Frontiers in physiology
-
Frontiers in physiology · Jan 2014
ReviewRole of sinoatrial node architecture in maintaining a balanced source-sink relationship and synchronous cardiac pacemaking.
Normal heart rhythm (sinus rhythm) depends on regular activity of the sinoatrial node (SAN), a heterogeneous collection of specialized myocytes in the right atrium. SAN cells, in general, possess a unique electrophysiological profile that promotes spontaneous electrical activity (automaticity). However, while automaticity is required for normal pacemaking, it is not necessarily sufficient. ⋯ Here, we review the important structural features of the SAN with a focus on how these elements help manage a precarious balance between electrical charge generated by the SAN ("source") and the charge needed to excite the surrounding atrial tissue ("sink"). We also discuss how compromised "source-sink" balance due, for example to fibrosis, may promote SAN dysfunction, characterized by slow and/or asynchronous pacemaker activity and even failure, in the setting of cardiovascular disease (e.g., heart failure, atrial fibrillation). Finally, we discuss implications of the "source-sink" balance in the SAN complex for cell and gene therapies aimed at creating a biological pacemaker as replacement or bridge to conventional electronic pacemakers.
-
Frontiers in physiology · Jan 2014
ReviewNeural reflex regulation of systemic inflammation: potential new targets for sepsis therapy.
Sepsis progresses to multiple organ dysfunction due to the uncontrolled release of inflammatory mediators, and a growing body of evidence shows that neural signals play a significant role in modulating the immune response. Thus, similar toall other physiological systems, the immune system is both connected to and regulated by the central nervous system. The efferent arc consists of the activation of the hypothalamic-pituitary-adrenal axis, sympathetic activation, the cholinergic anti-inflammatory reflex, and the local release of physiological neuromodulators. ⋯ Despite cytokine receptor expression in vagal afferent fibers, pro-inflammatory cytokines have no significant effect on vagus nerve activity. Thus, the CB may be the source of immunosensory inputs and incoming neural signals and, in fact, sense inflammatory mediators, playing a protective role during sepsis. Considering that CB stimulation increases sympathetic activity and adrenal glucocorticoids release, the electrical stimulation of arterial chemoreceptors may be suitable therapeutic approach for regulating systemic inflammation.
-
Frontiers in physiology · Jan 2014
ReviewSystematic review of near-infrared spectroscopy determined cerebral oxygenation during non-cardiac surgery.
Near-infrared spectroscopy (NIRS) is used to monitor regional cerebral oxygenation (rScO2) during cardiac surgery but is less established during non-cardiac surgery. This systematic review aimed (i) to determine the non-cardiac surgical procedures that provoke a reduction in rScO2 and (ii) to evaluate whether an intraoperative reduction in rScO2 influences postoperative outcome. The PubMed and Embase database were searched from inception until April 30, 2013 and inclusion criteria were intraoperative NIRS determined rScO2 in adult patients undergoing non-cardiac surgery. ⋯ Following thoracic surgery, major orthopedic, and abdominal surgery the occurrence of postoperative cognitive dysfunction (POCD) might be related to intraoperative cerebral desaturation. In conclusion, certain non-cardiac surgical procedures is associated with an increased risk for the occurrence of rScO2. Evidence for an association between cerebral desaturation and postoperative outcome parameters other than cognitive dysfunction needs to be established.
-
Frontiers in physiology · Jan 2014
Cardiovascular consequence of reclining vs. sitting beach-chair body position for induction of anesthesia.
The sitting beach-chair position is regularly used for shoulder surgery and anesthesia may be induced in that position. We tested the hypothesis that the cardiovascular challenge induced by induction of anesthesia is attenuated if the patient is placed in a reclining beach-chair position. Anesthesia was induced with propofol in the sitting beach-chair (n = 15) or with the beach-chair tilted backwards to a reclining beach-chair position (n = 15). ⋯ Continuous hemodynamic variables were recorded by photoplethysmography and frontal cerebral oxygenation (ScO2) by near infrared spectroscopy. Significant differences were only observed immediately after the induction when patients induced in a reclining beach-chair position had higher mean arterial pressure (MAP) (35 ± 12 vs. 45 ± 15 % reduction from baseline, p = 0.04) and ScO2 (7 ± 6 vs. 1 ± 8% increase from baseline, p = 0.02) and received less ephedrine (mean: 4 vs. 13 mg, p = 0.048). The higher blood pressure and lower need of vasopressor following induction of anesthesia in the reclining compared to the sitting beach-chair position indicate more stable hemodynamics with the clinical implication that anesthesia should not be induced with the patient in the sitting position.