Influence of posture on middle cerebral artery mean flow velocity in humans

Savin, E.; Bailliart, O; Checoury, A; Bonnin, Philippe; Grossin, C.; Martineaud, J. P.

doi:10.1007/bf00854974

Cited by 15 publications

(12 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The drops in MBF ICA and MFV MCA across the entire sample was ϳ8% (ranging from 7% in OLD to 10% in uHTN). This decrease is consistent with previously reported measurements of MBF and MFV during upright posture in healthy adults, ranging from 4 to 14% (3,33,41,42). The consistency of these findings is in agreement with the notion that intact sCA does not connote constant CBF, but rather an attenuation of the impact of changes in blood pressure on cerebral perfusion.…”

Section: Discussionsupporting

confidence: 92%

Assessing cerebrovascular autoregulation from critical closing pressure and resistance area product during upright posture in aging and hypertension

Robertson

Edgell

Hughson

2014

American Journal of Physiology-Heart and Circulatory Physiology

View full text Add to dashboard Cite

Robertson AD, Edgell H, Hughson RL. Assessing cerebrovascular autoregulation from critical closing pressure and resistance area product during upright posture in aging and hypertension. Am J Physiol Heart Circ Physiol 307: H124 -H133, 2014. First published May 23, 2014 doi:10.1152/ajpheart.00086.2014.-Static cerebral autoregulation (sCA) is believed to be resistant to aging and hypertensive pathology. However, methods to characterize autoregulation commonly rely on beat-by-beat mean hemodynamic measures and do not consider within-beat pulse wave characteristics that are impacted by arterial stiffening. We examined the role of critical closing pressure (CrCP) and resistance area product (RAP), two measures derived from the pulse wave, across supine lying, sitting, and standing postures in young adults, normotensive older adults, and older adults with controlled and uncontrolled hypertension (N ϭ 80). Traditional measures of sCA, using both intracranial and extracranial methods, indicated similar efficiency across all groups, but within-beat measures suggested different mechanisms of regulation. At rest, RAP was increased in hypertension compared with young adults (P Ͻ 0.001), but CrCP was similar. In contrast, the drop in CrCP was the primary regulator of change in cerebrovascular resistance upon adopting an upright posture. Both CrCP and RAP demonstrated group-by-posture interaction effects (P Ͻ 0.05), with older hypertensive adults exhibiting a rise in RAP that was absent in other groups. The posturerelated swings in CrCP and RAP were related to changes in both the pulsatile and mean components of arterial pressure, independent of age, cardiac output, and carbon dioxide. Group-by-posture differences in pulse pressure were mediated in part by an attenuated heart rate response in older hypertensive adults (P ϭ 0.002). Examination of pulsatile measures in young, elderly, and hypertensive adults identified unique differences in how cerebral blood flow is regulated in upright posture. middle cerebral artery; carotid arteries; Doppler ultrasound; pulse pressure ORTHOSTATIC INTOLERANCE is a primary contributing factor to hospitalizations of older adults, with syncope being a prevalent trigger for admittance to emergency departments (46). Syncope and falls are often precipitated by symptoms of cerebral hypoperfusion, including dizziness and confusion (39). Even in young adults, cerebral blood flow (CBF) is lower when sitting or standing compared with lying supine (33, 41). Hence, a lower resting CBF, as observed in aging and hypertension (6), increases the risk for transient hypoperfusion in upright postures and emphasizes the need for effective cerebrovascular control. Cerebral autoregulation (CA) characterizes the efficiency in maintaining CBF despite changes in arterial blood pressure (ABP) (48) and is commonly assessed by the change in cerebrovascular resistance (CVR) for a given change in pressure (21,26,48). When considering CVR as the solitary regulator (i.e., CVR ϭ ABP/CBF), CA has proven to be a robust physio...

show abstract

Section: Discussionsupporting

confidence: 92%

Assessing cerebrovascular autoregulation from critical closing pressure and resistance area product during upright posture in aging and hypertension

Robertson

Edgell

Hughson

2014

American Journal of Physiology-Heart and Circulatory Physiology

View full text Add to dashboard Cite

show abstract

“…10 The aggregate choroidal vasculature (represented herein as CT) has not been shown to have an intrinsic ability to regulate thickness/blood flow during positional changes 11 ; however, there may be situations by which a not-yet-identified mechanism increases choroidal blood flow when an eye is in a lower or supine position. 10,22,23 These findings would be consistent with our hypothesis for the changes in CCET with positioning that we found in healthy individuals. In the presence of such a responsive or autoregulatory mechanism, a drop in perfusion and choroidal blood flow might be anticipated in the supine position; however, what is observed is an increase in choroidal blood flow, which is consistent with hydrostatic intravascular changes.…”

Section: Discussionsupporting

confidence: 92%

Comparison of Retinal and Choriocapillaris Thicknesses Following Sitting to Supine Transition in Healthy Individuals and Patients With Age-Related Macular Degeneration

et al. 2015

View full text Add to dashboard Cite

The effects of position on retinal and choroidal structure are absent from the literature yet may provide insights into disease states such as age-related macular degeneration (AMD).OBJECTIVE To evaluate the effect of postural change on retinal and choroidal structures in healthy volunteers and patients with non-neovascular AMD.DESIGN, SETTING, AND PARTICIPANTS Prospective observational case series at an academic tertiary care retina service from September 2013 to April 2014 involving 4 unaffected volunteers (8 eyes) and 7 patients (8 eyes) with intermediate AMD. Healthy volunteers selected for the study had no evidence of ocular disease. Patients with AMD were required to have at least 10 intermediate-sized drusen.EXPOSURES Spectral-domain optical coherence tomography with enhanced depth imaging in upright (sitting) and supine positions. Stable imaging was achieved using a rotating adjustable mechanical arm that we constructed to allow the optical coherence tomography transducer to rotate 90°. The Iowa Reference Algorithms were used to quantify choroid and choriocapillaris thicknesses. MAIN OUTCOMES AND MEASURESChanges in sitting and supine position central macular thickness (in micrometers), total macular volume (in cubic millimeters), choroidal thickness (in micrometers), and choriocapillaris-equivalent thickness (CCET, in micrometers).RESULTS Choriocapillaris-equivalent thickness was thinner in healthy participants (9.89 μm; range, 7.15-12.5 μm) compared with patients with intermediate AMD (16.73 μm; range, 10.31-27.38 μm) (P = .02); there was no difference in overall choroidal thickness between the 2 groups (P = .38). There was a 15% CCET reduction among healthy participants when transitioning from a sitting (9.89 μm) to supine (8.4 μm; range, 6.92-10.7 μm) position (P = .02) vs a CCET reduction of 11.1% from sitting (16.73 μm) to supine (14.88 μm; range, 8.76-20.8 μm) positioning (P = .10) in patients with intermediate AMD. CONCLUSIONS AND RELEVANCEIntermediate AMD appears to be associated with an increase in CCET and with a lack of positional responses that are observed in the CCET of normal eyes. Our results suggest that although outer portions of the choroid do not appear to be responsive to modest positional or hydrostatic pressure, the choriocapillaris capacity is, and this is measurable in vivo. Whether this physiologic deviation that occurs in AMD is related to atrophy, inflammation, or changes in autoregulatory factors or growth factors remains to be determined.

show abstract

“…The rightward shift of the glycemia curve in leg-up position indicates a slower counterregulatory response and slower recovery from hypoglycemia in this position. This may be related to differences in cerebral blood flow in different body positions (Savin et al, 1995). It may be speculated that in head-up test, compared to the leg-up position, was decreased blood flow.…”

Section: Discussionmentioning

confidence: 97%

Body Position and the Neuroendocrine Response to Insulin-induced Hypoglycemia in Healthy Subjects

Radikova¹,

Penesova²,

Ježová³

et al. 2003

Archives of Physiology and Biochemistry

View full text Add to dashboard Cite

Changes in body fluid distribution are known to influence neuroendocrine function. The aim of the present study was to test the hypothesis that changes in plasma volume affect the counterregulatory neuroendocrine response to hypoglycemia. The tests were performed in 12 subjects in two situations: 'head-up' (+60°head-up tilt standing for 30 min and hypoglycemia in sitting position afterwards) and 'leg-up' (leg-up position for 30 min and hypoglycemia in leg-up position afterwards) in a random order. Insulin-induced hypoglycemia was adjusted to 2.7 mmol/l for 15 min by glucose infusion. Plasma volume was greater by 2.2% (p < 0.001) in leg-up and lower by 9.6% (p < 0.001) in head-up position compared to the basal value in sitting position. Head-up position was associated with increases in ACTH, aldosterone, norepinephrine levels and plasma renin activity (p < 0.01). Leg-up position resulted in decreases in plasma growth hormone and epinephrine concentrations (p < 0.05). Except epinephrine, the neuroendocrine response to hypoglycemia, if any, was mild. Hypoglycemia failed to activate ACTH release after head-up position. Body fluid redistribution did not modify hormonal changes during insulin hypoglycemia. In conclusion, we suggest that body position and accompanying plasma volume changes do not appear to affect neuroendocrine and counterregulatory responses to moderate, short duration hypoglycemia in healthy subjects.

show abstract

Influence of posture on middle cerebral artery mean flow velocity in humans

Cited by 15 publications

References 22 publications

Assessing cerebrovascular autoregulation from critical closing pressure and resistance area product during upright posture in aging and hypertension

Assessing cerebrovascular autoregulation from critical closing pressure and resistance area product during upright posture in aging and hypertension

Comparison of Retinal and Choriocapillaris Thicknesses Following Sitting to Supine Transition in Healthy Individuals and Patients With Age-Related Macular Degeneration

Body Position and the Neuroendocrine Response to Insulin-induced Hypoglycemia in Healthy Subjects

Contact Info

Product

Resources

About