Biomedical subjects

William T Yost

Publications and source records attributed to William T Yost.

5 recordsLinked to original sources

PubMed2006

Noninvasive measurements of intramuscular pressure using pulsed phase-locked loop ultrasound for detecting compartment syndromes: a preliminary report.

OBJECTIVES: To develop a human model for compartment tamponade and test the efficacy of ultrasonic pulsed phase-locked loop (PPLL) fascial displacement waveform analysis for noninvasive measurement of intramuscular pressure (IMP). DESIGN: Human subject experiment. SETTING: University Level 1 trauma center. PARTICIPANTS: Nine male and 1 female volunteers (age 20 to 59),3 male acute compartment syndrome (ACS) patients (age 31 to 38). INTERVENTION: Thigh tourniquet was inflated in a stepwise fashion from 40 to 100 mm Hg to increase IMP transiently in volunteers. MAIN OUTCOME MEASUREMENTS: Invasive IMP by slit catheter and PPLL fascial displacement waveform in volunteers with model ACS and patients with ACS. RESULTS: In the model compartment tamponade group, thigh cuff occlusion increased IMP in the anterior compartment from a mean of 12.1 mm Hg (SE = 1.5) to a mean of 27.4 mm Hg (SE = 2.4, N = 8, P < 0.0001). By fast Fourier transform, the ratio of the amplitude of the fundamental frequency to the amplitude of the second harmonic frequency of the fascial displacement waveform as measured by PPLL increased from a resting mean of 1.12 (SE = 0.07) to a mean of 1.85 (SE = 0.18) under the same protocol (N = 6, P = 0.001). Combined data with compartment syndrome patients revealed linear correlation between IMP and PPLL with an R value of 0.8887. CONCLUSIONS: Subarterial thigh cuff pressure causes a significant and transient increase in IMP, serving as a model for anterior compartment tamponade. PPLL is able to detect fascial displacement waveforms corresponding to arterial pulsation and furthermore distinguishes between normal and elevated IMP. There is a linear correlation between PPLL measurements and invasive IMP. The PPLL shows potential utility as a device for noninvasive measurement of IMP for detecting compartment syndromes.

Adult↗

PubMed2005

System for determination of ultrasonic wave speeds and their temperature dependence in liquids and in vitro tissues.

An interferometric technique capable of accurately measuring wave speed in liquids is reported. The hardware is adapted from a design to measure nonlinear responses of biological tissues to pressure changes (pressure derivatives) and temperature changes (temperature derivatives). It is used with the highly sensitive variable frequency pulsed phase-locked loop (VFPPLL) instrument. The system uses well-understood and well-characterized components and systems. The apparatus covers a temperature range from below 5 degrees C to above 45 degrees C. The system with the high-sensitivity VFPPLL is capable of measurement of wave speed to an uncertainty of less than 0.1%, and changes in wave speed to better than 0.001%. The transducer is an undamped temperature-characterized PZT-5A 500-kHz plate, whose output is corrected for off-resonance operation and for diffraction effects. To test the accuracy of the technique, measurement of ultrasonic compressional wave speed in water at temperatures from 10 degrees C to 45 degrees C are reported, with an estimated uncertainty of 0.07% and a temperature uncertainty of 0.15 degrees C. The agreement between mean values and literature values is better than 0.05%.

Acoustics↗

PubMed2005

Noninvasive assessment of intracranial pressure waveforms by using pulsed phase lock loop technology. Technical note.

Elevated intracranial pressure (ICP) is a major factor associated with incidences of morbidity and mortality in patients with neurological disorders. The use of conventional methods for ICP monitoring is currently limited to patients with severe neurological conditions because of the methods' invasive nature. The authors have developed an ultrasonic device capable of monitoring ICP waveforms noninvasively by using a pulsed phase lock loop (PPLL) technique. The PPLL device records skull movement (several meters) associated with ICP pulsations. The purpose of this study was to correlate PPLL waveforms with invasively measured ICP waveforms in patients at the University of California San Diego Medical Center (13 patients). A linear regression analysis revealed a high correlation between PPLL waveforms and invasively measured ICP waveforms during the same time domain (r2 = 0.88). A coherence function analysis, which provides the fractional portion of the mean square value at the output that is contributed by the input at a certain frequency, showed medium to high correlations (r2 = 0.50-0.90) between PPLL waveforms and invasively measured ICP waveforms at each harmonic wave components. Furthermore, there was a significant correlation (r2 = 0.680, p < 0.01) in the harmonic distortion ratio (an index representing how much a given waveform is distorted from a pure sine wave) between PPLL waveforms and invasively measured ICP waveforms. In conclusion, PPLL technology enables the noninvasive evaluation of ICP dynamics in clinical settings.

Adolescent↗

PubMed2005

Intracranial pressure dynamics assessed by noninvasive ultrasound during 30 days of bed rest.

INTRODUCTION: Intracranial pressure (ICP) may be an important contributor to symptoms of space adaptation syndrome during the initial days of microgravity exposure. The temporary nature of these symptoms suggests that some physiologic adaptation or compensation occurs. Fluid shifts similar to those in microgravity can be simulated on Earth using head-down tilt (HDT) bed rest. This study was performed to calibrate a new noninvasive ICP instrument and to investigate ICP adaptation during 30 d of HDT bed rest. METHODS: A noninvasive ultrasound technique that measures small skull expansions with fluctuations in ICP was used to measure cranial oscillations before and near the end of 30-d HDT bed rest in eight healthy, male volunteers. Pulse phase-locked loop (PPLL) output voltage and arterial BP were continuously monitored and correlated. RESULTS: The amplitude of intracranial distance pulsation decreased during 30-d bed rest. Prior to bed rest, the PPLL amplitude was 25 +/- 9 mV and this amplitude was reduced by 60% to 9 +/- 4 mV (a value consistent with that of upright posture) at the end of HDT bed rest (p = 0.01). DISCUSSION: PPLL measurements of skull pulsations are acutely posture dependent, being significantly higher in supine and HDT as compared with upright posture. A cephalad fluid shift is probably the responsible mechanism. Our results indicate that there are adaptations to intracranial pooling of blood and tissue fluid during bed rest that reduce skull pulsation amplitudes to values similar to those obtained in normal upright posture. Detailed studies of the time course of cranial vessel and bone adaptations may provide insights into the potential adaptative mechanisms.

Aerospace Medicine↗

PubMed2003

Cranial diameter pulsations measured by non-invasive ultrasound decrease with tilt.

INTRODUCTION: Intracranial pressure (ICP) may play a significant role in physiological responses to microgravity by contributing to the nausea associated with microgravity exposure. However, effects of altered gravity on ICP in astronauts have not been investigated, primarily due to the invasiveness of currently available techniques. We have developed an ultrasonic device that monitors changes in cranial diameter pulsation non-invasively so that we can evaluate ICP dynamics in astronauts during spaceflight. This study was designed to demonstrate the feasibility of our ultrasound technique under the physiological condition in which ICP dynamics are changed due to altered gravitational force. METHODS: Six healthy volunteers were placed at 60 degrees head-up, 30 degrees headup, supine, and 15 degrees head-down positions for 3 min at each angle. We measured arterial blood pressure (ABP) with a finger pressure cuff, and cranial diameter pulsation with a pulsed phase lock loop device (PPLL). RESULTS: Analysis of covariance demonstrated that amplitudes of cranial diameter pulsations were significantly altered with the angle of tilt (p < 0.001). The 95% confidence interval for linear regression coefficients of the cranial diameter pulsation amplitudes with tilt angle was 0.862 to 0.968. However, ABP amplitudes did not show this relationship. DISCUSSION: Our noninvasive ultrasonic technique reveals that the amplitude of cranial diameter pulsation decreases as a function of tilt angle, suggesting that ICP pulsation follows the same relationship. It is demonstrated that the PPLL device has a sufficient sensitivity to detect changes non-invasively in ICP pulsation caused by altered gravity.

Adult↗