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Biomedical subjects

R C Hill

Publications and source records attributed to R C Hill.

At least 37 records · Page 2Linked to original sources
PubMed1998

Resolution of experimental pneumothorax in rabbits by graded oxygen therapy.

BACKGROUND: Small pneumothoraces have been treated by observation and tube thoracostomy in asymptomatic patients. Using a rabbit model, we demonstrated previously that inspired oxygen at 60% FiO2 hastened the time to resolution of complete pneumothoraces compared with room air. The present study was designed to evaluate the use of lower levels of inspired oxygen and to establish a dose-response curve for the treatment of experimental pneumothoraces. METHODS: Forty New Zealand White rabbits were divided randomly into four groups: room air (21%) and 30, 40, and 50% FiO2. Experimental pneumothoraces were created in the rabbits, and the animals were placed in cages with the designated level of inspired oxygen. Serial chest radiographs were performed until the pneumothoraces resolved. RESULTS: Pneumothoraces treated with room air resolved in 61.65 +/- 12.30 hours. Those treated with 30% FiO2 resolved in 42.90 +/- 5.97 hours, with 40% FiO2 in 35.80 +/- 4.26 hours, and with 50% FiO2 in 33.80 +/- 4.66 hours. CONCLUSION: These results show a statistically significant (p < 0.01) dose-dependent improvement in the resolution of pneumothoraces with increasing levels of inspired oxygen. Supplemental oxygen therapy may be used to facilitate the resolution of small, uncomplicated pneumothoraces.

Animals↗
PubMed1998

Improved anti-G protection boosts sortie generation ability.

BACKGROUND: There is a need for evaluation of new G protection equipment. HYPOTHESIS: There is no difference between the two anti-G ensembles on affecting subjects' ability to tolerate multiple simulated aerial combat sorties. METHODS: There were 15 subjects wearing the standard CSU-13 B/P anti-G ensemble (STD) or COMBAT EDGE/ATAGS (CE/ATAGS) ensemble who were exposed to 3 centrifuge-based simulated air combat sorties during a 2-h period. Each sortie consisted of four different G-profiles: 1) a gradual onset profile; 2) simulated air combat maneuver consisting of +4.5 to +7 Gz plateaus (4.5-7 SACM); 3) simulated air combat maneuver derived from actual fighter maneuvers with peaks up to +9 Gz (TACM); 4) simulated air combat maneuver consisting of +5.0 to +9.0 Gz plateaus (5-9 SACM). Each sortie was separated by a 20-min rest period. We measured heart rate, peripheral light loss (PLL), subjective effort level, subjective fatigue level, and reported recovery time. RESULTS: There were no incidents of unintended G-induced loss of consciousness (G-LOC) with CE/ATAGS. There were four incidents of unintended G-LOC with STD. At the end of the third sortie, with CE/ATAGS, mean heart rate was lower during the 4.5-7 SACM (p < 0.001) and the TACM (p < 0.001); PLL was less during all three rapid onset profiles (p < 0.01); subjects reported less effort during the 4.5-7 SACM (p < 0.001), the TACM and the 5-9 SACM (p < 0.01); reported fatigue was significantly lower (p < 0.001); and reported recovery times were nearly halved (p < 0.01). CONCLUSION: CE/ATAGS provided significantly greater G-protection than the standard anti-G ensemble. There was no G-LOC with CE/ATAGS. This greater protection should be of significant operational value in enhancing sortie generation capability by increasing fighter aircrew G-tolerance and decreasing aircrew fatigue.

Adult↗
PubMed1998

Tactical vs. other simulated aerial combat maneuvers.

BACKGROUND: There is a need for a more operationally relevant +Gz profile for centrifuge-based research and evaluation. This article describes a simulated aerial combat maneuver (SACM) named the Tactical Aerial Combat Maneuver (TACM). HYPOTHESIS: A more representative centrifuge-based SACM can be devised for high-G acceleration research and evaluation. METHODS: TACM consists of 9G x 5 s, 5G x 1 s, 8G x 5 s, and 4G x 2 s. TACM was compared against the widely accepted 4.5-7G and 5-9G SACMs. There were 15 centrifuge subjects used in this study. RESULTS: TACM accounted for all four incidents of G-Induced Loss of Consciousness (G-LOC); and most incidents of blackouts (5 of 8) observed. CONCLUSION: TACM simulates the seesaw pattern of +Gz forces of aerial combat and retains the reproducibility needed for acceleration research and evaluation. TACM captures the high onset, high amplitude +Gz changes of aerial combat when G-LOC and blackouts are more likely to occur. TACM should be particularly useful for evaluation of G-protective equipment and maneuvers, as well as fighter aircrew medical evaluations.

Adult↗
PubMed1997

Female acceleration tolerance: effects of menstrual state and physical condition.

INTRODUCTION: The literature contains a paucity of information on female tolerance to high sustained acceleration. With women now flying high-performance aircraft, gender-specific factors that may affect female acceleration tolerance have become increasingly important. The purpose of this investigation was to determine how menstrual state and physical condition affect acceleration tolerance. We hypothesized the menstrual cycle would have no effect on acceleration tolerance and that a positive correlation would exist between physical fitness level and tolerance to high sustained acceleration. METHODS: Centrifuge exposures on 8 female subjects consisted of a relaxed gradual-onset run (0.1 G.s-1) to the visual endpoint, a rapid-onset run (6 G.s-1) to +5 GZ for 15 s, and a +4.5 to +7 GZ simulated aerial combat maneuver (SACM) to physical exhaustion. Acceleration tolerance data were collected at onset of menstruation and 1, 2 and 3 weeks following the onset for two complete menstrual cycles. On separate days, body composition, anaerobic power output and peak oxygen uptake were determined. Retrospective data from 10 male subjects who had performed the +4.5 to +7 GZ SACM were analyzed and compared to these data. RESULTS: Analysis of variance revealed no significant difference in relaxed tolerance or SACM duration between the four selected menstrual cycle time points. Time-to-fatigue on the +4.5 to +7 GZ SACM was positively (p < or = 0.05) correlated with absolute fat-free mass (r = 0.87) and anaerobic power production (r = 0.76) in female subjects. However, when these variables were adjusted for total body mass, the significant correlations no longer existed. No correlation was found between SACM duration and absolute (L min-1) nor relative (ml.kg-1.min-1) aerobic fitness. Time-to-fatigue during the SACM was not significantly different between male and female subjects (250 +/- 97 and 246 +/- 149 s, respectively).

Acceleration↗
PubMed1996

Selective lung ventilation during thoracoscopy: effects of insufflation on hemodynamics.

BACKGROUND: Positive-pressure insufflation during thoracoscopy has been advocated by some authors to facilitate exposure of the intrathoracic structures by expediting collapse of the lung. We hypothesized that insufflation during thoracoscopy may result in hemodynamic compromise despite selective lung ventilation. METHODS: After placement of invasive monitoring lines, six adult swine underwent selective lung ventilation and thoracoscopy. Baseline measurements of hemodynamic indices were taken before selective lung ventilation. The right lung then was collapsed; data were obtained at insufflation pressures up to 10 mm Hg and were compared with baseline values using Student's t test. RESULTS: Cardiac index, mean arterial pressure, and left ventricular stroke work index decreased, whereas pulmonary artery and central venous pressures increased (p < 0.05) at insufflation pressures of 5 mm Hg and greater. CONCLUSIONS: Positive-pressure insufflation during thoracoscopy resulted in significant hemodynamic compromise despite the use of selective lung ventilation. Conversion to thoracotomy may be an alternative if positive-pressure insufflation is necessary to perform the thoracoscopic procedure.

Animals↗
PubMed1996

The use of chromic oxide as a marker for measuring small intestinal digestibility in cannulated dogs.

Small intestinal digestibility can be measured by comparing feed with effluent collected from an ileal T-cannula. Nevertheless, a nondigestible, nonabsorbable marker, such as chromic oxide (Cr2O3), must be included in the diet because simple T-cannulae do not divert chyme completely. This study was conducted to evaluate the excretion pattern of Cr2O3 in cannulated dogs because the kinetics of Cr2O3 has not been previously investigated in this nonruminant species. Chromic oxide was added to four diets fed to eight cannulated mixed-breed dogs in a Latin-square design. The four diets contained reciprocal proportions of protein from texturized vegetable protein (0% to 57%) and from beef (100% to 43%), so protein and carbohydrate digestibility varied among diets. All feces were collected during wk 2 and all ileal effluent during wk 3 of each diet period. Ileal recovery of Cr2O3 was almost complete (94%) and was greater than fecal recovery (87%) (P < or = .03). Recovery was not different among diet groups. Ileal DM digestibility was approximately 2 percentage units lower on d 1 (P < or = .007) than on d 2 to 4. Nevertheless, ileal DM digestibility varied little on these subsequent days so single-day collections should be accurate. Chromic oxide concentration in chyme varied widely during each collection but increased at the start and declined towards the end of each collection. Spot sampling may therefore result in inaccurate estimates of nutrient digestibility. In conclusion, Cr2O3 may be used as a marker to measure digestibility in dogs with simple T-cannulae, but total collections should be attempted for greater accuracy.

Animals↗
PubMed1996

Ileal cannulation and associated complications in dogs.

Accurate measurement of small intestinal digestibility is important in dogs because it allows the formulation of pet foods that provide optimal nutrition at minimal cost. Digestibility measured by comparing nutrient intake to fecal excretion in intact animals does not distinguish small intestinal digestion from large intestinal bacterial fermentation. Ileal cannulation allows small intestinal digestion to be measured alone by comparing nutrient intake with ileal excretion of chyme. Nevertheless, ileal cannulation and its associated complications are not well documented in dogs. We describe the implantation of a simple T-cannula in the ileum of nine dogs for an average duration of 26 weeks. Established cannulas were well tolerated, and one dog retained the cannula for 14 months. Nevertheless, ileal effluent proved extremely caustic, and the incidence of complications in the immediate postoperative period was high. Only one dog had an unremarkable postoperative course. Complications included abscessation and cannula extrusion, followed by severe excoriation and ulceration of the skin. This excoriation could be prevented only by immediate surgical closure of the fistula. Chronic ileal cannulation is therefore a viable technique in dogs, but careful monitoring of the cannula site is essential. Dogs should be subjected to this procedure only if adequate veterinary and nursing care is available. It is preferable to maintain a colony of long-term cannulated dogs rather than to implant cannulas as needed.

Animals↗
PubMed1995

Resolution of experimental pneumothorax in rabbits by oxygen therapy.

The treatment of asymptomatic patients with small pneumothoraces (ie, less than 20% by volume) has included observation, tube thoracostomy, and operation. When observation is used, the anticipated expansion of the lung has been estimated to be 1.25% of the lung volume daily. This study was designed to evaluate the use of inhaled oxygen as a method to accelerate the resolution of a pneumothorax in a rabbit model. Experimental pneumothoraces were created in 23 white New Zealand rabbits. Group 1 (9 rabbits) were placed in a cage with room air and group 2 (11 rabbits) were placed in a cage with high oxygen concentration. Three rabbits died before completion of the study. Serial chest roentgenograms were performed until the pneumothoraces resolved. The majority of rabbits treated with oxygen had resolution of their pneumothoraces by 36 hours, whereas the majority of rabbits treated with room air did not show complete resolution before 48 hours. Biopsies showed no evidence of damage secondary to oxygen treatment. Oxygen treatment was found to be significantly better in the early resolution of pneumothoraces when compared with room air. This establishes an alternative treatment for some pneumothoraces that are small and asymptomatic.

Animals↗
PubMed1995

Biatrial approach to cardiac myxomas: a 30-year clinical experience.

Early surgical intervention for atrial myxomas mitigates morbidity and usually offers cure. The operative approach to resect these tumors is controversial. The purpose of this study was to review our experience with the biatrial approach between 1964 and 1994. The location of the myxoma was left atrium in 17 and right atrium in 3. Mean preoperative New York Heart Association functional classification was 2.7. Surgical approach to the tumor was biatrial in all patients. There were no perioperative strokes, myocardial infarctions, or deaths. Mean follow-up was 7.5 years (range, 2 mo to 27 years) with a postoperative New York Heart Association functional classification of 1.4. One late death occurred, which was unrelated to the myxoma. Advantages of biatrial approach include (1) definition of tumor pedicle by direct visualization, (2) minimal manipulation of the tumor, (3) adequate margins of excision, (4) inspection of all heart chambers, and (5) secure closure of the atrial septal defect. Long-term follow-up demonstrates the efficacy of this operative approach to atrial myxomas.

Adolescent↗
PubMed1995

Preservation of adenosine 5'-triphosphate and mitochondrial function during hypercalcemic reperfusion using verapamil cardioplegia.

Immediate hypercalcemic reperfusion results in ventricular dysfunction and loss of high-energy stores. The purpose of this study was to evaluate the effect of verapamil cardioplegia on the preservation of myocardial energy stores, mitochondrial ultrastructure, and ventricular dysfunction in the postischemic rat heart during immediate hypercalcemic reperfusion. Rats in the control group were subjected to cardioplegia with potassium, while rats in groups 1 to 3 were subjected to the same with verapamil (0.5 mg/L). The control and group 1 rats underwent normocalcemic reperfusion and groups 2 and 3 rats underwent hypercalcemic reperfusion. Myocardial samples were analyzed for adenosine 5'-triphosphate (ATP) content and mitochondrial ultrastructural damage. Hemodynamic parameters of heart rate, aortic flow (AF), and postischemic rate of aortic pressure change (dP/dT) also were evaluated. Data were analyzed using analysis of variance. The ATP stores were preserved at greater than 100% control levels in hearts subjected to verapamil cardioplegia. There was no evidence of irreversible mitochondrial damage. Heart rate, AF, and dP/dT were significantly (p < 0.05) depressed in hearts subjected to verapamil cardioplegia. This study suggests verapamil cardioplegia preserves ATP and mitochondrial function during immediate hypercalcemic reperfusion but does not improve postischemic hemodynamics.

Adenosine Triphosphate↗
PubMed1995

Successful case of extracorporeal life support in a patient with postcardiotomy cardiogenic shock.

Over the past five years, the use of extracorporeal life support in the adult population has gained acceptance. Indications have ranged from respiratory failure secondary to trauma, and adult respiratory distress syndrome, to cardiac failure secondary to a number of causes. The results of extracorporeal life support, when applied to postcardiotomy patients, have been variable. In this article, we present the successful utilization of extracorporeal life support for 28 hours in a patient with postcardiotomy cardiogenic shock following mitral valve replacement.

Extracorporeal Membrane Oxygenation↗
PubMed1994

Attempt at deriving a formula for setting general practitioner fundholding budgets.

OBJECTIVE: To explore the possibility of using routine Hospital Episode Statistics, census data, and vital statistics to derive weights for an equitable capitation formula for setting general practitioner fundholding budgets for buying acute hospital services. DESIGN: Analysis of a routine dataset of 9 million hospital episodes in 1991-2, extracting elective general practitioner fundholding procedures, combined with 1991 census variables, vital statistics, and data on supply of health care at ward level. Costs were attached to each procedure according to the average cost of the relevant "Mersey" band category. MAIN OUTCOME MEASURES: Variation in age and sex adjusted expenditure per head on fundholding procedures across wards modelled for the impact of health and social needs variables after adjusting for variations in supply. RESULTS: No sensible simple model including determinants of use other than age and sex could be derived. The most parsimonious but statistically acceptable model showed that though standardised mortality ratio and self reported illness and several social class variables were associated with utilisation, the signs and the size of the coefficients were contradictory. The most important explanation of variation was provided by age and sex differences between wards. CONCLUSIONS: An equitable system of setting general practitioner fundholders' budgets is needed. In the short term age and sex weighted capitation should form the principal basis of fundholder budgets. Utilisation data at ward level are inadequate for developing a formula which adequately adjusts for the differences in the health care needs of populations. A capitation formula based on information derived from individual cohort data may be the only means of promoting equity and efficiency and of avoiding discriminating against patients with known high cost health problems.

Adolescent↗
PubMed1994

Safe use of heparin-coated bypass circuits incorporating a pump-oxygenator.

Durable, covalently bonded, heparin-coated cardiopulmonary bypass (CPB) circuits with oxygenators have been developed. Proposed advantages of heparin-coated CPB circuits include improved biocompatibility and thromboresistance. The purpose of this study was to evaluate our experience with heparin-coated CPB circuits in 20 patients. Heparin was given to maintain an activated clotting time equal to or greater than 200 seconds, while flow rates were kept equal to or greater than 2 L/min. Indications for use of this circuit included recent stroke, posttraumatic injuries, recent gastrointestinal bleeding, protamine allergies, combined cardiac and noncardiac procedures, and ventricular assist. Mean heparin dosage was 0.50 +/- 0.18 mg/kg and protamine dosage was 57.14 +/- 39.36 mg. Postoperative blood loss and transfusion requirements were minimal. Postoperative complement levels of C3a and C5a were normal, suggesting excellent biocompatibility. There were no deaths or perioperative complications. Heparin-coated CPB circuits using a pump oxygenator can be used safely with low-dose heparin administration in select patients requiring CPB.

Adolescent↗
PubMed1994

The effect of head and body position on +Gz acceleration tolerance.

It has been suggested there is a relationship between acceleration-induced loss of consciousness (G-LOC) and head/body position. A two-part investigation was conducted to determine whether head and body position affects acceleration tolerance. A retrospective analysis of high-G training data (N = 1,914) compared G-LOC occurrence during straight-ahead exposure to a "check-6" exposure [10 s at +9 Gz; 6 G/s onset rate; G-suit inflated; anti-G straining maneuver (AGSM) performed]. A prospective study (N = 12) was conducted with acceleration exposures using light loss criteria with subjects in straight-ahead, above, over-the-right shoulder, or over-the-left shoulder positions. Profiles consisted of 0.1 G/s onset-rate runs (no G-suit inflation; relaxed) to a maximum of +9 Gz and 0.5 G/s onset-rate runs (G-suit inflated; AGSM performed) to +9 Gz for up to 26 s. In the retrospective study, no significant difference existed between G-LOC occurrence during straight-ahead (22/1914) and check-6 (32/1914) positions. During the prospective study with AGSM runs, there was no significant difference in the time at maximum G among any of the positions. During the relaxed runs, several comparisons yielded significant differences in peak G attained. These results indicate there may be an underlying physiologic effect of head and body position on acceleration tolerance; however, the AGSM and the G-suit overcame this effect. Although task saturation and distraction may compromise performance of the AGSM and subsequently predispose acceleration-related hazards, a proper AGSM, combined with effective protective systems, remains essential components of a protection strategy.

Acceleration↗