A new pressure chamber to study the biosynthetic response of articular cartilage to mechanical loading

A prototype chamber was used to apply a precise cyclic or static load on articular cartilage explants under sterile conditions. A variable pressure, pneumatic controller was constructed to power the chamber's air cylinder, capable of applying, with a porous load platen, loads of up to 10 MPa at cycles ranging from 0 to 10 Hz. Pig articular cartilage explants were maintained successfully in this chamber for 2 days under cyclic mechanical loading of 0.5 Hz, 0.5 MPa. Explants remained sterile, viable and metabolically active. Cartilage responded to this load with a decreased synthesis of fibronectin and a small but statistically significant elevation in proteoglycan content. Similar but less extensive effects on fibronectin synthesis were observed with the small static load (0.016 MPa) inherent in the design of the chamber.     

The influence of flange compliance and mechanical loading on the tissue response to percutaneous devices.

The failure of most percutaneous devices (PD) is caused by infection initiated by a lack of a tight seal at the skin-device interface. This interface can be disrupted by both extrinsic and intrinsic forces. Many stress reduction methods have been proposed, the most common being the application of a subcutaneous flange. It is widely believed that the bending compliance of the flange plays a significant role in the success or failure of a PD. A study was conducted to observe the effect of flange compliance on local host response in both a functional and nonfunctional setting. Two PDs having flanges with different bending rigidities were implanted percutaneously in goats (n = 8). After a healing period of 2 weeks, half of these devices were externally stimulated with a random load. All the implants were retrieved after 4 weeks and evaluated histologically. The tissue capsule was significantly thicker and the incidence of severe fibrosis and/or necrosis was higher at the flange rim of the functional implants, irrespective of flange compliance. The more compliant devices were encapsulated with a thick fibrous capsule more frequently than the less compliant ones, irrespective of functional status. The more compliant devices also had a greater incidence of foreign body giant cells in the corner region and elicited severe acute inflammation at the corner and top of the flange more frequently than the less compliant implants.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamic arterial elastance to predict arterial pressure response to volume loading in preload-dependent patients

Introduction  

Hemodynamic resuscitation should be aimed at achieving not only adequate cardiac output but also sufficient mean arterial pressure (MAP) to guarantee adequate tissue perfusion pressure. Since the arterial pressure response to volume expansion (VE) depends on arterial tone, knowing whether a patient is preload-dependent provides only a partial solution to the problem. The objective of this study was to assess the ability of a functional evaluation of arterial tone by dynamic arterial elastance (Ea_dyn), defined as the pulse pressure variation (PPV) to stroke volume variation (SVV) ratio, to predict the hemodynamic response in MAP to fluid administration in hypotensive, preload-dependent patients with acute circulatory failure.     

The effects of age and peripheral vascular disease on the circulatory and mechanical response of skin to loading

The skin and subcutaneous soft tissues of amputation residual limbs are required to withstand externally applied loads of greater magnitude than similar tissues of the intact lower limb. Increased age and poor circulatory status may contribute to the increased risk of tissue injury seen in this population. This study evaluates the effects of age and circulatory status as risk factors for skin injury resulting from externally applied forces. Twelve young control (YC), six elderly control (OC) and 11 subjects with peripheral vascular disease (PVD) were studied. After base-line ankle arm index (AAI) measurements, TcPO2 electrodes were applied 10 cm below the knee over the medial surface of the tibia and the muscle belly of tibialis anterior. TcPO2 measurements and tissue displacements were obtained under the influence of incremented, normally oriented, external loads. The sensitivity of the tissues to applied loads was determined by calculating the load at which the TcPO2 reached zero. The stiffness of the tissues (displacement/load) was calculated under high (greater than 40 mm Hg) and low (less than 20 mm Hg) loading conditions. No difference was noted in tissue sensitivity to applied loads between the OC and YC populations. The TcPO2 decreased to zero in the PVD population at significantly lower applied loads than both the OC and YC populations. The tissue stiffness of the PVD and the OC populations over bone was greater than the YC population, but no significant differences were noted between the PVD and the OC populations. In summary, increased age does not result in a greater tissue sensitivity to externally applied loads, in spite of the demonstrated increased tissue stiffness.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of prolonged lithium ingestion on the response to mineralocorticoids in rats.

The effect of long-term lithium administration on the response to mineralocorticoids was studied in rats which were adrenalectomized in order to avoid the effects of endogenous hormone. The hormone response was estimated from the changes in urinary excretion of sodium and potassium in rats on low and high sodium intake and from the consumption of a hypertonic NaCl solution by rats given a free choice between this and demineralized water. Lithium was found to lower the response to aldosterone and deoxycorticosterone acetate both in acute and chronic experiments. It was further found that in adrenalectomized rats given no hormone, those given lithium consumed significantly more NaCl solution than those given no lithium. The experiments therefore provide evidence that lithium induces a sodium requirement beyond that induced by the inhibition of the response to mineralocorticoids.     

Arterial mechanical properties in dilated cardiomyopathy. Aging and the response to nitroprusside.

The effects of aging on arterial mechanical properties and the response to nitroprusside were examined in 25 patients with dilated cardiomyopathy. High-fidelity pressures were recorded with a multisensor catheter. Pulse wave velocity was determined between two sensors in the thoracic aorta. Arterial compliance was determined by an analysis of the diastolic waveform and cardiac output. At baseline, despite a similar systemic vascular resistance, the pulsatile load (e.g., arterial compliance) and wave transmission characteristics (e.g., pulse wave velocity) were altered with aging. Arterial compliance was reduced in older (greater than 50 yr, n = 8) versus younger (less than 35 yr, n = 8) patients (0.51 +/- 0.17 vs. 1.33 +/- 0.63 ml/mmHg, P less than 0.01) and intermediate in those 35-50 yr of age (n = 9, 0.72 +/- 0.40 ml/mmHg). There was a positive correlation between age and pulse wave velocity (r = +0.90). Nitroprusside infusion decreased resistance, increased arterial compliance, and lowered pulse wave velocity in all groups. Yet, advancing age was associated with a greater fall in wave velocity for a given fall in aortic pressure. The slope (K) of the relation between pulse wave velocity and aortic diastolic pressure progressively increased with age (0.01 +/- 0.03, 0.06 +/- 0.02, and 0.09 +/- 0.03 m/s-mmHg). Multiple linear regression analysis revealed a significant relation between K and age. These data demonstrate that in older patients with dilated cardiomyopathy the left ventricle is coupled to an arterial circulation that has a greater pulsatile load, despite a similar steady load. Furthermore, these age-related changes in the arterial system affect the hemodynamic response to pharmacologically-induced vasodilatation.     

Myocardial perfusion pressure: a predictor of 24-hour survival during prolonged cardiac arrest in dogs

Myocardial perfusion pressure, defined as the aortic diastolic pressure minus the right atrial diastolic pressure, correlates with coronary blood flow during cardiopulmonary resuscitation (CPR) and predicts initial resuscitation success. Whether this hemodynamic parameter can predict 24-h survival is not known. We examined the relationship between myocardial perfusion pressure and 24-h survival in 60 dogs that underwent prolonged (20 min) ventricular fibrillation and CPR. Forty-two (70%) animals were initially resuscitated and 20 (33%) survived for 24 h. Myocardial perfusion pressure was significantly greater when measured at 5, 10, 15 and 20 min of ventricular fibrillation in the resuscitated animals than in the non-resuscitated animals (P less than 0.01). Likewise, the myocardial perfusion pressure was also greater in the animals that survived 24 h than in animals that were resuscitated, but died before 24 h (P less than 0.02). Myocardial perfusion pressure measured after 10 min of CPR was 11 +/- 2 mmHg in animals never resuscitated, 20 +/- 3 mmHg in those resuscitated that died before 24 h and 29 +/- 2 mmHg in those that survived 24 h (P less than 0.05). A myocardial perfusion pressure at 10 min of CPR of 20 mmHg or less is an excellent predictor of poor survival (negative predictive value = 96%). Myocardial perfusion pressure is a useful index of CPR effectiveness and therefore may be a useful guide in helping to optimize resuscitation efforts.     

The effects of the antagonists of the renin-angiotensin system on cardiovascular response to lower-body subatmospheric pressure in the anaesthetized cat

1. Lower-body subatmospheric (negative) pressure led to a prompt reduction in central venous pressure and arterial blood pressure. Arterial blood pressure was then restored within 30 s and there was a tachycardia. These reflex responses have been used to investigate the role angiotensin plays in blood pressure control. 2. The initial plasma renin activity (2.9 ng of angiotensin I h-1 ml-1) did not change during the brief lowering of pressure. Before pressure was lowered neither the angiotensin-converting enzyme inhibitor nor a competitive antagonist, [Sar1, Ala8]-angiotensin II, lowered arterial pressure. 3. Nevertheless, after inhibition of the renin-angiotensin system by these agents, the reduction in blood pressure induced by lower-body negative pressure became greater and the blood pressure recovery was impaired. 4. The findings suggest that angiotensin, at a blood concentration which has no direct effect on blood pressure, interacts with the sympathetic nervous system to maintain arterial blood pressure.     

Tracheoesophageal fistula and massive pneumoperitoneum after prolonged mechanical ventilation.

We describe a patient who had two unusual complications of prolonged mechanical ventilation-tracheoesophageal fistula and pneumoperitoneum-with a fatal outcome. Recurrent pulmonary aspirations and massive abdominal distention in the setting of longstanding artificial ventilation should alert the physician to these possibilities.     

Work capacity and metabolic and morphologic characteristics of the human quadriceps muscle in response to unloading

Summary. The response of skeletal muscle to unweighting was studied in six healthy males who were subjected to four weeks of lowerlimb suspension. They performed three bouts of 30 consecutive maximal concentric knee extensions, before unloading and the day after (POST 1), 4 days after (POST 2) and 7 weeks after (REC) resumed weight-bearing. Peak torque of each contraction was recorded and work was calculated as the mean of the average peak torque for the three bouts and fatigability was measured as the decline in average peak torque over bouts. Needle biopsies were obtained from m. vastus lateralis of each limb before and at POST 1. Muscle fibre type composition and area, capillarity and the enzyme activities of citrate synthase (CS) and phosphofructo-kinase (PFK) were subsequently analysed. Mean average peak torque for the three bouts at POST 1, POST2 and REC was reduced (P < 0.05) by 17,13 and 7%, respectively. Fatigability was greater (P < 0.05) at POST 2 than before unloading. Type I, HA and IIB percentage, Type I and II area and capillaries per fibre of Type I and II did not change (P > 005) in response to unloading. The activity of CS, but not PFK, decreased (P < 0.5) after unloading. The weight-bearing limb showed no changes in the variables measured. The results of this study suggest that this human lowerlimb suspension model produces substantial impairments of work and oxidative capacity of skeletal muscle. The performance decrements are most likely induced by lack of weight-bearing.     

Arthritic hand response to pressure gradient gloves.

Five women with osteoarthritis and 10 with rheumatoid arthritis and finger joint involvement wore a pressure gradient glove, a control glove, or no glove in a randomly assigned sequence. All were outpatients. Each patient wore the assigned glove nightly for 1 week, after which a battery of subjective and objective data, including number of tender joints, ring size, grip strength, palmar temperature, and hand function were obtained. In all, 105 separate examinaion sessions were completed over 7 visits, with each hand serving as its own control in the experimental design. The palmar skin temperature was elevated in both patient groups when either a pressure gradient or control glove was worn. In patients with rheumatoid arthritis, the only significant difference was that the pressure gradient glove reduced ring size when compared to the control glove or no glove. No differences were detected in the patients with osteoarthritis.     

大鼠膝关节负重与非负重区软骨组织学对比分析

目的观察大鼠膝关节软骨负重区与非负重区组织形态、基质中蛋白多糖成分和Ⅱ型胶原分布差异。方法 3月龄SD(Sprague-Dawley)大鼠8只,切取双膝关节,沿矢状面整体切片,采用HE染色、p H值1.0和2.5阿尔新蓝染色、番红O染色、阿尔新蓝-番红O复染观察软骨形态结构和基质蛋白多糖成分,并测量软骨厚度,免疫组化检测Ⅱ型胶原分布。分别观察负重区与非负重区软骨形态和基质染色差异,并利用图像分析系统,对基质成分染色深浅进行光密度定量,采用独立样本t检验进行统计分析。结果负重区与非负重区软骨厚度、细胞分布、形态结构均有较大差异。负重区软骨较非负重区明显增厚[胫骨平台(265±39)μm vs.(179±27)μm,t=5.128,P=0.000 2;股骨髁(219±33)μm vs.(132±21)μm,t=6.291,P<0.000 1],且软骨各层结构特征较非负重区更加明显。阿尔新蓝染色结果显示,负重区的非钙化层比非负重区染色更浅(胫骨平台0.073±0.013vs.0.354±0.034,t=21.83,P<0.000 1;股骨髁0.058±0.020 vs.0.131±0.022,t=6.945,P<0.000 1),而番红O深染(胫骨平台0.246±0.013 vs.0.158±0.034,t=6.838,P<0.000 1;股骨髁0.171±0.020vs.0.086±0.022,t=8.086,P<0.001),差异均有统计学意义,但上述两个区域钙化层的阿尔新蓝染色和番红O染色结果并无统计学差异。阿尔新蓝-番红O复合染色结果显示,负重区软骨的阿尔新蓝染色面积百分比明显少于非负重区[胫骨平台(19.3±5.1)%vs.(88.2±4.2)%,t=29.50,P<0.000 1;股骨髁(36.2±5.8)%vs.(69.5±7.1)%,t=10.27,P<0.000 1],而番红O染色面积百分比却大于非负重区[胫骨平台(72.6±8.2)%vs.(31.2±5.2)%,t=12.06,P<0.000 1;股骨髁(72.1±7.6)%vs.(26.1±8.1)%,t=11.71,P<0.000 1],差异均有统计学意义。负重区软骨非钙化层p H 2.5阿尔新蓝染色明显较p H 1.0阿尔新蓝染色加深。免疫组化未发现负重区与非负重区Ⅱ型胶原平均光密度存在统计学差异(胫骨平台0.033±0.005 vs.0.029±0.006,t=1.449,P=0.169 5;股骨髁0.031±0.009 vs.0.027±0.002,t=1.227,P=0.240 0)。结论胫骨和股骨髁负重区较非负重区厚度增加,软骨各层结构特征更加明显。负重区与非负重区比较,基质中糖胺多糖的含量明显增加,软骨透明质酸含量明显减少,硫酸软骨素和硫酸角质素含量明显增加,而Ⅱ型胶原含量并无差异。说明不同的受力环境可以造成软骨形态结构和基质成分差异,负重区软骨的形态结构更加适应于承受关节的力学作用。同时提示临床用来修复负重区软骨缺损的非负重区软骨缺乏适应负重区力学环境的组织结构,可能是骨软骨移植手术后移植物退化的重要因素。     

张力对小鼠增生性瘢痕形成及羟脯氨酸含量的影响

背景：张力在细胞增殖、分化、凋亡以及基因表达过程中起着重要的作用。目的：观察张力对小鼠增生性瘢痕形成及羟脯氨酸含量的影响。方法：4周龄大C57/BL小鼠随机分为2组,张力组小鼠背部制作一个2cm长直线性全层皮肤切口,用尼龙线缝合,4d后拆线,再用尼龙线将22-mm扩张螺丝固定到已经愈合的创面上,隔日扩张。对照组扩张螺丝不动。分别于伤后1,2,3,4,5周各取6只小鼠瘢痕组织观察瘢痕组织厚度、横截面积改变,测量瘢痕组织羟脯氨酸含量。结果与结论：张力组瘢痕增生明显,其厚度、横截面积显著大于对照组（P〈0.01）,张力组各时间点瘢痕组织羟脯氨酸含量显著高于对照组（P〈0.01）。表明张力导致小鼠瘢痕增生显著,羟脯氨酸含量显著增高。