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Biomedical subjects

L E Ostrander

Publications and source records attributed to L E Ostrander.

16 recordsLinked to original sources
PubMed1992

The relationship of surface reflectance measurements to optical properties of layered biological media.

Reflectance from a turbid biological tissue is discussed for a diffusive light source illuminating the surface of the medium, and is related to the optical property distribution within the medium and to photon propagation through the medium. A three-dimensional photon diffusion model with closed form is developed to describe the photon diffuse intensity in a homogeneous medium. The solution is extended by numerical methods to the medium with layered structure. The concepts of photon flux paths and of reflectance indexes are utilized, together with reflectance data, to extract information about the internal optical properties of a medium. The flux path concept was corroborated by successfully detecting in vivo and ex vivo layered differences in optical properties within the biological medium. These studies suggest that the optical properties of subdermal tissue can be measured from light reflectance and that the effect of the upper skin layers can be eliminated.

Absorption↗
PubMed1990

A compartment model for fluorometric indication of tissue perfusion.

Sodium fluorescein is an in vivo blood perfusion indicator for soft tissue. When fluorescein dye is introduced into the blood, it distributes throughout the vasculature and the extravascular space. Incident light from an external source causes the dye to fluoresce, the level of which is monitored by a photodetector placed over the tissue. In this study, theoretical analysis incorporating a multicompartmental model for dye distribution is applied to describe the relationship among perfusion, dye kinetics, and fluorescence readings. Errors in calculating perfusion from fluorescence are related to dye concentrations and to measurement errors. These error sources are minimized by selecting the measurement time. The alternatives of measurement during wash-in or during wash-out of dye are compared, as well as the alternatives of introducing dye by bolus injection or by constant infusion. Compensation of wash-in measurements for differences in skin pigmentation is accomplished by the matching of skin optical properties between incident and fluorescing wavelengths. A laboratory study at 80 measurement sites (from ten graded perfusion canine flaps) demonstrated a correlation of wash-in and wash-out perfusion data ranging from 0.88 to 0.96 at typical levels of fluorescein in blood. Since wash-in can be completed in a matter of a few minutes, this is likely to be preferable in the clinical setting to wash-out which can take much longer to complete.

Animals↗
PubMed1990

In vivo reflectance of blood and tissue as a function of light wavelength.

Light reflectance from soft tissue has been utilized in noninvasive clinical measurement devices such as the photoplethysmograph and the reflectance pulse oximeter. Incident light on the skin travels into the underlying layers and is in part reflected back to the surface. This paper describes the reflectance of light from in vivo tissue for wavelengths in the range from 420 to 940 nm, based on photon diffusion theory and on experimental results from studies of 17 subjects. The results show a minimum reflectance and a peak sensitivity to the blood pulsations in the wavelength range from 510 to 590 nm. Skin pigmentation is seen to attenuate reflectance rather than altering the character of the modulation spectra. Based on the model introduced in this paper, the dependence of modulation spectra on mean blood fractional volume as well as wavelength is also described theoretically, and corroborated by further experimental data at 570 and 630 nm. At these latter wavelengths, the signal-to-noise ratio was calculated for the blood volume pulsation signal in the presence of physiological noise. The median for calculated ratios of reflectance modulation by blood pulsation and ratios of signal to noise between the two wavelengths were 13.1 and 7.5, respectively, for 93 sites in nine subjects. These results are seen to be consistent with the theory.

Blood Volume↗
PubMed1990

Monitoring skin fluorescein delivery independent of skin pigmentation.

This study evaluated two changes in fluorometric assessment of fluorescein dye delivery: (1) monitoring the proportional, rather than the absolute, increase above the preinjection background reading at each site to obviate the effect of skin color and (2) employing gradual means of dye administration to facilitate monitoring uptake kinetics and to lessen the likelihood and severity of histamine-mediated reactions. In 15 beagles, background and postdye readings were obtained with the fiberoptic fluorometer at 27 pairs of matched light- and dark-skin sites of intact perfusion. After dye administration, the absolute increase in fluorescence at light sites averaged more than twice (approximately 225%) that at dark sites. However, the newly introduced proportional increase (PI) was independent of pigmentation. The PI of comparably perfused light and dark sites differed by an average of 3.9% (p greater than 0.05 for difference between PIdark and PIlight). This consistency was maintained after each of three methods of fluorescein administration. After the color independence of the PI was established, its relation to perfusion was assessed in nine 3 X 12 cm pedicle flaps of varied pigmentation. Background fluorometric readings were obtained at eight sites along the longitudinal axis of each flap. Dye was administered as a 20-minute 0.25 mg/kg/min infusion. The PI clearly delineated gradations in perfusion, correlating highly with more time-consuming kinetic indexes and accurately predicting viability. The pedicle row, last viable row (V1), and first nonviable row (N1) had mean PI values of 10.5 +/- 4.5, 4.2 +/- 2.6, and 0.1 +/- 0.1, respectively, at 25 minutes after the start of infusion (p less than 0.05 for pedicle vs V1, pedicle vs N1, and V1 vs N1).

Animals↗
PubMed1989

Constant infusion fluorometry to predict flap survival.

Prediction of surgical flap survival in a dog model was evaluated by using the technique of fluorometry. The model provides a graded variation of flap ischemia with tissue necrosis occurring at the distal end. The indicator sodium fluorescein was administered via the saphenous vein at a constant infusion rate for 20 minutes. Quantitative fluorescence measurements were obtained with surface illumination of the flap at 132 sites for 15 flaps in the five animals. Wash-in slopes and wash-out clearances, both measures of tissue perfusion, were compared with the survival of flap regions observed at seven days. The sensitivity and specificity of fluorometric wash-in and wash-out measurements were compared in their ability to predict flap survival. The study showed sensitivities of 100% and 95% and specificities of 97% and 86%, respectively for the two methods. The wash-in procedure with constant infusion may be preferable to the wash-out technique since it requires less time to complete. In addition, it avoids bolus injections thus reducing the risk of anaphylactoid reactions.

Animals↗
PubMed1987

Effect of lumbar sympathectomy on muscle blood flow: distribution of perfusion measured by hydrogen clearance in skeletal muscle.

Measurements of local tissue blood flow using a technique of hydrogen clearance were used to examine the effect of lumbar sympathectomy on skeletal muscle blood flow. Polarographic recordings on 25 hydrogen desaturations were obtained with platinized platinum electrodes. Lumbar sympathectomies were done on five canines leaving the contralateral limb as a control. The hydrogen clearance data were modeled with biexponential curves: the initial rapid component and the second slow component yielded a weighted average perfusion through tissue. Average volumetric blood flow in the control limb was 6.08 +/- 0.45 ml/min/100 g tissue while the sympathectomized limb averaged 9.54 +/- 0.61 ml/min/100 g tissue (p less than 0.005). Average blood flow increases ranged from 33 to 83 percent in the sympathectomized limb over the control limb. This significant increase in muscle blood flow following lumbar sympathectomy, if of prolonged duration, may be cause for re-evaluation of the role of sympathectomy in the management of arteriosclerotic occlusive disease.

Animals↗
PubMed1979

Airway response to hair spray in normal subjects and subjects with hyperreactive airways.

Short-term 20-second exposure to hair sprays A and B failed to show significant decreases in maximum expiratory flow rates at low pulmonary volumes in normal subjects; however, significant decreases were observed with hair spray B in eight subjects with hyperractive airways (abnormal response to inhalation of methacholine). On the partial flow-volume curves, flows at 40 percent and 25 percent of forced vital capacity decreased 8.9 to 10.3 percent and 14 to 18.7 percent, respectively. The hair sprays differed in their content of perfume and plasticizer, and since the latter is generally considered nontoxic at room temperature, the perfume may be the responsible agent. It would appear from this study that normal healthy individuals are at little risk, at least from brief exposure to hair spray; however, in the presence of hyperreactive airways, as seen in asthmatic subjects and in some people with allergic rhinitis and viral respiratory infections, an immediate response of the airways may result from exposure to some hair sprays.

Aerosols↗
PubMed1977

A comparison of central venous pressure and pleural pressure in supine dogs.

Respiration induced changes in central venous pressure were analyzed and compared with intrapleural pressure changes in dogs. During normal breathing intrapleural pressure changes were transmitted to the vena cava with distortion consisting of attenuation, addition of cardiac and mean pressure components, and a slight temporal delay. Attenuation and temporal delay increased in a regular manner as mean central venous pressure increased. Cardiac components could be removed by electronic filters. The presence of these distortions suggest the need for caution in interpreting intrapleural pressure changes from central venous pressure.

Animals↗