Alexander Kharlamov

Photothrombotic brain infarction results in seizure activity in aging Fischer 344 and Sprague Dawley rats

This study was designed to determine whether photothrombotic brain infarction could result in epileptic seizures in adult animals. Male Fischer 344 (F344) rats at 2, 6, 12, 24, and 30 months of age and male Sprague Dawley (SD) rats at 2 and 6 months of age underwent photothrombotic brain infarction with the photosensitive dye rose bengal by focusing a wide (6 mm) or narrow (3 mm) diameter white light beam on the skull overlying left hemisphere anterior frontal, midfrontal, frontoparietal, or parietal areas. Animals were monitored with video and EEG recordings. Morphological analysis of infarct size was performed with a computer-assisted image analysis system. The primary finding of this study was that epileptic seizures were recorded in post-mature rats 2 months after lesioning the frontoparietal cortex with large photothrombotic infarcts that extended to the cortical-subcortical interface. These seizures were characterized behaviorally by motor arrest, appeared to originate in the periinfarct area, and could be distinguished from inherited spontaneous bilateral cortical discharges by the morphology, frequency, duration, and laterality of the ictal discharges. Small cortical lesions were ineffective in producing seizures except for one animal that demonstrated recurrent prolonged focal discharges unaccompanied by behavioral change. Stage 3 seizures were observed in a small number of mid-aged and aged animals lesioned with large infarcts in anterior frontal and frontoparietal areas. These results suggest that the technique of photothrombosis can be used to produce neocortical infarction as a means to study mechanisms of secondary epileptogenesis.

Directed sampling for electrolyte analysis and water content of micro-punch samples shows large differences between normal and ischemic rat brain cortex.

Changes in sodium, potassium, and water content in brain tissue are important in the progression of pathology that follows ischemic stroke. Determining these parameters regionally in rodent models of experimental ischemia has been limited because typical tissue weights of more than 35 mg are too large. Identifying ischemic tissue to direct tissue sampling towards ischemic cortex is also represents a difficult generally unresolved area. We suggest that larger differences between normal and ischemic cortex of sodium, potassium, and water content than previously observed can be obtained from directed sampling of 2-mg brain tissue in a model of focal cerebral ischemia. In five rats, the middle cerebral artery and both common carotid arteries were occluded for 4.9+/-0.13 h (mean+/-SEM). Punch-sampling of 1-mm diameter tissue cores for water content (H(2)O%) by the wet-dry method, and [Na(+)] and [K(+)] by flame photometry, was guided by the observation of a subtle change in the surface reflectivity of ischemic cortex of quickly dried, 20-microm frozen brain sections, that was confirmed by MAP2 immunohistochemistry. The ratio of the lesion areas as determined by the reflective change and MAP2 immunoreactivity was 0.96+/-0.03 (n=5). In ischemic cortex H(2)O% was 79.9%+/-0.8%, [Na(+)] was 550+/-25 mEq/kg dry-weight, and [K(+)] 94.2+/-19.2 mEq/kg dry-weight (n=5), all significantly different from the values in border zone cortex, and in cortex contralateral to ischemic cortex and border zone (for all samples n=60, mean wet weight 2.037+/-0.046 mg). Differences between ischemic and normal cortex were 5.4+/-1.1%, 317+/-21 mEq/kg dry-weight, -304+/-27 mEq/kg dry-weight (n=5) for H(2)O%, [Na(+)], and [K(+)]. These differences between ischemic and normal cortex are 1.4-2.5, 1-3.11, and 1.4-3.5 times greater, respectively, than previous results obtained using samples weighing 35 mg or more. These results extend the association of sodium and potassium with ischemic brain edema in the rodent model, and show that these classical measurements can keep pace with the regionality of histochemical and morphological methods.

Comparing Biomechanical Properties, Repair Times, and Value of Common Core Flexor Tendon Repairs

Background: The aim of the study was to compare biomechanical strength, repair times, and repair values for zone II core flexor tendon repairs. Methods: A total of 75 fresh-frozen human cadaveric flexor tendons were harvested from the index through small finger and randomized into one of 5 repair groups: 4-stranded cross-stitch cruciate (4-0 polyester and 4-0 braided suture), 4-stranded double Pennington (2-0 knotless barbed suture), 4-stranded Pennington (4-0 double-stranded braided suture), and 6-stranded modified Lim-Tsai (4-0 looped braided suture). Repairs were measured in situ and their repair times were measured. Tendons were linearly loaded to failure and multiple biomechanical values were measured. The repair value was calculated based on operating room costs, repair times, and suture costs. Analysis of variance (ANOVA) and Tukey post hoc statistical analysis were used to compare repair data. Results: The braided cruciate was the strongest repair (P > .05) but the slowest (P > .05), and the 4-stranded Pennington using double-stranded suture was the fastest (P > .05) to perform. The total repair value was the highest for braided cruciate (P > .05) compared with all other repairs. Barbed suture did not outperform any repairs in any categories. Conclusions: The braided cruciate was the strongest of the tested flexor tendon repairs. The 2-mm gapping and maximum load to failure for this repair approached similar historical strength of other 6- and 8-stranded repairs. In this study, suture cost was negligible in the overall repair cost and should be not a determining factor in choosing a repair.

Variations in CBF during hypotension and in cortical eNOS in rats

Abstract Variations in the height of the autoregulatory curve near the lower limit present the intriguing suggestion that there are local differences in cortical vascular regulation. We suspect that these variations are related to local variations in the amount of cortical eNOS, [eNOS]br. Laser Doppler flowmetry (LDF) monitoring of CBF in rat cortex during hemorrhagic hypotension revealed that the CBF at a mean arterial pressure of 70 mmHg (%CBF70) was highly variable and distributed normally. Both paradoxical rises in CBF and pressure-passive CBF were common during moderate hypotension. In other experiments, similar variations in the concentration of eNOS, [eNOS]br, were observed in brain samples of similar volume to the volume sensed by LDF and differences in %CBF70 were noted in different regions of the same animals cortex. These observations suggest the surprising possibility that cortical variations in the amount of eNOS protein, not its regulation, relate to variations in the CBF response to moderate hypotension.

Role of Nitric Oxide in Variations of the Response of Cerebral Blood Flow to Hypotension and Focal Ischemia

We contend that there are similarities between the vasoregulatory mechanisms near the lower limit of autoregulation and the region surrounding the ischemic core in focal cerebral ischemia. Cortical nitric oxide synthase (NOS) inhibition raises the lower limit of autoregulation and is thus at least partially responsible for the vasodilation that maintains cerebral blood flow as blood pressure falls from 100 mmHg to 60 mmHg. There are wide variations among animals in the pattern of autoregulation that cannot be explained by damaged vessels or nonphysiological factors. Specific neuronal NOS inhibition does not change the lower limit, suggesting that endothelial NOS mediates the vasodilation near the lower limit. Endothelial NOS immunolocalization in focal ischemia parallels these findings.

The optimal number and location of sutures in conduit-assisted primary digital nerve repair:

We evaluated the strength of conduit-assisted primary digital nerve repairs, with varying suture location and number, in 56 digital nerves from cadavers. Maximum load to failure was tested for the following seven repairs, designated by the number of epineurial sutures followed by the number of sutures at each end of the conduit: 4 (epineurial sutures)/0 (sutures at each end of conduit), 4/4, 4/2, 2/2, 0/4, 0/2, 0/1. The 4/4 repair (3.0 N) was significantly stronger than 4/0 (1.5 N), 2/2 (1.6 N), 0/4 (2.0 N), 0/2 (1.4 N) and 0/1 (1.1 N). Considering all repair types, there was a significant correlation between suture number and failure load, with the strongest repair having a total of 12 sutures, which is impractical. Reasonable repair options, which have two sutures at each end of the conduit and either two or no epineurial sutures, are as strong as a four-suture epineurial repair but have less sutures at the coaptation site.

Fibrin Glue Increases the Tensile Strength of Conduit-Assisted Primary Digital Nerve Repair

Background: An ideal peripheral nerve repair construct does not currently exist. Our primary goal was to determine whether fibrin glue adds to the tensile strength of conduit-assisted primary digital nerve repairs. Our secondary goal was to evaluate the impact of varying suture number and location on the tensile strength. Methods: Ninety cadaveric digital nerves were harvested and divided equally into the following repair groups: A (4/4), B (2/2), C (0/2), D (0/1), and E (0/0) with the first number referring to the number of sutures at the coaptation and the second number referring to the number of sutures at each proximal and distal end of the nerve-conduit junction. When fibrin glue was added, the group was labeled prime. The nerve specimens were transected and then repaired with 8-0 nylon suture and conduit. The tensile strength of the repairs was tested, and maximum failure load was determined. The results were analyzed with a 2-way analysis of variance. The Tukey post hoc test compared repair groups if the 2-way analysis of variance showed significance. Results: Both suture group and glue presence significantly affected the maximum failure load. Increasing the number of sutures increased the maximum failure load, and the presence of fibrin glue also increased the failure load. Conclusions: Fibrin glue was found to increase the strength of conduit-assisted primary digital nerve repairs. Furthermore, the number of sutures correlated to the strength of the repair. Fibrin glue may be added to a conduit-assisted primary digital nerve repair to maintain strength and allow fewer sutures at the primary coaptation site.

Quantification of Long Head of the Biceps Tendon Motion After Loop ‘N’ Tack Suprapectoral Biceps Tenodesis

Objectives: Lesions of the long head of the biceps are one of the most frequent causes of shoulder pain, and they can be successfully treated with biceps tenotomy or tenodesis. The advantage of a biceps tenodesis is avoiding the potential development of a cosmetic deformity (“Popeye sign”) or cramping muscle pain that can remain after tenotomy. Proponents of a subpectoral tenodesis believe that “groove pain” may remain a problem after suprapectoral tenodesis due to persistent motion of the biceps tendon within the bicipital groove. The objective of this study was to evaluate the motion of the biceps tendon within the bicipital groove before and after a suprapectoral tenodesis performed using the Loop ‘N’ Tack technique. Our hypothesis was that there would be minimal to no motion of the biceps tendon within the bicipital groove after the tenodesis. Methods: Six fresh-frozen cadaveric arms were obtained and dissected to expose the long head of biceps tendon and the bicipital groove from the transverse humeral ligament to the pectoralis major insertion. The scapula and ulna were affixed with inclinometers to measure motion in multiple planes. The biceps tendon and bicipital groove were marked with fiducials, which were tracked by two cameras focused on this region. The shoulder and elbow were taken through a full range of motion including scapular abduction, forward flexion, extension, internal rotation, and external rotation and elbow flexion and extension with a supinated, neutral, or pronated forearm. The translation of the biceps tendon was quantified as a function of scapular or forearm motion in each plane. A suprapectoral biceps tenodesis was then performed using the Loop ‘N’ Tack technique. The scapula and forearm were taken through the same motions, and the translation of the biceps tendon was quantified. A paired t-test was performed for each motion to determine if maximum biceps tendon translation in the bicipital groove was a function of tendon condition (native vs post-tenodesis). Results: There was minimal translation of the biceps tendon during elbow flexion and extension, both before and after tenodesis. There was significant translation of the biceps tendon in all planes of scapular motion in the native state, and the largest amount of translation was 20.73mm +/- 8.21mm during shoulder flexion and extension (Table 1). The translation of the biceps tendon after tenodesis was significantly reduced in every plane of scapular motion compared to the native state (p = 0.01 or p < 0.01 in all planes of motion). The largest amount of translation in any plane after tenodesis was 1.57mm +/- 0.98mm, which occured during shoulder flexion and extension (Table 1). Conclusion: In the native state, the translation of the biceps tendon within the bicipital groove ranges from 5.14mm - 20.73mm with scapular motion. There is statistically significant reduction in translation of the biceps tendon in all planes of scapular motion after the Loop ‘N’ Tack tenodesis (Figure 1), with a maximum translation of only 1.57mm. These data suggest that motion of the biceps tendon within the bicipital groove is essentially eliminated and should not be a cause of persistent pain. The Loop ‘N’ Tack biceps tenodesis is a simple, all-arthroscopic technique for patients with proximal biceps pathology. It is a viable alternative to subpectoral tenodesis, essentially eliminating all motion of the biceps tendon within the bicipital groove, and it should not lead to persistent “groove pain”. Table 1. Native Post-Tenodesis Results Average (mm) S.D. (mm) Average (mm) S.D. (mm) P-Value Elbow Flexion: Supination 1.85 1.66 0.56 0.37 0.15 Elbow Flexion: Neutral 1.73 1.43 0.83 0.64 0.30 Elbow Flexion: Pronation 3.03 1.55 0.72 0.24 0.01 Glenohumeral: Internal/External Rot. 9.37 1.70 1.32 0.78 <0.01 Glenohumeral: Flexion/Extension 20.73 8.21 1.57 0.98 <0.01 Glenohumeral: Full Flexion 10.32 2.60 0.75 0.47 <0.01 Glenohumeral: Abduction 5.14 2.67 1.26 1.17 0.01