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Key points: Dynamic cerebral autoregulation (CA) is often expressed by the mean arterial blood pressure (MAP)–cerebral blood flow (CBF) relationship, with little attention given to the dynamic relationship between MAP and cerebrovascular resistance (CVR).In CBF velocity (CBFV) recordings with transcranial Doppler, evidence demonstrates that CVR should be replaced by a combination of a resistance–area product (RAP) with a critical closing pressure (CrCP) parameter, the blood pressure value where CBFV reaches zero due to vessels collapsing.Transfer function analysis of the MAP–CBFV relationship can be extended to the MAP–RAP and MAP–CrCP relationships, to assess their contribution to the dynamic CA response.During normocapnia, both RAP and CrCP make a significant contribution to explaining the MAP–CBFV relationship.Hypercapnia, a surrogate state of depressed CA, leads to marked changes in dynamic CA, that are entirely explained by the CrCP response, without further contribution from RAP in comparison with normocapnia. Dynamic cerebral autoregulation (CA) is manifested by changes in the diameter of intra‐cerebral vessels, which control cerebrovascular resistance (CVR). We investigated the contribution of critical closing pressure (CrCP), an important determinant of CVR, to explain the cerebral blood flow (CBF) response to a sudden change in mean arterial blood pressure (MAP). In 76 healthy subjects (age range 21–70 years, 36 women), recordings of MAP (Finometer), CBF velocity (CBFV; transcranial Doppler ultrasound), end‐tidal CO2 (capnography) and heart rate (ECG) were performed for 5 min at rest (normocapnia) and during hypercapnia induced by breathing 5% CO2 in air. CrCP and the resistance–area product (RAP) were obtained for each cardiac cycle and their dynamic response to a step change in MAP was calculated by means of transfer function analysis. The recovery of the CBFV response, following a step change in MAP, was mainly due to the contribution of RAP during both breathing conditions. However, CrCP made a highly significant contribution during normocapnia (P < 0.0001) and was the sole determinant of changes in the CBFV response, resulting from hypercapnia, which led to a reduction in the autoregulation index from 5.70 ± 1.58 (normocapnia) to 4.14 ± 2.05 (hypercapnia; P < 0.0001). In conclusion, CrCP makes a very significant contribution to the dynamic CBFV response to changes in MAP and plays a major role in explaining the deterioration of dynamic CA induced by hypercapnia. Further studies are needed to assess the relevance of CrCP contribution in physiological and clinical studies. Key points: Dynamic cerebral autoregulation (CA) is often expressed by the mean arterial blood pressure (MAP)–cerebral blood flow (CBF) relationship, with little attention given to the dynamic relationship between MAP and cerebrovascular resistance (CVR).In CBF velocity (CBFV) recordings with transcranial Doppler, evidence demonstrates that CVR should be replaced by a combination of a resistance–area product (RAP) with a critical closing pressure (CrCP) parameter, the blood pressure value where CBFV reaches zero due to vessels collapsing.Transfer function analysis of the MAP–CBFV relationship can be extended to the MAP–RAP and MAP–CrCP relationships, to assess their contribution to the dynamic CA response.During normocapnia, both RAP and CrCP make a significant contribution to explaining the MAP–CBFV relationship.Hypercapnia, a surrogate state of depressed CA, leads to marked changes in dynamic CA, that are entirely explained by the CrCP response, without further contribution from RAP in comparison with normocapnia. [ABSTRACT FROM AUTHOR]

Key points: Dynamic cerebral autoregulation (CA) is often expressed by the mean arterial blood pressure (MAP)–cerebral blood flow (CBF) relationship, with little attention given to the dynamic relationship between MAP and cerebrovascular resistance (CVR).In CBF velocity (CBFV) recordings with transcranial Doppler, evidence demonstrates that CVR should be replaced by a combination of a resistance–area product (RAP) with a critical closing pressure (CrCP) parameter, the blood pressure value where CBFV reaches zero due to vessels collapsing.Transfer function analysis of the MAP–CBFV relationship can be extended to the MAP–RAP and MAP–CrCP relationships, to assess their contribution to the dynamic CA response.During normocapnia, both RAP and CrCP make a significant contribution to explaining the MAP–CBFV relationship.Hypercapnia, a surrogate state of depressed CA, leads to marked changes in dynamic CA, that are entirely explained by the CrCP response, without further contribution from RAP in comparison with normocapnia. Dynamic cerebral autoregulation (CA) is manifested by changes in the diameter of intra‐cerebral vessels, which control cerebrovascular resistance (CVR). We investigated the contribution of critical closing pressure (CrCP), an important determinant of CVR, to explain the cerebral blood flow (CBF) response to a sudden change in mean arterial blood pressure (MAP). In 76 healthy subjects (age range 21–70 years, 36 women), recordings of MAP (Finometer), CBF velocity (CBFV; transcranial Doppler ultrasound), end‐tidal CO2 (capnography) and heart rate (ECG) were performed for 5 min at rest (normocapnia) and during hypercapnia induced by breathing 5% CO2 in air. CrCP and the resistance–area product (RAP) were obtained for each cardiac cycle and their dynamic response to a step change in MAP was calculated by means of transfer function analysis. The recovery of the CBFV response, following a step change in MAP, was mainly due to the contribution of RAP during both breathing conditions. However, CrCP made a highly significant contribution during normocapnia (P < 0.0001) and was the sole determinant of changes in the CBFV response, resulting from hypercapnia, which led to a reduction in the autoregulation index from 5.70 ± 1.58 (normocapnia) to 4.14 ± 2.05 (hypercapnia; P < 0.0001). In conclusion, CrCP makes a very significant contribution to the dynamic CBFV response to changes in MAP and plays a major role in explaining the deterioration of dynamic CA induced by hypercapnia. Further studies are needed to assess the relevance of CrCP contribution in physiological and clinical studies. Key points: Dynamic cerebral autoregulation (CA) is often expressed by the mean arterial blood pressure (MAP)–cerebral blood flow (CBF) relationship, with little attention given to the dynamic relationship between MAP and cerebrovascular resistance (CVR).In CBF velocity (CBFV) recordings with transcranial Doppler, evidence demonstrates that CVR should be replaced by a combination of a resistance–area product (RAP) with a critical closing pressure (CrCP) parameter, the blood pressure value where CBFV reaches zero due to vessels collapsing.Transfer function analysis of the MAP–CBFV relationship can be extended to the MAP–RAP and MAP–CrCP relationships, to assess their contribution to the dynamic CA response.During normocapnia, both RAP and CrCP make a significant contribution to explaining the MAP–CBFV relationship.Hypercapnia, a surrogate state of depressed CA, leads to marked changes in dynamic CA, that are entirely explained by the CrCP response, without further contribution from RAP in comparison with normocapnia. [ABSTRACT FROM AUTHOR]

Introduction: Cerebral autoregulation (CA) is impaired in acute ischemic stroke (AIS) and is associated with worse patient outcomes, but the underlying physiological cause is unclear. This study tests whether depressed CA in AIS can be linked to the dynamic responses of critical closing pressure (CrCP) and resistance area product (RAP)., Methods: Continuous recordings of middle cerebral blood velocity (MCAv, transcranial Doppler), arterial blood pressure (BP), end-tidal CO2 and electrocardiography allowed dynamic analysis of the instantaneous MCAv-BP relationship to obtain estimates of CrCP and RAP. The dynamic response of CrCP and RAP to a sudden change in mean BP was obtained by transfer function analysis. Comparisons were made between younger controls (≤50 years), older controls (&gt;50 years), and AIS patients., Results: Data from 24 younger controls (36.4 ± 10.9 years, 9 male), 38 older controls (64.7 ± 8.2 years, 20 male), and 20 AIS patients (63.4 ± 13.8 years, 9 male) were included. Dynamic CA was impaired in AIS, with lower autoregulation index (affected hemisphere: 4.0 ± 2.3, unaffected: 4.5 ± 1.8) compared to younger (right: 5.8 ± 1.4, left: 5.8 ± 1.4) and older (right: 4.9 ± 1.6, left: 5.1 ± 1.5) controls. AIS patients also demonstrated an early (0-3 s) peak in CrCP dynamic response that was not influenced by age., Conclusion: These early transient differences in the CrCP dynamic response are a novel finding in stroke and occur too early to reflect underlying regulatory mechanisms. Instead, these may be caused by structural changes to cerebral vasculature., (© 2024 S. Karger AG, Basel.)