Equilibration of hemoglobin concentration after transfusion in medical inpatients not actively bleeding.
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Adult↗
Biomedical subjects
R S Howard
Publications and source records attributed to R S Howard.
Parasitism, mutation accumulation and the maintenance of sex.
Two classes of models attempt to explain why obligate partheno-genesis only rarely replaces sexual reproduction in natural populations, in spite of the apparent reproductive advantage that parthenogens gain by producing only female offspring. The mutation-accumulation models suggest that sex is adaptive because it purges the genome of harmful recurrent mutations. The ecological genetic models postulate that sex is adaptive in variable environments, particularly when the relevant variation is generated by coevolutionary interactions with parasites. Both of these models have considerable merit, but would seem to have limitations. The mutation-accumulation models require high rates of mutation; the coevolutionary models require that parasites have severe fitness effects on their hosts. In addition, parasites could select for clonal diversity and thereby erode any advantage that sex gains by producing variable progeny. Here we consider the interaction between mutation accumulation and host-parasite coevolution. The results suggest that even moderate effects by parasites combined with reasonable rates of mutation could render sex evolutionarily stable against repeated invasion by clones.
Biological Evolution↗
Selection against deleterious mutations and the maintenance of biparental sex.
The mutational deterministic hypothesis postulates an advantage to sexual over asexual reproduction when mutation rates are on the order of 1.0 per genome per generation, provided that selection takes the form of a synergistic epistasis. While the efficacy of this mechanism has been investigated for infinite populations, its ability to protect sex in finite populations exhibiting stochastic dynamics remains untested. Stochastic processes have the potential to undermine protection for sex in two ways: (1) asexual lineages derived from sexual ancestors may, by chance, be founded by individuals bearing fewer than the equilibrium mean number of mutations, and (2) once established, such lineages will undergo random perturbations in the rates at which they grow and accumulate mutations. In the present study, I show using computer simulation that sexual populations of as many as 10,000 individuals are susceptible to invasion by asexual lineages for mutation rates higher than predicted under the mutational deterministic hypothesis. My simulations differ from previous investigations in that they model the progress of asexual lineages into sexual populations as both stochastic and deterministic processes for various mutation rates, selection regimes, and population sizes. It is suggested that ecological factors, such as parasitism or release from competition, could interact with selection against deleterious mutations to protect sex. To provide the sole explanation for sex, however, may require that selection against deleterious mutations be accompanied by mutation rates on the order of 2.0 per genome per generation.
Animals↗
Central alveolar hypoventilation associated with paraneoplastic brain-stem encephalitis and anti-Hu antibodies.
We describe a patient with a paraneoplastic brain-stem encephalitis due to an occult small cell carcinoma of the lung. He developed episodes of central sleep apnoea culminating in acute respiratory failure. Antibodies resembling anti-Hu antibodies were demonstrated in both serum and cerebrospinal fluid.
Animals↗
Respiratory abnormalities due to craniovertebral junction compression in rheumatoid disease.
OBJECTIVE: To assess the extent and severity of respiratory insufficiency associated with severe rheumatoid atlantoaxial dislocation and its relation to compression of the neuraxis. METHODS: Twelve patients with severe atlantoaxial dislocation due to rheumatoid disease were studied. Detailed clinical, CT myelography and respiratory assessment including nocturnal oximetry, were performed on all patients. RESULTS: All patients were severely disabled by their underlying disease but none had symptoms of hypoventilation. All the patients with C1 compression had myelopathic features. Those with medullary deformation (moulding and/or stretch) had abnormal noctural oximetry whilst no significant desaturations were seen in the remaining patients. Post-operative studies showed resolution of noctural desaturations. CONCLUSION: This study suggests that clinically unsuspected respiratory insufficiency may be common in patients with severe medullary compression associated with rheumatoid atlantoaxial dislocation. It emphasises the importance of careful respiratory monitoring including nocturnal oxygen saturation in patients with major atlantoxial dislocation due to rheumatoid disease.
Aged↗
Pseudobulbar palsy associated with trismus.
A 60 year old patient presented with an acute pseudobulbar palsy associated with trismus. A computed tomography scan revealed low attenuation areas consistent with infarction affecting the genu of the internal capsules bilaterally. Trismus has not previously been described as the presenting feature of a pseudobulbar palsy.
Brain↗
Sleep problems in multiple sclerosis.
Twenty-eight consecutive patients with multiple sclerosis (MS) were clinically evaluated to determine the presence of sleep-related disorders. There were 12 males and 16 females aged between 22 and 67 with disability ranging between 1.5 and 8.5 on Kurtzke extended disability status score (EDSS). Fifteen patients (54%) reported sleep-related problems. These included difficulties initiating sleep and/or frequent awakenings due to spasms or discomfort in the legs (8 patients), difficulty in initiating or maintaining sleep (3), habitual snoring (4) and nocturia (1). All-night oximetry was performed and the tracings analysed for the number of dips in oxygen saturation (SaO2) or more than 4%. Three patients showed significant sleep-related oxygen desaturation (> 5 dips of > 4% SaO2/h). Subsequent polysomnography performed in 2 of the 3 patients with significant oxygen desaturation confirmed the presence of sleep apnoea. MRI analysis of brain stem regions showed abnormalities in 20/22 cases. The 3 patients showing nocturnal oxygen desaturation had MRI brain stem lesions, but their locations were variable and their general appearance not different from that seen in the 17 without sleep apnoea. Sleep disturbance in MS is common but poorly recognised. It is usually due to leg spasms, pain, immobility, nocturia or medication. It is much less commonly associated with nocturnal respiratory insufficiency.
Adult↗
Use of the rocking bed in the treatment of neurogenic respiratory insufficiency.
We describe 53 patients who received ventilatory support with a rocking bed. Diagnoses included previous poliomyelitis (30), muscular dystrophy (12), motor neurone disease (4), adult-onset acid maltase deficiency (4) and a miscellaneous group (3). Patients presented with respiratory insufficiency characterized by diaphragm weakness, progressive nocturnal hypoventilation and/or acute or chronic respiratory failure. Domiciliary rocking beds were used by 43 patients for a mean of 16.0 years (range 1 month to 35 years). Most patients were able to breathe adequately by day when sitting or standing, but needed assistance by rocking bed for 6-11 h when lying down for sleep. The rocking bed was well-tolerated, and associated with both symptomatic relief and amelioration of arterial blood gas abnormalities. Seventeen of these 43 patients discontinued its use, either because of discomfort (9) or increasing respiratory insufficiency (8). The rocking bed is a valuable adjunct in the management of the respiratory insufficiency associated with neuromuscular disease.
Adult↗
A case of myopathy associated with a dystrophin gene deletion and abnormal glycogen storage.
A 30-year-old man with no family history of muscle disease presented with a progressive proximal myopathy and calf hypertrophy characteristic of Becker muscular dystrophy. A deletion of exons 45 to 48 in the dystrophin gene was confirmed by Southern blotting and multiplex polymerase chain reaction. However, muscle biopsy showed massive accumulation of glycogen, although no significant abnormality of glycolytic pathway enzymes could be demonstrated. This patient therefore has a previously undescribed myopathy associated with both Becker muscular dystrophy and a glycogen storage disorder of unknown aetiology.
Adult↗
A familial disorder associated with palatal myoclonus, other brainstem signs, tetraparesis, ataxia and Rosenthal fibre formation.
Three siblings presented with a progressive neurological disorder beginning in the third decade of life and characterised by palatal myoclonus, nystagmus, bulbar weakness and spastic tetraparesis. There was no evidence of intellectual deterioration or seizures. CT scan showed marked brainstem atrophy in two patients and basal ganglia calcification in one. MRI scan in one showed high signal in the brainstem and periventricular region and cerebral biopsy in this patient showed myelin loss and the presence of Rosenthal fibres. A similar disease affected the siblings' mother, maternal aunt and two of the aunt's daughters, suggesting an autosomal dominant mode of transmission of what appears to be a unique genetic disorder.
Adult↗
Intravenous immunoglobulin versus plasma exchange in Guillain-Barré syndrome.
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Evaluation Studies as Topic↗
Respiratory involvement in primary muscle disorders: assessment and management.
Eighty-four patients with primary disorders of muscle were referred for assessment of respiratory insufficiency between 1978 and 1991. The eventual diagnoses were: 'limb girdle syndromes' (18 patients), adult onset acid maltase deficiency (14), dystrophia myotonica (13), inflammatory disorders (10), congenital myopathies (nine), rigid spine syndromes (five), dystrophies (Duchenne (six), facioscapulohumeral (four), Becker (one)) and miscellaneous (four). Presentations were often insidious, with progressive nocturnal hypoventilation culminating in respiratory failure or arrest, recurrent respiratory tract infections, or obstructive sleep apnoea. Respiratory symptoms developed relatively early in patients with acid maltase deficiency and inflammatory disorders but parallelled the development of limb weakness in limb girdle, myotonic and congenital syndromes. Sixty-six patients received respiratory support for a median of 5 years (1-34 years) using various techniques of negative and positive pressure ventilation. Fourteen patients received short-term support for an episode of respiratory failure before being weaned, 51 required nocturnal domiciliary ventilation and one was dependent on continuous domiciliary support. Tracheostomy was performed in 32 patients and used for domiciliary nocturnal ventilation in 25. Twenty-eight patients have subsequently died.
Adult↗
Surface EMG in the recording of fasciculations.
The usefulness of multichannel surface recording of fasciculations was evaluated by a retrospective study of 116 patients with various neurological disorders. Eight channels of a conventional electroencephalograph were used with plate electrode recordings from the upper arms and legs. Wide-spread fasciculations (defined as five or more of the eight muscle groups) were recorded in 48 of 54 patients with motor neuron disease, spinal muscular atrophy or postpolio syndrome, but noted on routine clinical examination at presentation in only 6. Eleven of 23 patients with peripheral neuropathy or myelopathy had fasciculations in five or more leads compared to one clinically, and 3 of 39 with other neurological diseases had fasciculations electrically but in only one were they clinically observed. The method is a noninvasive and sensitive adjunct to clinical examination for detecting fasciculations. Its diagnostic value is limited by the relatively high incidence of fasciculations in neuropathies and myelopathies. However, this study suggests that "false negatives" are rare and that the diagnosis of motor neuron disease should be reconsidered when less than five leads shows fasciculations.
Adult↗
Respiratory involvement in multiple sclerosis.
Respiratory complications occur in advanced multiple sclerosis (MS) but may also complicate acute relapses earlier in the disease. We present 19 patients with MS who developed respiratory complications at a mean of 5.9 (range 1-12) yrs after the onset of neurological symptoms. Fourteen patients developed severe respiratory insufficiency presenting with a combination of reduced forced vital capacity (FVC), hypoxaemia or hypercapnia (12 patients) and respiratory arrest (four patients). Two patients presented with apneustic breathing, one with paroxysmal hyperventilation, one with obstructive sleep apnoea and one with bulbar weakness leading to aspiration pneumonia. Respiratory muscle weakness was a major factor in 14 patients (predominantly diaphragm involvement in six), bulbar weakness in seven patients, impaired voluntary control in three and impaired automatic control in three. Twelve patients received mechanical respiratory support of whom seven have subsequently died. The methods of support used were intermittent positive pressure ventilation (nine patients), iron lung (three), cuirass (two) and rocking bed (one). Six patients were maintained on respiratory support until they died after intervals varying from 24 h to 6 yrs (mean 17.7 mths). Five patients received temporary ventilation for between 6 d and 42 d: of these four remain alive at up to 4 yrs and one died after 16 yrs. One patient remains on domiciliary nasal intermittent positive pressure ventilation (IPPV) after 1 yr.
Adolescent↗
Ice cream scooper's hand. Report of an occupationally related stress fracture of the hand.
Stress fracture of the hand is uncommon but can be a significant source of morbidity if not promptly diagnosed. The authors present a case of metacarpal stress fracture in which the occupational history was key to the diagnosis and management of long-standing hand pain.
Female↗
Transient amnesia heralding brain stem infarction.
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Amnesia↗