Knight A D, Levick J R
J Physiol. 1985 Mar;360:311-32. doi: 10.1113/jphysiol.1985.sp015619.
A synovial cavity is separated from plasma by synovial intima in series with capillary endothelium. Because 20% of the intimal surface is bare interstitium, the system is a convenient model for the study of passive transport through serial endothelial and interstitial layers. Here hydraulic flow across the composite barrier was investigated in forty-seven knees of isolated, blood-perfused rabbit hindquarters, at intra-articular pressures between 4 and 30 cmH2O. In order to measure barrier conductance at constant intra-articular pressure, pressure on the opposite side of the barrier was varied, i.e. capillary blood pressure (PC). Capillary pressure was changed by alteration of vascular perfusion pressures, and the resulting changes in rate of absorption of Krebs solution from the synovial cavity (QS) were recorded. Trans-synovial absorption was a negative linear function of PC at each joint pressure, in verification of the applicability of Starling's hypothesis to this system. The hydraulic conductance of the blood-joint barrier was calculated as dQS/dPC. Conductance was independent of intra-articular pressure below 9 cmH2O and was 0.12 +/- 0.015 microliter min-1 mmHg-1 (mean +/- S.E. of mean). Barrier conductance increased as a curvilinear function of intra-articular pressure above 9.4 cmH2O (yield pressure). At 30 cmH2O conductance averaged 0.60 +/- 0.06 microliter min-1 mmHg-1, a 5-fold increase. A hyperbolic curve relating net barrier conductance to joint pressure was predicted from the hypothesis that interstitial conductance increases as a monotonic function of intra-articular pressure above yield pressure (Appendix). The data were in reasonable agreement with the theoretical hyperbola. Interstitial conductivity (3 X 10(-7)-7 X 10(-7) cm4 s-1 N-1 below yield pressure) and mean endothelial conductance (1.1 X 10(-4)-1.4 X 10(-4) cm3 s-1 N-1) were evaluated and compared with values in other tissues. Synovial endothelium contains on average 0.25 fenestrae micron-1 circumference. The conductance of a single fenestra was calculated to be 2.3 X 10(-13) cm5 s-1 N-1. Interstitial resistance accounted for roughly half the total resistance below yield point: therefore dQS/dPC should not be equated with 'capillary filtration capacity' in tissues with dense or fenestrated capillary beds. Large inconsistencies between interstitial conductivity and glycosaminoglycan concentration are noted, and mechanistic explanations of increases in conductivity with joint pressure are offered.
滑膜腔通过与毛细血管内皮连续的滑膜内膜与血浆分隔开。由于20%的内膜表面是裸露的间质，该系统是研究被动转运通过连续内皮和间质层的便利模型。在此，研究了47个离体、血液灌注的兔后肢膝关节在4至30 cmH₂O关节内压力下通过复合屏障的液压流动。为了在恒定关节内压力下测量屏障传导率，改变屏障另一侧的压力，即毛细血管血压（PC）。通过改变血管灌注压力来改变毛细血管压力，并记录滑膜腔中克雷布斯溶液吸收速率（QS）的相应变化。在每个关节压力下，滑膜吸收是PC的负线性函数，证实了斯塔林假设适用于该系统。血-关节屏障的液压传导率计算为dQS/dPC。在低于9 cmH₂O时，传导率与关节内压力无关，为0.12±0.015微升·分钟⁻¹·毫米汞柱⁻¹（平均值±平均值标准误）。在高于9.4 cmH₂O（屈服压力）时，屏障传导率随关节内压力呈曲线函数增加。在30 cmH₂O时，传导率平均为0.60±0.06微升·分钟⁻¹·毫米汞柱⁻¹，增加了5倍。根据间质传导率随屈服压力以上关节内压力呈单调函数增加的假设，预测了净屏障传导率与关节压力的双曲线关系（附录）。数据与理论双曲线合理吻合。评估了间质传导率（屈服压力以下为3×10⁻⁷ - 7×10⁻⁷ 厘米⁴·秒⁻¹·牛顿⁻¹）和平均内皮传导率（1.1×10⁻⁴ - 1.4×10⁻⁴ 厘米³·秒⁻¹·牛顿⁻¹），并与其他组织的值进行了比较。滑膜内皮平均每微米周长有0.25个窗孔。计算得出单个窗孔的传导率为2.3×10⁻¹³ 厘米⁵·秒⁻¹·牛顿⁻¹。在屈服点以下，间质阻力约占总阻力的一半：因此，在具有致密或有窗孔毛细血管床的组织中，dQS/dPC不应等同于“毛细血管滤过能力”。注意到间质传导率与糖胺聚糖浓度之间存在很大差异，并提供了传导率随关节压力增加的机理解释。
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