Anomalous Decay of Nanomechanical Modes Going Through Nonlinear Resonance.

Because of the small size of nanomechanical systems, their vibrations become nonlinear already for small amplitudes. Many nontrivial aspects of the vibration dynamics arise from the coexistence of several nonlinearly coupled modes. We show that such coupling can lead to anomalous decay of the modes where they go through nonlinear resonance, so that their amplitude-dependent frequencies become commensurate. We demonstrate the possibility of a strongly nonmonotonic dependence of the decay rate on the amplitude if one of the modes serves as a thermal reservoir for another mode. Where the decay of both modes is slow compared to the rate of resonant energy exchange, the decay is accompanied by amplitude oscillations. Depending on the initial conditions, with increasing time it can display an extremely sharp or a comparatively smooth crossover between different regimes. The results provide insight into recent experimental results by several groups and suggest new ways of characterizing and controlling nanomechanical systems.

Ovulation induction and risk of endometrial cancer: a pilot study.

OBJECTIVE: To determine whether women with endometrial carcinoma are more likely to have been exposed to fertility drugs, in particular clomiphene, than healthy population controls. STUDY DESIGN: A nationwide case-control, pilot study. About 128 living women 35-64 years old, with a histologically confirmed diagnosis of endometrial carcinoma that was first diagnosed and reported to The Israel Cancer Registry between 1 January 1989 and 31 December 1992 were enrolled. The controls were 255 women from the same dialing areas selected by random digit dialing. A variety of demographic and clinical parameters were compared between cases and controls. A multivariate logistic model, controlling for age, was used to assess the independent effects of factors found to be significantly associated with endometrial cancer on univariate analysis. RESULTS: About 7 women with endometrial carcinoma (5.5%) and 10 healthy controls (3.9%) reported that they had used any fertility drug (crude odds ratio (OR) 1.4; 95% confidence interval (CI) 0.47-4.2). Use of fertility drugs did not meet the criteria for entry into the logistic model. The following parameters were found to be independently associated with endometrial cancer controlling for age, European-American background OR=2.2, (95% CI 1.3-3.7, P=0.004); nulliparity OR=2.7 (95% CI 1.1-6.5, P=0.03); history of infertility OR=1.8 (95% CI 1.0-3.3, P=0.05); BMI> or =27 OR=2.3 (95% CI 1.4-3.9, P=0.001). The use of oral contraceptives and IUD were found to be protective, OR=0.29 and 0.37, respectively, (95% CI 0.14-0.61, P=0.001 and 0.19-0.70, P=0.003, respectively). CONCLUSIONS: We found no evidence that the use of ovulation induction agents, including clomiphene citrate, are associated with a higher risk of endometrial carcinoma. The association between infertility drugs and endometrial carcinoma should be examined in other, larger studies.

The role of frozen storage in preserving adipose tissue obtained by suction-assisted lipectomy for repeated fat injection procedures.

BACKGROUND: The injection of autologous free fat obtained by suction-assisted lipectomy for the correction of soft tissue defects is a common procedure in plastic surgery. However, unpredictable partial absorption of the injected fat often necessitates repeated procedures. OBJECTIVE: To examine the role of frozen storage as a means of preserving the fat obtained by suction-assisted lipectomy for repeated procedures. METHODS: Human adipose tissue obtained by suction-assisted lipectomy was stored in a domestic refrigerator at -18 degrees C for 2 weeks. After thawing, the fat was injected into nude mice. In the control group, the fat was injected immediately after the harvesting procedure. Grafts were dissected out and compared 15 weeks postinjection. RESULTS: Injected fat survived in both study and control groups. No significant differences were found between fat graft weight and volume, or in any of the histologic parameters examined. CONCLUSION: Fat obtained by suction-assisted lipectomy may be preserved for future use by freezing.

The effect of hyperbaric oxygenation on the viability of human fat injected into nude mice.

Autologous free-fat injection for the correction of soft-tissue defects has become a common procedure in plastic surgery. The main shortcoming of this method for achieving permanent soft-tissue augmentation is the partial absorption of the injected fat, an occurrence that leads to the need for both overcorrection and repeated fat reinjection. Improving the oxygenation of the injected fat has been suggested as a means of helping to overcome the initial critical phase that occurs postinjection (when the fat cells are nourished by osmosis), increasing phagocyte activity, accelerating fibroblast activity and collagen formation, and enhancing angiogenesis. In addition, the hyperbaric oxygen-mediated decrement in endothelial leukocyte adhesion will decrease cytokine release, thereby reducing edema and inflammatory responses. The purpose of the present study was to examine the effect of hyperbaric oxygenation on improving the viability of injected fat. Adipose tissue obtained from human breasts by suction-assisted lipectomy was injected into the subcuticular nuchal region in nude mice. The mice were then exposed to daily hyperbaric oxygen treatments, breathing 100% oxygen at 2 atmospheres absolute (ATA) for 90 minutes. The duration of the administered hyperbaric oxygen therapy was 5, 10, or 15 days, according to the study group. Mice exposed to normobaric air alone served as the control group, and each group included 10 animals. The rats were killed 15 weeks after fat injection. The grafts were dissected out, weight and volume were measured, and histologic evaluation was performed. In all of the study groups, at least part of the injected fat survived, giving the desired clinical outcome. No significant differences could be found between the groups regarding fat weight and volume. Histopathologic examination of the dissected grafts demonstrated a significantly better integrity of the fat tissue in the group that received hyperbaric oxygen for 5 days (p = 0.047). This finding was manifested by the presence of well-organized, intact fat cells, along with a normal appearance of the fibrous septa and blood vessels. The worst results were found in animals treated by hyperbaric oxygenation for 15 consecutive days. An inverse correlation was found between an increased dose of the high-pressure oxygen and fat tissue integrity (r = -0.87, p = 0.076). The toxic effects of highly reactive oxygen species on fat cells might explain the failure of an excessively high dose of hyperbaric oxygen to provide any beneficial outcome. The clinical relevance of these results should be further investigated.

Prolonged elimination half-life of phenol after dermal exposure.

BACKGROUND: Phenol is a general protoplastic poison which has been in use in medicine and industry for decades. It is readily absorbed through the skin causing both local and systemic toxicity. CASE REPORT: A 47-year-old male had 90% phenol spilled over his left foot and shoe (3% of body surface area). After a 4 1/2-hour exposure, manifestations included confusion, vertigo, faintness, hypotension, ventricular premature beats, atrial fibrillation, dark-green urine, and tense swelling, blue-black discoloration, hypalgesia, and hypoesthesia of the affected area. Treatment consisted of irrigation with copious amounts of water, incisions, and supportive measures. RESULTS: Peak serum phenol was 21.6 micrograms/mL, considered in the fatal range. Peak urine phenol plus urine-conjugated phenol was 13,416 mg/g creatinine, indicating a major absorption. Elimination half-life was 13.86 hours, considerably longer than previously reported. CONCLUSIONS: Prolonged skin contact with concentrated phenol in an occlusive environment may result in a major absorption and a long elimination half-life even if the area involved is small. Prolonged elimination may be explained by extensive tissue distribution or by "slow-release reservoir" properties of the skin. Such exposure may be associated with severe systemic and local toxicities. Immediate removal from exposure and aggressive decontamination of the skin are essential to reduce these risks.

Effect of hyperbaric oxygen on a rat transverse rectus abdominis myocutaneous flap model.

The single-pedicle transverse rectus abdominis myocutaneous (TRAM) flap is frequently associated with partial flap necrosis. Hyperbaric oxygen has previously been shown to increase the survival of skin flaps, although there has been no investigation of possible beneficial effects of hyperbaric oxygen on survival of the TRAM flap. The present study compares the effectiveness of hyperbaric oxygen therapy, normobaric 100% oxygen, a hyperbaric air-equivalent mixture, and no treatment at all (control group), in the prevention of TRAM flap necrosis in a rat model. Forty-eight animals were randomly assigned to one of the four above-mentioned groups. The surviving area of the flap was evaluated 7 days after surgery. The hyperbaric oxygen treatment protocol consisted of five 9-minute sessions breathing 100% oxygen at a pressure of 2.5 atmospheres absolute during the first 48 hours, starting within 1 hour of surgery. The areas of surviving skin paddles ranged from 38.5 percent in the control group to 52.5 percent in the group treated with hyperbaric oxygen. One-way analysis of variance indicated that flap area survival was significantly greater in the hyperbaric oxygen group (F = 2.69, p = 0.05). Tukey's pairwise comparison and the two-sample t test indicated that the group treated with hyperbaric oxygen differed significantly from the control group (Tukey's critical value = 3.8, rejection level = 0.05, t test p = 0.01). Our results suggest that the hyperbaric oxygen treatment protocol used improves survival in the rat TRAM flap. However, the optimal treatment protocol to achieve this objective even in the rat seems to be variable, and further studies are required before extrapolating these data to human applications.

Periurethral injection for the treatment of urinary incontinence.

Periurethral injection of substrates that compress, support, or narrow the bladder neck for the treatment of stress incontinence is not new. Several injectable compounds have been used in a small number of patients during the 1940s and through the 1960s; however, the results were not very successful and often led to significant complications. More recently, two major materials have been developed that seem to be useful in treating stress incontinence by periurethral injection: Polytef paste and GAX collagen. Other injectables include autologous fat tissue and silicone microimplants. The most suitable patients for periurethral injection are elderly women, patients who constitute high operative risk, and those with stress incontinence due to intrinsic sphincter failure. Patients with stress incontinence due to a combination of urethral hypermobility and intrinsic sphincter deficiency with failure of suspension procedure may also benefit from the procedure. The reported long-term (more than 24 months) success rates according to the various substances are as follows: Teflon (Polytef) (E.I.du Pont de Nemours and Co, Wilmington, DE): 30 to 38 percent cured or improved; repeated injections usually do not improve the outcome; mostly minor complications with case reports of more serious side effects such as periurethral granuloma formation and bladder outlet obstruction. GAX collagen: 69 to 77 percent subjectively cured or improved after 24 months; 54 to 57 percent objectively cured or improved, the reported morbidity in these procedures is minimal; repeated injections can improve the outcome. The experience with autologous fat and silicone microimplants is insufficient, with an overall success rate of 70 percent (1-40 months follow-up; mean 12 months) and 58 to 70 percent (17-36 months), respectively. Most of the procedures are performed as outpatient cases, and some under local anesthesia. These procedures are minimally invasive, usually safe and well tolerated, require shorter hospitalization, and are cost effective. In conclusion, in carefully selected patients, periurethral injection seems to be a reasonable option in the modern treatment of female stress incontinence.

Hyperbaric oxygen therapy for deep second degree burns: an experimental study in the guinea pig.

Most previous animal studies reporting improved epithelialisation and healing of burn wounds under hyperbaric oxygen (HBO) did not include the conventional treatment with topical antibiotics as part of the protocol, and did not compare the effectiveness of HBO therapy with that of normobaric 100% oxygen (NO). The purpose of our study was to compare the results of combined treatment with HBO + silver sulfadiazine (SS) and those of treatment with NO + SS or SS alone. Deep second degree burns were produced on the depilated backs of 54 guinea pigs using a validated burn protocol. The animals were assigned to three treatment groups: HBO + SS, NO + SS, and SS. Dressings were changed daily. HBO was administered at 2 atmospheres absolute (ATA) for 90 min BID, and NO for 90 min BID. The parameters compared among the groups were laser Doppler flowmetry, and burn wound contracture and re-epithelialisation data derived from computerised planimetry of photographs of the wound. No differences in laser Doppler flowmetry results or the magnitude of contracture were found between the groups. Significantly increased re-epithelialisation was observed under NO + SS starting 10 days after the burn (P = 0.02, ANOVA). This significance stems from the difference between the HBO + SS and NO + SS groups (Tukey test). These data indicate that excessively high levels of tissue PO2 might compromise burn healing, and explain our results. A further study comparing combined treatment using a milder HBO protocol + SS and NO + SS is indicated in the search for the optimal HBO regimen.

Clostridium septicum infection in children with cyclic neutropenia.

Atraumatic Clostridium septicum infection is rare in infancy and childhood and is associated with a high mortality rate. Although in adults it has been reported to occur mainly in patients with gastrointestinal malignancy, pediatric cases were always associated with neutropenia. About 70% of the cases were described in children with neutropenia caused by chemotherapy and 30% were found in children with cyclic neutropenia. No case was described in children with other forms of congenital severe neutropenia. We describe three children with cyclic neutropenia and severe Clostridium septicum infection, discuss the various possibilities of causation, and the need for prompt and aggressive treatment of this serious condition.

Is there really a decrease in sperm parameters among healthy young men? A survey of sperm donations during 15 years.

PURPOSE: Our purpose was to measure changes in semen quality and quantity in young healthy sperm donors in Jerusalem over time. METHODS: A retrospective analysis of semen parameters over 15 years using linear regression analysis, in a single sperm bank in a tertiary university center. Study population consisted of 188 young, healthy medical students, aged 20 to 30 years, who donated sperm samples for Artificial insemination between 1980 and 1995. RESULTS: There were no statistically significant changes in semen concentration and motility during the study period. The mean semen volume increased by 0.1 ml (5.1%) per year (P < 0.0001), with a concomitant mean rise of 5.8 x 10(6) (7.7%) per year in total motile sperm count. The percentage normal morphology decreased by a mean of 1.04% per year during the entire period (P < 0.0001). CONCLUSIONS: During the past 15 years, there has been an increase in total motile sperm count, secondary to an increase in semen volume, and a decline in normal morphology that are independent of the age and the duration of abstinence in fertile men.

Thermal status of wet-suited divers using closed circuit O2 apparatus in sea water of 17-18.5 degrees C.

A wet suit may not provide adequate thermal protection when diving in moderately cold water (17-18 degrees C), and any resultant mild hypothermia may impair performance during prolonged diving. We studied heat exchange during a dive to a depth of 5 m in sea water (17-18.5 degrees C) in divers wearing a full wet suit and using closed-circuit oxygen breathing apparatus. Eight fin swimmers dived for 3.1 h and six underwater scooter (UWS) divers propelled themselves through the water for 3.7 h. The measurements taken throughout the dive were the oxygen pressure in the cylinder and skin and rectal temperatures (Tre). Each subject also completed a cold score questionnaire. The Tre decreased continuously in all subjects. Oxygen consumption in the fin divers (1.40 l.min-1) was higher than that of the UWS divers (1.05 l.min-1). The mean total insulation was 0.087 degree C.m2.W-1 in both groups. Mean body insulation was 37% of the total insulation (suit insulation was 63%). The reduction in Tre over the 1st hour was related to subcutaneous fat thickness. There was a correlation between cold score and Tre at the end of 1 h, but not after that. A full wet suit does not appear to provide adequate thermal protection when diving in moderately cold water.

[Hyperbaric oxygen for carbon monoxide poisoning].

Severe cases of carbon monoxide (CO) poisoning from all over Israel are treated at the Israel Naval Medical Institute with hyperbaric oxygen (HBO). Between 1.11.94 and 15.2.95. 24 cases of CO poisoning were treated. Poisoning was usually due to domestic gas-fired heating systems, CO being the only toxin involved. Since delay between termination of CO exposure and arrival at the emergency department averaged 55 minutes, the level of carboxyhemoglobin measured on presentation did not always reflect the true severity of the poisoning. Poisoning was defined as severe and requiring HBO treatment when 1 or more of the following indications was present: evidence of neurological involvement, cardiographic signs of acute ischemic injury, metabolic acidosis, carboxyhemoglobin level greater than 25%, and pregnancy. 20 (84%) recovered consciousness during the course of 1 session (90 min.) of HBO treatment (pO2 2.8 ATA) or immediately thereafter, with resolution of other signs of CO poisoning. 3 required a second treatment session before their symptoms resolved. A patient who arrived in deep coma with severe cerebral edema died. HBO is an important element in the combined treatment of severe CO poisoning. There should be greater awareness of the danger of CO poisoning and the means of preventing it, both among medical staff and the population as a whole, mainly in areas in which cold weather requires use of heating systems, which may be gas-fired.

Oxy-helium treatment for refractory neurological decompression sickness: a case report.

A 49-yr-old male presented with paraparesis and urinary incontinence that appeared 10 min after surfacing from a dive. Treatment was started on an extended USN table 6, but the symptoms persisted. Twenty-four hours later, he was treated with oxy-helium table CX-30, resulting in marked improvement in gait and in sensory and motor function. Urodynamic examination indicated an upper motor neuron lesion; bilateral decreased amplitude of the somatosensory evoked potential was found on stimulation of the tibial nerves; no response below the upper limbs was elicited on central motor conduction time (CMCT) testing; MRI showed lesions in the lower dorsal cord. The patient's condition was further improved by an additional 10 hyperbaric oxygenation sessions, with complete restoration of urinary control and virtually complete sensory and motor recovery. Follow-up urodynamic studies were normal. CMCT recordings showed a bilateral lower limb small-amplitude response. The present case reinforces the limited clinical data regarding the value of oxy-helium in the treatment of neurological decompression sickness, even when primary treatment with oxygen tables is unsuccessful.

Necrotizing fasciitis: an indication for hyperbaric oxygenation therapy?

BACKGROUND: The accepted treatment protocol for necrotizing fasciitis (NF) consists of extensive surgery and wide spectrum antibiotics. Hyperbaric oxygenation (HBO) has been recommended as adjuvant therapy for NF, improving patient mortality and outcome. However, the beneficial effect of HBO for NF remains controversial. METHODS: A retrospective evaluation of treatment outcome in 37 patients treated for NF between 1984 and 1993 was carried out. The mortality rate, morbidity criteria, and risk factors for grave prognosis were compared between a group of 25 patients who received HBO as part of their treatment protocol and a group of the remaining 12 patients treated by surgical excision and antibiotics alone. RESULTS: The two groups were found to be similar with regard to age, gender, the incidence of individual risk factors for ominous prognosis, and the Acute Physiology and Chronic Health Evaluation (APACHE) II score for disease's severity on presentation. The mortality rate among the HBO-treated patients was 36%, as opposed to 25% in the non-HBO group. The mean number of surgical débridements required per patient was significantly higher in the HBO group: 3.3 compared with 1.5 in the non-HBO-treated patients. Although the average length of hospitalization for survivors was shorter for the HBO group, the difference between the groups did not reach statistical significance. CONCLUSIONS: The results of this study cast doubt on the suggested advantage of HBO in reducing patient mortality and morbidity when used as adjuvant therapy for NF.

Left ventriculography complicated by cerebral air embolism.

Cerebral air embolism is a severe complication of various invasive medical procedures. Hyperbaric oxygen is the sole definitive therapy. We describe a 68-year-old patient who presented with upper left limb motor and sensory deficits following the injection of a contrast medium for left ventriculography. Numerous air bubbles were seen on cineangiography concomitantly with injection of the contrast medium. Immediate compression with hyperbaric oxygen resulted in complete resolution of all neurological symptoms. Iatrogenic cerebral air embolism is an underdiagnosed condition that may result from cardiac catheterization. Physician awareness will improve prevention, and prompt diagnosis and the use of hyperbaric oxygen will result in an optimal outcome if it does occur.

[Hyperbaric oxygen for hydrogen sulfide poisoning].

Hydrogen sulfide (H2S) is a toxic gas produced in decaying substances containing organic sulfur. Exposure to the gas causes severe disturbances in the central nervous and respiratory systems. The mechanism of toxicity is disruption of the electron transport chain in mitochondria, resulting in intracellular hypoxia. Treatment of H2S poisoning includes mechanical ventilation with 100% oxygen and immediate administration of sodium nitrate. Treatment with hyperbaric oxygen (HBO) has been studied in animal models, and has also been used in a number of patients. However, the clinical effectiveness of this mode of therapy has not been clearly proven. Having recently treated a case of H2S poisoning, we suggest HBO to reduce mortality.

Viability of adipose tissue injected and treated by different methods: an experimental study in the rat.

Fat injection is being used for the correction of various soft-tissue defects. In this study, the manner of fat injection yielding the greatest transplant viability was examined. Autologous fat was obtained from the inguinal area of rats and subsequently reinjected to the nuchal region, an area naturally poor in subcutaneous fat. Before injection, the fat was processed by one or more of the following methods: suture of the recipient area, repeated washing to remove residual blood, and addition of insulin. Transplant status was evaluated by both macroscopic and microscopic examination of the recipient sites 2 weeks and 12 weeks after the injection. The results demonstrated that the injected fat remained in part as viable new fatty tissue in the nuchal area. No statistically significant improvement in the viability of the injection fat was noticed at 2 weeks and 12 weeks after its processing by the different methods just described. Significant positive correlation was demonstrated between the volume of the injected fat and the size of the bulging at the injection area only 2 weeks after the injection.