Distribution of Internal Strains Around Bony Prominences in Pigs

Deep tissue injury (DTI) is a type of pressure ulcer in which tissue breakdown initiates at the bone-muscle interface under intact skin. Excessive deformation in the soft tissue, particularly around bony prominences, is believed to be one of the causes leading to the development of DTI. The main goal of this study was to measure the magnitude and distribution of strains within muscles surrounding the ischial tuberosities, induced by levels of external loading that encompass the range of loading experienced by the soft tissue in seated individuals. The experiments were conducted in adult pigs with intact spinal cords (n = 5) and pigs with partial spinal cord injury (SCI) (n = 2), one of which also had a DTI. A secondary goal was to obtain a preliminary assessment regarding the capacity of intermittent electrical stimulation (IES), an intervention for preventing the formation of DTI, to counteract the muscle compression caused by external loading. In intact animals, muscles subjected to external loads equivalent to 25% of body weight experienced maximal principal strains, minimal principal strains, and shear strains of 0.68, -0.3, and 0.4, respectively. These magnitudes increased by 91.9, 17.6, and 87.5%, respectively, when external loading increased to 50% body weight. Minimal to no further increases in strain magnitudes were seen with the 75% body weight loading level. In one animal with SCI and no DTI, strain magnitudes were on average 9.7% higher than those in the intact animals at the corresponding loading levels. The presence of a DTI in another animal with SCI reduced strain magnitudes by 28% compared to intact animals. The regions in the muscle that underwent the largest deformations were those between the ischial tuberosity and the external surface, and up to 2 cm ventral to the ischial tuberosity (furthest measured). Muscle contractions produced by IES increased the thickness of the tissue between the ischial tuberosities and skin during the period of stimulation by 10-20% for loading levels up to 75% of body weight in both intact and spinal cord injured pigs. This study provides the first measurements of strain around the ischial tuberosities in an animal model that resembles humans.     

几种不同部位防压疮复合硅胶垫与人体接触的压力分布

背景：高压总是集中在骨突出部位,坐垫应能均匀分布压力,设计一种有效减压的坐垫对压疮预防有重要的作用。 目的：比较几种不同部位防压疮硅胶复合垫与人体接触的压力分布,研究减小界面压力的坐垫形式。 方法：将设计的海绵轮廓垫分为复合硅胶垫和单纯海绵垫两种,复合硅胶垫又分为整个坐面复合硅胶垫,臀部区域复合硅胶垫,坐骨区域复合硅胶垫。用X-sensor压力系统测量4种坐垫压力参数(最大压力,平均压力,压力标准差,坐骨区域压力,骶骨区域压力,大转子区域压力)和面积参数(总体接触面积,高压接触面积,低压接触面积,中压接触面积及高压百分比,中压百分比和低压百分比)。 结果与结论：与单纯海绵垫比较,复合硅胶垫有较小的压力值和高压接触面积及其占总体接触面积的百分比。与整个坐面复合硅胶垫比较,臀部区域复合硅胶垫有较小的压力值和高压接触面积及其占总体接触面积的百分比。与其他3种坐垫比较,坐骨区域复合硅胶垫有最小的压力参数值和高压接触面积及其占总体接触面积的百分比,坐骨区域压力值显著减小(P < 0.05)。表明在海绵轮廓垫上复合硅胶能起到减小界面压力的作用,硅胶垫的复合位置对界面压力值有显著影响。     

The false premise in measuring body-support interface pressures for preventing serious pressure ulcers

Presently, commercial cushioning products for pressure ulcer prevention are being evaluated for their protective effect exclusively based on interfacial pressures between the cushion/mattress and the patient. However, interface pressures cannot predict elevated mechanical stresses in deep tissues adjacent to bony prominences. Such deep tissue stress concentrations are associated with local ischaemia and hypoxia, which over time result in deep tissue necrosis, particularly of muscle tissue. In order to demonstrate this phenomenon, a physical phantom of the mechanical interaction between the ischial tuberosities (IT) and gluteus muscles of the buttocks was built, incorporating geometric replica of the human IT and real (bovine) muscle tissue. Internal muscle stresses directly under the IT were five to 11-fold greater than stresses at more distal locations, and a Pearson correlation test showed that they could not have been predicted from the interface pressures in the phantom. Accordingly, though pressure ulcer prevention clinics which utilize routine sitting pressure measurements report effective outcomes, the present results highlight a problem in using body-support pressure measurements to predict the risk for pressure-related deep tissue injury.     

The false premise in measuring body-support interface pressures for preventing serious pressure ulcers

Presently, commercial cushioning products for pressure ulcer prevention are being evaluated for their protective effect exclusively based on interfacial pressures between the cushion/mattress and the patient. However, interface pressures cannot predict elevated mechanical stresses in deep tissues adjacent to bony prominences. Such deep tissue stress concentrations are associated with local ischaemia and hypoxia, which over time result in deep tissue necrosis, particularly of muscle tissue. In order to demonstrate this phenomenon, a physical phantom of the mechanical interaction between the ischial tuberosities (IT) and gluteus muscles of the buttocks was built, incorporating geometric replica of the human IT and real (bovine) muscle tissue. Internal muscle stresses directly under the IT were five to 11-fold greater than stresses at more distal locations, and a Pearson correlation test showed that they could not have been predicted from the interface pressures in the phantom. Accordingly, though pressure ulcer prevention clinics which utilize routine sitting pressure measurements report effective outcomes, the present results highlight a problem in using body-support pressure measurements to predict the risk for pressure-related deep tissue injury.     

Assessment of humidity and temperature sensors and their application to seating

Humidity and temperature are considered to be important factors in designing comfortable seat surfaces. A small number of studies have attempted to address this; however the methods used were limited regarding the placement of their sensors. This study aimed to design a sensor array system to investigate changes in humidity and temperature for eventual use in the study of factors affecting sitting comfort and incontinence detection. The system was subjected to three types of experiments: sensor response verification, thermal radiation testing and in situ trials. The variance in output within each type of sensor was small (±3.5% and ±0.3°C) and there was no apparent change to the variance in output of the sensors, when used in air or on a foam cushion loaded with a 50 kg sandbag (p > 0.1). In the human sitting experiments, although the profile from sensors under the thighs and ischial tuberosities were similar, the magnitude of change could be affected by position and body mass of the subject. This was especially noticeable with the sensors under the coccyx. These results support the use of multiple sites for sensor placement over the use of a single site when studying these parameters at the interface between subject and seating material at the seat base.     

坐骨结节压力性损伤的分型及修复策略

目的分析归纳坐骨结节压力性损伤临床分型,总结各型的修复方法,探讨其修复重建效果,为坐骨结节压力性损伤的修复提供新治疗方案。 方法2013年1月至2018年1月,解放军总医院第四医学中心烧伤整形暨创面修复中心共收治坐骨结节压力性损伤患者92例,共109个创面,其中手术修复86例,共101个创面,其中男49例,女37例,年龄31～79岁,根据2016版国际压疮指南分期术语修订版将其分为Ⅲ类创面68个,Ⅳ类创面33个,创口面积1 cm×9 cm～11 cm×16 cm,深度1～6 cm,创基面积2 cm×8 cm～8 cm×14 cm,深部腔隙容积(盐水测定法)3～60 mL;根据彻底清创后组织缺损程度,分为4型,每种分型按相对应的方案修复：Ⅰ型采用直接清创缝合,Ⅱ型采用臀下动脉穿支皮瓣局部转移修复,Ⅲ型采用股薄肌肌瓣或臀大肌肌瓣填充修复,Ⅳ型采用股薄肌肌瓣或臀大肌肌瓣合并臀下动脉穿支皮瓣修复。术后观察愈合效果及随访情况。 结果本组86例患者101个创面中,Ⅰ型创面36个,一期愈合32个创面,翻修4个创面二期愈合;Ⅱ型创面29个,一期愈合23个创面,翻修6个,二期愈合4个;Ⅲ型创面30个,一期愈合28个创面,翻修2个创面二期愈合;Ⅳ型创面6个,一期愈合4个创面,翻修1个创面二期愈合。71例获得6～12个月随访,平均随访7.2个月,复发11例,新发6例。 结论坐骨结节部位特殊,发生压力性损伤后修复比较棘手,根据临床病例的总结归纳,将其分为4型,对不同分型创面选择合适的方案进行修复,可得到满意的修复效果,避免复发。     

坐姿下不同组织压力性损伤生物力学研究

目的 探讨坐姿下臀部压力性损伤易发部位以及不同软组织的生物力学响应,为有效预防深层组织压力性损伤提供参考。 方法 基于臀部 CT 扫描数据,建立坐位臀部有限元模型,包括骨骼、肌肉、脂肪和皮肤组织及坐垫模型,利用生死单元模拟组织损伤。 对比实验坐垫界面压力测量数据与有限元模拟结果,验证模型有效性。 模拟坐位力学状态,研究软组织的应力、应变情况,分析不同软组织中的压应力及超出极限值后可能造成的损伤情况。结果 通过对比坐垫模型仿真结果与实验界面压力测量结果,证明模型有效。 坐位时坐骨结节下方软组织区域出现应力集中现象。 其中,臀大肌组织中的横向压应力峰值约为 38 kPa,剪切应力峰值约为 3. 4 MPa;而脂肪组织中的最大压应力与剪切应力峰值分别为 22 kPa 与 4. 5 MPa,均未出现在坐骨结节正下方。 结论 软组织受到一定时间和大小的压力载荷作用,可能出现深层组织损伤。 当保持坐姿一定时间后,应及时变换体位,以降低压力性损伤出现的概率。 研究结果为预防压力性损伤提供生物力学依据,具有重要的临床研究价值。     

基于AVR的防褥疮气垫控制器设计

目的针对防褥疮气垫工作模式单一、故障报警措施缺乏、操作界面呆板等不足,本文提出基于 AVR单片机的防褥疮气垫微控制器设计方案.方法该微控制器以 Atmega16为核心,外设电路包括压力传感器、气压检测电路、液晶显示电路、气泵驱动电路等,可根据体重、周期、工作时间参数设置不同,控制气泵使气垫产生幅度、周期、时间可调的波动式翻滚达到防治褥疮的作用.连接气泵对气垫充气测试,设置不同的工作参数,观察并比较测试结果.结果测试结果表明控制器运行稳定,可使气垫产生规律的波动式翻滚,符合防治褥疮的要求.结论基于该微控制器的防褥疮气垫操作界面友好,工作模式多样,并且工作安全可靠,成本低廉.     

The Compression Intensity Index: a practical anatomical estimate of the biomechanical risk for a deep tissue injury.

Pressure-related deep tissue injury (DTI) is a severe form of pressure ulcer that initiates in compressed muscle tissues under bony prominences, and progresses superficially towards the skin. Patients with impaired motosensory capacities are at high risk of developing DTI. There is a critical medical need for developing risk assessment tools for DTI. A new anatomical index, the Compression Intensity Index: CII=(BW/Rt);[1/2], which depends on the body weight (BW), radius of curvature of the ischial tuberosities (R) and thickness of the underlying gluteus muscles (t), is suggested for approximating the loading intensity in muscle tissue during sitting in permanent wheelchair users, as part of a clinically-oriented risk assessment for DTI. Preliminary CII data were calculated for 6 healthy and 4 paraplegic subjects following MRI scans, and data were compared between the groups and with respect to a gold standard, being a previously developed subject-specific MRI-finite-element (MRI-FE) method of calculating muscle tissue stresses (Linder-Ganz et al., J. Biomech. 2007). Marked differences between the R and t parameters of the two groups caused the CII values of the paraplegics to be approximately 1.6-fold higher than for the healthy (p<0.001), thereby indicating on the sensitivity of this parameter to the pathoanatomical changes that occur in the buttocks with paraplegia. Data of CII correlated reasonably with the gold standard calculations of MRI-FE muscle stresses (correlation coefficient 0.65). Since CII measurements do not require highly-specialized biomechanical numerical analyses such as MRI-FE, CII has the potential to serve as a practical, quick, and cost-effective approximation of the loading intensity in muscles of wheelchair-bound or bedridden patients. Hence, CII measurements can be integrated into DTI-risk-assessment tools, the need of which is now being discussed intensively in the American and European Pressure Ulcer Advisory Panel meetings.     

Lose weight and win: a church-based weight loss program for blood pressure control among black women.

The Baltimore Church High Blood Pressure Program (CHBPP) offers a behaviorally oriented weight control program consisting of eight weekly 2-h diet counseling/exercise sessions. Pre- and post-program weight and blood pressure measurements were analyzed for 184 black and 3 white women aged 18-81 years (mean 51) who participated in the program in 1984-1986: 88 were taking antihypertensive medication (Rx) and 99 were not (no Rx). Mean weight loss was 6 lb in both groups: -18 to +7 lb in the Rx group and -31 to +3 lb in the no Rx group. The mean systolic/diastolic blood pressure (SBP/DBP) decrease was 10/6 mmHg in the Rx group and 5/3 mmHg in the no Rx group (P < 0.001 for all pre/post comparisons). Final SBP was < 140 mmHg for 74% of participants, versus 52% initially. Final DBP was < 90 mmHg in 92% versus 65% initially. Supporting the inference that BP decreases among weight control program participants reflect program effects, percent changes in SBP and DBP (week 2 to week 8) were significantly correlated with percent change in weight (rs = 0.23-0.36; P < 0.05). Comparison data for 25 women from the CHBPP population showed a mean SBP/DBP increase of 8/2 mmHg over an 8-week interval. Based on follow up measurements 6 months after the end of the 8-week program for 74 of the 187 women, weight lost during the 8-week program was maintained or exceeded by 65%. Net weight change at 8 months from baseline for women in the follow up subsample ranged from -28 to +4 lb; mean (SD) -6 (7) lb. Weight loss and related dietary or behavioral changes resulting from participation in a weight control program can enhance blood pressure control among black women.     

Effects of intermittent electrical stimulation on superficial pressure, tissue oxygenation, and discomfort levels for the prevention of deep tissue injury

The overall goal of this project is to develop effective methods for the prevention of deep tissue injury (DTI). DTI is a severe type of pressure ulcer that originates at deep bone–muscle interfaces as a result of the prolonged compression of tissue. It afflicts individuals with reduced mobility and sensation, particularly those with spinal cord injury. We previously proposed using a novel electrical stimulation paradigm called intermittent electrical stimulation (IES) for the prophylactic prevention of DTI. IES-induced contractions mimic the natural repositioning performed by intact individuals, who subconsciously reposition themselves as a result of discomfort due to prolonged sitting. In this study, we investigated the effectiveness of various IES paradigms in reducing pressure around the ischial tuberosities, increasing tissue oxygenation throughout the gluteus muscles, and reducing sitting discomfort in able-bodied volunteers. The results were compared to the effects of voluntary muscle contractions and conventional pressure relief maneuvers (wheelchair push-ups). IES significantly reduced pressure around the tuberosities, produced significant and long-lasting elevations in tissue oxygenation, and significantly reduced discomfort produced by prolonged sitting. IES performed as well or better than both voluntary contractions and chair push-ups. The results suggest that IES may be an effective means for the prevention of DTI.     

Oscillating wheelchair seat for prevention of decubitus ulcers

A wheelchair seat designed to prevent the occurrence of decubitus ulcers has been constructed and tested. The rear section of the seating surface is periodically lowered to allow a reduction in pressure for the highly stressed tissue underneath the ischial tuberosities. Several parameters in the seat can be easily adjusted to accommodate the needs of different individuals.     

膀胱压与腹内压相关性的临床研究

目的　研究膀胱压与腹内压相关性 .方法　选取腹腔镜胆囊切除术患者 30名 .排空膀胱后经Foley导管注入 5 0ml生理盐水 .置入 18G气腹穿刺针后 ,连接自动电子充气连续测压仪 ,选取腹内压为 0、5、10、15、2 0、2 5mmHg时记录相应的膀胱压 .结果　当膀胱注入 5 0ml的生理盐水后 ,腹内压由 0增至 2 5mmHg时 ,膀胱压与腹内压存在直线相关 ,相关系数r=0 .939(p<0 .0 1) ,决定系数r2 =0 .882 .结论　膀胱压能准确估计腹内压     

Cardiovascular responses in older adults with total knee arthroplasty at rest and with exercise on a positive pressure treadmill

Purpose

We investigated cardiovascular responses at rest and during submaximal exercise on a lower body positive pressure treadmill in older adults with total knee arthroplasty (TKA).

Methods

Twenty-four adults (mean age 64.6 ± 7.9 SD) with unilateral TKA participated (median time since surgery 8.0 weeks). Heart rate and blood pressure responses were measured at rest standing on the positive pressure treadmill with 0, 10, 20, and 30 mmHg applied. Heart rate, blood pressure, oxygen consumption, minute ventilation, knee pain and perceived exertion were measured during submaximal exercise tests (0 and 40 % body weight support) conducted 1 week apart.

Results

At rest there were no differences in blood pressure across different treadmill pressures, but heart rate was significantly lower when 30 mmHg was applied compared to ambient pressure conditions (P < 0.05). Participants averaged 5.1 exercise test stages with 0 % body weight support (maximum speed 2.5 mph, 0 % incline) and 6.4 stages with 40 % body weight support (maximum speed 3.0 mph, 10 % incline). During exercise, heart rate, systolic blood pressure, oxygen consumption, and minute ventilation were lower when 40 % body weight support was provided for a given test stage (P < 0.01). Diastolic blood pressure, knee pain and perceived exertion did not differ with body weight support but increased with increasing exercise test stages (P < 0.05).

Conclusions

Provision of body weight support allowed TKA patients to walk at faster speeds and/or to tolerate greater incline with relatively lower levels of heart rate, blood pressure, and oxygen consumption.     

Effect of cervical sympathetic nerve stimulation on canine carotid sinus reflex.

In the chloralose-anesthetized dog the carotid sinus on one side of the neck was isolated vascularly. Pressure in the isolated sinus [carotid sinus pressure (CSP)], electrocardiogram, and systemic arterial pressure were recorded. Both vagosympathetic trunks were cut and the contralateral common carotid artery was occluded or the contralateral sinus nerve was cut to reduce reflex buffering of arterial pressure changes. By varying CSP from 50 to 250 mmHg the full range of the reflex response was examined. Electrical stimulation of the peripheral end of the cut ipsilateral cervical sympathetic nerve brought about a rapid decrease in mean arterial pressure (MAP) and heart rate (HR) at lower CSPs, no change in these variables at midrange CSPs, and a gradual increase at higher CSPs, such that the gain of the reflex was reduced (1.89 +/- 0.19 to 1.33 +/- 0.15 mmHg/mmHg). The decrease in MAP and HR at lower CSPs implies an increase in baroreceptor activity whereas the converse would appear to occur at higher CSPs. These responses attained a maximum value at low stimulus frequencies (less than 10 Hz).     

Analysis of the tubuloglomerular feedback mechanism in renal autoregulation

Along the juxtaglomerular segment of the afferent arteriole the luminal pressure p approaches the glomerular capillary pressure of 55-60 mmHg. At such low luminal pressures the myogenic mechanism contracts only if extravascular pressure p(ex) is subatmospheric. According to Poiseuille's formula complete autoregulation requires that blood flow is F=5Kr(0)(4)/Deltax at arterial pressures exceeding 65 mmHg; r(0) is the radius of the relaxed segment at transmural pressure p - p(ex) < or =60 mmHg, where p(ex) is the extravascular pressure; Deltax is the length of the main preglomerular segment, 10 times longer than the juxtaglomerular segment. Consistent with in vitro studies a myogenic mechanism may reduce the relaxed juxtaglomerular radius r(jx)=0.7r(0) by 40% at a transmural pressure of 140 mmHg. Fifty and 60% reductions are also considered. Integration of Poiseuille's formula shows that complete autoregulation of preglomerular blood flow requires negative extravascular pressures p(ex)= -90 to -55 mmHg dependent on contractile force. Negative pressure of this magnitude is generated by effective hyperosmolality <5 mOsm across the membrane separating cleft from pole cushion. Negative pressure stays constant at arterial pressures exceeding 90-110 mmHg, implying constant tubuloglomerular feedback, but approaches atmospheric pressure at lower arterial pressure, suggesting maintenance of blood flow by reduction in the glomerular filtration rate; a rise in macula densa concentrations [NaCl](md) by 0.15 mM or [NaHCO(3)](md) by 2 mM raises extravascular pressure towards atmospheric levels by approximately 40 mmHg. A 40-mmHg rise in interstitial pressure exerts the same effect. Loop diuretics nullify osmotic force and dilate juxtaglomerular and main segments by raising juxtaglomerular extravascular pressure towards atmospheric levels.     

关于改进运动员睡眠床垫的研究

目的：研究优秀跳高运动员黄海强现有睡眠床垫的压力分布情况,设计一套改进的睡眠方案。方法：应用X-SEN—SOR压力床垫式检测系统,对黄海强现有两种床垫进行检测,分析后设计新的人机工学床垫,再进行效果评定。结果：原平板床与平面弹簧网海绵床垫平均压力,新设计的床垫能有效分散人体压力,新的床垫显示黄海强仰卧位平均压力为14．7mmHg,最大压力（臀部）为31．7mmHg,远低于以前的床垫。结论：针对黄海强体形设计睡眠床,能有效分散臀部与后背部压力,改善其睡眠状况。     

In vivo evaluation of a new sealant material on a rat lung air leak model.

The ability of an albumin-based hydrogel sealant (ABHS) to prevent air leakage through the suture line after pulmonary surgery was evaluated by comparison with that of a fibrin glue (FG). As an air-leak model, a rat lung was used in which a standard incision was made and the burst pressure for ABHS and FG was measured. The average burst pressures at time 0 for the FG and ABHS groups were 30.8+/-15.2 and 77.5 +/-19.1 mmHg, respectively. At Day 3, the value of ABHS (76.3 +/- 15.8 mmHg) was still significantly higher (P<0.05) than that of FG (60.0 +/- 21.9 mmHg). At Day 7, no statistical difference was observed between the FG group(71.2 +/- 18.6 mmHg) and the ABHS group(88.8 +/- 11.7 mmHg). Histological examination of the incision at Day 14 revealed that neither sealant was not visible at the incision site, and there was no evidence of adverse tissue reaction. It was concluded that ABHS had good sealing properties and is an alternative to FG for air leakage treatment in pulmonary surgery.     

Cardiovascular effects of anti-G suit inflation at 1 and 2 G

We sought to determine to which pressure a full-coverage anti-G suit needs to be inflated in order to obtain the same stroke volume during a brief exposure to twice the normal gravity (2 G) as that at 1 G without anti-G suit inflation. Nine sitting subjects were studied at normal (1 G) and during 20 s of exposure to 2 G. They wore anti-G suits, which were inflated at both G-levels to the following target pressures: 0, 70, 140 and 210 mmHg. Stroke volume was computed from cardiac output, which was measured by rebreathing. Heart rate and mean arterial pressure at heart level were recorded. Inflation to 70 mmHg compensated for the decrease in stroke volume and cardiac output caused by hypergravity. Mean arterial pressure at heart level was comparable at 1 G and at 2 G and increased gradually and similarly with inflation (P<0.001) at both gravity levels. Thus, anti-G suits act by increasing both preload and afterload but the two effects counteract each other in terms of cardiac output, so that cardiac output at 2 G is maintained at its 1 G level. This effect is reached already at 70 mmHg of inflation. Greater inflation pressure further increases mean arterial pressure at heart level and compensates for the increased difference in hydrostatic pressure between heart and head in moderate hypergravity.