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Biomedical subjects

S M Hilton

Publications and source records attributed to S M Hilton.

At least 19 recordsLinked to original sources
PubMed1996

Long-term health outcomes and medical effects of torture among US Navy prisoners of war in Vietnam.

OBJECTIVE: To characterize incidence of illnesses and injuries from 1979 to 1993 in former naval aviator prisoners of war (POWs) from the Vietnam War and a comparison group of naval aviators from the same war. DESIGN: Cohort analytic study. SETTING: A US Navy primary care clinic. PARTICIPANTS: Volunteer sample consisting of 70 former naval aviator POWs (white men, aged 47 to 69 years in 1993) and a comparison group of 55 naval aviators who served in Vietnam but were not POWs, matched on race, age, marital status, education, rank, year of entry into the navy, and pilot status. Subjects participated in an annual health screening program. This study reports data sampled on a biennial basis from subjects screening both in 1979 and 1993. MAIN OUTCOME MEASURE: Medically diagnosed incidence of illness and injury based on a standard protocol. RESULTS: POWs had higher incidence rates than the comparison group did of disorders of the peripheral nervous system (relative risk [RR], 8.4; 95% confidence interval [CI], 2.7-25.9; P<.001), joints (RR, 1.5; 95% CI, 1.2-2.0; P<.006), and back RR, 1.8; 5% CI, 1.0-3.0; P<.037). These findings also were statistically significant according to Kaplan-Meier survival analyses that included 131 (95%) of 138 POWs and 115 (83%) of the 138 members of the comparison group. Survival analyses revealed that, in addition to these disorders, POWs had higher hazard rates of peptic ulcer (P<.01). CONCLUSIONS: During captivity, ropes, ratchet handcuffs, leg irons, or stocks were used to put tightly constrictive pressure around the extremities of POWs as a means of torture, resulting in painful ischemia and subsequent neuropathies. Being a former POW was associated with increased cumulative incidence rates of chronic disorders of the peripheral nervous system, joints, and back and an increased hazard rate of peptic ulcer.

Aged↗
PubMed1990

Determinants of the delegation of healthcare aboard ships with women assigned.

The purpose of this study was to identify the potential determinants and distribution of shipboard patient delegation decisions. During a 1-month period, physicians aboard five U.S. Navy ships with women assigned estimated the minimum numbers of healthcare providers needed to diagnose and treat each patient (N = 2,725). Results indicated the following distribution of potential patient assignment: consultation 1.4%, medical officer 18.6%, physician assistant/nurse practitioner 8.7%, corpsman with additional OB/GYN training 2.2%, and corpsman 69.2%. Diagnosis was the best predictor of the indicated level of healthcare required. The patient's sex and pay grade were unrelated to the potential levels of care provided.

Allied Health Personnel↗
PubMed1987

Vasodilatation in hind-limb skeletal muscle evoked as part of the defence reaction in the rat.

Electrical stimulation of the hypothalamic and mid-brain defence area of the rat's brain elicits a consistent cardiovascular pattern of response of which vasodilatation in the skeletal muscle is an integral component: the mechanisms mediating this vasodilatation were investigated. It is not sensitive to atropine in this species, but it was substantially affected, particularly its later stage (the prolonged tail-end of the response), by either beta-adrenoreceptor antagonists (propranolol, sotalol) or bilateral adrenalectomy. A major part of the hind-limb vasodilatation can therefore be attributed to the action of catecholamines released from the adrenal glands. The initial part of the vasodilatation, which still remained after beta-adrenoreceptor blockade and adrenalectomy, was abolished by intravenous injection of guanethidine and phentolamine and seems therefore due simply to withdrawal of vasoconstrictor tone. In confirmation, stimulation of the sympathetic outflow to the hind-quarters after phentolamine and guanethidine had been used to block vasoconstriction did not reveal a sympathetic vasodilator nerve supply to the hind-limb vasculature.

Adrenalectomy↗
PubMed1986

The hypothalamic and brainstem areas from which the cardiovascular and behavioural components of the defence reaction are elicited in the rat.

Electrical stimulation has been employed to map areas of the rat's brain from which the cardiovascular and behavioural components of the defence reaction are elicited and hence to identify the defence areas in this species. In the anaesthetized rat, the cardiovascular pattern of response includes increases in arterial blood pressure and heart-rate, an atropine-resistant vasodilatation in the hind-limb skeletal muscle, with renal and splanchnic vasoconstriction. This was elicited from comparatively well localized areas, not confined to any particular nuclei. Responses were evoked from the rostro-caudal extent of the hypothalamus but most consistently from a region ventral to the fornix. In the midbrain, responsive sites were localized to the dorsal half of the central grey matter, the tegmentum ventro-lateral to it and a ventro-medial region which continued into the pons. Stimulation using implanted electrodes in conscious rats, within the hypothalamic and midbrain areas described above, elicited typical 'flight' and 'escape' behaviour: thus, the localized regions from which the visceral alerting response is elicited contain neurones or nerve fibres integrating the whole defence-alerting response in the rat, as in other species.

Animals↗
PubMed1986

A search for brain stem cell groups integrating the defence reaction in the rat.

The defence areas of the rat brain stem have been extensively explored using electrical and chemical stimulation in an attempt to locate the regions containing the perikarya of neurones which may initiate or integrate the visceral and behavioural components of the defence reaction. In rats anaesthetized with alphaxalone-alphadolone, a cannula electrode was used to compare the responses to electrical stimuli with those evoked by microinjection of the excitatory amino acid D,L-homocysteic acid (DLH), at the same site. A total of 128 sites throughout the brain stem was studied in 75 rats. The pattern of visceral and somatic changes characteristic of the defence reaction, viz. increases in arterial blood pressure and heart rate, vasodilatation in hind-limb muscles and vasoconstriction in the kidney, hyperpnoea and tachypnoea, exophthalmos, mydriasis, twitching of the vibrissae and retroflexion of the tail, was evoked by electrical stimulation within well-defined regions of the brain stem, from the anterior hypothalamus to the pons. Microinjection of DLH into the same regions could evoke the full defence reaction, as defined above, but only from the dorsomedial periaqueductal grey matter. Three other regions were defined from which almost all the autonomic components of the defence reaction were evoked, except that blood pressure fell. These were located: immediately dorsal to the optic chiasma, in the medial tuberal region of the hypothalamus and in the lateral pontine tegmentum. In conscious rats with implanted guide cannulae, darting and flight responses were evoked by microinjections of DLH into the periaqueductal grey matter but not from the hypothalamus or tegmentum. Brisk locomotion followed injections of DLH into the region overlying the optic chiasma. It is concluded that the brain stem neurones involved in integrating the somatic and visceral components of the defence reaction are concentrated within the four regions defined above. Whereas neurones in the periaqueductal grey matter can initiate the fully integrated defence reaction, those concentrated in the three other areas cannot be shown to do so. Of these three cell groups, the suprachiasmatic neurones seem to be closer in function to the periaqueductal group than are the neurones in the tuberal hypothalamus and pontine tegmentum.

Anesthesia, General↗
PubMed1985

Vasodilator and vasoconstrictor neurones of the ventrolateral medulla in the cat.

Microinjections of D,L-homocysteic acid into the ventrolateral medulla, in the region of nucleus paragigantocellularis lateralis (PGL) which lies caudal to the facial nucleus and adjacent to the rostral third of the inferior olive, evoke a rise in arterial blood pressure and vasoconstriction in hindlimb muscle. Activation of a group of neurones located in a more rostral strip of tissue ventral to the facial nucleus produces vasodilatation in the hindlimb but no significant change in blood pressure. It appears that the ventrolateral medulla contains several subpopulations of neurones which can alter resistance to blood flow and hence distribution of flow and level of blood pressure by selective control of individual vascular beds.

Animals↗
PubMed1984

Loss of peripheral chemoreflexes to hypoxia after carotid body removal in the rat.

Young Sprague-Dawley female rats (16-18 days old) were subjected to bilateral carotid glomectomy or the sham operation under halothane anaesthesia. After recovery, the rats were placed with non-operated peers. One to six months later glomectomised, sham-operated and control animals were anaesthetized with sodium pentobarbital. Respiratory minute volume and arterial pressure were recorded. Respiratory responses to few-breath administration of oxygen or nitrogen, and arterial pressure responses to carotid occlusion or tugging were tested. Oxygen produced transient hypoventilation and nitrogen transient hyperventilation in control, sham and 3 of 31 glomectomised rats. Bilateral vagotomy did not abolish these responses. In only those 3 glomectomised rats was carotid glomus tissue histologically identifiable. Carotid occlusion raised and tugging lowered arterial pressure in all animals. Glomectomy did not affect serum levels of GH, FSH, LH or PRL hormones but produced right ventricular hypertrophy. We conclude that peripheral chemoreception requires the presence of glomus tissue.

Animals↗
PubMed1984

Spinally projecting neurones near the ventral surface of the medulla in the cat.

In anaesthetized cats antidromic responses were recorded in nucleus paragigantocellularis lateralis following stimulation of the ventrolateral funiculus in the ipsilateral thoracolumbar cord. Conduction velocities ranged from 5.4-120 m/s but 50% of the fibres conducted at less than 20 m/s. About half of the neurones were facilitated by stimulation in the hypothalamic or midbrain defence areas. These neurones are superficially located at the site where application of glycine or a lesion blocks the effects of defence area stimulation and reduces blood pressure. They could therefore be involved in the regulation of vasomotor activity.

Animals↗
PubMed1984

Ventral medullary neurones excited from the hypothalamic and mid-brain defence areas.

In cats anaesthetised with chloralose, the ventral medulla was explored in and around the strip previously identified as the location of the efferent pathway from the hypothalamic and mid-brain defence areas to the spinal cord, in a search for neurones excited by electrical stimulation of the defence areas. Such units were found mostly in the caudal part of this strip, at a depth of not more than 500 microns from the surface. Nearly all were located in the ventral part of nucleus paragigantocellularis lateralis (PGL) at the level of the rostral pole of the inferior olive. There was evidence of temporal and spatial facilitation, indicating a convergent excitatory input from the defence areas onto neurones in PGL. This is consistent with earlier evidence of a synaptic relay in the efferent pathway at this site. When the pathway is blocked at this site, arterial blood pressure falls profoundly, so activity in these neurones may be essential for the normal level of sympathetic nerve activity.

Action Potentials↗
PubMed1983

Ventral medullary relay neurones in the pathway from the defence areas of the cat and their effect on blood pressure.

In cats anaesthetized with Althesin, the efferent descending pathway from the brain-stem defence areas has been traced through the medulla by identifying sites at which electrical stimulation evoked the characteristic pattern of the visceral alerting (defence) response. This response includes an increase in arterial blood pressure resulting from increased heart rate and cardiac output and vasoconstriction in renal and splanchnic beds, accompanied by active vasodilation in skeletal muscle. The efferent pathway runs as a narrow strip, about 3 mm from the mid line, ventral to the superior olive and the nucleus of the trapezoid body, extending caudally to the rostral portion of the inferior olive where it lies ventral to the facial nucleus. It was found to lie very close to the ventral medullary surface just rostral to and within the area at which bilateral topical application of glycine results in a profound fall in arterial blood pressure and cessation of respiration. On bilateral application of glycine to the sensitive area of the ventral medulla, the visceral alerting response evoked by stimulation in the defence areas of the amygdalo-hypothalamic complex, or the mid-brain central grey or tegmentum, was attenuated in parallel with the fall in arterial pressure, the vasoconstrictor responses being most strongly reduced. As soon as arterial blood pressure had fallen to its lowest level the visceral alerting response was virtually abolished. A small radio-frequency lesion made in the ventral medullary efferent pathway, in the rostral part of the 'glycine-sensitive area', had the same effect as that produced by unilateral application of glycine: it resulted in little respiratory or cardiovascular effect itself, but application of glycine to the contralateral area then produced the full effect otherwise seen only on bilateral application of glycine. It is suggested (1) that the effects of glycine result from blockade of a synaptic relay, close to the ventral surface of the medulla, in the efferent pathway from the defence areas to the preganglionic sympathetic neurones, and (2) that the neurones which receive an input from the alerting (defence) areas normally provide an essential, tonic excitatory drive to the sympathetic output and probably to respiration also. After sudden withdrawal of this drive, vasomotor tone and the normal level of arterial blood pressure are not maintained.

Animals↗
PubMed1982

The pattern of cardiovascular response to carotid chemoreceptor stimulation in the cat.

1. The pattern of cardiovascular response evoked by carotid chemoreceptor stimulation has been investigated in cats anesthetized by continuous infusion of Althesin (Glaxo). 2. A variety of chemoreceptor stimulants, injected retrogradely into the lingual artery with the external carotid artery ligated, evoked hyperventilation with variable changes in arterial pressure and heart-rate, but a consistent vasodilatation in limb muscles and vasoconstriction in renal, mesenteric and cutaneous vasculature. 3. The muscle vasodilatation was still obtained after vagotomy and when the animal was paralysed and artificially ventilated; thus, it was not secondary to the hyperventilation. 4. In the majority of experiments the muscle vasodilatation was much reduced or abolished by atropine indicating it was mediated by sympathetic cholinergic fibres, which is characteristic of the alerting stage of the defence reaction in the cat. The cardiovascular pattern was accompanied by the other autonomic features of the alerting response, viz. pupillary dilatation, retraction of the nictitating membranes and pilo-erection. 5. In one and the same animal the pattern of response evoked by carotid chemoreceptor stimulation was the same as that evoked by noxious cutaneous stimulation, and by electrical stimulation in the brain stem defence areas. 6. It is concluded that peripheral chemoreceptor stimulation acts as an excitatory input to the hypothalamic and brain stem defence areas and that it can readily evoke the autonomic components of the alerting stage of the defence reaction. It is suggested that this has been missed in previous studies on anaesthetized animals because of the depressant action of chloralose and barbiturates on transmission in the hypothalamus and mid-brain.

Animals↗
PubMed1982

The defence-arousal system and its relevance for circulatory and respiratory control.

It was proposed some fifty years ago that the visceral and hormonal changes accompanying fear and rage reactions can best be understood as adaptations which prepare an organism to cope with an emergency and specifically to perform the extreme muscular exertion of flight or attack. This is well exemplified by the pattern of cardiovascular response which is characteristic of the alerting stage of these reactions and consists of an increase in cardiac output directed mainly to the skeletal muscles. This group of behavioural responses has been collectively termed the defence reaction. The regions of the hypothalamus and brainstem which organize it have been mapped. They function as a reflex centre for the visceral components of the altering response as well as initiating the behavioural response. So far as the cardiovascular system is concerned, this is a preparatory reflex and not compatible with short-term homeostasis. Indeed, the baroreceptor reflex, which is homeostatic, is strongly inhibited. By contrast, the chemoreceptor reflex is facilitated. The input from peripheral chemoreceptors is itself an alerting stimulus. The visceral alerting response has been studied in most detail in the cat, but there is evidence for the same cardiovascular pattern and an accompanying group of respiratory changes in other mammalian species (rat, rabbit, dog, monkey and man). On the efferent pathway for the cardiovascular response pattern, there is a group of relay neurones near the ventral surface of the caudal medulla, which seem important for the maintenance of arterial blood pressure. The visceral alerting system may therefore be continually engaged to some extent in the awake state, as well as being acutely activated in response to novel, and especially to noxious, stimuli.

Animals↗
PubMed1980

Dorsal root vasodilatation in cat skeletal muscle.

1. A study has been made, in the cat anaesthetized with chloralose, of the effects of antidromic stimulation of dorsal roots L6-S1 on the blood flow through the gastrocnemius muscle. 2. Stimulation of the peripheral ends of the ligated dorsal roots with current pulses of 0.3-0.5 msec duration and at intensities most effective in activating the smaller afferent fibres, for periods of 15-20 sec, produced a 50-60% increase in muscle vascular conductance which was slow in onset and long outlasted the stimulus. 3. This muscle vasodilatation could be evoked in the paralysed animal and was unaffected by guanethidine or atropine. It was, however, greatly reduced or even abolished by the prostaglandin synthetase inhibitors, indomethacin or acetylsalicylic acid, in doses which had no effect on the dilatation produced by a local injection of acetylcholine or the functional hyperaemia induced by muscle contraction. 4. It is concluded that activity in the smaller myelinated or unmyelinated afferent fibres of skeletal muscle produces an increase in muscle blood flow which is mediated, at least in part, by prostaglandins locally synthesized within the muscle.

Acetylcholine↗
PubMed1979

The origin of the hind limb vasodilatation evoked by stimulation of the motor cortex in the cat.

In cats under Althesin anaesthesia, the hind limb area of the motor cortex has been stimulated by means of monopolar, semi-micro-electrodes with careful experimental control so as to avoid reflex effects evoked through stimulation of meningeal afferent fibres or stimulus spread to non-cortical structures. 2. Localized cortical stimulation which elicited muscle contractions in the contralateral hind limb also elicited vasodilation in the same limb: the stimulus threshold was the same for both effects, and the magnitude of the dilatation was related to the strength of contraction. 3. Reduction of the somatic motor response, caused by lesions in the medullary pyramidal tract, was accompanied by a parallel reduction of the vascular response. 4. Prevention of the motor response by gallamine or by spinal cord section at L4--L5 (which leaves the sympathetic outflow to the hind limbs intact) led to abolition of the vascular response. During recovery from gallamine, contraction and vasodilatation returned in parallel. 5. The muscle vasodilatation was insensitive to atropine or guanethidine. 6. It is concluded that the hind limb vasodilatation observed on stimulation of the motor cortex is simply a post-contraction hyperaemia, and that it is independent of the sympathic nervous system. Previous conclusions of a sympathetically mediated vasodilatation probably resulted from inadequate control of the stimulus or a failure to recognize weak muscle contractions.

Animals↗