The influence of seat backrest angle on perceived discomfort during exposure to vertical whole-body vibration.

National and International Standards (e.g. BS 6841 and ISO 2631-1) provide methodologies for the measurement and assessment of whole-body vibration in terms of comfort and health. The EU Physical Agents (Vibration) Directive (PAVD) provides criteria by which vibration magnitudes can be assessed. However, these standards only consider upright seated (90°) and recumbent (0°) backrest angles, and do not provide guidance for semi-recumbent postures. This article reports an experimental programme that investigated the effects of backrest angle on comfort during vertical whole-body vibration. The series of experiments showed that a relationship exists between seat backrest angle, whole-body vibration frequency and perceived levels of discomfort. The recumbent position (0°) was the most uncomfortable and the semi-recumbent positions of 67.5° and 45° were the least uncomfortable. A new set of frequency weighting curves are proposed which use the same topology as the existing BS and ISO standards. These curves could be applied to those exposed to whole-body vibration in semi-recumbent postures to augment the existing standardised methods. PRACTITIONER SUMMARY: Current vibration standards provide guidance for assessing exposures for seated, standing and recumbent positions, but not for semi-recumbent postures. This article reports new experimental data systematically investigating the effect of backrest angle on discomfort experienced. It demonstrates that most discomfort is caused in a recumbent posture and that least was caused in a semi-recumbent posture.

The influence of seat backrest angle on human performance during whole-body vibration.

This study investigated the effects of reclined backrest angles on cognitive and psycho-motor tasks during exposure to vertical whole-body vibration. Twenty participants were each exposed to three test stimuli of vertical vibration: 2-8 Hz; 8-14 Hz and 14-20 Hz, plus a stationary control condition whilst seated on a vibration platform at five backrest angles: 0° (recumbent, supine) to 90° (upright). The vibration magnitude was 2.0 ms(-2) root-mean-square. The participants were seated at one of the backrest angles and exposed to each of the three vibration stimuli while performing a tracking and choice reaction time tasks; then they completed the NASA-TLX workload scales. Apart from 22.5° seat backrest angle for the tracking task, backrest angle did not adversely affect the performance during vibration. However, participants required increased effort to maintain performance during vibration relative to the stationary condition. These results suggest that undertaking tasks in an environment with vibration could increase workload and risk earlier onset of fatigue. PRACTITIONER SUMMARY: Current vibration standards provide guidance for assessing exposures for seated, standing and recumbent positions, but not for semi-recumbent postures. This paper reports new experimental data systematically investigating the effect of backrest angle on human performance. It demonstrates how workload is elevated with whole-body vibration, without getting affected by backrest angle.

Gastric myoelectric activity during low frequency oscillation.

BACKGROUND: The normal 3 cycles per minute (3 c/m) resting activity of the stomach has been reported to shift into the range of 4-9 c/m (tachyarrhythmia) in subjects with symptoms of motion sickness. Previous studies have provoked motion sickness with an optokinetic stimulus and have not normally reported changes relative to a control condition. The present experiment investigated changes in the electrogastrogram (EGG) during a control condition and during exposure to 0.125 Hz off-axis yaw oscillation of the body. METHODS: There were 16 male subjects who participated in the two conditions 1 wk apart. The electrogastrogram, respiration rate and subjective ratings of sickness were monitored throughout both conditions. Spectral analysis of the EGG time histories provided measures of 3 c/m power and tachyarrhythmia power, which were also expressed as a percentages of EGG power over the total EGG frequency range (0.04 to 0.16 Hz.). The median frequency of the EGG over this bandwidth was also calculated. RESULTS: During motion exposure, the median frequency of the EGG and the percentage tachyarrhythmia power increased and the percentage 3 c/m power decreased relative to a pre-exposure baseline period and relative to the static control condition. CONCLUSIONS: Low frequency off-axis yaw oscillations disrupted the normal resting gastric myoelectric activity relative to a control condition.

Computerized continuous quality improvement methods used to optimize blood transfusions.

Blood transfusion, although common, is not without risk and expense. Recently there has been a national focus on both overtransfusion and undertransfusion. To provide the best quality of patient care, there must be a balance between both over and undertransfusion. We used a computer system to minimize overtransfusion by prompting physicians when orders that did not meet accepted criteria were made. Continuous quality improvement methods were used to optimize blood transfusions. We also evaluated undertransfusions by assessing patients who did not receive a red cell transfusion when the Hemoglobin or Hematocrit showed it was clearly indicated. Using our computerized alerting system we are able to promptly notify physicians when such conditions exist. Results of the blood ordering show that overtransfusions of red cells have been minimized. Reductions in both mean Hematocrit and the standard deviation have occurred as predicted by continuous quality improvement theory. Assessment of undertransfusions showed that it was a minimal problem, but one that can be easily addressed with our laboratory alerting system.