Biomedical subjects

W Qassem

Publications and source records attributed to W Qassem.

14 recordsLinked to original sources

PubMed2003

Impulse response due to jumping on shoes of various stiffness and damping.

The human body is a dynamic system with dynamic behaviour. Linear and nonlinear models of a standing human are investigated. The models simulated the body by 15-lumped masses connected by springs and dampers. A square wave impulse input is applied at the shoes and the lumbar spine response is presented as an example. The results show that the mechanical response is affected by the kind of representation (linear or nonlinear model) and the shoes stiffness and damping coefficients.

Computer Simulation↗

PubMed2001

Effect of vibrations with various duration exposure on the P-R interval of ECG.

ECG analysis of a human body subjected to vertical vibrations of various durations was carried out. Results obtained from a representative subject show that the exposure period has different effects on the P-R time interval of the ECG waves. Vibration increases the Percent Normalized Difference (PND) of the P-R time interval with time till it reaches a steady state value of 29.5. An increase of the exposure duration increases the time constant, while the steady state value remains constant. The PND behavior can be mathematically modeled as a first order system.

Biomedical Engineering↗

PubMed1997

Human body model response to mechanical impulse.

Despite our understanding of the importance of falling, previous studies have ignored the effects of falls from standing height. In this article, lumped parameter linear and nonlinear models of a standing human have been used to simulate the impact response of the body segments due to inputs at the shoes. The acceleration transfer and frequency response were determined. The effect of nonlinear damping was simulated. Nonlinear effects were found to be most significant when the input amplitude increases. Frequency response attenuation was significant, resulting in almost a shift in the magnitude plots in the range (0.1-100 Hz) of frequency. When the input amplitude was reduced, the nonlinear effects became apparent only in the medium frequency range. In the case simulating a human subject exposed to impulse at the foot, a large amount of energy is dissipated in the joints due to the friction resulting in a joint disorder. This is most significant at the medium frequency range that is expected to be induced by a running human subject.

Biomechanical Phenomena↗

PubMed1996

Vibration effects on setting pregnant women--subjects of various masses.

An electrical simulation of a mechanical model of a 60 kg pregnant woman subjected to horizontal and vertical vibrations has been investigated by using a computer software package (MICRO-CAP II). The results have shown that mechanical vibrations affect the body segments differently based on their location, the kind of vibration and pregnancy development. The vibrations' effect on the body varies from segment to segment and a lady driver is affected by vibrations more than a lady passenger. Horizontal vibrations affect body segments (lower arm, upper arm, head, thorax, torso, cervical spine, and lumbar spine) more than vertical vibrations, while the thorax is affected by vertical vibrations, more than horizontal vibrations.

Female↗

PubMed1996

Model prediction of vibration effects on human subject seated on various cushions.

Vertical and horizontal vibrations of a 100 kg seated human body on cushions of various mechanical parameters have been investigated. The vibration inputs were from (a) steering, (b) cushion and (c) a combination of the two. A previously developed model has been used in this study. Resonance frequencies and gains of body segments have been found. The results obtained have been tabulated and presented in graphical manner. It is found that each body segment response depends on the source (steering, cushion or a combination of the two) and the kind (vertical or horizontal) of vibrations as well as the mechanical parameters (mass, stiffness, and damping) of the cushion.

Biomechanical Phenomena↗

PubMed1996

The mechanical properties of catgut in holding and bonding fractured bones.

The mechanical properties of catgut (biodegradable material) have been investigated and presented in graphical manner. Two techniques (a) rings and (b) mesh have been used to study the ability to hold the fractured bones. A comparison of the mechanical properties of catgut with those of bones has been carried out. The results have shown that the mechanical properties of catgut are compatible with those of bones.

Animals↗

PubMed1996

A search for possible cytogenetic effects of low frequency vibrations in cultured human lymphocytes.

1. Acute cytogenetic effects expressed as sister-chromatid exchanges (SCE) in peripheral blood lymphocytes were investigated after in vitro exposure to low vibration regimes (5-30 Hz. at 0.1 cm amplitude) for 20 min intervals and compared to non-vibrated control cultures. 2. There was no significant (P < 0.05) increase in the range of SCE incidence at any vibration frequency compared to the mean value of control; 6.88 +/- 0.11 to 7.97 +/- 0.22 versus 6.83 +/- 0.86, respectively. 3. When cultures were incubated for 1 h in the presence of 0.5 microgram ml-1 mitomycin C (MMC; the positive control) significant elevations in the SCE frequency were observed (19.81 +/- 0.67), indicating the sensitivity of the system to in vitro SCE induction. 4. Other cell parameters, such as mitotic index and cell proliferation index were statistically similar in the experimental cultures and the negative control. 5. The observed differences in the investigated end-points are considered within those typically found in vitro. This suggests no relation between low frequency vibrations and cytogenetic effects.

Adult↗

PubMed1994

No significant increase in sister-chromatid exchanges in cultured blood lymphocytes from workers in a large oil refinery.

In order to assess the potential genotoxic effects of occupational exposure to petrochemicals, the incidence of sister-chromatid exchanges (SCE) in cultured lymphocytes was studied. Blood samples were taken from 233 individuals (184 exposed and 49 worksite controls) in an oil refinery and from 47 community control persons. The data showed a non-significant elevation of SCE frequency in occupationally exposed workers when compared to non-exposed individuals. The mean SCE frequency per cell ranged from 7.55 +/- 0.55 in blood of lube oil blending and canning (LOBC) workers to 9.13 +/- 0.71 in catalytic cracking and water treatment (CCWT) workers. The control values were 6.2 +/- 0.67 and 7.21 +/- 0.45 in the community and worksite individuals, respectively. Furthermore, the SCE frequencies were influenced neither by age nor by smoking.

Adult↗

PubMed1994

The effects of vertical and horizontal vibrations on the human body.

Vertical and horizontal vibrations of a 100 kg human have been investigated. A new mechanical model has been developed, and an analogous electric simulation has been carried out, which in turn has been analysed by using computer software (MICRO-CAP II). The vibration force comes from (a) hand, (b) seat and (c) combination of the two. The theoretical results obtained have been tabulated and are presented in a graphical manner. It has been found that the body segments (lower arm, head, torso, cervical spine and lumbar spine) are affected by horizontal vibrations when the input force (F(i)) comes from both hand and seat more than when (F(i)) comes from the seat alone. Similar results have been found also for the case of the lower arms and torso when the body is subjected to vertical vibrations. The head is affected by vertical vibrations when (F(i)) comes from the seat more than when (F(i)) comes from both hand and seat. An experimental set-up has been designed and measurements of vibrational signals from the human lower arm, head and torso have been carried out. Similar trends are shown for both theoretical results and experimental findings.

Adult↗

PubMed1991

Cytogenetic effects of pulsing electromagnetic field on human lymphocytes in vitro: chromosome aberrations, sister-chromatid exchanges and cell kinetics.

Exposure of human lymphocyte cultures to a pulsing electromagnetic field (PEMF; 50 Hz, 1.05 mT) for various durations (24, 48 and 72 h) resulted in a statistically significant suppression of mitotic activity and a higher incidence of chromosomal aberrations. Furthermore, the shorter exposure times (24 and 48 h) did not cause a significant delay in cell turnover (cell proliferation index) or an increase in the baseline frequency of sister-chromatid exchanges (SCE). However, cultures continuously exposed to PEMF for 72 h exhibited significant reduction of the cell proliferation index (CPI) and an elevation of SCE rate. These results suggest that exposure to PEMF may induce a type of DNA lesions that lead to chromosomal aberrations and cell death but not to SCE, except probably at longer exposure times.

Adult↗

PubMed1987

Three-dimensional curved beam stress analysis of the human femur.

We discuss an analytical approach to the investigation of the normal, shear, and principal stresses transmitted to the human femur. Two cases are considered: in the first the femur is treated as a three dimensional isotropic curved beam, and in the second as a three dimensional anisotropic composite curved beam, consisting of two different materials, the spongy bone and the cortical bone. The composite beam theory is used to investigate stresses in the femur, in which the spongy bone is surrounded by a cortical bone jacket; compatibility of stresses and strains being introduced at the interface of the two bones in order to derive the stress equations at any point in the cross section. General loading conditions are considered in the analysis, in which the femur is subjected to normal and shear forces, and to biaxial bending and twisting moments.

Biomechanical Phenomena↗

PubMedDate not supplied

ECG response of the human body subjected to vibrations.

In this paper, the ECG response of the human body subjected to vibrations is investigated. Measurements relied on recording the ECG and then computing the normalized difference of the ECG power spectrum density. Ten subjects aged 20-22 years old were exposed for 15 min to vertical vibrations in the frequency range 5-30 Hz. Results show either depression or elevation of the ST segment indicating heart muscle fatigue. The power spectrum density normalized difference also shows that the maximum difference takes place at 8 Hz vibrations frequency which is thought to be around the resonance frequency of the heart.

Adult↗

PubMedDate not supplied

Effect of vibrations with two different amplitudes on the ECG.

The ECG response of a human body exposed to vertical vibrations was investigated. The per cent normalized difference (PND) between the R-wave amplitude before and after vibrations was monitored. Results obtained from a representative subject show an oscillatory decay of the PND behaviour with time. This behaviour can be modelled as a linear second order damped system. The natural frequency, damping ratio and the recovery time of the cardiac system can be measured.

Adult↗

PubMedDate not supplied

Heart response to horizontal impulse.

Lumped body parameters linear and nonlinear models have been developed and used for the analysis of the response of the heart in a seated human body due to impulsive horizontal inputs at various body segments. The acceleration transfer magnitude and phase due to impulsive inputs at various body segments are reported. Time histories of the heart acceleration transfer were obtained for both linear and nonlinear models. The results indicate that the largest acceleration transfer occurs at 2-3 Hz frequency. Inputs at the upper body segments excite a second peak and in the acceleration transfer at 10-12 Hz. The nonlinear model shows large attenuation at the high frequency range (larger than 10 Hz) and less attenuation at the 1-5 Hz frequency range.

Abdomen↗