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. Author manuscript; available in PMC: 2022 Dec 24.
Published in final edited form as: Compr Physiol. 2021 Sep 23;11(4):2371–2432. doi: 10.1002/cphy.c200028

Figure 19.

Figure 19

Phase-angle relationship of the response of ICP to quasi-sinusoidal variations in arterial blood pressure (ABP) induced by frequency modulation of positive end-expiratory pressure in two-week-old piglets. When ABP was above the lower limit of autoregulation (LLA, open circles), the phase angle decreased when the ABP frequency increased from 1 to 6 cycles per minute (CPM). Assuming that ICP is related to cerebral blood volume, which is related to cerebral vasodilation and vasoconstriction responses, dynamic autoregulation is ineffective at periodicities less than 10 s. When ABP is below the LLA (closed circles), the phase angle is already reduced at low frequencies, confirming that frequency analysis at low ABP frequencies can be used to assess autoregulation. Source: Adapted, with permission, from Fraser CD, 2013 (144), © 2013, The American Physiological Society.