排序方式: 共有2条查询结果,搜索用时 0 毫秒
1
1.
Statler KD Keshner EA 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2003,148(2):202-210
Simultaneous video-fluoroscopic and neck muscle EMG data were recorded from one cat performing ±15° sinusoidal (0.25 Hz) head-tracking
movements in the sagittal plane in a standing body posture with two initial neck orientations and four inertial loads. Radio-opaque
markers were inserted into the anterior/posterior and lateral aspects of the occipital ridge and C1-C7 to measure vertebral displacement. Kinematic data were analyzed, and a computer model was applied to the data to characterize
the limits of movement in the cervical spine and to estimate the moment arms of the neck muscles at different orientations
of head-neck movement. For each initial neck orientation, the cat utilized a distinct set of vertebral alignments, relative
joint movements, and muscle-activation patterns to achieve the same movement outcome. As inertial load increased, vertebral
alignments and relative joint movements were constant with a vertically oriented neck but differed when the neck was more
horizontally oriented. Different muscle-activation patterns were used to maintain the same kinematic pattern with increased
inertial loads. Some muscle EMG response gains (rectus capitis major and splenius capitis) increased with increasing mass,
while others (biventer cervicis and occipitoscapularis) demonstrated an initial increase and then a plateau. EMG phases were
not affected by changing the mass of the system but were affected by changing neck orientation. The model predicted that muscle
moment arms would vary little for the different vertebral alignments, suggesting a robust biomechanical system minimally compensates
for small changes in task geometry.
Electronic Publication 相似文献
2.
Yukio Kuniyoshi Kageharu Koja Kazufumi Miyagi Mituyoshi Shimoji Tooru Uezu Katuya Arakaki Satoshi Yamashiro Katuhito Mabuni Shigenobu Senaha Yoshiyuki Nakasone 《Journal of artificial organs》2003,6(3):179-182
We present three patients who underwent repeat aortic valve replacement for prosthetic valve dysfunction caused by tissue ingrowth in the late postoperative period. These patients (three women aged 48–51 years, mean 49.3 ± 1.53 years) underwent operations for restriction of prosthetic valve leaflet movement by pannus in the left ventricular outflow tract. The interval from the previous operation ranged from 8.0 to 9.6 years (mean 9.6 ± 2.0 years). The symptoms of the patients were New York Heart Association functional class I, II, and IV in one patient each. Diagnosis was made by cinefluoroscopy in two patients and aortography in one patient. The operative procedures consisted of aortic valve replacement (n = 1) and aortic valve replacement with mitral valve replacement (n = 2). Pannus was found at the left ventricular aspect of the prosthetic valve in all patients. In two patients, the pannus directly restricted movement of the leaflet and also severely narrowed the inflow orifice of the prosthetic valve. In the other patient, the pannus had grown at a distance of 7mm from the valve and narrowed the left ventricular outflow tract circularly. The postoperative course was uneventful and all three patients were discharged in a good condition. One patient died of pneumonia 8 months after surgery and the other two patients have remained well and have been followed up for one and a half years. In conclusion, there may be a discrepancy between the clinical symptoms and the grade of subvalvular stenosis caused by pannus. Therefore, it is essential for satisfactory operative results that early diagnosis be made by various means. 相似文献
1