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Biomedical subjects

G Walsh

Publications and source records attributed to G Walsh.

At least 91 records · Page 5Linked to original sources
PubMed1989

Biochemical and functional correlates of myocardium-like transformed skeletal muscle as a power source for cardiac assist devices.

Skeletal muscles, such as the latissimus dorsi muscle, can be transformed to gain considerable fatigue resistance to be suitable either for cardiomyoplasty, or to power a cardiac assist device. Such transformation of the skeletal muscle can be achieved by low frequency electrical stimulation for several weeks. In this article, we reviewed the stimulation protocol, and subsequent histochemical, biochemical, and functional changes in the skeletal muscle, and compared them to those of the cardiac muscle. The parameters that should be useful for stimulating such a muscle to assist the heart are defined. The issues currently under study, including the optimal transformation parameters, the feasibility of working transformation, and the importance of device design to minimize vascular compromise of the muscle, are also discussed. It is concluded that there is a great potential to use the plasticity of skeletal muscle for clinical purposes, specifically by transforming the skeletal muscle to resemble the myocardium in order to use it either to replace or repair the myocardium, or as the endogenous power source for a cardiac assist device.

Animals↗
PubMed1989

The effect of defocus on the contrast and phase of the retinal image of a sinusoidal grating.

The variation with defocus in the contrast and phase of the retinal image of a grating stimulus is computed from a knowledge of the measured wavefront aberration of individual eyes. Contrast or modulation transfer is generally lower than in the aberration-free, diffraction-limited case, even at a pupil size of 3 mm, and marked spatial phase shifts, which can be seen as sideways shifts in the retinal image, frequently occur. A simple demonstration of these effects is given. The possible significance of the focus-dependent spatial phase shifts for the phase discrimination of the visual system and accommodation is discussed.

Accommodation, Ocular↗
PubMed1988

Visual sensitivity to temporal change in focus and its relevance to the accommodation response.

Measurements were made of the ability of observers, whose accommodation had been paralysed, to detect the small changes in contrast resulting from sinusoidal, oscillatory changes in the dioptric focus of test objects, as a function of the mean position of focus. Variables studied included the form and wavelength composition of the test object, the diameter of the entrance pupil of the eye and the temporal frequency of the focus change. The dioptric amplitudes of the thresholds found (approximately 0.1 D) were comparable with the normally observed amplitudes of the microfluctuations of the accommodation system of the eye. A maximum for the threshold change of focus was found to occur about a mean position of focus corresponding to the nominal "best-focus". Two threshold minima occurred symmetrically on either side of this position of optimal mean focus; the positions of these minima depended on the spatial frequency content of the test object and the pupil diameter. The results are interpreted in terms of the corresponding through-focus changes in optical modulation transfer of the eye and data on the sensitivity of the visual system to spatial and temporal modulation. For sinusoidal grating test objects, it appears that the results can qualitatively be explained if it is assumed that the detectable focus change is such that the ratio of the modulation change in the retinal image, produced by the focus change, to the modulation at the mean position of focus is constant. Results for targets of broad spatial bandwidth suggest that sensitivity to focus change may be dominated by spatial frequency components approximately 5 c/deg. The implications of the data for the understanding of the accommodation control system are briefly considered.

Accommodation, Ocular↗
PubMed1988

The effect of pupil centration and diameter on ocular performance.

The variation in sphero-cylindrical refractive error with position in the human eye pupil is derived from the wavefront error of two subjects. The modulation transfer function is also calculated for 1, 2 and 3 mm pupils decentred 1 and 2 mm nasally and temporally. Whilst decentration causes relatively little difference in the M.T.F. at the smaller pupil size, it can produce marked degradation for the larger pupils which can be of significance in the experimental determination of contrast sensitivity or other visual functions.

Humans↗
PubMed1988

Patterns of breast relapse after local excision +/- radiotherapy for early stage breast cancer.

One hundred patients with breast recurrence have been identified from patients at the Royal Marsden Hospital, treated by local excision +/- radiotherapy for early stage primary invasive breast cancer between 1961 and 1985. The mean follow-up was 58 months (range 1 month - 19 years). In 74/100 patients, breast recurrence occurred within the breast parenchyma, was not associated with systemic relapse and carried a relatively good prognosis with a median survival of 77 months from the time of breast relapse. In 67 patients with parenchymal relapse in whom the site of relapse could be reliably compared with that of the original tumour, 60 (90%) patients developed recurrent tumours at or close to the primary site. In 24/100 patients, breast recurrence occurred in the overlying skin and in only two of these patients (2% of total) did recurrence actually occur within the scar tissue. Skin relapse was associated with systemic relapse and carried a relatively poor prognosis with a median survival of 36 months from the time of recurrence. The pattern of breast relapse was similar in irradiated and unirradiated patients. Skin relapse appears to be a manifestation of metastatic disease while parenchymal relapse may represent regrowth of primary tumour. This pattern of breast relapse questions the requirement for radiotherapy to the whole breast after local excision for early stage breast cancer.

Adult↗
PubMed1988

The effect of mydriasis on the pupillary centration of the human eye.

The change in pupil centration occurring as the human eye pupil dilates, both naturally in darkness and following the use of a mydriatic drug (cyclopentolate HCl, 1%), has been measured photographically. In both cases, changes in centration of up to 0.4 mm have been found. Using available ocular wavefront aberration data, modulation transfer curves have been derived for two eyes for centration changes of 0.2 mm. The importance of these changes in the formation of the retinal image, and hence on visual performance, is discussed.

Adult↗
PubMed1988

Atrial natriuretic factor: response to cardiac operation.

Patients who undergo cardiopulmonary bypass experience derangements of complement activation, prostaglandin metabolism, and catecholamine secretion, which have all been posited to explain postoperative fluid retention and paroxysmal hypertension. Atrial natriuretic factor, a hormonal peptide released by the cardiac atria, regulates vascular volume by increasing sodium excretion and decreasing vasomotor tone and catecholamine synthesis. We examined its possible response to cardiopulmonary bypass in 23 patients (18 having cardiopulmonary bypass and, as a control group, five having thoracotomy) who underwent serial blood sampling to measure plasma atrial natriuretic factor levels before, during, and after operation. Thoracotomy alone had no effect on atrial natriuretic factor levels before, during, and after operation. Patients with cardiac valve lesions who had a higher incidence of arrhythmias and congestive heart failure showed elevated preoperative atrial natriuretic factor values (p less than 0.05). Normally, atrial natriuretic factor release is directly related to atrial filling pressure, but all patients having cardiopulmonary bypass revealed a paradoxical rise of atrial natriuretic factor during cardiopulmonary bypass (p less than 0.01) and a lack of correlation between atrial filling pressure and atrial natriuretic factor secretion in the early postoperative period. The atrial natriuretic factor response to pulmonary wedge pressure began to normalize 24 hours after operation. The unique reaction of this recently discovered cardiac hormone to cardiopulmonary bypass suggests its possible role in the pathophysiologic response to cardiac operation.

Atrial Natriuretic Factor↗
PubMed1987

Left ventricular full-thickness cardiomyoplasty with pericardial neoendocardium: experimental development of a surgical procedure.

Cardiomyoplasty, a surgical procedure using stimulated skeletal muscle graft to replace or repair damaged myocardium, has been successfully performed in experimental animals and clinical patients. Whenever feasible, endocardium of the damaged myocardial segment is retained and partial-thickness cardiomyoplasty should be carried out. However, if this procedure were to be applied to enlarge a hypoplastic ventricle or to maintain normal dimensions of the ventricular cavity in some repairs in adults, full-thickness replacement of the ventricular wall with contractile skeletal muscle mass would be required. To develop such a technique, several canine experiments were carried out. In 7 dogs, "simple full-thickness cardiomyoplasty" was performed by using a latissimus dorsi muscle graft to repair a full-thickness left ventricular wall defect. We found it was difficult to obtain adequate hemostasis between the nonscarred myocardial tissue and the skeletal muscle graft, and excessive suturing to obtain hemostasis resulted in strangulation of the muscle grafts. The skeletal muscle-blood interface in the left ventricle was found to be highly thrombogenic. The perioperative hemorrhage and the risk of muscle graft strangulation by excessive sutures were avoided by using a pericardial patch as neoendocardium in 5 dogs that underwent similar full-thickness cardiomyoplasty procedures. Although the pericardial neoendocardium was not fully antithrombogenic in this canine model, endothelialization of the endocardium occurred within several weeks after operation. Thus, when combined with an implantable synchronized burst stimulator, this technique may in the future provide an effective "full-thickness dynamic cardiomyoplasty" to enlarge the ventricles and augment myocardial function in select patients.

Animals↗
PubMed1987

A neurological study of hand function of hemiplegic children.

Twenty-five children with hemiplegic cerebral palsy between the ages of five and 15 years were examined in more detail, using a torque generator motor. A significant reduction in distal power, fatiguability and speed of movement was found on the hemiplegic side. Proximal power was relatively well preserved. Muscle tone, as would be expected, was significantly increased on the affected side and this was demonstrated by a significant rise in measured resonant frequency. Phasic spasticity in response to stretch was found on EMG to be much more common than phasic and tonic combined. Hand function correlated well with the loss of distal power and speed of movement. There was wide individual variation in the relationship between increased muscle tone and hand function. Thixotropy was normal in spastic muscles. Use of the unaffected hand had a marked effect on muscle tone and EMG of the affected side.

Adolescent↗
PubMed1986

Life salvage with fibrin glue in three cases of exsanguinating hemorrhage.

Fibrin glue, although widely used in Europe for a decade, has not been commercially available in North America because its fibrinogen component is obtained from multiple, pooled, human blood donors with the subsequent increased risk of blood transmissible diseases. Techniques developed recently to isolate fibrinogen from single-donor plasma will circumvent these potential hazards. In Canada the use of fibrin glue has not been widespread even though biologic fibrin glue can be made from components readily available within most hospitals. Equal amounts of cryoprecipitate from fresh frozen plasma and bovine thrombin will combine within 2 minutes to form the fibrin glue. Simultaneous injections of each component at bleeding sites form a film of the glue that will effectively control even small arterial bleeding. The authors present three case reports to illustrate how use of the glue can save lives in cases of exsanguinating hemorrhage. They discuss the multiple applications of the fibrin glue which they believe will soon be part of the armamentarium of all Canadian surgeons.

Aged↗
PubMed1985

Activation of neutrophils and monocytes after allergen- and histamine-induced bronchoconstriction.

To determine whether neutrophils and monocytes are activated after allergen-induced asthma, changes in the expression of complement (C3b) receptors were measured by use of the rosette technique. There was a time-dependent increase in the percentages of neutrophil and monocyte rosettes in 13 asthmatic patients for up to 60 min after allergen-inhalation challenge. This was preceded by elevations in the concentrations of serum neutrophil chemotactic activity and reductions in the FEV1. These changes were not observed in seven asthmatic patients who had histamine-induced bronchoconstriction. The present findings support the view that inflammatory cells are activated after allergen-induced asthma and that this may be the result of the release of mast cell-associated mediators rather than the consequence of bronchoconstriction per se.

Adult↗
PubMed1985

Measurement of the axial wavefront aberration of the human eye.

An objective variation of Howland and Howland's subjective crossed-cylinder aberroscope method of estimating ocular aberration is described. An ophthalmoscopic arrangement allows the distorted retinal image of the aberroscope grid to be directly photographed for later analysis. Results for 10 subjects show that the ocular wavefront aberration near the visual axis is rarely symmetrical about the pupil centre and that, as a result, the phase transfer function is generally non-zero. Calculated modulation transfer functions at various pupil diameters broadly agree with those of earlier authors but suggest that marked differences occur between individual eyes when the pupil diameter exceeds about 3 mm.

Humans↗
PubMed1984

Objective technique for the determination of monochromatic aberrations of the human eye.

The subjective crossed-cylinder aberroscope method of Howland and Howland [J. Opt. Soc. Am. 67, 1508 (1977)] has been modified by the addition of a beam splitter and a camera to permit direct photographic recording of the distorted retinal image of the aberroscope grid. The ocular aberration can then be deduced from direct measurements of the grid distortion. Preliminary results on 11 subjects confirm earlier findings that comalike, third-order aberrations are more important than spherical or other fourth-order aberrations in degrading the retinal image and for the average subject, the diffraction-limited pupil size is approximately 3 mm. This new objective method for measuring wave aberration yields significantly less variance in population estimates of the coefficients of the wave-aberration polynomial than that of the previous subjective method.

Astigmatism↗
PubMed1982

Antistaphylococcal IgE in patients with atopic dermatitis.

Levels of IgE antibodies to Staphylococcus aureus and Staphylococcus epidermidis were determined in eleven patients with typical atopic dermatitis, with no history of furuncles or severe staphylococcal infection. Increased IgE binding to S. aureus but not to S. epidermidis was observed. Fifteen patients with hyperimmunoglobulinemia E-staphylococcal abscess syndrome had increased IgE binding not only to S. aureus but also to S. epidermidis. Other control groups of patients with elevated IgE levels or recurrent staphylococcal infection had normal IgE binding activity to both strains of staphylococci. Interaction of staphylococcal antigens from bacteria on skin with antistaphylococcal IgE antibodies on mast cells could induce mast cell release, evoke itch, and aggravate atopic dermatitis.

Abscess↗
PubMed1981

Tamoxifen versus aminoglutethimide in advanced breast carcinoma: a randomized cross-over trial.

Altogether 117 patients with advanced breast cancer were treated with either tamoxifen 10 mg by mouth twice daily or aminoglutethimide 250 mg by mouth four times daily with hydrocortisone 20 mg twice daily in a randomised cross-over trial in which patients who failed to respond to the first treatment or relapsed while receiving it were switched to the other. Eighteen (30%) out of 60 patients initially treated with tamoxifen achieved an objective response and 11 (18%) showed stable disease. Seventeen (30%) out of 57 patients treated initially with aminoglutethimide achieved an objective response and 13 (23%) achieved stable disease. Objective responses in bone metastases were achieved more commonly with aminoglutethimide (11 patients (35%)) than with tamoxifen (five (17%)). The predicted median duration of response for tamoxifen was 15 months and for aminoglutethimide over 15 months (no significant difference). Five (15%) out of 34 patients who failed to respond to tamoxifen and four out of six patients who relapsed after responding to tamoxifen subsequently responded to aminoglutethimide. In contrast, only two (6%) out of 31 patients who failed to respond to aminoglutethimide and none out of four patients who relapsed while receiving aminoglutethimide subsequently responded to tamoxifen. The main side effects occurring in the 97 patients who received aminoglutethimide as first- or second-line treatment were lethargy and drowsiness (36 patients) and rash (29); seven patients had to stop treatment because of side effects. In contrast, side effects were rare and mild with tamoxifen and no patient had to stop treatment because of them. Both tamoxifen and aminoglutethimide appeared from this study to be equally effective in the medical endocrine treatment of advanced breast cancer.

Adult↗
PubMed1981

Aging and serum immunoglobulin E levels, immediate skin tests, RAST.

The changes of the serum IgE levels, specific immediate skin-test responses, and RAST measurements with age were evaluated. A total of 331 unrelated individuals were studied, consisting of 166 subjects with ragweed allergic rhinitis and/or asthma, 67 with idiopathic (intrinsic) asthma, and 98 who appeared in good health with no clinical evidence of atopic diseases. All subjects were evaluated by history and physical examination, intradermal skin testing to the common aeroallergens, measurements of IgE antibody to common aeroallergens with the RAST, and serum IgE levels. Results demonstrated a significant decrease in serum IgE levels with aging in atopic individuals. This decline was exponential in character. In addition, a tendency for RAST and immediate type skin-test responses for selected antigens and histamine to decrease with age was observed.

Adolescent↗