The current generation of non-linear vector network analysers (NVNA) relies on a multi-harmonic generator to establish an absolute phase reference. Here a hybrid NVNA is proposed that combines a ...sampling oscilloscope, a four-port VNA and phase-locked signal generators. A signal generator, phase locked to generators that are combined as the multi-tone excitation, provides the relative phase reference during swept power measurements using the VNA. The high dynamic range VNA-based measurements are corrected in absolute phase, using the oscilloscope-based NVNA measurement at a specific power level. The hybrid NVNA has high dynamic range and the lower bound on tone spacing is determined by the memory depth of the oscilloscope, the windowing effect of the VNA receivers and the phase noise of the multi-tone sources. At 2 GHz, the hybrid NVNA has a dynamic range of 40 dB at 200 Hz tone spacing for a two-tone signal, increasing to more than 80 dB for tone spacings of 200 kHz and greater.
ABSTRACT
Aims
Elevated left atrial (LA) pressure is a pathophysiologic hallmark of heart failure with preserved ejection fraction (HFpEF). Chronically elevated LA pressure leads to LA enlargement, ...which may impair LA function and increase pulmonary pressures. We sought to evaluate the relationship between LA volume and pulmonary arterial haemodynamics in patients with HFpEF.
Methods and results
Data from 85 patients (aged 69 ± 8 years) who underwent exercise right heart catheterization and echocardiography were retrospectively analysed. All had symptoms of heart failure, left ventricular ejection fraction ≥50% and haemodynamic features of HFpEF. Patients were divided into LA volume index‐based tertiles (≤34 ml/m2, >34 to ≤45 ml/m2, >45 ml/m2). A subgroup analysis was performed in patients with recorded LA global reservoir strain (n = 60), with reduced strain defined as ≤24%. Age, sex, body surface area and left ventricular ejection fraction were similar between volume groups. LA volume was associated with blunted increases in cardiac output with exercise (padjusted <0.001), higher resting mean pulmonary artery pressure (padjusted = 0.003), with similar wedge pressure (padjusted = 1). Pulmonary vascular resistance (PVR) increased with increasing LA volume (padjusted <0.001). Larger LA volumes featured reduced LA strain (padjusted <0.001), with reduced strain associated with reduced PVR–compliance time (0.34 0.28–0.40 vs. 0.38 0.33–0.43, p = 0.03).
Conclusion
Increasing LA volume may be associated with more advanced pulmonary vascular disease in HFpEF, featuring higher PVR and pulmonary pressures. Reduced LA function, worse at increasing LA volumes, is associated with a disrupted PVR–compliance relationship, further augmenting impaired pulmonary haemodynamics.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Patients undergoing transcatheter aortic valve implantation (TAVI) have a high comorbidity burden. We sought to stratify patients into functional outcomes using the Kansas City Cardiomyopathy ...Questionnaire (KCCQ-12), a patient-reported outcome with benefits over both the New York Heart Association (NYHA) classification and the original 23-item KCCQ, and to evaluate the importance of comorbidities in predicting failure of functional improvement post-TAVI in a contemporary cohort.
In total, 366 patients with severe aortic stenosis undergoing TAVI with baseline KCCQ-12 were retrospectively analysed and divided into two groups. Failure to improve was defined as a score <60 and a change in score <10 at 1 year in either overall score (KCCQ-OS) or clinical summary score (KCCQ-CSS).
Failure to improve was noted in 13% of patients, who were more likely to have lower KCCQ-OS at baseline (47 35–59 vs 56 42–74), chronic obstructive pulmonary disease (COPD) (19% vs 8%), severe chronic kidney disease (CKD) (13% vs 2%), a clinical frailty score (CFS) ≥5 (41% vs 14%), and lower serum albumin (36 g/L 34–38 vs 38 g/L 35–40). On multivariate analysis, with an area under the curve of 0.71 (0.63–0.78), baseline KCCQ-OS (adjusted odds ratio aOR 0.3 0.1–0.6, p=0.04), COPD (aOR 2.8 1.2–6.5, p=0.02), and severe CKD (aOR 5.7 1.7–18.5, p=0.004) remained independent predictors. CFS alone had a similar predictive value as the multivariable model (OR 2.0 1.3–3.4, area under the curve 0.69 0.59–0.80, p<0.001).
KCCQ scores were effective in delineating functional outcomes, with most patients in our relatively lower surgical risk cohort showing significant functional improvements post-TAVI. Low baseline KCCQ, moderate or worse COPD, and severe CKD were associated with failure of improvement post-TAVI. Baseline CFS appears to be a good screening tool to predict poor improvement. These factors should be evaluated and weighted accordingly in pre-TAVI assessments and decision-making.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Non-linear distortion and linear static errors (DC offset and gain/phase imbalance) are the major analogue impairments in microwave I/O. quadrature modulators. They can adversely impact the ...performance of the systems using them, especially for direct-conversion transceiver systems. The impacts of these impairments were investigated for three different modulator applications: double sideband modulation, zero intermediate frequency (IF) single sideband (SSB) orthogonal frequency-division multiplexing (OFDM) modulation and low-IF SSB OFDM modulation. A behavioural model for characterising the non-linear response and the linear static errors was developed. The non-linear characteristic of each input was modelled by a complex power series based on amplitude-to-amplitude modulation and amplitude-to-phase modulation measurements. The linear static errors were modelled as three static error terms added into the complex power series based on a four-DC-point vector network analyser measurement. The non-linear model was validated by measurements with three types of signals representing the three modulator applications.
The nonlinear characteristic of an RF front-end results in in-band distortion and spectral regrowth of digitally modulated signals with distortion being dependent on the statistical variation of the ...signal. In this paper, the interaction of the nonlinear response with the signal is explored using a time-averaged autocorrelation analysis applied to several limiter-amplifier models having characteristics ranging from soft-to-hard amplitude limiting. The analysis is verified by comparing measured and predicted adjacent channel power rejection for a code-division multiple-access amplifier.
An adaptive reduced-order procedure for developing grey-box models of radio frequency systems is presented. The stochastic model extraction combines a modified genetic algorithm and the Nelder-Mead ...simplex algorithm to present a user with a range of possible good models from which the user can use intuition to select the most physically realistic candidate. The procedure is ideal for identifying models given incomplete observations, noisy data and inexact model structure. This procedure replaces the commonly used human-in-the-loop ad hoc deterministic approach in which a skilled operator must guide the model fitting. Being able to use an expanded range of model architectures beyond the Wiener and Hammerstein family, the stochastic approach, utilisation of incomplete observations and extraction of multiple distinct model candidates, enables the insight and intuition of a skilled operator to be used to advantage. The extraction of a multistage microwave amplifier exhibiting long-term memory effects is used as an example.
The aim of this study was to determine whether specific echocardiographic phenotypes could identify patients with heart failure with preserved ejection fraction (HFPEF) that may respond more ...favorably to spironolactone. Results Patients with a lower lateral E/e’ (mean 8.3) were of a similar age, had a slightly lower blood pressure (126±16mmHg vs 130±16mmHg, p=0.03) and body mass index (33±8 vs 35±9, p=0.03), and were more likely to have a previous history of atrial fibrillation (44.3% vs 34.6%, p=0.057) but less likely to be previously hospitalized (54% vs 64%, p=0.052).
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A new waveform processing technique for reducing intermodulation distortion (IMD) generated by an amplitude-modulated signal is presented. The technique eliminates amplifier-generated IMD by ...time-multiplexing portions of the signal spectrum prior to amplification. The input signal is described as a sum of sinusoidal signals. The peak-to-average ratio of the time-multiplexed amplifier input is lower than that of its non-multiplexed counterpart, but it contains spectral aliases at multiples of the switching frequency. Thus, the reduction in distortion of the desired amplified signal is achieved at the expense of momentarily widening the signal bandwidth. Following amplification, the desired signal is recovered using a bandpass filter which spreads the signal in time and narrows its bandwidth. An analytical expression for distortion reduction when amplifying two multiplexed carriers is developed along with measurements verifying the theory. Distortion reduction is demonstrated experimentally at 3.6 GHz for 2-20 multiplexed carriers, and linear recovery is demonstrated for four multiplexed carriers. The technique reduces third-order IMD by 8-22 dB in experimental measurements of three different amplifiers. The presented technique has the unique property of improving linearity without requiring feedback, feedforward cancellation or calibration.
The effective signal-to-noise and distortion ratio (SNDR) at the output of a nonlinear amplifier is defined through the decomposition of the nonlinear output into the correlated output and ...uncorrelated distortion. The analysis is based on the orthogonalisation of the nonlinear behavioual model that allows the accurate estimation of the effective in-band (or co-channel) distortion and, hence, determination of SNDR. The fundamental issues regarding the evaluation of the effective in-band distortion and its effect on digitally modulated signals are discussed. The simulations of in-band distortion and SNDR of WCDMA signals are verified experimentally using feed-forward cancelation.
