Trigger points in painful muscle are a characteristic sign in patients with primary fibromyalgia. The MDO oxygen electrode was used to evaluate oxygenation in the subcutaneous tissue and in trigger points in the trapezius and brachioradial muscles. Ten patients and 8 normal controls were studied. The results in the patients were abnormal, with scattered or slalom-slope histograms, indicating low tissue oxygenation. The controls were normal, except in one case. The conclusion is that in patients with primary fibromyalgia, the muscle oxygenation is abnormal or low, at least in the trigger point area of the muscles.

Serotonin2 (5-HT2) receptor antagonists (ketanserin, ritanserin) can normalize a hyperoxemia-induced disturbance in skeletal muscle oxygenation, presumably by local microflow changes. The purpose of this study was to develop equipment for local hydrogen clearance measurements with a modified eight-channel platinum electrode to assess changes in local skeletal muscle capillary blood flow induced by hyperoxemia and ritanserin (0.035 mg/kg) during hyperoxemia. Laser-Doppler flowmetry was used for regional microflow measurements. Two groups of six anesthetized and artificially ventilated rabbits were studied: group I with normoxemia and hyperoxemia [arterial PO2 (PaO2) 48 kPa; 360 Torr] and group II before and after ritanserin with hyperoxemia (PaO2 46 kPa; 345 Torr). In group I, hyperoxemia induced a mean local hydrogen clearance decrease of 22% while laser-Doppler flowmetry signal decreased 31%. In group II, ritanserin induced a 125% mean local hydrogen clearance increase compared with hyperoxemia (or 37% compared with group I normoxemia); laser-Doppler flowmetry signal increased 30%. The sum distribution of local hydrogen clearances shifted to the left during hyperoxemia and to the right after ritanserin. The conclusion from this study is that local and regional microflow changes can explain the effects of hyperoxemia and ritanserin on skeletal muscle oxygenation.

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Oxygen and carbon dioxide are known to be heterogeneously distributed in tissues. Extracellular skeletal muscle tissue pH (pH_t) also exhibits a spatial variability in vitro, but this has not been examined in vivo. pH_t distributions in resting skeletal muscle and the effect of the dispersion of pH_t on ischemia and normoxic hypercarbia was therefore studied in an animal model with a multichannel pH microelectrode. Under resting conditions and spontaneous breathing, local pH_t (from all animals, n = 10) was found to vary between 6.96 and 7.68 (range), and 70% of the values were within a pH of 7.00-7.32. In each animal the maximum pH_t differences (maximum range between the 6 channels of the microelectrode) found were 0.32 ± 0.11 pH units (mean ± SD). During tissue acidosis, induced by ischemia, no significant change in the local pH_t differences in each animal was seen. During normoxic hypercarbia a 2-fold increase in pH_t variability within each animal was noticed (p < 0.01), which suggests that carbon dioxide and buffering effects of the blood are significant factors for the pH_t distribution. The pH_t distribution range found is of similar magnitude as previously described in in vitro studies on skeletal muscle. Locally varying pH_t levels may be of importance as they will affect cellular H⁺ extrusion, membrane potential and volume control of different cell populations differently.

Anesthetics affect tissue blood flow, which is of importance especially in situations of inadequate perfusion, as in hemorrhage. The present study compared the effect of three commonly used anesthetic agents on skeletal muscle capillary and regional blood flow during and after recovery from hemorrhage. Three groups of rabbits were anesthetized randomly with either pentobarbital, propofol or ketamine, chosen such that the anesthetic level, blood pressure and withdrawn blood volume were comparable in all groups. Capillary blood flow was measured using a local hydrogen clearance technique with a multiwire microelectrode, placed on the left vastus medialis muscle surface, and the contralateral site served for regional microcirculatory blood flow measurements using laser-Doppler flowmetry. Hemorrhage was induced by withdrawal of blood to a mean arterial pressure of 40 mm Hg and monitoring was continued during the subsequent spontaneous recovery period of 120 min. Both capillary and regional blood flow decreased significantly during hemorrhage in all groups. The flow values in the pentobarbital group were given a mean value of 100% and the other two groups were compared with this. Local hydrogen clearance flow decreased from a relative baseline level of 100 to 64% during hemorrhage with pentobarbital, from 87 to 43% with propofol and from 146 to 70% with ketamine. Laser-Doppler flowmetry flow decreased from relative baseline levels of 100, 96 and 139%, to 71, 77 and 103%, respectively, during hemorrhage, whereas the percentage of zero capillary flow values increased from 4 to 34, 19 to 50 and 5 to 27% in the three groups, respectively. The results of the present study indicate that capillary perfusion is best maintained in the ketamine group followed by pentobarbital and propofol last. Furthermore, the flow distribution shapes for each anesthetic indicate a more pronounced deregulation of capillary blood flow in the propofol group than in the others, even at baseline.