Effects of DBS on precision grip abnormalities in essential tremor.

Deep brain stimulation (DBS) of the ventrolateral thalamus is a highly effective procedure for the treatment of essential tremor (ET). The regularity of repetitive, self-paced finger tapping is known to be abnormal in patients with ET and improved following DBS. However, the more complex timing that underlies force development in the hands in ET and after DBS has not been evaluated. In this pilot study, we assessed precision grip performance in seven ET subjects before and after 5 months of DBS. Ten healthy controls were also studied. ET subjects showed a significant increase in preload duration (235 +/- 145 vs. 82 +/- 49 ms) and peak negative load (-0.524 +/- 0.35 vs. -0.174 +/- 0.14 N) during grip-lift compared with healthy subjects. No difference in load duration was observed between the groups. Following DBS, the magnitude of the peak negative load was significantly reduced (P = 0.03). In contrast, the duration of the load phase was worsened (non-significant) after DBS. We conclude that defects in the control of distal musculature necessary for establishing a stable grip exist in ET, whereas proximal muscles necessary for object lift-off remain relatively intact. Further, synergy paradigms governing grip-lift coordination may also be impaired. Although DBS is successful in alleviating tremor in ET, it produces only a partial restoration of normal precision grip.

Prediction of aerobic capacity in firefighters using submaximal treadmill and stairmill protocols.

Accurate assessments of aerobic capacity are essential to ensuring the health and well-being of firefighters, given their arduous and stressful working conditions. The use of a submaximal protocol, if proven accurate, addresses concerns such as administrative cost, time, and ease of test performance. The purposes of this study were to develop and validate graded submaximal and maximal stairmill protocols and to develop accurate maximal and submaximal equations to predict peak VO2 using both the stairmill and Gerkin treadmill protocols. Fifty-four subjects, men (36.3 +/- 5.6 years) and women (36.4 +/- 6.3 years), performed maximal graded exercise tests using both the stairmill and Gerkin treadmill protocols. Significant predictors of peak VO2 included body mass index, time to completion for maximal protocols, and time to 85% of predicted maximal heart rate for submaximal protocols. Maximal prediction equations were more accurate on both the treadmill (R = 0.654, standard error of the estimate [SEE] = 3.73 ml x kg(-1) x min(-1)) and stairmill (R = 0.816, SEE = 2.89 ml x kg(-1) x min(-1)) than developed submaximal prediction equations for both the treadmill (R = 0.325, SEE = 5.20 ml x kg(-1) x min(-1)) and stairmill (R = 0.480, SEE = 4.85 ml x kg(-1) x min(-1)). Both of the newly developed submaximal prediction equations more accurately predict peak VO2 than the current Gerkin equation. In summary, we support the use of both the stairmill and treadmill as a means for aerobic assessment in this population. The use of the developed submaximal prediction equations should lead to a reduced cost and time of assessment; however, direct measurement of maximal oxygen consumption remains the better alternative.

The blood-brain barrier and microvascular water exchange in Alzheimer's disease.

Alzheimer's disease (AD) is the most common form of dementia in the elderly. Although traditionally considered a disease of neurofibrillary tangles and amyloid plaques, structural and functional changes in the microvessels may contribute directly to the pathogenesis of the disease. Since vascular dysfunction often precedes cognitive impairment, understanding the role of the blood-brain barrier (BBB) in AD may be key to rational treatment of the disease. We propose that water regulation, a critical function of the BBB, is disturbed in AD and results in abnormal permeability and rates of water exchange across the vessel walls. In this paper, we describe some of the pathological events that may disturb microvascular water exchange in AD and examine the potential of a relatively new imaging technique, dynamic contrast-enhanced MRI, to quantify water exchange on a cellular level and thus serve as a probe of BBB integrity in AD.