Depression of baroreflex control of heart rate by halothane in growing piglets

Baroreflex activation in conscious rats modulates the joint inflammatory response via sympathetic function

The baroreflex is a critical physiological mechanism controlling cardiovascular function by modulating both the sympathetic and parasympathetic activities. Here, we report that electrical activation of the baroreflex attenuates joint inflammation in experimental arthritis induced by the administration of zymosan into the femorotibial cavity. Baroreflex activation combined with lumbar sympathectomy, adrenalectomy, celiac subdiaphragmatic vagotomy or splenectomy dissected the mechanisms involved in the inflammatory modulation, highlighting the role played by sympathetic inhibition in the attenuation of joint inflammation. From the immunological standpoint, baroreflex activation attenuates neutrophil migration and the synovial levels of inflammatory cytokines including TNF, IL-1β and IL-6, but does not affect the levels of the anti-inflammatory cytokine IL-10. The anti-inflammatory effects of the baroreflex system are not mediated by IL-10, the vagus nerve, adrenal glands or the spleen, but by the inhibition of the sympathetic drive to the knee. These results reveal a novel physiological neuronal network controlling peripheral local inflammation.

Coherence analysis overestimates the role of baroreflex in governing the interactions between heart period and systolic arterial pressure variabilities during general anesthesia

During general anesthesia positive pressure mechanical ventilation (MV) profoundly affects intrathoracic pressure and venous return, thus soliciting cardiopulmonary reflexes and modifying stroke volume. As a consequence heart period, approximated as the temporal distance between two consecutive R peaks on the ECG (RR), and systolic arterial pressure (SAP) variability series are usually highly correlated at the MV frequency (MVF) and this significant correlation is commonly taken as an indication of an active baroreflex. In this study the involvement of baroreflex was tested according to a time-domain linear Granger causality approach accounting explicitly for MV in two experimental protocols. In the first protocol volatile (VA) or intravenous (IA) anesthetic was administered in humans during pressure controlled MV (PCMV). In the second protocol IA was administered in pigs during PCMV or pressure support MV (PSMV). Causality analysis was contrasted with RR-SAP squared coherence. Significant coherence values at MVF were always found in both protocols. On the contrary, a significant causal link from SAP to RR was less frequently found in humans independently of the anesthesiological strategy and in animals during PCMV. PSMV was superior to PCMV in animals because it was able to better preserve a link from SAP to RR. During general anesthesia the involvement of baroreflex in governing RR-SAP variability interactions is largely overestimated by RR-SAP squared coherence and causality analysis can be exploited to rank anesthesiological strategies and MV modes according to the ability of preserving a working baroreflex.

The Hemodynamic Effects of Ephedrine on the Onset Time of Rocuronium in Pigs

Several studies have found a correlation between the onset time of muscle relaxants, cardiac index, and muscle blood flow. Ephedrine increases these hemodynamic variables and shortens onset time of rocuronium in humans. Our aim in this animal study was to determine the effect of ephedrine on the onset time of rocuronium, cardiac index, and muscle blood flow after administration of thiopental. At predefined measuring points, mean arterial blood pressure and cardiac index were measured invasively and onset time was determined mechanomyographically. Twenty-four pigs were randomly assigned to three groups. Group I received etomidate and subsequently rocuronium (2 x 95% effective dose). Instead of etomidate, Group II received thiopental. In Group III, ephedrine 100 mug/kg was given before thiopental; additionally, muscle blood flow was measured (fluorescent microspheres). Although there were differences in hemodynamics between Groups I and II, this was not reflected in different onset times of rocuronium. In Group III, ephedrine compensated the thiopental-induced decrease of mean arterial blood pressure, cardiac index, and muscle blood flow, but no significant shortening of onset time (Group I: 74 +/- 21 s; Group II: 71 +/- 24; Group III: 69 +/- 22 s) was found. Our results demonstrated that ephedrine-related increases in cardiac index and blood flow did not shorten onset time of rocuronium in healthy pigs.

Estrous cycle phase variations in visceromotor and cardiovascular responses to colonic distension in the anesthetized rat

Visceromotor and cardiovascular responses to colonic distension were measured in female rats, anesthetized with halothane in oxygen, in the proestrus, estrus, metestrus and diestrus phases of the estrous cycle. Ten rats were studied in each group and responses were measured at 5-min intervals for 60 min. A mixed model analysis of variance showed that there was no real change in either the visceral or cardiovascular response with time. There was a highly significant difference in visceromotor responses between the phases of the estrous cycle (P < 0.001). During the phase of proestrus the balloon pressure at which a response was triggered was much lower, with a mean value (95% confidence interval) of 18.7 (16.1, 21.8) mmHg, than the other phases with mean values (95% confidence interval) of 31.9 (27.4, 37.2) mmHg for estrus, 28.1 (24.2, 32.8) mmHg for metestrus, and 31.1 (26.7, 36.3) mmHg for diestrus. The mean arterial blood pressure increased in all groups (range 3.2, 5.4%) as a response to the stimulus, but there was no associated heart rate variability and no significant differences in cardiovascular changes between the groups (P = 0.6). The visceromotor responses measured during the phase of proestrus occurred at a significantly lower threshold than in the other phases of estrous.

Sevoflurane anesthesia maintains reflex tachycardia on position change from supine recumbent to head-up tilt

This study evaluated the effects of inhalational anesthetics on hemodynamic changes in response to head-up tilt in humans. Twenty-four patients were randomly divided into three groups that received either halothane, isoflurane, or sevoflurane. Changes in heart rate, blood pressure, and plasma norepinephrine concentrations were determined before and during head-up tilt position in the awake and anesthetized state. Head-up tilt caused a significant increase in the heart rate, concomitantly with a decrease or no significant changes in systolic blood pressure in the awake state. However, under 2 minimum alveolar concentrations (MAC) of halothane and isoflurane anesthesia, the heart rate did not significantly change during head-up tilt in spite of significant decreases in systolic blood pressure. In contrast, under 2 MAC of sevoflurane anesthesia, the heart rate significantly increased during head-up tilt. Plasma norepinephrine did not significantly alter during head-up tilt in the awake as well as the anesthetized state. These results suggest that sevoflurane maintains an increase in heart rate in response to head-up tilt, whereas halothane and isoflurane attenuate the response.