Fluctuations of estimated glomerular filtration rate outside kidney disease improving global outcomes diagnostic criteria for acute kidney injury in end-stage liver disease outpatients and outcome postliver transplantation

Background. Renal dysfunction in end-stage liver disease (ESLD) results fromsystemic conditions that affect both liver and kidney with activation of vasoconstrictor systems. In this setting, estimated glomerular filtration rate (eGFR) may undergo variations often outside Kidney Disease Improving Global Outcomes criteria for acute kidney injury (AKI) diagnosis, whose meaning is not clear. The aim of this study was to evaluate eGFR variations in ESLD outpatients listed for liver transplant (liver Tx) and the association with post-Tx outcome. Methods. Fifty-one patients with ESLD were retrospectively evaluated from listing to transplant (L-Tx time), intraoperatively (Tx time), and up to 5 years post-Tx time. Variations between the highest and the lowest eGFR occurring in more than 48 hours, not satisfying Kidney Disease Improving Global Outcomes guideline, were considered as fluctuations (eGFR-F). Fluctuations of eGFR greater than 50%were defined as eGFR drops (DeGFR). Early graft dysfunction, AKI within 7 days, chronic kidney disease, and short- and long-term patient survivals were considered as outcomes. Results. All patients presented eGFR-F, whereas DeGFR were observed in 18 (35.3%) of 51 (DeGFR+ group). These patients presented higher levels of Model for End-stage Liver Disease score, pre-Tx bilirubin and significantly greater incidence of post-Tx AKI stages 2 to 3 compared with patients without drops (DeGFR−). DeGFR was the only independent predictive factor of the occurrence of post-Tx AKI. The occurrence of AKI post-Tx was associated with the development of chronic kidney disease at 3 months and 5 years post-Tx. Conclusions. Drops of eGFR are more frequently observed in patients with a worse degree of ESLD and are associated with a worse post-Tx kidney outcome

On Precoding for Constant K-User MIMO Gaussian Interference Channel with Finite Constellation Inputs

This paper considers linear precoding for constant channel-coefficient $K$-User MIMO Gaussian Interference Channel (MIMO GIC) where each transmitter-$i$ (Tx-$i$), requires to send $d_i$ independent complex symbols per channel use that take values from fixed finite constellations with uniform distribution, to receiver-$i$ (Rx-$i$) for $i=1,2,\cdots,K$. We define the maximum rate achieved by Tx-$i$ using any linear precoder, when the interference channel-coefficients are zero, as the signal to noise ratio (SNR) tends to infinity to be the Constellation Constrained Saturation Capacity (CCSC) for Tx-$i$. We derive a high SNR approximation for the rate achieved by Tx-$i$ when interference is treated as noise and this rate is given by the mutual information between Tx-$i$ and Rx-$i$, denoted as $I[X_i;Y_i]$. A set of necessary and sufficient conditions on the precoders under which $I[X_i;Y_i]$ tends to CCSC for Tx-$i$ is derived. Interestingly, the precoders designed for interference alignment (IA) satisfy these necessary and sufficient conditions. Further, we propose gradient-ascent based algorithms to optimize the sum-rate achieved by precoding with finite constellation inputs and treating interference as noise. Simulation study using the proposed algorithms for a 3-user MIMO GIC with two antennas at each node with $d_i=1$ for all $i$, and with BPSK and QPSK inputs, show more than 0.1 bits/sec/Hz gain in the ergodic sum-rate over that yielded by precoders obtained from some known IA algorithms, at moderate SNRs.Comment: 15 pages, 9 figure

Adaptive Nonlinear RF Cancellation for Improved Isolation in Simultaneous Transmit-Receive Systems

This paper proposes an active radio frequency (RF) cancellation solution to suppress the transmitter (TX) passband leakage signal in radio transceivers supporting simultaneous transmission and reception. The proposed technique is based on creating an opposite-phase baseband equivalent replica of the TX leakage signal in the transceiver digital front-end through adaptive nonlinear filtering of the known transmit data, to facilitate highly accurate cancellation under a nonlinear TX power amplifier (PA). The active RF cancellation is then accomplished by employing an auxiliary transmitter chain, to generate the actual RF cancellation signal, and combining it with the received signal at the receiver (RX) low noise amplifier (LNA) input. A closed-loop parameter learning approach, based on the decorrelation principle, is also developed to efficiently estimate the coefficients of the nonlinear cancellation filter in the presence of a nonlinear TX PA with memory, finite passive isolation, and a nonlinear RX LNA. The performance of the proposed cancellation technique is evaluated through comprehensive RF measurements adopting commercial LTE-Advanced transceiver hardware components. The results show that the proposed technique can provide an additional suppression of up to 54 dB for the TX passband leakage signal at the RX LNA input, even at considerably high transmit power levels and with wide transmission bandwidths. Such novel cancellation solution can therefore substantially improve the TX-RX isolation, hence reducing the requirements on passive isolation and RF component linearity, as well as increasing the efficiency and flexibility of the RF spectrum use in the emerging 5G radio networks.Comment: accepted to IEE