Measurement of oxygen and carbon dioxide partial pressures in synovial fluid after tonometry

Electroacupuncture improves articular microcirculation and attenuates cartilage hypoxia in a male rabbit model of knee osteoarthritis

Background and aim

Hypoxia of the cartilage has been considered as a potential pathogenic factor in knee osteoarthritis (KOA). Studies have shown that impaired blood perfusion of joint leads to cartilage hypoxia. Electroacupuncture (EA) has proven effects on pain relief and improving microcirculation. This study aimed to explore the effect of EA on articular microcirculation and cartilage anoxic and the underlying mechanisms.

Procedures

Videman's method was used for 6 weeks to establish the KOA model. EA intervention was performed in four points around the knee for 3 weeks after KOA modeling. The Lequesne MG score was used to assess ethology. We recorded the oxygen tension of synovial fluid and the synovial microcirculation in vivo. HE-staining was used to assess cartilage morphology, and immunohistochemistry (IHC), Western blotting, and RT-PCR were used to assess expression of the major glycolytic enzymes glucosetransporter1 (GLUT1), pyruvate kinase M2(PKM2), and lactate dehydrogenase A (LDHA). Enzyme-linked immunosorbent assay (Elisa) was used to detect lactate content.

Results and conclusion

There was a significant decrease in Lequesne MG score and improvement in Mankin score after EA intervention (P < 0.01), a significant increase in synovial microcirculation (P < 0.05) and synovial fluid oxygen tension (P < 0.01), and there was significant decrease in the expression of GLUT1, PKM2 and LDHA (P < 0.01) and lactate (P < 0.05). This study suggested that EA ameliorate cartilage hypoxia and regulate glycolytic metabolism in chondrocytes in KOA model rabbits by improving articular microcirculation and oxygen tension.

Swelling of synovial joints - An anatomical, physiological and energy metabolical approach

The direction and part of the rate of fluid filtration between synovial capillary (subscript capill) plasma and joint (subscript j) cavity fluid depends on the hydrostatic (P(capill)-P(j)) and colloid osmotic (COP(plasma)-COP(j)) pressure differences and on the osmotic efficiency (coefficient sigma) of 'colloids' across the barrier between plasma and synovial fluid. The rate of filtration also depends on capillary endothelial hydraulic conductance (L(p)) and surface area (A). Synovial fluid protein is removed by lymphatics, or split to be resorbed or used up by cells. Physiologists put together as equations the above, as well as other terms, all of these influenced by numerous factors. The equations offer a frame for a multifactorial approach to diseases associated with joint swelling and suggest, among others, that in the presence of weak generalized exsudation, synovial joints are loci minores resistentiae to swelling. The influence of joint cartilage energy demands on synovial blood flow may have been underrated. There are many accepted clinical, laboratory and morphological findings that fit this physiological frame that merits further clinical research.

Factors influencing the acid-base changes in the air-pouch exudate following carrageenan induced inflammation in rats

The interactions between the acid-base variables that contribute to exudate acidosis were studied in the subcutaneous air-pouch after carrageenan injection in rats. We studied the concurrent changes of exudate gases (PCO2 and PO2), main ions ([Na+], [K+], [Ca2+], [Mg2+], [Cl-] and [Lac-]), inorganic phosphate (P(i)) and albumin in acutely inflamed rats (4, 8, 12, 24 and 48 h of inflammation). A notable hypercapnia was found in the exudate after only 8 h (exudate PCO2 = 64.3 +/- 2.9 mm Hg) but this hypercapnia decreased after 48 h (32.9 +/- 12.7 mm Hg), coincident with the greatest increase in exudate cells. With respect to the metabolic acid-base variables, the most important changes found were a parallel decrease in the strong ion difference ([SID]) and exudate pH, as well as increases in the exudate weak acid buffers ([ATOT]) due to albumin and inorganic phosphate (P(i)) increases. However, after 12 h, the exudate acidosis was stable at around pH 7. A similar acid pH was obtained after 24 h of inflammation when the carrageenan solution injected was previously adjusted to a physiological pH (7.4). This pH, analogous to that of the exudate, was the result of compensation by the acid-base independent variables, a fact which suggests that acid pH may be a beneficial condition for cells taking part in inflammatory processes.

High hydrostatic pressures in traumatic joints require elevated synovial capillary pressure probably associated with arteriolar vasodilatation

Three out of the four Starling pressures were determined at arthroscopy of traumatic effusions of the knee. The range of the joint fluid hydrostatic pressure Pjoint was 5-83 cmH2O (0.5-8.1 kPa, 4-61 mmHg), that of the colloid osmotic pressure difference COPplasma-COPjoint 0-21.7 cmH2O. In 11 of 15 cases the sum Pjoint+COP difference exceeded 32.6 cmH2O (3.19 kPa, 24 mmHg), a high estimate of average capillary pressure at the level of the heart. The number of 'exceeding' cases was 8/15 if only 80% of the COP difference was considered effective. Pjoint and the COP difference oppose filtration of fluid from plasma into joints, indicating that mean capillary pressure, the only Starling pressure not determined, was elevated unless the effusions were being resorbed back into the blood. The findings can be explained by tamponade compensated by arteriolar vasodilatation, suspected to be metabolically mediated.

Direct assessment of synovial blood flow and its relation to induced hydrostatic pressure changes

A method for measuring synovial blood flow changes using the laser Doppler technique is described. Mean blood flow and mean pulse amplitude decreased by 50-70% in relation to the reference level when the intra-articular hydrostatic pressure in effusive knee joints of patients with rheumatoid arthritis was increased. As an increase of intra-articular pressure of as little as 20 mmHg decreased synovial blood flow significantly it is suggested that hypoxia may occur in vivo during joint use in the presence of an effusion. This may be of aetiopathogenetic importance for tissue destruction and the persistence of chronic synovitis.