Cerebral Blood Flow Based Computer Modeling of Gz-Induced Effects.

BACKGROUND: There is continued interest in acceleration (G) effects in civil aviation, as G-induced loss of consciousness (G-LOC), impaired consciousness, and visual effects play a role in aerobatic, agricultural, and military aviation accidents.METHODS: A software model [the Civil Aerospace Medical Institute G-Effects Model (CGEM)] based on physical and physiological variables related to in-flight tissue resupply and using oxygen flow as a proxy for supply availability, was developed to evaluate risk of G-LOC and related phenomena in aeronauts. Aeronauts were modeled using several parameters, including sex, cardiovascular fitness, and other common modifiers such as G-suits, positive pressure breathing gear, anti-G straining, and other muscle tensing. The software was validated by comparison with experimental data from the peer-reviewed literature.RESULTS: CGEM predicted physiological effects of Gz exposure accurately, particularly for rapid onset rates. Predicted times to G-LOC and absolute incapacitation periods were consistently within 1 SD of pooled results obtained during centrifuge experiments using U.S. Navy (USN) and U.S. Air Force (USAF) pilots. Predictions of G tolerance based on visual effects onset also compared well with published data, as did evaluation of symptoms expected during a difficult aerobatic maneuver.DISCUSSION: CGEM is a new tool for civil and military aviation. Rather than providing a simple G tolerance number, flight surgeons, pilots, and accident investigators can gain insight into changes in risk-from factors such fatigue, medications, dehydration, and anti-G countermeasures used-through proper selection of parameters.Copeland K, Whinnery JE. Cerebral blood flow based computer modeling of Gz-induced effects. Aerosp Med Hum Perform. 2023; 94(5):409-414.

A new equation for calculating the maximum wait time for pilots who use an impairing medication.

INTRODUCTION: Pilots who use an impairing medication to treat a medical condition are required to wait an appropriate amount of time after completing the treatment before returning to duty. However, toxicology findings from fatal aviation accidents indicate not all pilots wait a sufficient period of time. Methods used today do not take into consideration the time required for the drug to reach subtherapeutic concentrations. METHODS: An equation was developed based on the therapeutic range and the maximum expected half-life of the medication to objectively calculate a safe return-to-duty time for pilots. The new equation assumes the treating physician will not dose the patient beyond the upper therapeutic range of the medication and the person taking the medication has the maximum half-life reported in the literature. The equation N ln(0.5*Cmin/Cmax)/ln(0.5) was developed to determine the number of half-lives (n) required to reach one-half of Cmin, where Cmin = lower therapeutic concentration and Cmax = upper therapeutic concentration. Anonymous subjects were recruited under an approved IRB protocol. Blood and plasma were collected at approximately Cmax (2-3 h) and again after waiting approximately another 5 h. Toxicological analysis was performed on the specimens collected. RESULTS: One subject taking a 25-mg dose had a 0.033 ug x ml(-1) blood concentration after waiting 8 h, well above the 0.025 ug x ml(-1) reported as impairing concentration. The new equation estimated a mean wait time for the 18 medications composed of 4 half-lives. DISCUSSION: The new CAMI equation takes into consideration safety without grossly over estimating pilot wait times.

Effects of fluid load on human urine characteristics related to workplace drug testing.

During workplace drug testing, urine is tested for dilution, substitution and adulteration. Donors argue that these findings are due to medical, health or working conditions or diet and genetic differences. There is a paucity of data correlating changes in urine characteristics after a fluid load to various body parameters. Therefore, five urine specimens (one in the morning, one prior to drinking 800 mL of a beverage, and three time intervals thereafter) from 12 males and 12 females were tested for four different beverages on separate occasions. Of the 480 samples, 376 were in sufficient amounts. Of these 376, 36 (10%) had creatinine <20 mg/dL but ≥2 mg/dL; 27 (75%) of 36 had specific gravity <1.0030 but >1.0010. Thus, these 27 samples can be considered to be dilute; 20 (74%) of 27 were from females. For males with at least one dilute sample, body fat was 11% less and resting metabolic rate (RMR) was 29% more than males with no dilute samples (p > 0.05); for females with at least one dilute sample, height was 8% less and weight 20% less than females with no dilute samples (p > 0.05). Individuals with a higher RMR appear to have a greater potential for producing dilute urine specimens than those with a lower RMR. Thus, a dilute sample does not necessarily indicate that it was intentionally diluted. Such samples must be carefully evaluated in consideration with recent consumption of liquid by donors to avoid false accusations.

Drugs and alcohol found in civil aviation accident pilot fatalities from 2004-2008.

INTRODUCTION: The Federal Aviation Administration (FAA) Office of Aerospace Medicine sets medical standards needed to protect the public and pilots from death or injury due to incapacitation of the pilot. As a part of this process, toxicology testing is performed by the FAA on almost every pilot who is fatally injured in an aviation accident to determine the medical condition of the pilot, medications used by the pilot at the time of the accident, and the extent of impairment, if any. METHOD: The data were extracted from the FAA toxicology database for all pilots who died from 2004 to 2008 in aviation accidents. RESULTS: The laboratory received and tested specimens from 1353 pilots who died in aviation accidents between 2004 and 2008; 507 of these pilots were found to be taking drugs and 92 had ethanol in excess of 0.04 g x dl(-1). DISCUSSION: This study was conducted to determine the extent of drug use in pilots who have died in aviation accidents from 2004 to 2008 and to determine the types of drugs most commonly found. A comparison of previously published reports with this study's report was made to determine trends in drug use by pilots who have died in aviation accidents over the past 20 yr. Factors were discussed that could influence drug trends. Diphenhydramine, an H1 antihistamine with impairing properties, is the most commonly found drug in pilots who died in an aviation accident.

Increased cannabinoids concentrations found in specimens from fatal aviation accidents between 1997 and 2006.

The National Institute on Drug Abuse (NIDA) and the Office of National Drug Control Policy (ONDCP) reported a 1.5-fold increase in the delta-9-tetrahydrocannabinol (THC) content of street cannabis seizures from 1997 to 2001 versus 2002 to 2006. This study was conducted to compare the changes, over those years, in blood and urine cannabinoid concentrations with the potency of THC reported in the cannabis plant. Cannabinoids were screened using radioimmunoassay (RIA) for blood and fluorescence polarization immunoassay (FPIA) for urine and confirmed using GC/MS. A total of 95 individuals were found to be using cannabis from a total number of 2769 (3.4%) individuals tested over the period 1997 through 2006. Other impairing drugs were found in 38% of the cannabinoids-positive individuals. The mean concentration of THC in blood for 1997-2001 was 2.7 ng/mL; for 2002-2006, it was 7.2 ng/mL, a 2.7-fold increase in the mean THC concentration of specimens from aviation fatalities, compared to a 1.5-fold increase in cannabis potency reported by the NIDA and ONDCP. The mean age for cannabis users was 40 years (range 18-72) for aviation fatalities. For all blood and urine specimens testing negative for cannabinoids from aviation fatalities, the mean age of the individuals was 50 years (range 14-92). More than half of the fatalities tested were 50 years or older, whereas, 80% of the positive cannabis users were under 50. As indicated by these findings, members of the transportation industry, government regulators, and the general public should be made aware of the increased potential for impairment from the use of high-potency cannabis currently available and being used.

Aircraft-assisted pilot suicides in the United States, 1993-2002.

Our laboratory was interested in epidemiological and toxicological findings from aircraft-assisted pilot suicides. Between 1993-2002 there were 3,648 fatal aviation accidents. The NTSB determined that 16 were aircraft-assisted suicides; 15 from intentional crashing of an aircraft and 1 from exiting the aircraft while in-flight. All pilots involved in these aircraft-assisted suicides were male, with a median age of 40 years. Seven of the 14 pilots for which specimens were available were positive for disqualifying substances. Based on the few cases conclusively attributed to suicide, death by the intentional crashing of an aircraft appears to be an infrequent and uncommon event.

Pilot medical history and medications found in post mortem specimens from aviation accidents.

INTRODUCTION: Federal Aviation Administration (FAA) regulations require pilots to report all medications and medical conditions for review and consideration as to the overall suitability of the pilot for flight activities. METHODS: Specimens were collected by local pathologists from aviation accidents and sent to the Bioaeronautical Sciences Research Laboratory for analysis. The results of such tests were entered into the Forensic Case Management System. This database was searched to identify all pilots found positive for medications used to treat cardiovascular, psychological, or neurological conditions over the period January 1, 1993, through December 31, 2003. RESULTS: Toxicological evaluations were performed on 4143 pilots. Psychotropic drugs were found in 223 pilots. Cardiovascular medications were found in 149 pilots. Neurological medications were found in 15 pilots. Pilots reported psychological conditions in 14 of the 223 pilots found positive for psychotropic drugs. Only 1 of the 14 pilots reporting a psychological condition to the FAA reported the psychotropic medication found after the accident. Cardiovascular disease was reported by 69 of the pilots found with cardiovascular drugs in their system. Cardiovascular medications found in the pilots were reported by 29 of the 69 pilots reporting a cardiovascular condition. Only 1 of the 15 pilots reported having a neurological condition to the FAA; none of the pilots found with neurological medications reported the medication. CONCLUSIONS: Toxicology successfully identified 93% of the medications reported by the pilots. Pilots involved in fatal accidents taking psychotropic or neurological medications rarely reported the medication or their underlying medical condition to the FAA.

Toxicological findings from 1587 civil aviation accident pilot fatalities, 1999-2003.

INTRODUCTION: The prevalence of drug and ethanol use in aviation is monitored by the Federal Aviation Administration (FAA). Under such monitoring, toxicological studies for the 1989-1993 and 1994-1998 periods indicated lower percentages of the presence of controlled substances (illegal drugs) than that of prescription and nonprescription (over-the-counter) drugs in aviation accident pilot fatalities. In continuation, a toxicological assessment was made for an additional period of 5 yr. METHODS: Biosamples from aviation accident pilot fatalities submitted to the FAA Civil Aerospace Medical Institute (CAMI) are analyzed, and those findings are stored in a database. This database was examined for the 1999-2003 period for the presence of controlled substances (Schedules I-V), prescription/nonprescription drugs, and ethanol in the fatalities. RESULTS: Out of 1629 fatal aviation accidents from which CAMI received biosamples, pilots were fatally injured in 1587 accidents. Drugs and/or ethanol were found in 830 (52%) of the 1587 fatalities. Controlled substances from Schedules I-II (SI-II) and Schedules III-V (SIII-V) were detected in 113 and 42 pilots, respectively. Prescription drugs were present in 315 pilots, nonprescription drugs in 259, and ethanol in 101. SI-II substances were detected in 5 of 122 first-class medical certificate-holding airline transport pilots. In addition to the controlled substances, many of the prescription/nonprescription drugs found in the fatalities have the potential for impairing performance. CONCLUSIONS: Findings from this study were consistent with those of two previous toxicological studies and support the FAA's programs aimed at reducing the usage of performance-impairing substances.

Characteristics and toxicological processing of postmortem pilot specimens* from fatal civil aviation accidents.

INTRODUCTION: Autopsied biosamples from civil aviation accident pilot fatalities are submitted to the Civil Aerospace Medical Institute (CAMI) for toxicological evaluation. However, such evaluation is dependent on types and amounts of submitted samples, and obtaining suitable samples is governed by the nature of the accident. Characteristics of those samples and associated toxicological processing have not been well documented in the literature. METHOD: Therefore, the CAMI Toxicology Database was searched for these aspects. RESULTS: CAMI received samples from the pilot fatalities (CAMI cases) of approximately 80% of the 1990-2000 aviation accidents reported by the National Transportation Safety Board. Accidents and cases during June-September were higher than the other months, and more than half of the received cases had multiple samples in sufficient amounts. For example, out of 1891 cases processed for the 1996-2000 accidents, 1211 had at least adequate amounts of blood, urine, and/or vitreous humor; 324 had inadequate amounts of blood and urine; and 356 had no blood or urine. Muscle, liver, lung, and/or kidney samples were submitted in 90% of the cases, while cerebrospinal fluids were submitted in only 8% of the cases. The toxicologically preferred samples, blood and urine, were available in 78% and 56% of the 1891 cases, respectively. Out of 51 cases containing only one sample type, 46 had muscle and the remaining 5 had other sample types. Samples were primarily analyzed for combustion gases, alcohol/volatiles, and drugs. Generally, the presence of analytes is demonstrated in at least two different sample types by using two different analytical techniques for reporting a particular case as "positive." An effective quality-assurance/quality-control is maintained throughout the process. CONCLUSION: In the majority of the aviation accidents, sufficient amounts and types of biological samples were submitted for toxicological evaluation.