Evaluating the risk of decompression sickness for a yo-yo dive using a rat model.

PURPOSE: The frequent ascents made during yo-yo diving may contribute to gas bubble clearance but paradoxically may also increase the risk of central nervous system decompression illness (DCI). We evaluated the risk of DCI due to yo-yo dives with very short surface intervals, using a controlled animal model. METHODS: Dives were conducted on air to a depth of 90 meters (10 atmospheres absolute) for 32 minutes of bottom time, at a descent/ascent rate of 10 meters/ minute. Sprague-Dawley rats weighing ~ 300 grams were divided randomly into three groups. Group A performed a square dive protocol without any surface intervals, Group B conducted a protocol that included two surface intervals during the dive, and Group C performed a protocol with three surface intervals. Ascent/descent rate for surface intervals, each lasting one minute, was also 10 meters/minute. RESULTS: Manifestations of DCI were observed in 13 of 16 animals in Group A (81.3%), six of 12 in Group B (58.3%), and two of 12 in Group C (16.7%). Mortality rates were similar in all groups. CONCLUSIONS: Surface intervals during dives breathing air significantly reduced DCI risk in the rat. Further studies are required using a larger animal model to reinforce the results of the present investigation.

Heparanase induces signal transducer and activator of transcription (STAT) protein phosphorylation: preclinical and clinical significance in head and neck cancer.

Activity of heparanase is implicated strongly in dissemination of metastatic tumor cells and cells of the immune system. In addition, heparanase enhances the phosphorylation of selected signaling molecules, including SRC and EGFR, in a manner that requires secretion but not enzymatic activity of heparanase and is mediated by its C-terminal domain. Clinically, heparanase staining is associated with larger tumors and increased EGFR phosphorylation in head and neck carcinoma. We hypothesized that signal transducer and activator of transcription (STAT) proteins mediate the protumorigenic function of heparanase downstream of the EGFR. We provide evidence that heparanase enhances the phosphorylation of STAT3 and STAT5b but not STAT5a. Moreover, enhanced proliferation of heparanase transfected cells was attenuated by STAT3 and STAT5b siRNA, but not STAT5a or STAT1 siRNA. Clinically, STAT3 phosphorylation was associated with head and neck cancer progression, EGFR phosphorylation, and heparanase expression and cellular localization. Notably, cytoplasmic rather than nuclear phospho-STAT3 correlated with increased tumor size (T-stage; p = 0.007), number of metastatic neck lymph nodes (p = 0.05), and reduced survival of patients (p = 0.04).

Association Between the BNT162b2 Messenger RNA COVID-19 Vaccine and the Risk of Sudden Sensorineural Hearing Loss.

IMPORTANCE: Identification of adverse events after vaccination increases awareness of vaccine-associated complications, leading to early diagnosis and treatment. Evidence remains scarce on the association between the BNT162b2 messenger RNA (mRNA) COVID-19 vaccine (Pfizer-BioNTech) and sudden sensorineural hearing loss (SSNHL). OBJECTIVE: To assess the association between the BNT162b2 mRNA COVID-19 vaccine and SSNHL. DESIGN, SETTING, AND PARTICIPANTS: This retrospective, population-based cohort study was performed from December 20, 2020, to May 31, 2021, using data from the largest health care organization in Israel. Patients 16 years or older who received the first vaccine dose between December 20, 2020, and April 30, 2021, and the second vaccine dose between January 10, 2021, and April 30, 2021, were included. EXPOSURES: Receipt of first and second BNT162b2 mRNA COVID-19 vaccine doses. MAIN OUTCOMES AND MEASURES: The main outcome was SSNHL based on International Classification of Diseases, Ninth Revision (ICD-9) codes in conjunction with concurrent prednisone dispensing. Observed cases of SSNHL, occurring within 21 days after each of the first and second vaccine doses, were compared with the expected cases based on the experience of the population in 2018 and 2019. Standardized incidence ratios (SIRs) and attributable risks were computed. RESULTS: Overall, 2 602 557 patients (mean [SD] age, 46.8 [19.6] years; 51.5% female) received the first dose of BNT162b2 mRNA COVID-19 vaccine, with 91 cases of SSNHL reported. Of these patients, 2 441 719 (93.8%) received the second vaccine dose, with 79 cases of SSNHL reported. The age- and sex-weighted SIRs were 1.35 (95% CI, 1.09-1.65) after the first vaccine dose and 1.23 (95% CI, 0.98-1.53) after the second vaccine dose. After the first vaccine dose, the estimated SIRs were more pronounced in female patients aged 16 to 44 years (SIR, 1.92; 95% CI, 0.98-3.43) and female patients 65 years or older (SIR, 1.68; 95% CI, 1.15-2.37). After the second vaccine dose, the highest estimated SIR was observed in male patients 16 to 44 years (SIR, 2.45; 95% CI, 1.36-4.07). The attributable risks were generally small, and the results were similar when 2019 was used as a reference to estimate the expected number of SSNHL cases. CONCLUSIONS AND RELEVANCE: This study suggests that the BNT162b2 mRNA COVID-19 vaccine might be associated with increased risk of SSNHL; however, the effect size is very small. Further studies are warranted to establish this possible association.

Symptoms of central nervous system oxygen toxicity during 100% oxygen breathing at normobaric pressure with increasing inspired levels of carbon dioxide: a case report.

The greatest danger faced by divers who use oxygen-enriched gas mixtures is central nervous system oxygen toxicity (CNS-OT). CNS-OT is characterised by convulsions resembling grand-mal epileptic seizures, which may terminate in drowning and death. Elevated arterial levels of carbon dioxide (CO2) (hypercapnia) represent a major risk factor for CNS-OT when breathing hyperoxic gas mixtures. To reduce the risk of a diver being involved in a CNS-OT incident due to hypercapnia, candidates for combat diving are examined at our institute using a routine physiological training procedure, in which they are tested for CO2 detection and retention. We present the case of a candidate for combat diving, who unexpectedly exhibited signs typical of CNS-OT while breathing pure oxygen under normobaric conditions with > 3 kPa inspired CO2. Severe headache and nausea, as well as facial muscle twitching, appeared during one of these routine tests. Subsequent medical examination including neurological tests, magnetic resonance imaging and an electroencephalogram were unremarkable. To the best of our knowledge, an event such as this has never previously been published in the medical literature. We present a discussion of the case, and a review of the relevant literature regarding CO2 as a risk factor for the development of CNS-OT.

Evaluating the thermal protection provided by a 2‒3 mm wet suit during fin diving in shallow water with a temperature of 16‒20°C.

INTRODUCTION: The purpose of the study was to evaluate the thermal protection provided by a 2-3 mm surfing wet suit during at least two hours of fin diving in shallow water with a temperature of 16-20°C. We examined the effect of wearing the suit while diving in cold water on cognitive performance, muscle strength, and hand motor function. METHODS: Subjects were six male well-trained rebreather divers, 19-23 years old, acclimatised to cold. They attended the laboratory on three separate occasions, when we conducted the experiment at one of three temperatures, 16, 18, and 20°C. Core temperature (gastrointestinal system), skin temperature, oxygen consumption, and cold perception were evaluated during the test. Before and immediately after the dives, subjects performed a series of cognitive, manual dexterity, and muscle strength tests. RESULTS: Core temperature decreased by 0.35-0.81°C over the two hours at all three water temperatures. No subject reached a core temperature below 35°C. The decrease in upper body skin temperature during the two hour dive ranged between 5.97 and 8.41°C (P < 0.05). Two hours diving in 16-20°C water resulted in a significant increase in the time taken to perform the task of unlinking and reassembling four shackles (∼30% longer, P < 0.05). No effect was found on the cognitive or muscle strength tests. CONCLUSIONS: A 2-3 mm wet suit provides adequate thermal protection in trained and cold-acclimatised young males engaged in active diving in shallow water with a temperature of 16°C and above.

Regional metastases in well-differentiated thyroid carcinoma: pattern of spread.

OBJECTIVES/HYPOTHESIS: To determine the pattern of spread of WDTC to regional lymph nodes, in patients who presented with clinically positive nodes. STUDY DESIGN: Retrospective chart review. MATERIALS AND METHODS: Between October 2001 and December 2006, a total of 27 consecutive patients (12 males, 15 females) with clinical evidence of cervical metastasis of well-differentiated thyroid carcinoma (WDTC) underwent 28 neck dissections (ND) with a mean follow-up 33.7 months. Papillary carcinoma was found in 24 patients and follicular carcinoma in 3. All neck dissection specimens were separated during surgery into levels, and analysis was done with respect to the levels of the neck. Clinical and demographic parameters were correlated to the pathologic parameters, including number of pathologic nodes, size of tumor, and the patient's age, with univariate and multivariate analysis. RESULTS: The mean number of pathologic nodes in ND specimen was 6.7. The predominant site of metastasis was level VI (95%), followed by level III (68%), level IV (57%), and level II (54%). Metastases above the XI nerve were found in 7% of the patients. Level V showed 20% of nodal metastasis. A correlation was found between size of primary tumor and number of positive pathologic lymph nodes (P = .02) and an inverse correlation between the age of the patient and the number of pathologic nodes (P = .043). CONCLUSIONS: The high incidence of metastatic disease in levels II through VI supports the recommendation for posterolateral and anterior ND in patients with WDTC and clinically positive nodes. The correlation between tumor size, the age of the patient, and the number of positive nodes is an interesting finding that warrants further study.

The Effect of Aging on the Ventilatory Response to Wearing a Chemical, Biological, Radiological, and Nuclear Hood Respirator at Rest and During Mild Exercise.

BACKGROUND: Structural changes in the human body resulting from aging may affect the response to altered levels of O2 and CO2. An abnormal ventilatory response to a buildup of CO2 in the inspired air due to rebreathing may result in adverse effects, which will impair the individual's ability to function under stress. The purpose of this study was to evaluate the effect of age on the respiratory response to wearing an escape hood at rest and during mild exercise. METHODS: Subjects were seven healthy, young adult males (20-30 years) and seven healthy, middle-aged males (45-65 years). Inspired CO2 and O2, breathing pattern (tidal volume [VT] and breathing frequency [F]), and mouth inspiratory and expiratory pressures, were measured at rest and during mild exercise (50 w) while wearing the CAPS 2000 escape hood (Shalon Chemical Industries and Supergum-Rubber and Plastic Technology, Tel Aviv, Israel). FINDINGS: Resting inspired CO2 was higher in the middle-aged group compared with the young group (2.25% ± 0.42% and 1.80% ± 0.34%, respectively; p < 0.05). Breathing pattern in the middle-aged group tended to be shallower and faster compared with the young group (VT: 0.69 ± 0.27 L and 0.79 ± 0.32 L, respectively; F: 14.7 ± 4.0 breaths/min and 12.4 ± 2.8 breaths/min, respectively). During exercise, there was a trend toward a high inspired CO2 in the middle-aged group compared with the young group (2.18% ± 0.40% CO2 and 1.94% ± 0.70% CO2, respectively). A correlation was found between age and inspired CO2 when wearing the escape hood (r2 = 0.375; p < 0.05). DISCUSSION: The age-related decrease in pulmonary function, together with the finding in this study of a higher inspired CO2 in middle-aged subjects wearing the CAPS 2000, may represent a greater risk for persons of middle age wearing an escape hood. RECOMMENDATIONS: On the basis of this study, it would appear reasonable to recommend that new respirators be evaluated on subjects from different age groups, to ensure the safety of both young and old.

Evidence for the infiltration of gas bubbles into the arterial circulation and neuronal injury following "yo-yo" dives in pigs.

"Yo-yo" diving may place divers at a greater risk of neurologic decompression illness (DCI). Using a rat model, we previously demonstrated that "yo-yo" diving has a protective effect against DCI. In the current study, we evaluated the risk of neurologic DCI following "yo-yo" dives in a pig model. Pigs were divided into four groups. The Control group (group A) made a square dive, without excursions to the surface ("peeps"). Group B performed two "peeps," group C performed four "peeps," and group D did not dive at all. All dives were conducted on air to 5 atm absolute, for 30-min bottom time. Echocardiography was performed to detect cardiac gas bubbles before the dive, immediately after, and at 90-min postdive. Motor performance was observed during the 5-h postdive period. Symptoms increased dramatically following a dive with four "peeps." Gas bubbles were detected in the right ventricle of all animals except for the sham group and in the left ventricle only after the four-peep dive. Neuronal cell injury was found in the spinal cord in each of the three experimental groups, tending to decrease with an increase in the number of "peeps." A four-peep "yo-yo" dive significantly increased the risk of neurologic DCI in pigs. Following a four-peep dive, we detected a higher incidence of bubbles in the left ventricle, supporting the common concern regarding an increased risk of neurologic DCI, albeit there was no direct correlation with the frequency of "red neurons" in the spinal cord.

Underwater hearing and sound localization with and without an air interface.

HYPOTHESIS: Underwater hearing acuity and sound localization are improved by the presence of an air interface around the pinnae and inside the external ear canals. BACKGROUND: Hearing threshold and the ability to localize sound sources are reduced underwater. The resonance frequency of the external ear is lowered when the external ear canal is filled with water, and the impedance-matching ability of the middle ear is significantly reduced due to elevation of the ambient pressure, the water-mass load on the tympanic membrane, and the addition of a fluid-air interface during submersion. Sound lateralization on land is largely explained by the mechanisms of interaural intensity differences and interaural temporal or phase differences. During submersion, these differences are largely lost due to the increase in underwater sound velocity and cancellation of the head's acoustic shadow effect because of the similarity between the impedance of the skull and the surrounding water. METHODS: Ten scuba divers wearing a regular opaque face mask or an opaque ProEar 2000 (Safe Dive, Ltd., Hofit, Israel) mask that enables the presence of air at ambient pressure in and around the ear made a dive to a depth of 3 m in the open sea. Four underwater speakers arranged on the horizontal plane at 90-degree intervals and at a distance of 5 m from the diver were used for testing pure-tone hearing thresholds (PTHT), the reception threshold for the recorded sound of a rubber-boat engine, and sound localization. For sound localization, the sound of the rubber boat's engine was randomly delivered by one speaker at a time at 40 dB HL above the recorded sound of a rubber-boat engine, and the diver was asked to point to the sound source. The azimuth was measured by the diver's companion using a navigation board. RESULTS: Underwater PTHT with both masks were significantly higher for frequencies of 250 to 6000 Hz when compared with the thresholds on land (p <0.0001). No differences were found in the PTHT or the reception threshold for the recorded sound of a rubber-boat engine for dry or wet ear conditions. There was no difference in the sound localization error between the regular mask and the ProEar 2000 mask. CONCLUSIONS: The presence of air around the pinna and inside the external ear canal did not improve underwater hearing sensitivity or sound localization. These results support the argument that bone conduction plays the main role in underwater hearing.

Assessment of the Risk of Fractures Because of Service on Diesel Submarines: A Retrospective Cohort Study.

INTRODUCTION: Submariners are known to have decreased bone mass following periods of long submersion. We examined whether this produces a higher predilection to fractures. METHODS: This is a retrospective cohort study. Data were collected from the computerized medical records of 457 consecutive submariners (serving 1091.42 man-years). The control group included 3,219 consecutive sailors, (serving 5845.04 man-years). Groups were stratified according to age at induction, body mass index, place of birth, and status of service (i.e., compulsory versus professional). Analysis of fracture incidence and comparison of proportions between the groups was conducted using χ(2) tests and Fisher's exact test. The hazard ratio for fractures was performed using a survival analysis regression model for each group (Cox Proportional Hazard Model). RESULTS: Nineteen submariners (4.2%) and 94 sailors (2.9%) were shown to have fractures during their service (RR = 1.42, p = 0.15). A Cox proportional hazard model was employed. No statistically significant difference was found between the 2 groups (HR = 1.037, p = 0.89). No correlation was found between length of service and risk of fracture. Most fractures suffered by submariners occurred outside their work environment. CONCLUSIONS: Submariners are repeatedly exposed to prolonged submersions that are deleterious to bone strength. However, no statistically significant difference in the incidence of fractures was found between submariners and surface sailors. This is an important finding for the bone and occupational health of submariners in general.

Pulmonary edema following closed-circuit oxygen diving and strenuous swimming.

Acute pulmonary edema may be induced by diving and strenuous swimming. We report the case of a diver using closed-circuit, scuba equipment who developed acute dyspnea, hemoptysis, and hypoxemia following a dive in 18 degreesC (64.4 degrees F) water and physical exertion during the swim back to shore. With the growing popularity of recreational scuba diving, emergency physicians are liable to be faced with increasing numbers of diving-related medical problems. Diving-induced pulmonary edema should be included in the differential diagnosis of acute hypoxemia, sometimes accompanied by acid-base abnormalities, when this is seen in a diver.

Hyperbaric therapy for bilateral visual loss during hemodialysis.

Bilateral vision loss during hemodialysis is a rare but devastating entity, with grim prognosis for sight. The etiologies are diverse but share ischemia as a common mechanism. This is a report of a patient with bilateral sight loss during hemodialysis, with early hyperbaric treatment and return of visual acuity to baseline. Hyperbaric treatment should be considered, where early administration is possible, for bilateral blindness during hemodialysis.

Induction of early meconium evacuation: is it effective in reducing the level of neonatal hyperbilirubinemia?

This prospective randomized trial evaluated the effect of induction of early meconium evacuation on neonatal jaundice in healthy term neonates. The study group was given glycerin suppository immediately after birth and every 4 hours thereafter, until evacuation of first stool. Glycerin suppository caused faster meconium evacuation but had no effect on mean bilirubin levels at 48 hours. However, males had significantly lower mean bilirubin levels, especially if they also had type A blood group. Glycerin suppository cannot be routinely recommended as a means for reducing the severity of neonatal jaundice. Nonetheless, male newborn with type A blood group may benefit from such a therapy.

Cardiogenic shock complicating acute carbon monoxide poisoning despite neurologic and metabolic recovery.

We report the cases of 2 previously healthy young patients with acute carbon monoxide intoxication who deteriorated to cardiogenic shock in the face of apparent metabolic and neurologic recovery. Prolonged exposure to sublethal levels of carbon monoxide (>24 hours, carboxyhemoglobin level of 20.4% and 22.6%) and massive binding of the toxin to myocardial myoglobin and mitochondrial cytochrome chain enzymes might explain their protracted cardiac failure. The good response to inotropic agents and the findings of repeated echocardiographic studies support the probable diagnosis of myocardial stunning. Complete cardiac recovery was observed in both patients.

Performance of infusion pumps during hyperbaric conditions.

BACKGROUND: Many hyperbaric facilities use infusion pumps inside the chamber. It is therefore important to ensure that this equipment will perform accurately during hyperbaric conditions. The authors tested the function and accuracy of the Imed 965 and Infutec 520 volumetric infusion pumps, the Easy-pump MZ-257 peristaltic infusion pump, and the Graseby 3100 syringe pump. METHODS: The authors calculated the deviations of infused volumes at low and high rates (12-18 and 60-100 ml/h) on three different hyperbaric protocols (up to 2.5, 2.8, and 6 atmospheres absolute [ATA]), resembling a standard hyperbaric oxygen treatment and US Navy treatment tables used for decompression illness and for arterial gas embolism. Two examples of each pump model were examined in every experiment. RESULTS: The Easy-pump MZ-257 failed to function completely beyond a chamber pressure of 1.4 ATA, making it unsuitable for use inside the hyperbaric chamber. The Graseby 3100 failed to respond to all keyboard functions at 2.5-2.8 ATA, making it unsuitable for use in most hyperbaric treatments. The Imed 965 performed within an acceptable volume deviation (< or =10%) during most hyperbaric conditions. During the compression phase of the profiles used, and for the low infusion rates only, exceptional volume deviations of 20-40% were monitored. The Infutec 520 demonstrated an acceptable deviation (within 10%) throughout all the hyperbaric profiles used, unaffected by changes in ambient pressure or infusion rate. CONCLUSIONS: Commercially available infusion pumps operating during hyperbaric conditions demonstrate substantial variations in performance and accuracy. It is therefore important that the hyperbaric facility staff make a careful examination of such instruments to anticipate possible deviations in the accuracy of the equipment during use.