Biomedical subjects

X C Geng

Publications and source records attributed to X C Geng.

9 recordsLinked to original sources

PubMed2001

Decreased +gz tolerance following lower body positive pressure: simulated push-pull effect.

OBJECTIVE: The purpose of this study was to attempt to simulate the push-pull maneuver on a single-axis human centrifuge using lower body positive pressure (LBPP), and to observe the effect of the push-pull maneuver on +Gz tolerance. METHODS: Six volunteers participated in the experiment. They were subjected to LBPP of up to 300 mm Hg for 1 min. Blood pressure (BP) and heart rate (HR) were monitored before, during and after LBPP. Immediately after LBPP, +Gz tolerance was measured on a human centrifuge. RESULTS: During LBPP, systolic BP (SBP) and diastolic BP (DBP) increased significantly, mean arterial pressure (MAP) increased but not significantly, and HR decreased significantly. After LBPP, SBP and MAP decreased significantly, while DBP and HR decreased but not significantly. In all subjects, +Gz tolerance decreased after LBPP. The decreased value was 0.70 +/- 0.06 G, maximum 1.0 G and minimum 0.5 G. CONCLUSION: The push-pull maneuver can be simulated on a single-axis human centrifuge using LBPP. The physiologic effects of LBPP were similar to those of -Gz. We observed that +Gz tolerance decreased after LBPP, which confirmed the push-pull effect from the experiment.

Acceleration↗

PubMed2001

[The progress on +Gz stress-induced injuries of the cardiac structure and function and their mechanisms].

The heart is the dynamic pump of the circulation. To some extent, high +Gz acceleration exposure can result in injuries on cardiac ultrastructure, metabolism and function. Specifically, repeated +Gz exposures can produce harmful effects on aviators, as reported by French and American researchers. However, the mechanisms of injuries on heart under high +Gz stress have not been studied systematically till now; nor have some protective measures been adopted. In this article, acute and chronic +Gz stress induced injuries on cardiac structure and function in animals and detrimental effects on the hearts of pilots are reviewed. Moreover, the related mechanisms are also explained basing on stress injury, oxidative stress and genetic regulation.

Acceleration↗

PubMed2000

Cerebral blood flow velocity by transcranial Doppler during a vertical-rotating table simulation of the push-pull effect.

BACKGROUND: The push-pull effect (PPE) has been suspected of causing many aircraft accidents. The perfusion and then withdrawal of cerebral blood during the PPE may change the state of the cerebral blood vessel. HYPOTHESIS: During head-down tilt (HDT) cerebral vasoconstriction occurs in response to the elevated perfusion pressure to maintain cerebral blood flow, and during subsequent head-up tilt (HUT) the increased resistance of the cerebral blood vessel recovers slowly. METHODS: Ten healthy male non-pilots were exposed to the following protocol using a rotating-table to simulate the push-pull maneuver: HUT (+1 Gz) for 1 min followed by transition to HDT (-1 Gz) 10 s followed by transition to HUT (+1 Gz) 1 min. Cerebral blood flow velocity and pulsatility indices in the left middle cerebral artery were continually measured with a transcranial Doppler (TCD) instrument. RESULTS: Mean blood flow velocity (Vm) increased significantly by 10%, during the first 5 s of HDT, recovered to baseline during HDT 5 10 s, and remained unchanged during subsequent HUT. Systolic blood flow velocity (Vs) increased by 9% during HDT 5-10 s and 11% during HUT 0-5 s. Diastolic blood flow velocity (Vd) decreased by -9% during HDT 5-10 s, and -22% during HUT 0-5 s. Vs-Vd increased by 26% during HDT 5 10 s, and 41%, during HUT 0-5 s. Pulsatile indices (PI) and resistance index (RI) increased by 26%) and 15% during HDT 5-10 s, and by 40% and 27% during HUT 0-5 s, respectively. Vs, Vs-Vd, PI, and RI remained at the higher level, and Vd remained at the lower level to HDT 15-20 s. CONCLUSIONS: The results indicate that cerebral vasoconstriction occurred to prevent brain over-perfusion during HDT. During HUT, the elevated resistance of the cerebral vessel remained at the higher level for about 20 s, and may have worsened the cerebral perfusion from exposure to +Gz. This may be one of the mechanisms of PPE.

Adaptation, Physiological↗

PubMed2000

The protection against +Gz afforded by pressure breathing with different pressure schedules.

OBJECTIVE: System of pressure breathing for +Gz (PBG) has been incorporated into service in the high performance fighter aircraft, but there were significant differences among PBG pressure schedules used in different countries. The purpose of this study was to define an optimal pressure schedule in PBG system. METHOD: Five male subjects wearing GZ-2 anti-G suit and medium-sized bladder vest, plus PBG with 1.6, 2.4, and 3.2 kPa/G pressure schedules, respectively, were exposed to rapid onset (3.0 G/s) centrifuge +Gz runs. +Gz protection of PBG with each of the three pressure schedules were measured and the subjective ratings were collected. RESULT: The +Gz protection afforded by PBG with 1.60, 2.40, and 3.20 kPa/G pressure schedules were 2.00 +/- 0.31, 2.54 +/- 0.32, and 2.44 +/- 0.31 G, respectively. Subjective ratings showed that the PBG with 2.40 kPa/G pressure schedule was better than the other two. CONCLUSION: Our data suggest that a PBG pressure schedule of 2.4 kPa/G in PBG system is optimal. It not only assures the anti-G performance of PBG, but also reduces its side effects.

Acceleration↗

PubMed2000

[Data analysis of 492 times centrifuge examination].

Objective. To sum up the experiences and to find the regularity of centrifuge examinations. Method. The data of nine years of centrifuge examination (from 1988 to 1996) of pilots who suffered from black out or LOC frequently were analyzed. Result. There were totally 492 times centrifuge examinations. First centrifuge examination included 229 pilots, 49 qualified, 180 unqualified. Second centrifuge examination included 263 pilots, 50 qualified, 213 unqualified. The pilots were all male. The average age of first centrifuge examination was 29.27 +/- 4.87 years. Average flying time was 1015.24 +/- 131.89 h. 68.7% of their plane was JJ-6 or above. Conclusion. Most pilots undergoing centrifuge examination these nine years were 26-35 year old, and had flown for 601-1200 h. The planes they flew are mostly high-performance fighter aircraft. Close attention must be paid to pilots under similar condition by the flight surgeon. It is recommended that the special equipment of G-tolerance training should be added to the fighter aircraft units.

Acceleration↗

PubMed2000

[Effects of rotating-table simulated "push-pull maneuver" on cerebral circulation function].

OBJECTIVE: To investigate the change and regulation of cerebral circulation during rotating-table simulated push-pull maneuver. METHOD: A special rotating-table was used to simulate the push-pull maneuver. 10 healthy adults were subjected to a series of "head-up stand (+1Gz) 1 min head-down stand (-1Gz) 10 s and head-up stand (+1Gz) 1 min" changes. Cerebral blood flow velocity and pulsatility indices in the left middle cerebral artery were constantly measured with a TC2020TCD using Transcranial Doppler [correction of Transcanial Dopplor] instrument. RESULT: During 10 s head-down stand (-1Gz) systolic velocity (Vs) increased, diastolic velocity (Vd) decreased, and the pulsatility indices (PI and RI) increased significantly in the left middle cerebral artery. During subsequent head-up stand (+1Gz), these changes didn't resume immediately and maintained for at least 20 s. CONCLUSION: This result implied that the push-pull maneuver increased the resistance of the cerebral vessels, which might be one of the mechanisms of the push-pull effect.

Adult↗

PubMed1999

[Two high performance fighter pilots with low +Gz tolerance rectified by centrifuge training].

OBJECTIVE: To demonstrate the effects of training on rectifying two high performance fight aircraft pilots with low +Gz tolerance. METHODS: Anti-G straining maneuver (AGSM) and pressure breathing for +Gz (PBG) maneuver were trained during centrifuge +Gz stress. RESULTS: After training, the +Gz tolerances with AGSM, and with PBG and anti-G suit were enhanced by 3.0 ~ 3.25 G and 2.75 ~ 3.0 G, respectively. The combined +Gz tolerance was higher than the relaxed +Gz tolerance by 4.25 ~ 4.5 G. Both two pilots had passed the 8 G 10 s SACM +Gz profile and reached the standard of training.

Acceleration↗

PubMed1999

[Integrated protection capability afforded by a new type capstan anti-G equipment and anti-G straining maneuver].

Objective. To investigate the integrated protection capability afforded by a new type capstan anti-G equipment and anti-G straining maneuver, as a result we discussed the feasibility of protection for 8 G 10 s (rapid onset runs at 2 G/s) acceleration using an associated precept with the above both anti-G measures. Method. This study was accomplished using the human centrifuge with rapid onset at 2 G/s. First, we determined the relaxed +Gz tolerance of nine male aviation students, and then determined theirs most + Gz tolerance while thereinto the five aviation students using a new type capstan anti-G suit (NKH) + a new type anti-G valve (NKT) + L-1 anti-G straining maneuver (L-1) and the other four aviation students using a new type capstan counterpressure suit (NDC) + the new type anti-G valve (NKT) + L-1. Result. The most +Gz tolerance of five students was 8.80 +/- 0.27 G while using NKH + NKT + L-1 and was higher than their relaxed +Gz tolerance at 4.60 +/- 0.42 G (P< 0.01) and that the most +Gz tolerance of four students was 8.75 +/- 0.50 G while using NDC + NKT + L-1 and was higher than their relaxed +Gz tolerance at 4.50 +/- 0.46 G (P< 0.01). Conclusion. Pilot will be capable against the 8 G 10 s (rapid onset runs at 2 G/s) effectively using the new type capstan anti +/- G equipment and anti +/- G straining maneuver, and the provided precept has availability.

Acceleration↗

PubMed1999

[Technical consideration of setting up a specification for human centrifuge evaluation of anti-G equipment].

Anti-G equipment needs to be evaluated using human centrifuge before further developed. However, there isn't a general specification for human centrifuge evaluation of anti-G equipment. From related literature and from our over thirty years experience in this area, we sum up to five aspect technical consideration below: human centrifuge, medical specification for using human in +Gz stress experiment, anti-G equipment experimental assembly, principle should be abided by during human centrifuge evaluation of anti-G equipment. We hope that the technical considerations mentioned in the paper should be helpful to the work of setting up a specification for human centrifuge evaluation anti-G equipment. After we have a specification, the research will be conducted orderly and the anti-G [correction of an-G] equipment will be developed sequentially.

Acceleration↗