Objective measurement of upper limb activity and mobility during everyday behavior using ambulatory accelerometry: the upper limb activity monitor.

Ambulatory accelerometry is a technique that allows objective measurement of aspects of everyday human behavior. The aim of our research has been to develop, validate, and apply this technique, which recently resulted in an upper limb activity monitor (ULAM). The ULAM consists of body-mounted acceleration sensors connected to a waist-worn data recorder and allows valid and objective assessment of activity of both upper limbs during performance of also automatically detected mobility-related activities: lying, sitting, standing, walking, cycling, and general movement. The ULAM can be used to determine (limitations of) upper limb activity and mobility in freely moving subjects with upper limb disorders. This article provides a detailed description of its characteristics, summarizes the results of a feasibility study and four application studies in subjects having upper limb complex regional pain syndrome, discusses the most important practical, technical, and methodological issues that were encountered, and describes current and future research projects related to measuring (limitations of) upper limb activity.

Age-related changes in the circadian modulation of sleep-spindle frequency during nap sleep.

STUDY OBJECTIVES: Sleep spindles exhibit a clear circadian modulation in healthy younger people. During the biological night (when melatonin is secreted), spindle density and spindle amplitude are high and spindle frequency and its variability are low, as compared with the biological day. We investigated whether this circadian modulation of spindle characteristics changes with age. DESIGN: A 40-hour multiple-nap paradigm under constant-routine conditions SETTING: Chronobiology Laboratory, University Psychiatric Hospitals, Basel, Switzerland PARTICIPANTS: Seventeen younger (20-31 years) and 15 older (57-74 years) volunteers. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Whereas the circadian modulation of spindle density, amplitude, duration, and intraspindle frequency variability was not greatly affected by age, we found significant changes in the circadian modulation of spindle frequency. The pronounced circadian modulation of spindle frequency in younger, but not older, subjects was phase locked with the circadian rhythm in melatonin secretion. In the latter, circadian modulation was attenuated and tended to be advanced with respect to the timing of melatonin secretion. There was no difference between age groups in the phase of the sleep-wake cycle or that of melatonin, nor did the phase angle between them differ. Although changes in the circadian modulation of spindle frequency in older subjects were accompanied by reduced amplitude in the sleep consolidation profile, there was no significant correlation between spindle frequency and sleep consolidation. CONCLUSION: This multiple-nap protocol under constant-routine conditions revealed an age-dependent weaker coupling of the circadian rhythms of spindle frequency and sleep propensity to the circadian rhythm of melatonin secretion.

Human sleep spindle characteristics after sleep deprivation.

OBJECTIVE: Sleep spindles (12-15 Hz oscillations) are one of the hallmarks of the electroencephalogram (EEG) during human non-rapid eye movement (non-REM) sleep. The effect of a 40 h sleep deprivation (SD) on spindle characteristics along the antero-posterior axis was investigated. METHODS: EEGs during non-REM sleep in healthy young volunteers were analyzed with a new method for instantaneous spectral analysis, based on the fast time frequency transform (FTFT), which yields high-resolution spindle parameters in the combined time and frequency domain. RESULTS: FTFT revealed that after SD, mean spindle amplitude was enhanced, while spindle density was reduced. The reduction in spindle density was most prominent in the frontal derivation (Fz), while spindle amplitude was increased in all derivations except in Fz. Mean spindle frequency and its variability within a spindle were reduced after SD. When analyzed per 0.25 Hz frequency bin, amplitude was increased in the lower spindle frequency range (12-13.75 Hz), whereas density was reduced in the high spindle frequency range (13.5-14.75 Hz). CONCLUSIONS: The observed reduction in spindle density after SD confirms the inverse homeostatic relationship between sleep spindles and slow waves whereas the increase in spindle amplitude and the reduction in intra-spindle frequency variability support the hypothesis of a higher level of synchronization in thalamocortical cells when homeostatic sleep pressure is enhanced.