Resonance frequency in patellar tendon.

The aim of this study was to the measure resonance frequency of the patellar tendon in order to determine whether the resonance frequency exists in the soft tissue of the human body. A vibrator was attached to the medial aspect of the tibia of 10 healthy subjects to provide different frequencies of vibration, and an accelerometer was attached to the patellar tendon to measure the vibration of the patellar tendon. Measurements were obtained at 0 degrees , 60 degrees and 90 degrees of knee flexion. A mean resonance frequency of 22.5+/-0.8, 23.0+0.7 and 24.0+0.8 Hz was produced in the right patellar tendon when the knee joint was at 0 degrees , 60 degrees and 90 degrees of flexion, respectively. The increase in resonance frequency from 0 degrees to 60 degrees was not statistically significant. However, the increase from 60 degrees to 90 degrees was significant (P<0.05). No differences in the measured parameters were evident for the left and right patellar tendons. These results indicate that resonance frequencies exist in soft tissues of the body and that this characteristic may be useful in detecting changes in soft tissue physical properties.

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.

Noninvasive assessment of laryngeal phonation function using color Doppler ultrasound imaging.

Color Doppler imaging (CDI) was used to identify the morphology of vocal folds (VF) and to quantify the tissue horizontal displacement velocity (HDV) in the vibrating portion of VF. Mucosal HDV that gives an estimate of the stiffness of the VF cover is very important clinically. The VF and its cover were shown to be very hypoechoic and not adequately visible in B-scan image. However, in this study, we found that the structure of the true VF, especially the mucosa and the superficial layer of the lamina propria, the so-called "cover," can be easily identified and evaluated using CDI. The mean VF displacement velocity was measured by decoding the pseudocolor codes of the ultrasound (US) image at the vibrating sites. The mucosal mean HDV obtained from 10 normal men of age 34 +/- 8 years phonating at their most comfortable pitch and intensity (98 +/- 12 Hz, 55-65 dB) was about 68 +/- 10 cm/s, which agreed reasonably with the literature. Therefore, the CDI could be used as a potential tool for assessing the phonation function in the larynx nonintrusively.

Non-invasive assessment of arterial distension waveforms using gradient-based hough transform and power Doppler ultrasound imaging.

The peripheral arterial vessel often appears as an elliptic shape under the constraints of the surrounding tissues. In this study, the gradient-based Hough transform was used to detect the central location of the ellipse and the lumen area of the arterial vessel non-invasively using power Doppler imaging. Sequential ultrasound images were used to construct arterial distension waveforms in both the major- and minor-axis directions for a few cardiac cycles. The common carotid arteries (CCAs) for nine healthy male volunteers (mean age 24 years), in the sitting position, were investigated in vivo. The CCAs (n = 9) had a mean diameter of 5.83mm, and the pulsatile diameter distension was 13.7+/-1.9%. The brachial artery and dorsalis pedis artery for five healthy male volunteers (mean age 26 years), in the supine position, had mean diameters of 4.03mm and 2.83mm and distensions of 16.7+/-4.6% and 15.5+/-5.4%, respectively. The movement of the arterial centre location during the cardiac cycle reflected the asymmetry of the reaction forces produced by the surrounding soft tissues. The present method can obtain the response of vessel distension to pulse pressure, as well as the constrained conditions of the arteries.

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

AIMS: To compare the heel-pad mechanical properties in patients with Type 2 diabetes mellitus with forefoot ulceration, without forefoot ulceration and age-matched healthy subjects. METHODS: Heel-pad mechanical properties in 40 heels of 20 healthy subjects (group I) age-matched with the other groups, 42 heels of 21 diabetic patients without forefoot ulceration (group II), and 14 heels of 12 diabetic patients with active forefoot ulceration (group III) were assessed using a self-constructed loading-unloading device and a 10-MHz linear-array ultrasound transducer. RESULTS: There were no differences in the unloaded heel-pad thickness, compressibility index and elastic modulus between the three groups. When compared with group I subjects (mean +/- SD, 27.9 +/- 6.1%), a significant increase (P < 0.001) was found in both group II (36.1 +/- 8.7%) and group III patients (43.2 +/- 6.6%) for the energy dissipation ratio. This ratio was also significantly different (P = 0.003) between groups II and III. CONCLUSIONS: The higher impact energy dissipated in the heel-pad may put patients with Type 2 diabetes at higher risk for developing foot ulceration.

Ultrasonographic measurement of the mechanical properties of the sole under the metatarsal heads.

The sole under the metatarsal heads functions as a shock absorber during walking and running. The mechanical properties of the sole provide the primary defense against the development of metatarsalgia and foot ulceration. However, limited information about these properties has been documented. In this study, we used ultrasonography to evaluate the mechanical properties, including unloaded thickness, compressibility index, elastic modulus, and energy dissipation ratio, of the sole in 20 healthy subjects. The unloaded thickness decreased progressively from the first to the fifth metatarsal heads, with values of 1.50, 1.36, 1.25, 1.14, and 1.04 cm. The sole under the first metatarsal head had the greatest values for the compressibility index and elastic modulus (55.9% and 1.39 kg/cm2), and the sole under the third metatarsal head had the smallest values (50.8% and 1.23 kg/cm2). The sole under the fifth metatarsal head had the greatest energy dissipation ratio (33.7%), followed by that under the third, second, first, and fourth metatarsal heads. Multivariate adjusted linear regression showed that the unloaded thickness, compressibility index, and elastic modulus values increased significantly with age and body weight (p < 0.05) and that the energy dissipation ratio increased significantly with body weight (p < 0.05)

Sonographic evaluation of the posterior cruciate ligament in amputated specimens and normal subjects.

The purpose of this study was to define the sonographic appearance and echogenicity of the normal posterior cruciate ligament. We examined the posterior cruciate ligament of five amputated specimens and five normal subjects using a 10 MHz linear array transducer. One K-wire was inserted into the substance of the posterior cruciate ligament of the amputated knee specimens to verify the location of the ligament on the sonogram. Various angles of insonation were used to examine the echogenicity of the posterior cruciate ligament. The results showed that the in situ posterior cruciate ligament appeared as a hypoechoic band relative to the surrounding tissue on sonograms, but it appeared hyperechoic when it was isolated and immersed in a water bath. The specific spatial orientation of the posterior cruciate ligament and anisotropy phenomenon contributed to the hypoechogenicity of the posterior cruciate ligament in situ on sonogram.

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.

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.

Variations in heel pad mechanical properties variation between children and young adults.

The purpose of this study was to compare the mechanical properties of the heel pads of adults and children, using ultrasound to assess the responses of the heel pad during compression. Thirty volunteers without heel problems, aged from 4 to 36 years, were recruited. There were 10 children (< 15 years old) and 20 adults (> 18 years old). A 7.5-MHz linear array ultrasound transducer was incorporated into a specially designed device to measure the thickness of the heel pad under different loads. The load on the heel pad was increased serially in increments of 0.5 kg, to a maximum of 3 kg, and then reduced sequentially. The load-displacement curve of the heel pad during a loading-unloading cycle was then plotted. Mechanical properties of the heel, including unloaded heel-pad thickness (UHPT), compressibility index, elastic modulus, and energy dissipation ratio (EDR), were calculated from the load-displacement curves. The average UHPT was 1.53 +/- 0.09 cm in children and 1.76 +/- 0.20 cm in adults (p < 0.001). The EDR, which represents the shock absorbency of the heel pad, was 13.5 +/- 2.0% in the children and 23.7 +/- 6.9% in adults (p < 0.001). The average compressibility index and elastic modulus were also higher in adults than in children, although the differences were not statistically significant. These findings suggest that the mechanical properties of the heel pad change from childhood to adulthood. Less energy is absorbed in the heel pad of children, which may partially explain why children tend to have fewer heel problems than adults.

Analog transmission line model for simulation of systemic circulation.

A simple four-tube arteries-microvessels-veins system which simulates a more realistic loading for human circulation was built using transmission line network. Hemodynamic data from literature are used in the fluid-circuit analogy, and the flow leakage and viscoelastic properties of the blood vessels have been considered. The effect of veins on the input impedance spectrum was found to be negligibly small above 0.5 Hz. The predicted input impedance spectra agree reasonably well with the published measurements both in shape and magnitude. Parametric analysis shows that the changes of vascular properties in the lower body affect the first minimum, and the changes in the upper body influence the second minimum. The blood flow in and out of kidney and liver dominates the aortic impedance from 0 to 5 Hz. Decreasing capacitance (i.e., increasing arterial stiffness due to aging), reducing the lumen area, or decreasing the length of blood vessels result in an increase in the impedance modulus, and the first minimum shift to a higher frequency which agree well with experiments. In the current model, the pressure, flow waveform, and local impedance can be predicted at any location along the circulatory tree. The characteristic of arterial pulse propagation resembles published measurements.