Search PubMed⌕ Search

Biomedical subjects

G M Allen

Publications and source records attributed to G M Allen.

At least 19 recordsLinked to original sources
PubMed2004

Computational simulations of airflow in an in vitro model of the pediatric upper airways.

In order to understand mechanisms of gas and aerosol transport in the human respiratory system airflow in the upper airways of a pediatric subject (male aged 5) was calculated using Computational Fluid Dynamic techniques. An in vitro reconstruction of the subject's anatomy was produced from MRI images. Flow fields were solved for steady inhalation at 6.4 and 8 LPM. For validation of the numerical solution, airflow in an adult cadaver based trachea was solved using identical numerical methods. Comparisons were made between experimental results and computational data of the adult model to determine solution validity. It was found that numerical simulations can provide an accurate representation of axial velocities and turbulence intensity. Data on flow resistance, axial velocities, secondary velocity vectors, and turbulent kinetic energy are presented for the pediatric case. Turbulent kinetic energy and axial velocities were heavily dependant on flow rate, whereas turbulence intensity varied less over the flow rates studied. The laryngeal jet from an adult model was compared to the laryngeal jet in the pediatric model based on Tracheal Reynolds number. The pediatric case indicated that children show axial velocities in the laryngeal jet comparable to adults, who have much higher tracheal Reynolds numbers than children due to larger characteristic dimensions. The intensity of turbulence follows a similar trend, with higher turbulent kinetic energy levels in the pediatric model than would be expected from measurements in adults at similar tracheal Reynolds numbers. There was reasonable agreement between the location of flow structures between adults and children, suggesting that an unknown length scale correlation factor could exist that would produce acceptable predictions of pediatric velocimetry based off of adult data sets. A combined scale for turbulent intensity as well may not exist due to the complex nature of turbulence production and dissipation.

Air↗
PubMed2002

Urinary tract ultrasonography in the evaluation of haematuria--a report of over 1,000 cases.

Over a 5-year period, 1007 patients with haematuria were investigated, using a protocol based on ultrasonography as the upper tract imaging modality of choice. Intravenous urography (IVU) was only used in selected individuals, including those patients with bladder cancer suspected on cystoscopy, suspicious or malignant cytology, previous investigation for haematuria, on-going haematuria at the time of their clinic visit, a history of flank pain or hydronephrosis on ultrasonography. Of this series, 840 (83%) had visible haematuria, 158 (15%) had microscopic or chemical haematuria and 9 (0.9%) had unspecified haematuria. A total of 133 bladder transitional cell tumours, 21 renal cell cancers and 2 upper tract transitional cell cancers (TCC) were diagnosed. The sensitivity of ultrasound with respect to bladder cancer was 63% and the specificity 99%. The odds ratio of diagnosing cancer in patients with visible haematuria compared to microscopic or unspecified haematuria was 3.3. No upper tract tumours were missed using this investigational protocol. An ultrasonography-based protocol could miss fewer upper tract TCCs than a standard IVU-based service would miss renal cell cancer. Provided there is no history of flank pain, no malignant cytology, no hydronephrosis and no previously investigated haematuria, IVU could be safely omitted.

Carcinoma, Renal Cell↗
PubMed2001

Thoracoscopic sympathectomy for palmar hyperhidrosis.

Palmar hyperhidrosis (i.e., excessive sweating of the palms) usually appears at puberty and causes psychological, social, educational, and occupational problems for people who suffer from it. Although many treatments have been used, the only treatment that permanently eradicates the condition is sympathectomy. The advent of thoracoscopic surgery has allowed surgeons to perform sympathectomy as an outpatient procedure that is safe and effective and produces life-changing results for patients.

Adult↗
PubMed2001

Pelvic pain and menstrual related illnesses.

When approaching the patient with acute pelvic pain, it is imperative to keep in mind the subtle differences each diagnosis can present with. Narrowing down pelvic pain to a specific location in the body while maintaining a high index of suspicion for acute pelvic pain emergencies will aid in a more rapid and accurate diagnosis. Bear in mind that acute pelvic pain is a clinical challenge, and although an exact diagnosis maybe elusive, emergency treatment should always be provided first and foremost despite an exact diagnosis.

Acute Disease↗
PubMed2001

Ultrasound of the shoulder.

Ultrasound of the shoulder is a powerful and accurate method for the examination of the rotator cuff, biceps mechanism and the synovium. This article describes the anatomy, standard examination technique, indications, pitfalls and potential errors. It lists suggested imaging algorithms for a range of shoulder pathology.

Algorithms↗
PubMed2000

Supraspinal fatigue during intermittent maximal voluntary contractions of the human elbow flexors.

Responses to transcranial magnetic stimulation in human subjects (n = 9) were studied during series of intermittent isometric maximal voluntary contractions (MVCs) of the elbow. Stimuli were given during MVCs in four fatigue protocols with different duty cycles. As maximal voluntary torque fell during each protocol, the torque increment evoked by cortical stimulation increased from approximately 1.5 to 7% of ongoing torque. Thus "supraspinal" fatigue developed in each protocol. The motor evoked potential (MEP) and silent period in the elbow flexor muscles also changed. The silent period lengthened by 20-75 ms (lowest to highest duty cycle protocol) and recovered significantly with a 5-s rest. The MEP increased in area by >50% in all protocols and recovered significantly with 10 s, but not 5 s, of rest. These changes are similar to those during sustained MVC. The central fatigue demonstrated by the torque increments evoked by the stimuli did not parallel the changes in the electromyogram responses. This suggests that part of the fatigue developed during intermittent exercise is "upstream" of the motor cortex.

Adult↗
PubMed1999

Proximal patellar tendinosis and abnormalities of patellar tracking.

OBJECTIVE: To assess whether an association exists between patellar tendinosis and abnormal patellar tracking. DESIGN AND PATIENTS: The MRI examinations of 630 patients (i.e. 860 knees) referred with anterior knee pain over a 4-year period were assessed in retrospect for the presence of patellar tendinosis and abnormal patellar tracking. The images of the patients with patellar tendinosis were reviewed and the location within the patellar tendon was recorded. RESULTS: There were 44 knees with proximal patellar tendinosis. Twenty-four of these were considered to have normal patellar tracking and 20 to have abnormal patellar tracking. In the group of 816 knees without proximal patellar tendinosis, 581 were considered to have normal patellar tracking and 235 knees to have abnormal patellar tracking. When the two groups were compared there was a statistically significant difference in the ratio of patients with and without abnormal tracking. CONCLUSION: In patients referred with anterior knee pain or suspected abnormal patellar tracking there is a significant association between proximal patellar tendinosis and abnormal patellar tracking.

Adolescent↗
PubMed1999

Response to local anaesthetic injection as a predictor of successful hip surgery.

AIM: To compare the outcome of hip therapy with the response to local anaesthetic into the hip. MATERIALS AND METHODS: A retrospective hip arthrographic study of 60 patients complaining of hip pain was performed. The average age of the patients was 58 +/- 20 years with ratio of men to women of 11:19. Thirty-eight of these patients underwent local anaesthetic intracapsular injection. Twenty-three (61%) obtained relief from pain whereas two (5%) experienced worsened pain. RESULTS: Of the 23 patients who experienced pain relief 17 (74%) had a positive post-operative course, in comparison with eight (44%) who had a positive post-operative course from the group where intra-articular local anaesthetic was not used. It was also noted that patients over 30 years of age had favourable post-operative results in the presence or absence of local anaesthetic testing. CONCLUSION: These results indicate that hip arthrography with a pain relieving intracapsular local anaesthetic injection, is a positive post-operative prognostic factor in a patient group of disparate disorders. A positive response to local anaesthetic injection into a hip may predict which patients are likely to respond well to surgery. We advise alterations to the consent procedure to add a warning concerning the small risk of increased hip pain. If further studies were to confirm our results it may be wise to recommend that local anaesthetic intracapsular injection and judgement of its efficacy should precede many surgical procedures involving the hip.

Adolescent↗
PubMed1998

Twitch interpolation of the elbow flexor muscles at high forces.

We investigated factors affecting maximal voluntary torque and the assessment of the level of voluntary drive in the elbow flexor muscles. First, the effective compliance of the system was tested by using single, paired, and trains of four stimuli to measure voluntary activation. At high voluntary torques the responses to all these stimuli were identical, suggesting that single stimuli are adequate for estimating voluntary drive. Second, the contribution of torque from synergist elbow flexor muscles was assessed. In attempted maximal voluntary contractions (MVCs), the voluntary activation of brachioradialis (median 91.5%, range 68.9-100%) was lower than for biceps brachii (median 99.1%, range 78.5-100%; P < 0.01). This suggests extra torque may be generated by brachioradialis during elbow flexion, beyond the torque where biceps brachii is maximally activated. Finally, lengthening of the elbow flexors occurred during MVCs, due to slight shoulder movements. This would allow force to increase independently of an increase in voluntary drive.

Adult↗
PubMed1998

Human respiratory muscles: sensations, reflexes and fatiguability.

1. Given the importance of the ventilatory 'pump' muscles, it would not be surprising if they were endowed with both sensory and motor specializations. The present review focuses on some unexpected properties of the respiratory muscle system in human subjects. 2. Although changes in blood gas tension were long held not to influence sensation directly, studies in subjects who are completely paralysed show that increases in arterial CO2 levels elicit strong sensations of respiratory discomfort. 3. Stretch reflexes in human limb muscles contain a monosynaptic spinal excitation and a long-latency excitation. However, inspiratory muscles show an initial inhibition when tested with brief airway occlusions during inspiration. This inhibition does not depend critically on input from pulmonary or upper airway receptors. 4. Human inspiratory muscles (including the diaphragm) have been considered to fatigue during inspiratory resistive loading. However, recent studies using phrenic nerve stimulation to test the force produced by the diaphragm show that carbon dioxide retention (hypoventilation) and voluntary cessation of loading occur before the muscles become overtly fatigued.

Carbon Dioxide↗
PubMed1997

Effect of contraction strength on responses in biceps brachii and adductor pollicis to transcranial magnetic stimulation.

The sizes of the motor-evoked potentials (MEPs) and the durations of the silent periods after transcranial magnetic stimulation were examined in biceps brachii, brachioradialis and adductor pollicis in human subjects. Stimuli of a wide range of intensities were given during voluntary contractions producing 0-75% of maximal force (maximal voluntary contraction, MVC). In adductor pollicis, MEPs increased in size with stimulus intensity and with weak voluntary contractions (5% MVC), but did not grow larger with stronger contractions. In the elbow flexors, MEPs grew little with stimulus intensity, but increased in size with contractions of up to 50% of maximal. In contrast, the duration of the silent period showed similar changes in the three muscles. In each muscle it increased with stimulus intensity but was unaffected by changes in contraction strength. Comparison of the responses evoked in biceps brachii by focal stimulation over the contralateral motor cortex with those evoked by stimulation with a round magnetic coil over the vertex suggests an excitatory contribution from the ipsilateral cortex during strong voluntary contractions.

Arm↗
PubMed1997

Pulmonary nodule resection during lung volume reduction surgery.

Lung volume reduction surgery (LVRS) and concomitant pulmonary nodule resection can improve the respiratory function of and remove malignant lesions in patients with chronic obstructive pulmonary disease and lung cancer. Previously, using standard selection criteria, some patients with emphysema who also had lung nodules were denied surgery because of the severity of their pulmonary dysfunction. In this article, the authors report improved pulmonary function in 11 patients with severe emphysema who underwent combined LVRS and nodule resection.

Aged↗
PubMed1997

Quantitative assessments of elbow flexor muscle performance using twitch interpolation in post-polio patients: no evidence for deterioration.

A large number of patients previously affected by polio have symptoms, including increased weakness and fatigue, which are collectively known as a post-polio syndrome. Prospective measurements of strength and endurance using twitch interpolation in post-polio patients are lacking and hence the exact rate of decline in muscle function in these patients is not well defined. We therefore measured performance of the elbow flexor muscles twice, at a mean of 2.5 years apart in a group of selected post-polio subjects (Group A, n = 13) and matched control subjects (n = 11), and in a second group of unselected polio patients from a post-polio clinic (Group B, n = 40) at a mean of 1.7 years apart. All subjects performed 10 attempted maximal voluntary isometric contractions of the elbow flexor muscles, during which voluntary activation of the elbow flexor muscles was measured using a sensitive form of twitch interpolation. The first group of selected polio subjects (Group A) and matched control subjects also performed 45 min of submaximal exercise. During this time, at 5-min intervals, maximal voluntary force, voluntary activation and the amplitude of twitch responses to single and paired stimuli were measured in order to investigate central and peripheral components of muscle fatigue. There was no change in the polio patients' strength, voluntary activation or peripheral muscle endurance between testing sessions, despite an 80% probability of detecting a 2.5% change per year in these variables. The unselected group of patients from the post-polio clinic (Group B) showed no change in maximal voluntary strength or voluntary activation between the first and second test. There was an absence of decline in muscle performance in these polio patients over the test interval, despite a subjective deterioration in muscle function consistent with the 'post-polio syndrome'. This supports the view that symptoms of the post-polio syndrome are not due to a progressive neuronal dysfunction.

Adult↗
PubMed1997

Task failure with lack of diaphragm fatigue during inspiratory resistive loading in human subjects.

Task failure during inspiratory resistive loading is thought to be accompanied by substantial peripheral fatigue of the inspiratory muscles. Six healthy subjects performed eight resistive breathing trials with loads of 35, 50, 75 and 90% of maximal inspiratory pressure (MIP) with and without supplemental oxygen. MIP measured before, after, and at every minute during the trial increased slightly during the trials, even when corrected for lung volume (e.g., for 24 trials breathing air, 12.5% increase, P < 0.05). In some trials, task failure occurred before 20 min (end point of trial), and in these trials there was an increase in end-tidal PCO2 (P < 0.01), despite the absence of peripheral muscle fatigue. In four subjects (6 trials with task failure), there was no decline in twitch amplitude with bilateral phrenic stimulation or in voluntary activation of the diaphragm, even though end-tidal PCO2 rose by 1.6 +/- 0.9%. These results suggest that hypoventilation, CO2 retention, and ultimate task failure during resistive breathing are not simply dependent on impaired force-generating capacity of the diaphragm or impaired voluntary activation of the diaphragm.

Adult↗
PubMed1996

Changes in motor cortical excitability during human muscle fatigue.

1. The excitability of the motor cortex was investigated during fatiguing con of the elbow flexors in human subjects. During sustained contractions at 30 and 1 voluntary force (MVC), the short-latency electromyographic responses (EMG) evoke brachii and brachioradialis by transcranial magnetic stimulation increased in si EMG in the elbow flexors following the evoked muscle potential (silent period), duration during a sustained MVC but not during 30% MVCs nor during a sustained M muscle (adductor pollicis). 2. When the blood supply to brachioradialis was blocked with sphygmomanometer cuff sustained MVC, the changes in EMG responses to transcranial stimulation rapidly control values, This suggests that changes in these responses during fatigue wer small-diameter muscle afferents. 3. Tendon vibration during sustained MVCs indicated that the changes in the resp cortial stimulation were not mediated by reduced muscle spindle inputs. 4. Muscle action potentials evoked in brachioradialis by electrical stimulation cervicomedullary junction did not increase in size during sustained MVCs. Thus, cortically evoked responses during sustained MVCs reflects a change in cortical Although the silent period following cervicomedullary stimulation lengthened, it substantially shorter than the cortically evoked silent period. 5. The altered EMG responses to transcranial stimulation during fatigue suggest exitation and increased inhibition in the motor cortex. As these changes were un manipulation of afferent input they presumably result from intrinsic cortical pr altered voluntary drive to the motor cortex.

Action Potentials↗
PubMed1996

Supraspinal factors in human muscle fatigue: evidence for suboptimal output from the motor cortex.

1. Voluntary activation of elbow flexor muscles can be optimal during brief maximal voluntary contractions (MVCs), although central fatigue, a progressive decline in the ability to drive the muscle maximally, develops during sustained or repeated efforts. We stimulated the motor cortex and motor point in human subjects to investigate motor output during fatigue. 2. The increment in force (relative to the voluntary force) produced by stimulation of the motor point of biceps brachii increased during sustained isometric MVCs of the elbow flexors. Motoneuronal output became suboptimal during the contraction, i.e. central fatigue developed and accounted for a small but significant loss of maximal voluntary force. During 3 min MVCs, voluntary activation of biceps fell to an average of 90.7% from an average of > 99%. 3. The increment in force (relative to the voluntary force) produced by magnetic cortical stimulation was initially small (1.0%) but also increased during sustained MVCs to 9.8% (with a 2 min MVC). Thus, cortical output was not optimal at the time of stimulation nor were sites distal to the motor cortex already acting maximally. 4. A sphygmomanometer cuff around the upper arm blocked blood supply to brachioradialis near the end of a sustained MVC and throughout subsequent brief MVCs. Neither maximal voluntary force nor voluntary activation recovered during ischaemia after the sustained MVC. However, fatigue-induced changes in EMG responses to magnetic cortical stimulation recovered rapidly despite maintained ischaemia. 5. In conclusion, during sustained MVCs, voluntary activation becomes less than optimal so that force can be increased by stimulation of the motor cortex or the motor nerve. Complex changes in excitability of the motor cortex also occur with fatigue, but can be dissociated from the impairment of voluntary activation. We argue that inadequate neural drive effectively 'upstream' of the motor cortex must be one site involved in the genesis of central fatigue.

Adult↗