Teaching Signal Processing to the Medical Profession

Knowledge of signal processing is very important for medical students. A medical signal may be used for monitoring, constructing an image, or for extracting the numerical quantity of a parameter. This information forms a basis for medical decisions. However, the processing of the signal may lead to distortion and an incorrect interpretation. The present article describes an educational practical for first year medical students. It uses the electrocardiogram, which can be obtained easily, as a convenient example of a medical signal. The practical was developed at the VU University Amsterdam and summarizes the elementary concepts of signal processing

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Is slow walking more stable?

Several efforts have been made to study gait stability using measures derived from nonlinear time-series analysis. The maximum finite time Lyapunov exponent (

The effects of arm swing on human gait stability

Arm swing during human gait has been shown to reduce both angular momentum about the vertical and energy expenditure, and has been hypothesized to enhance gait stability. To examine this hypothesis, we studied the effect of arm swing on the local and global stability of steady-state gait, as well as the ability to perform adequate recovery actions following a perturbation. Trunk kinematics of 11 male subjects was measured in treadmill walking with normal and with restricted arm swing. In half of the trials, gait was perturbed by a position-controlled forward pull to the trunk. We constructed state spaces using data recorded from the unperturbed steady-state walking trials, and quantified local gait stability by calculating maximum Lyapunov exponents. In addition, we analyzed perturbation forces, the distance from the unperturbed gait pattern, and the return toward the normal gait pattern following an external perturbation. Walking without arm swing led to a non-significantly lower Lyapunov exponent (P0.06), significantly higher perturbation forces (P<0.05), and significantly slower movements away from the attractor (P<0.01). These results suggest that gait without arm swing is characterized by similar local stability to gait with arm swing and a higher perturbation resistance. However, return towards the normal gait pattern was significantly slower (P<0.05) when walking with restricted arms, suggesting that the arms play an important role in the recovery from a perturbation. Collectively, the results suggest that arm swing as such does not enhance gait stability, but rather that recovery movements of the arms contribute to the overall stability of human gait. © 2010. Published by The Company of Biologists Ltd

Regulation of rest, rather than activity, underlies day-night activity differences in mice

The suprachiasmatic nucleus (SCN), which serves as the central pacemaker in mammals, regulates the 24-h rhythm in behavioral activity. However, it is currently unclear whether and how bouts of activity and rest are regulated within the 24-h cycle (i.e., over ultradian time scales). Therefore, we used passive infrared sensors to measure temporal behavior in mice housed under either a light-dark (LD) cycle or continuous darkness (DD). We found that a probabilistic Markov model captures the ultradian changes in the behavioral state over a 24-h cycle. In this model, the animal's behavioral state in the next time interval is determined solely by the animal's current behavioral state and by the "toss" of a proverbial "biased coin." We found that the bias of this "coin" is regulated by light input and by the phase of the clock. Moreover, the bias of this "coin" for an animal is related to the average length of rest and activity bouts in that animal. In LD conditions, the average length of rest bouts was greater during the day compared to during the night, whereas the average length of activity bouts was greater during the night compared to during the day. Importantly, we also found that day-night changes in the rest bout lengths were significantly greater than day-night changes in the activity bout lengths. Finally, in DD conditions, the activity and rest bouts also differed between subjective night and subjective day, albeit to a lesser extent compared to LD conditions. The ultradian regulation represented by the model does not result in ultradian rhythms, although some weak ultradian rhythms are present in the data. The persistent differences in bout length over the circadian cycle following loss of the external LD cycle indicate that the central pacemaker plays a role in regulating rest and activity bouts on an ultradian time scale.Circadian clocks in health and diseas

Using surgical wrapping material for the fabrication of respirator masks

Given the current shortage of respirator masks and the resulting lack of personal protective equipment for use by clinical staff, we examined bottom-up solutions that would allow hospitals to fabricate respirator masks that: (i) meet requirements in terms of filtering capacities, (ii) are easy to produce rapidly and locally, and (iii) can be constructed using materials commonly available in hospitals worldwide. We found that Halyard H300 material used for wrapping of surgical instruments and routinely available in hospitals, met these criteria. Specifically, three layers of material achieved a filter efficiency of 94%, 99%, and 100% for 0.3 mu m, 0.5 mu m, and 3.0 mu m particles, respectively; importantly, these values are close to the efficiency provided by FFP2 and N95 masks. After re-sterilization up to 5 times, the filter's efficiency remains sufficiently high for use as an FFP1 respirator mask. Finally, using only one layer of the material satisfies the criteria for use as a 'surgical mask'. This material can therefore be used to help protect hospital staff and other healthcare professionals who require access to high quality masks but lack commercially available solutions.Circadian clocks in health and diseas