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Background Dexmedetomidine combined with local anesthetics can decrease the concentration of epidural ropivacaine. However, the optimal dose of epidural dexmedetomidine combined with ropivacaine for labor analgesia is still uncertain. This study investigated the effect of adding different dose of epidural dexmedetomidine to ropivacaine during epidural labor analgesia. Methods One hundred women were randomly assigned to one of the four groups (Groups A, B, C, and D received 0.25, 0.5, 0.75, and 1 μg/ml of dexmedetomidine plus 0.1% ropivacaine, resp.). The onset of epidural anesthesia and stages of labor were studied, and pain was assessed using a visual analogue scale (VAS). Hemodynamic parameters and fetal heart rate were monitored. Apgar scores and umbilical artery pH were recorded. The side effects, if any, were recorded also. Results The addition of 0.25, 0.5, and 0.75 μg/ml of dexmedetomidine to 0.1% ropivacaine provided safe and effective analgesia, but 1 μg/ml of dexmedetomidine resulted in increasing incidence of motor block. The hemodynamic parameters were similar between groups (P > 0.05). Side effects in Group D were significantly higher than those in the other three groups (P < 0.05). Conclusions When dexmedetomidine is combined with 0.1% ropivacaine, the optimal concentration of dexmedetomidine is 0.5 μg/ml for epidural labor analgesia (this trial is registered with ChiCTR-OPC-16008548).

A simultaneous phase-shifting dual-wavelength interferometry based on two-step demodulation algorithm is proposed in this Letter. First, two lasers with different wavelengths go through the same inline phase-shifting interference system simultaneously, and a sequence of five frames of simultaneous phase-shifting dual-wavelength interferograms (SPSDWIs) with the special phase shifts are captured by a monochrome CCD. Subsequently, using the subtraction between the first SPSDWI and the other SPSDWI, each wavelength of two frames of single-wavelength interference images (SWIIs) without the background can be achieved. Finally, using two-step demodulation algorithm, the wrapped phase of each single-wavelength can be determined easily and quickly with high accuracy.

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Based on the quotient of inner products, a simple and rapid algorithm is proposed to retrieve the measured phase from two-frame phase-shifting interferograms with unknown phase shifts. Firstly, we filtered the background of interferograms by a Gaussian high-pass filter. Secondly, we calculated the inner products of the background-filtered interferograms. Thirdly, we extracted the phase shifts by the quotient of the inner products then calculated the measured phase by an arctangent function. Finally, we tested the performance of the proposed algorithm by the simulation calculation and the experimental research for a vortex phase plate. Both the simulation calculation and the experimental result showed that the phase shifts and the measured phase with high accuracy can be obtained by the proposed algorithm rapidly and conveniently.