The controllability of cardiac rhythm in elderly

Introduction: Recent reports have shown that rare fluctuations in cardiac cycles are ‘forgotten’ quickly in healthy individuals and it is possible to quantify the “memory length” of a physiological time-series using an inverse statistical approach. Methods: In the present study, we assessed the effect of aging on memory length in cardiac rhythm. Results: There was a longer memory length in cardiac time-series of elderly subjects in comparison with younger adults for both decelerating and accelerating rare fluctuations in cardiac rhythm. Conclusion: The increased memory length of the cardiac time-series in elderly subjects may indicate reduced controllability of cardiovascular regulatory system

The effect of fractal-like mechanical ventilation on vital signs in a rat model of acute-on-chronic liver failure

OBJECTIVE: The network of interactions between different organs is impaired in liver cirrhosis. Liver cirrhosis is associated with multi-system involvement, which eventually leads to multiple organ failure. This process is accelerated by a precipitating factor such as bacterial infection, which leads to respiratory distress, circulatory shock, neural dysfunction and very high mortality. Cirrhotic patients often have blunted respiratory sinus arrhythmia and impaired cardio-respiratory variability. Fractal-like mechanical ventilation is reported to enhance respiratory sinus arrhythmia and attenuate respiratory distress in experimental models. In the present study we hypothesise that fractal-like mechanical ventilation may improve the outcome of cirrhotic rats with multiple organ failure. APPROACH: Cirrhosis was induced by chronic biliary obstruction in rats. Acute multiple organ failure was induced by intraperitoneal injection of bacterial endotoxin in cirrhotic rats. The effect of conventional mechanical ventilation (with constant tidal volume and respiratory rate) or fractal-like ventilation (with the same average but variable tidal volume and respiratory rate) were assessed on vital signs, oxygen saturation and plasma alanine aminotransferase in anaesthetised cirrhotic rats. MAIN RESULTS: We demonstrated that fractal-like mechanical ventilation was accompanied by improved oxygen saturation, reduced heart rate and decreased liver injury following injection of bacterial endotoxin. Moreover, variable mechanical ventilation in cirrhotic rats reduced mortality and prevented a fall in short-term heart rate variability following endotoxin challenge in comparison with rats with constant mechanical ventilation. Significance: We suggest further investigations into the beneficial effects of fractal-like ventilation strategy in critically ill patients with liver failure requiring organ support and mechanical ventilation

Neonatal Sepsis Alters the Excitability of Regular Spiking Cells in the Nucleus of the Solitary Tract in Rats

OBJECTIVE: Sepsis is a leading cause of mortality and morbidity in infants. Although the measures of autonomic dysfunction (e.g. reduced heart rate variability) predict mortality in sepsis, the mechanism of sepsis-induced autonomic dysfunction has remained elusive. The nucleus of the solitary tract hjh(NTS) is a vital structure for the integrated autonomic response to physiological challenges. In the present study we hypothesized that sepsis alters the excitability of NTS neurons in a rat model of neonatal sepsis (14-day old rats). METHODS AND RESULTS: Sepsis was induced by intraperitoneal injection of cecal slurry (CS) in rat neonates. The presence of autonomic dysfunction was confirmed by observing a significant reduction in both short-term and long-term heart rate variably following CS injection. We investigated the effect of polymicrobial sepsis on the electrophysiological properties of the medial NTS neurons using a whole cell patch clamp recording. Our results showed that the resting membrane potential in regular spiking neurons was significantly less polarized in the septic group (-37.6 ± 1.76 mv) when compared with the control group (-54.7 ± 1.73 mv, P < 0.001). The number of spontaneous action potentials in the septic group, was also significantly higher than the control group (P < 0.05). In addition, the frequency and amplitude of the spontaneous excitatory post synaptic potentials (EPSPs) was significantly higher in neurons recorded in the septic group (P < 0.001). Interestingly, regular spiking cells in the CS group exhibited a rebound action potential following hyperpolarization. Injection of depolarizing currents was associated with lower first spike latency and changes in rise slope of action potential (P < 0.001). CONCLUSIONS: We showed that polymicrobial sepsis increases the excitability of regular spiking cells in the medial NTS. These alterations can potentially affect neural coding and thus may contribute to an abnormal homeostatic or allostatic physiological response to sepsis and systemic inflammation

Quantifying memory in complex physiological time-series.

In a time-series, memory is a statistical feature that lasts for a period of time and distinguishes the time-series from a random, or memory-less, process. In the present study, the concept of “memory length” was used to define the time period, or scale over which rare events within a physiological time-series do not appear randomly. The method is based on inverse statistical analysis and provides empiric evidence that rare fluctuations in cardio-respiratory time-series are ‘forgotten’ quickly in healthy subjects while the memory for such events is significantly prolonged in pathological conditions such as asthma (respiratory time-series) and liver cirrhosis (heart-beat time-series). The memory length was significantly higher in patients with uncontrolled asthma compared to healthy volunteers. Likewise, it was significantly higher in patients with decompensated cirrhosis compared to those with compensated cirrhosis and healthy volunteers. We also observed that the cardio-respiratory system has simple low order dynamics and short memory around its average, and high order dynamics around rare fluctuations