High frequency deep brain stimulation: what are the therapeutic mechanisms?

High frequency deep brain stimulation (HFS) used to treat the symptoms of Parkinson's disease (PD) was first assumed to act by reducing an excessive tonic GABAergic inhibitory output from the internal globus pallidus (GPi). Stimulation in GPi might produce this directly by mechanisms such as depolarization block or activation of presynaptic inhibitory fibers, and the same mechanisms evoked by HFS in the subthalamic nucleus (STN) could reduce the excitatory action of STN on GPi neurons. Although somatic recordings from neurons near the stimulation site may appear to support this potential mechanism, the action downstream from the site of stimulation often is not consistent with this interpretation. A more parsimonious explanation for the similar effects of HFS in STN or GPi and a lesion of either of these structures is that both HFS and pallidotomy interrupt an abnormal pattern of firing in cortico-basal ganglia-thalamocortical loops that is responsible for the symptoms of PD.

Plasma concentrations of N-terminal brain natriuretic peptide in healthy children, adolescents, and young adults: effect of age and gender

Children with congenital heart disease need adequate diagnostic classification regarding their cardiovascular status (CVS). N-terminal brain natriuretic peptide (N-BNP) plasma concentration indicates dysfunction of the cardiovascular system and guides decisions concerning treatment and prognosis. Reference values are established for adults, with age-dependent increasing values and higher values in women. To avoid misclassification concerning the CVS, a large group of healthy children and adolescents can be used show the relationship between gender, age, and N-BNP and these can serve as reference values. N-BNP was measured in 434 healthy subjects (240 female and 194 male) with ages ranging from 0 to 32 years without any cardiovascular disease or renal or hepatic impairment. Measurements were performed with an electrochemiluminescence immunoassay from Roche Diagnostics. Mean N-BNP decreased from 12.6 fmol/ml (0-9 years; n = 79) to 9.41 fmol/ml (10-14 years; n = 154) and in adolescents from 6.1 (15-19 years; n = 99) to 4.8 fmol/ml (> 19 years; n = 102) in adults (p < 0.05). Mean N-BNP concerning gender did not differ in any age group younger than 19 years. In contrast, the adult female group had 78% higher N-BNP compared to the male group (p < 0.05). There was a significant peak in N-BNP at the age of 12-14 years. This study shows that reference values for N-BNP differed profoundly in children compared to adults and were up to 260% higher in children without any gender difference. Therefore, these reference values will help to avoid CVS misclassification in children for the biomarker N-BNP.

Surface EMG activity of the back musculature during axial spinal unloading using an LTX 3000 Lumbar Rehabilitation System

Electromyographic (EMG) analysis has been used successfully to identify back muscle impairment in patients with low back pain. EMG signals from normal subjects during axial spinal unloading using an LTX 3000 device were obtained and spectral parameters of the electromyographic (EMG) signal were analyzed. The purpose of the study was to determine the optimal time for effective traction using the LTX 3000 rehabilitation device. These data will serve as a baseline for future studies to help assess back muscle function in low back patients undergoing rehabilitation. Three time points during axial spinal unloading were compared to pre-unloading to detect alterations in median power frequency (MPF), root-mean-square (RMS) and rectified integrated EMG (riEMG) during axial spinal unloading. There were reductions of riRMG during 0-10 minutes of axial spinal unloading in all muscle groups, followed by an increase in riEMG value from 10 to 15 minutes. A similar trend was seen in the RMS values. The MPF did not change during the course of unloading, indicating that there was likely no change in fatigue properties of the paraspinal muscles during axial spinal unloading. The optimal time for effective axial spinal unloading on the basis of muscle activity was determined to be 10 minutes of axial spinal unloading, and a back assessment procedure was presented that uses surface EMG electrodes to objectively characterize muscle activity and relative fatigue properties. Future studies will use this methodology to assess treatment outcome in a chronic low back pain population.