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Micro/nanostructured surfaces (MNSS) have shown the ability to inactivate bacterial cells by physical means. An enormous amount of research has been conducted in this area over the past decade. Here, we review the various surface factors that affect the bactericidal efficiency. For example, surface hydrophobicity of the substrate has been accepted to be influential on the bactericidal effect of the surface, but a review of the literature suggests that the influence of hydrophobicity differs with the bacterial species. Also, various bacterial viability quantification methods on MNSS are critically reviewed for their suitability for the purpose, and limitations of currently used protocols are discussed. Presently used static bacterial viability assays do not represent the conditions of which those surfaces could be applied. Such application conditions do have overlaying fluid flow, and bacterial behaviours are drastically different under flow conditions compared to under static conditions. Hence, it is proposed that the bactericidal effect should be assessed under relevant fluid flow conditions with factors such as shear stress and flowrate given due significance. This review will provide a range of opportunities for future research in design and engineering of micro/nanostructured surfaces with varying experimental conditions.

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A variety of descriptor indices for the umbilical arterial Doppler waveform are currently in use for predicting perinatal outcome. However, there is a paucity of data regarding the relative diagnostic merits of these indices. We addressed this issue in a prospective, blind study in which the diagnostic efficacy of the following Doppler indices was compared: resistance index, systolic/diastolic ratio, pulsatility index, and diastolic average ratio. The analytic technique consisted of the receiver operating characteristic method, which evaluates a test's ability to discriminate a diseased from a healthy population. The patient population consisted of 350 pregnant patients with gestational ages of 34 to 36 weeks. A continuous-wave Doppler device with a 4 MHz transducer was used to investigate the umbilical vessels. The test was performed only once in each patient. The abnormal outcome parameters included small for gestational age (less than 10th percentile), Apgar score less than 7 at 5 minutes, fetal distress (late and severe variable decelerations, absent variability, fetal scalp pH less than 7.20), umbilical cord arterial pH less than 7.10, presence of thick meconium, and admission to neonatal intensive care unit (greater than 48 hours). The results showed that the resistance index had the best discriminatory ability when compared with other Doppler indices: the systolic/diastolic ratio (p less than 0.05), the pulsatility index (p less than 0.001), and the diastolic/average ratio (p less than 0.05). It is concluded that of the various Doppler indices assessed in this investigation, the resistance index offers the best diagnostic efficacy in predicting perinatal compromise.

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Changes in umbilical arterial Doppler waveform in response to acute maternal hypoxemia were assessed in a chronic ovine model. Maternal heart rate, blood gases, fetal heart rate and umbilical arterial Doppler indices measured at baseline conditions and during periods of maternal hypoxemia were compared. The indices measured were systolic-diastolic ratio (S/D), pulsatility index (PI) and resistance index (RI). Fetal heart rate decreased (less than 80 beats/min) and umbilical arterial Doppler indices increased (P less than 0.001) during the periods of hypoxemia. Furthermore, the Doppler indices were highly but negatively correlated with alterations in the fetal heart rate (FHR) (P less than 0.001). Analysis of the Doppler waveform phase intervals revealed nearly constant systolic intervals while diastolic intervals varied inversely with the heart rate alterations. Moreover, the umbilical arterial Doppler indices, when corrected for FHR changes, were relatively unchanged from baseline measurements. This study indicates that maternal hypoxemia induced changes in the umbilical arterial Doppler indices may be primarily attributable to the changes in FHR.

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This prospective blinded study investigated the diagnostic efficacy of the umbilical arterial systolic/diastolic ratio performed at 34 to 36 weeks' gestation for identifying pregnancies at a high risk for adverse perinatal outcomes. A series of 350 consecutive singleton pregnancies were included in the study. A continuous-wave Doppler instrument with a 4 MHz transducer was used. The criteria for an abnormal perinatal outcome included intrauterine growth retardation, an Apgar score of less than 7 at 5 minutes, umbilical arterial pH at birth less than 7.20, presence of thick meconium, fetal distress in labor, and neonatal complications necessitating admission to the neonatal intensive care nursery. The analytic techniques included determination of the receiver operating characteristic curve, sensitivity, specificity, positive and negative predictive values, and the kappa index. The results demonstrated that although the cutoff value of 2.9 showed the maximum inherent discriminatory power, its diagnostic efficacy (sensitivity, 0.83; specificity, 0.87 positive predictive value, 0.74; negative predictive value, 0.92; and kappa index, 0.68) was not substantially different from that of the more common cutoff value of 3.0 (sensitivity, 0.79; specificity, 0.93; positive predictive value, 0.83; negative predictive value, 0.91; and kappa index, 0.73). Both values were rated good to excellent by the kappa index. The study also demonstrated that the systolic/diastolic ratio was a better predictor of general abnormal outcome than of the suboptimal fetal growth.

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Doppler ultrasound velocimetry offers a noninvasive method for assessing velocities in the various components of the fetal circulation including the cardiac, umbilical, cerebral, and aortic flows. As the volumetric flow measurement in these circumstances is prone to significant errors, the major approach has been to analyze the maximum frequency shift envelope of the Doppler waveform. Numerous studies have demonstrated not only the feasibility, but also the diagnostic efficacy of this approach. The latter is particularly true in relation to the Doppler evaluation of the umbilical circulation in various complications of pregnancy. Although these findings do not establish the role of Doppler technology as a standard of practice, they clearly demonstrate its immense potential as a fetal surveillance technique.

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Several clinical studies suggest that the Doppler indices (DI) derived from Doppler waveform analysis may be powerful predictors of perinatal compromise. In contrast, significant paucity exists in experimental verification of the central premise that the DI reliably reflect hemodynamic state downstream from the measurement point. This paper presents the results from two sets of acute animal experiments in which experimentally induced changes in the ovine fetoplacental circulation as reflected by the independently measured hemodynamic parameters were correlated with the corresponding variations in the DI. Doppler velocimetric measurements were performed under general anesthesia in ovine fetuses with gestational ages ranging from 100 to 110 days. A continuous wave Doppler instrument with a 4-MHz transducer was used. In three fetuses, variable vascular constriction was produced by a ligature placed approximately 10 cm from the probe location. In four fetuses, vasopressin was rapidly infused. The hemodynamic parameters measured included the peripheral resistance, volumetric flow, and pressure. The DI included the systolic-diastolic ratio, pulsatility index, and resistance index. The results indicate that, in hemodynamically stable and well-defined obstruction to downstream flow as achieved in the constriction experiments, the DI highly correlated with the hemodynamic state (p less than .005); however, during the more complex and unstable circulatory changes associated with vasopressin administration, these correlations were inconsistent and poor (p greater than .05). This study experimentally establishes in an in vivo animal system the hemodynamic validity of the DI within certain limits. However, the validity does not extend to hemodynamic changes associated with vasopressin administration. Further studies are required to address this issue.(ABSTRACT TRUNCATED AT 250 WORDS)

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Umbilical arterial Doppler indices (UaDI) are recognized as potentially useful tools for fetal surveillance. However, elucidation of the diagnostic reliability of UaDI requires further analysis of the factors that affect the variance of the indices. This prospective study was undertaken to analyze the effects of one such factor, the fetal heart rate (FHR). The study population consisted of 194 cases of uncomplicated pregnancy with normal outcome, with the gestational age (GA) ranging from 27 to 39 weeks. A continuous wave Doppler instrument with a 4-MHz transducer was used. The UaDI measured were diastolic/average (D/A) ratio, systolic/diastolic (S/D) ratio, pulsatility index (PI), and resistance index (RI). Linear regression of the data grouped in 2 week GA intervals demonstrated a moderate but statistically significant (p less than .05) correlation between FHR and UaDI. The influence of FHR on UaDI was then further analyzed by multiple regression technique using GA as the second independent variable. The regression demonstrated that 15% to 18% of the total UaDI variance was attributable to FHR effect. Moreover, when UaDI data were standardized for a FHR of 140 beats per minute and GA of 34 weeks using a multiple regression-based equation, the 95% limits of the UaDI were reduced by 32%, 34%, 26%, and 32% for D/A, S/D, PI, and RI, respectively. This study demonstrates a statistically significant effect of FHR on UaDI. However, clinical significance of this observation requires further investigation.

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