Assisting walking balance using a bio-inspired exoskeleton controller.

BACKGROUND: Balance control is important for mobility, yet exoskeleton research has mainly focused on improving metabolic energy efficiency. Here we present a biomimetic exoskeleton controller that supports walking balance and reduces muscle activity. METHODS: Humans restore balance after a perturbation by adjusting activity of the muscles actuating the ankle in proportion to deviations from steady-state center of mass kinematics. We designed a controller that mimics the neural control of steady-state walking and the balance recovery responses to perturbations. This controller uses both feedback from ankle kinematics in accordance with an existing model and feedback from the center of mass velocity. Control parameters were estimated by fitting the experimental relation between kinematics and ankle moments observed in humans that were walking while being perturbed by push and pull perturbations. This identified model was implemented on a bilateral ankle exoskeleton. RESULTS: Across twelve subjects, exoskeleton support reduced calf muscle activity in steady-state walking by 19% with respect to a minimal impedance controller (p < 0.001). Proportional feedback of the center of mass velocity improved balance support after perturbation. Muscle activity is reduced in response to push and pull perturbations by 10% (p = 0.006) and 16% (p < 0.001) and center of mass deviations by 9% (p = 0.026) and 18% (p = 0.002) with respect to the same controller without center of mass feedback. CONCLUSION: Our control approach implemented on bilateral ankle exoskeletons can thus effectively support steady-state walking and balance control and therefore has the potential to improve mobility in balance-impaired individuals.

Ultrasound-Based Optimal Parameter Estimation Improves Assessment of Calf Muscle-Tendon Interaction During Walking.

We present and evaluate a new approach to estimate calf muscle-tendon parameters and calculate calf muscle-tendon function during walking. We used motion analysis, ultrasound, and EMG data of the calf muscles collected in six young and six older adults during treadmill walking as inputs to a new optimal estimation algorithm. We used estimated parameters or scaled generic parameters in an existing approach to calculate muscle fiber lengths and activations. We calculated the fit with experimental data in terms of root mean squared differences (RMSD) and coefficients of determination (R2). We also calculated the calf muscle metabolic energy cost. RMSD between measured and calculated fiber lengths and activations decreased and R2 increased when estimating parameters compared to using scaled generic parameters. Moreover, R2 between measured and calculated gastrocnemius medialis fiber length and soleus activations increased by 19 and 70%, and calf muscle metabolic energy decreased by 25% when using estimated parameters compared to using scaled generic parameters at speeds not used for estimation. This new approach estimates calf muscle-tendon parameters in good accordance with values reported in literature. The approach improves calculations of calf muscle-tendon interaction during walking and highlights the importance of individualizing calf muscle-tendon parameters.

Can Momentum-Based Control Predict Human Balance Recovery Strategies?

Human-like balance controllers are desired for wearable exoskeletons in order to enhance human-robot interaction. Momentum-based controllers (MBC) have been successfully applied in bipeds, however, it is unknown to what degree they are able to mimic human balance responses. In this paper, we investigated the ability of an MBC to generate human-like balance recovery strategies during stance, and compared the results to those obtained with a linear full-state feedback (FSF) law. We used experimental data consisting of balance recovery responses of nine healthy subjects to anteroposterior platform translations of three different amplitudes. The MBC was not able to mimic the combination of trunk, thigh and shank angle trajectories that humans generated to recover from a perturbation. Compared to the FSF, the MBC was better at tracking thigh angles and worse at tracking trunk angles, whereas both controllers performed similarly in tracking shank angles. Although the MBC predicted stable balance responses, the human-likeness of the simulated responses generally decreased with an increased perturbation magnitude. Specifically, the shifts from ankle to hip strategy generated by the MBC were not similar to the ones observed in the human data. Although the MBC was not superior to the FSF in predicting human-like balance, we consider the MBC to be more suitable for implementation in exoskeletons, because of its ability to handle constraints (e.g. ankle torque limits). Additionally, more research into the control of angular momentum and the implementation of constraints could eventually result in the generation of more human-like balance recovery strategies by the MBC.

Ventricular taps in the neonate under ultrasonic guidance. Technical note.

A method of ultrasonically guiding ventricular taps in children is described. The needle is introduced through a needle guide in the ultrasound field of a sectorscanner. The direction of the needle is accurately determined and the needle itself is clearly visualized on the television monitor during its introduction into the brain. The results of seven punctures are presented. All these punctures were successful at the first attempt, and no complications occurred.

Influence of pathological state on the acoustic attenuation coefficient slope of liver.

The acoustic attenuation coefficient slope (beta) of liver was estimated in vivo from the spectral difference of returned echoes. beta of normal young subjects was lower than that of older subjects (mean: 0.340 vs 0.418 dB/cm.MHz). Limited fluid withdrawal from the body by haemodialysis did not affect beta. In alcoholic liver disease beta was related to the amount of fat and of fibrous tissue in liver biopsy specimens. High values of beta were observed as soon as the degree of steatosis exceeded 5 vol%. There was a similar increase of beta in the presence of fibrous interlobular septa. In normal liver beta was related to the amount of triglycerides in the liver specimen.

Floating thrombi: diagnosis and follow-up by duplex ultrasound.

The clinical features and evolution of floating thrombi (FT) diagnosed by duplex ultrasound were examined. In 76 consecutively diagnosed above-knee deep venous thromboses the prevalence of FT was 18%. Of 44 FT diagnosed in 39 patients, 18 (39%) were located in the common femoral, 12 (26%) in the popliteal and seven (15%) in the external iliac veins. Serial duplex examinations revealed that 31% of FT in the iliofemoral segment disappeared 33% remained unchanged and 36% adhered to the vein wall within 2 weeks following diagnosis. After 3 months, 87% of the floating segments had disappeared, irrespective of the localization or therapeutic regimen. Thirteen patients experienced pulmonary embolism before (12/13) or following (4/13) diagnosis of floating thrombosis; three of four superficial femoral vein FT embolized. Fifteen per cent of the patients with FT died during the study period and 28% of the thrombi were associated with a malignant neoplasm; the incidence of malignancy was 60% in superficial and 39% in common femoral vein FT.

Demonstration of nodules in the normal thyroid by echography.

An ultrasound examination was performed of the normal thyroid in 300 patients (164 males and 136 females). Small echoic nodules were demonstrated in 19% of the patients and fluid-filled masses in 6%. Echoic nodules occurred frequently (greater than 40%) in the seventh decade. 71% of the nodules were situated in the right lobe.

Ultrasound and CT changes of liver parenchyma in acute schistosomiasis.

Acute schistosomiasis in travellers to endemic regions often remains unrecognized. Early diagnosis is important to avoid progression to chronic disease. Diagnosis is based on clinical, epidemiological and laboratory data. The role of imaging techniques as diagnostic tools remains to be established in acute clinical schistosomiasis. We describe hypodense nodules in the liver on ultrasound and CT scanning in a patient with acute schistosomiasis (Katayama syndrome). To our knowledge this is the first description of nodular hepatic lesions in acute schistosomiasis.

Renal function in the oldest-old on an acute geriatric ward.

AIM: Evaluation of renal function and relation to risk factors for renal failure in very old patients admitted to an acute geriatric ward. METHODS: Retrospective chart review of patients aged 80 years and over, admitted to the acute geriatric ward from August 1998 till August 1999. Recorded data were: age, gender, previous medical history, primary diagnosis, medication use, weight, serum creatinine, BUN, sodium, potassium, cholesterol, urine and ultrasound of the kidney. The creatinine clearance was estimated by the Cockcroft-Gault formula, the glomerular filtration rate by the MDRD equation. RESULTS: 220 (60 males/160 females) patients were included. The mean serum creatinine on admisssion and discharge was 1.17 +/- 0.45 mg/dL and 1.11 +/- 0.48 mg/dL respectively. The mean estimated creatinine clearance in the very old was 38.11 +/- 12.04 mL/min on admission and 39.00 +/- 11.01 mL/min on discharge. Renal failure arbitrarily defined as an estimated creatinine clearance on admission of less than 30 mL/min was found in 26.4% of the patients. Only a significant correlation between failure to thrive and renal failure was found (p < 0.0001). The correlation coefficient between the Cockcroft-Gault and the MDRD formula was r = 0.66 (p < 0.0001); between the Cockcroft-Gault and the reciprocal serum creatinine was r = 0.60 (p < 0.0001) and between the MDRD and the reciprocal serum creatinine was r = 0.87 (p < 0.0001). CONCLUSION: The weak correlation between the Cockcroft-Gault and other estimations of GFR in the acutely ill elderly, confirms the need to have a reliable estimation of glomerular filtration rate in the elderly. Renal failure defined as a Cockgroft-Gault <30 mL/min is found in 26.4% of the oldest-old admitted to an acute geriatric department. The elderly with renal failure is more often admitted for failure to thrive. No great differences were observed between renal function on admission and discharge.

[Thyroid diseases in the elderly]. / Schildklierafwijkingen bij bejaarden.

Thyroid dysfunction in the elderly differs from that in the young, because most symptoms at presentation are absent, or non specific or atypical. Hypothyroid patients generally present with cardiovascular or central nervous system symptoms. A serious complication, occurring more easily in elderly is hypothyroid coma. The diagnosis of hypothyroidism is confirmed by a high serum TSH and low values of FT4 and T4. Elderly patients should be started on low doses of thyroid-hormone replacement that are increased slowly. Particular caution must be used in patients with underlying cardiovascular disease. Hyperthyroid patients are more likely to show cardiovascular symptoms, central nervous system symptoms or gastrointestinal symptoms. The diagnosis is confirmed by a low serum TSH value and elevated values for the serum FT4 and/or T3. Radioiodine (131I) therapy is the most efficient treatment in this age group. A diffusely enlarged thyroid gland in the elderly is most often caused by a multinodular goiter. Solitary thyroid nodules which appear cold on isotope scan may represent a carcinoma. The diagnosis of malignancy can be made after fine needle-aspiration of the nodule.

[Echographically controlled ventricle punctures]. / Echografisch geleide ventrikelpuncties.

Ventricular taps are performed either for diagnostic or for therapeutic purposes. They are not free of risks. A new technique is presented, in which the placement of the needle is echographically monitored. Fifteen punctures were done in five children. All punctures were successful at first attempt, and were uneventful.

Contrast-enhanced ultrasonography in hepatosplenic sarcoidosis.

We report a case of a 38-year-old woman with atypical pain in the left lower hemi-abdomen. On abdominal B-mode ultrasonography the liver was normal; the spleen showed multiple subcentimetric hypoechoic nodules. A multidetector CT-examination revealed multiple small low-attenuation nodules in the liver and the spleen, suggestive for metastatic disease. Contrast-enhanced ultrasound (CEUS) revealed two hypoechoic nodules in the liver that were visible in the portal phase and disappeared in the late phase. The focal splenic lesions were visible as irregular hypo-enhancing nodules. An MRI examination, including T1, T2 and contrast-enhanced images, could not confirm the exact nature of the lesions. A core biopsy of a splenic nodule yielded non-caseating epithelioid cell granulomas. Different complementary examinations were normal and hepatosplenic sarcoidosis was diagnosed. The pain in the left lower hemi-abdomen was ascribed to irritable bowel syndrome.