Dragana Bajic

Temporal analysis of the spontaneous baroreceptor reflex during mild emotional stress in the rat

The effect of emotional stress on the spontaneous baroreceptor reflex (sBRR) in freely moving rats was investigated. Six male Wistar rats equipped with an intra-arterial polyethylene catheter were exposed to a 2-min air-jet stress. For time course analysis of the sBRR response to stress, the records of systolic blood pressure (SBP) and pulse interval (PI) were divided into five regions: baseline (BASELINE), acute exposure to air-jet stress (STRESS), immediate recovery (IMMED. RECOVERY), remaining recovery (RECOVERY), and delayed response (DELAYED RESPONSE). In addition to sBRR sensitivity and effectiveness, we introduce the sequence coverage area and its median for evaluation of the sBRR operating range and set point. During exposure to STRESS and IMMED. RECOVERY, sBRR sensitivity was preserved, its effectiveness was decreased, its operating range was enlarged, and the set point was shifted towards higher SBP and lower PI values. According to the joint symbolic dynamics analysis, the SBP and PI relationship became less predictable hence more prone to respond to stress. In RECOVERY the parameters regained baseline values and DELAYED RESPONSE occurred during which re-setting of sBRR was noted. It follows that emotional stress modulates sBRR differentially during the time course of stress and recovery, affecting both linearity and unpredictability of the BP and PI relationship.

Temporal Sequence Parameters in Isodistributional Surrogate Data: Model and Exact Expressions

In this paper, a set of formulae for the temporal spontaneous baroreceptor reflex (sBRR) sequence parameters in isodistributional (ID) surrogate data is derived. This is facilitated by representing successive positive or negative amplitude changes as a Markov chain model. The obtained analytical tool measures the effect of random fluctuations on the overall number of sequences, estimated from the original biomedical time series. The formulae are tested using ID surrogates of systolic blood pressure and pulse-interval signals recorded from 13 healthy male Wistar rats at baseline conditions.

Autonomic mechanisms underpinning the stress response in borderline hypertensive rats

This study investigates blood pressure (BP) and heart rate (HR) short‐term variability and spontaneous baroreflex functioning in adult borderline hypertensive rats and normotensive control animals kept on normal‐salt diet. Arterial pulse pressure was recorded by radio telemetry. Systolic BP, diastolic BP and HR variabilities and baroreflex were assessed by spectral analysis and the sequence method, respectively. In all experimental conditions (baseline and stress), borderline hypertensive rats exhibited higher BP, increased baroreflex sensitivity and resetting, relative to control animals. Acute shaker stress (single exposure to 200 cycles min‐1 shaking platform) increased BP in both strains, while chronic shaker stress (3‐day exposure to shaking platform) increased systolic BP in borderline hypertensive rats alone. Low‐ and high‐frequency HR variability increased only in control animals in response to acute and chronic shaker (single exposure to restrainer) stress. Acute restraint stress increased BP, HR, low‐ and high‐frequency variability of BP and HR in both strains to a greater extent than acute shaker stress. Only normotensive rats exhibited a reduced ratio of low‐ to high‐frequency HR variability, pointing to domination of vagal cardiac control. In borderline hypertensive rats, but not in control animals, chronic restraint stress (9‐day exposure to restrainer) increased low‐ and high‐frequency BP and HR variability and their ratio, indicating a shift towards sympathetic cardiovascular control. It is concluded that maintenance of BP in borderline hypertensive rats in basal conditions and during stress is associated with enhanced baroreflex sensitivity and resetting. Imbalance in sympathovagal control was evident only during exposure of borderline hypertensive rats to stressors.

On the optimal frame synchronization markers for channels with memory

It is shown that the optimal frame synchronization markers for channels with memory, considering the widely used postdetection maintenance and the minimum average rule, are not the ones optimized for an AWGN channel. A method for obtaining the optimal marker using the channel state diagram and the corresponding trellis is presented. >

Multiple window-sliding search

A search for a single pattern in random data is a topic that had attracted attention of both mathematicians and engineers. This paper derives the statistical parameters of an extended problem - a search for multiple patterns - introducing an analytical tool for a broad range of applications.

A simple suboptimal construction of cross-bifix-free codes

Cross-bifix-free sets are sets of bifix-free sequences with the property that no prefix of any sequence is a suffix of any other sequence. This paper presents a general construction method for cross-bifix-free sequences based on kernels. The cardinality of cross-bifix-free sets follows the Fibonacci progression. A simplified method, applicable to a limited number of so-called “regular kernel sets”, is proposed as well. Properties of such sequences with an outline for further research are discussed.

Search process and probabilistic bifix approach

An analytical approach to a search process is a mathematical prerequisite for digital synchronization acquisition analysis and optimization. A search is performed for an arbitrary set of sequences within random but not equiprobable L-ary data. This paper derives in detail an expression for probability distribution function, from which other statistical parameters - expected value and variance - can be obtained. The probabilistic nature of (cross-) bifix indicators is shown and application examples are outlined, ranging beyond the usual telecommunication field

Heart rate dynamics in doxorubicin-induced cardiomyopathy

The clinical use of doxorubicin, an effective chemotherapeutic is hampered by the development of irreversible cardiotoxicity. Here we test time-frequency analysis of heart rate (HR) variability (HRV) for early detection of doxorubicin-induced cardiotoxicity. Experiments were conducted in adult male Wistar rats treated for 15 days with doxorubicin (DOXO, total dose 15 mg kg(-1), i.p.) or saline (CONT). DOXO rats exhibited cardiotoxicity confirmed by histological examination without developing heart failure as estimated by echocardiography. However, HR variability increase reflected subtle microscopic changes of cardiac toxicity in DOXO rats. The results recommend time-frequency analysis of HRV for early detection of doxorubicin-induced cardiomyopathy.

PHY-MAC Cross-Layer Approach to Energy-Efficiency and Packet-Loss Trade-off in Low-Power, Low-Rate Wireless Communications

In this paper we analyze energy-efficiency and packet-loss trade-off at physical and medium access control layers. The trade-off can be tuned by proper setting of packet length, transmission power and maximal number of allowed transmissions per packet. Our approach is multi-objective without decision making preferences. We show how energy-efficiency vs. packet-loss Pareto Frontier can be determined. We present numerical results for the case when CC1000 transceiver is used. Contrary to intuition, we find that Pareto Frontier is not a continual locus, meaning that energy-efficiency and packet-loss can not be traded continually in Pareto Optimality sense.

Channel Loss Based Energy Consumption Model for Low-Power Wireless Communications

Transmission power control can significantly improve energy-efficiency of wireless sensor network communications. Power consumption models are typically based on dependence of channel attenuation on distance. However, in practice, information on distance is usually not available and the dependence of channel attenuation on distance is not sufficiently accurate. Therefore, we propose more accurate power consumption model that uses information on total channel-loss, available on the most current low-power transceivers. We formulate the problems of selecting single-hop vs. multi-hop communication, and minimal energy route optimization, based on the proposed power consumption model.