Pilots Of High-performance Aircraft Research Articles

The effect of helmet mass and aircraft acceleration on cervical spine loads during typical fast jet aircraft pilot head motions

ObjectivesGravitational Force (Gz), head motion, and helmet mass are associated with neck pain in high performance aircraft pilots. Few studies have quantified neck kinetics (intersegmental neck moments) during aerial combat manoeuvres. DesignCross-sectional. MethodsWe quantified net joint moments between the skull and C1, and C6–7 during typical flight related headchecks using the Musculoskeletal Model for the Analysis of Spinal Injuries (MASI). We measured the influence of pilot-specific helmets and Gz on joint moments. Nineteen fighter pilots performed four head checks (check6 left, check6 right, extension hold and extension scan) under two helmet conditions. Motion data were transferred to OpenSim where joint moments were calculated at 1G to 9G. Net joint moments were compared across helmet conditions, Gz and headchecks. ResultsThe Joint Helmet Mounted Cueing System (JHMCS) resulted in higher moments at each segment- by a factor of 1.25 per unit of Gz, at C1, and by a factor of 1.08 per unit of Gz for C7. ExtensionScan and Check6Left were associated with the highest peak (96.13 Nm and 92.56 Nm). ExtensionScan and ExtensionHold accrued the highest mean cumulative loads at C7 at 9Gz (607.35 Nm.sec/motion, 362.99 Nm.sec/motion respectively). Asymmetries were observed between the Left and Right Check6 motions. High variability was evident between and within pilots. ConclusionsThe MASI model has been successfully applied to quantify intersegmental neck joint moments for typical headchecks that are performed during combat flight manoeuvres. In future, data derived from this model may inform conditioning, rehabilitative and preventative interventions to reduce neck pain in fast jet pilots.

Cuff-Method Thigh Arterial Occlusion Counteracts Cerebral Hypoperfusion Against the Push-Pull Effect in Humans.

Exposure to acute transition from negative (−Gz) to positive (+ Gz) gravity significantly impairs cerebral perfusion in pilots of high-performance aircraft during push—pull maneuver. This push—pull effect may raise the risk for loss of vision or consciousness. The aim of the present study was to explore effective countermeasures against cerebral hypoperfusion induced by the push—pull effect. Twenty healthy young volunteers (male, 21 ± 1 year old) were tested during the simulated push–pull maneuver by tilting. A thigh cuff (TC) pressure of 200 mmHg was applied before and during simulated push—pull maneuver (−0.87 to + 1.00 Gz). Beat-to-beat cerebral and systemic hemodynamics were measured continuously. During rapid −Gz to + Gz transition, mean cerebral blood flow velocity (CBFV) was decreased, but to a lesser extent, in the TC bout compared with the control bout (−3.1 ± 4.9 vs. −7.8 ± 4.4 cm/s, P < 0.001). Similarly, brain-level mean blood pressure showed smaller reduction in the TC bout than in the control bout (−46 ± 12 vs. −61 ± 13 mmHg, P < 0.001). The systolic CBFV was lower but diastolic CBFV was higher in the TC bout. The systemic blood pressure response was blunted in the TC bout, along with similar heart rate increase, smaller decrease, and earlier recovery of total peripheral resistance index than control during the gravitational transition. These data demonstrated that restricting thigh blood flow can effectively mitigate the transient cerebral hypoperfusion induced by rapid shift from −Gz to + Gz, characterized by remarkable improvement of cerebral diastolic flow.

Pulling back on the push-pull effect: use of lower body negative pressure to protect against drops in cerebral perfusion during airflight manoeuvres.

Pulling back on the push-pull effect: use of lower body negative pressure to protect against drops in cerebral perfusion during airflight manoeuvres.

Dissociation Between Mental Workload, Performance, and Task Awareness in Pilots of High Performance Aircraft

The purpose of this study was to demonstrate how the inclusion of a tactical task goal awareness measure complemented mental workload and performance measures in a simulated air combat mission. It was hypothesized that the evaluation of the tactical task goal awareness could provide additional information concerning the cognitive demands a pilot is exposed to during a complex air combat task. A test setting was developed to test this hypothesis in a virtual flight training device. To highlight the impact of task complexity, high performance aircraft pilots' heart rate (HR), interbeat-interval (IBI), and performance in two simple flying tasks were first compared. Then, a similar comparison, complemented with the tactical task goal awareness measure, was made with two complex flying tasks. It was found that when the pilot's awareness of the tactical goals was low, a combination of low performance and low mental workload occurred. It was concluded that when the pilots' performance is evaluated on a complex air combat task, the awareness of the tactical goals, performance, and mental workload should be studied together as the pilot's awareness can explain some of HR/IBI responses that could be otherwise misinterpreted. More generally, mental workload, performance, and task goal awareness should all be considered when the operator's performance in any complex human-machine system is assessed.

A review of high G-stress induced problems and their solutions

G stress can debilitate pilots of modern fighter aircraft and consequence accidents due to G-induced loss of consciousness (G-LOC). The physiological effects of high G stress include reduction in head level blood pressure and cardiac output that subsequently results loss of vision and G-LOC. The body's natural resistance system helps the pilot to fight against the effects of G stress to some level. To understand the medical and physiological consequences of high G forces on humans, research around the world is conducted using centrifuges, tilt tables, lower body negative pressure (LBNP) devices, etc. Physiological effects due to G-stress are experienced by the pilot on the cardiovascular, respiratory, musculoskeletal and central nervous systems. Many physiological, environmental and habitual conditions are found responsible for decreasing the G-tolerance. Mechanical, physiological and educational countermeasures are suggested to protect the pilots of high performance aircraft against the extreme acceleration. Expected inventions of more manoeuvrable aircrafts will possibly demand the use of advanced countermeasures to protect the pilots from the effect of high G forces.

Career perspective: Victor A. Convertino.

This review focuses on a career of unique opportunities to participate in various areas of research related to extreme physiology and medicine. My experience as a volunteer subject in exercise experiments conducted at NASA included the study of acute and chronic physiological responses and adaptations to exercise in environments of hypoxia, heat stress, and simulated microgravity (bed rest), and eventually to my doctoral work on mechanisms underlying expansion of plasma and blood volume with acute and repeated exercise and heat exposure. My career has taken me to research positions at NASA, the Stanford University School of Medicine, the University of Arizona, and the U.S. Air Force Research Laboratory before assuming my present location at the U.S. Army Institute of Surgical Research. As a result of these multiple experiences across a period of 45 years, I have had opportunities to translate basic research to astronauts, high-performance aircraft pilots, and critically ill patients who are challenged by conditions of extreme physiology and medicine.

Infrared Thermographic Analysis of Craniofacial Muscles in Military Pilots Affected by Bruxism

Due to the physical stresses to which they are subjected, military pilots may experience bruxism, an "oral parafunction." Parafunction can cause masticatory muscle suffering and serious dental, periodontal, and temporomandibular joint damage. The aim of this pilot study was to analyze the temperature distribution in masticatory and upper trapezius muscles in a sample of bruxist air force pilots, to evaluate whether an occlusal splint would be able to induce skin temperature variations in the stomatognathic apparatus using the technology of infrared thermography. A total of 11 male Italian Air Force pilots of high performance aircraft, ages from 27 to 40 yr (mean 34.91 ± 2.15 yr) with 1000-3000 flight hours, were enrolled in the study and analyzed using an infrared camera in order to evaluate the temperature of the masticatory muscles. All the recordings were taken on each subject using the same protocol with and without a temporary occlusal splint. The occlusal splint statistically increased each muscle temperature (0.10-0.20°C) on both the sides of the body. No statistically significant differences were found between the left and right muscles (asymmetries) before or after the wearing of the splint except for the anterior temporalis muscle. No significant improvement or variations in temperature symmetry of this muscle was found after the application of the splint. The use of an occlusal splint could help in increasing muscles temperatures in Air Force pilots with consequent relaxation of their facial muscular system.

Back pain and its consequences among Polish Air Force pilots flying high performance aircraft

Back pain in Air Force fast jet pilots has been studied by several air forces and found to be relatively common. The objective of the study was to determine the prevalence and degree of the pain intensity in the cervical, thoracic and lumbar spine, subjective risk factors and their effect on the pilots' performance while flying high maneuver aircrafts and the consequences for cognitive deficiencies. The study was designed as a retrospective, anonymous questionnaire survey, collecting data on the age, aircraft type, flying hours, pain characteristics, physical activity, etc. The study was participated by 94 pilots aged 28-45 years (mean age: 35.9 ± 3.3 years), actively flying fast jet aircrafts Su-22, Mig-29 and F-16. The estimates regarding the level of the subjective back pain were established using visual analogue scales (VAS). The values of the Cochran and Cox T-test for heterogeneous variances are as follows: for the total number of flying hours: F = 2.53, p = 0.0145, for the pilot's age: F = 3.15, p = 0.003, and for the BMI factor F = 2.73, p = 0.008. Our questionnaire survey showed a significant problem regarding spinal conditions in high performance aircraft pilots. The determination of the risk factors may lead to solving this problem and help eliminate the effect of the unfavorable environment on piloting jet aircrafts. Experiencing back pain during the flight might influence the mission performance and flight safety. The costs of pilots education are enormous and inability to fly, or even disability, leads to considerable economic loss. More research on specific prevention strategies is warranted in order to improve the in-flight working environment of fighter pilots.

Cardiac responses to long duration and high magnitude +Gz exposure in pilots: An observational study

In military aviation, high performance aircraft pilots are exposed to +Gz acceleration at longer durations and higher magnitude than transport/helicopter pilots. The purpose of this study was to reveal the negative or positive cardiac responses to this occupational high +Gz exposure. Our study design was cross-sectional and observational. We have evaluated 21 echocardiographic parameters of 63 pilots who applied for aircrew periodic medical examination. Of 63 pilots, 33 were grouped as high performance aircraft pilots group (Group A) and 30 were grouped as control group (Group B) whose aircraft type was transport or helicopter. Means of demographic and echocardiography parameters between two groups were compared statistically with Student's t-test, Mann- Whitney U or Chi-square test as appropriate. Among all echocardiographic parameters, mean TV A (tricuspid valve peak velocity during late diastolic filling) was significantly higher and TV E (peak velocity during early diastolic filling)/ A ratio was significantly lower for Group A pilots (p<0.05). In Group A pilots, mean TV A and TV E/A ratio were (52.12 ± 13.85) and (1.36 ± 0.30) respectively. In Group B pilots, mean TV A and TV E/A ratio were (42.61 ± 6.42) and (1.53 ± 0.20) respectively (p=0.001 for TVA and p=0.005 for TV E/A). Mean pulmonary artery pressure (PAP) of Group A pilots (32.04 ± 9.09) was higher than Group B pilots (28.76 ± 7.9) but it was not statistically significant (p>0.05). We conclude that according to the results of our study, long term +Gz exposure has no effects on cardiac morphologic and systolic functions but has effects on right ventricular diastolic functions. We have considered that these effects may be a result of chronic +Gz adaptation or high PAP levels.

Role of Carotid Baroreflex and Sympathetic Responses in the Push-Pull Effect: A Simulation Study

The push-pull maneuver (PPM) can lead to loss of consciousness in pilots of high-performance aircraft. This paper presents a mathematical model for the simulation of carotid baroreflex function and sympathetic responses during PPM. The previous model was first modified by incorporating a submodel of the carotid baroreflex and then validated by comparing the simulation results with experimental data. Then the role of the carotid baroreflex was evaluated by varying the time delay and gain of the baroreflex independently during PPM and control runs, and the influence of different PPM profiles on sympathetic efferent activities were predicted. Model outputs suggest that the effects of carotid baroreflex regulation with different time delays and gain factors on the push-pull effect (PPE) are almost the same as those on the control run. Meanwhile, simulation of sympathetic responses indicates that the frequency of spikes in the efferent sympathetic nerves increases with higher magnitude and longer duration of -Gz exposure, as well as with higher magnitude of +Gz exposure. However, the effect of changed sympathetic responses may be alleviated when transferred to baroreflex effectors. The simulation results support that the carotid baroreflex and sympathetic responses might have little specific influences on the PPE. It also suggests that the limited range of G alteration and transition rate should be considered when using tilting experiments to investigate sympathetic response to PPE. The limitation of the present model due to the lack of sufficient data on the contribution of different peripheral vascular beds and their myogenic response is discussed.

On Tracking the Course of Cerebral Oxygen Saturation and Pilot Performance During Gravity-Induced Loss of Consciousness

The aim of this study was to track the course of cerebral tissue oxygen saturation (rSO2) and pilot performance during an episode of gravity-induced loss of consciousness (GLOC). GLOC, a major problem facing pilots of high-performance aircraft, is brought about by a sudden reduction in rSO2 as a result of increased +Gz force. It consists of 24 s of complete functional impairment followed by a prolonged period of performance recovery. This study tested the hypothesis that delayed recovery in GLOC is caused by a slow return of rSO2 following removal of the g-force that induced the episode. GLOC was induced in U.S. Air Force personnel via a centrifuge with math and tracking tasks emulating flight performance. A near-infrared spectroscopy unit provided the rSO2 measure. Declines in rSO2 from baseline pinpointed when pilots would cease active flight control and when GLOC would set in. Counter to expectation, rSO2 returned to baseline levels shortly after the centrifuge came to a complete stop following GLOC onset. Nevertheless, performance deficits continued for 49.45 s thereafter. The prolonged performance recovery time in GLOC cannot be attributed to delays in the return of rSO2. This finding explains why previous ergonomic efforts to shorten the duration of GLOC episodes by increasing the rate of return of rSO2 have not been fruitful. Evidently, another approach is needed. Such an approach might use the close linkage between loss of rSO2, performance deterioration, and GLOC onset to develop a warning system that would permit pilots to take effective action to avoid GLOC incapacitation.

Critical action procedures testing: a novel method for test-enhanced learning

Human error is a leading cause of adverse events in anaesthesia. Residents' knowledge of how to respond to rare, yet potentially life-threatening events has been shown to deteriorate over time and thus cost-effective educational interventions are indicated. Previous research has shown that test-enhanced learning has the potential to strengthen both clinical knowledge and performance. We hypothesised that critical action procedures (CAPs) tests, similar to those employed by high-performance aircraft pilots, would help improve resident knowledge about how to respond to rare and potentially catastrophic events encountered during the perioperative period. Knowledge assessments were administered to 29 first-year anaesthesiology residents over the course of 9 months. Five-minute closed-book tests were administered with fill-in-the-blank questions regarding the American Society of Anesthesiologists' difficult airway guideline, advanced cardiac life support protocols, an institutional airway fire protocol and drug dosing for malignant hyperthermia. Inter-group comparisons were evaluated using the Kruskal-Wallis test. The difference between the pre-test and final test scores for each subsection was determined with the Mann-Whitney U-test for independent samples. Composite subtest scores, when compared with baseline pre-test scores and subsequent scores, and when adjusted for attrition, significantly improved over the course of 9 months (20.5% versus 80%; P < or = 0.001). Likert-based survey data indicated a positive report for attainment of knowledge. In this longitudinal observational study of first-year anaesthesiology residents, CAPs testing helped improve knowledge about critical events. Although the study was limited by its small number of subjects, a significant attrition rate and the lack of a control group, it demonstrates a cost-effective educational intervention that improved resident knowledge. This intervention may enable residents to transfer learned skills from theoretical testing situations to real-life scenarios. We propose the use and further study of CAPs testing as a cost-effective modality to augment both simulated and actual experiential learning.

Mathematical Modeling of the Push-Pull Effect for Various Acceleration Profiles and Countermeasures

The push-pull maneuver (PPM) can lead to loss of consciousness in pilots of high-performance aircraft. Modeling of the physical and physiological aspects of this phenomenon should allow improved countermeasures. A structurally based mechanistic computer model was developed to incorporate dynamic carotid baroreflex responses and detailed modeling of vessel segments for different anatomic regions. The model was used to predict the effect of the PPM on cardiovascular responses and the protection afforded by extended coverage anti-G suits (ECGS) and neck pressure. The model was validated by comparing the simulation results with previously published experimental data obtained during centrifuge and tilt-table studies. Simulations of various PPM acceleration profiles indicated that +Gz tolerance was reduced in the presence of higher +Gz levels prior to the push phase, more -Gz levels during the push phase, and prolongation of the push phase. On the other hand, the onset rate for the two phases had only minor effects on +Gz tolerance. Model output suggested that improved protection could be provided by an ECGS with minimal inflation delay and a multilevel pressure schedule in which the leg bladders inflated to a higher pressure than the abdominal bladder. Modeling application of a 100-mmHg neck pressure during the push phase partly inactivated the carotid baroreflex, but induced only a small increase in tolerance. Mathematical modeling and simulation showed that +Gz tolerance for the PPM might be increased by improving the design and inflation schedule of the ECGS.

Cardiovascular consequences of high-performance aircraft maneuvers: implications for effective countermeasures and laboratory-based simulations

The gravitational stress encountered by pilots of high-performance aircraft can cause dramatic shifts in blood volume and circulatory pressure, thus placing the cardiovascular system under significant stress, sometimes resulting in loss of consciousness due to cerebral under-perfusion. Since pilots experience both increased and decreased gravitational stress in high-risk environments, it is important not only to examine the cardiovascular effects of altered gravitational exposure, but also to create effective countermeasures that will increase pilot safety. In this review, we discuss the cardiovascular consequences of rapid changes in gravitational forces. We also examine the effectiveness of the countermeasures that have been developed to combat gravity-induced loss of consciousness. Finally, we examine those current laboratory-based techniques that simulate hyper-gravity and the "push-pull effect"; making it possible to investigate the cardiovascular mechanisms responsible for maintaining cerebral perfusion and consciousness.

Alternobaric vertigo: prevalence in Portuguese Air Force pilots

Conclusion. Having found a prevalence rate of alternobaric vertigo in Portuguese Air Force pilots that is somewhat higher than previously reported, we underline the importance of implementing education on the management of this condition as part of routine Air Force pilot training programs. Objectives. Alternobaric vertigo is a condition in which transient vertigo with spatial disorientation occurs suddenly during flying or diving activities, caused by bilateral asymmetrical changes in middle ear pressure. Its prevalence is very likely underestimated and under-reported, with the 10–17% prevalence rate mentioned in early literature not being challenged by recent data. Subjects and methods. To assess its actual prevalence, the authors requested all high performance aircraft pilots presently on active duty in the Portuguese Air Force to anonymously answer a questionnaire on alternobaric vertigo symptoms, after a short briefing on the subject. Results. A 29% prevalence rate of in-flight episodes consistent with alternobaric vertigo was obtained.

Consciousness monitoring using near-infrared spectroscopy (NIRS) during high +Gz exposures

The relationship between human consciousness and oxygen saturation (rSO 2) in cerebral tissue under high +Gz stress was non-invasively monitored by near-infrared multiple wavelength spectroscopy (NIRS). We studied the drop in rSO 2 levels in human subjects during exposure to various head-to-foot acceleration (+Gz) profiles. These profiles included sustained +Gz plateaus and repeated short duration +Gz pulses of varying duration. The end point in this study was +Gz-induced loss of consciousness (G-LOC). The rSO 2 levels under normal (asymptomatic), almost loss of consciousness (A-LOC) and G-LOC conditions were recorded. Correlations among decrease in rSO 2, +Gz pulse duration, +Gz stress level and incapacitation time (ICAP) after G-LOC were also investigated. It was found that once rSO 2 fell to a certain level, G-LOC occurred. This threshold was repeatable and independent of the +Gz level or duration. It was also observed that the total ICAP after G-LOC was dependent on the length of time that rSO 2 remained below the G-LOC threshold level, i.e. the longer the rSO 2 level remained below the G-LOC induction level, the longer the subject remained unconscious. These results may prove to be useful in designing closed loop control systems for personal protective gear for pilots of high performance aircraft.

Human and Behavioral Factors Contributing to Spine-Based Neurological Cockpit Injuries in Pilots of High-Performance Aircraft: Recommendations for Management and Prevention

In high-performance aircraft, the need for total environmental awareness coupled with high-g loading (often with abrupt onset) creates a predilection for cervical spine injury while the pilot is performing routine movements within the cockpit. In this study, the prevalence and severity of cervical spine injury are assessed via a modified cross-sectional survey of pilots of multiple aircraft types (T-38 and F-14, F-16, and F/A-18 fighters). Ninety-five surveys were administered, with 58 full responses. Fifty percent of all pilots reported in-flight or immediate post-flight spine-based pain, and 90% of fighter pilots reported at least one event, most commonly (> 90%) occurring during high-g (> 5 g) turns of the aircraft with the head deviated from the anatomical neutral position. Pre-flight stretching was not associated with a statistically significant reduction in neck pain episodes in this evaluation, whereas a regular weight training program in the F/A-18 group approached a significant reduction (mean = 2.492; p < 0.064). Different cockpit ergonomics may vary the predisposition to cervical injury from airframe to airframe. Several strategies for prevention are possible from both an aircraft design and a preventive medicine standpoint. Countermeasure strategies against spine injury in pilots of high-performance aircraft require additional research, so that future aircraft will not be limited by the human in control.

Interaction of Semicircular Canal Stimulation with Carotid Baroreceptor Reflex Control of Heart Rate

The carotid-cardiac baroreflex contributes to the prediction of orthostatic tolerance; experimental attenuation of the reflex response leads to orthostatic hypotension in humans and animals. Anecdotal observations indicate that rotational head movements about the vertical axis of the body can also induce orthostatic bradycardia and hypotension through increased parasympathetic activity. We therefore measured the chronotropic response to carotid baroreceptor stimulation in 12 men during varying conditions of vestibulo-oculomotor stimulation to test the hypothesis that stimulation of the semicircular canals associated with head movements in the yaw plane inhibits cardioacceleration through a vagally mediated baroreflex. Carotid-cardiac baroreflex response was assessed by plotting R-R intervals (ms) at each of 8 neck pressure steps with their respective carotid distending pressures (mmHg). Calculated baroreflex gain (maximal slope of the stimulus-response relationship) was measured under 4 experimental conditions: 1) sinusoidal whole-body yaw rotation of the subject in the dark without visual fixation (combined vestibular-oculomotor stimulation); 2) yaw oscillation of the subject while tracking a small head-fixed light moving with the subject (vestibular stimulation without eye movements); 3) subject stationary while fixating on a small light oscillating in yaw at the same frequency, peak acceleration, and velocity as the chair (eye movements without vestibular stimulation); and 4) subject stationary in the dark (no eye or head motion). Head motion alone and with eye movement reduced baseline baroreflex responsiveness to the same stimulus by 30%. Inhibition of cardioacceleration during rotational head movements may have significant impact on functional performance in aerospace environments, particularly in high-performance aircraft pilots during high angular acceleration in aerial combat maneuvers or in astronauts upon return from spaceflight who already have attenuated baroreflex functions.

Concomitant EEG, lactate, and phosphorus changes by 1H and 31P NMR spectroscopy during repeated brief cerebral ischemia.

Pilots of high-performance aircraft are subject to transient loss of consciousness due to cerebral ischemia resulting from sudden high gravitational stress. To assess the effects of gravitational stress-induced blackout on cerebral metabolism and electrical function, we developed an animal model in which global cerebral ischemia is produced repeatedly at short intervals. Rats were prepared by ligation of subclavian and external carotid arteries and the right carotid artery was cannulated bidirectionally to measure circle of Willis and systemic pressures. Ischemia was induced by inflation of an occluder about the left carotid artery. Interleaved 31P and 1H NMR spectra were acquired on a 4.7-T Biospec system simultaneously with EEG recordings. We report results from 20 experiments of 30-min duration in which rats were subject to 30 1-min ischemia:reflow cycles of 10I:50R, 20I:40R, 30I:30R, and 40I:20R [numbers are seconds of ischemia (I) and reflow (R) during each 1-min cycle]. During ischemia the graded delivery of the ischemic insult permitted direct correlations between 2- to 5- and 7- to 20-Hz EEG activity and progressive changes in pH, lactate, ATP, phosphocreatine (PCr) and Pi. The best correlations were found between EEG activity and pH and PCr; correlation coefficients ranged from 0.93 to 0.95. A loss of EEG activity was observed without significant sustained energy loss in all but the most severe cycle.

Evaluation of lactate production and clearance kinetics by 1H NMR in a model of brief repetitive cerebral ischemia.

Pilots of high-performance aircraft are subject to repeated transient cerebral ischemia during high-gravitational stress maneuvers. Previously we have demonstrated that repeated episodes of transient cerebral ischemia and reflow are cumulative and lactate accumulations appear to be exponential. To evaluate the metabolic events determining the kinetics of lactate accumulation, and therefore the rates of substrate utilization, we have used in vivo 1H nuclear magnetic resonance with a 5-s time resolution to measure lactate production and clearance. The individual rates for each animal were then used to predict the accumulation of lactate in the same animal during 30 episodes of ischemia and reflow. Lactate accumulation was modeled as the balance between a zero-order production process during the ischemic period and a first-order clearance process. The predicted lactate accumulation showed excellent agreement with the observed time course, validating the predictive power of the simple model used. The highly reproducible nature of this model and its accuracy in predicting lactate accumulation should enable more accurate studies of the deleterious effects of lactate accumulation in cerebral ischemia by providing a highly reproducible means for generating a specific level of lactate accumulation.