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.

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.

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.

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.

Progressive disseminated histoplasmosis 10 years after return out of Africa in an immunocompetent host.

We report on a patient without immunologic dysfunction who developed a reactivation of a latent histoplasma infection, acquired during a previous stay in Africa more than 10 years before. The current reactivation resulted in a subacute progressive disseminated histoplasmosis. He developed progressive weight loss, prostration and different oropharyngeal lesions together with bilateral adrenal masses on CT scan. The diagnosis was made on histology of biopsies of the oropharyngeal lesions. All systemic symptoms normalised, the oropharyngeal lesions disappeared and the adrenal masses regressed under amphotericin B therapy followed by itraconazole consolidation therapy.

Is there a rationale for prescription of benzodiazepines in the elderly? Review of the literature.

Benzodiazepines (BZDs) constitute the most widely used symptomatic treatment of insomnia and anxiety. Many of these drugs are associated with adverse effects, such as daytime sedation and dependence with continued use. There is a concern about the rationale for and extent of benzodiazepine (BZD) use in the elderly. The sedation due to BZD use is a main risk factor for falls and other accidents. Impaired cognitive function with continuous use appears to be a major side effect. There is a general awareness that BZD use is inappropriate in many patients, and therefore discontinuation should be recommended whenever possible. Moreover, long-term use of these drugs should be actively discouraged. Although no unanimous recommendations concerning the optimal duration of the withdrawal process exist, BZDs may easily be withdrawn during a short period in most patients who are habituated to a low dose, if an initial phase with dose reduction and psychological support are provided. Alternative approaches involve sleep hygiene guidelines, behavioural treatment and psychotherapy tailored to the needs of the individual patient.

Fast withdrawal from benzodiazepines in geriatric inpatients: a randomised double-blind, placebo-controlled trial.

OBJECTIVE: We have previously demonstrated that temporary substitution with a low-dose hypnosedative drug may lead to successful withdrawal from chronic benzodiazepine (BZD) use in the majority of patients admitted to a geriatric ward. In the present study, a withdrawal programme was evaluated in which the habitual treatment with BZDs was replaced by either 1 mg lormetazepam or placebo, defining withdrawal success rate, sleep quality and withdrawal symptoms as main outcomes. METHODS: The target population was geriatric inpatients who had been taking BZDs for at least 3 months. Subjects suffering from mental disorders were excluded. Lormetazepam or placebo were randomly assigned and given in a double-blind fashion. After 1 week, the replacement therapy was discontinued. Subjective estimations of sleep quality and withdrawal symptoms were registered at predefined intervals, four times in a period of 30 days, using standard questionnaires (the Pittsburgh Sleep Quality Index and the Benzodiazepine Withdrawal Symptom Questionnaire, respectively). RESULTS: The success rate was significantly higher in the lormetazepam substitution group (80% vs 50% in the placebo group, P < 0.05). Both the subjective quality of sleep and withdrawal symptoms were significantly better in the lormetazepam substitution group. Important withdrawal effects were observed in the control group in two patients with a history of chronic alcohol abuse. CONCLUSIONS: Initial replacement therapy with a low-dose BZD is preferred over placebo, since the latter alternative is associated with worse sleep quality and a lower success rate. Placebo must only be used under medical scrutiny, given the potential for unmasking delirious symptoms, especially in patients with concomitant alcoholism.

Paralysis due to severe hypokalemia.

We report two cases of a patient with paresis/paralysis caused by a severe iatrogenic hypokalemia. In both cases, the extreme muscle weakness disappeared with correction of the electrolyte disturbance. The mechanisms of hypokalemia due to nephrotoxic drugs and treatment of this electrolyte disturbance are discussed.

Relationship between periventricular or deep white matter lesions and arterial elasticity indices in very old people.

OBJECTIVE: To examine the relationship between the presence of cerebral white matter lesions and large and small artery elasticity indices in a population of healthy, very old subjects. METHODS: We studied 24 subjects (14 women, 10 men) with a mean age of 84+/-5 years, who were free from overt neurological, cardiovascular or psychiatric illness. We measured blood pressure and heart rate in supine and standing positions. Elasticity indices of the large arteries (C1) and small arteries (C2) were derived from radial artery pulse waves. Each subject had multi-slice spin-echo cerebral magnetic resonance imaging. The severity of white matter lesions was graded as 0, 1 or 2. RESULTS: Cerebral white matter lesions on magnetic resonance imaging were common in very old apparently healthy subjects: grade 0 (n=4, C1=2.68+/-1.80 ml/mmHg and C2=0.045+/-0.017 ml/mmHg), grade 1 (n=7, C1=2.13+/-0.36 ml/mmHg and C2=0.040+/-0.016 ml/mmHg) and grade 2 (n=13, C1=1.12+/-0.36 ml/mmHg and C2=0.018+/-0.003 ml/mmHg). There was no significant association between elasticity indices and blood pressure. CONCLUSION: In very old, apparently healthy subjects, both large and small artery elasticity indices were inversely related to the severity of cerebral white matter lesions on magnetic resonance imaging.

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.

Spontaneous internal jugular vein thrombosis: primary manifestation of a colorectal adenocarcinoma in a very old woman.

We report the history of a very old woman with a spontaneous internal jugular vein thrombosis as the presenting feature of an occult adenocarcinoma of the caecum. Spontaneous internal jugular vein thrombosis is an unusual form of venous thrombosis. Doppler ultrasound and Computed Tomography or Magnetic Resonance Imaging should confirm signs and symptoms suggesting thrombosis. Immediate anticoagulation with heparin followed by oral anticoagulation is mandatory to reduce associated mortality and morbidity. If no risk factors for internal jugular vein thrombosis are present, a work-up for hypercoagulable states and a careful search for distant malignancy should been obtained. If screening shows no obvious malignancy, further follow-up is necessary.

A programme for short-term withdrawal from benzodiazepines in geriatric hospital inpatients: success rate and effect on subjective sleep quality.

OBJECTIVE: We tested the hypothesis that a short-term programme for withdrawal of benzodiazepines (BZD) is feasible in hospitalized geriatric patients. METHODS: Fifty-six geriatric subjects who had been taking BZD for at least 3 months were asked to discontinue these drugs upon admission to the inpatient ward. A withdrawal programme including initial substitution therapy combined with psychological consulting was offered. The usual BZD medication was replaced by either lormetazepam 1 mg or trazodone 50 mg, administered at bedtime. After 1 week of replacement therapy all sedative medication was stopped. The subjective estimations of sleep quality were evaluated four times during a period of 6 weeks. RESULTS: Forty-nine patients agreed to participate. In this group four subjects (8.2%) resumed BZD use while in the hospital and another seven subjects (14.3%) relapsed after discharge. Therefore, the overall success rate was 77.6% in the group of volunteers and 67. 9% in the total group of eligible patients. The data of the present study further demonstrate that no major withdrawal symptoms occurred and that the subjective quality of sleep remained virtually unchanged in the course of the programme. The sleep quality was not significantly different in patients on trazodone versus patients on lormetazepam. The success rate was similar in both drug substitution groups. CONCLUSIONS: Short-term withdrawal of BZD may be achieved in two-thirds of elderly hospital inpatients without deterioration of sleep quality or other deleterious side-effects.

Intensive care for very elderly patients: outcome and risk factors for in-hospital mortality.

OBJECTIVES: To evaluate outcome and risk factors, particularly the Acute Physiology and Chronic Health Evaluation (APACHE) II scoring system, for in-hospital mortality in very elderly patients after admission to an intensive care unit (ICU). METHODS: Retrospective chart review of patients > or =85 years admitted to the ICU. We recorded age, sex, previous medical history, primary diagnosis, date of admission and discharge or death, APACHE II score on admission, use of mechanical ventilation and inotropics, and complications during ICU admission. RESULTS: 104 patients > or =85 years (1.3% of all ICU admissions) were studied. The ICU and in-hospital mortality rates for these patients were 22 and 36% respectively. Factors correlated with a greater in-hospital mortality were: an admission diagnosis of acute respiratory failure (chi2; P = 0.007), the use of mechanical ventilation (chi2; P = 0.00005) and inotropes (chi2; P = 0.00001), complications during ICU admission (chi2; P = 0.004), in particular acute renal failure (chi2; P = 0.005), and an APACHE II score > or =25 (chi2; P = 0.001). The APACHE II scoring system and the use of inotropes were independently correlated with mortality. CONCLUSION: ICU and in-hospital mortality are higher in very elderly patients, particularly in those with an APACHE II score > or =25. The most important predictors of mortality are the use of inotropes and the severity of the acute illness.

Gallstone recurrence after successful shock wave therapy: the magnitude of the problem and the predictive factors.

OBJECTIVE: Reports concerning long term recurrence of gallstones after successful extracorporeal shock wave lithotripsy (ESWL) show a high probability of stone recurrence. There is still discussion on the factors influencing stone recurrence. In this study we wanted to evaluate the long term recurrence of gallstones after stone clearance with ESWL and oral bile acids, and to assess possible risk and preventive factors of stone recurrence. METHODS: A total of 322 consecutive patients with stone clearance between December 1988 and December 1995 were included. All patients were contacted for ultrasonography and were interviewed for additional information on daily intake of aspirin, NSAIDs, cholesterol lowering medication, estrogen therapy, and biliary pain during follow-up. RESULTS: A total of 187 patients were still stone-free after a mean follow-up of 35 months (range: 3-89 months); 135 patients had recurrence. There was a significant association between stone recurrence and estrogen intake (p = 0.04), number of lithotripsy sessions (p = 0.0007), time until stone disappearance (p = 0.0003), and biliary pain (p < 0.0001). There was no difference in recurrence rate between solitary and multiple stones. CONCLUSIONS: Long-term recurrence of gallstones after lithotripsy is high: < or = 69% after 6 yr. We found a significant association of stone recurrence with estrogen intake, number of lithotripsy sessions, and time until stone disappearance. Intake of aspirin or NSAIDs was not associated with decreased stone recurrence. Of the patients with recurrent stones, 57% had biliary pain.

Lyme borreliosis--a review of the late stages and treatment of four cases.

Difficulties in diagnosis of late stages of Lyme disease include low sensitivity of serological testing and late inclusion of Lyme disease in the differential diagnosis. Longer treatment modalities may have to be considered in order to improve clinical outcome of late disease stages. These difficulties clinical cases of Lyme borreliosis. The different clinical cases illustrate several aspects of late borreliosis: false negative serology due to narrow antigen composition of the used ELISA format, the need for prolonged antibiotic treatment in chronic or recurrent forms and typical presentations of late Lyme disease, such as lymphocytic meningo-encephalitis and polyradiculoneuritis.

Treatment of pancreatic pseudocysts by percutaneous drainage. Review and personal experience.

Pseudocysts are serious complications of acute and chronic pancreatitis. Asymptomatic pseudocysts require no specific treatment. Symptomatic pseudocysts can be decompressed by surgical, ultrasonographically and endoscopically guided methods. In the absence of randomised prospective trials it can not be stated that one of these technique is superior to others. Ultrasonographic and endoscopic approaches should be confined to centres with particular expertise in these techniques.

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.