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Biomedical subjects

D Gravenstein

Publications and source records attributed to D Gravenstein.

14 recordsLinked to original sources
PubMed1998

A computer model of intracranial dynamics integrated to a full-scale patient simulator.

The ability to visualize intracranial dynamics during simulated clinical scenarios is a valuable tool for teaching brain physiology and the consequences of different medical interventions on the brain. Studies have isolated physiologic variables and shown their effects on brain dynamics. However, no studies have shown the combined effects of these variables on intracranial dynamics. This brain model offers one approach that brings all these relationships together and shows how they affect the dynamics of the brain. The brain model obtains its physiologic inputs from a full-scale patient simulator which responds to clinical interventions. This integration allows individuals working on the patient simulator to see the effects of their actions on brain dynamics. The brain model gives a real-time display of intracranial events (cerebral metabolic rate, cerebral blood flow, cerebral blood volume, cerebral perfusion pressure, and intracranial pressure) and responds to changes in the pulmonary and cardiovascular condition of the patient simulator.

Blood Volume↗
PubMed1998

Influence of plasma expansion on plasma protein binding of ketorolac.

STUDY OBJECTIVE: To determine the effect of dilution with intravascular volume expanders commonly used by anesthesiologists on clinically relevant levels of free serum ketorolac. DESIGN: In vitro study. SETTING: Pharmaceutics laboratory of a medical college. INTERVENTIONS: The effect of 6% hydroxyethylstarch, 5% albumin, 6% dextran 60, and lactated Ringer's solution on in vitro plasma protein binding of ketorolac was investigated by ultrafiltration. The binding was studied at three different drug concentrations: low therapeutic (0.3 microgram/ml), high therapeutic (3 micrograms/ml), and toxic (10 micrograms/ml), and at two or more volume expander dilutions. MEASUREMENTS AND MAIN RESULTS: The effect of plasma dilution on free ketorolac was consistent across all volume expanders tested and for each ketorolac concentration studied. As the plasma dilution with albumin, hydroxyethylstarch, dextran 60, or lactated Ringer's solution increased, the unbound ketorolac also increased from 3.2% to 3.3% in undiluted plasma to 5.0% to 8.7% in 50% dilution of the plasma with the investigated expanders. Dilution of plasma by only 10% resulted in a significant, but relatively minor, increase of unbound ketorolac to 3.2% to 3.8%. CONCLUSION: Because of the pharmacokinetic properties of ketorolac, this pharmacokinetic interaction can be expected to have only minor effects on unbound ketorolac concentrations when ketorolac is administered after the plasma expander. When ketorolac administration is followed by rapid plasma expander infusion, a transient increase of unbound ketorolac in plasma can be expected.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1998

Performance of a plastic optical fiber stylet for tracheal intubation of a dog.

OBJECTIVE: We set out to establish whether a novel plastic optical fiber incorporated into an endotracheal tube (ETT) stylet could be used for intubation of a dog. A secondary objective examined the need for a direct illumination source from a laryngoscope. Lastly, the fragility of the system was tested. METHODS: An anesthetized dog was repeatedly intubated using a laryngoscope to elevate the tongue and the view of the larynx conducted through the plastic optical fiber stylet (placed within an endotracheal tube) and displayed on a television monitor. Four prototype identical stylets were tested. Repeated intubations were attempted with each stylet and graded as either successful or failed. All four stylets were tested 10 times each using a Miller 4 blade and direct illumination from the laryngoscope. Two of the four stylets were reused during an additional 10 intubation attempts using a Miller 4 blade and laryngoscope (without batteries) with only ambient light. Finally, one stylet was used for intubation after 10, 20, 30, 40 and 50 sharp 90 degree bend-and-straighten cycles using a Miller 4 blade and laryngoscope for direct illumination. RESULTS: All attempted intubations were successful. However, the image quality was dramatically better when direct illumination from a laryngoscope was used than when ambient light was used. One plastic optical fiber stylet was successfully used to intubate after having been used for 20 intubations and 50 sharp 90 degree bend-and-straighten cycles. A partial lens separation occurred between the 41st and 50th bend cycle but the image remained adequate enough to successfully intubate again. CONCLUSIONS: A novel plastic optical fiber incorporated into an ETT stylet can be used with a laryngoscope for intubation of a dog. Direct illumination from a laryngoscope provides a better television monitor image than when only ambient light is used. The system was durable, withstanding over 20 uses and 40 sharp bend-and-straighten cycles before a lens separation failure occurred.

Animals↗
PubMed1997

False low pulse oximetry reading associated with the concomitant use of a peripheral nerve stimulator and an evoked-potential stimulator.

One of the sources of error in pulse oximetry readings is associated with an abnormal signal-to-noise ratio. The pulse oximeter distinguishes the light absorbance of arterial blood from that of other absorbers by differentiating between a constant component and a pulsating component. The pulsating component is almost exclusively the result of arteriolar bed pulsations. Because pulse oximetry is based on the assumption that arterial blood is the only pulsatile absorber, any other fluctuating phenomenon could constitute a source of error. We report a case in which a low pulse oximetry reading was associated with concomitant use of a pulse oximeter and a peripheral nerve stimulator on the same arm. Further tests conducted using a nerve stimulator and a sensory evoked potential stimulator with different amplitudes and frequencies confirmed the association and delineated the relationship between frequency and amplitude of stimulation and the degree of artificial desaturation. A theoretical explanation for this phenomenon is presented.

Electric Stimulation↗
PubMed1997

An integrated graphic data display improves detection and identification of critical events during anesthesia.

OBJECTIVE: To show that an integrated graphic data display can shorten the time taken to detect and correctly identify critical events during anesthesia. METHODS: We developed a graphic display which presents 30 anesthesia-related physiologic variables as shapes and colors, rather than traditional digits and waveforms. To evaluate the new display, we produced four critical events on a computer-based anesthesia simulator and asked two groups of five anesthesiologists to identify the events as quickly as possible. One group observed the new display while the other group viewed a traditional cardiovascular monitor with digital and waveform displays. RESULTS: The group which observed the integrated graphic display saw changes caused by inadequate paralysis 2.4 min sooner, and changes caused by a cuff leak 3.1 min sooner than those observing the traditional display. The integrated display group correctly identified the reason for the change 2.8 min sooner for inadequate paralysis, 3.1 min sooner for cuff leak and 3.1 min sooner for bleeding. These differences were all statistically significant. CONCLUSIONS: The results show that some simulated critical events are detected and correctly identified sooner, when an anesthesiologist views an integrated graphic display, rather than a traditional digital/waveform monitor.

Adult↗
PubMed1996

Kaleidoscopes.

Explore the source record for details and available documents.

Humans↗
PubMed1985

Somatosensory evoked potentials in hysterical paraplegia.

Somatosensory evoked potentials were determined in three patients with hysterical neurologic deficits after minor trauma. In each case the patient denied any sensation of the stimulus in the affected extremity; however, normal evoked potentials were recorded. Objective evidence of the hysterical nature of the neurologic deficit was, therefore, provided.

Adult↗
PubMed1985

Intraoperative brain-stem auditory evoked potentials during posterior fossa microvascular decompression.

Recent technological advances have led to increased interest in intraoperative evoked potential monitoring. Although theoretically valuable, its precise role remains to be defined, and useful criteria for predicting neurological deficit are not well established. The authors used brain-stem auditory evoked potential (BAEP) monitoring during 21 posterior fossa microvascular decompression procedures to assess the value of this technique in predicting postoperative deficit. The surgeon was notified only if there was complete disappearance of wave V. Although no patients had postoperative deafness, BAEP latencies changed significantly in all cases. In four patients, wave V totally disappeared during cerebellar retraction. The BAEP appears to be a very sensitive monitor of auditory function, such that "false positive" results will be frequent if latency criteria alone are used to trigger alterations in surgical technique.

Adult↗