Biomedical subjects

J C Farmer

Publications and source records attributed to J C Farmer.

14 recordsLinked to original sources

PubMed1992

The inositol phosphate pathway as a mediator in the proliferative response of rat calvarial bone cells to cyclical biaxial mechanical strain.

Isolated newborn rat calvarial bone cells grown in monolayer on polyurethane membranes in specially constructed culture chambers and subjected to a cyclical biaxial mechanical strain of 0.17% at a frequency of 1 Hz for 30 min demonstrated a 16% increase in DNA synthesis during the subsequent 24 h. The metabolites of the inositol phosphate pathway, shown to be an important second messenger in many cell types, were shown to be elevated using high-performance liquid chromatography to separate and quantitate the various inositol polyphosphates. Inositol 1,4,5-trisphosphate, inositol 1,4-bisphosphate, and inositol 1,3,4,5-tetrakisphosphate reached peak accumulations after 20 s of mechanical strain. Inositol 1,3,4-trisphosphate reached a peak accumulation after 2 min, and inositol 1,2,3,4,5,6 phosphate reached a peak accumulation after 60 min of mechanical strain. Neomycin, an inhibitor of phospholipase C, a membrane-bound enzyme that hydrolyzes phosphatidyl inositol 4,5-bisphosphate to start the inositol phosphate cascade, completely inhibited accumulation of the above inositol phosphates during mechanical straining of the bone cells. Neomycin also completely abolished the increase in DNA synthesis that was seen after a mechanical strain of 0.17%. It is concluded from this study that the inositol phosphate pathway is activated by mechanical strain in bone cells and that this pathway is an important and primary mediator in the transduction of mechanical strain into cellular proliferation in these cells.

Analysis of Variance↗

PubMed1992

Pressure transfer between the perilymph and the cerebrospinal fluid compartments in cats.

This is a review of our studies of the labyrinthine fluid pressure in cats subjected to pressure changes in the middle ear (implosive routes) and the cerebrospinal fluid compartment (explosive routes) as well as to changes in vascular and ambient pressures. The perilymph, cerebrospinal fluid (CSF), middle ear, venous and arterial pressures were measured with the cochlear aqueduct (CA) patent as well as surgically blocked. Experiments on explosive pressure changes revealed that the perilymph pressure was regulated by the CSF in case of CA patency. The CSF influence was dominant enough to obscure any direct effect on the labyrinth from other sources. With the CA obstructed the CSF influence on the labyrinth was apparently mainly via the endolymphatic sac and duct although limited and much delayed. Systemic arterial pressure changes had a pronounced influence on the perilymph pressure, but this effect was revealed only when the CSF influence was reduced by CA obstruction. Experiments on implosive and ambient pressure changes suggested that there was no fundamental difference in the perilymph response to equivalent levels of implosive versus hypobaric pressure. Three factors determined the effect of implosive and hypobaric pressure: the patency of the CA, the rate of the pressure change, and the eustachian tube function.

Air Pressure↗

PubMed1991

Concentration-dependent regulatory effects of prostaglandin E1 on human neutrophil function in vitro.

Prostaglandin E1 (PGE1) has recently been used clinically as a purported modulator of activated neutrophils in certain forms of the adult respiratory distress syndrome (ARDS). We now report that PGE1 does not have a uniform inhibitory effect upon human neutrophil functions in vitro. Cells were first pretreated with PGE1 followed by incubation with either N-formyl-methionyl-leucyl-phenylalanine (FMLP), phorbol myristate acetate (PMA), or C5a. Lysosomal enzyme release (myeloperoxidase, lysozyme), superoxide anion generation, and chemotaxis were then quantitated. PGE1 alone lacked any appreciable effect on these neutrophil functions. However, neutrophils pretreated with PGE1 (50 to 100 microM) followed by stimulation with FMLP (50 nM) showed as much as 40% inhibition of lysosomal enzyme release compared with control values (p less than 0.0005). In contrast, 0.1 nM to 1 microM PGE1 enhanced FMLP-stimulated enzyme release as much as 50% above baseline control values (p less than 0.05). Preincubation with 0.1 nM PGE1 followed by stimulation with variable doses of FMLP also resulted in enhancement of lysosomal enzyme release by as much as 187 +/- 3% of control values. The enhancing but not inhibitory effects of PGE1 were reversible with serial washing of the neutrophil preparations. Enhancement of enzyme release was not observed when either PMA or C5a was used as a stimulus after PGE1 pretreatment. However, cells pretreated with PGE1 (50 to 100 microM) and subsequently stimulated with C5a showed as much as 40% inhibition of lysosomal enzyme release. Preincubation of neutrophils with PGE1 (1 microM) resulted in a slight (15%) enhancement of chemotaxis to FMLP, but it had no significant effect on C5a-induced chemotaxis.(ABSTRACT TRUNCATED AT 250 WORDS)

Alprostadil↗

PubMed1991

Disaster management. Organizations and academic perspective.

The world has to cope with the results of an increasing number of disasters. If the planning and preparation for these disasters are to be effective, then national and international organizations are necessary to integrate the sources of advice and relief. Studies of disaster management have consistently highlighted coordination of resources as an essential element of effective response. These organizations, both governmental and voluntary, aim to do just that, and awareness of them and their work will add support.

Aircraft↗

PubMed1990

Ultrasound guidance improves the success rate of internal jugular vein cannulation. A prospective, randomized trial.

STUDY OBJECTIVE: To compare conventional versus ultrasound-guided internal jugular vein cannulation techniques. DESIGN: Patients were randomly assigned to receive either conventional or two-dimensional ultrasound-guided internal jugular vein cannulation. Patients who could not be cannulated with five or fewer passes by either technique, were crossed over to the other technique. SETTING: Clinical research unit in a tertiary care center. PATIENTS: All consecutive patients who required urgent or urgent-elective internal jugular vein cannulation during the study period. INTERVENTIONS: The two-dimensional ultrasound transducer imaged all cannulation attempts. For patients randomized to ultrasound guidance, the operator viewed two-dimensional ultrasound images, and received verbal guidance from the ultrasound technician. For patients randomized to the conventional arm, two-dimensional ultrasound images were recorded without visual or verbal feedback. MEASUREMENTS AND MAIN RESULTS: Two-dimensional ultrasound was significantly better than conventional guidance in reducing the number of failed site cannulations from 6/17 (35 percent), to 0/12 (0 percent), p less than 0.05. Two-dimensional ultrasound also reduced the mean number of passes required to cannulate the vein from 3.12 to 1.75 (p less than .05), and was also successful in six/six (100) of patients who failed cannulation by conventional means (p less than 0.05). CONCLUSIONS: Intensivists can increase successful internal jugular vein cannulation using ultrasound guidance. Two-dimensional ultrasound should be considered for patients difficult to cannulate or those at high risk of cannulation complications.

Catheterization, Central Venous↗

PubMed1979

Spinal cord seizures elicited by high pressures of helium.

Rats with complete spinal transections were compressed in helium-oxygen to 120 bars. Tremors and increased EMG activity in limbs rostral as well as caudal to the lesions were observed beginning at 30 bars. Spinal seizures occurred at 95 bars, similar to cortical seizure thresholds of intact rats. Denervated limbs remained flaccid throughout the dives. No rostro-caudal progression of symptoms was evident in normal animals, but fluctuation of symptoms with increasing pressure was frequently observed. These findings are consistent with the hypothesis that the effects of pressure on aggregates of neurons exceed those on isolated components.

Animals↗

PubMed1978

Effect of cerebellar ablation on the high pressure nervous syndrome in rats.

To evaluate the interaction between high pressure nervous syndrome (HPNS) seizures and cerebellar integrity, seizure threshold pressure (Pc) of normal rats was compared with that of rats sustaining cerebellar ablation two weeks prior to exposure to 136 ATA in a helium-oxygen atmosphere. All rats exhibited severe HPNS symptoms which culminated in seizures. Pc was reduced in cerebellectomized animals, and the number of seizure episodes increased twofold, but the average duration of seizure episodes was unchanged. The spike-and-wave pattern in the electroencephalogram remained a prominent feature in both groups.

Animals↗

PubMed1978

Hyperoxic myopia.

We have reported the development of 1.6 diopters of myopia in a group of patients exposed to reptitive oxygen breathing at two atmospheres absolute pressure. No significant change in corneal curvature accompanied this refractive change. During the three months following termination of the hyperoxic exposure, the myopia gradually disappeared. It is speculated that hyperoxygenation alters the metabolism of the adult lens producing an increase in its dioptric power.

Aged↗

PubMed1977

Temporal arteriography and immunofluorescence as diagnostic tools in temporal arteritis.

Nineteen patients with polymyalgia rheumatica and/or temporal arteritis were classified by degree of clinical and arteriographic abnormality, biopsy grade of arteriosclerosis, and giant cell arteritis (GCA). Temporal arteriograms were very sensitive in detecting abnormal arteries. However, the assumption of some previous studies, that certain angiographic abnormalities are synonymous with GCA, was not supported, since biopsies from distal sites in a Class I and a Class II arteriogram revealed only arteriosclerosis. Class III arteriograms correlated with proximal biopsies of GCA. Immunofluorescent staining was negative in all cases.

Aged↗

PubMed1977

Cerebellar and cerebral electroencephalogram during the high pressure nervous syndrome (HPNS) in rats.

Electroencephalographic activity of the frontal cortex, cerebellar vermis, and superior vestibular nucleus was recorded in awake rats during the high pressure nervous syndrome (HPNS) by means of permanently implanted electrodes. Power-spectrum analysis revealed a decline in the faster frequencies and an increase in the slow frequences as the seizure end-point was approached. Effects of compression to 4500 fsw varied from severe tremor and myoclonic jerks to status epilepticus, with seizures occurring at an average depth of 3560 fsw. In all animals, multifocal-spiking activity progressed in severity with increasing depth. The predominant seizure pattern observed was a spike and slow-wave pattern reminiscent of absence seizures. Initial evidence of generalized seizure activity was equally divided between the cerebellum and cortex. It is concluded that the cerebellum participates in HPNS seizures. Possible evolution of the syndrome by loss of Purkinje cell inhibitory influence on subcortical sites that modulate cortical excitability is discussed.

Animals↗

PubMed1976

Inner ear decompression sickness.

With recent increases in commercial, military, and sport diving to deeper depths, inner ear injuries during such exposures have been encountered more frequently and noted during several phases of diving: during compression, at stable deep depths, with excessive noise exposure in diving, and during decompression. The pathophysiology of these injuries differs, depending upon the phase of diving in which the injuries occur. In this report, 23 cases of hearing loss, tinnitus, and/or vertigo occurring during or shortly after decompression are presented. Thirteen of these cases occurred in helium-oxygen dives involving a change to air during the latter stages of decompression. A significant correlation is present between prompt recompression treatment, relief of symptoms, and lack of residual deficits. Current knowledge indicates that the management of otologic decompression sickness should include: 1. prompt recompression to at least 99 feet deeper than the symptom onset depth; 2. recompression using the previous helium-oxygen mixture when the injuries occur during or shortly after a switch from helium-oxygen to air during the latter stages of decompression; 3. the use of parenteral diazepam for symptom relief and cyclic inhalations of oxygen enriched treatment gases; and 4. the avoidance of further diving by divers who exhibit permanent inner ear injuries after the acute symptoms have subsided.

Adult↗

PubMed1975

Promontory dehiscence: a case report.

Dehiscence of the bony promontory without preoperative fistula formation occurred in a patient with a history of chronic otitis media and perforation of the tympanic membrane without cholesteatoma.

Audiometry↗

PubMedDate not supplied

Diving injuries to the inner ear.

Most of the previous literature concerning otologic problems in compressed gas environments has emphasized middle ear barotrauma. With recent increases in commercial, military, and sport diving to deeper depths, inner ear disturbances during these exposures have been noted more frequently. Studies of inner ear physiology and pathology during diving indicate that the causes and treatment of these problems differ depending upon the phase and type of diving. Humans exposed to simulated depths of up to 305 meters without barotrauma or decompression sickness develop transient, conductive hearing losses with no audiometric evidence of cochlear dysfunction. Transient vertigo and nystagmus during diving have been noted with caloric stimulation, resulting from the unequal entry of cold water into the external auditory canals, and with asymmetric middle ear pressure equilibration during ascent and descent (alternobaric vertigo). Equilibrium disturbances noted with nitrogen narcosis, oxygen toxicity, hypercarbia, or hypoxia appear primarily related to the effects of these conditions upon the central nervous system and not to specific vestibular end-organ dysfunction. Compression of humans in helium-oxygen at depths greater than 152.4 meters results in transient symptoms of tremor, dizziness, and nausea plus decrements in postural equilibrium and psychomotor performance, the high pressure nervous syndrome. Vestibular function studies during these conditions indicate that these problems are due to central dysfunction and not to vestibular end-organ dysfunction. Persistent inner ear injuries have been noted during several phases of diving: 1) Such injuries during compression (inner ear barotrauma) have been related to round window ruptures occurring with straining, or a Valsalva's maneuver during inadequate middle ear pressure equilibration. Divers who develop cochlear and/or vestibular symptoms during shallow diving in which decompression sickness is unlikely or during compression in deeper diving, should be placed on bed rest with head elevation and avoidance of maneuvers which result in increased cerebrospinal fluid and intralabyrinthine pressure. With no improvement in symptoms after 48 hours, exploratory tympanotomy and repair of a possible labyrinthine window fistula should be considered. Recompression therapy is contraindicated in these cases...

Action Potentials↗

PubMedDate not supplied

Treatment of radiation-induced tissue injury by hyperbaric oxygen.

Hyperbaric oxygen therapy appears to be a beneficial adjunctive treatment modality in the management of radionecrosis of bone and soft tissue in the head and neck. The mechanism of such wound healing enhancement appears to be related to oxygen stimulation of fibroblastic activity and neovasculation. In this pilot study, involving 13 cases of refractory mandibular radionecrosis treated with hyperbaric oxygen, complete healing of soft tissue disease with covering of exposed bone has been noted in seven cases 11 to 27 months posttreatment; transient healing was seen in three cases; moderate to marked improvement in soft tissue disease has been noted in three cases. Pain relief was marked in six cases, moderate in four cases, and slight in one case of the 11 patients with significant pretreatment pain. Radiographic improvement was slight to moderate in ten cases. Four of the five patients with pathologic fractures developed a firm fibrous union of the mandibular segments during or shortly after treatment. Three additional cases of head and neck radionecrosis of other sites have noted significant improvement in their lesions during treatment. Three other patients with radionecrosis of the foot, hip, and vagina have also been treated with good results only in the vaginal case. None of the 19 patients treated with hyperbaric oxygen developed persistent or significant complications.

Female↗