White Mountain Expedition 2019: Peaks and Valleys ‐ Oscillatory cerebral blood flow at high altitude

Abstract

IntroductionCerebral tissue oxygenation can be impaired by decreases in oxygen delivery as a result of reduced cerebral blood flow, and environmental conditions such as ascent to high altitude. Recent evidence suggests that an oscillatory pattern in cerebral blood flow (at ~0.1 Hz) may protect cerebral oxygenation under conditions of cerebral hypoperfusion. In this study, we hypothesized that inducing oscillations in cerebral blood flow at 0.1 Hz would protect cerebral blood flow and cerebral tissue oxygen saturation during exposure to combined simulated hemorrhage and sustained hypobaric hypoxia (ascent and partial acclimatization to high altitude).Methods8 healthy human subjects (4 M, 24.7 ± 4.1 y; 4 F, 34.3 ± 8.3 y) participated in two experiments at high altitude (White Mountain, California, USA; altitude, 3800 m): 1) a control condition (CTRL) where lower body negative pressure (LBNP) was used to induce central hypovolemia by reducing chamber pressure to −60 mmHg for 10‐min, and 2) oscillatory LBNP (OLBNP) where chamber pressure was reduced to −60 mmHg, then oscillated every 5‐s between −30 mmHg and −90 mmHg for 10‐min (0.1 Hz). Measurements included internal carotid artery (ICA) blood flow via duplex Doppler ultrasound, middle cerebral artery velocity (MCAv) via transcranial Doppler ultrasound, and cerebral tissue oxygen saturation via near‐infrared spectroscopy. Frequency analysis (via fast Fourier transform) was performed to verify that oscillations in mean MCAv were generated at ~0.1 Hz. Data were analyzed with a linear mixed‐model. All data are represented as mean ± SE.ResultsLow frequency power (0.07–0.15 Hz) in mean MCAv increased during OLBNP vs. CTRL (P = 0.02). OLBNP did not protect ICA flow (OLBNP: −32.5 ± 4.5 Δ%; CTRL: −19.9 ± 8.9 Δ%; P = 0.18) or mean MCAv (OLBNP: −18.5 ± 3.4 Δ%; CTRL: −15.3 ± 5.4 Δ%; P = 0.58), but cerebral tissue oxygenation was protected (OLBNP: −0.67 ± 1.0 Δ%; CTRL: −4.07 ± 2.0 Δ%; P = 0.004).ConclusionsThese results support our hypothesis that inducing oscillatory blood flow leads to protection of cerebral tissue oxygenation, despite no differences in ICA blood flow or mean MCAv. Overall, these data suggest that therapies using oscillatory perfusion may help preserve cerebral tissue oxygen saturation under conditions of reduced oxygen delivery.Support or Funding InformationAHA 17GRNT33671110