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Biomedical subjects

J W Fanton

Publications and source records attributed to J W Fanton.

54 records · Page 3Linked to original sources
PubMed1991

Performance recovery following +Gz-induced loss of consciousness.

Seven male baboons (average weight, 20.6 kg) were trained in a simple shock-avoidance performance task on the USAFSAM centrifuge. A red light was presented to the baboon at approximate 2-s intervals. The animal was allowed 1 s to turn off the light or receive a 1-s shock. The shock could be abbreviated by a late trigger pull. Thus, the animal could avoid, escape, or accept the full shock. EEG was monitored from three transcranial stainless steel electrodes. Loss of consciousness (LOC) was induced by a rapid onset (4 or 6/s) exposure to 8 +Gz and sustained until LOC was identified by a near isoelectric EEG signal. Performance recovery time was measured from the return of EEG activity to the time when the animal resumed the performance task. These data were compared with previously obtained human data and found to be very similar. Also, it was found that time of performance recovery became significantly shorter after multiple LOC exposures and the performance recovery time significantly increased with increased time of unconsciousness. This study demonstrates the utility of the baboon as an animal model for G-induced LOC (G-LOC) research.

Aerospace Medicine↗
PubMed1990

Force necessary to fracture the orbital floor.

Current thought on the pathophysiology of orbital wall fractures postulates either a "hydraulic" or a "buckling" mechanism. Evidence from cadaver, dried skull, and theoretical model studies supports both theories. No in vivo data, human or nonhuman primate, are available that quantitate the force necessary to fracture the orbital floor by either of the two mechanisms. We developed an apparatus that delivers quantifiable force only to the globe, without occluding the orbital opening or striking the orbital rim. We used it on 11 anesthetized Macaca fascicularis monkeys. Following a single bilateral application, the orbits were exenterated, and the orbital walls and orbital contents were examined to determine the extent of injuries. Fractures were described, diagrammed, and photographed. Fracture of the orbital floor was consistently produced at and above a force of 2.08 J. Posterior ruptures of five eyes occurred over the same range. We provide the first accurate measurements of the force required to produce orbital blow-out fractures in a live primate model. We show that orbital floor fractures can occur at low energies with direct ocular trauma only ("pure" hydraulic mechanism). Orbital wall fractures failed to protect the globe from rupture in 23% of cases.

Animals↗
PubMed1989

Effects of dipyridamole on the cardiovascular response to +Gz stress in miniature swine.

Eight conscious female miniature swine experienced acceleration levels of 3, 5, and 7 +Gz before and after infusion of dipyridamole (1-2 mg.kg-1). Each animal was instrumented to measure ECG, heart level arterial pressure (AP), eye level arterial pressure (ELBP), left arterial pressure (LAP), heart rate (HR), and regional tissue blood flows. Each was also fitted with an abdominal anti-G suit which automatically inflated. Dipyridamole infusion had no direct effect on HR or LAP but AP was significantly reduced. All cardiovascular responses to +Gz were qualitatively similar before and after dipyridamole. Tachycardia always occurred. AP and CNS blood flow were maintained better prior to dipyridamole and AP always fell in proportion to acceleration intensity. +Gz was generally associated with increased blood flow to respiratory muscles and heart, decreased blood flow throughout the viscera and to the eyes. ELBP paralleled AP, but was always lower in direct proportion to the +Gz level. We conclude that dipyridamole reduces arterial pressure thus compromising the ability of the animal to sustain cerebral perfusion pressure (ELBP) during +Gz.

Animals↗
PubMed1987

Renal medullary solute depletion resulting from psychogenic polydipsia in a rhesus monkey.

A rhesus monkey developed psychogenic polydipsia after a change in feeding regimen was instituted. Hyposthenuria, hyponatremia, hypochloremia, and an abnormal calculated plasma osmolality were found. Water deprivation testing and administration of antidiuretic hormone indicated that renal medullary solute depletion had resulted from the prolonged polyuria. Restricted water consumption resulted in resolution of the electrolyte abnormalities and restored ability to excrete concentrated urine.

Animals↗
PubMed1986

Air travel and intraocular gas.

The safety of air travel for persons with intraocular gas after ocular surgery has been in question since the mid 1970s, when the use of intraocular gases after vitrectomy became widespread. After vitrectomy, air-fluid exchange was performed on six Rhesus monkeys. During simulated air travel in an altitude chamber, intraocular pressure rose an average of 42 mmHg with intraocular air volumes as small as 0.25 cc. Hypotony was observed after return to ground level in all cases. Transient central retinal artery occlusion and pupillary block was observed. Patient safety and comfort is endangered during air travel with very small volumes of intraocular gas.

Aircraft↗
PubMed1986

Endometriosis: clinical and pathologic findings in 70 rhesus monkeys.

Endometriosis was histologically confirmed in 70 female rhesus monkeys (Macaca mulatta). Severity of endometriosis was staged as minimal (14% of the monkeys), moderate (20%), or massive (66%). Clinical examination indicated masses in the abdomen and/or pelvic cavity palpable abdominally (64% of the monkeys) or rectally (93%), constipation (29%), anorexia (39%), irregular menses (17%), and radiographic evidence of abdominal soft tissue masses (38%). Pathologic findings were of intra-abdominal endometrial cyst formation (73% of the monkeys), and adhesions involving the ureters (51%), colon (66%), urinary bladder (50%), or ovaries (81%). Metastatic growth of endometrial tissue was found in 4 (6%) of the monkeys.

Animals↗
PubMed1986

Surgical treatment of endometriosis in 50 rhesus monkeys.

Surgical treatment of endometriosis was attempted in 50 female rhesus monkeys (Macaca mulatta). Endometriosis was clinically staged as minimal (8% of the monkeys), moderate (18%), or massive (74%). Elective euthanasia was performed in 15 (30%) of the monkeys. Total abdominal hysterectomy with bilateral salpingo-oophorectomy was performed in 30 (60%) of the monkeys, and bilateral salpingo-oophoretomy alone was performed in 5 (10%) monkeys. Statistical differences were not found in Kaplin-Meier survival curves between the different stages of endometriosis (P = 0.6297).

Animals↗
PubMed1985

Cosmetic repair of chronic head restraint defects.

Surgically implanted head restraint devices have been used in nonhuman primate research for more than a decade. Superficial scalp defects are created by the implantation procedures and remain after the devices are removed, a factor that occasionally hinders continued use of the animals by investigators on esthetic grounds. A technique is described whereby the scalp defects are surgically repaired, resulting in a good cosmetic appearance and effectively increasing the potential for reuse of these animals.

Animals↗
PubMed1984

Paralysis due to a glomangioma in a Macaca mulatta.

A glomangioma at the 6-7 thoracic intervertebral space caused compression of the spinal cord with posterior paralysis in an irradiated 20-year-old female rhesus monkey (Macaca mulatta). Glomangiomas are tumors of arterial-venous shunts, are rare and have only been reported in irradiated rhesus monkeys.

Animals↗
PubMed1983

Spontaneous endometriosis in a cynomolgus monkey (Macaca fascicularis).

An adult female Macaca fascicularis developed anorexia and minimal fecal production. Abdominal palpation was unrewarding. Rectal palpation revealed a rectal stricture and a large soft tissue mass in the area of the uterus. Clinical pathology tests were within normal limits. Exploratory surgery and histopathology confirmed a diagnosis of endometriosis.

Animals↗
PubMedDate not supplied

Effects of 12 days exposure to simulated microgravity on central circulatory hemodynamics in the rhesus monkey.

Central circulatory hemodynamic responses were measured before and during the initial 9 days of a 12-day 10 degrees head-down tilt (HDT) in 4 flight-sized juvenile rhesus monkeys who were surgically instrumented with a variety of intrathoracic catheters and blood flow sensors to assess the effects of simulated microgravity on central circulatory hemodynamics. Each subject underwent measurements of aortic and left ventricular pressures, and aortic flow before and during HDT as well as during a passive head-up postural test before and after HDT. Heart rate, stroke volume, cardiac output, and left ventricular end-diastolic pressure were measured, and dP/dt and left ventricular elastance was calculated from hemodynamic measurements. The postural test consisted of 5 min of supine baseline control followed by 5 minutes of 90 degrees upright tilt (HUT). Heart rate, stroke volume, cardiac output, and left ventricular end-diastolic pressure showed no consistent alterations during HDT. Left ventricular elastance was reduced in all animals throughout HDT, indicating that cardiac compliance was increased. HDT did not consistently alter left ventricular +dP/dt, indicating no change in cardiac contractility. Heart rate during the post-HDT HUT postural test was elevated compared to pre-HDT while post-HDT cardiac output was decreased by 52% as a result of a 54% reduction in stroke volume throughout HUT. Results from this study using an instrumented rhesus monkey suggest that exposure to microgravity may increase ventricular compliance without alternating cardiac contractility. Our project supported the notion that an invasively-instrumented animal model should be viable for use in spaceflight cardiovascular experiments to assess potential changes in myocardial function and cardiac compliance.

Aerospace Medicine↗
PubMedDate not supplied

A conscious baboon model for evaluation of hemodynamics in altered gravity.

A model was developed for evaluation of cardiovascular parameters in conscious baboons exposed to altered gravitational environments. Baboons were trained to sit quietly in a confinement chair of unique design which allowed a range of normal physical activity. They were then instrumented with high-fidelity blood pressure transducers in the aorta and left ventricle, electromagnetic flow probes encircling the proximal ascending aorta, left and right atrial fluid catheters, left ventricular sonomicrometer crystals in a 3-axis configuration, and a hydraulic occluder cuff encircling the inferior vena cava. Catheters and transducer wires were exteriorized at the midscapular region of the back. Viability of percutaneous exit sites was enhanced by use of velour cuffs on the transducer wires, providing a scaffold for wound healing. Pressure transducers and flow probes were calibrated and balanced during postoperative cardiac catheterization procedures. This instrumentation allowed measurement of beat-to-beat stroke volume and cardiac output not reliant on thermodilution techniques. Postoperative longevity was from 1 to 10 months. Instrumentation failure included endocardial trapping of ventricular pressure transducers, corrosion of ventricular sonomicrometer crystals, and catheter tip thrombosis. Acquisition of high quality data was possible with this model in several different environments of altered gravitational stress, allowing characterization of aortic flow and ventricular performance.

Animals↗
PubMedDate not supplied

A method for repeated high-fidelity micromanometer measurement of intracardiac pressures.

Dial-tipped, high-fidelity micromanometers were inserted through polyurethane catheters to acutely measure blood pressures within the chambers of the heart and the great vessels of baboons, rhesus monkeys, and goats. Repeated measurements of atrial, ventricular, aortic, and pulmonary artery pressure were possible with this method, with calibration of micromanometers accomplished immediately prior to and after pressure recordings to assure data accuracy. All attempts to pass micromanometers into the atria in all species were successful. Passage of micromanometers from the left ventricle across the aortic valve and into the aorta was successful in 97% of the attempts in baboons, 100% for rhesus monkeys, and 75% for goats; while insertions into the pulmonary artery from the right ventricle were successful in 64% of the baboons, 40% of the rhesus monkeys, and 75% of the goats. Advantages of this technique are that a permanent conduit for cardiac vascular access is available and that high-fidelity pressure signals may be acquired.

Animals↗
PubMedDate not supplied

Evaluation of transit-time and electromagnetic flow measurement in a chronically instrumented nonhuman primate model.

The Physiology Research Branch at Brooks AFB conducts both human and nonhuman primate experiments to determine the effects of microgravity and hypergravity on the cardiovascular system and to identify the particular mechanisms that invoke these responses. Primary investigative efforts in our nonhuman primate model require the determination of total peripheral resistance, systemic arterial compliance, and pressure-volume loop characteristics. These calculations require beat-to-beat measurement of aortic flow. This study evaluated accuracy, linearity, biocompatability, and anatomical features of commercially available electromagnetic (EMF) and transit-time flow measurement techniques. Five rhesus monkeys were instrumented with either EMF (3 subjects) or transit-time (2 subjects) flow sensors encircling the proximal ascending aorta. Cardiac outputs computed from these transducers taken over ranges of 0.5 to 2.0 L/min were compared to values obtained using thermodilution. In vivo experiments demonstrated that the EMF probe produced an average error of 15% (r = .896) and 8.6% average linearity per reading, and the transit-time flow probe produced an average error of 6% (r = .955) and 5.3% average linearity per reading. Postoperative performance and biocompatability of the probes were maintained throughout the study. The transit-time sensors provided the advantages of greater accuracy, smaller size, and lighter weight than the EMF probes. In conclusion, the characteristic features and performance of the transit-time sensors were superior to those of the EMF sensors in this study.

Animals↗