Acute reduction in posterior cerebral blood flow following isometric handgrip exercise is augmented by lower body negative pressure

Q: What is the clinical evidence from this study?

Population: Healthy subjects undergoing isometric handgrip exercise and orthostatic stress (n=9). Intervention: 3-minute isometric handgrip exercise at 30% maximum voluntary contraction during lower body negative pressure (-40 Torr) vs. 3-minute isometric handgrip exercise at 30% maximum voluntary contraction without lower body negative pressure (CONTROL). Primary outcome: Relative change in vertebral artery (VA) blood flow (index of posterior cerebral blood flow) immediately following isometric handgrip exercise (0 to 15 seconds of recovery) (p=0.005).

Q: What does this research mean for the field?

Orthostatic stress induced by lower body negative pressure selectively augments the acute reduction in posterior cerebral blood flow following isometric exercise without affecting anterior cerebral blood flow. Novelty: ClaimNovelty.NOVEL_FINDING. Consensus alignment: ConsensusAlignment.NEUTRAL.

Takuro Washio; Jennifer R. Vranish; Jasdeep Kaur; Benjamin E. Young; Keisho Katayama; Paul J. Fadel; Shigehiko Ogoh

doi:10.14814/phy2.13886

October 1, 2018Physiological ReportsOpen Access

Acute reduction in posterior cerebral blood flow following isometric handgrip exercise is augmented by lower body negative pressure

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Key result

Lower body negative pressure augments post-exercise vertebral artery flow reduction by ~11 percentage points vs. control.

P=0.005
n=9

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Why the study?

Does orthostatic stress induced by lower body negative pressure (-40 Torr) augment the acute reduction in posterior and anterior cerebral blood flow immediately following isometric handgrip exercise in healthy young men?

Key Points

To determine whether orthostatic stress selectively augments the acute reduction in posterior cerebral blood flow compared with anterior cerebral blood flow following isometric exercise.
Nine healthy subjects performed 3 minutes of isometric handgrip exercise at 30% maximum voluntary contraction under control conditions and with lower body negative pressure (-40 Torr).
Vertebral artery blood flow and middle cerebral artery blood velocity were recorded to assess posterior and anterior cerebral blood flow, alongside mean arterial pressure and cardiac output.
Vertebral artery blood flow decreased significantly more during lower body negative pressure than under control conditions immediately postexercise (-24.2 ± 9.5% vs. -13.4 ± 6.6%, P = 0.005; absolute flow 117.5 ± 30.5 vs. 133.7 ± 27.2 mL/min, P = 0.048).
Reductions in middle cerebral artery blood velocity immediately after handgrip exercise were unaffected by the application of lower body negative pressure (P = 0.22).
Mean arterial pressure decreased immediately following exercise without significant difference between control and lower body negative pressure conditions (-15.4 ± 4.0% vs. -17.0 ± 6.2%, P = 0.42).

Structured PICO

Does orthostatic stress induced by lower body negative pressure (-40 Torr) augment the acute reduction in posterior and anterior cerebral blood flow immediately following isometric handgrip exercise in healthy young men?

P

Population

9 healthy young men (mean age 25.0 years, 0% female) free of cardiovascular, cerebrovascular, or pulmonary disorders and history of pre-syncope, evaluated during acute 3-minute exercise and 1-minute post-exercise recovery protocols.

I

Intervention

3-minute isometric handgrip exercise at 30% maximum voluntary contraction (MVC) performed in the supine position during lower body negative pressure (LBNP; -40 Torr applied from 1 minute prior to exercise through 1 minute of post-exercise recovery).

C

Comparator

3-minute isometric handgrip exercise at 30% MVC performed in the supine position without lower body negative pressure (CONTROL), separated by at least 15 minutes of supine rest.

O

Outcome

Relative percent change in vertebral artery (VA) blood flow (an index of posterior cerebral blood flow, measured via duplex color-coded ultrasound) immediately following handgrip exercise (0 to 15 seconds of recovery phase).surrogate

Main Result

Absolute Event Rate: -24.2% vs -13.4%

p-value: p=0.005

This physiological study demonstrates that the posterior cerebral circulation is selectively vulnerable to orthostatic stress immediately following isometric exercise, providing a potential hemodynamic mechanism for post-resistance exercise syncope.

Limitations

Used transcranial Doppler ultrasound to measure middle cerebral artery blood velocity rather than duplex Doppler ultrasound due to availability of only one ultrasound unit, relying on the assumption of constant arterial diameter.
Used small muscle mass isometric handgrip exercise at moderate intensity, which may not reflect the hemodynamic responses of larger muscle mass resistance exercise (e.g., leg press).
Recruited only young male subjects (n=9), so findings cannot be extrapolated to women.
Simulated orthostatic stress using supine lower body negative pressure rather than head-up tilt or standing, which lacks a hydrostatic pressure gradient.
Did not use duplex Doppler ultrasound to measure anterior cerebral blood flow (middle cerebral artery) because only one ultrasound unit was available, relying on transcranial Doppler blood velocity under the assumption of constant vessel diameter.
Used small muscle mass isometric handgrip exercise at moderate intensity (30% MVC), which may not reflect the hemodynamic responses of larger muscle mass resistance exercise such as leg press.
Only recruited male subjects (n=9), so findings cannot be extrapolated to women.
Used supine lower body negative pressure rather than head-up tilt or upright standing to simulate orthostatic stress, which omits the hydrostatic pressure gradient.

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Implication

Orthostatic stress may selectively worsen post-exercise posterior cerebral hypoperfusion; hypothesis-generating for mechanisms of post-resistance exercise syncope.

Abstract

The mechanism(s) for the increased occurrence of a grayout or blackout, syncope, immediately after heavy resistance exercise are unclear. It is well-known that orthostatic stress increases the occurrence of postexercise syncope. In addition, previous findings have suggested that hypo-perfusion, especially in the posterior cerebral circulation rather than anterior cerebral circulation, may be associated with the occurrence of syncope. Herein, we hypothesized that the postexercise decrease in posterior, but not anterior, cerebral blood flow (CBF) would be greater during orthostatic stress. Nine healthy subjects performed 3-min isometric handgrip (HG) at 30% maximum voluntary contraction without (CONTROL) and during lower body negative pressure (LBNP; -40 Torr) while vertebral artery (VA) blood flow, as an index of posterior CBF, and middle cerebral artery blood velocity (MCAv), as an index of anterior CBF, were measured. Immediately after HG (0 to 15 sec of recovery phase), mean arterial pressure decreased but there was no difference in this reduction between CONTROL and LBNP conditions (-15.4 ± 4.0% and -17.0 ± 6.2%, P = 0.42). Similarly, MCAv decreased following exercise and was unaffected by the application of LBNP (P = 0.22). In contrast, decreases in VA blood flow immediately following HG during LBNP were significantly greater compared to CONTROL condition (-24.2 ± 9.5% and -13.4 ± 6.6%, P = 0.005). These findings suggest that the decrease in posterior CBF immediately following exercise was augmented by LBNP, whereas anterior CBF appeared unaffected. Thus, the posterior cerebral circulation may be more sensitive to orthostatic stress during the postexercise period.

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Cite This Study

Washio et al. (2018) studied Healthy subjects undergoing isometric handgrip exercise and orthostatic stress (n=9). 3-minute isometric handgrip exercise at 30% maximum voluntary contraction during lower body negative pressure (-40 Torr) vs. 3-minute isometric handgrip exercise at 30% maximum voluntary contraction without lower body negative pressure (CONTROL) was evaluated on Relative change in vertebral artery (VA) blood flow (index of posterior cerebral blood flow) immediately following isometric handgrip exercise (0 to 15 seconds of recovery) (p=0.005). Lower body negative pressure (-40 Torr) augmented the post-exercise reduction in vertebral artery blood flow compared to control.

synapsesocial.com/papers/6a8426839cea0905630b9887 https://doi.org/10.14814/phy2.13886

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Acute reduction in posterior cerebral blood flow following isometric handgrip exercise is augmented by lower body negative pressure

Figures

Key Points

Structured PICO

Main Result

Limitations

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Implication

Abstract

Discussion

Cite This Study

Acute reduction in posterior cerebral blood flow following isometric handgrip exercise is augmented by lower body negative pressure

Figures

Key Points

Structured PICO

Main Result

Limitations

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Implication

Abstract

Discussion

Cite This Study

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