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Biomedical subjects

T D Williams

Publications and source records attributed to T D Williams.

At least 91 records · Page 5Linked to original sources
PubMed1992

Retention of central visual field in retinitis pigmentosa.

According to Kanski, roughly one in four patients with retinitis pigmentosa retains visual acuity adequate for reading, although the electroretinogram may be extinguished and the visual field constricted to 2 to 3 degrees (whether diameter or radius is not stated). Under the age of 20 years, an acuity as poor as 6/60 is relatively uncommon, whereas over the age of 50 years such an acuity becomes common. Heckenlively comments that by the end of the 4th decade of life, most males with X-linked retinitis pigmentosa have vision reduced to hand motion or light perception. Women tend to be less severely affected than men: in a study by Bird, only 3 of 48 female heterozygotes had an acuity of less than 6/9, whereas only 8 of 28 hemizygous males had an acuity of 6/9 or better. I thought it would be instructive to analyze the visual field data for a female patient who, although she had suffered considerable loss of peripheral vision, is continuing to function visually quite well.

Adult↗
PubMed1990

Mechanisms of impaired excretion of a fluid load after cardiac denervation in dogs.

The influence of cardiac innervation on the renal response to volume expansion was investigated. Systemic hemodynamic, plasma hormone, and renal clearance measurements were made before, during, and after intravenous administration of 1,000 ml 0.9% saline over 10 min to six control and six cardiac-denervated, chloralose-anesthetized mongrel dogs. Volume expansion resulted in a two- to threefold rise in plasma atrial natriuretic peptide (ANP) concentrations and a 50% rise in glomerular filtration rate (GFR) in both groups. Plasma renin activity (PRA) and plasma arginine vasopressin remained higher throughout in cardiac-denervated compared with control dogs. The marked increases in urine flow rate and sodium and free water clearances seen in the controls were attenuated or abolished after cardiac denervation. These differences were due to the influence of higher PRA and vasopressin in these animals compared with the controls, rather than differences in hemodynamic responses operating via GFR or in direct humoral responses via ANP secretion.

Animals↗
PubMed1990

Altered cardiovascular and neurohumoral responses to head-up tilt after heart-lung transplantation.

Heart-lung transplantation results in afferent and efferent denervation of the transplanted organs including interruption of the central connections from the low-pressure receptors in the atria and pulmonary veins. We investigated whether the cardiovascular and neurohumoral responses to the postural stimulus of head-up tilt were affected after transplantation. Responses in eight heart-lung transplant recipients were studied and compared with those in eight normal subjects matched for age and sex during passive head-up tilt at 45 degrees for 1 hour. The transplant group had a higher initial heart rate (99 +/- 2 versus 68 +/- 2 beats/min, p less than 0.001) and diastolic blood pressure (88 +/- 5 versus 76 +/- 2 mm Hg, p less than 0.05) than did the control group. The increases in heart rate and diastolic blood pressure during head-up tilt were similar in the two groups. Systolic blood pressure remained unchanged. The decrease in cardiac output (30% versus 18%, p less than 0.05) and the increase in systemic vascular resistance (52% versus 28%, p less than 0.05) were greater in the transplant group. Baseline levels of norepinephrine, epinephrine, vasopressin, and plasma renin activity were similar in the two groups. Atrial natriuretic peptide concentrations were higher in the transplant group (26 +/- 3.8 versus 9.7 +/- 1.6 pmol/l, p less than 0.001). During head-up tilt, plasma norepinephrine levels increased to a greater extent in the transplant group than in the control group (83% versus 53%, p less than 0.01), indicating an increased sympathetic response. In contrast, plasma renin activity increased significantly in the control group but not in the transplant group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Full recovery following massive overdose with insulin and thyroxine.

Specific treatment is available for only a few substances taken in overdose. We report here a patient who attempted suicide with a massive overdose of insulin and thyroxine, a combination not previously reported, and discuss the specific treatments given to mitigate the harmful effects of this combination.

Drug Overdose↗
PubMed1989

Vasopressin secretion in diabetic subjects with and without autonomic neuropathy: responses to osmotic and postural stimulation.

1. The release of arginine vasopressin (AVP) after an osmotic stimulus and head-up tilt was assessed in diabetic subjects with and without autonomic neuropathy. 2. Six diabetic subjects with (DAN +ve) and five without (DAN -ve) evidence of autonomic neuropathy and five normal subjects were infused with 5% (w/v) NaCl at a rate of 0.05 ml min-1 kg-1 body weight for 120 min. Blood pressure, heart rate and plasma AVP were measured over this period. 3. Seven DAN +ve, six DAN -ve and six normal subjects were tilted head-up to 45 degrees for 120 min. Blood pressure, heart rate and plasma AVP were measured during the study. 4. Infusion of 5% (w/v) NaCl produced appropriate rises in plasma osmolality and plasma AVP levels which did not differ between the three groups, confirming the normal osmotic release of AVP in the diabetic subjects. 5. During head-up tilt, there were no differences in AVP responses between the three groups, despite a major hypotensive stimulus in the DAN +ve group. 6. We conclude that osmotic release of AVP is normal in diabetes, but that cardiovascular release of AVP is impaired in diabetic subjects with cardiovascular reflex evidence of autonomic neuropathy, reflecting an afferent defect.

Adult↗
PubMed1989

Visual fields, acuity, and intraocular pressure in a pseudophakic patient.

A 55-year-old white male underwent an uneventful cataract extraction with implantation of a posterior chamber intraocular lens (IOL) in his left eye. Two years after the cataract surgery, his visual acuity decreased due to opacification of the posterior lens capsule. This report addresses the effect of laser capsulotomy on the patient's visual acuity, intraocular pressure (IOP), and visual field. Although the first two have improved nicely, the size of the last remains considerably below the norm for his phakic contemporaries.

Humans↗
PubMed1989

Selective defect in gonadotrophin secretion in patients with autonomic failure.

We studied the neuroendocrine effects of a condition associated with abnormal hypothalamic amines. Hypothalamo-anterior pituitary function was assessed in five male subjects with autonomic failure (AF) and in five age and sex-matched controls. All subjects showed normal gonadotrophin and TSH responses to GnRH and TRH, respectively. In control subjects, intravenous infusion of naloxone caused a significant rise in overall LH concentrations as well as increased frequency and amplitude of LH pulses. In contrast, in AF subjects naloxone did not alter LH concentrations or increase LH pulse frequency. Naloxone also caused an increase in neurosecretory GH pulses not only in AF subjects but also in the controls. These results suggest that in man, ascending catecholamine pathways are important in the control of gonadotrophin secretion. The markedly different response of GH to an opioid antagonist in elderly subjects should be further investigated.

Aged↗
PubMed1989

Atrial natriuretic peptide response to rapid atrial pacing in cardiac-denervated dogs.

The effects of rapid atrial pacing on central hemodynamics, plasma hormones, and renal function were investigated in eight control and nine cardiac-denervated dogs under chloralose anesthesia. Pacing at approximately 250 ppm for 60 min caused similar increases in pulmonary wedge and right atrial pressures, systemic vascular resistance, and plasma atrial natriuretic peptide (ANP) in both groups. In control dogs, pacing produced a fall in both plasma vasopressin (AVP) and plasma renin activity (PRA) and a rise in urine flow rate associated with an increase in free water but not sodium clearance. In contrast, in cardiac-denervated dogs, both plasma AVP and PRA increased during pacing; urine flow rate did not change, and marked sodium retention occurred. This study supports the concept that the increase in urine flow during rapid atrial pacing is mediated by inhibition of renin and AVP secretion through intact cardiac nerves. The secretion of ANP is unaffected by cardiac denervation. The natriuretic and vasodilator actions of high plasma ANP concentrations during rapid atrial pacing can be inhibited either by neurally mediated cardiorenal effects in normal animals or by stimulation of the renin-angiotensin system after cardiac denervation.

Animals↗
PubMed1989

Dependent effect of drinking volume on vasopressin but not atrial peptide in humans.

The act of drinking causes a fall in plasma arginine vasopressin (AVP) concentration that precedes changes in plasma osmolality. To investigate the specificity of this drinking stimulus on hormone secretion, six volunteers (5 male, 1 female, aged 22-39 yr) were water deprived for 36 h and then drank 15 ml/kg water at 10-12 degrees C using 15-20 swallowing actions/min over 3.5 +/- 0.5 min (mean +/- SE). This caused a fall in plasma AVP from 4.5 +/- 0.7 to 3.2 +/- 0.5 pmol/l (P less than 0.05) and in thirst (by 5.7 +/- 0.6 on a 10-cm linear analog scale) (P less than 0.05) 5 min after drinking. No significant changes occurred in mean arterial pressure, heart rate, or plasma atrial natriuretic peptide (ANP) concentration. A second study was undertaken to determine whether the reflex inhibition of AVP secretion is activated simply by the act of swallowing regardless of the volume of liquid consumed. The six volunteers were water deprived for 36 h and then sipped and swallowed 1 ml/kg water at 10-12 degrees C using 15-20 swallowing actions/min over 3.0 +/- 0.1 min. There was no change in plasma AVP concentration, although thirst was reduced by 2.3 +/- 0.6 (P less than 0.05) at 5 min. Plasma AVP 10 min after sipping and swallowing (4.2 +/- 0.8 pmol/l) was significantly greater than at 10 min after drinking 15 ml/kg (2.8 +/- 0.5 pmol/l) (P less than 0.05) despite the fact that plasma osmolality at this stage was similar in both studies. We conclude that the drinking-mediated reflex inhibition of AVP secretion in humans is dependent on swallowing an adequate volume and is not accompanied by changes in hemodynamics or in plasma ANP concentration.

Adult↗
PubMed1988

Rebound increase in plasma renin and vasopressin following graded infusions of atrial natriuretic peptide in man.

The effects of graded infusions of atrial natriuretic peptide (ANP) on hemodynamics, renal function, plasma renin activity (PRA) and plasma arginine vasopressin (AVP) were investigated in a two part study in 6 volunteers. Three 30-min iv infusions of either saline control or ANP at graded rates of 4, 10 and 40 pmol kg-1 min-1 were given. ANP infusions were associated with a significant increase in sodium clearance from 1.08 +/- 0.21 to 2.83 +/- 0.50 ml/min, an increase in hematocrit and a net fluid loss. Plasma AVP remained constant during ANP infusions but increased significantly afterwards when plasma ANP concentrations were falling rapidly, and this was accompanied by marked antidiuresis. PRA fell by 23% during the saline control infusions and by 50% during ANP infusions. Following cessation of ANP infusions there was a significant rebound increase in PRA. No changes were observed in blood pressure, heart rate, glomerular filtration rate or renal plasma flow. These results suggest an interaction in man between ANP and the hormones renin and AVP.

Adult↗
PubMed1988

Decline of atrial natriuretic peptide release in dogs during sustained rapid cardiac pacing.

1. To assess the ability of the atria to maintain elevated plasma concentrations of atrial natriuretic peptide (ANP), the temporal changes in plasma ANP concentrations were studied in seven chloralose-anaesthetized dogs during 4 h of sustained rapid cardiac pacing. 2. Heart rate increased from 124 +/- 26 (mean +/- SEM) to 278 +/- 28 beats/min for the 4 h duration of rapid cardiac pacing. Mean pulmonary wedge pressure increased from 3.6 +/- 1.8 to 17.4 +/- 7.1 mmHg at 30 min (P less than 0.01) and mean right atrial pressure rose from -1.7 +/- 1.9 to 2.0 +/- 2.8 mmHg at 30 min (P less than 0.01). Both remained constant at these elevated pressures for the entire 240 min of rapid pacing. 3. Arterial ANP concentrations increased in all dogs from 87 +/- 11 to a maximum of 1263 +/- 592 pmol/l at 30 min (P less than 0.01), falling to 411 +/- 42 pmol/l after 60 min and to 146 +/- 70 pmol/l after 240 min of rapid continuous pacing (P less than 0.01 compared with 30 min). Coronary sinus ANP concentrations showed a similar pattern, rising from 241 +/- 79 to a maximum of 1837 +/- 203 pmol/l after 30 min (P less than 0.01). These peak values likewise were not sustained, falling to 962 +/- 198 pmol/l after 60 min and 297 +/- 41 pmol/l after 240 min of rapid pacing (P less than 0.01 compared with 30 min). 4. It is concluded that atria are unable to maintain the peak concentrations of ANP reached after 30 min of rapid pacing despite persistently elevated atrial pressures.

Animals↗
PubMed1988

Atrial natriuretic peptide released by rapid ventricular pacing in dogs does not cause a natriuresis.

1. The relationships between the haemodynamic, renal and endocrine changes induced by rapid ventricular pacing were studied in ten chloralose-anaesthetized dogs paced from the right ventricular apex for 60 min at 250 beats/min. 2. Pacing increased mean right atrial and mean pulmonary wedge pressure (P less than 0.05), and decreased cardiac output and mean arterial pressure (P less than 0.05). 3. Coronary sinus atrial natriuretic peptide (ANP) concentrations were approximately fourfold greater than arterial concentrations; both increased markedly during pacing (P less than 0.01). Plasma concentrations of arginine vasopressin and plasma renin activity did not change significantly. 4. Urine flow and free water clearance increased during the latter 30 min of pacing (P less than 0.05). There was no significant change in sodium clearance despite high sustained concentrations of ANP. 5. Without the availability of specific inhibitors of ANP release or action, we are unable to exclude the possibility that ANP may have prevented sodium clearance from otherwise decreasing during rapid ventricular pacing. Nevertheless, the dissociation between elevated ANP concentrations and natriuresis in this study indicates that a rise in ANP concentrations per se is not sufficient to produce a natriuresis.

Animals↗
PubMed1988

Correlation of nerve head and blind spot elliptical features.

Ellipses were fitted to 129 nerve heads and corresponding blind spots in an attempt to determine how faithfully the elliptical nature of the nerve head is reflected in the blind spot. The blind spots are found to be 2 to 3 times more elliptical (based on the ratio of the long axis to the short axis) than the nerve heads. The correlation between the ratios mentioned above is found to be negligible (Pearson r = 0.07 for Goldmann 1-2 blind spots and 0.18 for Goldmann 1-4 blind spots).

Adult↗