Biomedical subjects

R Crocker

Publications and source records attributed to R Crocker.

4 recordsLinked to original sources

PubMed2000

Cerebral intravascular oxygenation correlates with mean arterial pressure in critically ill premature infants.

OBJECTIVES: Premature infants experience brain injury, ie, germinal matrix-intraventricular hemorrhage (GMH-IVH) and periventricular leukomalacia (PVL), in considerable part because of disturbances in cerebral blood flow (CBF). Because such infants are susceptible to major fluctuations in mean arterial blood pressure (MAP), impaired cerebrovascular autoregulation would increase the likelihood for the changes in CBF that could result in GMH-IVH and PVL. The objectives of this study were to determine whether a state of impaired cerebrovascular autoregulation could be identified reliably and conveniently at the bedside, the frequency of any such impairment, and the relation of the impairment to the subsequent occurrence of severe GMH-IVH and PVL. PATIENTS AND METHODS: To monitor the cerebral circulation continuously and noninvasively, we used near-infrared spectroscopy (NIRS) to determine quantitative changes in cerebral concentrations of oxygenated hemoglobin (HbO(2)) and deoxygenated hemoglobin (Hb) from the first hours of life. Our previous experimental study showed a strong correlation between a measure of cerebral intravascular oxygenation (HbD), ie, HbD = HbO(2) - Hb, determined by NIRS, and volemic CBF, determined by radioactive microspheres. We studied 32 very low birth weight premature infants (gestational age: 23-31 weeks; birth weight: 605-1870 g) requiring mechanical ventilation, supplemental oxygen, and invasive blood pressure monitoring by NIRS from 1 to 3 days of age. MAP measured by arterial catheter pressure transducer and arterial oxygen saturation measured by pulse oximetry were recorded simultaneously. The relationship of MAP to HbD was quantitated by coherence analysis. RESULTS: Concordant changes (coherence scores >. 5) in HbD and MAP, consistent with impaired cerebrovascular autoregulation, were observed in 17 of the 32 infants (53%). Eight of the 17 infants (47%) developed severe GMH-IVH or PVL or both. Of the 15 infants with apparently intact autoregulation, ie, coherence scores <.5, only 2 (13%) developed severe ultrasonographic lesions. Thus, for the entire study population of 32 infants, 8 of the 10 with severe lesions exhibited coherence scores >.5. CONCLUSIONS: We conclude that NIRS can be used in a noninvasive manner at the bedside to identify premature infants with impaired cerebrovascular autoregulation, that this impairment is relatively common in such infants, and that the presence of this impairment is associated with a high likelihood of occurrence of severe GMH-IVH/PVL.

Blood Pressure↗

PubMed1999

The Missouri Disability Epidemiology and Health Project.

INTRODUCTION: Estimates of disability in this country are as high as 20%. State health departments need to provide the core activities to deal with this public health problem including assessment, policy development, and assurance. A collaboration among academic institutions and the Missouri Department of Health (MDOH) is a model for providing this core. METHODS: A disability workgroup was established among bureaus of the MDOH and three universities. This group selected the disability domain of mobility impairments for initial work. Existing data from the Centers for Disease Control and Prevention's (CDC) Behavioral Risk Factor Surveillance System (BRFSS) in Missouri and data from the 1990 Census were analyzed. Dissemination of the findings involved community and consumer participation via an advisory group and a public health-sponsored conference on disability. In addition, new data collection efforts are underway using the BRFSS. Education and training activities include both public health students and public health practitioners in learning the content and methodology associated with disability epidemiology. RESULTS: Data analyses have identified rural geographic areas of the State with high levels of disability and a trend of increasing work disability since 1993. A selected key condition, arthritis, has been confirmed as having a high prevalence (28%) in Missouri. These data also demonstrate that there is a strong risk of limitations associated with arthritis [adjusted odds ratio (OR) 3.57; 95% confidence intervals 3.0, 4.2]. These results will be applied to program planning. CONCLUSIONS: The Missouri program is succeeding in providing both academic and public health practice partners with a productive experience that meets the needs of each.

Data Interpretation, Statistical↗

PubMed1998

Near infrared spectroscopy detects cerebral ischemia during hypotension in piglets.

We have previously reported concordant changes in cerebral intravascular oxygenation measured by near infrared spectroscopy (NIRS) and mean arterial blood pressure (MAP) in premature infants. We hypothesized that the cerebral oxygenation changes are caused by MAP-induced alterations in cerebral blood flow (CBF) and studied these parameters in neonatal piglets (n = 6). Changes in cerebral intravascular oxygenation were measured by NIRS from the hemoglobin difference (HbD) signal (oxyhemoglobin-deoxyhemoglobin). CBF was measured by the radioactive microsphere technique. The cerebral circulation was also monitored by Doppler determinations of CBF velocity (time average mean velocity) in the anterior cerebral artery. Hypotension to <50% of baseline MAP was achieved by a ligature around the ascending aorta. Arterial oxygenation was maintained constant by mechanical ventilation. As observed in our studies of premature infants, cerebral HbD and MAP showed concordant changes. Hypotension was accompanied by significant decreases both in CBF (42.8 +/- 12.5% of baseline p < 0.01) and HbD (-65.0 +/- 22.0 micromol/L x dpf, p < 0.01). HbD was significantly correlated with MAP (p < 0.05) and time average mean velocity (p = 0.01). Importantly, decreases in cerebral total hemoglobin (HbT), a measure of cerebral blood volume, did not correlate significantly with decreases in MAP. We conclude that 1) decreases in cerebral intravascular oxygenation, as assessed by NIRS, observed with decreases in MAP reflect a decline in CBF, and hence oxygen delivery, 2) the HbD signal is more sensitive to changes in CBF than the HbT signal, and 3) NIRS recordings may have clinical utility in detecting cerebral ischemia.

Animals↗

PubMed1977

Trichromatic vision in the cat.

Many cat retinal ganglion cells (types X, Y, and W) have inputs from three separate cone systems. Those with peak sensitivities at 450 and 555 nanometers have been previously shown. A gamma max cone with a peak sensitivity of 500 nanometers can be differentiated from other cones by spectral sensitivity and from rods by receptive field differences, functioning above rod saturation levels, and by cone-rod breaks in the dark-adaptation curves. The similarity of the three-cone cat retina to the extramacular retina of the rhesus monkeys suggests that the cat may have photopic trichromatic vision.

Action Potentials↗