Dual wavelength spectrophotometry as a diagnostic test of the pulp chamber contents.

The purpose of this in vitro study was to determine the feasibility of using dual wavelength spectrophotometry to identify teeth with pulp chambers that are either empty, filled with fixed pulp tissue, or filled with oxygenated blood. In phase I of the experiment, a human third molar was prepared so that its pulp space could be filled with oxygenated blood and later emptied. In phase II, the lower jaw of a beagle dog was removed and placed in formalin, thereby fixing the pulps of the teeth. The pulp of the right canine was removed via an apical approach, and attachments were placed in a similar position to those on the human tooth, to allow filling and emptying of the pulp space. Cavit was placed over the exposed fixed pulp in the left canine. Ten readings, which were separated by light source and detector removal and replacement, were taken of the right canine pulp space when it was empty or filled with oxygenated blood, or the left canine pulp space when it was filled with fixed tissue. Distinct and reproducible changes were measured for pulp spaces filled with air, tissue, or oxygenated blood. In phase III, simulated pulp testing on a dog tooth model was performed. Blood was introduced into the root canal space, the chamber was rinsed with water and replaced with air, according to a predetermined code. Spectrophotometer readings were recorded. The identification of pulpal contents was correctly determined in all 20 of the predetermined conditions. The findings indicate that continuous wave spectrophotometry may become a useful pulp testing method.

Fluctuations in cerebral oxygenation and blood volume during endotracheal suctioning in premature infants.

To investigate the effect that suctioning of the endotracheal tube has on the cerebral circulation, we monitored brain intravascular hemoglobin saturation (tHbo2%), cerebral blood volume (CBV), and arterial hemoglobin saturation (Spo2) during suctioning in 12 infants (24 to 33 weeks of gestational age) with respiratory distress syndrome treated with mechanical ventilation. The tHbo2% and CBV values were monitored over the forebrain by dual-wavelength near-infrared spectroscopy, and Spo2 was monitored by pulse oximetry of a finger. The monitored variables were stable during the baseline period. With suctioning, Spo2 decreased from 94% +/- 1% to 84% +/- 1%, tHbo2% decreased, and CBV increased (p less than 0.05). Desaturation in the arterial and cerebral circulations began within 5 seconds of the onset of suctioning. Arterial reoxygenation began with the onset of reventilation, whereas reoxygenation in the brain was delayed by 15 seconds. The Spo2, tHbo2%, and CBV values returned to baseline within 1 minute of reventilation. Studies were repeated in six of the infants after the fraction of inspired oxygen was increased to attain a baseline Spo2 of 100%. In the preoxygenated infants, tHbo2%, CBV, and Spo2 remained constant during suctioning. These studies confirm that endotracheal suctioning results in transient hypoxemia, and demonstrate that this is reflected in the brain by vasodilation and deoxygenation. These effects are preventable by preoxygenation before suctioning.

Compartment syndrome: a quantitative study of high-energy phosphorus compounds using 31P-magnetic resonance spectroscopy.

The purpose of this study was to quantitate the intracellular high-energy phosphate compounds during 6 hours of tissue ischemia in the anterior tibial compartment of beagles subjected to an induced traumatized compartment syndrome. The goal of this work was to provide clinicians with objective criteria to augment clinical judgment regarding surgical intervention in the impending compartment syndrome. A beagle model was utilized in which the Delta pressure (difference between the mean arterial pressure and compartment pressure) could be controlled. The model, in conjunction with 31P-magnetic resonance spectroscopy (MRS), allowed a measure of high-energy phosphate compounds and pH in the compartment at various Delta pressures. The extent of ischemic metabolic insult in the compartment was then quantitated. Our data suggest the following: 1) lower Delta pressures result in a proportionally greater drop in the intracellular phosphocreatine ratio and pH; 2) at lower Delta pressures, there is proportionally greater decline in the percentage recovery post-fasciotomy; 3) blood pressure is extremely important and periods of hypotension may result in increased muscle damage at lower compartment pressures.

The compartment syndrome. An experimental and clinical study of muscular energy metabolism using phosphorus nuclear magnetic resonance spectroscopy.

In an experimental ischemic compartment syndrome in dogs, phosphorus (31P) nuclear magnetic resonance (NMR) spectroscopy was used to determine the tissue pressure threshold at which resting skeletal muscle begins to use anaerobic energy sources due to insufficient cellular oxygen delivery. The interactive effects of systemic perfusion pressure and moderate muscle trauma on this anaerobic threshold were also evaluated. The severity of cell injury produced by various degrees of compartment pressurization over an eight-hour period was concomitantly studied using muscle biopsy and electron microscopy. Clinical correlation of a preliminary patient series studied using 31P-NMR demonstrated that the threshold for cellular metabolic derangement in skeletal muscle subjected to increased tissue pressure was more closely associated with the difference between mean arterial blood pressure (MABP) and compartment pressure than with the absolute compartment pressure alone. The difference is termed MABP-compartment pressure, or delta P. The lowest delta P at which a normal cellular metabolic state can be maintained is approximately 30 mmHg in normal muscle and 40 mmHg in moderately traumatized muscle. It is imperative to interpret compartment pressure measurements in light of the degree of soft tissue trauma sustained and the patient's blood pressure, as well as the clinical signs and symptoms.

Nuclear magnetic resonance: an overview of its spectroscopic and imaging applications in pediatric patients.

Magnetic resonance (MR) is a technique that permits the noninvasive evaluation of morphologic features and function based on the distribution of protons and other selected elements. We present a basic description of MR and illustrate both 31P-MR spectroscopy and proton imaging applications in pediatric patients. The applications of these techniques are diverse, and are presented concisely in an attempt to give pediatricians an overview of this new technology and its potential role in patient management.