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Biomedical subjects

M D Fischer

Publications and source records attributed to M D Fischer.

16 recordsLinked to original sources
PubMed2001

The effect of exposure to 35,000 ft on incidence of altitude decompression sickness.

INTRODUCTION: Exposure to 35,000 ft without preoxygenation (breathing 100% oxygen prior to decompression) can result in severe decompression sickness (DCS). Exercise while decompressed increases the incidence and severity of symptoms. Clarification of the level of activity vs. time to symptom onset is needed to refine recommendations for current operations requiring 35,000-ft exposures. Currently, the U.S. Air Force limits these operations to 30 min following 75 min of preoxygenation. The objective of this study was to determine the effect of exercise intensity on DCS incidence and severity at 35,000 ft. METHODS: Following 75 or 90 min of ground-level preoxygenation, 54 male and 38 female subjects were exposed to 35,000 ft for 3 h while performing strenuous exercise, mild exercise, or seated rest. The subjects were monitored for venous gas emboli (VGE) with an echo-imaging system and observed for signs and symptoms of DCS. RESULTS: Exposures involving strenuous and mild exercise resulted in higher incidence (p < 0.05) and earlier onset of symptoms (p < 0.05) of DCS than exposure at rest. Mild and strenuous exercise during exposure did not differ in incidence or rate of onset. Incidence at 30 min of exposure was 8% at rest and 23% while exercising. CONCLUSION: The results showed that current guidelines for 35,000-ft exposures keep DCS risk below 10% at rest. Exercise, even at mild levels, greatly increases the incidence and rate of onset of DCS.

Aerospace Medicine↗
PubMed1999

Exercise-induced altitude decompression sickness.

BACKGROUND: It has been known since World War II that exercise at altitude increases incidence of decompression sickness (DCS). However, data on the effects of specific exercise types at altitude are lacking. This research focused on the relative hazards of exercise without motion (isometric, straining) vs. dynamic exercise involving motion. The study also compared arm vs. leg exercise. METHODS: There were 32 healthy male subjects exposed, while resting, to 29,500 ft (8992 m) for 4 h or until DCS occurred, at which time they were brought to ground level. If the subject developed DCS on this exposure, he was exposed in successive months to lower altitudes, using the same procedure, until the subject was free of symptoms for the 4-h exposure. At this symptom-free altitude, as low as 20,000 ft (6096 m), the subject performed isometric arm, isometric leg, dynamic arm and dynamic leg exercises at less than 10% of maximal oxygen consumption, each during separate exposure months. Precordial venous gas emboli (VGE) were monitored every 20 min during each exposure with a Hewlett-Packard SONOS 1000 Echo Imaging System. RESULTS: Dynamic arm, dynamic leg, isometric arm, and isometric leg exercise induced DCS in 50%, 38%, 41% and 31% of the subjects, respectively. VGE incidence varied from 47-66%. No significant differences in DCS or VGE were found. CONCLUSIONS: Under our test conditions, there was no difference between dynamic and isometric exercise in eliciting DCS. Exercise during exposure to the symptom-free altitude for 4 h produced a 40% incidence DCS.

Adult↗
PubMed1998

Male/female SACM endurance comparison: support for the Armstrong Laboratory modifications to the CSU-13B/P anti-G suit.

BACKGROUND: The standard anti-G suit (CSU-13B/P) was designed based on male body structure. Females differ from males with respect to body proportionality. In Armstrong Laboratory (AL) studies, females have terminated centrifuge simulated air combat maneuvers (SACM) because of anti-G suit (CSU-13B/P modified according to original T.O. 14P3-6-121)(OTO) discomfort. AL modifications to the suit have since been adopted in the OTO in an attempt to provide females a best-fit suit (AL Mod). The study examined male/female SACM endurance with females wearing both the OTO and the AL Mod suits. METHODS: There were 6 females and 8 males who performed a +5.0 to +9.0 Gz SACM to fatigue using the anti-G straining maneuver with anti-G suit inflation. The females performed in both the OTO and AL Mod suits while the males performed in the OTO suit only (OTO was their best-fit suit). RESULTS: Wearing the OTO, males performed the SACM significantly longer than the females, three of whom reported severe suit discomfort. However, when the females wore the AL Mod suit, their SACM endurance almost doubled over their OTO performance and none reported suit discomfort. When wearing their best-fit suits, there was no significant gender difference in SACM endurance. CONCLUSIONS: These data support the efficacy of the AL modifications to the CSU-13B/P anti-G suit through greatly improved performance during the +5.0 to +9.0 SACM in females. These data also suggest that, in the small sample examined, when fitted with a best-fit anti-G suit, females can endure the +5.0 to +9.0 SACM to the same degree as males.

Acceleration↗
PubMed1997

Treatment of unstable distal radius fractures: methods and comparison of external distraction and ORIF versus external distraction-ORIF neutralization.

Twenty-six closed unstable distal radius fractures were treated using a combination of internal fixation, external distraction (intraoperative), and, in some cases, up to 4 weeks of postoperative external fixation (neutralization). Intraoperative stability check determined the need for external neutralization. This combined technique allowed a comprehensive approach to even the most unstable fracture by merging the advantages of internal and external fixation. Up to 4 weeks of external fixation (neutralization) was not associated with the complications of external fixation usually reported.

Absenteeism↗
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

Exercise-enhanced preoxygenation increases protection from decompression sickness.

INTRODUCTION: Prevention of decompression sickness (DCS) during exposure to altitude equivalents of 30,000 ft (9144 m) requires extensive denitrogenation. In preparation for extravehicular activity (EVA), present NASA policy is to denitrogenate using a 10.2 psia staged decompression of the entire shuttle for at least 12 h, including 100 min of preoxygenation (breathing 100% oxygen at 14.7 psia prior to decompression), before decompression to the 4.3 psia (30,000 ft; 9144 m) suit pressure. This staged decompression provides the same or better protection from DCS as a 3.5- or 4-h preoxygenation used on earlier Shuttle EVA's. For high altitude reconnaissance flights at similar cockpit altitudes, a 1-h preoxygenation is currently required. METHODS: We have investigated the use of a 1-h and a 15-min preoxygenation period, each beginning with 10 min of dual-cycle ergometry performed at 75% of each subject's peak oxygen consumption (VO2peak) to enhance preoxygenation efficiency by increasing perfusion and ventilation. Male subjects accomplished a 1-h preoxygenation with exercise, a 15-min preoxygenation with exercise, or a 1-h resting preoxygenation before exposure to 4.3 psia for 4 h while performing light to moderate exercise. RESULTS: Incidence of DCS following the 1-h preoxygenation with exercise (42%; n = 26) was significantly less than that following the 1-h resting preoxygenation (77%; n = 26). Incidence and onset of DCS following the 15-min preoxygenation with exercise (64%; n = 22) was not significantly different from the incidence following the 1-h resting control. CONCLUSION: Preoxygenation with exercise has been shown to provide significantly improved DCS protection when compared with resting preoxygenation.

Adult↗
PubMed1994

Physeal and periphyseal injuries of the hand. Patterns of injury and results of treatment.

To the authors' knowledge, this is the largest study assembled of finger fractures in children. Distribution of fractures according to location within the hand (see Fig. 1), location within the phalanges themselves, and the percent of epiphyseal fractures as well as the age distribution of the patients are all similar to what has previously been presented in smaller studies. Previously unreported synchronous and double epiphyseal injuries were identified. For the most part, thanks to the remodeling capacity and rapid healing of children's bone, treatment is short and complications are few. Nevertheless, as in other locations, there is a limited capacity to remodel angular deformity and no capacity to remodel rotational deformity. The clinical information in our study conflicts somewhat with previously described anatomic information about the insertion of ligaments with respect to the growth plate. Bogumill and Hankin and Janda have suggested that the ligaments insert primarily on the epiphysis in the proximal phalanx, and on the epiphysis and metaphysis in the middle and distal phalanges. Taken by itself, this information would suggest that a Salter-Harris III mechanism would be relatively more common at the MP joint, and the Salter-Harris II and IV mechanism (where the proximal fragment includes bone both proximal and distal to the growth plate at the point where the ligament is attached) would be relatively more common at the more distal levels. In fact, the opposite was true. The Salter-Harris II mechanism made up an overwhelming majority of the percentage of injuries of the MP joint, whereas the Salter-Harris III mechanism predominated at the PIP joint and was relatively common at the DIP joint as well. This would seem to suggest that either the contribution of ligament insertion distal to the growth plate of the PIP and DIP joints is not functionally important or that other factors are involved in the injury mechanism at both levels and play a role in producing these injuries. Further study will be required, possibly involving experimental fracture production to help elucidate this issue. Finally, it is critical to recognize and properly treat the four major categories of injury that constitute a small percentage of the total but a large percentage of the complications. The condylar and subcondylar fractures must be identified by obtaining a true lateral film by whatever means necessary. If undisplaced, they need to be adequately immobilized, possibly including the entire arm of a small child, and if displaced, they almost always require internal fixation.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1991

The timing of flap coverage, bone-grafting, and intramedullary nailing in patients who have a fracture of the tibial shaft with extensive soft-tissue injury.

The cases of forty-three patients who had a Type-IIIB open fracture of the tibial shaft were reviewed to determine the effect of treatment of the soft-tissue injury on the rate of major complications. An infection developed in two of the eleven patients who had had early muscle-flap coverage compared with ten of the nineteen who had been managed by open care of the wound and nine of the thirteen who had had later flap coverage. Patients who had had bone-grafting after complete re-epithelialization of the wound, regardless of the method of closure, had a lower rate of early infection (none of sixteen compared with four of fifteen) and an earlier average time to union (fifty-four compared with sixty-three weeks) than those in whom the wound was not completely closed or was draining at the time of bone-grafting. Delayed intramedullary nailing with reaming was associated with a high rate of infection (nine of nineteen patients), regardless of the condition of the soft tissue at the time of nailing. In our opinion, adequate débridement and early assessment of the soft-tissue defect are necessary so that appropriate soft-tissue coverage can be provided within the first one to two weeks. When the soft-tissue portion of the injury is addressed promptly and definitively and then allowed to heal completely, secondary osseous reconstruction may proceed with fewer complications.

Adult↗
PubMed1979

Adrenocorticotropin-cortisol axis abnormalities in hemodialysis patients.

The ACTH-cortisol axis was studied in 15 hemodialysis patients. Basal plasma cortisol concentrations were found to be elevated and ACTH to be in the high normal range. Cortisol responded normally to exogenous ACTH, but neither cortisol nor ACTH were suppressed in response to oral dexamethasone. 11-Deoxycortisol and ACTH concentrations did not rise normally in response to either oral or iv metyrapone. We conclude that standard testing of the ACTH-cortisol axis in dialysis patients yields results suggesting Cushing's syndrome.

Adrenocorticotropic Hormone↗