Ulf I. Balldin

Air Break During Preoxygenation and Risk of Altitude Decompression Sickness

INTRODUCTION To reduce the risk of decompression sickness (DCS), current USAF U-2 operations require a 1-h preoxygenation (PreOx). An interruption of oxygen breathing with air breathing currently requires significant extension of the PreOx time. The purpose of this study was to evaluate the relationship between air breaks during PreOx and subsequent DCS and venous gas emboli (VGE) incidence, and to determine safe air break limits for operational activities. METHODS Volunteers performed 30 min of PreOx, followed by either a 10-min, 20-min, or 60-min air break, then completed another 30 min of PreOx, and began a 4-h altitude chamber exposure to 9144 m (30,000 ft). Subjects were monitored for VGE using echocardiography. Altitude exposure was terminated if DCS symptoms developed. Control data (uninterrupted 60-min PreOx) to compare against air break data were taken from the AFRL DCS database. RESULTS At 1 h of altitude exposure, DCS rates were significantly higher in all three break in prebreathe (BiP) profiles compared to control (40%, 45%, and 47% vs. 24%). At 2 h, the 20-min and 60-min BiP DCS rates remained higher than control (70% and 69% vs. 52%), but no differences were found at 4 h. No differences in VGE rates were found between the BiP profiles and control. DISCUSSION Increased DCS risk in the BiP profiles is likely due to tissue renitrogenation during air breaks not totally compensated for by the remaining PreOx following the air breaks. Air breaks of 10 min or more occurring in the middle of 1 h of PreOx may significantly increase DCS risk during the first 2 h of exposure to 9144 m when compared to uninterrupted PreOx exposures.

Acceleration tolerance after ingestion of a commercial energy drink.

BACKGROUND Caffeine ingestion has been demonstrated to increase physical performance in some situations. This study examined the ability of a commercial energy drink containing caffeine to enhance acceleration tolerance and strength under G load. METHODS Eight experienced centrifuge subjects completed three separate experimental acceleration exposures following ingestion of 11.5 ml x kg(-1) bodyweight of (1) a commercial energy drink, providing 5.0 mg caffeine/kg bodyweight; (2) a commercial energy drink without caffeine; or 3) a placebo. The acceleration exposures consisted of a relaxed gradual onset run to peripheral light loss, a rapid onset run to 6 G for 15 s, and a simulated air combat maneuver (SACM) run of repeated alternations between 4.5 G for 15 s and 7 G for 15 s until volitional exhaustion. RESULTS Relaxed G tolerance was 13% higher under the caffeinated energy drink session, whereas SACM duration did not differ among the drink conditions. Hip adductor muscle strength was 37% lower during the placebo session than during the other two sessions. CONCLUSION Consumption of a caffeine-based energy drink may enhance relaxed G tolerance and may increase strength, but does not impact acceleration tolerance duration.

An electrical muscle stimulation suit for increasing blood pressure.

BACKGROUND Electrical muscle stimulation (EMS) is used to strengthen muscles in rehabilitation of patients and for training of athletes. Voluntary muscle straining and an inflated anti-G suit increase the arterial blood pressure (BP) and give a pilot G protection during increased +Gz. This studys aim was to measure whether BP also increases with EMS of lower body muscles. METHODS A suit with new cloth electrodes sewn into the garment was developed. There were 12 subjects who were tested in sitting position during 3 conditions with 10 consecutive periods of EMS, inflated anti-G suit (GS), or lower body muscle anti-G straining maneuvers (AGSM). BP was continuously measured noninvasively. RESULTS The means of the baseline systolic BP, before each of the test conditions, were 127 +/- 16, 128 +/- 1, and 145 +/- 14 mmHg for GS, AGSM, and EMS, respectively. During inflation of the GS, execution of the AGSM, and EMS, mean systolic BP during the first 10 s was 143 +/- 15, 146 +/- 13, and 150 +/- 13 mmHg, respectively, with no statistical difference between the conditions. The corresponding mean resting heart rate before each test was 57-63 bpm for all conditions. During the test periods with GS, AGSM, and EMS, heart rate was 59 +/- 11, 79 +/- 16, and 61 +/- 15 bpm, respectively, with statistical differences (P < 0.001) between AGSM and the other two conditions. CONCLUSION EMS created similar BP as GS and AGSM at 1 G and also had higher pre- and post-control values. Further studies are required to evaluate if this principle may be used for G protection of pilots.

Cognition Effects of Low-Grade Hypoxia

INTRODUCTION The effects of low-grade hypoxia on cognitive function are reported in this paper. The study compared cognitive function during short exposures at four different altitudes. METHODS Ninety-one subjects were exposed to simulated altitudes of ground level, 1524, 2438, and 3658 m (5000, 8000, and 12,000 ft) in the Brooks City-Base altitude pressure chamber in a balanced design. Oxygen saturation, heart rate, and cognitive performance on seven different cognitive tasks were measured. In addition, subjects indicated their symptoms from a 33-item subjective symptom survey. RESULTS As designed, oxygen saturation decreased and heart rate increased with higher altitudes. Very small degradations in performance were found at the two highest altitudes for only two of the cognitive tasks (continuous performance and grammatical reasoning). In the subjective symptom survey, 18 of the 33 possible symptoms were more common at 3658 m (12,000 ft) than at ground level. CONCLUSIONS The findings indicated a minimal influence of low-grade hypoxia on cognitive performance in contrast to some existing classic symptoms of hypoxia. Pilmanis AA, Balldin UI, Fischer JR. Cognition effects of low-grade hypoxia. Aerosp Med Hum Perform. 2016; 87(7):596-603.

G Protection When Adding Pressurized Sleeves and Gloves to a Representative G-Suit Ensemble.

BACKGROUND In a previous study, pressurized sleeves and gloves were found to substantially diminish or eliminate G-induced arm pain. Since this equipment presumably acts similarly to a G suit for the arms and hands, it was hypothesized that higher inflation pressures might provide an additional increment of G protection. METHODS In a human-rated centrifuge, 15 well trained subjects using Combat Edge and ATAGS G-protective equipment were exposed to gradual and rapid onset relaxed G exposures as well as rapid onset straining and simulated aerial combat maneuver G exposures up to + 9 Gz with and without pressurized sleeves and gloves. RESULTS The pressurized sleeves and gloves did not show any improvement in G tolerance or endurance compared to the control. However, significantly lower heart rates (6-12%) and subjective effort (11%), along with slightly less peripheral vision loss, suggest a decreased work load when wearing the pressurized sleeves and gloves. A trend to shorter time on target in a tracking task was found with the pressurized sleeves and gloves, likely due to decreased mobility of the hands, thus affecting control stick input. CONCLUSIONS G tolerance and endurance were not improved by the pressurized sleeves and gloves. However, a lower heart rate and a decreased subjective effort level and peripheral vision loss indicated that the subjects did not have to work as hard with this equipment.

Acceleration endurance with pressure breathing during G with and without a counterpressure vest.

INTRODUCTION The purpose of this study was to test whether pressure breathing during G (PBC) without a counterpressure vest negatively influences G endurance or increases breathing fatigue during extended duration high-G exposures. METHODS While using PBG, 10 subjects underwent 2 trials of +3 Gz exposures: once when wearing a counterpressure vest and once without. The exposures consisted of a relaxed, gradual G onset run until peripheral or central light loss, a straining rapid onset GC run to +6 Gz for 15 s, and a simulated aerial combat maneuver (SACM) G profile consisting of 10-s periods varying between +5 Gz and +9 Gz, during which subjects executed a hand-eye tracking task. The SACM endpoint was light loss or exhaustion. Subjects provided ratings of subjective effort and discomfort after the SACM. RESULTS Significant differences were found between the vest and no-vest conditions for only 3 of 19 measures: heart rate under G and two measures of tracking ability. The vast majority of data indicated no difference between the vest and no-vest conditions for performance under G. DISCUSSION This experiment supports previous studies and expands those previous results by increasing the duration of PBG exposure shown to not be influenced by wearing of the vest. We conclude that there is likely no practical advantage to wearing a counterpressure vest during PBG.

Inferior g protection with an electrical muscle stimulation suit compared to a standard g-suit.

BACKGROUND At +1 Gz, electrical muscle stimulation (EMS) has been shown to increase systemic blood pressure similarly to a standard G-suit or lower body muscle straining. It was hypothesized that EMS might improve G protection at increased G levels. METHODS An EMS suit was developed with electrodes over the calves, thighs, gluteal, and abdominal muscles. Using nine subjects, the EMS suit was compared to a standard five-bladder G-suit during various G profiles up to +9 Gz in a human-rated centrifuge with EMS activated by electrical muscle stimulators at G levels at or above +4 Gz. The optimal EMS stimulation for a solid muscle contraction was determined for each muscle group in each subject prior to the G exposures. RESULTS The mean maximal G level attained in the standard suit was 1.1 G higher during a relaxed gradual onset profile, 1.5 G higher during a relaxed rapid onset profile, and 2.0 G higher during a straining rapid onset profile when compared to the EMS suit. During a simulated aerial combat maneuver (SACM) ride, duration was 46 s longer with the standard suit compared to the EMS. During the SACM, the average heart rate was 23 bpm lower with the standard suit compared to EMS. All of the above differences were statistically significant. Finally, there were four G-LOCs with the EMS and none with the standard suit. CONCLUSION The tested EMS suit did not give sufficient G protection at high Gs for pilots, nor substitute for a standard G-suit, as indicated by lower G protection and the episodes of G-LOC.