The laser-induced retinal injury thresholds for repetitive-pulse exposures to 100-μs-duration pulses at a wavelength of 532 nm have been determined for exposures of up to 1000 pulses in an in vivo model. The ED50 was measured for pulse repetition frequencies of 50 and 1000 Hz. Exposures to collimated beams producing a minimal retinal beam spot and to divergent beams producing a 100-μm-diameter retinal beam spot were considered. The ED50 for a 100-μs exposure was measured to be 12.8 μJ total intraocular energy for a minimal retinal beam spot exposure and 18.1 μJ total intraocular energy for a 100-μm-diameter retinal beam spot. The threshold for exposures to N > 1 pulse was found to be the same for both pulse repetition frequencies. The variation of the ED50 with the number of pulses is described well by the probability summation model, in which each pulse is considered an independent event. This is consistent with a threshold-level damage mechanism of microcavitation for single-pulse 100-μs-duration exposures. The data support the maximum permissible exposure levels for repetitive-pulse exposure promulgated in the most recent laser safety guidelines.
Impedance plethysmography (IPG) has a reputed sensitivity of 95% in the detection of proximal, clinically significant deep venous thrombosis (DVT). A review of the radiologic studies of 100 consecutive patients who underwent both venography and IPG showed venographic evidence of proximal DVT in 40 patients. The IPG was negative in 15 (38%) of these 40 cases. The specificity of the IPG was 83%. The predictive value of a negative study, with this 40% prevalence of DVT, was 77%. These disturbing results indicate a continuing role for venography in the workup of DVT.
A case of a type of popliteal entrapment syndrome that does not include an anomalous course of the popliteal artery is presented. In situ thrombosis secondary to entrapment-induced stasis was the presumed cause of ischemic symptomatology. Thorough knowledge of the possible causes of entrapment and biplane angiography (of the popliteal artery) with provocative maneuvers often are required for diagnosis. As in our patient, surgical release of the entrapment can lead to complete resolution of symptoms.
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