Key result
Combined lower body negative pressure and mental stress decreased middle cerebral artery blood velocity (Δ-4.6±2.0 cm/s), not statistically different from LBNP alone (Δ-2.6±1.1 cm/s).
Why the study?
Does combined mental stress and lower body negative pressure prevent LBNP-induced reductions in middle cerebral artery blood velocity compared to LBNP alone?
RCT (n=18)
randomized
Does combined mental stress and lower body negative pressure prevent LBNP-induced reductions in middle cerebral artery blood velocity compared to LBNP alone?
Absolute Event Rate: -4.6% vs -2.6%
Mental stress does not effectively preserve middle cerebral artery blood velocity when combined with central hypovolemia induced by lower body negative pressure.
Mental stress does not offset LBNP-induced MCAv reductions; leaves open relevance for orthostatic tolerance in aerospace settings.
BACKGROUND: Lower body negative pressure (LBNP) decreases middle cerebral artery blood velocity (MCAv) and can induce hypotension. Mental stress increases MCAv, but the MCAv response to combined LBNP and mental stress (COMBO) is unknown. We hypothesized that performing a stressful cognitive challenge (i.e., mental stress) concurrently with LBNP would prevent LBNP-induced reductions of MCAv. METHODS: There were 18 subjects (9 men, 9 women; ages 20.1±0.3 yr) who completed 3 randomized 3-min trials: 1) LBNP (-40 mmHg); 2) mental stress (serial subtraction); and 3) COMBO (LBNP+mental stress). All reported values are mean±SE. Mean arterial pressure (MAP), heart rate (HR), forearm blood flow (FBF), and MCAv were measured continuously. Subjects also reported perceived stress following the mental stress and COMBO trials. RESULTS: LBNP decreased MAP (Δ-1.4±0.5 mmHg), MCAv (Δ-2.6±1.1 cm s(-1)) and FBF (Δ-0.8±0.1 units), and increased HR (Δ2.7±1.2 bpm). Mental stress increased MAP (Δ10.1±1.3 mmHg), HR (Δ17.4±2.2 bpm), and FBF (Δ2.4±0.4 units), while MCAv (Δ2.8±1.3 cm s(-1)) tended to increase. COMBO increased MAP (Δ5.3±2.3 mmHg) and HR (Δ21.3±2.6 bpm), and tended to increase FBF (Δ0.5±0.3 units). However, MCAv (Δ-4.6±2.0 cm s(-1)) decreased during COMBO. Decreases in MCAv during COMBO were not statistically different from LBNP-induced decreases (Δ-4.6±2.0 vs. Δ-2.6±1.1 cm s(-1)). Subjective ratings of perceived stress (standard 0 to 4 scale) tended to be higher during COMBO than mental stress (2.9±0.1 vs. 2.5±0.1 units). CONCLUSION: Our results suggest that mental stress does not effectively preserve MCAv when combined with central hypovolemia (i.e., LBNP).
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Durocher et al. (2015) reported an RCT. Combined lower body negative pressure (LBNP) and mental stress (COMBO) vs. LBNP alone and mental stress alone was evaluated on Middle cerebral artery blood velocity (MCAv) change. Combined lower body negative pressure and mental stress decreased middle cerebral artery blood velocity (Δ-4.6±2.0 cm/s), not statistically different from LBNP alone (Δ-2.6±1.1 cm/s).
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