Performance of the Uni-Vent Eagle™ Model 754 ventilator under hyperbaric conditions.

Critically ill patients needing mechanical ventilation may require hyperbaric oxygen therapy. Some institutions still use ventilators that were available prior to the advent of hyperbaric-specific units, such as the Uni-Vent Eagle™ Model model 754. Here we examine the performance of the Uni-Vent model 754 under hyperbaric conditions and investigate concerns of an oxygen leak in the ventilator housing, which poses a fire risk. We studied the ventilator at 1.0, 2.4 and 2.8 ATA in assist control mode using a Michigan test lung and a variety of tidal volumes and respiratory rates. We recorded the delivered volumes, peak pressures, and oxygen percentages within the hyperbaric chamber at 2.4 and 2.8 ATA and within the ventilator housing. At those pressures the ventilator delivered approximately 25% less volume than at 1.0 ATA. We observed breath stacking at high respiratory rates, but this was blunted at both 2.4 and 2.8 ATA. Oxygen levels did not rise in the housing during our investigation. In addition, we fit a linear regression to the data comparing set tidal volumes and delivered tidal volumes in order to model the changes observed. Hyperbaric conditions caused decreased delivered tidal volumes in a depth-dependent fashion, and oxygen levels within the housing did not rise. The Uni-Vent Eagle model 754 performed safely and effectively at depth but requires spirometry to correctly program desired ventilator settings.

Evaluation of the ventilatory effects on human subjects in prolonged hip-flexed/head-down restraint position.

BACKGROUND: The restraint chair is a tool used by law enforcement and correction personnel to control aggressive, agitated individuals. When initiating its use, subjects are often placed in a hip-flexed/head-down (HFHD) position to remove handcuffs. Usually, this period of time is less than two minutes but can become more prolonged in particularly agitated patients. Some have proposed this positioning limits ventilation and can result in asphyxia. The aim of this study is to evaluate if a prolonged HFHD restraint position causes significant ventilatory compromise. METHODS: Subjects exercised on a stationary bicycle until they reached 85% of their predicted maximal heart rate. They were then handcuffed with their hands behind their back and placed into a HFHD seated position for five minutes. The primary outcome measurement was maximal voluntary ventilation (MVV). This was measured at baseline, after initial placement into the HFHD position, and after five minutes of being in the position while still maintaining the HFHD position. Baseline measurements were compared with final measurements for statistically significant differences. RESULTS: We analyzed data for 15 subjects. Subjects had a mean MVV of 165.3 L/min at baseline, 157.8 L/min after initially being placed into the HFHD position, and a mean of 138.7 L/min after 5 min in the position. The mean baseline % predicted MVV was 115%; after 5 min in the HFHD position the mean was 96%. This 19% absolute difference was statistically significant (p = 0.001). CONCLUSIONS: In healthy seated male subjects with recent exertion, up to five minutes in a HFHD position results in a small decrease in MVV compared with baseline MVV levels. Even with this decrease, mean MVV levels were still 96% of predicted after five minutes. Though a measurable decrease was found, there was no clinically significant change that would support that this positioning would lead to asphyxia over a five-minute time period.

Diving after SARS-CoV-2 (COVID-19) infection: Fitness to dive assessment and medical guidance.

Scuba diving is a critical activity for commercial industry, military activities, research, and public safety, as well as a passion for many recreational divers. Physicians are expected to provide return-to-diving recommendations after SARS-CoV-2 (COVID-19) infection based upon the best available evidence, often drawn from experience with other, similar diseases. Scuba diving presents unique physiologic challenges to the body secondary to immersion, increased pressure and increased work of breathing. The long-term sequelae of COVID-19 are still unknown, but if they are proven to be similar to other coronaviruses (such as Middle East respiratory syndrome or SARS-CoV-1) they may result in long-term pulmonary and cardiac sequelae that impact divers' ability to safely return to scuba diving. This review considers available literature and the pathophysiology of COVID-19 as it relates to diving fitness, including current recommendations for similar illnesses, and proposes guidelines for evaluation of divers after COVID-19. The guidelines are based upon best available evidence about COVID-19, as well as past experience with determination of diving fitness. It is likely that all divers who have contracted COVID-19 will require a medical evaluation prior to return to diving with emphasis upon pulmonary and cardiac function as well as exercise capacity.

Assessment of stress markers in restrained individuals following physical stress with and without sham CED activation.

INTRODUCTION: Law enforcement and pre-hospital care personnel often confront individuals who must be physically restrained. Many are under the influence of illicit substances, and law enforcement officers may need to use a controlled electrical device (CED) to gain control of the individual and they are often placed into the prone maximum restraint (PMR) position. These techniques have previously been evaluated for their physiologic effects. The purpose of this study was to investigate the psychological effects of anticipating and experiencing a sham CED activation in healthy human subjects who were exercised and restrained compared with no sham activation by assessing the differences in a panel of several known biomarkers of stress. METHODS: We performed a randomized, crossover controlled human subject trial to study the stress associated with exercise, physical exhaustion, and restraint with and without an added psychological stress simulating the field use of a CED. Twenty five total subjects; each subject performed two different trials each consisting of a brief period of intense exercise on a treadmill to exhaustion followed by placement in the PMR with and without induced psychological stress. Blood samples were collected for analysis pre and post exercise, as well as 10 min after completion of the exercise. A panel of hormones and stress markers were measured. RESULTS: We found no significant differences in any of the stress biomarkers measured between the two study groups. A trend towards higher levels of copeptin was measured in the sham CED activation arm. CONCLUSION: During a brief period of intense exercise followed by the psychological stress of anticipated CED application, there did not appear to be statistically significant changes in the stress panel of biomarkers measured, only a trend towards significance for higher copeptin levels in the patients exposed to the psychological stress.

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.

Evaluation of the ventilatory effects of the prone maximum restraint (PMR) position on obese human subjects.

UNLABELLED: The study sought to determine the physiologic effects of the prone maximum restraint (PMR) position in obese subjects after intense exercise. We designed an experimental, randomized, cross-over trial in human subjects conducted at a university exercise physiology laboratory. Ten otherwise healthy, obese (BMI>30) subjects performed a period of heavy exertion on a cycling ergometer to 85% of maximum heart rate, and then were placed in one of three positions in random order for 15min: (1) seated with hands behind the back, (2) prone with arms to the sides, (3) PMR position. While in each position, mean arterial blood pressure (MAP), heart rate (HR), minute ventilation (V˙E), oxygen saturation (SaO2), and end tidal CO2(etCO2) were measured every 5min. There were no significant differences identified between the three positions in MAP, HR, V˙E, or O2sat at any time period. There was a slight increase in heart rate at 15min in the PMR position over the prone position (95 vs. 87). There was a decrease in end tidal CO2 at 15min in the PMR over the prone position (32mmHg vs. 35mmHg). In addition, there was no evidence of hypoxia or hypoventilation during any of the monitored 15min position periods. CONCLUSION: In this small study of obese subjects, there were no clinically significant differences in the cardiovascular and respiratory measures comparing seated, prone, and PMR position following exertion.

The effect of the prone maximal restraint position with and without weight force on cardiac output and other hemodynamic measures.

BACKGROUND: The prone maximal restraint (PMR) position has been used by law enforcement and emergency care personnel to restrain acutely combative or agitated individual. The position places the subject prone with wrists handcuffed behind the back and secured to the ankles. Prior work has indicated a reduction in inferior vena cava (IVC) diameter associated with this position when weight force is applied to the back. It is therefore possible that this position can negatively impact hemodynamic stability. OBJECTIVES: We sought to measure the impact of PMR with and without weight force on measures of cardiac function including vital signs, oxygenation, stroke volume (SV), IVC diameter, cardiac output (CO) and cardiac index (CI). METHODS: We conducted a randomized prospective cross-over experimental study of 25 healthy male volunteers (22-43 years of age) placed in 5 different body positions: supine (SU), prone (PR), prone maximal restraint with no weight force (PMR-0), prone maximal restraint with 50 lbs added to the subject's back (PMR-50), and prone maximal restraint with 100 lbs added to the subject's back (PMR-100) for 3 min. Heart rate (HR), blood pressure (BP), and oxygenation saturation (O2 sat) were monitored. In addition, echocardiography was performed to measure left ventricular outflow tract diameter (LVOTD), and SV, CO, and CI were then calculated. Data were analyzed using repeated measures ANOVA with pair-wise comparisons when appropriate to evaluate changes with each variable with respective positioning. RESULTS: Despite a small decrease in SV between SU and PMR positions, there were no statistically significant differences in CO between the 5 different positions. There were also no differences in CI between positions other than a small decrease when comparing SU and PMR-50 only (mean difference -0.39 L/stroke, p = 0.005). There was no evidence of hemodynamic compromise in any of the PMR positions when evaluating HR, MAP or O2 sat. CONCLUSIONS: PMR with and without weight force did not result in any changes in CO or other evidence of cardiovascular or hemodynamic compromise.

Incidence of DCS and oxygen toxicity in chamber attendants: a 28-year experience.

Decompression sickness (DCS) and central nervous system oxygen toxicity are inherent risks for "inside" attendants (IAs) of hyperbaric chambers. At the Hyperbaric Medicine Center at the University of California San Diego (UCSD), protocols have been developed for decompressing IAs. Protocol 1: For a total bottom time (TBT) of less than 80 minutes at 2.4 atmospheres absolute (atm abs) or shallower, the U.S. Navy (1955) no-decompression tables were utilized. Protocol 2: For a TBT between 80 and 119 minutes IAs breathed oxygen for 15 minutes prior to initiation of ascent. Protocol 3: For a TBT between 120-139 minutes IAs breathed oxygen for 30 minutes prior to ascent. These protocols have been utilized for approximately 28 years and have produced zero cases of DCS and central nervous system oxygen toxicity. These results, based upon more than 24,000 exposures, have an upper limit of risk of DCS and oxygen toxicity of 0.02806 (95% CI) using UCSD IA decompression Protocol 1, 0.00021 for Protocol 2, and 0.00549 for Protocol 3. We conclude that the utilization of this methodology may be useful at other sea-level multiplace chambers.

Evaluation of the ventilatory effects of a restraint chair on human subjects.

BACKGROUND: Combative individuals often require physical restraint in the prehospital and law enforcement setting. Specialized restraint chairs have been utilized for this purpose in the latter case, but concern has arisen that restrained individuals are at risk for ventilatory compromise and asphyxiation. OBJECTIVE: We sought to determine if placement in a restraint chair results in alterations of respiratory or ventilatory function. METHODS: We conducted a randomized, cross-over, controlled experimental trial in 10 healthy human volunteers performed at a university exercise physiology laboratory. After exercise on a cycle ergometer to 85% of the age-predicted maximal heart rate, subjects were randomized to either a sitting position or restraint chair with arms, legs, and chest secured using standard law enforcement protocol. Subjects remained in each position for 30 min, during which pulmonary function testing of maximal voluntary ventilation (MVV) was performed at 11 and 30 min. Arterial oxygen saturation (O(2)sat) and end-tidal PCO(2) levels (PETCO(2)) were monitored continuously. Subjects repeated the experimental trial in the alternate position after a 45-min rest period. Measures between restraint and sitting positions were compared using a paired t-test at each time measurement. RESULTS: There was no evidence of hypoxemia. Mean PETCO(2) levels were not statistically different between the two groups at any time (p > 0.05), and there was no evidence of hypercapnia. CONCLUSION: In healthy subjects, placement in a restraint chair resulted in a small decrease in MVV, but did not result in any changes in O(2)sat or PETCO(2).

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.

Serum troponin I measurement of subjects exposed to the Taser X-26.

The Taser is a high-voltage, low-amperage conducted energy device used by many law enforcement agencies as a less lethal force weapon. The objective of this study was to evaluate for a rise in serum troponin I level after deployment of the Taser on law enforcement training volunteers. A prospective, observational cohort study was performed evaluating serum troponin I levels in human subjects 6 h after an exposure to the Taser X-26. Outcome measures included abnormal elevation in serum troponin I level (> 0.2 ng/mL). There were 66 subjects evaluated. The mean shock duration was 4.36 s (range 1.2-5 s). None of the subjects had a positive troponin I level 6 h after exposure. It was concluded that human volunteers exposed to a single shock from the Taser did not develop an abnormal serum troponin I level 6 h after shock, suggesting that there was no myocardial necrosis or infarction.

Twelve-lead electrocardiogram monitoring of subjects before and after voluntary exposure to the Taser X26.

OBJECTIVES: The Taser (Taser International, Scottsdale, Ariz) uses high-voltage electricity to incapacitate subjects. We sought to evaluate cardiac rhythm changes during deployment of the Taser on healthy volunteers. METHODS: This prospective study was performed on 32 healthy volunteer subjects receiving a Taser X26 discharge. The subjects had baseline 12-lead electrocardiogram (ECG) monitoring performed immediately before and within 1 minute after the Taser discharge. Changes in cardiac rhythm, morphology, and interval duration were evaluated. Descriptive statistics and paired-sample t test comparisons are reported. RESULTS: All 32 subjects had an interpretable 12-lead ECG obtained before and after the Taser activation, although 1 subject's post-PR interval could not be determined. The mean age and body mass index were 33 years and 26.5 kg/m2, respectively. Overall, there was a significant increase in heart rate (2.4; 95% confidence interval [CI], 0.0-4.9) and a decrease in PR interval (-6.5; 95% CI, -9.7 to -3.3). When stratified by sex, only the PR interval in men significantly decreased (-5.9; 95% CI, -9.2 to -2.5). There were significant changes in heart rate (4.0; 95% CI, 1.3-6.7), PR interval (-6.0; 95% CI, -11.3 to -0.7), and QT interval (-18.8; 95% CI, -33.2 to -4.3) among those with a normal body mass index, and in PR interval among those who were overweight/obese (-6.7; 95% CI, -10.8 to -2.5). None of the statistically significant differences between ECG measures were clinically relevant. CONCLUSIONS: There were no cardiac dysrhythmia and interval or morphology changes in subjects who received a Taser discharge based on a 12-lead ECG performed immediately before and within 1 minute after a Taser activation.

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.

Weight force during prone restraint and respiratory function.

Prone maximal restraint position (PMRP, also known as hogtie or hobble) is often used by law enforcement and prehospital personnel on violent combative individuals in the field setting. Weight force is often applied to the restrained individual's back and torso during the restraint process. We sought to determine the effect of 25 and 50 lbs weight force on respiratory function in human subject volunteers placed in the PMRP. We performed a randomized, cross-over, controlled trial on 10 subjects placed in 4 positions for 5 minutes each: sitting, PRMP, PRMP with 25 lbs weight force (PMRP+25), and PRMP with 50 lbs weight force placed on the back (PMRP+50). We measure pulse oximetry, end-tidal CO2 levels, and forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1). FVC and FEV1 were significantly lower in all restraint positions compared with sitting but not significantly different between restraint positions with and without weight force. Moreover, mean oxygen saturation levels were above 95% and mean end-tidal CO2 levels were below 45 mm Hg for all positions. We conclude that PMRP with and without 25 and 50 lbs of weight force resulted in a restrictive pulmonary function pattern but no evidence of hypoxia or hypoventilation.