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Biomedical subjects

Tom Chau

Publications and source records attributed to Tom Chau.

At least 19 recordsLinked to original sources
PubMed2006

A radial basis classifier for the automatic detection of aspiration in children with dysphagia.

BACKGROUND: Silent aspiration or the inhalation of foodstuffs without overt physiological signs presents a serious health issue for children with dysphagia. To date, there are no reliable means of detecting aspiration in the home or community. An assistive technology that performs in these environments could inform caregivers of adverse events and potentially reduce the morbidity and anxiety of the feeding experience for the child and caregiver, respectively. This paper proposes a classifier for automatic classification of aspiration and swallow vibration signals non-invasively recorded on the neck of children with dysphagia. METHODS: Vibration signals associated with safe swallows and aspirations, both identified via videofluoroscopy, were collected from over 100 children with neurologically-based dysphagia using a single-axis accelerometer. Five potentially discriminatory mathematical features were extracted from the accelerometry signals. All possible combinations of the five features were investigated in the design of radial basis function classifiers. Performance of different classifiers was compared and the best feature sets were identified. RESULTS: Optimal feature combinations for two, three and four features resulted in statistically comparable adjusted accuracies with a radial basis classifier. In particular, the feature pairing of dispersion ratio and normality achieved an adjusted accuracy of 79.8 +/- 7.3%, a sensitivity of 79.4 +/- 11.7% and specificity of 80.3 +/- 12.8% for aspiration detection. Addition of a third feature, namely energy, increased adjusted accuracy to 81.3 +/- 8.5% but the change was not statistically significant. A closer look at normality and dispersion ratio features suggest leptokurticity and the frequency and magnitude of atypical values as distinguishing characteristics between swallows and aspirations. The achieved accuracies are 30% higher than those reported for bedside cervical auscultation. CONCLUSION: The proposed aspiration classification algorithm provides promising accuracy for aspiration detection in children. The classifier is conducive to hardware implementation as a non-invasive, portable "aspirometer". Future research should focus on further enhancement of accuracy rates by considering other signal features, classifier methods, or an augmented variety of training samples. The present study is an important first step towards the eventual development of wearable intelligent intervention systems for the diagnosis and management of aspiration.

Journal Article↗
PubMed2006

A novel instrument for quantifying grip activity during handwriting.

OBJECTIVE: To describe and exemplify a noninvasive instrumentation system that uniquely records grip forces exerted on the barrel of the writing utensil along with typical temporal and kinematic parameters. DESIGN: Exploratory case series. SETTING: A tertiary care, pediatric rehabilitation hospital. PARTICIPANTS: Convenience sample of 6 primary school children with spastic hemiplegic cerebral palsy (CP) with documented fine motor difficulties and 6 children with no known handwriting difficulties. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Grip and normal forces during handwriting. RESULTS: The instrumentation revealed nontrivial correlations between normal and grip forces (0.55 +/- 0.16), a temporal delay between normal and grip forces (97.7 +/- 16 ms), and a consistent grip-to-normal force ratio (4.3 +/- 1.5), across all participants. Grip force distributions agreed intuitively with qualitative observations of individual grasps of the writing utensil. Further, 5 new parameters derived from grip force measures statistically differentiated between able-bodied children and those with hemiplegic CP. CONCLUSIONS: The proposed instrumentation provides new insight into grip and normal force coordination and has the potential to uncover discriminatory grip force characteristics between writers with and without handwriting difficulties. Further study with larger populations is required to define functional ranges for the new grip measures.

Biomechanical Phenomena↗
PubMed2005

Electroactive polymeric sensors in hand prostheses: bending response of an ionic polymer metal composite.

In stark contrast to the inspiring functionality of the natural hand, limitations of current upper limb prostheses stemming from marginal feedback control, challenges of mechanical design, and lack of sensory capacity, are well-established. This paper provides a critical review of current sensory systems and the potential of a selection of electroactive polymers for sensory applications in hand prostheses. Candidate electroactive polymers are reviewed in terms of their relevant advantages and disadvantages, together with their current implementation in related applications. Empirical analysis of one of the most novel electroactive polymers, ionic polymer metal composites (IPMC), was conducted to demonstrate its potential for prosthetic applications. With linear responses within the operating range typical of hand prostheses, bending angles, and bending rates were accurately measured with 4.4+/-2.5 and 4.8+/-3.5% error, respectively, using the IPMC sensors. With these comparable error rates to traditional resistive bend sensors and a wide range of sensitivities and responses, electroactive polymers offer a promising alternative to more traditional sensory approaches. Their potential role in prosthetics is further heightened by their flexible and formable structure, and their ability to act as both sensors and actuators.

Artificial Limbs↗
PubMed2005

Managing variability in the summary and comparison of gait data.

Variability in quantitative gait data arises from many potential sources, including natural temporal dynamics of neuromotor control, pathologies of the neurological or musculoskeletal systems, the effects of aging, as well as variations in the external environment, assistive devices, instrumentation or data collection methodologies. In light of this variability, unidimensional, cycle-based gait variables such as stride period should be viewed as random variables and prototypical single-cycle kinematic or kinetic curves ought to be considered as random functions of time. Within this framework, we exemplify some practical solutions to a number of commonly encountered analytical challenges in dealing with gait variability. On the topic of univariate gait variables, robust estimation is proposed as a means of coping with contaminated gait data, and the summary of non-normally distributed gait data is demonstrated by way of empirical examples. On the summary of gait curves, we discuss methods to manage undesirable phase variation and non-robust spread estimates. To overcome the limitations of conventional comparisons among curve landmarks or parameters, we propose as a viable alternative, the combination of curve registration, robust estimation, and formal statistical testing of curves as coherent units. On the basis of these discussions, we provide heuristic guidelines for the summary of gait variables and the comparison of gait curves.

Journal Article↗
PubMed2005

A self-contained, mechanomyography-driven externally powered prosthesis.

The measurement of the low-frequency (5-50 Hz) "sounds" or vibrations produced by contracting muscles is termed mechanomyography (MMG). As a control signal for powered prostheses, MMG offers several advantages over conventional myoelectric control, including, nonspecific sensor placement, distal signal measurement, robustness to changing skin impedance, and reduced sensor costs. The objectives of this study were to demonstrate 2-function prosthesis control based on a triplet of distally recorded, normalized root mean square MMG signals and to identify necessary future research toward full clinical implementation of MMG signals in upper-limb externally powered prostheses. A novel self-contained MMG-driven prosthesis for below-elbow amputees was designed, implemented, and preliminarily tested on 2 subjects. This prosthesis was composed of specialized software and hardware modules that emulate a 2-site electromyography sensing system. Although the use of MMG signals for prosthesis control has been shown previously, we report, for the first time, successful control within a self-contained unit in unconstrained environments. Specifically, essential requirements for practical use, such as standardized sensor attachment, basic noise elimination, and miniaturization of the system, have been achieved. Both subjects were able to voluntarily open and close the prosthesis hand with no significant delays from intention to action (approximately 120 ms). Quantitative analyses revealed 88% and 71% control accuracy for subjects 1 and 2, respectively.

Adult↗
PubMed2005

Biochemical and etiological characteristics of acute hyponatremia in the emergency department.

Hyponatremia can be classified as acute or chronic depending on its duration, and treatment options are tailored to this classification. However, it is sometimes difficult to differentiate acute from chronic hyponatremia in the Emergency Department (ED). The objective of this study was to identify characteristics to help diagnose and manage acute hyponatremia in the ED. Patients with acute hyponatremia in the ED were enrolled from a retrospective 2-year chart review. Eleven patients (0.8%) were identified with acute hyponatremia out of a total of 1321 hyponatremic patients. There were nine women and two men. The mean age was 48.9 years. The mean sodium (Na(+)) level was 115+/-4 mmol/L. Accompanying biochemical abnormalities included hypouricemia and hypouremia with increased fractional excretions of uric acid (UA) and urea. The estimated amount of water intake ranged from 2.5 to 10 liters (mean, 5.1+/-2.3 liters) during the day before ED presentation. All patients were treated with hypertonic saline and furosemide at a correction rate of 1.6+/-0.5 mmol/L/h. No patients had neurological sequelae after treatment. The causes of acute hyponatremia included induction of abortion with oxytocin (n=1), primary polydipsia on neuroleptic agents (n=2), polyethylene glycol (PEG) preparation for colonoscopy (n=1), diuretic therapy for hypertension (n=4), ecstasy use (n=1), and weight-reducing herbal teas (n=2). We conclude that in the right clinical setting, high free water intake and low serum urea and UA favor acute hyponatremia. A detailed drug history may be helpful in the differential diagnosis of acute hyponatremia.

Acute Disease↗
PubMed2005

Acquired bartter-like syndrome associated with gentamicin administration.

Although acute nonoliguric renal failure is a well-known nephrotoxic effect of aminoglycoside antibiotics, less recognized is acquired Bartter-like syndrome. Herein, we describe four female patients who presented with marked paresthesia, muscle weakness, and tetany following gentamicin therapy with total dose ranging from 1.2 g to 2.6 g. All were normotensive. Biochemical abnormalities included hypokalemia (K+ 1.8-2.3 mmol/L), metabolic alkalosis (HCO(3-) 31.9-34.2 mmol/L), hypomagnesemia (Mg2+ 0.9-1.2 mg/dL), hypermagnesiuria (fractional excretion of Mg 3-6%), hypocalcemia (free Ca2+ 2.0-4.1 mg/dL), and hypercalciuria (molar ratio of Ca2+/creatinine 0.23-0.53), all consistent with Bartter-like syndrome. Serum immunoreactive parathyroid hormone concentration was low despite the hypocalcemia. The Bartter-like syndrome lasted for 2 to 6 weeks after cessation of gentamicin, coupled with supplementation of K+, Ca2+, and Mg2+. These biochemical abnormalities resembled those seen in patients with gain-of-function mutations in the calcium-sensing receptor. We hypothesize that gentamicin, a polyvalent cationic molecule, induces the action of calcium-sensing receptor on the thick ascending loop of Henle and distal convoluted tubule to cause renal wasting of Na+, K+, Cl-, Ca2+, and Mg2+.

Adult↗
PubMed2005

A mathematical model for source separation of MMG signals recorded with a coupled microphone-accelerometer sensor pair.

Recent advances in sensor technology for muscle activity monitoring have resulted in the development of a coupled microphone-accelerometer sensor pair for physiological acousti signal recording. This sensor can be used to eliminate interfering sources in practical settings where the contamination of an acoustic signal by ambient noise confounds detection but cannot be easily removed [e.g., mechanomyography (MMG), swallowing sounds, respiration, and heart sounds]. This paper presents a mathematical model for the coupled microphone-accelerometer vibration sensor pair, specifically applied to muscle activity monitoring (i.e., MMG) and noise discrimination in externally powered prostheses for below-elbow amputees. While the model provides a simple and reliable source separation technique for MMG signals, it can also be easily adapted to other aplications where the recording of low-frequency (< 1 kHz) physiological vibration signals is required.

Acceleration↗
PubMed2005

Investigating the stationarity of paediatric aspiration signals.

An aspiration signal is the time-varying anterior-posterior acceleration measured infero-anterior to the thyroid notch when foreign material enters the airway during inspiration. The hypothesis of weak stationarity is tested on aspiration signals by the reverse arrangements test. Results indicate that aspiration signals cannot be uniformly regarded as weakly stationary. Forty-five percent of the examined signals violated the stationarity hypothesis. For these signals, time-varying variance and spectral density structure are identified as major sources of nonstationarity. Stationarity test results generally corroborate qualitative clinical descriptions of aspiration. However, stationarity analysis indicates that aspiration signals are highly heterogenous, a finding which poses significant challenges to the automatic detection of aspirations by accelerometry.

Acceleration↗
PubMed2005

Diagnosis of ankylosis in permanent incisors by expert ratings, Periotest and digital sound wave analysis.

The objectives of this investigation were to: (i) assess the reliability of expert raters to detect ankylosis from recordings of percussion sounds, (ii) measure differences in Periotest values (PTV) between ankylosed and non-ankylosed incisors and (iii) identify characteristic differences in recorded percussion sounds from ankylosed and non-ankylosed incisors using digital sound wave analysis. A convenience sample of healthy children (age range 7-18 years) was invited to participate. Ankylosis group children had one or more documented ankylosed maxillary incisors. Control group children had intact, non-ankylosed incisors. Digital recordings of percussion sounds and PTV were acquired for each incisor of interest. Four experienced pediatric dentists rated the randomized percussion sound pairs for the presence of ankylosis. Percussion sounds were also subjected to digital sound wave analysis. Overall agreement for the expert raters was substantial (kappa = 0.7). Intra-rater agreement was substantial to almost perfect (kappa = 0.6-0.9). Diagnosis of ankylosis demonstrated sensitivity of 76-92% and specificity of 74-100%. PTV from ankylosed incisors were statistically lower than PTV from non-ankylosed incisors. Ankylosed incisor digital sound wave signals exhibited significantly more energy in high-frequency bands than non-ankylosed incisors. This investigation demonstrated that: (i) experienced pediatric dentists reliably detected ankylosis by percussion sound alone; (ii) PTV for ankylosed incisors were statistically lower than PTV from non-ankylosed incisors; and (iii) ankylosed incisors exhibited a higher proportion of their signal energy in high-frequency bands.

Adolescent↗
PubMed2004

A hidden cause of hypokalemic paralysis in a patient with prostate cancer.

Hypokalemic paralysis is a medical emergency due to the risks of cardiac arrhythmia, respiratory failure, and rhabdomyolysis. Besides supplementing patients with KCl to hasten recovery, the astute physician must search for the underlying cause to avoid missing a treatable and curable disorder. We report on an elderly Korean man who presented with marked limb paralysis, myalgias, and mild hypertension. He had prostate cancer treated with orchiectomy and hormone therapy 2 years previously. The major biochemical abnormalities were hypokalemia (K+: 1.7 mmol/l) associated with high renal K+ wasting and metabolic alkalosis (HCO3-: 42.6 mmol/l). Low plasma renin activity, low aldosterone concentration, and normal cortisol concentration pointed to a state of pseudohyperaldosteronism. While reviewing his drug history, the patient revealed he had been consuming eight packs (100 ml/pack) of a Korean herbal tonic daily to treat his prostate cancer for the past 2 months. A significant amount of glycyrrhizic acid (0.23 mg/ml), an active ingredient of licorice, was detected in the tonic. Discontinuation of the herbal tonic along with KCl supplementation achieved recovery in 2 weeks. As many complementary/alternative medicines for cancer contain licorice, this must be kept in mind as a cause of hypokalemia in cancer patients.

Aged↗
PubMed2004

Acute hypercapnic respiratory failure due to thyrotoxic periodic paralysis.

Acute hypercapnic respiratory failure is a potentially life-threatening complication of profound hypokalemia usually seen in patients with large total-body potassium (K+) deficits. It has rarely been reported in thyrotoxic periodic paralysis (TPP), which is due to intra-cellular shifts of K+. The authors report on a 29-year-old man who presented with sudden onset of muscle paralysis in all extremities and acute progressive respiratory insufficiency requiring artificial respiratory support. He was treated with intravenous KCl. After six hours, muscular strength had returned to normal, with plasma K+ concentration of 3.0 mmol/L. At the eighth hour, rebound hyperkalemia (6.6 mmol/L) developed with high-tented T waves, even after the KCl was discontinued. Ventilatory support was uneventfully weaned at 14 hours. Elevated free thyroxine and undetectable thyroid-stimulating hormone confirmed the diagnosis of TPP. TPP should be kept in mind as a cause of acute respiratory failure in association with acute muscle weakness to avoid delayed diagnosis and improper management.

Acute Disease↗
PubMed2004

On the robustness of stride frequency estimation.

The robustness of stride frequency estimation (location and spread) from stride period data is investigated using influence functions. Theoretical analysis reveals that stride frequency estimates by Stokes et al. and by direct calculation have unbounded influence functions and zero breakdown points, implying a lack of both local and global robustness. Comparison of estimates obtained from an ensemble of pathological gait stride time series shows that on average, differences among estimators are not statistically significant (p > or = 0.59) for long time series (hundreds of strides). Specific circumstances under which nonrobust estimates depart from robust estimates are investigated in terms of outlier influence. We recommend some heuristic rules-of-thumb for prudent selection of nonrobust stride frequency estimators for a given stride time series. The theoretical and empirical estimator comparisons suggest that in general, more research on estimator robustness in quantitative gait analysis is warranted.

Adult↗
PubMed2003

A simple and rapid approach to hypokalemic paralysis.

Hypokalemia with paralysis (HP) is a potentially reversible medical emergency. It is primarily the result of either hypokalemic periodic paralysis (HPP) caused by an enhanced shift of potassium (K(+)) into cells or non-HPP resulting from excessive K(+) loss. Failure to make a distinction between HPP and non-HPP could lead to improper management. The use of spot urine for K(+) excretion rate and evaluation of blood acid-base status could be clinically beneficial in the diagnosis and management. A very low rate of K(+) excretion coupled with the absence of a metabolic acid-base disorder suggests HPP, whereas a high rate of K(+) excretion accompanied by either metabolic alkalosis or metabolic acidosis favors non-HPP. The therapy of HPP requires only small doses of potassium chloride (KCl) to avoid rebound hyperkalemia. In contrast, higher doses of KCl should be administered to replete the large K(+) deficiency in non-HPP.

Acid-Base Equilibrium↗
PubMed2003

An unrecognized cause of paralysis in ED: thyrotoxic normokalemic periodic paralysis.

Hypokalemic paralysis associated with hyperthyroidism (TPP) is a well-known acute electrolyte and muscle function disorder. Lesser known is normokalemic periodic paralysis associated with hyperthyroidism. We describe two cases of young men with acute muscular paralysis and bilateral impairment of sensation over the lower legs who had normal plasma potassium concentrations. They were initially misdiagnosed as having Guillain-Barré syndrome or hysterical paralysis. However, thyroid function tests showed elevated serum T(3) and T(4) and markedly depressed thyroid-stimulating hormone findings consistent with hyperthyroidism. Control of the hyperthyroidism completely abolished their periodic paralysis. Thyrotoxic normokalemic periodic paralysis (TNPP) should be kept in mind as a cause of acute muscle weakness to avoid missing a treatable and curable condition.

Adult↗
PubMed2003

Thyrotropin-secreting pituitary adenoma presenting as hypokalemic periodic paralysis.

Thyrotropin (TSH)-secreting pituitary adenoma presenting with hypokalemic periodic paralysis is extraordinarily rare and may be misdiagnosed. We describe a 44-year-old man who suffered from acute muscle weakness and inability to ambulate upon awakening in the morning. Physical examination showed hypertension, tachycardia, and symmetrical flaccid paralysis of all extremities. The major biochemical abnormality was hypokalemia (K+, 2.0 mmol/L) with low urine K+ excretion. A thyroid function study revealed elevated thyroid hormone levels and inappropriately high TSH concentrations (2.10 microU/mL). Brain magnetic resonance imaging delineated a pituitary tumor with suprasellar extension. After trans-sphenoidal removal of tumor, he became clinically and biochemically euthyroid without any further attack of paralysis. Pathological findings confirmed a TSH-secreting adenoma with exclusive TSH immunostaining. TSH-secreting pituitary adenoma must be kept in the differential diagnosis in any thyrotoxic periodic paralysis patients with detectable TSH levels to avoid delaying diagnosis and management.

Adenoma↗
PubMed2003

An unusual cause of hypokalemic paralysis: chronic licorice ingestion.

Long-term licorice ingestion is a well-known cause of secondary hypertension and hypokalemia. Nevertheless, its initial presentation with a very severe degree of hypokalemia and paralysis is exceedingly rare. We report an elderly Asian man who presented to the emergency department with marked muscle weakness that progressed to paralysis. His blood pressure was 160/96 mm Hg. The major biochemical abnormalities were hypokalemia (plasma K+ concentration, 1.8 mmol/L) and metabolic alkalosis (HCO - 3 , 36 mmol/L). His renal potassium excretion was higher (transtubular potassium gradient of 9). Plasma renin activity and aldosterone concentration were suppressed and cortisol concentration was normal. A detailed history revealed that he had ingested tea flavored with 100 g of natural licorice root containing 2.3% glycyrrhizic acid daily for 3 years. Note that renal potassium wasting and hypertension persisted for 2 weeks after discontinuing licorice consumption along with KCl supplement and spironolactone. Long-term licorice ingestion should be kept in mind as a cause of paralysis with an extreme degree of hypokalemia to avoid missing this recognizable and curable medical disorder.

Acid-Base Imbalance↗