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Biomedical subjects

K R Denninghoff

Publications and source records attributed to K R Denninghoff.

6 recordsLinked to original sources
PubMed2000

Retinal imaging techniques in diabetes.

Diabetic retinopathy is progressive, and detection early is essential for the prevention of blindness. Doppler flowmetry, retinal photography, scanning laser ophthalmoscopy, and retinal oximetry measurements may identify proliferative disease early. Drawbacks of these methods include lack of compliance, failure to refer, and failure to identify disease early. As a result, diabetic retinopathy is a leading cause of blindness. Our retinal oximeter measures the blood oxygen saturation in the large vessels of the retina near the optic disc. Retinal vessel oxygen saturations measured with our instrument are sensitive indicators of blood loss and hypoxia in swine. We are generating scientific data that suggests that retinal vessel oxygen saturations may be used to identify retinal hypoxia prior to changes in retinal vessel architecture. We expect to study humans within the next two years, and a clinically useful eye oximeter should be available in the near future.

Animals↗
PubMed2000

Optical model of the blood in large retinal vessels.

Several optical techniques that investigate blood contained within the retinal vessels are available or under development. We present a mechanical model that simulates the optical properties of the eye, the retinal vessels, and the ocular fundus. A micropipette is chosen as the retinal vessel model, and a mechanical housing is constructed to simulate the eyeball. Spectralon is used to simulate the retinal layers. Filling the eye with fluid index matched to the glass pipette eliminates reflection and refraction effects from the pipette. An apparatus is constructed and used to set the oxygen, nitrogen, and carbon dioxide concentrations in whole human blood. These whole blood samples are pumped through the pipette at 34 microL/min. Measurements made in the model eye closely resemble measurements made in the human eye. This apparatus is useful for developing the science and testing the systems that optically investigate blood and blood flow in the large retinal vessels.

Blood Flow Velocity↗
PubMed2000

Enrollment of sudden cardiac death victims into a limited cardiac autopsy study in the emergency department.

The lack of balanced recruitment for racial and ethnic groups in research protocols is an important ethical issue. African Americans have a history of forced participation, unethical research, and unwilling human dissection/demonstration that leads to a lack of participation in clinical research. We have embarked on a study of the pathophysiology of sudden death among African Americans which requires a limited autopsy of the heart. Our objective was to improve the recruitment rate in this study when compared with historical rates seen in clinical research and organ donation. We have screened 14 and enrolled 10 African Americans with sudden death (95% CI 0.41-0.91). By addressing the concerns of the African-American community and involving qualified input in the planning stages of the study we have been able to significantly improve the recruitment rate for this important population subgroup.

Alabama↗
PubMed1998

Retinal venous oxygen saturation correlates with blood volume.

OBJECTIVES: To evaluate the sensitivity of retinal venous O2 saturation (SrvO2) for early blood loss and reinfusion. A secondary objective was to measure the correlation between SrvO2 and mixed venous O2 saturation (SvO2) during blood loss and reinfusion. METHODS: Seven anesthetized swine were bled at 0.8 mL/kg/min to 16 mL/kg. Shed blood was re-infused at the same rate and the swine were allowed to equilibrate. After equilibration, repeat hemorrhages were performed at 1.6 mL/kg/min and 2.4 mL/kg/min. SrvO2 was measured using an eye oximeter (EOX) and SvO2 was measured using a fiber-optic catheter. RESULTS: During blood loss, SrvO2 correlated with blood removed (r = -0.88, -0.97, -0.96) and SvO2 (r = 0.87, 0.98, 0.92). During reinfusion, SrvO2 correlated with blood re-infused (r = 0.63, 0.76, 0.82) and SvO2 (r = 0.80, 0.93, 0.96). SrvO2 decreased 1.22 +/- 0.60%/mL/kg of blood removed. The rate of decrease in SrvO2 per minute (deltaSrvO2) when blood was removed at 2.4 mL/kg/min was significantly greater than deltaSrvO2 when blood was removed at 0.8 mL/kg/min (p < 0.007). The rates of change in blood pressure (BP) and pulse were not significantly different at any rate of blood removal. CONCLUSIONS: In this model, retinal venous O2 saturation correlated with blood volume and central venous O2 saturation. Unlike the rate of change in BP and heart rate, deltaSrvO2 values were significantly different at different rates of blood removal. Use of an EOX to monitor for blood loss, estimate the rate of hemorrhage, and evaluate the response to therapy during resuscitation warrants further study.

Animals↗
PubMed1997

Retinal large vessel oxygen saturations correlate with early blood loss and hypoxia in anesthetized swine.

BACKGROUND: Noninvasive monitoring would likely improve trauma care. Using laser technology, we monitored the oxygen saturation in retinal vessels during exsanguination and hypoxia. METHODS: Seven anesthetized swine were bled at 0.4 mL/kg/min for 40 minutes. During exsanguination, retinal venous saturation (SrvO2) was measured using an eye oximeter, and central venous saturation (SvO2) was measured using a fiber-optic catheter. After the shed blood was reinfused, the FiO2 was progressively decreased from 0.97 to 0.07. Femoral artery oxygen saturation (SaO2) and retinal artery oxygen saturation (SraO2) were measured at each increment. RESULTS: During exsanguination, SrvO2 correlated with blood loss (r = -0.93) and SvO2 (r = 0.94). SraO2 correlated with SaO2 during incremental hypoxia (R2 = 0.93 +/- 0.15). CONCLUSIONS: In this model of exsanguination, retinal venous oxygen saturation correlates with blood volume and with central venous oxygen saturation. The SraO2 correlates with SaO2 during graded hypoxia. Use of an eye oximeter to noninvasively monitor trauma patients appears promising and warrants further study.

Anesthesia↗