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An intracavitary probe for magnetic resonance imaging of the pelvis has been developed that takes advantage of the “inside-out” spatial characteristics of a birdcage resonator. The probe consists of an eight-leg, birdcage resonator in a low-pass configuration operating in receive-only mode. The resonator circuit is mounted on a solid rod, is encased in Teflon®, and has been used to obtain detailed images of pelvic anatomy in a male canine. The approximate cylindrical symmetry of the external sensitivity profile of this type of circuit, employed in an intracavitary application, demonstrates the potential superiority of this type of probe design over single-loop intracavitary coils. Axial, coronal, and sagittal MR images, obtained with 8 and 16 cm fields of view, are presented to illustrate the advantages of this type of intracavitary probe compared with conventional body-coil images. The prototype described in this report has been designed for clinical use in human subjects and is currently undergoing testing to determine its efficacy in the evaluation of rectal, prostate, and gynecologic pathology.

Mass spectrometers are used in ICUs and ORs to measure the concentration of medical and anesthetic gases gathered from multiple sites. This investigation was designed to determine the accuracy of a clinical system, which included 12 ICU bedside stations monitored by a medical mass spectrometer (Perkin-Elmer RMS III, Pomona, CA). Each site station was connected to the analyzing unit via two Teflon tubes, one permanently installed, 30-m long, and the second disposable, 2.4-m long. A gas mixture containing 95% O2 and 5% CO2, alternating with room air, was delivered to a solenoid valve and from there to the connecting tubes. Gas flow-rate, delay time, rise time, and peak and trough concentrations were determined for each gas at solenoid cycling frequencies of 25, 50, and 100/min. After the first set of measurements, the 30-m tubes were thoroughly cleaned and all measurements repeated. In addition, the authors also measured CO2 delay and rise times when the gas was delivered to the mass spectrometer through an unused 30-m tube or a new 2.4-m tube. Gas flow-rate increased from 143 +/- 12 ml/min (mean +/- SD) to 238 +/- 9 ml/min after the tubes were cleaned. Delay time was identical for all gases at all solenoid cycling rates but decreased significantly (P less than 0.05), from 11.5 +/- 0.3 to 4.8 +/- 0.7 s after the ceiling tubes were cleaned. As solenoid valve rate increased, the difference between measured and actual gas concentration increased. The lowest accuracy was 63.6 +/- 2.1%, for CO2 at 100 cycles/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Expired gas analysis has been largely relegated to the measurement of VO2 and VCO2 by a variety of methods. We designed and built a new flexible automated expired gas analysis instrument, the Volume Accumulating Metabolic Monitor (VAMM), capable of simultaneous and continuous quantitative expired gas analysis for a multiplicity of gas species. All expired gas is collected into one of two twin reservoirs. This approach allows analysis of one reservoir while collection occurs into the other. The instrument mixes the expired gas and determines the volume of the desired gas species using a combination of indicator gas dilution and mass spectrometry. We tested the VAMM's ability to measure the 13CO2 2-hr collection after intravenous 13C-aminopyrine. Aminopyrine is metabolized to CO2. Ten healthy volunteers underwent expired gas collection and analysis for 140 min. All studies were performed in the recumbent posture after an 8 hr fast. The initial 20 min were used to establish a baseline 13CO2 production. Following the injection of 2 mg/kg 13C-aminopyrine, expired gas was collected for an additional 120 min. The mean 2-hr 13CO2 enrichment was 7.1 ?2.9 ml (range 3.5 ml to 13.2 ml). This represented a percent collection of 26.8 ?9.1 (range 16.5 to 48.6). Peak excretion occurred at 84.9 ?17.5 min (range 50 min to 108 min). The VAMM provided significantly better 13CO2 excretion profiles than previously described. This technology can easily be customized to study not only other similar metabolic processes but also other gas excretions.

ObjectivesThis study was designed to evaluate autonomic changes preceding atrial fibrillation/flutter (AF) after thoracotomy.BackgroundAutonomic fluctuations before the onset of postoperative AF have been reported but with conflicting results.MethodsIn 48 patients with postoperative AF, 2-h Holter recordings before the onset of AF were compared with corresponding data from 48 age- and gender-matched surgical controls without AF. Five-minute segments of heart rate variability (HRV) were studied using linear regression methods.ResultsThere was a near-significant trend for the RR interval among patients with AF to be lower than controls (p = 0.06), whereas the standard deviation of RRs (p < 0.0001), root mean square of successive RR differences (p < 0.0001), proportion of RRs >50 ms different (p < 0.0001), low-frequency power (p = 0.0003) and its log (p < 0.0001), and high-frequency-power (p < 0.0001) and its log (p < 0.0001) were all significantly greater in patients with AF, respectively. In comparison to controls, AF patients had a significant decrease in RR interval (p = 0.02) and significant increments in all time- and frequency-domain analyses studied.ConclusionsIn the period before the onset of postoperative AF, there are significant increases in HRV during a time when heart rate also increases. These novel findings are consistent with parasympathetic resurgence competing with increasing sympathetic activity as the triggering mechanism for postoperative AF.

Background & Aims: Metabolic monitoring devices used in the critical care setting are subject to a range of conditions that may compromise their accuracy. We sought to investigate the error and precision of the Deltatrac metabolic monitor under these conditions. Methods: A modified version of the funnel burner, described by Miodownik et al. (8), was ventilated by a mechanical ventilator. This was used to examine the performance of the Deltatrac metabolic monitor over a wide range of inspired oxygen concentrations, minute ventilation, and positive end expiratory pressure at different levels of oxygen consumption and carbon dioxide production. Results: The Deltatrac measured V 0 2 with a mean error±precision of 9.4%±19.5% (range, 9.3%±1.9%–72.6%±13.6%). The mean V CO 2 error±precision was 1.2%±3.1% (range–2.0%±1.2%–5.4%±3.1%). Error was significantly affected by oxygen concentration and minute ventilation but was largely independent of positive and expiratory pressure. Conclusions: The methodology of Miodownik et al. permits the expression of metabolic device errors over a wide range of simulated clinical conditions.

Resection of carcinoma of the esophagus may be curative or palliative and usually results in either total esophagectomy or esophagogastrectomy. Continuity of the upper gastrointestinal tract is maintained via a gastric pull-up procedure or, when feasible, by primary reanastomosis of the gastric remnant to the proximal esophagus. 1 If a large part of the stomach has been previously resected or is unsuitable for use, colonic or jejunal interposition may be utilized to maintain continuity. However, these operations are associated with substantial surgical morbidity and mortality and a myriad of postoperative complications, including luminal narrowing caused by edema or ischemia, anastomotic leaks, formation of fistulae and strictures, and development of graft ischemia. 2, 3 These procedures may be precluded in the elderly or in patients with complex medical problems who are poor surgical risks. In these patients and in those with unresectable esophageal carcinoma, palliative cervical esophagostomies are sometimes performed to reduce the discomfort of dysphagia and lessen the at tendant risk for aspiration pneumonia. Nutrition is maintained through surgically placed gastrostomies or jejunostomies and, in rare instances when feeding tube place: ment is not possible or the distal gastrointestinal tract is obstructed, total parenteral nutrition. 2 Although these procedures are palliative, patients usually remain uncomfortable, are unable to eat, and have the extra burden of repeatedly emptying the esophagostomy bag, in which saliva accumulates. They also have the problem of administering enteral feedings and fluids to replace the salivary losses. We have developed an active esophageal prosthesis (AESOP) that, via a small pneumatically driven extracorporeal pump, can maintain a functioning conduit between a cervical esophagostomy and the remainder of the gastrointestinal tract in a closed circuit.

To elucidate the delayed effects of midazolam, we assessed electrophysiologic and motor responses by measuring auditory event-related potentials and a button-press reaction time response in 10 normal volunteers (aged 25-36 yr). Fifty minutes after intravenous infusion of 0.07 mg/kg of midazolam, subjects were mildly sedated, oriented, and readily responsive to verbal commands. To obtain ERPs, frequent tones (85%: 1000 Hz) and rare tones (15%: 2500 Hz) were presented at intervals of 1.5 s. Electroencephalographic signals were collected from FZ, CZ, and PZ for 1000 ms after stimulus presentation until 40 artifact-free rare-tone responses were obtained (average time, 6 min). Peak-to-peak amplitudes and latencies for N2, P3, and the subsequent negative slow wave (N3) were averaged within condition and were analyzed by repeated measures analysis of variance. After midazolam infusion, there was a 50% decrease in amplitude of P3 in response to target tones (P less than 0.006), whereas N3 latency increased by 40 ms (P less than 0.05). Event-related potential amplitudes were still significantly larger to rare (target) stimuli (P less than 0.003) after midazolam infusion. Although reaction time increased by 70 ms (P = 0.031), performance accuracy remained unchanged. Self-ratings of sleepiness and concentration show that a significant sedation effect was still present 50 min after infusion. Although routine clinical examination may be normal, full recovery from the effects of a typical intravenous dose of midazolam requires more than 50 min. The potential for adverse drug interaction, particularly with narcotics, is still present at this time.

Respiratory failure of different origins often requires therapy with mechanical ventilation and positive end-expiratory pressure (PEEP). These supports are occasionally inadequate if the damage to one lung is significantly more pronounced than that to the other lung. Technical means exist to ventilate each lung independently or to provide a different PEEP to each lung. The findings from nine patients in whom one of these techniques was applied are presented, and advantages and disadvantages are discussed.

We used indirect calorimetry to measure oxygen consumption (VO2) and carbon dioxide production in 29 mechanically ventilated patients. These data were compared to VO2 measured simultaneously by a standard thermodilution technique. A good correlation was demonstrated between the methods, but VO2 measured by indirect calorimetry was 15% higher than VO2 measured by thermodilution.

A variety of technical decisions are required for the proper selection and safe and efficacious application of high-frequency jet ventilation (HFJV). Criteria for analyzing the performance of an HFJV system are presented, along with discussions of some of the more common respiratory measurements and their applicability to HFJV.

The usefulness of medical mass spectrometers in intensive care units can be limited by too frequent obstruction of the tubing that transports gases from the patients to the analyzing unit. To overcome this problem, we developed an automated system consisting of an infrared light sensor and a three-way valve. One port of the three-way valve connects to 2.4-m disposable tubing that collects gases from the patient's airway. The second port is connected to a mass spectrometer analyzing unit through 30-m permanently installed tubing. The third port is connected to a pressurized oxygen source. An infrared light sensor is placed on the shorter tubing, between the patient and the three-way valve. When increased optical density is detected, due to entrainment of respiratory secretions, the three-way valve is activated. Gas flow is closed between the patient and the mass spectrometer and opened between the pressurized oxygen source and patient tubing to flush its contents. During the six years that the protection system has been in use, the frequency with which the disposable gas collection tubing is changed has been halved. Furthermore, periodic tests of delay and response times, performed at each bedside station, indicate that permanent connection tubing only needed cleaning at 2- to 3-year intervals. The system has decreased the cost of operating our mass spectrometers while also reducing periods of unavailability due to equipment failure.

Capnography, the science of CO2 waveforms analysis, can play a role in the management of mechanically ventilated patients. Mass spectrometers are the devices most commonly used to collect sequentially and examine CO2 waveforms from multiple patients in the ICU or operating rooms. We present here a review of some clinical and technical problems, which may be resolved efficiently and expeditiously through the use of mass spectrometry and capnography. Mechanical failures, especially those that lead to rebreathing of exhaled gases, can be readily detected. The patient's progress during weaning and the consequences of changes in mechanical assistance can be virtually and noninvasively determined. An expanded role of capnography in mechanically ventilated patients can increase the use of mass spectrometers in the ICU.

A pneumatic-to-electrical circuit analog is used to describe 2 separate mechanisms by which high-frequency jet ventilators sustain ventilation and oxygenation in the presence of large airway disruptions. The frequency-dependent mechanism is based on variations in the pneumatic equivalent to capacitive reactance. The pressure-dependent mechanism models lung defects on a voltage-controlled resistor. The electrical circuit model is also used to explain the factors leading to gas trapping and inadvertent positive end-expiratory pressure during high-frequency jet ventilation.