Yio-Wha Shau

Altered heel-pad mechanical properties in patients with Type 2 diabetes mellitus

SUMMARY

ELASTICITY OF HUMAN VOCAL FOLDS MEASURED IN VIVO USING COLOR DOPPLER IMAGING

Noninvasive measurement of human vocal fold (VF) vibratory length was made during normal phonation to calculate the corresponding elasticity. A fixed-ends rubber string phantom that was driven by a vibrating motor was built to simulate the horizontal VF movement. The vibratory artefact of color Doppler imaging (CDI) was used to characterize and quantify the high-frequency tissue vibration with small amplitude. Because the frequency and the length of vibrating VFs were obtained simultaneously, the stress-strain relation and the Youngs moduli of the VFs could be calculated. For the six vocally normal adult volunteers (3 M, 3 F, ages from 19 to 51 years old), the effective vibrating lengths of the vocal fold in low pitch were about 1.4 to 1.6 cm and 1.3 to 1.5 cm for men and women, respectively. The VFs lengths extended to about 1.7 to 1.8 cm in pitch over an octave higher and the stress-strain relation was nonlinear. However, in the range of lower pitch, the VF stress was relatively linear with respect to the strains and the Youngs moduli were about 30 to 120 kPa in men and 120 to 300 kPa in women.

Noninvasive assessment of the viscoelasticity of peripheral arteries

Currently used methods of examining the mechanical properties of blood vessel walls are either indirect or invasive, or measure vessel diameter and pressure waveforms at different sites. We developed a noninvasive technique to assess the mechanical properties and viscoelasticity of peripheral arteries. The pressure-strain elastic modulus (Ep) and the viscoelastic properties (energy dissipation ratio, EDR) of the common carotid artery (CCA), brachial artery (BA), radial artery (RA) and dorsalis pedis artery (DPA) were determined by means of palpating pressure and diameter distension waveforms extracted from high-resolution ultrasonography. The methodology was validated in vitro using an elastic tube phantom, as well as in vivo. In vivo study in 10 healthy volunteers (mean age 22 y) showed that the pressure-diameter curves were nonlinear, with an inflection at about 85-90 mmHg, and routed clockwise with slight hysteresis. The CCA (n = 5) had a mean diameter of 6.74 mm and the pulsatile diameter distension was 12.2%. The Ep calculated at the CCA was 0.44 x 10(6) dyne/cm2 with an EDR of 7.18%. The BA, RA and DPA (n = 10) had mean diameters of 3.91 mm, 2.21 mm and 2.12 mm; arterial strains of 4.60%, 4.25% and 8.91%; mean Ep of 1.39, 1.45, 0.90 x 10(6 )dyne/cm2; and mean EDRs of 6.34%, 6.15% and 5.60%, respectively. The method presented is relatively simple to implement clinically and has potential as a new diagnostic tool for detecting local vascular changes.

ASSESSMENT OF ZEBRAFISH CARDIAC PERFORMANCE USING DOPPLER ECHOCARDIOGRAPHY AND POWER ANGIOGRAPHY

The zebrafish (Danio rerio) has become a new animal model for cardiac researches. Although it is equipped with a prototypical vertebrate heart, the zebrafish studies for cardiac mutations and genetic control of development can reveal some hints for solving human problems. Despite the simplicity of the zebrafish heart, the objective parameters of cardiac performance are not easily available, except for the morphological description, due to its small size. Because the four components (sinus venosus, atrium, ventricle and bulbus arteriosus) of the zebrafish heart are connected in series, we studied it by applying ultrasonic imaging methods for the vascular system. A total of 20 fishes that were ages of 3 to 4 months were studied. Their mean body weight and height were 562 +/- 173 mg and 4.6 +/- 0.7 cm, respectively. Power angiography and routine Doppler echocardiography were used to evaluate the cardiac performance of zebrafish at 25 degrees C and 15 degrees C. The zebrafish hearts could be easily identified with color Doppler (8.5 MHz) or power angiography (7 MHz). The ventricular filling flow contained two components (E and A-flow). The E-flow velocities were lower than the A-flow velocities at both 25 and 15 degrees C. The cycle length was prolonged (p < 0.05) and the velocities of ventricular filling and bulbus arteriosus decreased significantly at 15 degrees C (p < 0.05). A significant decrease in early diastolic deceleration slope and significant prolongation in early diastolic and late-diastolic deceleration times were found at a lower temperature (15 degrees C). The acceleration:deceleration ratio for early and late diastole also showed a significant difference at 15 degrees C. In conclusion, the cardiac performance of the zebrafish could be approached using commercially available clinical instruments equipped with Doppler echocardiography and power angiography.

Reliability and Relationship Between 2 Measurements of Transversus Abdominis Dimension Taken During an Abdominal Drawing-in Maneuver Using a Novel Approach of Ultrasound Imaging

STUDY DESIGN Reliability study of clinical measurement. OBJECTIVES The primary purpose was to develop a reliable method for measuring muscle length changes of the transversus abdominis (TrA) during contraction. The secondary purpose was to investigate the relationship between changes in thickness and length (as indicated by the lateral sliding of the anterior muscle-fascia junction) of the TrA muscle during an abdominal drawing-in maneuver. We also provide data on between-day reliability of change in thickness (ΔT) of the TrA. BACKGROUND Ultrasound imaging measurements of TrA thickness at rest (Thr) and during maximal contraction (Thm) have been shown to be reliable. However, limited data exist on quantifying changes in TrA length (as indicated by the lateral sliding of the muscle-fascia junction [Δx]) and ΔT during contraction. METHODS Eighteen healthy adults (mean ± SD age, 22.6 ± 2.5 years) participated in this study. Brightness mode ultrasound images of the TrA were collected at rest and during an abdominal drawing-in maneuver. Subjects were examined by the same examiner twice within a 48-hour period. ΔT, ΔT/Thr, Thr, Thm, and Δx of the TrA were calculated. Medial-lateral movement of the transducer during measurement was corrected through a custom-written program that used an internal marker created by an echo-absorptive thread attached to the skin. Intraclass correlation coefficients (ICC3,1), within-subject coefficient of variance, and standard error of measurement were calculated. The relationship between ΔT and adjusted Δx of the TrA muscle was investigated. RESULTS The ICC values for Thr, Thm, and ΔT of the TrA muscle were greater than 0.75, with the exception of the left ΔT (0.62) and left ΔT/Thr (0.49). After adjusting for medial-lateral motion of the transducer, the ICC values of adjusted Δx were above 0.75, and the within-subject coefficient of variance was below 10%. There was no significant correlation between ΔT and adjusted Δx of the TrA. CONCLUSION Ultrasound imaging measurements of TrA thickness and length change were shown to be reliable using a novel method to control for medial-lateral transducer motion. Measuring different but unrelated dimensional changes in the TrA might provide further insight as to the function of the TrA.

Diabetic effects on microchambers and macrochambers tissue properties in human heel pads.

BACKGROUND The study attempted to highlight the differences of mechanical properties in microchambers and macrochambers between patients with type 2 diabetes mellitus and age-matched healthy volunteers. METHODS A total of 29 heels in 18 diabetic patients and 28 heels in 16 age-matched healthy participants were examined by a loading device consisting of a 10-MHz compact linear-array ultrasound transducer, a Plexiglas cylinder, and a load cell. Subjects in both groups were on average about 55 years old with a body mass index of approximately 25 kg/m(2). A stepping motor was used to progressively load the transducer on the tested heels at a velocity of 6mm/s from zero to the maximum stress of 78 kPa. Unloaded thickness, strain, and elastic modulus in microchambers, macrochambers and heel pads were measured. FINDINGS Microchambers strain in diabetic patients was significantly greater than that in healthy subjects (0.291 (SD 0.14) vs. 0.104 (SD 0.057); P<0.001). Macrochambers strain in diabetic patients was significantly less than that in healthy subjects (0.355 (SD 0.098) vs. 0.450 (SD 0.092); P=0.001). Microchambers stiffness in diabetic patients was significantly less than that in healthy persons (393 (SD 371)kPa vs. 1140 (SD 931)kPa; P<0.001). Macrochambers stiffness in diabetic patients was significantly greater than that in healthy persons (239 (SD 77)kPa vs. 181 (SD 42)kPa; P=0.001). INTERPRETATION Heel pad tissue properties are altered heterogeneously in people with diabetes. Increased macrochambers but decreased microchambers stiffness may cause diminished cushioning capacities in diabetic heels.

Measurement of cervical multifidus contraction pattern with ultrasound imaging

Deep muscle training has become the focus of research and exercise for patients with chronic neck pain. The objective of this in vivo study was to establish a non-invasive assessment tool for the activation of deep cervical muscles. The pattern of the change in the thickness of the cervical multifidus is described with a mathematical equation and used to compare the changes among different levels of resistance (0%, 25%, 50%, 75%, and 100%) and at different cervical levels (fourth, fifth, and sixth cervical (C4, C5, and C6) vertebrae). Twenty asymptomatic subjects (five women and 15 men; 24.3+/-4.7 years old) were recruited for this experiment. Ultrasonography (US) with synchronized force recording was used to measure the thickness of the cervical multifidus during progressive isometric extension against resistance. Linear and quadratic models were used to estimate the patterns of change in the thickness of cervical multifidus in relation to force. Two-way analysis of variance with repeated measurement and post hoc analysis were used to investigate the differences in thickness. The change in thickness and force was better fitted by quadratic model (y=ax(2)+bx+c) than by the linear model. The thickness at 50% of maximum contraction was significantly increased compared with that at 25% of maximum contraction. This quantitative non-invasive measurement may provide an assessment tool for further investigation for the physiological function of the deep muscles. Further research is required to investigate whether the change of thickness was predominately determined by the recruitment of muscle fibers or the extensibility of non-contractile tissues.

Noninvasive assessment of vocal fold mucosal wave velocity using color doppler imaging

The vibratory movement of the vocal folds (VF) plays an important role in normal function of phonation. We developed a noninvasive technique to quantify the human mucosal wave velocity (MWV) in vivo using color Doppler imaging (CDI). During phonation, the motion of mucosa-air interface generates a unique pattern of US color artefacts that assist the identification of true VF location. An in vitro study using a vibrating string phantom was conducted to investigate how the CDI displayed a vibrating soft tissue at high frequency. The vibrating amplitude, frequency, mass density and the acoustic impedance of the soft tissues were found to dominate the formation of color artefacts. Based on the model of finite string with fixed ends, we estimated the mean MWV for 10 adult volunteers (6 men, 4 women, ages 34 +/- 5 years) with normal VF function. The mean MWVs for the men were found to vary from 2.1 to 10 m/s in a frequency range of 85 to 310 Hz at their comfortable pitch and intensity, and the women typically had higher MWVs that varied from 5.0 to 16.5 m/s in a frequency range of 180 to 480 Hz. The MWV increased linearly with the frequency and there was no observable difference in mucosa stiffness due to the effect of gender. The variation in MWV as it propagates vertically can be seen from the color and shape of the artefacts. The VF polyp resulted in abnormal MWV and different CDI vibratory artefacts. The CDI artefacts provide insight on the dynamics of mucosa structure during phonation, and the method presented is promising for noninvasive monitoring of laryngeal functions clinically.

Mechanical properties of heel pads reconstructed with flaps

We compared the mechanical properties of normal and reconstructed heel pads in seven patients. Four had latissimus dorsi flaps and one each an anterior thigh flap, a local dorsalis pedis flap and a sural arterial flap. The thickness of the heel pad was measured under serial incremental loads of 0.5 kg to a maximum of 3 kg and then relaxed sequentially. The load-displacement curve of the heel pad during a loading-unloading cycle was plotted and from this the unloaded heel-pad thickness (UHPT), compressibility index (CI), elastic modulus (Ep), and energy dissipation ratio (EDR) were calculated. The EDR was significantly increased in the reconstructed heels (53.7 +/- 18% v 23.4 +/- 6.5%, p = 0.003) indicating that in them more energy is dissipated as heat. Insufficient functional capacity in the reconstructed heel pad can lead to the development of shock-induced discomfort and ulceration.

Quantification of Skeletal Muscle Fibrosis at Different Healing Stages Using Sonography A Morphologic and Histologic Study in an Animal Model

This study attempted to quantify the degree of muscle fibrosis on sonograms of injured gastrocnemius muscles at different healing stages in a rat model. Correlations between the quantifications and histologic assessments of the injured muscles were also determined.