A Novel, Inexpensive Method to Monitor, Record, and Analyze Breathing Behavior During Normobaric Hypoxia Generated by the Reduced Oxygen Breathing Device.

OBJECTIVES: Since hypoxia remains one of the most important physiological hazards the aviation environment poses, military aviators are trained to recognize symptoms of hypoxia in order to implement appropriate safety procedures and countermeasures when hypoxia occurs. A widely used commercial instrument for hypoxia training, demonstration, and research is the Reduced Oxygen Breathing Device (ROBD). Here we describe a novel, inexpensive method to use the ROBD's breathing loop pressure (BLP) to measure respiration rate, a critically important response parameter for hypoxia. METHODS: The ROBD can be controlled by a computer to export several variables including BLP, via the ROBD's RS232 port. An archived database was reanalyzed to assess the BLP data. New instrumentation added independent measures of respiration and expired oxygen and carbon dioxide; these measures were integrated with the ROBD output. RESULTS: Analysis of the archived data showed that the BLP reflected realistic breathing patterns. The new instrumentation integrated well with the ROBD, and independently supported the potential of the BLP as a valid measure of respiration. DISCUSSION: The ROBD's BLP data may provide a basis for a reliable, sensitive measure of respiration that is available at no additional cost.

Uncovering latent deficits due to mild traumatic brain injury by using normobaric hypoxia stress.

Memory deficits and other cognitive symptoms frequently associated with mTBI are commonly thought to resolve within 7-10 days. This generalization is based principally on observations made in individuals who are in the unstressed environmental conditions typical of a clinic and so does not consider the impact of physiologic, environmental, or psychological stress. Normobaric hypoxic stress can be generated with normal mean sea level (MSL) air, which is about 21% oxygen (O2) and 78% nitrogen (N), by reducing the percentage of O2 and increasing the percentage of N so that the resultant mixed-gas has a partial pressure of O2 approximating that of specified altitudes. This technique was used to generate normobaric hypoxic equivalents of 8,000, 12,000, and 14,000 feet above MSL in a group of 36 volunteers with a mTBI history and an equal number of controls matched on the basis of age, gender, tobacco smoking consumption, weight, height, and body mass index. Short-term visual memory was tested using the Matching to Sample (M2S) subtest of the BrainCheckers analog of the Automated Neuropsychological Assessment Metrics. Although there were no significant differences in M2S performance between the two groups of subjects at MSL, with increased altitude, the mTBI group performance was significantly worse than that of the control group. When the subjects were returned to MSL, the difference disappeared. This finding suggests that the "hypoxic challenge" paradigm developed here has potential clinical utility for assessing the effects of mTBI in individuals who appear asymptomatic under normal conditions.

An independent, objective calibration check for the reduced oxygen breathing device.

INTRODUCTION: Normobaric hypoxia, which does not entail an altitude chamber, but reduces the fraction of inspired oxygen (02) by diluting air with nitrogen, is finding increased use. The reduced oxygen breathing device (ROBD-2) is one of several commercial devices for generating such normobaric hypoxia. Reported here are results of a procedure to check the calibration of the ROBD-2 using methods that may be readily available in physiology and psychophysiology facilities. METHODS: The %O2 output by the ROBD-2 was measured concurrently in two ways for altitudes from mean sea level (MSL) to 34,000 ft above MSL at 2000-ft intervals five times over 2 d. One measurement method used was the one built into the ROBD-2, which reports the %O2 the device is delivering at the selected target altitude. The other method diverted a sample of the ROBD-2's output gas to the paramagnetic O2, sensor of a metabolic measuring system via its sampling line. The %O2, measured with the two techniques was compared using Bland-Altman statistical procedures. RESULTS: The two measurement methods produced %O2 readings differing by no more than 0.18% O2 from MSL to 34,000 ft (from 20.95 to about 4.40% oxygen, respectively), the full operating range of the device. Calculating altitude from the measured %O2 showed the ROBD-2 operated within its design error margins over its whole operational range. DISCUSSION: The purpose for which the ROBD-2 is used should determine whether the reliability of its output in normobaric equivalent altitude is adequate. Differences between devices and device stability over time and with use have yet to be assessed. Our assessment does not address the accuracy of the algorithm the ROBD-2 uses to provide an equivalent target altitude under normobaric conditions.

Hypoxia and flight performance of military instructor pilots in a flight simulator.

INTRODUCTION: Military aircrew and other operational personnel frequently perform their duties at altitudes posing a significant hypoxia risk, often with limited access to supplemental oxygen. Despite the significant risk hypoxia poses, there are few studies relating it to primary flight performance, which is the purpose of the present study. METHODS: Objective, quantitative measures of aircraft control were collected from 14 experienced, active duty instructor pilot volunteers as they breathed an air/nitrogen mix that provided an oxygen partial pressure equivalent to the atmosphere at 18,000 ft (5486.4 m) above mean sea level. The flight task required holding a constant airspeed, altitude, and heading at an airspeed significantly slower than the aircraft's minimum drag speed. The simulated aircraft's inherent instability at the target speed challenged the pilot to maintain constant control of the aircraft in order to minimize deviations from the assigned flight parameters. RESULTS: Each pilot's flight performance was evaluated by measuring all deviations from assigned target values. Hypoxia degraded the pilot's precision of altitude and airspeed control by 53%, a statistically significant decrease in flight performance. The effect on heading control effects was not statistically significant. There was no evidence of performance differences when breathing room air pre- and post-hypoxia. DISCUSSION: Moderate levels of hypoxia degraded the ability of military instructor pilots to perform a precision slow flight task. This is one of a small number of studies to quantify an effect of hypoxia on primary flight performance.

Head position of helicopter pilots during slalom maneuvers.

INTRODUCTION: Pilots typically tilt their heads when executing coordinated banking turns, a phenomenon commonly attributed to the putative opto-kinetic cervical reflex (OKCR). The OKCR is usually described as a reflex, primarily driven by stimuli in the visual periphery, and is important to a pilot's spatial orientation by providing a relatively stabilized horizontal frame of reference. The present paper presents an alternative hypothesis for the observed head tilting seen in pilots. METHODS: An archived data set, originally collected for other purposes, contained the head turn, pitch, and tilt of 4 helicopter pilots recorded at 10 Hz as the pilots executed 42 slalom maneuvers in an AH Mk 7 Lynx helicopter under visual flight conditions. The analytic method was a correlational analysis of head turn, pitch, and tilt. RESULTS: As expected, pilots routinely tilted their heads during the slaloms in a fashion typically attributed to the OKCR. Correlations among head turn, tilt, and pitch showed that when the helicopter turned left, the head, presumably to look into the turn, turned left and also pitched up and tilted right. Similarly, when the helicopter turned right, the head, presumably to look into the turn, turned right, pitched up, and tilted left. CONCLUSIONS: The head tilting usually attributed to a neuromuscular reflex driven by visual stimuli may be a biomechanical consequence of the head posture pilots assume when they simply look where they are going, eliminating the need to postulate the existence of a novel neuromuscular reflex.