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Biomedical subjects

U I Balldin

Publications and source records attributed to U I Balldin.

At least 19 recordsLinked to original sources
PubMed2000

Pressurized sleeves and gloves for protection against acceleration-induced arm pain.

BACKGROUND: Acceleration (or G) induced arm pain may develop in centrifuge runs and in flight with low arm position and assisted pressure breathing during G (PBG) in combination with an extended coverage anti-G suit. To decrease this arm pain, pressurized sleeves and gloves were developed. METHODS: Eight subjects who earlier exhibited G-induced arm pain were tested on the centrifuge. The G-exposures consisted of a gradual onset run up to a maximum of +9 G2, rapid onset runs to +3, +4, +5, +6, +7, +8, and +9 Gz and a simulated aerial combat maneuver (SACM) with peaks up to +9 Gz. On separate days, the subjects were tested without the sleeves and gloves, and with the sleeves and gloves pressurized to a maximum of 40, 60, or 80 mmHg at +9 Gz. The subjects reported their left and right arm pain on a subjective rating scale. RESULTS: G-induced arm pain, usually starting above +6 Gz, was often the reason for termination of the G-exposure without the pressurized sleeves and gloves. The pressurized sleeves and gloves significantly (p < 0.001) decreased arm pain, put no significant difference was found among the different pressures used. Heart rate was not different with and without the pressurized sleeves and gloves. CONCLUSIONS: The pressurized sleeves and gloves are an effective method to alleviate and sometimes eliminate G-induced arm pain.

Adult↗
PubMed1999

Premature ventricular contractions during +Gz with and without pressure breathing and extended coverage anti-G suit.

BACKGROUND: High +Gz is known to provoke cardiac dysrhythmias. Pressure breathing during G (PBG) and extended coverage anti-G suits (ECGS) are used to enhance +Gz-endurance and reduce fatigue during high +Gz flying. It is not known whether PBG in combination with ECGS increases the risk for premature ventricular contractions (PVC). HYPOTHESIS: PBG in combination with ECGS increases the risk of PVCs during high +Gz-loads. METHODS: Retrospective data were obtained from 14 subjects exposed to three different simulated aerial combat sorties each, in the centrifuge with a standard anti-G suit ensemble or with PBG in combination with ECGS. Each sortie consisted of a gradual onset G-exposure (GOR) and three simulated aerial combat maneuvers (SACM) containing four cycles of a +4.5 to +7 GzSACM; four cycles of +4 to +9 Gz tactical aerial combat maneuver (TACM) with several rapid transitions from +4 or +5 Gz to +8 or +9 Gz; and four cycles of +5 to +9 Gz SACM (5-9 SACM) with four cycles. ECG was recorded during the +Gz exposures to reveal any cardiac dysrhythmias. RESULTS AND CONCLUSIONS: No PVCs occurred during the GORs. During 4.5-7 SACMs, TACMs, and 5-9 SACMs there were 83, 50, and 24 PVCs with standard equipment, respectively, and 63, 54, and 39 PVCs with PBG and ECGS, respectively. There was no statistically significant difference between the equipment in any of the different types of +Gz exposures. No episodes of supraventricular tachycardia or relative bradycardia were found with either equipment.

Adult↗
PubMed1999

Assessment of two methods to reduce simulated +Gz-induced arm pain using a non-centrifuge model.

Complaints of +Gz-induced arm pain have been expressed by centrifuge subjects and, to a lesser degree, by high performance fighter pilots, usually when the control stick and throttle are positioned below heart level; the pain may be higher during pressure breathing for +Gz protection. Elevated transmural pressure and overdistension of the blood vessels in the arms have been suggested as causal factors. An earlier-developed non-centrifuge model was used to provoke arm pain similar to that induced by +Gz exposure. Eleven healthy subjects placed inside a hyperbaric chamber with an arm externalized through a sealed opening. They were exposed to chamber pressures at 75, 100 and 125 mmHg fitted with elastic bandage of the arm, or a localized pressure of 50 mmHg applied to the vessels of the upper arm or were provided no protection (control). Arm pain was estimated using a modified Borg scale. The sizes of the ulnar, radial and interosseous arteries, and corresponding veins, at the elbow level were measured using a sonographic imaging system. No statistically significant differences in pain were detected comparing control to proposed (counteracting) devices. There were no statistical differences in arm arterial or venous vessel size with the different devices at the different pressures. Thus, the devices tested did not show any protection against the provoked arm pain.

Adult↗
PubMed1998

Improved anti-G protection boosts sortie generation ability.

BACKGROUND: There is a need for evaluation of new G protection equipment. HYPOTHESIS: There is no difference between the two anti-G ensembles on affecting subjects' ability to tolerate multiple simulated aerial combat sorties. METHODS: There were 15 subjects wearing the standard CSU-13 B/P anti-G ensemble (STD) or COMBAT EDGE/ATAGS (CE/ATAGS) ensemble who were exposed to 3 centrifuge-based simulated air combat sorties during a 2-h period. Each sortie consisted of four different G-profiles: 1) a gradual onset profile; 2) simulated air combat maneuver consisting of +4.5 to +7 Gz plateaus (4.5-7 SACM); 3) simulated air combat maneuver derived from actual fighter maneuvers with peaks up to +9 Gz (TACM); 4) simulated air combat maneuver consisting of +5.0 to +9.0 Gz plateaus (5-9 SACM). Each sortie was separated by a 20-min rest period. We measured heart rate, peripheral light loss (PLL), subjective effort level, subjective fatigue level, and reported recovery time. RESULTS: There were no incidents of unintended G-induced loss of consciousness (G-LOC) with CE/ATAGS. There were four incidents of unintended G-LOC with STD. At the end of the third sortie, with CE/ATAGS, mean heart rate was lower during the 4.5-7 SACM (p < 0.001) and the TACM (p < 0.001); PLL was less during all three rapid onset profiles (p < 0.01); subjects reported less effort during the 4.5-7 SACM (p < 0.001), the TACM and the 5-9 SACM (p < 0.01); reported fatigue was significantly lower (p < 0.001); and reported recovery times were nearly halved (p < 0.01). CONCLUSION: CE/ATAGS provided significantly greater G-protection than the standard anti-G ensemble. There was no G-LOC with CE/ATAGS. This greater protection should be of significant operational value in enhancing sortie generation capability by increasing fighter aircrew G-tolerance and decreasing aircrew fatigue.

Adult↗
PubMed1998

Tactical vs. other simulated aerial combat maneuvers.

BACKGROUND: There is a need for a more operationally relevant +Gz profile for centrifuge-based research and evaluation. This article describes a simulated aerial combat maneuver (SACM) named the Tactical Aerial Combat Maneuver (TACM). HYPOTHESIS: A more representative centrifuge-based SACM can be devised for high-G acceleration research and evaluation. METHODS: TACM consists of 9G x 5 s, 5G x 1 s, 8G x 5 s, and 4G x 2 s. TACM was compared against the widely accepted 4.5-7G and 5-9G SACMs. There were 15 centrifuge subjects used in this study. RESULTS: TACM accounted for all four incidents of G-Induced Loss of Consciousness (G-LOC); and most incidents of blackouts (5 of 8) observed. CONCLUSION: TACM simulates the seesaw pattern of +Gz forces of aerial combat and retains the reproducibility needed for acceleration research and evaluation. TACM captures the high onset, high amplitude +Gz changes of aerial combat when G-LOC and blackouts are more likely to occur. TACM should be particularly useful for evaluation of G-protective equipment and maneuvers, as well as fighter aircrew medical evaluations.

Adult↗
PubMed1997

Influence of a reduced G-suit pressure schedule on G-duration tolerance using enhanced G-protection ensembles.

BACKGROUND: Reducing pressure to enhanced G-protection ensembles may diminish potential undesirable physiologic effects, as well as improve wear comfort and garment durability. HYPOTHESIS: G-duration tolerance will not be affected by reducing pressure to the Swedish tactical flight combat suit (TFCS). A second objective tested the similarity in G-duration tolerance between the TFCS and Combined Advanced Technology Enhanced Design G-Ensemble (COMBAT EDGE) combined with a prototype enhanced coverage G-suit. METHODS: There were 12 Swedish pilots (mean = 30 yr) who experienced gradual onset (+0.1 G.s-1) runs (GOR) to +9 Gz, rapid (+6 G.s-1) onset runs (ROR) and simulated aerial combat maneuvers (SACM) with +5 to +9 Gz cycles. The GOR and ROR profiles had a sustained times of 60 s after reaching +9 Gz. RESULTS: GOR duration tolerance was statistically decreased (p < 0.01) by the lower pressure (1.1 psig.G-1) when compared to standard pressure (1.5 psig.G-1). No statistical difference between TFCS and COMBAT EDGE was observed during the GOR trials. For all conditions, during the RORs, 90% of the subjects completed at least 30 s at +9 Gz. Many technical or medical difficulties during SACM trials limited statistical treatment of these data. However, no obvious among-condition differences were observed. Noteworthy among SACM trials were those of 3 subjects enduring more than 9 min before stopping; one completing 12.5 min (35 cycles). Neither heart rate, blood pressure, nor perceived exertion data revealed a condition-effect difference. CONCLUSION: Moderately reduced pressure to the extended coverage anti-G suit, combined with positive pressure breathing, may yield decreased G-tolerance results during laboratory evaluation; however, observed differences are sufficiently small they are likely operationally insignificant.

Adult↗
PubMed1996

Centrifuge man-rating of a conceptual internal abdominal bladder restraint in an extended coverage anti-G suit.

An extended coverage anti-G suit, has been demonstrated to improve +Gz tolerance substantially. In some pilots/subjects, however, the abdominal bladder of the anti-G suit may expand excessively upward and inward causing discomfort and pain. This man-rating was performed to evaluate the effects on +Gz protection of an internal abdominal bladder restraint in the Swedish Tactical Flight Combat Suit (TFCS) used in conjunction with pressure breathing during G (PBG). The tests were executed in the Armstrong Laboratory Centrifuge at Brooks AFB with four Swedish test fighter pilots. The centrifuge profiles included gradual onset runs (GOR, relaxed) and rapid onset runs (ROR, with straining), as well as simulated aerial combat maneuver (SACM) runs up to +9 Gz until subjects experienced light loss or fatigue or surpassed 228 s. All subjects withstood 60 s at +9 Gz during GOR and ROR runs with and without abdominal bladder restraint. No difference There was no difference in SACM duration times. In three of four subjects, abdominal pain or discomfort experienced without abdominal bladder restraint disappeared with the addition of a bladder restraint. Ratings of perceived exertion (after 5 peaks at +9 Gz in the SACM), subjective +Gz tolerance, overall comfort, fatigue, and heat stress demonstrated no relevant differences with and without abdominal bladder restraint. Therefore, to enhance comfort, it seems possible to modify the TFCS by adding an abdominal bladder internal restraint without compromising its operational +Gz protection.

Abdomen↗
PubMed1996

Cerebral artery blood flow velocity changes following rapid release of lower body negative pressure.

BACKGROUND: Circulatory changes occur during exposure to Lower Body Negative Pressure (LBNP). These changes may have some similarities to exposure to moderately and slowly increased G-loads in a relaxed subject without anti-G suit. HYPOTHESIS: Changes will also occur in cerebral blood circulation during a rapid release of LBNP. METHODS: Transcranial Doppler ultrasound (TCD) was used to measure middle cerebral artery blood flow velocity (CBFV) in 14 human subjects following rapid release of a ramped lower body negative pressure (LBNP) (0.33 mm Hg.s) to presyncope (mean peak negative pressure of -124 mm Hg). RESULTS: The mean CBFV decreased to an average of 60% (p < 0.05) of the baseline value at peak LBNP. Mean CBFV was still decreased to 65% and 84% of the baseline value (p < 0.05) at the third heart beat and 30 s, respectively, after pressure release. The systolic CBFV decreased similarly to 57% (p < 0.05) of baseline during peak LBNP, and was still 63% (p < 0.05) at the third heart beat after pressure release. Heart rate increased by a mean of 51% (p < 0.001) and systolic heart level blood pressure decreased by 28% (p < 0.001) during peak negative pressure. Both heart rate and blood pressure returned to baseline levels within 30 s after pressure release. CONCLUSIONS: Following a presyncopal LBNP, the CBFV is not fully restored up to 30 s after the release of the negative pressure. This delayed returning of cerebral circulation following orthostatic stress may have some similarities to what occurs after the release of a gradual onset G-load in a relaxed subject without anti-G suit.

Adult↗
PubMed1994

Reduced pressure in extended coverage anti-G-trousers with assisted pressure breathing.

Six Swedish Air Force pilots and two Armstrong Laboratory subjects volunteered for this study to determine whether reduced pressure in extended coverage anti-G trousers (ECT), in combination with positive pressure breathing for G protection, affected +Gz tolerance. Group mean gradual onset run (GOR) time for the low pressure schedule (0.8 psig.G-1) was significantly different from the other two conditions (1.1, 1.5 psig.G-1)--84.1, 95.6, and 94.1 s, respectively. Group mean simulated aerial combat maneuver (SACM) times statistically differed between the low and middle pressure rates compared to the highest pressure schedule--147.6, 164.8 and 232.3 s, respectively. SACM heart rate (HR) responses for the +9 Gz plateaus were not statistically different among conditions. However, +5 Gz HR's were lower for the highest pressure condition. Similarities were identified between the middle and high pressurization conditions for GOR. However, reducing pressure in the ECT during SACM exposures was not supported by these data.

Gravity Suits↗
PubMed1994

Perceived exertion during submaximal G exposures before and after physical training.

Ratings of perceived exertion (RPE) were registered at submaximal levels in G endurance tests of a combined strength and endurance training program in 17 pilots. After 12 months of physical training, the endurance G tolerance (time to exhaustion during simulated aerial combat maneuver), increased by a mean of 40% (p < 0.001), while the mean RPE at 5 min submaximal G exposure decreased by 1.2 units (p < 0.02). Following 12 months of physical training, a significant relationship was observed between the improvement of the endurance G tolerance and the decrease of the RPE at 5 min (p = 0.05). Mean SaO2 at 5 min increased from 84 to 90% (p < 0.01) after training, while heart rate responses to G stress did not change. It is concluded that mean RPE and, to some extent, mean SaO2 during submaximal G exposures may be used as indicators of shifts in endurance G tolerance. The procedure may reduce the need for exhaustive G tolerance tests with associated risks and discomfort.

Aerospace Medicine↗
PubMed1993

Prevention of decompression sickness in current and future fighter aircraft.

United States Air Force oxygen regulators set to "NORMAL OXYGEN" deliver up to 60% nitrogen to the pilot at cockpit altitudes of 15,000 to 20,000 ft (4573-6096 m). Research chamber exposure to these altitudes while breathing 50% nitrogen has resulted in high grades of venous gas emboli. Expansion of existing gas emboli following an unplanned decompression to ambient aircraft altitude (e.g., loss of canopy) could result in rapid development of decompression sickness (DCS) symptoms. To reduce this potential problem, regulators in current fighters should be set to "100% OXYGEN" until descent from cruise to increase denitrogenation. The United States' Advanced Tactical Fighter and the European Fighter Aircraft may be designed to cruise above 50,000 ft (15,240 m), where cockpit altitudes exceed 20,000 ft with a 5-psi differential (psid) cockpit pressurization schedule. Increasing cockpit differential pressure to 7 psid while breathing 100% oxygen would greatly reduce the chance of significant emboli formation and the potential for DCS, but would slightly elevate the risks associated with pulmonary overpressure during rapid decompression.

Air Pressure↗
PubMed1992

G-endurance during heat stress and balanced pressure breathing.

The effect of heat stress and balanced pressure breathing during G (PBG) on G-endurance was investigated. Ten fighter pilots wearing anti-G-suits with increased bladder coverage were warmed to 38.2 degrees C and exposed to 15-s periods at 4.5 and 7 G in a heated human centrifuge gondola until exhaustion during PBG and normal breathing (NB). During both NB and PBG, the rectal temperature rose to a mean of 38.3 degrees C, and the dehydration was about 1.2 kg. With NB the endurance was a mean of 254 s, while it was 300 s with PBG (n.s.). Oxygen saturation and ratings of perceived exertion were mainly unchanged, while the maximum heart rate decreased by a mean of 13 bpm during PBG. In conclusion, the G-endurance was not deteriorated with PBG, in comparison with NB, during heat stress. In conjunction with experiences from other studies, however, it emphasizes the importance of avoiding heat stress and dehydration during G-loads, even with PBG.

Adult↗
PubMed1988

Assisted positive pressure breathing for augmentation of acceleration tolerance time.

The addition of assisted (chest counterpressure), positive pressure breathing (APPB) at 50 mm Hg (PPB50) and 70 mm Hg (PPB70) was compared to the current operational support of the G-suit and the anti-G straining maneuver (AGSM) without PPB (PPB0), during acceleration exposures of sustained 9 +Gz for 45 s and a 5-9 +Gz simulated aerial combat maneuver (SACM) to exhaustion. We selected 7 highly motivated male centrifuge subjects from a group of 31 volunteers. Positive pressure breathing was applied to the oronasal cavity with a Royal Air Force P/Q mask. Mask pressure was monitored continuously. Counterpressure was applied to the chest with a Canadian counterpressure garment at the same pressure as the mask. Lower body pressure was provided by a standard USAF G-suit inflated with the standard pressure schedule of 1.5 psi/G after 2.0 G. Positive pressure breathing was provided linearly in proportion to the +Gz level beginning at about 1.2 +Gz and reaching a peak of either 50 or 70 mm Hg (6.7 and 9.3 kPa, respectively) at 9 +Gz. Prepressurization (ready pressure) was used for both PPB (2.1 mm Hg) and G-suit (10.3 mm Hg) inflation. All subjects were monitored for heart rate and rhythm, SaO2 with an ear oximeter, inspired air flow, and rectus femoris electromyogram (EMG). Assisted positive pressure breathing provided a significant (p less than 0.01) increase in mean tolerance time at PPB50 (108%) and PPB70 (88%) compared to PPB0 during the 5-9 SACM.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗
PubMed1987

Induction and prevention of acceleration atelectasis.

Acceleration atelectasis is the absorptional collapse of alveoli in the dependent lung due to increased accelerative forces. It is exacerbated by breathing 100% oxygen and, during +Gz exposure, by the use of an anti-G suit. Experiments were conducted on 12 subjects using simulated aerial combat maneuvers (SACM) with G profiles having peak exposures of either 4.5 G or 9 G. Decreases in vital capacity (VC) measurements were used as quantification of atelectasis, two types of reduction being identified and described. Labile reductions in VC were readily restored by a deep breath or cough. Such reduction approximated 28% following the 4.5-G SACM and 25% following the 9-G SACM. More persistent (so called) stable reductions were of lesser degree, values of -20% being seen following both 9 G and 4.5 G maneuvers. Acceleration atelectasis causes symptoms of chest pain, coughing, and shortness of breath. Subjective ratings of the severity of these symptoms were obtained from the subjects, and these were much greater following the 4.5-G SACM exposures than after the 9-G runs. Acceleration atelectasis was reduced by dilution of the inspired oxygen concentration by argon and nitrogen (evaluated at 95, 82.5, 70, 50, and 20% oxygen); the addition of unassisted positive pressure at 30 mm Hg (4 kPa) to the breathing mask; or the performance of the anti-G straining maneuver (AGSM).

Acceleration↗
PubMed1987

Pulmonary mechanics and atelectasis during immersion in oxygen-breathing subjects.

It has been suggested that vital capacity (VC) reduction seen during head-out immersion and oxygen breathing is due to atelectasis formation. In this study VC was reduced in 8 healthy subjects by 8.7% as an effect of immersion per se and by a further 14.3% as an effect of oxygen breathing during 30 min of immersion. Every 2nd min during the exposure, functional residual capacity (FRC), dynamic compliance (C-dyn), and static esophageal pressure at end-expiration (Pes-frc) were measured by body plethysmographic technique. Results were compared with an air-breathing, immersed control situation to evaluate any possible atelectasis formation. The only significant changes during immersion were observed after 30 min of air breathing, where FRC decreased linearly by 8.5% and C-dyn by 13.2%. The main conclusion is that atelectases acting solely as volume restrictors cannot explain the whole VC reduction without other additive or synergistic mechanisms. We suggest that the linear decrements in FRC and C-dyn as an effect of immersion time might be explained by either inspiratory muscle fatigue or increasing thoracic fluid compartment during the first 30 min of head-out immersion.

Adult↗
PubMed1986

Influence of inspired oxygen concentration on acceleration atelectasis.

The USAF is developing an On Board Oxygen Generation System (OBOGS) for use in fighter aircraft. This study was conducted to determine the inert gas dilution requirements of the OBOGS necessary to prevent acceleration atelectasis. Human subjects were exposed to either 21, 50, 70, 82.5, 95 or 100% inspired oxygen, along with an increased +Gz Simulated Aerial Combat Maneuver (SACM) profile using the USAF School of Aerospace Medicine human centrifuge. The SACM profile utilized four +4.5z peaks (136 s at this +Gz) superimposed on a +3 Gz baseline, representing a total ride time of 276 s. A significant reduction in vital capacity (VC) occurred at inspired oxygen concentrations of 70% and greater. The addition of 5% argon (a natural product of OBOGS) to pure oxygen did not reduce the magnitude of acceleration atelectasis observed, nor the severity of breathing symptoms. A 30-s exposure to positive pressure breathing at 30 mm Hg during the end of the SACM reduced the level of VC reduction caused by subjects breathing 100% oxygen during +Gz.

Acceleration↗