Figure 2.

Relationship between arterial BP and BFV in the middle cerebral artery. a | Dominant spontaneous oscillations of BP and BFV in a 72-year-old healthy control woman. b | Dominant spontaneous oscillations of BP and BFV in a 68-year-old man with type 2 diabetes mellitus, in the supine position. BP, BFVL and BFVR were decomposed into different modes, each mode corresponding to fluctuations at a different timescale. BP and BFV fluctuations exhibit continuous and dominant oscillations at frequencies 0.07–0.4 Hz. Instantaneous phases of BP and BFV oscillations (solid lines, bottom graphs) and the mean BP–BFV phase shift (dashed lines) were obtained. c | Phase shift between arterial BP and BFV. Results were obtained from 12 healthy controls, 10 patients with hypertension, and 10 patients with history of stroke, by calculating the instantaneous phase shift during the Valsalva maneuver. Dynamic autoregulation in controls was characterized by specific BP–BFV phase shifts. The reduction of the phase shifts observed in participants with hypertension who had never had a stroke and patients with history of stroke indicates impaired autoregulation. Abbreviations: BFV, blood flow velocity; BFVL, left BFV; BFVR, right BFVR; BP, blood pressure. Parts a and b modified with permission from Hu et al.¹⁹ Part c reprinted with permission from Hu et al.³⁵