Background: Hypotension due to vasodilatation after spinal anesthesia (SA) may be harmful. Heart rate variability, an indirect measure of autonomic control, may predict hypotension.
Methods: One hundred patients were studied. Retrospectively, heart rate variability was analyzed in 30 patients, classified depending on the lowest systolic blood pressure (SBP) after SA. Seventy patients were studied prospectively, assigned to one of two groups by their low to high frequency ratio (LF/HF) before SA. Sensitivity and specificity of LF/HF for prediction of decrease of SBP greater 20% of baseline were tested.
Results: Retrospective analysis showed differences of LF/HF depending on the degree of hypotension after SA. Prospective analysis demonstrated significant differences of SBP after SA depending on baseline LF/HF (mean +/- SD): low LF/HF (1.3 +/- 0.7) = > SBP: 91 +/- 8% of baseline versus high LF/HF (5.5 +/- 2.4) = > SBP: 66 +/- 10% of baseline (P < 0.05). Baseline LF/HF as well as high frequency and proportional decrease of SBP after SA correlated significantly, in contrast to baseline hemodynamic parameters heart rate and SBP. A receiver operator curve characteristic analysis showed a sensitivity and specificity of LF/HF > 2.5 of 85% to predict SBP decrease of greater than 20% of baseline after SA. 相似文献
Background: Hypotension due to vasodilation during subarachnoid block (SAB) for elective cesarean delivery may be harmful. Heart rate variability (HRV), reflecting autonomic control, may identify patients at risk of hypotension.
Methods: Retrospectively, HRV was analyzed in 41 patients who were classified into one of three groups depending on the decrease in systolic blood pressure (SBP): mild (SBP > 100 mmHg), moderate (100 > SBP > 80 mmHg), or severe (SBP < 80 mmHg). Prospectively, HRV and hemodynamic data of 19 patients were studied. Relative low frequency (LF), relative high frequency (HF), and LF/HF ratio were analyzed.
Results: Retrospective analysis of HRV showed a significantly higher sympathetic and lower parasympathetic drive in the groups with moderate and severe compared with mild hypotension before SAB (median, 25th/75th percentiles): LF/HF: mild: 1.2 (0.9/1.8), moderate: 2.8 (1.8/4.6), P < 0.05 versus mild; severe: 2.7 (2.0/3.5), P < 0.05 versus mild. Results were confirmed by findings of LF and HF. Prospectively, patients were grouped according to LF/HF before SAB: low-LF/HF: 1.5 (1.1/2.0) versus high-LF/HF: 4.0 (2.8/4.7), P < 0.05; low-LF: 58 +/- 9% versus high-LF: 75 +/- 10%, P < 0.05; low-HF: 41 +/- 10% versus high-HF: 25 +/- 10%, P < 0.05. High-risk patients had a significantly lower SBP after SAB (76 +/- 21 vs. 111 +/- 12 mmHg; P < 0.05). 相似文献
A simple mathematical method for the determination of the cardinal points of pseudophakic eyes after implantation of an accommodative intraocular lens [posterior chamber intraocular lenses (PCIOL)] is presented. The purpose of this study was to explore the changes during pseudophakic accommodation (PAC) in (1). the positions of the cardinal points, (2). the distance of the object conjugate with the retina, and (3). the image-object magnification. These theoretical accommodation data are compared with clinical measurements. METHODS AND PATIENTS: Using biometrical measurements of the axial length, equivalent power of the cornea and the anterior chamber depth (ACD) in the non-accommodated state we used linear geometric optics for determination of the cardinal points and object distance as well as lateral magnification (the ratio of image to object size). With the measurement of ACD decrease (following pharmacological stimulation of the ciliary muscle with 2% pilocarpine eye drops) we determined the changes of the cardinal points and magnification to assess PAC amplitude from the shortening of the object distance. Calculated values of PAC amplitude were compared with the respective measured values derived from amplitude measures by accommodometer, defocusing and streak retinoscopy. We analysed the results of a prospective study on 35 eyes of 28 patients after cataract surgery (target refraction: -0.2 D) and accommodative PCIOL implantation (1 CU, Human Optics AG, Erlangen, Germany) 3 months after surgery. RESULTS: After pilocarpine eye drops, ACD (mean +/- S.D., range; median) decreased by 0.88 +/- 0.48 mm (0.51-1.91; 0.66). Distance of the in-focus object decreased from the non-accommodated state (-5.62 +/- 1.83 m, -25 to -1.1; -4.83 m) to the accommodated state (ACD decrease) (-0.81 +/- 0.21, -2.11 to -0.65; -0.79 m). For a theoretical ACD decrease of 1.0 mm (the intrinsic limitation of the PCIOL design) it was -0.59 +/- 0.28, -1.31 to -0.51; -0.63 m and resulted in an objective accommodative response of 1.49 +/- 0.16, 1.21-1.81; 1.46 D, depending on the actual geometry of the individual eye. On average, magnification as induced by PAC in contrast to that induced by adequate spectacle addition differed by only about 1%. Accommodation measured with defocusing and the accommodometer correlated significantly with the theoretical value based on IOLMaster measurement of ACD decrease (r = 0.752, p = 0.005 and r = 0.676, p = 0.02). Likewise, accommodation measured with streak retinoscopy correlated weakly with the theoretical value based on IOLMaster ACD decrease (r = 0.465, p = 0.05). CONCLUSIONS: Using geometrical optics, PAC can be derived from the biometric data of the eye and the measured ACD decrease. This approach may be an additional indicator for the accommodative response in pseudophakic patients and may allow a subdivision of the measured accommodation into true PAC and pseudoaccommodation, for example, because of increased depth of focus induced by pupillary constriction. 相似文献
MRI with non-Cartesian sampling schemes can offer inherent advantages. Radial acquisitions are known to be very robust, even in the case of vast undersampling. This is also true for 1D non-Cartesian MRI, in which the center of k-space is oversampled or at least sampled at the Nyquist rate. There are two main reasons for the more relaxed foldover artifact behavior: First, due to the oversampling of the center, high-energy foldover artifacts originating from the center of k-space are avoided. Second, due to the non-equidistant sampling of k-space, the corresponding field of view (FOV) is no longer well defined. As a result, foldover artifacts are blurred over a broad range and appear less severe. The more relaxed foldover artifact behavior and the densely sampled central k-space make trajectories of this type an ideal complement to autocalibrated parallel MRI (pMRI) techniques, such as generalized autocalibrating partially parallel acquisitions (GRAPPA). Although pMRI can benefit from non-Cartesian trajectories, this combination has not yet entered routine clinical use. One of the main reasons for this is the need for long reconstruction times due to the complex calculations necessary for non-Cartesian pMRI. In this work it is shown that one can significantly reduce the complexity of the calculations by exploiting a few specific properties of k-space-based pMRI. 相似文献
Loprazolam (1) is a tricyclic benzodiazepine containing a new butazadiene moiety, which has not been investigated by polarography up to now. 1 is reduced in three waves at a DME over the whole pH-region. In BRP (pH 2-9) 10 electrons are consumed in this process. The first step is suitable for the determination of 1 in Loprazolam tablets containing 1 or 2 mg. These tablets are on the pharmaceutical market in several European countries. The mechanism of the electrode process will be reported in the communication XXXIV. 相似文献
Summary The present experiments were carried out to investigate the cardiovascular effects of endothelin 1 (ET) in pithed spontaneously hypertensive (SH) rats and to evaluate its mechanism of action. The results show that ET (0.1 – 3 nmol/kg i.v.) is a powerful vasoconstrictor agent in the pithed rat. However, at a dose of 3 nmol/kg i.v. all the pithed animals died following a gradual decrease in mean arterial blood pressure and pulse pressure and changes in the form of the electrocardiogram (ECG). The predominant feature of the change in the ECG was a progressive decrease in the amplitude of the T wave resulting in a depression of the curve representing repolarization. Investigations in isolated perfused SH rat hearts showed that ET powerfully reduces coronary flow concentration-dependently (IC50 2.1 ±0.3 nM) an effect associated with sinus bradycardia and a decrease in coronary pressure amplitude. No overt ECG changes were seen. Control experiments with mechanical flow restriction suggest that bradycardia is a consequence of reduced coronary flow and that the ECG changes observed in vivo can be explained on the basis of coronary insufficiency and resulting myocardial hypoxia. Vasoconstrictor responses to angiotensin II (0.4 g/kg i.v.), phenylephrine (8 g/kg i.v.) and ET (0.5 nmol/kg i.v.) were antagonised by around 70% by isradipine (0.03 mg/kg i.a.). The results suggest that endothelin-induced vasoconstriction may involve receptor operated channel activation and opening of voltage sensitive Ca2+ channels.Send offprint requests to A. K. Mir at the above address 相似文献
Single anion-selective channels were studied in excised membrane patches of adult frog toe muscle. The conductance and the probabilitypo of the main open state were determined for various ionic compositions of the extra-and intracellular solutions. =280 pS in symmetrical 110 mM NaCl, pH 7.4 solutions at 15°C. Higher values were found at elevated internal or external NaCl concentrations, in 70 mM external CaCl2 and at lower extracellular pH. Thepo(E) curve declined steeply with hyperpolarization and was shifted towards more negative potentials at increased internal ionic strength and at higher external pH. Positive shifts were induced by extracellular Ca. The results show that the anion channel saturates at Cl concentrations >110 mM, that the potential profile of an open channel is almost symmetrical and that channel gating is affected by neighboring channels. It is suggested that the anion channel has a voltage sensor (effective gating charge 4.3) and a similar collection of local fixed charges on the extra- and intracellular sides as voltage-gated cation channels. 相似文献