Anterior-posterior transcranial ultrasound to measure cranial oscillations.

BACKGROUND: We aimed to provide information on whether or not the correlation between body tilt and the pulse amplitude of transcranial ultrasonic time-of-flight waveform can be observed in the anterior-posterior skull direction. Also, we asked the question whether or not the skull pulsation can be detected since the cranial bones involved are thicker. METHODS: The experimental model of body tilt that alters intracranial pressure by shifting body fluid headward was employed. Transcranial ultrasound waveforms were examined in 15 healthy volunteers positioned at five tilt angles of +30 degrees, 0 degrees, -30 degrees, -60 degrees, and -90 degrees from the horizontal body position. A pulse-echo transducer was placed on the middle forehead and ultrasound waveforms were recorded. Synchronized variations in the ultrasonic time-of-flight with heartbeats were monitored using the pulsed phase locked loop technique for the output voltage of the ultrasound transducer. Simultaneous effects of body tilt on cardiovascular parameters were also evaluated. RESULTS: Pulse amplitudes of ultrasonic time-of-flight waveforms were found to vary with body tilt. Repeated-measures ANOVA and regression analysis showed a negative correlation between body tilt angle and pulse amplitude. The regression line has the equation: pulse amplitude = (1.158-0.01023 x tilt angle) x 10(-4) voltage. There was no such relationship between head-down body tilt and altered mean blood pressure or heart rate. CONCLUSION: An increase in the pulse amplitude of the anterior-posterior transcranial ultrasonic time-of-flight waveform can be detected when the head-down body tilt angle increases.

Noninvasive Measurements of Pressure for Detecting Compartment Syndromes.

BACKGROUND: We tested a noninvasive ultrasound, Pulse Phase Locked Loop (PPLL) technique for estimating Intramuscular Pressure (IMP) in a model Acute Compartment Syndrome (ACS); and compared it to a Near-Infrared Spectroscopy (NIRS) method. QUESTIONS: We wanted to validate our model compartment syndrome, and to compare and validate the PPLL and NIRS methods of detecting compartment syndrome. METHODS: To simulate the tamponade of an ACS, external-pressure levels from 10 to 70 mm Hg were applied to the legs of 15 healthy adult subjects to raise their IMP. Receiver Operator Characteristic (ROC) curves were used to determine the sensitivity and specificity of diagnosing elevated IMP by the two noninvasive techniques. RESULTS: NIRS data varied significantly with compression (p=0.003) with large subject-to-subject variability (p<0.001). PPLL data also varied significantly with compression (p=0.004), but subject-to-subject variation was not significant (p=0.47), suggesting that individual variation does not affect the diagnostic accuracy of the PPLL technique. Sensitivity and specificity for diagnosing normal IMP by the PPLL (<30 mm Hg from a slit catheter reading) from elevated IMP (>30 mm Hg) were 0.75 and 0.75, respectively, and the area under the curve (AUC) was 0.78. For the NIRS, the sensitivity and specificity were 0.65 and 0.65, respectively, and the AUC was 0.68. CONCLUSIONS: Both NIRS and PPLL recordings are able to differentiate a simulated ACS up to 70 mm Hg. However, the PPLL technique is a slightly better diagnostic predictor than NIRS with less subject-to-subject variability and slightly better sensitivity and specificity. LEVEL OF EVIDENCE: Level II, Diagnostic test.

Stereoselective total synthesis of (-)-spirofungin†A by utilising hydrogen-bond controlled spiroketalisation.

The stereoselective total synthesis of the spiroketal containing Streptomyces metabolite (-)-spirofungin A (1) is described. A key step involved a spiroketalisation controlled by an intramolecular H-bond which favoured the desired spiroketal 4 (13:1 ratio). The presence of the intramolecular H-bond in 4 is possibly due to a 1,5-alkyne-oxygen interaction. Other key steps include an efficient cross-metathesis to form the spiroketal precursor, a tin mediated syn-aldol reaction and a Stille cross-coupling reaction to create the C22C23 bond. A final Wittig extension followed by deprotection gave (-)-spirofungin A (1).

Bruxism and temporal bone hypermobility in patients with multiple sclerosis.

In this study, the authors investigated the link between jaw clenching/bruxism and temporal bone movement associated with multiple sclerosis (MS). Twenty-one subjects participated in this study (10 patients with MS and 11 controls). To quantify the change in intracranial dimension between the endocranial surfaces of the temporal bones during jaw clenching, an ultrasonic pulsed phase locked loop (PPLL) device was used. A sustained jaw clenching force of 100 lbs was used to measure the mean change in acoustic pathlength (delta L) as the measure of intracranial distance. In the control subjects the mean delta L was 0.27 mm +/- 0.24. In subjects with MS the mean delta L was 1.71 mm +/- 1.18 (p<0.001). The increase in magnitude of bi-temporal bone intracranial expansion was approximately six times greater in subjects with MS compared to controls. Therefore, jaw clenching/bruxism is associated with more marked displacement of the temporal bones and expansion of the cranial cavity in patients with MS than in control subjects.

Monitoring microemboli during cardiopulmonary bypass with the EDAC quantifier.

Gaseous emboli may be introduced into the bypass circuit both from the surgical field and during perfusionist interventions. While circuits provide good protection against massive air embolism, they do not remove gaseous microemboli (GME) from the bypass circuit. The purpose of this preliminary study is to assess the incidence of GME during bypass surgery and determine if increased GME counts were associated with specific events during bypass surgery. In 30 cases divided between 15 coronary artery bypass grafts and 15 valve repairs, GME were counted and sizedt the three locations on the bypass circuit using the EDAC" Quantifier (Luna Innovations, Roanoke, VA). A mean of 45,276 GME were detected after the arterial line filter during these 30 cases, with significantly more detected (p = .04) post filter during valve cases (mean = 72,137 +/- 22,113) than coronary artery bypass graft cases (mean = 18,416 +/- 7831). GME detected post filter were significantly correlated in time with counts detected in the venous line (p < .001). Specific events associated with high counts included the initiation of cardiopulmonary bypass, heart manipulations, insertion and removal of clamps, and the administration of drugs. Global factors associated with increased counts post filter included higher venous line counts and higher post reservoir/bubble trap counts. The mean number of microemboli detected during bypass surgery was much higher than reported in other studies of emboli incidence, most likely due to the increased sensitivity of the EDAC Quantifier compared to other detection modalities. The results furthermore suggest the need for further study of the clinical significance of these microemboli and what practices may be used to reduce GME incidence. Increased in vitro testing of the air handling capability of different circuit designs, along with more clinical studies assessing best clinical practices for reducing GME activity, is recommended.

New noninvasive ultrasound technique for monitoring perfusion pressure in a porcine model of acute compartment syndrome.

OBJECTIVES: Acute compartment syndrome (ACS) is the result of decreased perfusion pressure (PP), and the diagnosis frequently requires invasive monitoring. Our objective was to test a new noninvasive ultrasound device for correlating PP with measurements of fascial displacement in a controlled porcine model of ACS. We hypothesized that fascial displacement in experimental compartments with impaired PP would be significantly greater than that in control compartments with normal baseline PP. METHODS: ACS was generated in right anterior compartments of 7 anesthetized pigs, and contralateral compartments served as normal controls. Intramuscular pressure in all compartments was monitored by slit catheters, whereas intramuscular pressure in experimental compartments was elevated in 10 mm Hg increments by infusing 0.045% albumin in saline. A noninvasive ultrasound device continuously recorded fascial displacement corresponding to arterial pressure pulses in all compartments. Mean fascial displacement amplitude was grouped by PP and analyzed using 2-way repeated measures analysis of variance and contrast analysis. RESULTS: As PP ranged from 80 to -40 mm Hg, the change in fascial displacement of the infused compartments was significantly greater than that in the control compartments (analysis of variance, P = 0.03). At each PP increment between 40 and -20 mm Hg, fascial displacement in the infused compartments was significantly greater than that in the control compartments (contrast analysis, P < 0.014). CONCLUSIONS: Fascial displacement is significantly greater in muscle compartments with decreased PP. Furthermore, changes in PP are associated with changes in fascial displacement over a clinically relevant range of PP, making this noninvasive technique potentially useful for monitoring in ACS.

Noninvasive monitoring of elevated intramuscular pressure in a model compartment syndrome via quantitative fascial motion.

Compartment syndromes, conditions of elevated intramuscular pressure (IMP) resulting from trauma or chronic overuse, frequently require invasive IMP monitoring for accurate diagnosis. Our objective was to test a noninvasive ultrasound technique for estimating IMP based on fascial displacement waveforms from arterial blood pressure pulses. IMP was increased in the legs of 23 healthy adult subjects up to 80 mmHg using two blood pressure cuffs covering the region from the knee to the ankle. Receiver operator characteristic curves and recursive partitioning were used to determine the sensitivity and specificity of diagnosing elevated IMP using fascial displacement. For one curve, in which several ultrasonic measurement parameters were used along with subject body mass index and blood pressure, the sensitivity and specificity for diagnosing normal IMP (below 30 mmHg) from elevated IMP (30 mmHg and up) was 0.61 and 0.94, respectively. Recursive partitioning, in which IMP was divided into three ranges (normal <30 mmHg, midrange of 30-40 mmHg, and elevated >or=50 mmHg), resulted in improved diagnostic sensitivity (0.77) with almost no change in specificity (0.93).

Gaseous microemboli sizing in extracorporeal circuits using ultrasound backscatter.

This paper describes efforts to estimate the size of gaseous microemboli (GME) in extracorporeal blood circuits based on the amplitude of backscattered ultrasound, starting with analytic modeling of the scattering behavior of GME in blood. After neglecting resonance effects, this model predicts a linear relationship between the amplitude of backscattered echoes and the diameter of GME. Computer simulations based on the cylindrical acoustic finite integration technique were performed to test some of the simplifying assumptions of the analytical model, with the simulations predicting small deviations from the linear approximation that could be treated as random scatter. Ultrasonic and microscopic measurements of injected GME were then performed on a test circuit to determine the linear correlation coefficient between echo amplitude and GME diameter in conditions like those employed in real cardiopulmonary bypass (CPB) circuits. The correlation coefficient determined through this study was further validated in a closed-loop CPB circuit using canine blood. This study shows that the amplitude of ultrasonic backscattered echoes can be used to accurately estimate the size distribution of a population of detected GME when the spacing of emboli is great enough to minimize interference and other multi-path scattering effects. With the high flow rates found in CPB circuits, typically ranging from 2 to 6 L per minute (equivalent to a flow velocity of 0.3 to 1 m/s through the circuit tubing), this assumption will be valid even when hundreds of emboli per second pass through the circuit. Therefore, sizing of GME using the ultrasonic backscatter models described in this paper is a viable method for estimating embolic load delivered to a patient during a CPB procedure.

Ultrasonic device for the noninvasive diagnosis of compartment syndrome.

An ultrasonic device for the diagnosis of acute compartment syndrome is described and results on six human cadaveric legs are presented. The ultrasonic device uses a pulsed phase locked loop (PPLL) to measure sub-micrometer displacements of the fascia wall. These displacements occur as a result of volume expansion of the muscle compartment of the lower leg and are related to changes in intramuscular pressure (IMP). In the cadaveric tests, the PPLL detected changes in compartment diameter resulting from IMP changes of 1 mmHg and from infusions of 0.25 ml saline increments. Based on these results, the ultrasonic PPLL appears to have the potential to become a low-cost, portable and noninvasive alternative to current methods for diagnosing acute compartment syndrome.