Acute forces required for fatal compression asphyxia: A biomechanical model and historical comparisons

Background Fatalities from acute compression have been reported with soft-drink vending machine tipping, motor vehicle accidents, and trench cave-ins. A major mechanism of such deaths is flail chest but the amount of force required is unclear. Between the range of a safe static chest compression force of 1000 N (102 kg with earth gravity) and a lethal dynamic force of 10-20 kN (falling 450 kg vending machines), there are limited quantitative human data on the force required to cause flail chest, which is a major correlate of acute fatal compression asphyxia. Methods We modeled flail chest as bilateral fractures of six adjacent ribs. The static and dynamic forces required to cause such a ribcage failure were estimated using a biomechanical model of the thorax. The results were then compared with published historical records of judicial "pressing," vending machine fatalities, and automobile safety cadaver testing. Results and conclusion The modeling results suggest that an adult male requires 2550 ± 250 N of chest-applied distributed static force (260 ± 26 kg with earth gravity) or 4050 ± 320 N of dynamic force to cause flail chest from short-term chest compression.

Recommendations for rescue of a submerged unresponsive compressed-gas diver

The Diving Committee of the Undersea and Hyperbaric Medical Society has reviewed available evidence in relation to the medical aspects of rescuing a submerged unresponsive compressed-gas diver. The rescue process has been subdivided into three phases, and relevant questions have been addressed as follows. Phase 1, preparation for ascent: If the regulator is out of the mouth, should it be replaced? If the diver is in the tonic or clonic phase of a seizure, should the ascent be delayed until the clonic phase has subsided? Are there any special considerations for rescuing rebreather divers? Phase 2, retrieval to the surface: What is a "safe" ascent rate? If the rescuer has a decompression obligation, should they take the victim to the surface? If the regulator is in the mouth and the victim is breathing, does this change the ascent procedures? If the regulator is in the mouth, the victim is breathing, and the victim has a decompression obligation, does this change the ascent procedures? Is it necessary to hold the victim's head in a particular position? Is it necessary to press on the victim's chest to ensure exhalation? Are there any special considerations for rescuing rebreather divers? Phase 3, procedure at the surface: Is it possible to make an assessment of breathing in the water? Can effective rescue breaths be delivered in the water? What is the likelihood of persistent circulation after respiratory arrest? Does the recent advocacy for "compression-only resuscitation" suggest that rescue breaths should not be administered to a non-breathing diver? What rules should guide the relative priority of in-water rescue breaths over accessing surface support where definitive CPR can be started? A "best practice" decision tree for submerged diver rescue has been proposed.

Ventilation-perfusion inequality in the human lung is not increased following no-decompression-stop hyperbaric exposure

Venous gas bubbles occur in recreational SCUBA divers in the absence of decompression sickness, forming venous gas emboli (VGE) which are trapped within pulmonary circulation and cleared by the lung without overt pathology. We hypothesized that asymptomatic VGE would transiently increase ventilation-perfusion mismatch due to their occlusive effects within the pulmonary circulation. Two sets of healthy volunteers (n = 11, n = 12) were recruited to test this hypothesis with a single recreational ocean dive or a baro-equivalent dry hyperbaric dive. Pulmonary studies (intrabreath V_A/Q (iV/Q), alveolar dead space, and FVC) were conducted at baseline and repeat 1- and 24-h after the exposure. Contrary to our hypothesis V_A/Q mismatch was decreased 1-h post-SCUBA dive (iV/Q slope 0.023 ± 0.008 ml⁻¹ at baseline vs. 0.010 ± 0.005 NS), and was significantly reduced 24-h post-SCUBA dive (0.000 ± 0.005, p < 0.05), with improved V_A/Q homogeneity inversely correlated to dive severity. No changes in V_A/Q mismatch were observed after the chamber dive. Alveolar dead space decreased 24-h post-SCUBA dive (78 ± 10 ml at baseline vs. 56 ± 5, p < 0.05), but not 1-h post dive. FVC rose 1-h post-SCUBA dive (5.01 ± 0.18 l vs. 5.21 ± 0.26, p < 0.05), remained elevated 24-h post SCUBA dive (5.06 ± 0.2, p < 0.05), but was decreased 1-hr after the chamber dive (4.96 ± 0.31 L to 4.87 ± 0.32, p < 0.05). The degree of V_A/Q mismatch in the lung was decreased following recreational ocean dives, and was unchanged following an equivalent air chamber dive, arguing against an impact of VGE on the pulmonary circulation.

Physiologic effects of the TASER after exercise

OBJECTIVES

Incidents of sudden death following TASER exposure are poorly studied, and substantive links between TASER exposure and sudden death are minimal. The authors studied the effects of a single TASER exposure on markers of physiologic stress in humans.

METHODS

This prospective, controlled study evaluated the effects of a TASER exposure on healthy police volunteers after vigorous exercise, compared to a subsequent, identical exercise session that was not followed by TASER exposure. Subjects exercised to 85% of predicted heart rate (HR) on an ergometer and then were given a standard 5-second TASER activation. Measures before and for 60 minutes after the TASER activation included minute ventilation, tidal volume, respiratory rate, end-tidal pCO(2), oxygen saturation, HR, blood pressure (systolic BP/diastolic BP), 12-lead electrocardiogram, and arterialized blood for pH, pO(2), pCO(2), and lactate. Each subject repeated the exercise and data collection session on a subsequent data, without TASER activation. Data were analyzed using paired Student's t-tests with differences and 95% confidence intervals (CIs). Statistical significance was adjusted for multiple comparisons.

RESULTS

A total of 25 officers (21 men and 4 women) completed both portions of the study. After adjusting for multiple comparisons, the TASER group was significantly higher for systolic BP at baseline (difference of 14.1, 95% CI = 8.7 to 19.5, p < 0.001) and HR at 5, 30, and 60 minutes with the largest difference at 30 minutes (difference of 7.0, 95% CI = 2.5 to 11.5, p = 0.004). There were no other significant differences between the two groups in any other measure at any time.

CONCLUSIONS

A 5-second exposure of a TASER following vigorous exercise to healthy law enforcement personnel does not result in clinically significant changes in ventilatory or blood parameters of physiologic stress.

Physiological Effects of a Conducted Electrical Weapon on Human Subjects

STUDY OBJECTIVE

Sudden death after a conducted electrical weapon exposure has not been well studied. We examine the effects of a single Taser exposure on markers of physiologic stress in healthy humans.

METHODS

This is a prospective trial investigating the effects of a single Taser exposure. As part of their police training, 32 healthy law enforcement officers received a 5-second Taser electrical discharge. Measures before and for 60 minutes after an exposure included minute ventilation; tidal volume; respiratory rate (RR); end-tidal PCO2; oxygen saturation, pulse rate; blood pressure (systolic blood pressure/diastolic blood pressure); arterialized blood for pH, PO2, PCO2, and lactate; and venous blood for bicarbonate and electrolytes. Troponin I was measured at 6 hours. Data were analyzed using a repeated-measures ANOVA and paired t tests.

RESULTS

At 1 minute postexposure, minute ventilation increased from a mean of 16 to 29 L/minute, tidal volume increased from 0.9 to 1.4 L, and RR increased from 19 to 23 breaths/min, all returning to baseline at 10 min. Pulse rate of 102 beats/min and systolic blood pressure of 139 mm Hg were higher before Taser exposure than at anytime afterward. Blood lactate increased from 1.4 mmol/L at baseline to 2.8 mmol/L at 1 minute, returning to baseline at 30 minutes. pH And bicarbonate decreased, respectively, by 0.03 and 1.2 mEq/L at 1 minute, returning to baseline at 30 minutes. All troponin I values were normal and there were no EKG changes. Ventilation was not interrupted, and there was no hypoxemia or hypercarbia.

CONCLUSION

A 5-second exposure of a Taser X26 to healthy law enforcement personnel does not result in clinically significant changes of physiologic stress.

Ventilatory and Metabolic Demands During Aggressive Physical Restraint in Healthy Adults

We investigated ventilatory and metabolic demands in healthy adults when placed in the prone maximal restraint position (PMRP), i.e., hogtie restraint. Maximal voluntary ventilation (MVV) was measured in seated subjects (n=30), in the PMRP, and when prone with up to 90.1 or 102.3 kg of weight on the back. MVV with the heaviest weight was 70% of the seated MVV (122+/-28 and 156+/-38 L/min, respectively; p<0.001). Also, subjects (n=27) were placed in the PMRP and struggled vigorously for 60 sec. During the restrained struggle, ventilatory function (V(E)/ MVV) was 44% of MVV in the resting PMRP. While prone with up to 90.1 or 102.3 kg on the back, the decrease in MVV was of no clinical importance in these subjects. Also, while maximally struggling in the PMRP, V(E) was still adequate to supply the ventilatory needs.

Arterial gas embolism and decompression sickness

Decompression sickness occurs when a sufficiently large gas phase forms within the tissues of the body after a reduction in ambient pressure. Arterial gas embolism occurs secondary to pulmonary barotrauma when gas is forced into the pulmonary vasculature. Although they may clinically present in a similar fashion, the underlying pathophysiology of the two conditions is quite different.

Fatal pulmonary barotrauma due to obstruction of the central circulation with air

Cardiac arrest in cases of barotraumatic arterial gas embolism (AGE) is usually ascribed to reflex dysrhythmias secondary to brainstem embolization or secondary to coronary artery embolization. Several case reports suggest that obstruction of the central circulation (i.e., the heart, pulmonary arteries, aorta, and arteries to the head and neck) may play a role in the pathogenesis of sudden death in victims of pulmonary barotrauma. We report three consecutive cases of fatal AGE in patients in whom chest roentgenograms demonstrated confluent air lucencies filling the central vascular bed, the heart, and great vessels. In none of the victims was there evidence by history or at autopsy that the intravascular gas was iatrogenically introduced. Total occlusion of the central vascular bed with air is a mechanism of death in some victims of AGE, and resuscitation efforts for such patients should take this possibility into consideration.

Abnormal serum biochemistries in association with arterial gas embolism

Although diving-associated arterial gas emboli have been thought to embolize the cerebral circulation preferentially, more recent evidence suggests that gas bubbles disseminate widely and may cause dysfunction in multiple organ systems. We performed a retrospective survey of the records of patients presenting with diving-associated gas embolism over a 10-yr period to determine the maximal levels of serum transaminases and lactate dehydrogenase after a diving accident. Twenty-nine subjects with arterial gas embolism were identified whose dive profiles suggested that decompression sickness was unlikely. Maximal transaminase levels (aspartate amino transaminase = 442 +/- 187 IU/L; alanine amino transaminase = 315 +/- 205 IU/L) and lactate dehydrogenase level (800 +/- 227 IU/L) were significantly greater in the gas embolism patients than those levels measured in a group of normal individuals undergoing training dives of similar depth and duration. These preliminary studies suggest that arterial gas embolism frequently produces significant abnormalities in serum enzyme activity in sport divers whose dives would not be expected to produce decompression sickness. Arterialized gas bubbles may circulate widely, causing injury outside of the cerebral circulation.

Asthma and diving

BACKGROUND

Approximately 10 to 15 million Americans are scuba divers. The prevalence of scuba diving and asthma makes it likely some asthmatics will be interested in scuba diving and some scuba divers will have asthma. Conditions present during scuba diving may provoke airway obstruction in asthmatic patients. Further, asthmatic patients may, in theory, face a greater than normal risk of pulmonary barotrauma from lung overdistension on ascent through the water column.

OBJECTIVE

The purpose of this paper is to review the theoretical issues underlying the prohibition against scuba diving for asthmatic patients as advanced by most major diving organizations in the United States and critically examine the relevant accident data.

METHODS

All reports that dealt with asthma and diving, and all available American accident data including both fatal and nonfatal accidents were reviewed.

RESULTS

Actuarial data on the risk of scuba accidents attributable to asthma do not define several important variables likely to affect accident risk during scuba diving. Despite these limitations, careful review indicates the risks of serious morbidity or mortality during scuba diving appears to be inconsequentially elevated in subjects whose asthma was not characterized.

CONCLUSIONS

Additional data are needed to define accurately risks of diving in subjects with different forms of asthma, however, the available data suggest asthmatic patients with normal airway function at rest, and with little airway reactivity in response to exercise or cold air inhalation, have a risk of pulmonary barotrauma similar to that of normal subjects.

Arterial gas embolism and hemoconcentration

The charts of all patients with diving-related accidents presenting between 1983 and 1991 were reviewed. Individuals who sustained a neurologic deficit attributable to occlusion of part of the cerebral circulation within 10 minutes of surfacing from a dive and who had a depth time profile less than 80% of the U.S. Navy "no-stop" limits were considered to have had an arterial gas embolism. Their records were reviewed to determine the hematocrit upon first presentation and the final hematocrit prior to discharge or death. Twenty-three patients had hematocrit determinations on more than one occasion. There was a significant decrease from initial to final hematocrit for these patients. No source of significant blood loss was identified in any patient. A significant correlation was found between the magnitude of the fall in hematocrit and the eventual neurologic outcome. We conclude that gas embolism diagnosed using the above criteria produces hemoconcentration, and the degree of hemoconcentration correlates with the severity of the gas embolism. These observations suggest that the pathophysiology of gas embolism is more complex than previously thought and must include diffuse endothelial injury resulting in leak of fluid from the intravascular space.

Elevation of serum creatine kinase in divers with arterial gas embolization

BACKGROUND

Arterial gas embolism due to pulmonary barotrauma and the resultant cerebral gas embolism are catastrophic complications of diving. Previous studies have only rarely noted evidence of gas embolism to noncranial sites.

METHODS

Among 142 persons with diving-related injuries evaluated between January 1982 and July 1991, we identified 29 who had arterial gas embolism and who underwent biochemical studies indicative of muscle injury. Of the 29 patients, 4 were excluded because cardiopulmonary resuscitation had been performed and 3 were excluded because the duration of their dives met or exceeded standard limits set for dives not requiring staged decompression. The outcome at the time of hospital discharge in the remaining 22 patients was correlated with clinical factors and the results of biochemical studies. We also studied 22 subjects after uncomplicated dives and 11 patients who had sustained blunt trauma.

RESULTS

All the patients with diving-associated gas embolism had elevated serum creatine kinase activity (normal, < or = 175 U per liter); the values were markedly elevated (> 900 U per liter) in 14. The MB isoenzyme of creatine kinase was detected in the serum of 13 of 20 patients in whom it was measured and was > or = 4 percent of total creatine kinase activity in 6 patients. In three patients electrocardiography showed myocardial injury. Changes in serum creatine kinase activity of similar magnitude were not present in the subjects who had uncomplicated dives or in the patients with blunt trauma. Thirteen patients recovered fully, four had minor residual neurologic deficits, three were severely impaired, and two died. Logistic-regression analysis revealed a significant correlation between peak serum creatine kinase values and clinical outcome.

CONCLUSIONS

Biochemical evidence of muscle injury is frequently found after diving-associated arterial gas embolism. The correlation between serum creatine kinase activity and outcome suggests that serum creatine kinase is a marker of the size and severity of arterial gas embolism.

The roentgenographic findings associated with air embolism in sport scuba divers

Records on all patients with arterial gas embolism (AGE) presenting to UCSD from 1982-1989 and for whom chest radiographs were available were reviewed. Of the 31 patients, 13 roentgenograms (42%) showed evidence of pulmonary barotrauma demonstrated by pneumomediastinum (N = 8), subcutaneous emphysema (N = 3), pneumocardium (N = 2), pneumoperitoneum (N = 1), or pneumothorax (N = 1). Pneumopericardium was not seen. Sixteen (52%) of the 31 patients had pulmonary infiltrates. Radiographic evidence of barotrauma was on occasion subtle, and in four cases was overlooked. Evidence of barotrauma (i.e., extra-alveolar air) was often identified along the left cardiac border, aortic arch, descending aorta, and hilar vessels. Subtle findings of ectopic air can confirm the clinical diagnosis of AGE; however, radiographic evidence of concomitant near drowning occurs more frequently.

Combined arterial gas embolism and decompression sickness following no-stop dives

Decompression sickness (DCS) has been clinically classified as Type I (predominantly joint pain) or Type II (predominantly spinal cord lesions). We present 3 cases that are all characterized by severe (Type II) DCS with signs and symptoms of spinal cord injury occurring in conjunction with arterial gas embolism (AGE). We consider the AGE "minor" because only 2 of the 3 subjects initially lost consciousness, and in all cases the signs and symptoms of the AGE had essentially resolved within 1 h or by the time recompression therapy began. DCS was resistant to recompression therapy, even though treatment began promptly after the accident in 2 of the 3 cases. None of the cases had a good neurologic outcome and there has been one death. None of the divers exceeded the U.S. Navy "no-stop" limits for the depths at which they were diving. We have observed a previously unreported clinical syndrome characterized by severe Type II DCS subsequent to AGE following pressure-time exposures that would normally not be expected to produce DCS. We postulate that AGE may have precipitated or predisposed to this form of DCS.

The impact of a regionalized trauma system on trauma care in San Diego County

A review of autopsy reports on traumatic deaths in 1986 was conducted to determine the impact on trauma mortality of the regionalized trauma system instituted in San Diego County in 1984. Determination of preventable death was made by a panel of experts and compared with an identical review of traumatic deaths in 1979, five years before the institution of regionalized trauma care. Of 211 traumatic deaths reviewed from 1986, two (1%) were classified as preventable, compared with 20 of 177 (11.4%) deaths in 1979 (P less than .001). A breakdown of trauma deaths into central nervous system and noncentral nervous system categories revealed the overall decline was in large part a consequence of the decline in non-central nervous system deaths from 16 of 83 in 1979 to one of 62 in 1986 (P less than .005). The decrease in central nervous system-related preventable deaths from four of 94 in 1979 to one of 149 in 1986 (P less than .10) was not statistically significant. Although it is likely the trauma system introduced in 1984 contributed to the decline in preventable death, it is not possible to isolate this variable from other changes that occurred during the interval between studies. A review of trauma deaths over the same time interval in a community with similar demographics but without a trauma system might help determine the relative contribution of the trauma system.

Diving medicine

This article orients the practicing physician to the physical and physiologic basis for the more common medical problems encountered in diving, discusses the common presenting manifestations for these disorders, and provides a framework for their treatment. Medical fitness for diving is also briefly addressed.

Barotraumatic cerebral air embolism and the mental status examination: a report of four cases

Barotraumatic cerebral air embolism is described as sudden loss of consciousness accompanied by major motor disturbances. However, arterial gas embolism can have disturbances of cortical function that are much more subtle. Four patients presented with significant abnormalities of mental status. In two patients, the findings were subtle enough that the patients were initially regarded as normal. In the other two, cortical dysfunction was relatively resistant to therapy and might have gone unrecognized without careful examination. In order to detect disturbances in cortical function the neurologic examination should include testing beyond the usual emergency evaluation of consciousness and degree of orientation.

Fatal poisoning from acute hydrofluoric acid ingestion

A case of accidental oral poisoning with hydrofluoric acid in an adult is presented. The patient ingested the product from a drinking glass, mistaking it for water, and died approximately 90 minutes after the exposure. Severe acidemia and hypocalcemia were present, which resulted in refractory asystole. A plasma fluoride determination showed an extremely high fluoride level.

An autopsy study of traumatic deaths; San Diego County, 1979

All traumatic deaths in San Diego County were analyzed for the year of 1979. Death certificates, coroner's reports, and autopsy data served as the basis for this review. A total of 177 deaths were studied, of which 94 were associated with CNS injury and 83 were not. Sixteen (20 percent) of the deaths not CNS-associated and four (5 percent) of the CNS-associated deaths were classified as preventable. One hundred seventeen deaths were due to motor vehicle accidents, of which 11 of 35 (31 percent; all not CNS-associated) were deemed preventable. Preventable causes of death included hemorrhage, unrecognized hemopneumothorax, and unrecognized epidural hematoma.

Cardiopulmonary consequences of decompression stress

Clinically undetectable venous gas emboli (VGE) can be routinely demonstrated in both animals and men undergoing clinically uneventful decompression from hyperbaric environments. The effect of VGE on gas exchange and pulmonary hemodynamics in this setting is unclear. We therefore have studied the cardiopulmonary effects of clinically uneventful decompression on unanesthetized sheep. Sheep were instrumented with a femoral arterial catheter, Swan-Ganz catheter, chronic tracheostomy, and were loosely restrained in the prone position. Following baseline measurements of pulmonary artery pressure (pPA), mean pulmonary artery wedge pressure (pPAw), cardiac output (CO), arterial and mixed venous blood gases, Doppler ultrasonic bubble detection, and V/Q scans using 133Xe, the animals were exposed to: (a) a 15-min exposure to 6.03 ATA (n = 8), (b) a 17.5-min exposure to 6.03 ATA, or (c) a 15-min control period at 1 ATA (n = 7). All measured parameters remained unchanged in the control group. VGE were detected in all animals exposed to pressure. In both exposure groups CO fell 20% (P < 0.05) and pulmonary vascular resistance (PVR) rose 60% (P < 0.05) compared to the control group. This rise in PVR was significantly in excess of that predicted for the observed fall in CO. Analysis of pPA and pPAw suggested neither right nor left ventricular failure. No significant abnormalities of gas exchange were detected. V/Q scans remained unchanged in all animals. We conclude that CO and PVR are altered by clinically uneventful decompression stress.

Urinary excretion of water and electrolytes during open-sea saturation diving to 850 fsw

The dive was carried out in the open sea to a depth of 850 fsw (26.7 ATA) for 6 days (DD 1--6) in the saturated mode, with personnel transfer capsule (PTC) excursions between 0 and 150 fsw and diver excursions between 0 and 50 fsw from the saturation base. Each diver had two excursion dives on alternate days. Although each PTC excursion lasted approximately 7 h, the actual time spent in the water averaged 10.5 min per diver. For 12 divers, daily excretion of water, electrolytes, aldosterone, and antidiuretic hormone (ADH) was studied, along with plasma composition (including prolactin), before, during, and after hyperbaric exposure. A significant increase in urine flow was observed on DD2--4 (1604 ml/day predive vs. 2300 ml/day on DD 4; P less than 0.05), after which the degree of diuresis decreased to about 1800 ml/day. Urine osmolality changed inversely with urine flow, with the lowest value of 532 mOsm/kg on DD 4. During the postdive period, both urine flow and urine osmolality returned to the predive level. The endogenous creatinine clearance was maintained at about 200 liters/day throughout the dive. The fractional excretion of Na+ remained unchanged while that of K+ increased significantly during hyperbaric exposure, thus decreasing the urinary Na+/K+ ratio. The fractional excretion of total osmotic substances showed a small hyperbaric exposure. Body weight decreased progressively during the initial 4 days of pressure exposure, equalling 2.6 kg on DD 4. These findings suggest that the observed diuresis may be accompanied by a net loss of body water. Neither the plasma prolactin level nor urinary excretion of aldosterone and ADHshowed any consistent change throughout the dive. It thus appears that, although there is a small osmotic component, the observed diuresis is primarily due to the ADH-independent inhibition of fre water reabsorption from the collecting duct by means of a mechanism yet to be identified.

Venous gas bubbles: production by transient, deep isobaric counterdiffusion of helium against nitrogen

When awake goats were subjected to isobaric gas switching from saturation (17 hours) on 4.7 atmospheres of nitrogen (0.3 atmosphere of oxygen) to 4.7 atmospheres of helium (0.3 atmosphere of oxygen), bubbles detected by 5-megahertz Doppler ultrasound in the posterior vena cava 20 to 60 minutes after the switch continued for 4 hours. Similar experiments carried out at 6.7 atmospheres of inert gas and 0.3 atmosphere of oxygen produced more bubbles for as long as 12 hours after the gas switch. This is believed to be the first objective demonstration of the phenomenon of deep isobaric supersaturation under transient operational diving conditions at relatively shallow diving depths. Detection of bubbles by Doppler ultrasound confirms the potential importance of the phenomenon to shallow saturation diving and holds promise for better quantitification of its effects as well as those of its counterpart, isobaric undersaturation, which can confer a decompression advantage.

Hematologic changes in man during decompression: relations to overt decompression sickness and bubble scores

In order to determine whether asymtomatic gas phase separation causes hematologic abnormalities, studies were carried out following two dive series, one to 210 feet of sea water (FSW) for 50 min and the other to 132 FSW for 30 min. Studies included white and red cell count, red cell indices, platelet count, ESR, fibrinogen, fibrin split products, prothrombin time, partial thromboplastin time, coagulation factors II, V, VII, VIII, and X, clot retraction, platelet aggregation and adhesion, euglobulin lysis time, and platelet factor III. Changes were seen in platelet and white cell count, prothrombin time and partial thrombo-plastin time. White cell count was the only variable which correlated with total bubble score. The results are presented and implications of the findings discussed.

Blood viscosity in man following decompression: correlations wiht hematocrit and venous gas emboli

Whole blood viscosities were measured in U.S. Navy personnel before and after chamber compressions to 5 ATA (132FSW) and 7.4 ATA (210 FSW) by a new method described here. Bubble scores as a quantitative measure of venous gas emboli were determined during decompression and for 30 min thereafter. Hematocrit was measured both before and after each dive. There were five cases of decompression sickness in the two groups. No significant changes in whole blood viscosity, or hematocrit, were noted either in the group that was affected by decompression sickness or in all of the subjects taken as a group. No correlations between total bubble score and changes in viscosity or hematocrit could be made. These results imply that no major changes in viscosity occur in the usual forms of decompression sickness encountered in human beings.

Gas phase separation during decompression in man: ultrasound monitoring

During two dive series, one to 132 fsw and one to 210 fsw, Doppler ultrasonic bubble detectors were used to monitor venous gas bubbles in divers during decompression and for 30 min thereafter. Various decompression schedules were used. Bubble scores were evaluated by independent listerners to tape recordings in a blind manner. A significant increase in bubble scores throughout the stages of decompression and postdecompression was demonstrated as well as a statistically significant relationship between bubble score and decompression sickness. A reduction in mean bubble score was found in divers who made an additional deep decompression stop that was unrelated to the extension of the decompression time. The implications of these findings are discussed.