Muscle membrane properties in A pig sepsis model: Effect of norepinephrine

INTRODUCTION

Sepsis-induced myopathy and critical illness myopathy are common causes of muscle weakness in intensive care patients. This study investigated the effect of different mean arterial blood pressure (MAP) levels on muscle membrane properties following experimental sepsis.

METHODS

Sepsis was induced with fecal peritonitis in 12 of 18 anesthetized and mechanically ventilated pigs. Seven were treated with a high (75-85 mmHg) and 5 were treated with a low (≥60 mmHg) MAP target for resuscitation. In septic animals, resuscitation was started 12 h after peritonitis induction, and muscle velocity recovery cycles were recorded 30 h later.

RESULTS

Muscles in the sepsis/high MAP group showed an increased relative refractory period and reduced early supernormality compared with the remaining septic animals and the control group, indicating membrane depolarization and/or sodium channel inactivation. The membrane abnormalities correlated positively with norepinephrine dose.

DISCUSSION

Norepinephrine may contribute to sepsis-induced abnormalities in muscle by impairing microcirculation. Muscle Nerve 57: 808-813, 2018.

Early changes of muscle membrane properties in porcine faecal peritonitis

Introduction

Sepsis-induced myopathy and critical illness myopathy (CIM) are possible causes of muscle weakness in intensive care patients. They have been attributed to muscle membrane dysfunction. The aim of this study was to investigate membrane properties in the early stage of experimental sepsis by evaluating muscle excitability.

Methods

In total, 20 anaesthetized and mechanically ventilated pigs were randomized to either faecal peritonitis (n = 10) or to non-septic controls (n = 10). Resuscitation with fluids and vasoactive drugs was started 3 hours after peritonitis induction. Muscle membrane properties were investigated by measuring muscle velocity recovery cycles before induction of peritonitis as well as 6, 18 and 27 hours thereafter. Muscle relative refractory period (MRRP) and early supernormality (ESN) were assessed.

Results

Peritonitis lasting 27 hours was associated with an increase of MRRP by 28% from 2.38 ± 0.18 ms (mean ± SD) to 3.47 ± 1.79 ms (P <0.01) and a decrease of ESN by 31% from 9.64 ± 2.82% to 6.50 ± 2.64% (P <0.01). ESN reduction was already apparent 6 hours after induction of peritonitis. Values in controls did not show any significant alterations.

Conclusions

Muscle membrane abnormalities consistent with membrane depolarization and/or sodium channel inactivation occurred within 6 hours of peritonitis induction. This indicates that changes that have been described in established sepsis-induced myopathy and/or CIM start early in the course of sepsis. Muscle excitability testing facilitates evaluation of the time course of these changes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0484-2) contains supplementary material, which is available to authorized users.

Velocity recovery cycles of human muscle action potentials: repeatability and variability

OBJECTIVE

Velocity recovery cycles (VRCs) of human muscle action potentials have been proposed as a new technique for assessing muscle membrane function in myopathies. This study was undertaken to determine the variability and repeatability of VRC measures such as supernormality, to help guide future clinical use of the method.

METHODS

To assess repeatability, VRCs with one and two conditioning stimuli were recorded from brachioradialis muscle by direct muscle stimulation in 20 normal volunteers, and the measurements repeated 1 week later. To further assess variability and dependence on electrode separation, age and sex, recordings from an additional 20 normal volunteers were added.

RESULTS

There was a high intraclass correlation between repeated recordings of early supernormality, indicating excellent reliability of this VRC measure. However, relative refractory period had a smaller coefficient of repeatability in relation to the changes previously described during ischemia. We found no evidence that any of the excitability measures depended on electrode separation, conduction time or apparent velocity. There were also no significant differences between the recordings from men and women, or between the recordings from older (mean 44.9 y) and younger (26.5 y) subjects.

CONCLUSIONS

VRC measures are sufficiently consistent to be suitable for comparing muscle membrane function both within subjects and between groups. Early supernormality measurements benefit most from within subject comparisons.

SIGNIFICANCE

These normative data sets provide a firm basis for planning clinical studies.