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Impairment of cardiovascular and vasomotor responses during tilt table simulation of "push-pull' maneuvers.
Aviat Space Environ Med. 2002 Oct; 73(10):971-9.AS

Abstract

BACKGROUND

Numerous studies have shown that tolerance to positive acceleration (+Gz) is impaired subsequent to an exposure of less than +1 Gz.

HYPOTHESIS

Vasodilation induced by antecedent negative Gz (-Gz) exposure delays sympathetic vasoconstriction during subsequent +Gz, further reducing G-tolerance.

METHODS

There were 20 subjects tested on an electronic tilt table, and exposed to the following randomized head-up tilt (HUT) and head-down tilt (HDT) conditions: +75 degrees HUT for 60 s, followed by transition to either 0 degrees (supine) HDT, or -25 degrees HDT, or -45 degrees HDT for 7 or 15 s at tilt rate of 45 degrees x s(-1). This was followed by HUT, divided into three periods: HUT1 (approximately 3-10 s), HUT2 (approximately 15-22 s), and HUT3 (approximately 27-35 s). Systolic blood pressure (SBP) was normalized to heart and head-levels. Stroke volume (SV) was estimated using impedance cardiography; forearm blood flow (FBF) estimated by venous occlusion plethysmography and forearm vascular resistance (FVR) was calculated from FBF and SBP. Total peripheral resistance (TPR) was estimated by MAP/(SV*HR).

RESULTS

Heart-level SBP decreased significantly during HDT for both HDT durations (p < 0.01). SBP increased significantly at head-level during HDT (p < 0.001). During HUT1 heart and head-level SBP decreased for all conditions (p < 0.001), recovering to baseline levels by HUT2. TPR decreased significantly for all HDT conditions (p < 0.001), with this decrease related to the degree of HDT angle (p < 0.05). During HUT1, TPR remained depressed below baseline. At HUT2, TPR remained decreased for the -45 degrees/7-s condition only (p < 0.01). FBF decreased significantly during HDT (p < 0.02), with the magnitude related to the HDT angle. FBF remained elevated during HUT1 (p < 0.01). FVR decreased as a function of HDT angle during HDT (p < 0.001), with the decrease persisting into the HUT1 phase (p < 0.01). By the HUT2 and HUT3 periods, FVR were above baseline levels for the -45 degrees HDT condition (p < 0.01).

CONCLUSION

These results confirm in humans the delayed recovery of peripheral vascular resistance observed in animal studies when -Gz precedes +Gz. Since SV recovered to baseline levels during the "pull" phase (HUT1-3), with TPR and forearm vascular resistance remaining depressed, baroreflex-mediated peripheral vascular control is delayed. This delay at higher subsequent +Gz levels is dangerous for the military pilot, since symptoms of G-intolerance due to delay in head-level BP recovery will ensue at lower absolute +Gz levels during push-pull type maneuvers.

Authors+Show Affiliations

Defence and Civil Institute of Environmental Medicine, Defence Research Development Canada, Toronto, ON. len.goodman@drdc.rddc.gc.caNo affiliation info available

Pub Type(s)

Journal Article

Language

eng

PubMed ID

12398258

Citation

Goodman, Len S., and Susan LeSage. "Impairment of Cardiovascular and Vasomotor Responses During Tilt Table Simulation of "push-pull' Maneuvers." Aviation, Space, and Environmental Medicine, vol. 73, no. 10, 2002, pp. 971-9.
Goodman LS, LeSage S. Impairment of cardiovascular and vasomotor responses during tilt table simulation of "push-pull' maneuvers. Aviat Space Environ Med. 2002;73(10):971-9.
Goodman, L. S., & LeSage, S. (2002). Impairment of cardiovascular and vasomotor responses during tilt table simulation of "push-pull' maneuvers. Aviation, Space, and Environmental Medicine, 73(10), 971-9.
Goodman LS, LeSage S. Impairment of Cardiovascular and Vasomotor Responses During Tilt Table Simulation of "push-pull' Maneuvers. Aviat Space Environ Med. 2002;73(10):971-9. PubMed PMID: 12398258.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Impairment of cardiovascular and vasomotor responses during tilt table simulation of "push-pull' maneuvers. AU - Goodman,Len S, AU - LeSage,Susan, PY - 2002/10/26/pubmed PY - 2003/2/7/medline PY - 2002/10/26/entrez SP - 971 EP - 9 JF - Aviation, space, and environmental medicine JO - Aviat Space Environ Med VL - 73 IS - 10 N2 - BACKGROUND: Numerous studies have shown that tolerance to positive acceleration (+Gz) is impaired subsequent to an exposure of less than +1 Gz. HYPOTHESIS: Vasodilation induced by antecedent negative Gz (-Gz) exposure delays sympathetic vasoconstriction during subsequent +Gz, further reducing G-tolerance. METHODS: There were 20 subjects tested on an electronic tilt table, and exposed to the following randomized head-up tilt (HUT) and head-down tilt (HDT) conditions: +75 degrees HUT for 60 s, followed by transition to either 0 degrees (supine) HDT, or -25 degrees HDT, or -45 degrees HDT for 7 or 15 s at tilt rate of 45 degrees x s(-1). This was followed by HUT, divided into three periods: HUT1 (approximately 3-10 s), HUT2 (approximately 15-22 s), and HUT3 (approximately 27-35 s). Systolic blood pressure (SBP) was normalized to heart and head-levels. Stroke volume (SV) was estimated using impedance cardiography; forearm blood flow (FBF) estimated by venous occlusion plethysmography and forearm vascular resistance (FVR) was calculated from FBF and SBP. Total peripheral resistance (TPR) was estimated by MAP/(SV*HR). RESULTS: Heart-level SBP decreased significantly during HDT for both HDT durations (p < 0.01). SBP increased significantly at head-level during HDT (p < 0.001). During HUT1 heart and head-level SBP decreased for all conditions (p < 0.001), recovering to baseline levels by HUT2. TPR decreased significantly for all HDT conditions (p < 0.001), with this decrease related to the degree of HDT angle (p < 0.05). During HUT1, TPR remained depressed below baseline. At HUT2, TPR remained decreased for the -45 degrees/7-s condition only (p < 0.01). FBF decreased significantly during HDT (p < 0.02), with the magnitude related to the HDT angle. FBF remained elevated during HUT1 (p < 0.01). FVR decreased as a function of HDT angle during HDT (p < 0.001), with the decrease persisting into the HUT1 phase (p < 0.01). By the HUT2 and HUT3 periods, FVR were above baseline levels for the -45 degrees HDT condition (p < 0.01). CONCLUSION: These results confirm in humans the delayed recovery of peripheral vascular resistance observed in animal studies when -Gz precedes +Gz. Since SV recovered to baseline levels during the "pull" phase (HUT1-3), with TPR and forearm vascular resistance remaining depressed, baroreflex-mediated peripheral vascular control is delayed. This delay at higher subsequent +Gz levels is dangerous for the military pilot, since symptoms of G-intolerance due to delay in head-level BP recovery will ensue at lower absolute +Gz levels during push-pull type maneuvers. SN - 0095-6562 UR - https://www.unboundmedicine.com/medline/citation/12398258/Impairment_of_cardiovascular_and_vasomotor_responses_during_tilt_table_simulation_of_"push_pull'_maneuvers_ DB - PRIME DP - Unbound Medicine ER -