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Biomedical subjects

K Alexander

Publications and source records attributed to K Alexander.

At least 253 records · Page 14Linked to original sources
PubMedDate not supplied

The development of the RISK tool for fall prevention.

The authors tailored a 26-item risk assessment tool (RAT) for falls based on a literature review and an analysis of causative factors of falls that had occurred over a 3-month period at the Olin E. Teague VA Medical Center, an 1,100-bed acute medical-surgical, psychiatric, and extended care facility in Temple, TX. The RAT was completed by nursing staff on 10 patient units (four medical, four surgical, and two nursing home units) for all admissions during the period. A 25% sample of the completed RATs was randomly selected (n = 208). Pearson's correlation coefficient was used to identify factors that would most likely predict falls from the RATs of the randomly selected group and of the patients who fell (n = 78). Only 4 of the 26 items were statistically related to falls. Based on findings from this study, the RAT was shortened to the four items and called the RISK (Reassessment Is Safe "Kare") tool.

Accidental Falls↗
PubMedDate not supplied

Color and conventional image-directed Doppler ultrasonography: accuracy and sources of error in quantitative blood flow measurements.

Accuracy of two systems--conventional (DRF 400, Diasonics) and color-coded (Angiodynograph, Quantum/Phillips) image-directed Doppler ultrasonography--was investigated using an in vitro model that generated both monophasic and triphasic pulsatile flow patterns. Estimated and actual blood volume flow rates showed good correlations, but the sampling with a hand-held transducer led to wide variations in measurement error for the conventional (-69.2% to 50%) and the color-coded (-79.3% to 265.7%) systems. By performing multiple measurements, one could improve accuracy considering only the maximal values of a series instead of the mean values. Accuracy was impaired by interposed muscular or fatty tissue due to false low time-average velocity measurements caused by a loss of Doppler signal. Comparison of both systems revealed significant differences between pulsatility index values (p less than 0.001), blood flow velocities (p less than 0.001), and blood volume flow rates (p less than 0.05 for program flow, p less than 0.001 for manual and automatic flow program of the color-coded system).

Blood Flow Velocity↗
PubMedDate not supplied

Good design practice for medical devices and equipment, Part I: A review of current literature.

Changes to the medical device regulations within the past few years have forced medical device manufacturers to take an integrated approach to design and validation in order to ensure that their products are reliable and fit for purpose. Good design practice encourages fitness for purpose within commercial reality. This paper contains a review of the current literature that is relevant to good design practice. The results show that there is inadequate guidance regarding the integration of validation with design. Thus, there is a need for good design practice to include 'design for validation' which is aimed at designing medical devices to make them easier and more economic to validate. Research has been carried out at the Cambridge Engineering Design Centre in order to develop an approach that provides guidance in order to help designers achieve integrated design, development and validation. This will be reported in part II of this paper.

Equipment Design↗
PubMedDate not supplied

Good design practice for medical devices and equipment, Part II: Design for validation.

Medical devices and their associated process equipment must be reliable and fit for purpose. In light of the recent changes to the medical device regulations, manufacturers must now take an integrated approach to design, development and validation. Good design practice encourages this integrated approach while ensuring fitness for purpose within commercial reality. A review of current literature related to good design practice carried out in Part I of this paper showed that there is inadequate guidance regarding the integration of validation with design. This paper proposes a practical approach to design for validation aimed at making devices easier and more economic to validate. The approach comes in the form of a model of design for validation that illustrates the basic relationship between design, development and validation and a series of design tactics that were formulated in order to help designers take a more proactive approach to validation during design.

Biomedical Engineering↗
PubMedDate not supplied

Quantitative reflection spectrophotometry: spatial and temporal variation of Hb oxygenation in human skin.

Applying a fast scanning reflection spectrophotometer and multicomponent spectra analysis, oxygen saturation (SHb) and relative concentration (CHb) of hemoglobin in the skin were determined at eight skin sites in 11 healthy persons. SHb was significantly higher at the tip of the index finger and big toe (90 +/- 3.9 and 92 +/- 4.2%, respectively) compared with the forehead, volar forearm, back of hand, abdomen, calf and forefoot where mean values varied between 52 and 67% (p < 0.001). CHb also was higher at acral sites (big toe: 2.04 +/- 0.14 arbitrary units (AU); index finger: 2.13 +/- 0.19 AU) than at the other locations (p < 0.0001) where it was between 0.56 +/- 0.12 AU (abdomen) and 0.95 +/- 0.28 AU (forefoot). In the course of time, rhythmical oscillations of both parameters at a frequency of 3-5/min were seen in 68% of the measurements, predominantly at the six proximal sites. Heating the measuring site to 44 degrees C caused a biphasic increase of CHb and SHb which was significant at the proximal sites (p < 0.0001). SHb values came into the range of arterial blood. Temporal and spatial variation of both parameters decreased. Reflection spectrophotometry gives the possibility to directly assess dermal hemoglobin saturation, its physiological variability and reactions to provocation stimuli. Concentration and saturation of hemoglobin in dermal vessels appear definitely different at acral compared with proximal sites.

Hemoglobins↗
PubMedDate not supplied

Vital capillary microscopy of skin areas at the forefoot of diabetic patients using intraarterial injection of Na-fluorescein.

A modified technique of vital capillary microscopy with intraarterial application of Na-fluorescein has been introduced in the study of nutritional skin microcirculation to assess skin microcirculation of different diabetic patients, comprising one group without neurocutaneous complications (group 2; n = 9), one suffering only from neuropathy (group 3; n = 9) and one with trophic skin lesions in the contralateral foot (group 4; n = 8), all without macroangiopathy, compared to healthy controls (group 1; n = 9). Femoroarterial injection of small boli (10 mg) of Na-fluorescein allowed repeated investigation of the dye appearance times (AT) and capillary-filling times of forefoot skin capillaries within small periods of time before, during and after reactive hyperemia. At rest, AT was significantly shorter in patients of group 4 (16.8 +/- 4.4 s; p < 0.05) compared with groups 1-3 (34.3 +/- 12.8; 31.7 +/- 11.7 and 35.9 +/- 15.3 s). Fifteen seconds after the end of arterial occlusion, dye propagation to the skin was markedly accelerated in groups 1-3 (19.8 +/- 14.0; 14.4 +/- 7.6 and 18.7 +/- 10.6 s, respectively; p < 0.001), but prolonged in group 4 (18.4 +/- 7.4 s). After 10 min, the values at rest were reestablished. No differences between the four groups were found concerning capillary density and morphology. It is concluded that the development of skin lesions in diabetic patients without significant macroangiopathy may be favored by hyperperfusion and impaired vasoregulation. Intraarterial dye injection presents a valuable tool to assess dynamic alterations of the microcirculation at the level of skin capillaries.

Adult↗
PubMedDate not supplied

Local cerebral blood flow following transient cerebral ischemia. I. Onset of impaired reperfusion within the first hour following global ischemia.

Using the hydrogen clearance technique, local cerebral blood flow (LCBF) in 22 dogs was estimated at 6 parietal sites prior to and following 5 min of total global ischemia. Ischemia was immediately followed by an initial reactive hyperemia during which the electrocorticogram (ECoG) usually began to recover, and within the first 30 min, most of the LCBF's decreased to subnormal values. This onset of hypoperfusion was accompanied by a concomitant decrease in ECoG activity. Two animals that maintained normal local perfusion after the initial hyperemia recovered ECoG activity quickly. These results suggest that the subsequent poor reperfusion was caused by an increased microvascular resistance rather than by blood aggregates, increased blood viscosity, or a variety of other mechanism which have been proposed. Increased vascular tonus was, at least, partly responsible for the increased vascular resistance. This report supports the hypothesis that impaired reperfusion (which occurs some time after an initial hyperemia) may be responsible for ultimate neuronal death, rather than the period of global ischemic hypoxia per se.

Animals↗
PubMedDate not supplied

Local cerebral blood flow following transient cerebral ischemia. II. Effect of arterial PCO2 on reperfusion following global ischemia.

Following 5 minutes of global ischemia, local cerebral blood flow (LCBF) was shown to have an initial reactive hyperemia that was followed, within the first hour, by persistent hypoperfusion (Part I). Intracranial pressure (ICP) was never elevated during the period of poor reperfusion. These experiments attempted to reverse the state of subnormal LCBF by inducing hypercarbia or hyocarbia or maintaining normocarbia. Although hypocarbia did increase LCBF at several electrode sites, neither the intracerebral steal syndrome nor the "squeeze" syndrome are a dominant consequence of hypercarbia in this model of global ischemia. Hypercarbia was consistently more effective in elevating LCBFs and in recovery of the electrocorticogram. It appears that, in the absence of raised ICP, hypercarbia may be preferred to normal or low PACO2,. Even though hypercarbia was superior to normocarbia or hypocarbia, hypercarbia was not a completely satisfactory regimen for reversing the state of poor reperfusion.

Animals↗
PubMedDate not supplied

Influence of contralateral obstructions on Doppler-frequency spectral analysis of ipsilateral stenoses of the carotid arteries.

Contralateral obstructions have been suggested to be responsible for inaccuracy in Doppler sonographic diagnosis and estimation of severity of internal carotid artery stenoses. Therefore correlations of the systolic peak frequency of the internal carotid artery (Doppler-Frequency-Spectrum-Analysis) and severity of stenoses found by angiography have been compared in subgroups with (n = 36) and without (n = 48) additional contralateral obstructions. The linear regressions in both subgroups were found to be very similar (Y = 0.0098X - 12.4 and Y = 0.0099X - 14.0), the coefficients of correlation identical (r = 0.83). In 26 patients, the systolic peak frequency of the internal carotid artery did not demonstrate a significant change due to operation of the contralateral vascular lesion; thus indicating that contralateral obstructions do not influence CW-Doppler sonographic findings of an ipsilateral vessel wall lesion concerning diagnostic accuracy and non-invasive estimation of the severity of stenoses.

Arterial Occlusive Diseases↗
PubMedDate not supplied

Reproducibility of carotid artery Doppler frequency measurements.

Doppler sonography of 29 extracranial carotid arteries was performed twice within three days or less. Angiography revealed stenoses with from 10 to 95% diameter reduction in 25 internal carotid arteries whereas four vessels were found to be normal. The systolic peak frequency of the internal carotid artery read from the Doppler spectrum (n = 29) could be reproduced very well. This was shown by a linear regression nearest the line of identical values with a coefficient of correlation r = 0.97 (p less than 0.001). Other values derived from the spectral analysis of the Doppler shift signal were not so well reproduced including the peak frequency ratio (systolic peak frequency of the internal carotid artery/systolic peak of the common carotid artery) (n = 22; r = 0.81; p less than 0.001). The mean frequencies read from the zero-crossing detector recordings (n = 20) could not be reproduced as demonstrated by a linear regression far away from the line of identical measurements with a coefficient of correlation r = 0.43 (p less than 0.05).

Arterial Occlusive Diseases↗
PubMedDate not supplied

Women's preferences for gynecological examiners: sex versus role.

Preferences for gynecological examiners are studied in a cervical cancer screening program. Sex appears to be a more important factor in preference than the professional level of the examiner. Female health professionals were preferred by a majority of patients; the distinction between physicians and nurse practitioners was a much less important factor. Female examiners were particularly important to low-income and Mexican-American participants, and to women who were reluctant to participate in screening programs.

Female↗