MIDDLE CEREBRAL ARTERY BLOOD FLOW DURING SIMULATED PUSH PULL EFFECT

Transcription

1 MIDDLE CEREBRAL ARTERY BLOOD FLOW DURING SIMULATED PUSH PULL EFFECT Maj Binu Sekhar M* Wg Cdr SK Sharma (Retd) Gp Capt A Agarwal Institute of Aerospace Medicine, Indian Air Force Bangalore, India * ask4binu@rediffmail.com 1

2 DISCLOSURE INFORMATION Maj (Dr) Binu Sekhar M I have no financial relationships to disclose I will not disclose off-label use and/or investigational use in my presentation 2

3 MIDDLE CEREBRAL ARTERY BLOOD FLOW DURING SIMULATED PUSH PULL EFFECT Introduction Objective Methodology Results Discussion Limitations Conclusion 3

4 Introduction Fighter jets often engage in air combat manoeuvres 4

5 Introduction -Gz is followed by +Gz exposure Banks et al. called it Push pull effect Decreases +Gz tolerance 5

6 Introduction Implicated in G-LOC related accidents USAF : %* (Michaud et al 1998) Incidents of inflight G-LOC due to Push-pull effect RAF : 31.3%** Canadian Air Force : 17%*** Michaud VJ, Lyons TJ. The push pull effect and G-induced loss of consciousness accidents in the US Air Force. Aviat Space Environ Med. 1998; 69: ** Green NDC, Ford SA. G-induced loss of consciousness: retrospective survey results from 2259 military aircrew. Aviat Space Environ Med. 2006; 77: *** Banks RD, Brush ML, Wrieht HL. Operational implications of Push-pull effect. Aviat Space Environ Med.1997; 68: 614 6

7 Introduction Counter measures - not effective Research works Tilt tables Coriolis acceleration platform Human Centrifuges Physiologic basis: Delay in the sympathetic baroreceptor mediated peripheral vasoconstriction 7

8 Introduction Cerebral vasoconstriction contributing to Push pull effect (Zhang et al)* Auto-regulation mediated??contribution on Cerebral ishemia Carotid Siphon effect Monroe Kellie doctrine * Zhang WS, Zhan CL, Geng XC, Lu X, Yan GD, Chu X. Cerebral flow velocity by transcranial Doppler during a vertical-rotating table simulation of push-pull effect. Aviat Space Environ Med. 2000; 71:

9 Introduction Trans Cranial Doppler ultrasound (TCD) Low frequency (2MHz) common Acoustic windows of skull access to intracerebral vessels Middle Cerebral Arteries - 80% of intracerebral blood flow 9

10 Objective To determine the blood flow characteristics in MCA using TCD during simulated Push-pull effect in a high performance human centrifuge To gain better understanding of cerebral blood flow and its contribution to reduction in +Gz tolerance if any, during Push-pull effect 10

11 Methodology 10 healthy male volunteers High Performance Human Centrifuge (HPHC) Trans Cranial Doppler (TCD) 2 MHz probe Middle Cerebral Artery Temporal window 50 mm depth 11

12 Methodology 12

13 Methodology 13

14 Methodology Control run Push pull run 14

15 Methodology TCD Cm/sec +Gz Time (in 5 milli sec) Control run 15

16 Methodology TCD Cm/sec Gz Time (in 5 milli sec) Push pull run 16

17 Analysis Mean MCA velocities Peak systolic (PSV) End diatolic (EDV) Phases measured Control run Baseline +3Gz Post +3Gz Push pull run Baseline -1.5Gz +Gz [Mean +2.53(±0.14)] Post +Gz 17

18 Analysis Statistics Student s two tailed paired t test Between the runs One way Anova with Tukey s post hoc analysis With in the run Level of significance (p) less than 5% 18

19 Results 19

20 Results Control run Peak systolic velocity (PSV) Parameters Mean ± SD (cm/sec) P value PSV_baseline Vs PSV_+Gz 99.4±18 Vs 106±24 NS PSV_baseline Vs PSV_Post+Gz 99.4±18 Vs 102.5±16 NS PSV_+Gz Vs PSV_Post+Gz 106±24 Vs 102.5±16 NS End diastolic velocity (EDV) Parameters Mean ± SD (cm/sec) P value EDV_baseline Vs EDV_+Gz 42.7±11 Vs 35.7±15 NS EDV_baseline Vs EDV_Post+Gz 42.7±11 Vs 31.3±9 <0.05* EDV_+Gz Vs EDV_Post+Gz 35.7±15 Vs 31.3±9 NS * Significant; NS: Not significant 20

21 Results 21

22 Results Push pull run Peak systolic velocity (PSV) Parameters Mean ± SD (cm/sec) P value PSV_baseline Vs PSV_-Gz 99.5±43 Vs 108±20 NS PSV_baseline Vs PSV_+Gz 99.5±43 Vs 98.3±15 NS PSV_baseline Vs PSV_Post+Gz 99.5±43 Vs 95.4±14 NS PSV_-Gz Vs PSV_+Gz 108±20 Vs 98.3±15 NS PSV_-Gz Vs PSV_Post+Gz 108±20 Vs 95.4±14 NS PSV_+Gz Vs PSV_Post+Gz 98.3±15 Vs 95.4±14 NS NS: Not significant 22

23 Results Push pull run End diastolic velocity (EDV) Parameters Mean ± SD (cm/sec) P value EDV_baseline Vs EDV_-Gz 42.7±11 Vs 27.5±8 <0.05* EDV_baseline Vs EDV_+Gz 42.7±11 Vs 21±13 <0.001** EDV_baseline Vs EDV_Post+Gz 42.7±11 Vs 26.8±12 <0.05* EDV_-Gz Vs EDV_+Gz 27.5±8 Vs 21±13 NS EDV_-Gz Vs EDV_Post+Gz 27.5±8 Vs 26.8±12 NS EDV_+Gz Vs EDV_Post+Gz 21±13 Vs 26.8±12 NS ** Highly significant; *Significant; NS: Not significant 23

24 Results Comparison b/w Control run & Push pull run TCD in cm/sec End diastolic velocities (EDV) 24

25 Phase of run MCA velocity type (cm/sec) Results Comparison b/w Control run & Push pull run +3Gz run (Mean±SD) Push-pull run (Mean±SD) P value Base line PSV 99.4± ± NS EDV 42.7± ± NS +Gz PSV 106± ± NS EDV 35.7±15 21± ** Post +Gz PSV 102.5± ± NS EDV 31.3±9 26.8± NS ** Highly significant; NS: Not significant 25

26 Discussion Cerebral blood flow is autoregulated extremely well The mean arterial pressure can be decreased as low as 60 mm Hg or increased to as high as 140 mm Hg without significant change in cerebral blood flow. Guyton AC, Hall JE. Cerebral blood flow, cerebrospinal fluid and brain metabolism. In: Text book of Medical Physiology. 11 th ed. Elsevier Saunders ; 2006:

27 Discussion Cerebral circulatory system has strong sympathetic innervation - from Superior cervical ganglia Causes constriction of large & intermediate sized blood vessels when mean arterial pressure is exceptionally high Guyton AC, Hall JE. Cerebral blood flow, cerebrospinal fluid and brain metabolism. In: Text book of Medical Physiology. 11 th ed. Elsevier Saunders ; 2006:

28 Discussion In Push pull run MCA velocities (both PSV & EDV) increased at the onset of Gz Gradually deceased below baseline once the Cerebral vasoconstriction sets in Significant (p<0.05) decrement in mean EDV below baseline during Gz phase 28

29 Discussion In Push pull run EDV was significantly less than baseline during +Gz phase (p<0.001) and post +Gz phase (p<0.05) Cerebral vasoconstriction is persistent during +Gz and post +Gz phases Similar findings by Zhang et al* * Zhang WS, Zhan CL, Geng XC, Lu X, Yan GD, Chu X. Cerebral flow velocity by transcranial Doppler during a vertical-rotating table simulation of push-pull effect. Aviat Space Environ Med. 2000; 71:

30 Discussion Push pull run v/s Control run EDV was significantly lower (p=0.002) during +Gz phase Can be attributed to reflex mediated cerebral vasoconstrictor response Can contribute to decreased +Gz tolerance 30

31 Limitations Small sample size +Gz values compared in Control & Push pull run were different Mean MCA velocity was not studied Derived parameters such as Pulsatility index & Resistance index were not studied 31

32 Conclusion Cerebral autoregulation and sympathetically mediated cerebral vasoconstriction are important contributing factors for early onset cerebral ischemia during Push pull effect Further extensive research works to under stand the exact Pathophysiological mechanisms will be an important step towards development of countermeasures against Push pull effect 32

33 Acknowledgements Commandant IAM All subjects Staff at the Dept of Acceleration Physiology & all maintenance personnel of HPHC 33

34 THANK YOU 34