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Biomedical subjects

B J Robinson

Publications and source records attributed to B J Robinson.

At least 55 records · Page 3Linked to original sources
PubMed1992

Heart rate periodicities during induction of propofol-nitrous oxide-isoflurane anaesthesia.

This study examined the variation in cardiac inter-beat interval during induction of anaesthesia with propofol and subsequent inhalation anaesthesia with nitrous oxide and isoflurane. In comparison with preoperative control values, heart rate variability was reduced by anaesthesia and there was a complex, but consistent, pattern of R-R interval change during induction. Immediately after propofol 2 mg kg-1, high frequency heart rate oscillations were replaced by low frequency oscillations (0.05 Hz). Subsequently, with decreasing propofol and deepening nitrous oxide-isoflurane anaesthesia, high frequency components returned towards, although not reaching, control values; low and, to a greater extent, mid range (0.1-Hz) frequency components remained reduced. We postulate that these alterations are consistent with an immediate but transient post-induction ventilatory depression, subsequent decrease in efferent sympathetic activity and reduction in baroreflex responsiveness. R-R interval analysis is suggested to be a useful tool in the evaluation of autonomic function during anaesthesia.

Adolescent↗
PubMed1992

Fault in a Selectatec manifold resulting in awareness.

The Selectatec Vaporising System is a quick change system consisting of anaesthetic vaporisers of the Tec 3 and Tec 4 models and the compatibility manifold block on which these are seated on the anaesthetic machine backbar. There have been reports of difficulties with the seating and locking of the vaporisers which can cause a leak and failure of vapour delivery. The Faculty of Anaesthetists, Royal Australasian College of Surgeons (now Australian and New Zealand College of Anaesthetists) issued a hazard alert in March 1991 drawing attention to this potential fault. We present two cases of awareness associated with failure of internal seals within a Selectatec compatibility manifold block which did not have a detectable leak.

Adult↗
PubMed1992

Betamethasone-induced resistance to neuromuscular blockade: a comparison of atracurium and vecuronium in vitro.

Steroids induce resistance to neuromuscular blocking drugs. Betamethasone-induced resistance to vecuronium has been demonstrated in vitro, and a presynaptic site of interaction has been suggested. This study investigated whether atracurium is similarly affected. Rat phrenic nerve-hemidiaphragm preparations were bathed in a physiologic solution, and one-half were exposed to betamethasone (1 mumol/L). Dose responses were recorded for atracurium (8-13 mumol/L) and vecuronium (2-12 mumol/L) for control and betamethasone-treated preparations. In comparison to control, the betamethasone groups had significantly less depression of muscle contraction force at all concentrations of atracurium (P = 0.0004) and vecuronium (P = 0.002). The calculated ED50 (50% depression of muscle contraction force, expressed as mean +/- SEM) for atracurium was 8.83 +/- 0.62 mumol/L for controls and 11.19 +/- 0.54 mumol/L for betamethasone-treated preparations. The calculated ED50 for vecuronium was 4.72 +/- 0.41 mumol/L for controls and 6.84 +/- 0.66 mumol/L for betamethasone-treated preparations. Betamethasone therefore increased the ED50 for atracurium by 27% and vecuronium by 45%; however, the magnitudes of these differences were not significant (P = 0.74) between the neuromuscular blocking agents. These results indicate that betamethasone-induced resistance to nondepolarizing neuromuscular blockade affects both atracurium and vecuronium to similar degrees in vitro.

Animals↗
PubMed1991

Interaction between betamethasone and vecuronium.

A possible interaction between betamethasone and vecuronium was examined in 20 rat phrenic nerve-hemidiaphragm preparations. Ten preparations were bathed in a physiological solution with betamethasone 1 mumol litre-1 added and, after a 30-min period were exposed to vecuronium at concentrations of 4, 6, 8 and 10 mumol litre-1 with vecuronium free washings between each exposure. Ten control experiments were performed also using a betamethasone-free bathing solution. In comparison with control, the betamethasone group had significantly (P = 0.0008) less depression of muscle contraction (twitch) force at all concentrations of vecuronium. The calculated ED50 (50% depression of muscle contraction force) was 5.65 mumol litre-1 for controls and 7.39 mumol litre-1 for betamethasone-pretreated preparations. This study confirms our previous clinical observations that an interaction occurs between vecuronium and betamethasone which is characterized by resistance to neuromuscular block.

Animals↗
PubMed1991

Level of consciousness on arrival in the recovery room and the development of early respiratory morbidity.

An audit review of 16,065 patients undergoing operative procedures under general anaesthesia was carried out to examine the relationship between early postoperative respiratory complications and the level of consciousness of patients on arrival in the recovery room. In patients aged over ten years, the incidence of respiratory complications was significantly (P less than 0.005) related to the level of consciousness independent of ASA grade or age. Since the level of consciousness of patients arriving in the recovery room could be modified by changes to anaesthetic practice it is concluded that a significant reduction in respiratory complications might be possible if anaesthetists used general anaesthetic techniques which returned patients awake to the recovery room.

Age Factors↗
PubMed1990

Effects of recombinant human erythropoietin on HLA sensitization and cell mediated immunity.

Highly presensitized patients wait longer for a renal allograft than unsensitized patients and have a poorer allograft survival rate. Repeated blood transfusions have been implicated in the induction and maintenance of sensitization. To determine the effect of recombinant human erythropoietin (rHuEPO) therapy on five transfusion dependent, highly sensitized adolescents on dialysis, we serially measured percentage panel reactive antibody (%PRA) levels, titers of identifiable discrete anti-HLA Class I antibody specificities, and non-specific indices of cellular immunity before and following initiation of rHuEPO therapy. Although four of the five patients had previously rejected at least one renal allograft, the removal of chronic antigenic stimulation from blood transfusions led to a marked reduction in anti-HLA antibody titers to recognizable private and public specificities (P less than 0.001) and a reduction of mean %PRA from 80% to 56% (P less than 0.05). Each patient demonstrated a reduction of two or more dilutions to at least two anti-HLA antibody specificities. A control group of five patients matched for age, transfusion dependence and sensitization status demonstrated no change during a comparable time interval. PHA responsiveness decreased significantly in the rHuEPO group whereas autologous and allogenic mixed lymphocyte response, spontaneous blastogenesis and T-cell subsets did not. These data indicate that in highly sensitized dialysis patients rHuEPO may lead to decreased sensitization, shorter waiting time on dialysis and possibly improved allograft survival rates.

Adolescent↗
PubMed1990

Is orthostatic hypotension in the elderly due to autonomic failure?

In order to investigate whether orthostatic hypotension in elderly people is due to autonomic nervous system dysfunction or blood vessel abnormalities, we have measured platelet and lymphocyte adrenoceptor numbers and agonist binding in addition to venous plasma catecholamine concentrations. Eight elderly subjects with orthostatic hypotension and six control elderly subjects were studied. None of the subjects had other symptoms of autonomic failure. There was no significant difference between the heart rate or plasma catecholamine responses to standing of the two groups. The orthostatic hypotension subjects had a significant rise of their plasma vasopressin levels whereas the control group had no significant change. The number of alpha 2-adrenoceptor sites in platelets was lower in the orthostatic hypotensive group compared to the controls and the binding affinity was greater than in the controls. There were no significant differences in beta-adrenoceptor binding sites or affinities in isolated lymphocytes between the two groups. The similar changes in heart rate and catecholamines together with the vasopressin changes suggest that, in these elderly patients with an abnormal drop of blood pressure on standing, there is no dysfunction of autonomic pathways concerned with cardiovascular function. The lower numbers of alpha 2-adrenoceptor sites on isolated platelets in subjects with orthostatic hypotension could indicate reduced alpha 2-adrenoceptor numbers on their blood vessels which could contribute to their inability to maintain blood pressure while standing.

Aged↗
PubMed1990

Comparison of pulse oximeters: accuracy at low arterial pressure in volunteers.

A laboratory model was developed of limb hypoperfusion in volunteers, using parital occlusion of the brachial artery with consequent reduction in radial artery pulse pressure. This was used to compare the function of 13 pulse oximeters and the effect of reduced pulse pressure and mild hypoxia on these devices. With the exception of one device, all the pulse oximeters studied demonstrated similar accuracies at pulse pressures exceeding 20 mm Hg. There were however, significant differences between several of the pulse oximeters in both ability to display readings and accuracy of readings displayed when brachial artery occlusion reduced radial artery pulse pressures equal to or less than 20 mm Hg.

Adult↗
PubMed1990

Do thermoregulatory reflexes pass through the hypothalamus? Studies of chronic hypothermia due to hypothalamic lesion.

A 38-year-old man presented with chronic hypothermia. He also had evidence of hypothalamo-pituitary dysfunction and CT scans showed a discrete hypothalamic lesion. Thermoregulatory impairment was found although there was normal circulatory control of blood pressure. Reflex vasodilatation could be initiated when hypothermia was present and also in response to raised body temperature. Shivering was initiated reflexly but did not otherwise occur. These observations imply that thermoregulatory reflexes are independent of central thermoregulatory mechanisms and do not pass through the hypothalamus.

Adult↗
PubMed1990

Mechanism of ethanol-induced vasodilation.

The mechanism by which ethanol ingestion causes dermal vasodilation is unclear, but it may result from a direct action on central vascular control mechanisms. Forearm blood flow and peripheral skin temperatures were examined in five quadriplegics (lesions above T7) and five control subjects, before and after the ingestion of ethanol (0.75 ml/kg body wt). The lack of vasomotor efferent function was confirmed in the quadriplegics by the absence of vasodilation in response to radiant heating of the torso. There were no significant changes in peripheral temperatures or forearm blood flow after ethanol in the quadriplegics. The control subjects had a significant increase in forearm blood flow (1.12 +/- 0.2 ml.min-1.100 ml-1) and skin temperature (finger 2.4 +/- 0.4 degrees C, toe 3.4 +/- 0.3 degrees C) after ethanol. These data suggest that ethanol may induce peripheral vasodilation by modulation of central vasomotor control mechanisms.

Adult↗
PubMed1989

Is clonidine useful in the treatment of alcohol withdrawal?

The comparative efficacy of clonidine and chlormethiazole has been examined in the management of acute alcohol withdrawal. A double blind randomized study was conducted in consecutive patients admitted to a hospital detoxification unit. Patients were assessed regularly by a standard alcohol withdrawal rating-scale. Thirty-two patients received either clonidine or chlormethiazole in reducing dosages over 96 hr. All the patients receiving chlormethiazole had uneventful withdrawals. However, eight patients treated with clonidine were withdrawn from the trial due to hallucinations (two), seizures (two), symptomatic orthostatic hypotension (three) or drowsiness (one), indicating that clonidine is less effective than chlormethiazole in the prevention of the major manifestations of alcohol withdrawal.

Adult↗
PubMed1988

Why does vasodilatation occur during syncope?

1. Syncopal or near syncopal episodes have been observed in five subjects who stood or were tilted and in whom blood samples were being taken. 2. In all subjects bradycardia and hypotension developed before the onset of symptoms. Increases in plasma adrenaline concentrations occurred in all subjects, beginning before the faint. Changes in plasma noradrenaline concentrations were variable: in three subjects there was a marked fall and in the other two subjects an increase. Plasma vasopressin increased in all subjects. 3. Increase in plasma adrenaline may be contributing to the vasodilatation and arterial hypotension which occur during syncope.

Adult↗
PubMed1988

Mortality in alcoholics with autonomic neuropathy.

Seventy-nine male chronic alcoholics who had been tested for autonomic neuropathy using four tests of vagus nerve function were followed for up to 7 years (mean 5.5 years). Thirty-two subjects had no vagal neuropathy, 25 had one abnormal test and 22 had two or more abnormal vagal function tests and two of these also had orthostatic hypotension. There were no differences between the reported alcohol consumptions and evidence of central or peripheral nerve or liver damage between the three groups. Twelve patients died during the follow-up period. At 7 years the percentage survival for the subjects with no evidence of vagal neuropathy was 91%, with one abnormal test it was 66% and with two or more abnormal tests it was 79%. The expected percentage survival for each of the group was 94%, 91% and 88% respectively. The results suggest that evidence of vagal neuropathy in chronic alcoholics is associated with a significantly higher mortality than in the general population and that deaths due to cardiovascular disease are a major cause.

Adult↗
PubMed1987

Local autonomic failure affecting a limb.

Three patients are described who presented with autonomic failure affecting predominantly one limb. Physiological studies revealed that there was sweating loss in the limb which appeared to be due to a preganglionic autonomic lesion and not to a sweat gland abnormality. In all three patients there was also evidence of failure of vasomotor control. There was no evidence of more generalised autonomic failure or neurological deficit. In two patients the condition appeared to be static and, according to the patients' accounts was life long. In the third the sweating loss was present for three years prior to pain loss becoming evident from C2/3 to T1 on the same side as the sweating loss. These patients, together with two recent case reports, indicate that isolated local autonomic failure, probably from a discrete cord lesion, can be a cause of presenting symptoms related to sweating loss or to change in temperature in a limb.

Adult↗
PubMed1986

Postnatal development of corneal endothelium.

Comparison specular micrographs of infant and adult corneas from cats, cows, dogs, rabbits, and humans demonstrate that a large decrease in central endothelial cell density occurs during maturation of the cornea. Central endothelial cell counts of developing cat, dog, and rabbit corneas decrease rapidly during the first months of life. This rapid decline in endothelial cell density correlates with growth of the cornea to the adult size. Central endothelial cell counts of adult cat, cow, deer, dog, pig, rabbit, and human corneas are similar (2500 cells/mm2) despite a wide variation in corneal size. Comparison of observed endothelial cell counts with two hypothetical situations, one of unrestricted endothelial mitosis and the other of only endothelial hypertrophy, indicates that hypertrophy of individual cells is primarily responsible for achieving the adult cell density of 2500 cells/mm2 for these species. This observation is true for species that have a high adult endothelial mitotic capacity (rabbit) as well as those that do not (cat). The human cornea is a special case because the decline in central endothelial cell density indicates that a large apparent corneal endothelial cell loss (approximately 45%) occurs early in postnatal development.

Adult↗