Estimating stroke volume from oxygen pulse during exercise

This investigation aimed at verifying whether it was possible to reliably assess stroke volume (SV) during exercise from oxygen pulse (OP) and from a model of arterio-venous oxygen difference (a-vO(2)D) estimation. The model was tested in 15 amateur male cyclists performing an exercise test on a cycle-ergometer consisting of a linear increase of workload up to exhaustion. Starting from the analysis of previous published data, we constructed a model of a-vO(2)D estimation (a-vO(2)D(est)) which predicted that the a-vO(2)D at rest was 30% of the total arterial O(2) content (CaO(2)) and that it increased linearly during exercise reaching a value of 80% of CaO(2) at the peak workload (W(max)) of cycle exercise. Then, the SV was calculated by applying the following equation, SV = OP/a-vO(2)D(est), where the OP was assessed as the oxygen uptake/heart rate. Data calculated by our model were compared with those obtained by impedance cardiography. The main result was that the limits of agreement between the SV assessed by impedance cardiography and the SV estimated were between 22.4 and -27.9 ml (+18.8 and -24% in terms of per cent difference between the two SV measures). It was concluded that our model for estimating SV during effort may be reasonably applicable, at least in a healthy population.     

Plasma volume changes during hypoglycaemia: the effect of arterial blood sampling

To investigate whether previously reported changes in venous blood volume and composition induced by acute hypoglycaemia in humans are representative for the entire body we measured erythrocyte 51Cr content, haematocrit, plasma volume, intravascular albumin content and transcapillary escape rate of albumin in arterial and venous blood in seven healthy subjects before and during insulin-induced hypoglycaemia. In both vascular sites blood 51Cr content and the haematocrit increased, plasma volume and intravascular albumin content decreased and the transcapillary escape rate of albumin increased during hypoglycaemia. The magnitude of the changes in arterial and venous blood were not significantly different. These results indicate that the above changes in blood volume and composition are whole-body phenomena: furthermore, the major part of the changes are likely to occur in tissues other than upper extremity muscles.     

Estimating the elastographic signal-to-noise ratio using correlation coefficients

In conventional elastography, strain is estimated from the gradient of the displacement (time-delay) estimates. The displacement estimates involve estimating the peak location of the cross-correlation function between matching pre- and post-compression A-lines. Bias errors in estimating the peak location of the cross-correlation function, amplified by the gradient operation on the displacement estimates (needed for the computation of the strain), could result in values of elastographic signal-to-noise ratio (SNR(e)) that exceed the theoretical upper bounds, thereby hindering a consistent interpretation of this parameter. These algorithmic errors have not been accounted for by the theory. We propose the use of the measured correlation coefficients in the theoretical SNR(e) expressions to estimate the SNR(e), rather than computing them directly from the elastograms. This methodology results in values of SNR(e) that are lower than the theoretical upper bounds, thereby avoiding the problems associated with computing SNR(e) directly from the elastograms. Using simulated models of uniformly elastic phantoms, a proof of principle of such an SNR(e) measure is shown.     

Estimating left ventricular contractility using inspiratory-hold maneuvers

Objective To compare estimates of left ventricular (LV) end-systolic elastance created by inferior vena caval (IVC) occlusion with those by apneic continuous positive airway pressure (CPAP). Design and setting Prospective interventional study in a university large animal research laboratory. Subjects Sixteen intact, pentobarbital-anesthetized mongrel male dogs. Interventions Insertion of LV conductance and pressure catheters, then during apnea sequentially performed IVC occlusion and CPAP of 5, 10, and 15 mmHg for 10 s, each interspersed by positive-pressure breathing. In the final 11 dogs runs were repeated during both esmolol (2 mg min^-1) and dobutamine (5 μg kg^-1 min^-1) infusions. Measurements LV pressure-volume relationships during apneic baseline and then as LV end-diastolic volume decreased by each maneuver to calculate LV end-systolic elastance and preload-recruitable stroke work as measures of contractility. Results End-systolic elastance estimated at 5 mmHg CPAP levels and IVC occlusions were similar while 10 and 15 mmHg CPAP gave different values. However, end-systolic elastance was lower during esmolol infusion and higher during dobutamine for all CPAP and IVC occlusion maneuvers. Preload-recruitable stroke work measures were similar across maneuvers. With increasing CPAP the LV filling and end-systolic elastance were progressively shifted upward and to the left, with volume on the x-axis, consistent with an unaccounted for increase in intrathoracic pressure. Conclusions The use of 5 mmHg CPAP-induced preload-reduction allows estimation of LV end-systolic elastance and preload-recruitable stroke work in intact dogs. Increasing CPAP to more than 10 mmHg creates estimates of LV contractility that are different but covary with IVC occlusion-derived values. This work was supported by NIH grants HL67181 and HL073198.     

Estimating the POLDER sensitivity to aerosol size using PARASOL observations

The POLDER sensitivity to aerosol size is investigated based on PARASOL and AERONET observations made during 2005–2013. In this study, three AERONET sites: Xianghe, Beijing (China) and Banizoumbou (Niger) where aerosols are dominated by the rural emission, urban pollution and desert dust, respectively, are selected, and the data are screened and matched with PARASOL observations. Then, the AOD870 (aerosol optical depth at the central wavelength of 870 nm) within different size ranges is calculated using AERONET data and compared with POLDER AOD. The POLDER sensitivity is determined by looking for the best fit between the calculated AOD and the POLDER AOD. The results show: (1) The POLDER sensitivity is around 0.27 μm. (2) The AOD contributed by particles with radius less than 0.27 μm can be retrieved with high quality by using POLDER measurements. (3) Even using POLDER measurements, the retrievals in rural areas are still better than in urban. This study will help us properly understand the POLDER remote-sensing products and use them in climate studies, therefore improve our understanding of the role of human activities in climate change.     

Estimating tissue strain from signal decorrelation using the correlation coefficient

A simple relationship between the correlation coefficient and the applied strain, applicable only at low strains, is presented in this article. This relationship is derived for a Gaussian modulated cosine point spread function. The performance of the strain estimator is analyzed using a theoretical expression for the correlation coefficient along with simulation and experimental results. Both the theoretical and simulation results diverge from the ideal relationship between the strain and the correlation coefficient as the applied strain is increased. Simulation results illustrate that the strain estimate obtained using the correlation coefficient is a biased estimate with a large variability. Experimental results, however, illustrate that strain estimation using the 1-D correlation coefficient estimate is applicable only at high signal-to-noise ratios in the radiofrequency signal and in the absence of lateral and elevational signal decorrelation.     

Estimating nurses' workload using the Diagnosis Procedure Combination in Japan

Aim:  To examine the methods used to estimate nurse staffing levels in acute care settings with Diagnosis Related Groups, which in Japan are called the Diagnosis Procedure Combination (DPC).
Methods:  For estimating staffing requirements, the study used four DPC groups: (1) acute or recurrent myocardial infarction (AMI) with stenting, (2) angina pectoris with coronary artery bypass grafting (CABG), (3) sub-arachnoid haemorrhage (SAH) with clipping surgery, and (4) cerebral infarction with carotid endarterectomy (CEA). Registered nurses with more than 3-year nursing experience in nine university hospitals in the Tokyo metropolitan area completed self-report questionnaires in order to obtain nursing care time and care intensity per each DPC. The concordance rate was measured by Kendall's coefficient of concordance. The relationship between the care time and the care intensity was examined by a time series graph per DPC. Care intensity consisted of professional judgement, mental effort for helping patients, professional skill, physical effort for providing activities of daily living support, and nurse stress, based on the Hsiao and colleagues' model of resource-based relative value scale.
Results:  Twenty-five nurses in nine university hospitals answered for a hypothetical typical patient with AMI and with CABG, and 28 nurses in nine university hospitals answered for a hypothetical typical patient with SAH and with CEA. Kendall's coefficient of concordance was 0.896 for AMI, 0.855 for CABG, 0.848 for SAH, 0.854 for CEA. The time series data of the care time and the care intensity items showed different patterns for each DPC.
Conclusion:  The DPC for cardiovascular and cerebral surgical procedures can be used for estimating nurses' workload.     

Blood flow measurement using the attenuation-compensated volume flowmeter

Measurement of blood volume flow using Doppler ultrasound has traditionally required determination of the Doppler angle, vessel size, and shape of the velocity profile. In transcutaneous measurements of blood flow, this problem has been a serious drawback in clinical usage.Volume flow is formally defined as the area integral of fluid flux normal to an arbitrary sample plane. Based on this definition, a pulsed Doppler volume flowmeter has been developed which measures flow normal to a thin uniformly illuminated sample volume. Calibration of the flowmeter is described, and implications for clinical use are discussed.     

Estimating the class composition of mixed pixels using a self-addressed lookup table

There have been many studies in remote sensing imagery to solve mixed pixels problem of estimating endmembers proportions in order to determine their class composition. This paper aims at solving this problem efficiently when the available information consists of only one spatial resolution.To this end, we introduce a novel simple approach which uses a lookup table of pixels with known subpixel composition, derived from the input data. The composition of each pixel of the same input is determined by finding a similar pixel in the table. We show that these similar pixels, with approximately equal amplitudes in all bands, consist of equal endmembers composition, and use this fact to decompose the mixed pixels to a set of mostly pure subpixels. The classes of these subpixels are determined by an arbitrary classification process such as c-means. Simulation results on real and artificial data confirm that the proposed method improves estimation of mixed pixels class composition compared to those of unsupervised fuzzy c-means (FCM) and hard classification.     

假肢质心测定装置的研制

目的:测量假肢的质心参数,为假肢设计提供数据保证.方法:基于静态称重技术,利用称重传感器测量支反力,并将其测量数据传输到数据采集和处理系统,计算出假肢的质量与质心坐标.测量时,取一矩形均质长方体构件为对象测其质量和质心参数(由于质量易测,因此主要分析质心的测量),同时作为标准件来检验该装置的测量误差,其中该误差包括装置的加工误差,和传感器的测量精度误差等.结果:实验测量得到的质心绝对误差为ΔXc=–0.313 0 mm,ΔYc=–0.108 6 mm,ΔZc=–0.234 6 mm;相对误差为:Xc%= 2.65%,Yc%=3.77%,Zc%=4.82%.结论:①测试相对误差均小于工程误差允许的5%,用该装置测试的假肢质心位置是可信的.②为假肢设计者提供依据,使得假肢的质量和质心与健肢各部分大体一致.③对于像假肢这样形状复杂物体的质心测定,提升假肢设计水平具有重要意义.④该装置测量便捷、准确,精度满足使用要求,是一个兼具测试,研发双重功能的实验平台.     

Blood sampling for biochemical analysis from central venous catheters: minimizing the volume of discarded blood.

The purpose of the work was to establish a reliable procedure for blood sampling from central venous catheters with a minimal loss of blood. Based on previous studies of potassium measurements, the routine procedure had been to discard 12 ml of blood. In order to clear the catheter from substances from the infusion including potassium, the catheters were first flushed with 5 ml of saline. Repeated samples in fractions of 3 ml for hematological analyses (ethylenediaminetetraacetic acid plasma; seven patients), coagulation tests (citrate plasma; seven patients) and for serum measurements (eight patients) showed that a discarded volume of 3 ml corresponding to at least six times the dead-space of the catheters was sufficient after initial flushing with saline.     

Assessment of residual-limb volume change using bioimpedence

We investigated electrical bioimpedance as a potential measurement modality to assess residual-limb volume change in lower-limb amputees. Four strip electrodes were positioned across the anterior lateral to posterior lateral aspects of the proximal lower leg or residual limb such that the outer pair applied current and the inner pair sensed voltage. A commercial bioimpedance analyzer supplied current at 50 fre quencies between 5 kHz and 1 MHz and then used a well-validated model to determine fluid resistance. From these data, extracellular fluid volume (V(ECF)) could be estimated. Bench test evaluation showed the instrument to have a root-mean-square error of less than 0.014% over a 1 h interval. Tests of subjects who had been transtibial amputees for at least 2 yr showed V(ECF) changes from postural adjustments well outside the instrument error and normal minute-to-minute biological variability. The rate of V(ECF) change while standing with the prosthesis donned was greater for diabetic subjects than for nondiabetic subjects. Bioimpedance analysis may have use in prosthetics research, where comparing residual-limb volume at different time points or under different treatment conditions is of interest.     

Estimating potato leaf chlorophyll content using ratio vegetation indices

Chlorophyll content at leaf level is an important variable because of its crucial role in photosynthesis and in understanding plant functioning. In this study, we tested the hypothesis that the ratio of a vegetation index (VI) for estimating canopy chlorophyll content (CCC) and one for estimating leaf area index (LAI) can be used to derive chlorophyll content at the leaf level. This hypothesis for estimating chlorophyll content at the leaf level was tested using simulations with the PROSAIL radiative transfer model and field spectroradiometry measurements in five consecutive years (2010–2014) for potato crops on experimental fields. During the growing season, in-situ field measurements of LAI and leaf chlorophyll content (LCC) were performed. Results showed that good estimates of LCC were feasible using ratio vegetation indices (VIs). This was tested at satellite level using RapidEye images. This letter presents a proof of concept for estimating LCC using Sentinel-2 data. Results confirm the importance of the red-edge bands for agricultural applications, but also showed that indices using the red-edge bands may be replaced by indices using green bands. It should now be tested with real Sentinel-2 data whether its spectral bands at 10 m spatial resolution are suitable for estimating LCC, avoiding the need for red-edge bands that only are available at 20 m.     

Estimating the transfer function from neuronal activity to BOLD using simultaneous EEG-fMRI

Previous studies using combined electrical and hemodynamic measurements of brain activity, such as EEG and (BOLD) fMRI, have yielded discrepant results regarding the relationship between neuronal activity and the associated BOLD response. In particular, some studies suggest that this link, or transfer function, depends on the frequency content of neuronal activity, while others suggest that total neuronal power accounts for the changes in BOLD. Here we explored this dependency by comparing different frequency-dependent and -independent transfer functions, using simultaneous EEG-fMRI. Our results suggest that changes in BOLD are indeed associated with changes in the spectral profile of neuronal activity and that these changes do not arise from one specific spectral band. Instead they result from the dynamics of the various frequency components together, in particular, from the relative power between high and low frequencies. Understanding the nature of the link between neuronal activity and BOLD plays a crucial role in improving the interpretability of BOLD images as well as on the design of more robust and realistic models for the integration of EEG and fMRI.