Introduction: Critically ill patients may experience reduced mobility and sensation related to va... more Introduction: Critically ill patients may experience reduced mobility and sensation related to various pharmacologic therapies and treatments, making this patient population especially susceptible to pressure ulcers. An alert patient may be better able to reposition in response to discomfort, therefore preventing the development of pressure ulcers. However, little is known about the effect of an individual's alertness level on skin interface pressures. This study describes the effect of alertness level and backrest elevation on skin interface pressures. Materials and methods: Fifty healthy participants were recruited from the Virginia Commonwealth University (Richmond, VA) population. Participants simulated each of 2 alertness levels (sedated or alert) while in 3 backrest elevations (30°, 45°, or 60°). Activity level, backrest elevation, and interface pressures were recorded continuously for 30 seconds. Random effects models were used to examine the effects of alertness level and backrest elevation on average and peak pressure. Participants had a mean age of 30 and 82% were female. Results: There was a significant interaction between alertness level and angle as related to average pressure (P < 0.0001) and peak pressure (P < 0.0001). Increases in backrest elevation increased average pressure and peak pressure. Interface pressures were generally greater when participants were simulating the alert state. Conclusion: These findings may indicate that interface pressure is a poor indicator of patient discomfort. Higher body mass index (BMI) was associated with higher average pressure (P < 0.0001), but lower peak pressure (P < 0.0001), suggesting better pressure distribution across the patient's body area. These findings are similar to previous studies in which low BMI is associated with increased pressure ulcer risk. .
The Fiber Optic Helmet Mounted Display (FOHMD) projects high and low resolution computer generate... more The Fiber Optic Helmet Mounted Display (FOHMD) projects high and low resolution computer generated imagery via fiber optic bundles through collimated helmet mounted optics to each eye. Combined head and eye position information is then used to position a high resolution area of interest within the head tracked low resolution background. Methods for evaluation of the eye tracker are described and experimental results presented that reveal its present performance characteristics.
To achieve the full potential of an area-of-interest (A0I) display requires that a high resolutio... more To achieve the full potential of an area-of-interest (A0I) display requires that a high resolution area be accurately aligned with the direction of gaze. Two methods of eye position measurement with the Fiber Optic Helmet Mounted Display (FOHMD) have been developed and are described. This paper describes requirements necessary for successful eye tracking in aircraft simulators and introduces two approaches to monitoring eye position. In order to measure eye position over a wide field of view with sufficient accuracy, the oculometer must be able to measure various types of eye movements and also provide sufficient information to distinguish between eye movements and associated artifacts such as eye blinks and any anomalies introduced by spurious reflections or movement of the oculometer optics relative to the eye. In addition, the device must take into account variations in pupil size caused by changes in scene brightness and distinguish between pupil image displacements caused by actual eye movements or helmet slip. Under development are two oculometers that monitor both the center of the pupillary image and the corneal reflection and which possess both high temporal and spatial resolution.
Background: Night-vision goggles (NVGs) provide only a restricted field of view and have other ch... more Background: Night-vision goggles (NVGs) provide only a restricted field of view and have other characteristics that may affect the head and eye movements used in visual search. Methods: We measured head scan patterns, the magnitude and duration of gaze saccades, and fixation duration as subjects searched computer generated imagery either with or without NVGs. Subjects searched for either a large (6 degrees) target on a low-detail background (high conspicuity condition) or a small (2 degrees) target on a high-detail background (low conspicuity condition). Results: All subjects displayed head-scan patterns that were qualitatively similar to those reported in the literature. Although both head-scan speed and amplitude were higher for the NVG condition as compared with the no-NVG condition, the difference was not statistically significant. Head-scan speed did vary significantly with target conspicuity, however. Gaze saccade amplitude varied with target conspicuity but only when NVGs were used. Fixation duration did not vary with either NVG use or target conspicuity. A two-parameter (exponent and scaling parameter) power function was fitted to the amplitude-duration data. The power-function exponents varied from about 0.30 to 0.44, but there was a concommitant variation in the scaling parameter, and the result was no significant difference in the form of the power functions fitted to the data. Conclusions: NVG use did not significantly affect any of the individual head or eye movement variables involved in searching the computer-generated imagery studied here. However, the decrease in gaze-saccade amplitude with increased target conspicuity when NVGs were used is evidence of the sensitivity of the head and eye movement measurement techniques used here, and suggests that all available measures of response efficiency be considered when evaluating NVGs using complex stimuli.
Introduction: Critically ill patients may experience reduced mobility and sensation related to va... more Introduction: Critically ill patients may experience reduced mobility and sensation related to various pharmacologic therapies and treatments, making this patient population especially susceptible to pressure ulcers. An alert patient may be better able to reposition in response to discomfort, therefore preventing the development of pressure ulcers. However, little is known about the effect of an individual's alertness level on skin interface pressures. This study describes the effect of alertness level and backrest elevation on skin interface pressures. Materials and methods: Fifty healthy participants were recruited from the Virginia Commonwealth University (Richmond, VA) population. Participants simulated each of 2 alertness levels (sedated or alert) while in 3 backrest elevations (30°, 45°, or 60°). Activity level, backrest elevation, and interface pressures were recorded continuously for 30 seconds. Random effects models were used to examine the effects of alertness level and backrest elevation on average and peak pressure. Participants had a mean age of 30 and 82% were female. Results: There was a significant interaction between alertness level and angle as related to average pressure (P < 0.0001) and peak pressure (P < 0.0001). Increases in backrest elevation increased average pressure and peak pressure. Interface pressures were generally greater when participants were simulating the alert state. Conclusion: These findings may indicate that interface pressure is a poor indicator of patient discomfort. Higher body mass index (BMI) was associated with higher average pressure (P < 0.0001), but lower peak pressure (P < 0.0001), suggesting better pressure distribution across the patient's body area. These findings are similar to previous studies in which low BMI is associated with increased pressure ulcer risk. .
The Fiber Optic Helmet Mounted Display (FOHMD) projects high and low resolution computer generate... more The Fiber Optic Helmet Mounted Display (FOHMD) projects high and low resolution computer generated imagery via fiber optic bundles through collimated helmet mounted optics to each eye. Combined head and eye position information is then used to position a high resolution area of interest within the head tracked low resolution background. Methods for evaluation of the eye tracker are described and experimental results presented that reveal its present performance characteristics.
To achieve the full potential of an area-of-interest (A0I) display requires that a high resolutio... more To achieve the full potential of an area-of-interest (A0I) display requires that a high resolution area be accurately aligned with the direction of gaze. Two methods of eye position measurement with the Fiber Optic Helmet Mounted Display (FOHMD) have been developed and are described. This paper describes requirements necessary for successful eye tracking in aircraft simulators and introduces two approaches to monitoring eye position. In order to measure eye position over a wide field of view with sufficient accuracy, the oculometer must be able to measure various types of eye movements and also provide sufficient information to distinguish between eye movements and associated artifacts such as eye blinks and any anomalies introduced by spurious reflections or movement of the oculometer optics relative to the eye. In addition, the device must take into account variations in pupil size caused by changes in scene brightness and distinguish between pupil image displacements caused by actual eye movements or helmet slip. Under development are two oculometers that monitor both the center of the pupillary image and the corneal reflection and which possess both high temporal and spatial resolution.
Background: Night-vision goggles (NVGs) provide only a restricted field of view and have other ch... more Background: Night-vision goggles (NVGs) provide only a restricted field of view and have other characteristics that may affect the head and eye movements used in visual search. Methods: We measured head scan patterns, the magnitude and duration of gaze saccades, and fixation duration as subjects searched computer generated imagery either with or without NVGs. Subjects searched for either a large (6 degrees) target on a low-detail background (high conspicuity condition) or a small (2 degrees) target on a high-detail background (low conspicuity condition). Results: All subjects displayed head-scan patterns that were qualitatively similar to those reported in the literature. Although both head-scan speed and amplitude were higher for the NVG condition as compared with the no-NVG condition, the difference was not statistically significant. Head-scan speed did vary significantly with target conspicuity, however. Gaze saccade amplitude varied with target conspicuity but only when NVGs were used. Fixation duration did not vary with either NVG use or target conspicuity. A two-parameter (exponent and scaling parameter) power function was fitted to the amplitude-duration data. The power-function exponents varied from about 0.30 to 0.44, but there was a concommitant variation in the scaling parameter, and the result was no significant difference in the form of the power functions fitted to the data. Conclusions: NVG use did not significantly affect any of the individual head or eye movement variables involved in searching the computer-generated imagery studied here. However, the decrease in gaze-saccade amplitude with increased target conspicuity when NVGs were used is evidence of the sensitivity of the head and eye movement measurement techniques used here, and suggests that all available measures of response efficiency be considered when evaluating NVGs using complex stimuli.
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