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Biomedical subjects

Robert D Henderson

Publications and source records attributed to Robert D Henderson.

18 recordsLinked to original sources
PubMed2006

Circadian blood pressure variation after acute stroke.

We aimed to characterise the patterns of circadian blood pressure (BP) variation after acute stroke and determine whether any relationship exists between these patterns and stroke outcome. BP was recorded manually every 4 h for 48 h following acute stroke. Patients were classified according to the percentage fall in mean systolic BP (SBP) at night compared to during the day as: dippers (fall > or = 10-<20%); extreme dippers (> or = 20%); non-dippers (> or = 0-<10%); and reverse dippers (<0%, that is, a rise in mean nocturnal SBP compared to mean daytime SBP). One hundred and seventy-three stroke patients were included in the study (83 men, 90 women; mean age 74.3 years). Four patients (2.3%) were extreme dippers, 25 (14.5%) dippers, 80 (46.2%) non-dippers and 64 (36.9%) reverse dippers. There was a non-significant trend in the proportion of patients who were dead or dependent at 3 months in the extreme dipper (p=0.59) and reverse dipper (p=0.35) groups. Non-dipping and reverse-dipping were relatively common patterns of circadian BP variation seen in acute stroke patients. These patterns were not clearly associated with outcome.

Aged↗
PubMed2006

Motor unit number estimation--a Bayesian approach.

All muscle contractions are dependent on the functioning of motor units. In diseases such as amyotrophic lateral sclerosis (ALS), progressive loss of motor units leads to gradual paralysis. A major difficulty in the search for a treatment for these diseases has been the lack of a reliable measure of disease progression. One possible measure would be an estimate of the number of surviving motor units. Despite over 30 years of motor unit number estimation (MUNE), all proposed methods have been met with practical and theoretical objections. Our aim is to develop a method of MUNE that overcomes these objections. We record the compound muscle action potential (CMAP) from a selected muscle in response to a graded electrical stimulation applied to the nerve. As the stimulus increases, the threshold of each motor unit is exceeded, and the size of the CMAP increases until a maximum response is obtained. However, the threshold potential required to excite an axon is not a precise value but fluctuates over a small range leading to probabilistic activation of motor units in response to a given stimulus. When the threshold ranges of motor units overlap, there may be alternation where the number of motor units that fire in response to the stimulus is variable. This means that increments in the value of the CMAP correspond to the firing of different combinations of motor units. At a fixed stimulus, variability in the CMAP, measured as variance, can be used to conduct MUNE using the "statistical" or the "Poisson" method. However, this method relies on the assumptions that the numbers of motor units that are firing probabilistically have the Poisson distribution and that all single motor unit action potentials (MUAP) have a fixed and identical size. These assumptions are not necessarily correct. We propose to develop a Bayesian statistical methodology to analyze electrophysiological data to provide an estimate of motor unit numbers. Our method of MUNE incorporates the variability of the threshold, the variability between and within single MUAPs, and baseline variability. Our model not only gives the most probable number of motor units but also provides information about both the population of units and individual units. We use Markov chain Monte Carlo to obtain information about the characteristics of individual motor units and about the population of motor units and the Bayesian information criterion for MUNE. We test our method of MUNE on three subjects. Our method provides a reproducible estimate for a patient with stable but severe ALS. In a serial study, we demonstrate a decline in the number of motor unit numbers with a patient with rapidly advancing disease. Finally, with our last patient, we show that our method has the capacity to estimate a larger number of motor units.

Action Potentials↗
PubMed2005

The effect of admission physiological variables on 30 day outcome after stroke.

INTRODUCTION: Potentially modifiable physiological variables may influence stroke prognosis but their independence from modifiable factors remains unclear. METHODS: Admission physiological measures (blood pressure, heart rate, temperature and blood glucose) and other unmodifiable factors were recorded from patients presenting within 48 hours of stroke. These variables were compared with the outcomes of death and death or dependency at 30 days in multivariate statistical models. RESULTS: In the 186 patients included in the study, age, atrial fibrillation and the National Institutes of Health Stroke Score were identified as unmodifiable factors independently associated with death and death or dependency. After adjusting for these factors, none of the physiological variables were independently associated with death, while only diastolic blood pressure (DBP) > or = 90 mmHg was associated with death or dependency at 30 days (p = 0.02). CONCLUSIONS: Except for elevated DBP, we found no independent associations between admission physiology and outcome at 30 days in an unselected stroke cohort. Future studies should look for associations in subgroups, or by analysing serial changes in physiology during the early post-stroke period.

Adolescent↗
PubMed2005

Chronic inflammatory demyelinating polyneuropathy and respiratory failure.

Neuromuscular respiratory failure is not considered to be a clinical feature of chronic inflammatory demyelinating polyneuropathy (CIDP). We present 4 patients with CIDP who required respiratory assistance and mechanical ventilation. Two patients needed emergent intubation and one patient lapsed in a stupor from hypercapnia. Respiratory failure in CIDP should be considered exceptional, but more formal studies in CIDP may be needed to assess its prevalence.

Aged↗
PubMed2005

Assessment of disease progression in motor neuron disease.

Motor neuron disease (MND) is characterised by progressive deterioration of the corticospinal tract, brainstem, and anterior horn cells of the spinal cord. There is no pathognomonic test for the diagnosis of MND, and physicians rely on clinical criteria-upper and lower motor neuron signs-for diagnosis. The presentations, clinical phenotypes, and outcomes of MND are diverse and have not been combined into a marker of disease progression. No single algorithm combines the findings of functional assessments and rating scales, such as those that assess quality of life, with biological markers of disease activity and findings from imaging and neurophysiological assessments. Here, we critically appraise developments in each of these areas and discuss the potential of such measures to be included in the future assessment of disease progression in patients with MND.

Algorithms↗
PubMed2005

Guidelines for filming digital camera video clips for the assessment of gait and movement disorders by teleneurology.

Digital still cameras capable of filming short video clips are readily available, but the quality of these recordings for telemedicine has not been reported. We performed a blinded study using four commonly available digital cameras. A simulated patient with a hemiplegic gait pattern was filmed by the same videographer in an identical, brightly lit indoor setting. Six neurologists viewed the blinded video clips on their PC and comparisons were made between cameras, between video clips recorded with and without a tripod, and between video clips filmed on high- or low-quality settings. Use of a tripod had a smaller effect than expected, while images taken on a high-quality setting were strongly preferred to those taken on a low-quality setting. Although there was some variability in video quality between selected cameras, all were of sufficient quality to identify physical signs such as gait and tremor. Adequate-quality video clips of movement disorders can be produced with low-cost cameras and transmitted by email for teleneurology purposes.

Evaluation Studies as Topic↗
PubMed2004

Decrement in surface-recorded motor unit potentials in amyotrophic lateral sclerosis.

BACKGROUND: A decrement to repetitive stimulation sometimes occurs in ALS. The ability to isolate individual surface-recorded motor unit potentials (SMUPs) indirectly allows the analysis of the decrement by comparing the effect of different rates of stimulation on the size of the isolated SMUP. METHODS: The median or ulnar nerve or both were studied in 11 patients with reduced compound muscle action potential (CMAP) amplitude. Isolated SMUPs were identified and studied using standard electrophysiologic techniques. One- and 3-Hz stimulation frequencies were compared in isolated SMUP by collecting > or =100 responses to a nonvarying stimulus. Changes in individual SMUP size and activation with change in stimulus frequency were compared with the size of the SMUP and with the CMAP decrement to a train-of-four stimulus. RESULTS: Fifteen studies were obtained from the 11 subjects. Eight studies showed a decrement of the total CMAP to a train-of-four stimulus. Twenty-nine well-defined, isolated SMUPs were studied. SMUP size reductions of 1 to 16% occurred with an increase in the stimulus frequency. No conduction block of individual SMUP occurred with the SMUP size reduction. No consistent change in variance was found. The SMUP size reduction was related to the size of the CMAP and the CMAP train-of-four decrement and less so to the size of the SMUP. CONCLUSION: The decrement of the total compound muscle action potential to repetitive stimulation appears to arise from individual surface-recorded motor unit potentials and does not result from loss of activation of the main motor axon. The probable mechanism lies at the nerve terminal and neuromuscular junction. No consistent change in variance occurs with different rates of stimulation.

Action Potentials↗
PubMed2004

Impact of premorbid undernutrition on outcome in stroke patients.

BACKGROUND AND PURPOSE: To assess the prevalence of premorbid undernutrition and its impact on outcomes 1 month after stroke. METHODS: The study recruited from consecutive stroke admissions during a 10-month period. Premorbid nutritional status (using the subjective global assessment [SGA]), premorbid functioning (modified Rankin scale [MRS]), and stroke severity (National Institutes of Health Stroke Scale [NIHSS] score) were assessed at admission. The associations between premorbid nutritional status, poor outcome (defined as MRS > or =3), and mortality were examined before and after adjustment for confounding variables, including age, gender, stroke risk factors, stroke severity, and admission serum albumin. RESULTS: Thirty of 185 patients were assessed as having undernutrition at admission. Significant unadjusted associations were observed between undernutrition and poor outcome (odds ratio [OR], 3.4; 95% CI, 1.3 to 8.7; P=0.01), and mortality (OR, 3.1, 95% CI, 1.3 to 7.7; P=0.02) at 1 month. NIHSS, age, and premorbid MRS were also significantly associated with poor outcomes. After adjustment for these factors, the effect size of associations remained important but not significant (poor outcome: OR, 2.4; 95% CI, 0.7 to 9.0, P=0.18; mortality: OR, 3.2; 95% CI, 1.0 to 10.4, P=0.05). CONCLUSIONS: Premorbid undernutrition, as assessed using the SGA, appears to be an independent predictor of poor stroke outcome. Stroke prevention strategies should target undernutrition in the population at risk for stroke to improve outcomes.

Aged↗
PubMed2004

More than one dilemma.

We present an unusual case that highlights a number of management dilemmas: the cause, investigation and treatment of subarachnoid hemmorrhage in patients iwth vascular connective tissue diseases; the further investigation of small aneurysms identified on CT angiography; and the difficulties associated with anticoagulation, mechanical cardiac valves and cerebral hemorrhage.

Adult↗
PubMed2003

Emergency intubation for respiratory failure in Guillain-Barré syndrome.

BACKGROUND: The consequences of emergency intubation in Guillain-Barré syndrome are not known. OBJECTIVE: To review data from patients admitted to the intensive care unit with recent diagnosis of Guillain-Barré syndrome and intubation for respiratory failure. DESIGN, SETTING, AND PATIENTS: The database of patients with Guillain-Barré syndrome admitted to the intensive care units during the past 2 decades was reviewed. Emergency intubation was defined as need for ventilation in a patient with sudden dyspnea, cyanosis, or respiratory arrest. Outcome and pulmonary morbidity were assessed by comparing these patients with patients intubated electively. RESULTS: Six patients were intubated for acute respiratory distress and 1 patient for respiratory arrest. Thirty-six patients were intubated electively. Prolonged weaning was twice as common in the emergent group as in the elective group; a larger sample size might have demonstrated statistical significance. One patient with respiratory arrest developed marked anoxic encephalopathy; in all others, no differences were found in mortality, pulmonary morbidity, or duration of ventilatory assistance. None of the emergency intubations occurred in the last 15 years of the study. CONCLUSIONS: Emergency intubation in Guillain-Barré syndrome is uncommon but, when associated with respiratory arrest, can lead to anoxic encephalopathy. Duration of ventilator use and pulmonary morbidity are not increased in these patients.

Emergency Treatment↗
PubMed2003

Effect of changing data collection parameters on statistical motor unit number estimates.

The effect of number of samples and selection of data for analysis on the calculation of surface motor unit potential (SMUP) size in the statistical method of motor unit number estimates (MUNE) was determined in 10 normal subjects and 10 with amyotrophic lateral sclerosis (ALS). We recorded 500 sequential compound muscle action potentials (CMAPs) at three different stable stimulus intensities (10-50% of maximal CMAP). Estimated mean SMUP sizes were calculated using Poisson statistical assumptions from the variance of 500 sequential CMAP obtained at each stimulus intensity. The results with the 500 data points were compared with smaller subsets from the same data set. The results using a range of 50-80% of the 500 data points were compared with the full 500. The effect of restricting analysis to data between 5-20% of the CMAP and to standard deviation limits was also assessed. No differences in mean SMUP size were found with stimulus intensity or use of different ranges of data. Consistency was improved with a greater sample number. Data within 5% of CMAP size gave both increased consistency and reduced mean SMUP size in many subjects, but excluded valid responses present at that stimulus intensity. These changes were more prominent in ALS patients in whom the presence of isolated SMUP responses was a striking difference from normal subjects. Noise, spurious data, and large SMUP limited the Poisson assumptions. When these factors are considered, consistent statistical MUNE can be calculated from a continuous sequence of data points. A 2 to 2.5 SD or 10% window are reasonable methods of limiting data for analysis.

Action Potentials↗