Objective To investigate the correlation between dynamic intrinsic positive endexpiratory pressure ( PEEPidyn) and volume dependence of elastance and resistance of respiratory system ( Evd/Rvd) derived from nonlinear analysis of respiratory mechanics in COPD patients during pressure support ventilation ( PSV) . Methods Twenty-five COPD patients mechanically ventilated using mode of PSV were ventilated at a PSV level of no less than 20 cm H2O in a period of 15 minutes to attain so-callednear-relaxation state. The pressure( P) , flow( V′) and volume( V) data were analyzed by nonlinear mode of respiratory motion. PEEPidyn was determined by esophageal balloon-tipped catheter technique. The correlations between PEEPidyn and Evd, Rvd as well as Evd ×Rvd were analyzed. Results The correlation coefficients between PEEPidyn and Evd, Rvd as well as Evd ×Rvd were 0. 85,0. 80, and 0. 90, respectively. Conclusions Nonlinear mode of respiratory motion is suitable to analyze respiratory mechanics of COPD patients mechanically ventilated using mode of PSV. There are good correlations between PEEPidyn and Evd,Rvd as well as Evd ×Rvd which may be used to noninvasively monitor PEEPidyn in mechanically ventilated COPD patients using mode of PSV.
A non-linear rectification based on immune genetic algorithm (IGA) is proposed in this paper, for the shortcoming of the non-linearity rectification. This algorithm introducing the biologic immune mechanism into the genetic algorithm can restrain the disadvantages that the poor precision, slow convergence speed and early maturity of the genetic algorithm. Computer simulations indicated that the algorithm not only keeps population diversity, but also increases the convergent speed, precision and the stability greatly. The results have shown the correctness and effectiveness of the method.
It will cause hidden trouble on clinical application if the uroflowmeter is out of control. This paper introduces a scheme of uroflowmeter calibration device based on digital signal processor (DSP) and gear pump and shows studies of its feasibility. According to the research plan, we analyzed its stability, repeatability and linearity by building a testing system and carried out experiments on it. The flow test system is composed of DSP, gear pump and other components. The test results showed that the system could produce a stable water flow with high precision of repeated measurement and different flow rate. The test system can calibrate the urine flow rate well within the range of 9~50 mL/s which has clinical significance, and the flow error is less than 1%, which meets the technical requirements of the calibration apparatus. The research scheme of uroflowmeter calibration device on DSP and gear pump is feasible.
Sleep apnea syndrome (SAS) is a kind of common and harmful systemic sleep disorder. SAS patients have significant iconography changes in brain structure and function, and electroencephalogram (EEG) is the most intuitive parameter to describe the sleep process which can reflect the electrical activity and function of brain tissues. Based on the non-stationary and nonlinear characteristics of EEG, this paper analyzes the correlation dimension of sleep EEG in patients with SAS. Six SAS patients were classed as SAS group and six healthy persons were classified into a control group. The results showed that the correlation dimension of sleep EEG in the SAS group and the control group decreased gradually with the deepening of sleep, and then increased to the level of awake and light sleep stage with rapid eye movement (REM). The correlation dimension of SAS group was significantly lower than that of control group (P<0.01) throughout all the stages. The results suggested that there were significant nonlinear dynamic differences between the EEG signals of SAS patients and of healthy people, which provided a new direction for the study of the physiological mechanism and automatic detection of SAS.
The gradient field, one of the core magnetic fields in magnetic resonance imaging (MRI) systems, is generated by gradient coils and plays a critical role in spatial encoding and the generation of echo signals. The uniformity or linearity of the gradient field directly impacts the quality and distortion level of MRI images. However, traditional point measurement methods lack accuracy in assessing the linearity of gradient fields, making it difficult to provide effective parameters for image distortion correction. This paper introduced a spherical measurement-based method that involved measuring the magnetic field distribution on a sphere, followed by detailed magnetic field calculations and linearity analysis. This study, applied to assess the nonlinearity of asymmetric head gradient coils, demonstrated more comprehensive and precise results compared to point measurement methods. This advancement not only strengthens the scientific basis for the design of gradient coils but also provides more reliable parameters and methods for the accurate correction of MRI image distortions.