experiment, participants judged the simultaneity of near–threshold vibrations and suprathreshold tones. Precision in judging vibration–tone simultaneity was directly related to the detectability of the mechanical stimuli, thereby supporting use of the simultaneity paradigm to assess heartbeat detection. In the second experiment, we examined the influences of sensitivity to mechanical stimuli and the ability to make intermodality simultaneity judgments on the precision of heartbeat detection. We measured participants' vibrotactile thresholds, precision in judging light–tone simultaneity, and precision in judging heartbeat–tone simultaneity. The ability to judge the simultaneity of lights and tones accounted for 24.3% of the variance in precision of heartbeat detection, and mechanical sensitivity accounted for a further 8.5%.     

Energy cost and mechanical efficiency of riding a four-wheeled, human-powered, recumbent vehicle

Oxygen consumption at steady state (V˙O ₂, l · min⁻¹) and mechanical power (W˙, W) were measured in five subjects riding a human-powered vehicle (HPV, the Karbyk, a four-wheeled recumbent cycle) on a flat concrete road at constant sub-maximal speeds. The external mechanical work spent per unit of distance (W, J · m⁻¹), as calculated from the ratio of W˙ to the speed (v, m · s⁻¹), was found to increase with the square of v: W˙=8.12+(0.262 ·v ²) (r=0.986, n=31), where the first term represents the mechanical energy wasted, over a unit of distance, against frictional forces (rolling resistance, R_r), and the second term (k · v ²) is the work performed, per unit distance, to overcome the air drag. The rolling coefficient (C_r, obtained dividing R_r by m · g, where m is the overall mass and g is the acceleration of gravity) amounted to [mean (SD)] 0.0084 (0.0008), that is about 60% higher than that of a racing bicycle. The drag coefficient was calculated from the measured values of k, air density (ρ) and frontal area (A) [C_x=k · (0.5 · A · ρ)⁻¹], and amounted to 1.067 (0.029), that is about 20% higher than that of a racing bicycle. The energy cost of riding the HPV (C_k, J · m⁻¹) was measured from the ratio of metabolic power above rest (net V˙O ₂, expressed in J · s⁻¹) to the speed (v, m · s⁻¹); the value of this parameter increased with the square of v, as described by: C_k=61.45 + (0.675 · v ²) (r=0.711, n=23). The net mechanical efficiency (η) was calculated from the ratio of W to C_k: over the investigated speed range this turned out to be 0.22 (0.021). Best performance times (BPTs) of a “typical”élite athlete riding the Karbyk were calculated over the distances of 1, 5 and 10 km: these were about 8% longer than the BPTs calculated, on the same subjects, when riding a conventional racing bicycle. Accepted: 7 August 2000     

Ventilatory and upper-airway resistance responses to upper-airway cooling and CO2 in anaesthetised rats

The effects of upper airway (UA) cool air and CO₂ on breathing and on laryngeal and supraglottic resistances were studied in anaesthetised rats breathing spontaneously through a tracheostomy. Warm, humidified air containing 0, 5 and 9–10% CO₂ and cool, room-humidity air were delivered at constant flow to either the isolated larynx to exit through a pharyngotomy or to the supraglottic UA to exit through the mouth and/or nose (nose open or sealed). Spontaneous tracheal airflow and UA airflows, temperatures and pressures were recorded. CO₂ had no effect on breathing but caused a slight increase in laryngeal resistance which was abolished by cutting the superior laryngeal nerves (SLN). Cool air caused a decrease in respiratory frequency and/or peak inspiratory flow when applied to the isolated larynx or to the supraglottic airway with the nose closed. These effects were abolished by SLN section. With the nose open, the ventilatory inhibition was not abolished by SLN section. Cool air also caused substantial decreases in laryngeal and supraglottic resistances which were attenuated by SLN section and which persisted following recurrent laryngeal nerve section. In conclusion, whilst UA cooling inhibits breathing and decreases UA resistances, UA CO₂ has minimal effects.     

Severe hypoxia decreases oxygen uptake relative to intensity during submaximal graded exercise

Summary The effect of severe acute hypoxia (fractional concentration of inspired oxygen equalled 0.104) was studied in nine male subjects performing an incremental exercise test. For power outputs over 125 W, all the subjects in a state of hypoxia showed a decrease in oxygen consumption ( O₂) relative to exercise intensity compared with normoxia (P < 0.05). This would suggest an increased anaerobic metabolism as an energy source during hypoxic exercise. During submaximal exercise, for a given O₂, higher blood lactate concentrations were found in hypoxia than in normoxia (P < 0.05). In consequence, the onset of blood lactate accumulation (OBLA) was shifted to a lower O₂ ( O₂ 1.77 l·min^–1 in hypoxia vs 3.10 l·min^–1 in normoxia). Lactate concentration increases relative to minute ventilation ( _E) responses were significantly higher during hypoxia than in normoxia (P < 0.05). At OBLA, _E during hypoxia was 25% lower than in the normoxic test. This study would suggest that in hypoxia subjects are able to use an increased anaerobic metabolism to maintain exercise performance.     

Kappa Delta Award paper. Osteoregulatory nature of mechanical stimuli: function as a determinant for adaptive remodeling in bone

The capacity for functional adaptation within the skeleton was studied using the functionally isolated turkey ulna preparation. The results of this study would suggest that adaptive bone remodeling is extremely sensitive to alterations in both the magnitude and distribution of the strain generated within the bone tissue. At present, it appears that a loading regime can only influence bone remodeling when it is dynamic in nature. The full osteogenic potential of its influence is then achieved after only an extremely short exposure to this stimulus. The potency of the stimulus appears to be proportional to the magnitude of the strain engendered. As strain levels that are acceptable in one location induce adaptive remodeling in others, it would appear that each region of each bone is "genetically programmed" to accept a particular amount and pattern of intermittent strain as "normal." Deviation from this "optimal strain environment" will stimulate changes in the bone's remodeling balance, resulting in adaptive increases or decreases in its mass.     

机械通气下应用肺表面活性物质治疗新生儿肺炎合并呼吸衰竭的疗效

目的：探讨新生儿肺炎合并呼吸衰竭治疗中机械通气下应用肺表面活性物质的疗效。方法：回顾性选取2017年2月至2022年2月无锡市儿童医院新生儿科收治的新生儿肺炎合并呼吸衰竭患儿80例,依据治疗方法分为机械通气下应用肺表面活性物质治疗组(观察组)、机械通气治疗组(对照组)两组,各40例。分析两组患儿血气指标、平均动脉压(MAP)和呼吸力学指标、机械通气时间、总吸氧时间、住院时间、并发症发生情况之间的差异。结果：治疗前,两组患儿的动脉血氧分压(PaO₂)、氧合指数(PaO₂/FiO₂)、动脉血二氧化碳分压(PaCO₂)、氢离子浓度指数(pH)、MAP、呼气末正压(PEEP)、平台压(Pplat)、气道峰压(PIP)之间比较,差异均无统计学意义(P> 0.05);治疗后,两组患儿的PaO₂、PaO₂/FiO₂均高于治疗前,PaCO₂、MAP、PEEP均低于治疗前,差异均具有统计学意义(P <0.05),但治疗...     

急性缺血性脑卒中伴心房颤动患者行 机械取栓的临床疗效及预后因素

〔摘 要〕 目的：研究机械取栓治疗急性缺血性脑卒中（AIS）伴心房颤动患者的疗效及预后因素。 方法：选取北 京市红十字会急诊抢救中心 2020 年 2 月至 2021 年 12 月期间收治的 90 例 AIS 伴心房颤动患者,均行机械取栓治疗, 入院时、治疗后 24 h、7 d、90 d 评估患者的美国国立卫生研究院卒中量表（NIHSS）评分,并在治疗 90 d 后评估患 者的预后效果,参考改良 Rankin 修订量表（mRS）评价,并对影响预后的危险因素总结分析。 结果：入院时所有患 者 NIHSS 评分为（11.25 ± 2.34）分,治疗后 24 h 的 NIHSS 评分为（8.21 ± 1.52）分,治疗后 7 d 的 NIHSS 评分为 （5.12 ± 0.93）分,治疗后 90 d 的 NIHSS 评分为（3.06 ± 0.54）分,NIHSS 评分逐渐下降,差异具有统计学意义 （P ＜ 0.05）。预后良好组、预后不良组患者比较,年龄、高血压、糖尿病、血糖、收缩压、舒张压、侧支循环建立情况、 开始治疗时间、血管再通时间及入院 NIHSS 评分比较,差异具有统计学意义（P ＜ 0.05）;多因素 logistic 回归分析 显示,导致 AIS 伴心房颤动患者机械取栓术后预后不良的独立危险因素有：年龄≥ 60 岁、高血压、未建立侧支循环、 血管再通时间≥ 4 h、入院 NIHSS 评分≥ 14 分,差异具有统计学意义（P ＜ 0.05）。 结论：机械取栓术治疗 AIS 伴 心房颤动患者可减缓神经功能缺损程度,导致患者预后不良的独立危险因素是年龄≥ 60 岁、高血压、未建立侧支循环、 血管再通时间≥ 4 h、入院 NIHSS 评分≥ 14 分,故临床需引起高度重视。     

慢性阻塞性肺疾病急性加重期伴呼吸衰竭患者机械通气治疗失败的影响因素分析

目的探讨慢性阻塞性肺疾病急性加重期(AECOPD)伴呼吸衰竭患者机械通气治疗失败的影响因素。方法回顾性分析2018年6月至2020年6月我院收治的57例行机械通气治疗的AECOPD伴呼吸衰竭患者的临床资料,采用单因素和多元Logistic回归分析探讨机械通气治疗失败的影响因素。结果57例AECOPD伴呼吸衰竭患者中,机械通气治疗失败率为31.58%(18/57)。单因素和多元Logistic回归分析显示,血清NT-proBNP高表达、合并基础疾病、低pH值是AECOPD伴呼吸衰竭患者机械通气治疗失败的独立影响因素(OR>1,P<0.05)。结论AECOPD伴呼吸衰竭患者机械通气治疗失败与血清NT-proBNP高表达、合并基础疾病、低pH值密切相关,临床需对上述危险因素重点关注。