Cerebral Autoregulation in Orthostatic Intolerance

Schondorf, Ronald; Benoit, Julie; Stein, Reuben D.

doi:10.1111/j.1749-6632.2001.tb03702.x

Cited by 53 publications

(27 citation statements)

References 61 publications

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“…Calculation of CVR is complicated by unknown values of intracranial and venous pressures. During our resting conditions, since subjects were in a supine position, it is likely that the major determinant of cerebral perfusion pressure was MAP (39). Although the calculation of CVR in the upright position has been used extensively in previous studies, we acknowledge that MAP cannot be relied on to reflect cerebral perfusion pressure under all circumstances, especially in the upright posture.…”

Section: Discussionmentioning

confidence: 99%

Alterations in cerebral autoregulation and cerebral blood flow velocity during acute hypoxia: rest and exercise

Ainslie¹,

Barach²,

Murrell³

et al. 2007

American Journal of Physiology-Heart and Circulatory Physiology

107

111

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Ainslie PN, Barach A, Murrell C, Hamlin M, Hellemans J, Ogoh S. Alterations in cerebral autoregulation and cerebral blood flow velocity during acute hypoxia: rest and exercise. Am J Physiol Heart Circ Physiol 292: H976 -H983, 2007. First published September 29, 2006; doi:10.1152/ajpheart.00639.2006.-We examined the relationship between changes in cardiorespiratory and cerebrovascular function in 14 healthy volunteers with and without hypoxia [arterial O2 saturation (SaO 2 ) ϳ80%] at rest and during 60 -70% maximal oxygen uptake steady-state cycling exercise. During all procedures, ventilation, end-tidal gases, heart rate (HR), arterial blood pressure (BP; Finometer) cardiac output (Modelflow), muscle and cerebral oxygenation (near-infrared spectroscopy), and middle cerebral artery blood flow velocity (MCAV; transcranial Doppler ultrasound) were measured continuously. The effect of hypoxia on dynamic cerebral autoregulation was assessed with transfer function gain and phase shift in mean BP and MCAV. At rest, hypoxia resulted in increases in ventilation, progressive hypocapnia, and general sympathoexcitation (i.e., elevated HR and cardiac output); these responses were more marked during hypoxic exercise (P Ͻ 0.05 vs. rest) and were also reflected in elevation of the slopes of the linear regressions of ventilation, HR, and cardiac output with SaO 2 (P Ͻ 0.05 vs. rest). MCAV was maintained during hypoxic exercise, despite marked hypocapnia (44.1 Ϯ 2.9 to 36.3 Ϯ 4.2 Torr; P Ͻ 0.05). Conversely, hypoxia both at rest and during exercise decreased cerebral oxygenation compared with muscle. The low-frequency phase between MCAV and mean BP was lowered during hypoxic exercise, indicating impairment in cerebral autoregulation. These data indicate that increases in cerebral neurogenic activity and/or sympathoexcitation during hypoxic exercise can potentially outbalance the hypocapniainduced lowering of MCAV. Despite maintaining MCAV, such hypoxic exercise can potentially compromise cerebral autoregulation and oxygenation.hypocapnia; hypoxemia AN IMPORTANT PROTECTIVE FEATURE of the cerebral circulation is the ability to maintain cerebral blood flow (CBF) over a wide range of cerebral perfusion pressures (36). At rest, lowering of arterial PCO 2 (Pa CO 2 ) (hypocapnia) as a result of hyperventilation and elevations in sympathetic activation act to enhance cerebral autoregulation (i.e., by widening the cerebral autoregulation curve and causing a rightward shift, respectively), thus preventing cerebral hyperperfusion (36). During exercise, however, it has been shown that dynamic cerebral autoregulation was impaired by exhaustive exercise despite a hyperventilation-induced reduction in Pa CO 2 and likely exercise-induced elevations in sympathetic activation (35).Acute hypoxia in resting and exercising humans results in an enhanced muscle sympathetic discharge, cardiac output, skeletal muscle blood flow, and increased heart rate with little or no alteration in mean arterial blood pressure (MAP) (15, 38). In the brain, the vasod...

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Section: Discussionmentioning

confidence: 99%

Alterations in cerebral autoregulation and cerebral blood flow velocity during acute hypoxia: rest and exercise

Ainslie¹,

Barach²,

Murrell³

et al. 2007

American Journal of Physiology-Heart and Circulatory Physiology

107

111

View full text Add to dashboard Cite

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“…21,24 Others note that MCAv mean decreases much less than does MAP, implying that dynamic cerebral autoregulatory mechanisms are intact and functioning at syncope. 50 …”

Section: Differential Changes In Cbf Velocity Pulsatility During Hypomentioning

confidence: 99%

“…49 The preferential declines in MCAv diastolic and maintained MCAv systolic are consistent with the changes that occur during profound hypotension at the point of syncope. 11,50 Some consider this increase in MCAv pulsatility to be indicative of a paradoxical increase in cerebrovascular resistance before syncope. 21,24 Others note that MCAv mean decreases much less than does MAP, implying that dynamic cerebral autoregulatory mechanisms are intact and functioning at syncope.…”

Section: Differential Changes In Cbf Velocity Pulsatility During Hypomentioning

confidence: 99%

Influence of Changes in Blood Pressure on Cerebral Perfusion and Oxygenation

et al. 2010

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Abstract-Cerebral autoregulation (CA) is a critical process for the maintenance of cerebral blood flow and oxygenation.Assessment of CA is frequently used for experimental research and in the diagnosis, monitoring, or prognosis of cerebrovascular disease; however, despite the extensive use and reference to static CA, a valid quantification of "normal" CA has not been clearly identified. While controlling for the influence of arterial PCO 2 , we provide the first clear examination of static CA in healthy humans over a wide range of blood pressure. In 11 healthy humans, beat-to-beat blood pressure (radial arterial), middle cerebral artery blood velocity (MCAv; transcranial Doppler ultrasound), end-tidal PCO 2 , and cerebral oxygenation (near infrared spectroscopy) were recorded continuously during pharmacological-induced changes in mean blood pressure. In a randomized order, steady-state decreases and increases in mean blood pressure (8 to 14 levels; range: Ϸ40 to Ϸ125 mm Hg) were achieved using intravenous infusions of sodium nitroprusside or phenylephrine, respectively. MCAv mean was altered by 0.82Ϯ0.35% per millimeter of mercury change in mean blood pressure (R 2 ϭ0.82). Changes in cortical oxygenation index were inversely related to changes in mean blood pressure (slopeϭϪ0.18%/mm Hg; R 2 ϭ0.60) and MCAv mean (slopeϭϪ0.26%/cm ⅐ s Ϫ1; R 2 ϭ0.54). There was a progressive increase in MCAv pulsatility with hypotension. These findings indicate that cerebral blood flow closely follows pharmacological-induced changes in blood pressure in otherwise healthy humans. Thus, a finite slope of the plateau region does not necessarily imply a defective CA. Moreover, with progressive hypotension and hypertension there are differential changes in cerebral oxygenation and MCAv mean . (Hypertension. 2010;55:698-705.)

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“…2 Similarly, orthostatic intolerance after space flight also occurs more frequently in women. 3 However, in older populations, orthostatic hypotension-related hospitalization rates are higher in men than in women.…”

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confidence: 99%

Elderly Women Regulate Brain Blood Flow Better Than Men Do

Deegan

Sorond

Galica

et al. 2011

Stroke

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Background and Purpose-Orthostatic intolerance and falls differ between sexes and change with age. However, it remains unclear what role cerebral autoregulation may play in this response. This study was designed to determine whether cerebral autoregulation, assessed using transcranial Doppler ultrasound, is more effective in elderly females than in males. Methods-We used transcranial Doppler ultrasound to evaluate cerebral autoregulation in 544 (236 male) subjects older than age 70 years recruited as part of the MOBILIZE Boston study. The MOBILIZE Boston study is a prospective cohort study of a unique set of risk factors for falls in seniors in the Boston area. We assessed CO 2 reactivity and transfer function gain, phase, and coherence during 5 minutes of quiet sitting and autoregulatory index during sit-to-stand tests. Pϭ0.002) in the autoregulatory band, implying less effective cerebral autoregulation. However, reduced autoregulation in males was not below the normal range, indicating autoregulation was intact but less effective. Conclusions-Female subjects were better able to maintain cerebral flow velocities during postural changes and demonstrated better cerebral autoregulation. The mechanisms of sex-based differences in autoregulation remain unclear but may partially explain the higher rates of orthostatic hypotension-related hospitalizations in elderly men. (Stroke.

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Cerebral Autoregulation in Orthostatic Intolerance

Cited by 53 publications

References 61 publications

Alterations in cerebral autoregulation and cerebral blood flow velocity during acute hypoxia: rest and exercise

Alterations in cerebral autoregulation and cerebral blood flow velocity during acute hypoxia: rest and exercise

Influence of Changes in Blood Pressure on Cerebral Perfusion and Oxygenation

Elderly Women Regulate Brain Blood Flow Better Than Men Do

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