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HOBOE (Head-of-Bed Optimization of Elevation) Study: Association of Higher Angle With ReducedCerebral Blood Flow Velocity inAcute Ischemic Stroke

Abigail Jade Hunter, Suzanne J. Snodgrass, Debbie Quain, Mark W. Parsons,Christopher R. Levi

Background. Cerebral autoregulation can be impaired after ischemic stroke, with potential adverse effects on cerebral blood ow during early rehabilitation.

Objective. The objective of this study was to assess changes in cerebral bloodow velocity with orthostatic variation at 24 hours after stroke.

Design. This investigation was an observational study comparing mean ow veloc-ities (MFVs) at 30, 15, and 0 degrees of elevation of the head of the bed (HOB).

Methods. Eight participants underwent bilateral middle cerebral artery (MCA)transcranial Doppler monitoring during orthostatic variation at 24 hours after isch-emic stroke. Computed tomography angiography separated participants into recana-lized (artery completely reopened) and incompletely recanalized groups. Friedmantests were used to determine MFVs at the various HOB angles. Mann-Whitney U tests were used to compare the change in MFV (from 30 to 0) between groups andbetween hemispheres within groups.

Results. For stroke-affected MCAs in the incompletely recanalized group, MFVsdiffered at the various HOB angles (30: median MFV 51.5 cm/s, interquartile range[IQR] 33.0 to 103.8; 15: median MFV 55.5 cm/s, IQR 34.0 to 117.5; 0: medianMFV 85.0 cm/s, IQR 58.8 to 127.0); there were no signicant differences for other MCAs. For stroke-affected MCAs in the incompletely recanalized group, MFVsincreased with a change in the HOB angle from 30 degrees to 0 degrees by a medianof 26.0 cm/s (IQR 21.3 to 35.3); there were no signicant changes in the recanalizedgroup ( 3.5 cm/s, IQR 12.3 to 0.8). The changes in MFV with a change in theHOB angle from 30 degrees to 0 degrees differed between hemispheres in theincompletely recanalized group but not in the recanalized group.

Limitations. Generalizability was limited by sample size.

Conclusions. The incompletely recanalized group showed changes in MFVs at various HOB angles, suggesting that cerebral blood ow in this group may besensitive to orthostatic variation, whereas the recanalized group maintained stableblood ow velocities.

A.J. Hunter, BPhysio(Hons), StGeorge Hospital, Sydney, NewSouth Wales, Australia.

S.J. Snodgrass, BSc(PhysTher), ATC, MMedSc(Physio), PhD, Dis-cipline of Physiotherapy, School

of Health Sciences, University of Newcastle, Hunter Building, Cal-laghan, New South Wales, 2308

Australia. Address all correspon-dence to Dr Snodgrass at:[email protected].

D. Quain, BSN, Hunter StrokeService, John Hunter Hospital,Newcastle, New South Wales,

Australia.

M.W. Parsons, BMed, PhD,FRACP, Priority Research Centre

for Brain and Mental Health,Hunter Medical Research Insti-tute, University of Newcastle,Newcastle, New South Wales,

Australia.

C.R. Levi, BMedSc, MBBS, FRACP,RACP, Priority Research Centre for Brain and Mental Health, Hunter Medical Research Institute, Uni-versity of Newcastle.

[Hunter AJ, Snodgrass SJ, Quain D,et al. HOBOE (head-of-bed opti-mization of elevation) study:association of higher angle with

reduced cerebral blood owvelocity in acute ischemic stroke.Phys Ther. 2011;91:15031512.]

2011 American Physical Therapy Association

Published Ahead of Print: August25, 2011

Accepted: June 16, 2011Submitted: August 18, 2010

Research Report

Post a Rapid Response tothis article at:ptjournal.apta.org

October 2011 Volume 91 Number 10 Physical Therapy f 1503
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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A cute ischemic stroke adversely affects cerebral autoregula-tion, a homeostatic mecha-nism that maintains adequate cere-bral blood ow despite variations

in systemic blood pressure and cere-bral perfusion pressure. 16 Cerebralautoregulation ensures sufcientblood ow with changes in body position that affect blood pressure,such as lying, sitting, standing, or walking. 7,8 Orthostatic positionscloser to vertical present a greater challenge to this mechanism, partic-ularly when it is impaired after stroke. 5,9 Current physical therapy guidelines emphasize early rehabili-tation after ischemic stroke, includ-ing sitting, standing, and walking,to facilitate optimal functional recov-ery. 1012 The clinical implications of changes in blood ow velocities inresponse to such orthostatic varia-tions in the acute phase after isch-emic stroke remain unclear.

The mechanisms contributing tocerebral autoregulation are complex,and no direct measure of this mech-anism is currently available. Investi-

gations of the physiological effectsof orthostatic variation have usedmeasures of cerebral blood ow velocity to indirectly reect themaintenance of cerebral autoregula-tion. Transcranial Doppler (TCD)ultrasound is a valid measure of blood ow velocity in the major cerebral arteries and is an acceptedindex of cerebral autoregulation. 6,1316Transcranial Doppler ultrasound hasbeen used in several studies investi-

gating autoregulation.3,8,14,1719

How-ever, TCD studies of orthostaticblood ow changes in patients with stroke are limited. 20,21

Ischemic stroke typically is causedby occlusion of a cerebral blood ves-sel22 (commonly the middle cere-bral artery [MCA]). Obstructed bloodow, over time, results in the devel-opment of a necrotic infarct core sur-rounded by the ischemic penumbra,

an area of neural tissue with poten-tially reversible damage. Salvage of thepenumbra is the focus of treatment for acute stroke. The delivery of intrave-nous thrombolytic drugs to dissolve

clots and recanalize (reopen) blood vessels is now standard practice inthe medical management of acuteischemic stroke. 14,16,23,24 Although thrombolytic therapy is consideredthe best practice for achievingarterial recanalization, its successdepends on early delivery and many individual patient factors. Intrave-nous thrombolytic therapy hasbeen reported to achieve arterialrecanalization in 46% of appropriatepatients; in comparison, 24% of patients with acute ischemic strokeshow spontaneous recanalization without receiving active revascular-ization treatment. 25 Patients whosestroke-affected arteries are recana-lized often display rapid neurologicalimprovement and often progressreadily to rehabilitation and goodrecovery. To date, studies have notspecically investigated the physio-logical effects of orthostatic changesin patients showing early recanaliza-

tion, and the extent of any potentialimpairment in cerebral autoregulationis not clear.

One report 9 described the use of TCD ultrasound to measure theimpact of orthostatic changes onblood ow velocities in patients with acute ischemic stroke. Cerebral bloodow velocity increased when thehead of the bed (HOB) was loweredfrom 30 degrees to 0 degrees, indi-

cating an improvement in cerebralblood ow with the bed at. Thisincrease in blood ow velocity wasaccompanied by clinically observedneurological improvement. However,patients were excluded from thestudy if they showed recanalization,and measurements from the non-affected MCA were not obtained.Thus, it is unknown whether bloodow velocities respond differently to orthostatic changes in patients

who show recanalization or whether there are differences betweenhemispheres.

The primary aim of this study was to

describe changes in cerebral bloodow velocities in response to varia-tions in orthostatic positions at 24hours after ischemic stroke. Second-ary aims were to determine any dif-ferences in blood ow velocities with changes in positions betweenarteries that had recanalized andthose that had not and betweenstroke-affected and nonaffectedhemispheres. We hypothesized thatpatients whose arteries had notrecanalized would display greater changes in blood ow velocities with orthostatic variations thanpatients whose arteries had recana-lized and that the stroke-affectedhemisphere would similarly experi-ence greater changes in blood ow velocities than the nonaffected hemi-sphere. Establishing the impact of orthostatic changes for patients after ischemic stroke may contribute tomore effective care and rehabilita-tion for patients with acute stroke.

MethodParticipantsPatients referred to a tertiary carehospital from April to August 2009participated in this study; the samplesize was determined by the number of eligible patients presenting withinthe 5-month data collection timeframe. All patients had acute isch-emic stroke with a duration of lessthan 6 hours since symptom onset

and were considered for intrave-nous thrombolytic therapy. 26 Patientsenrolled in the study met the follow-ing criteria: 18 years of age or older,anterior circulation ischemia oncomputed tomography (CT) perfu-sion imaging, a National Institutes of Health Stroke Scale (NIHSS) score of 3 or greater, and a prestroke modi-ed Rankin Scale score of 3 or less.The NIHSS is a nonlinear ordinalscale with scores from 0 to 42 that

HOBOE Study: Bed Angle, Blood Flow, and Stroke

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provides a valid and reliable assess-ment of acute stroke-related de-cits. 27,28 A score of 3 or greater indi-cates a stroke of sufcient severity tobe considered for thrombolytic ther-

apy. The modied Rankin Scale provides a measure of functional disabil-ity and physical dependence 29 ; thescore was obtained from family inter- view upon a patients presentationto the hospital. A score of 3 or lessindicates no signicant preexistingdisability.

Patients were excluded from par-ticipation if CT imaging revealed pos-terior circulation or hemorrhagicstroke, if temporal bone windows were insufcient to enable ultra-sound penetration, or if they hadsubstantial comorbidities that werelife threatening or that limited their ability to lie at in bed. In addition,patients were excluded if they dis-played symptomatic orthopnea atthe time of TCD data collection,for example, secondary to chronicobstructive pulmonary disease,asthma, or congestive cardiac failure.Patients unable to tolerate the TCD

ultrasound procedure because of agi-tation were also excluded.

Written informed consent wasobtained from all patients familiesbefore recruitment into the study.Figure 1 shows the progression of participants through the study.

Computed tomography or magneticresonance angiography at 24 hoursafter stroke was used to determine

arterial recanalization status andgroup participants accordingly. Com- plete recanalization was dened asfull reopening of the affected artery and restoration of normal blood ow velocity (mean ow velocity [MFV]in a normal MCA is approximately 55 cm/s [SD 12] 30,31 ). Incompleterecanalization was dened as par-tial or complete MCA occlusion andincomplete restoration of blood ow velocity.

Study Design and ProtocolThis observational study followed arepeated-measures design. Thedependent variable was MCA bloodow velocity, measured by TCD

ultrasound. The manipulated inde-pendent variable was the angle of HOB elevation: 0, 15, and 30degrees.

Equipment. Blood ow velocities were measured by TCD ultrasoundexamination with a digital power-motion Doppler unit (PMD 100;Spencer Technologies, Seattle, Washington) and 2-MHz pulsed-wavediagnostic transducers at depths of 40 to 65 mm. A 10-mm area of insonation enabled optimal wave-form visualization. Bilateral transduc-ers were attached to the participant with a Marc 600 head frame (Spen-cer Technologies), positioned over the temporal bone windows, andangled to detect the optimal MCA signal. Blood ow velocities weremeasured at 5-mm increments alongthe MCA to detect the site of occlu-sion. The area of insonation then waspositioned in the mid-M1 MCA seg-

ment in participants with completerecanalization and at the point justproximal to the site of occlusion where blood ow was detected inparticipants with incomplete recan-alization. The head frame was ttedand all measurements were obtainedby the same experienced neuro-sonographer to maintain consistency throughout the procedure.

The angle of HOB elevation was stan-

dardized with a Plurimeter (Austral-asian Medical & Therapeutic Instru-ments, Albany Creek, Queensland, Australia), a liquid pendulum incli-nometer. The Plurimeter wasattached to the bed frame with Vel-cro (Velcro USA Inc, Manchester,New Hampshire) and calibratedagainst the horizontal position by one researcher before testing for each participant.

Procedure. A rapid-response stroketeam (a neurologist and a specialistnurse) examined the participantsand completed a thorough neurolog-ical assessment. Plain head CT was

used to exclude hemorrhagic strokeand was followed by CT perfusionimaging and angiography to deter-mine the extent of ischemia andthe site of occlusion. Thrombolytictherapy was administered subse-quent to specic criteria beingmet. 26,32 A specialist nurse qualiedin administering the NIHSS deter-mined a baseline NIHSS score duringthe initial neurological examinationand repeated the test after 24 hours.Computed tomography or magneticresonance angiography at 24 hoursafter stroke was used to determinerecanalization status and group par-ticipants accordingly. The TCD ultra-sound protocol then was used toinvestigate MCA blood ow veloci-ties at various HOB elevations.

The TCD ultrasound protocol wasinitiated at an HOB elevation angle of 30 degrees because the participantsroutinely rested in this position. The

participants hip joints were aligned with the hinge of the bed to ensureconsistency of body position whenthe HOB was lowered and raised. Anacclimatization period of 5 minutes with continuous TCD observationensured the stability of blood ow velocities in the participants, who were expected to have impairedautoregulation because of stroke;autoregulation typically respondsrapidly to positional changes in peo-

ple who are healthy.1,21

Early reha-bilitation includes prolonged periodsof upright positions, such as sittingand standing; hence, monitoring thestabilization of cerebral blood ow in these positions was important. Theacclimatization period was followedby 1 minute of data recording. Next,the HOB was lowered to 15 degrees;this step was followed by a 5-minuteacclimatization period and then 1minute of data recording. This pro-




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Consecutive patients with stroke=35

Enrolled in study=8Inclusion criteria:

CT: MCA circulation ischemiaNIHSS score 3Modied Rankin Scale score 3Written consent from family member

24 hours

Thrombolytic therapycommenced for appropriate

patients=5

Thrombolytic therapy not commenced=3

Patients did not meet standard criteria toqualify for thrombolytic therapy*

MR angiography

Recanalized=4 Incompletely recanalized=4

TCD protocol30 HOB15 HOB0 HOB

Excluded=27

Reasons for exclusion:No MCA territory on CT imaging=7Insufficient temporal bone windows for TCD=5Unable to tolerate position changes due to:

orthopnea=4 agitation=2 critically unwell=2

Unable to complete TCD protocol due to: death or discharge from hospital=3 CT angiography not performed=1 neurosonographer unable to attend=2 patient declining participation=1

Figure 1.Flow diagram showing the progression of participants through the study. CT computed tomography, HOB head of bed elevation,MCA middle cerebral artery, MR magnetic resonance, NIHSS National Institutes of Health Stroke Scale, TCD transcranialDoppler ultrasound. *Eligibility for thrombolytic therapy was described by Quain et al. 26




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cess was repeated at an angle of HOBelevation of 0 degrees (bed at). Thisprotocol provided 1 minute of con-tinuous data for analysis per HOBangle per participant.

The safety of the participants wasensured by beginning the protocol atthe normal resting HOB elevation(30) and progressively loweringthe bed to the horizontal position.Blood ow velocity was expected tobe greater in the horizontal positionthan at higher angles of HOB eleva-tion in participants in the acutephase after ischemic stroke 9 ; there-fore, the horizontal position poten-tially posed less risk of ischemic dam-age than the participants normalresting position.

Outcome MeasuresTranscranial Doppler ultrasoundproduced a 1-minute recording of ow velocity waveforms. The MFV was determined for each waveform,and the values were then averagedover the 1-minute recording periodafter acclimatization at each HOBangle. The MCA MFV was the pri-

mary outcome measure used to com-pare differences between HOBangles. The change in MFV (from30 to 0) was used to compare dif-ferences between affected and non-affected MCAs both within andbetween the recanalized and incom-pletely recanalized groups.

To ensure participant safety, a pulsa-tility index (a TCD measure of resis-tance to ow) was monitored

throughout the procedure. A high pulsatility index reects elevatedresistance to ow and may be indic-ative of increased intracranial pres-sure. 33 However, complications of increased intracranial pressure werenot expected within the rst 24hours because increased intracranialpressure usually peaks at 48 hoursafter ischemic stroke or later. 20,34,35To further monitor participantsafety, mean arterial pressure, heart

rate, and blood oxygen saturation(Spacelabs Healthcare telemetry,model 90369; Spacelabs Healthcare,Issaquah, Washington) were concur-rently measured during data collec-

tion to identify any physiologicalchanges with manipulation of theHOB angle.

Data Analysis Analysis of TCD waveforms was per-formed by reviewing the continuousTCD data les (Fig. 2). The les wereassessed at a time and a location sep-arate from those for participant datacollection by an experienced neuro-sonographer and a neurologist, andthe MFVs from each assessor wereaveraged to obtain a single value that was used in further analysis. Both assessors were unaware of partici-pants identication, diagnosis, andCT images to ensure unbiased andaccurate interpretation of wave-forms. The MFV was calculated for each waveform over the 1-minuterecording period. Friedman tests were used to compare MFVs at the3 HOB angles for affected and non-affected MCAs in the incompletely

recanalized and recanalized groups,and Wilcoxon signed rank tests were used to determine differencesbetween pairs of HOB angles. Mann- Whitney U tests were used to com-pare changes in MFVs (from those at30 to those at 0) between groupsand between affected and nonaf-fected sides within groups. Statisticalanalyses were performed with PASW Statistics 18.0 (SPSS Inc, Chicago,Illinois).

Role of the Funding SourceNo funding was required for thisresearch, and there are no nancialconicts of interest.

ResultsOf 35 patients who were screenedfor inclusion, 8 patients (5 womenand 3 men; median age 66 years;interquartile range [IQR] 47.0 to74.5 years) were enrolled in the

study (Fig. 1). Five participants (4 women and 1 man) received throm-bolytic therapy after being selectedas eligible for this therapy accord-ing to current clinical guidelines. 26

Angiography at 24 hours after strokedetermined that 4 participantsshowed complete recanalization of the affected artery (recanalized group)and that 4 participants showedpartial recanalization (incompletely recanalized group). No participantsshowed persistent complete occlu-sion at 24 hours. Participant demo-graphics and NIHSS scores areshown in Table 1.

Blood Flow VelocitiesThe MFVs for individual participantsare shown in Table 2. The stroke-affected MCA in the incompletely recanalized group was the only artery to demonstrate a signicantdifference in MFVs at various HOBangles (30: median MFV 51.5 cm/s,IQR 33.0 to 103.8; 15: medianMFV 55.5 cm/s, IQR 34.0 to117.5; 0: median MFV 85.0 cm/s,IQR 58.8 to 127.0) ( P .039). There were no signicant differences for

nonaffected MCAs, for the stroke-affected MCA in the recanalizedgroup, or between pairs of HOBangles for any group or hemisphere.

Figure 3 shows the observed changein the MFV (from that at 30 of HOBelevation to that at 0 of HOB eleva-tion) for the stroke-affected MCA inthe incompletely recanalized group.For the stroke-affected MCA in theincompletely recanalized group,

there was a median increase in theMFV (from that at 30 of HOB eleva-tion to that at 0 of HOB elevation)of 26.0 cm/s (IQR 21.3 to 35.3), whereas in the recanalized group,there was no observable change(median difference 3.5 cm/s,IQR 12.3 to 0.8) ( P value for between-group difference for MFV change .021). The MFVs in thenonaffected MCAs in both groupsalso did not change signicantly




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Figure 2.Sample blood ow velocities in affected and nonaffected middle cerebral arteries (MCAs) at 30 and 0 degrees of elevation of the headof thebed (HOB) in a participant in the recanalized group anda participant in the incompletely recanalized group.Blood ow velocityin the affected MCA in the participant in the incompletely recanalized group was greater at 0 degrees than at 30 degrees, whereasin the nonaffected MCA, ow remained relatively unchanged.




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(median difference in MFV between30 and 0 of HOB elevation in theincompletely recanalized group 4.0 cm/s, IQR 9.0 to 4.0;

median difference in the recanalizedgroup 1.3, IQR 3.9 to 1.8)( P value for between-group differ-ence for median MFV change .564).The difference between affectedand nonaffected hemispheres in thechange in MFV (from 30 of HOBelevation to 0) was signicant for the incompletely recanalized group( P .020) but not for the recanalizedgroup ( P .309).

SafetyNo adverse events occurred duringtesting. There were no marked dif-ferences in the pulsatility index at

the 3 HOB angles. Median mean arte-rial pressures (all participants) were98.5 mm Hg (IQR 90 to 108.5),97.5 mm Hg (IQR 90.5 to 105), and95.5 mm Hg (IQR 87.5 to 103.5) atHOB angles of 30, 15, and 0 degrees,respectively. In addition, no clini-cally signicant changes in heartrate or blood oxygen saturation wereobserved.

DiscussionThe main nding of the presentstudy was that MFVs in stroke-affected MCAs with incomplete

recanalization increased as the HOB was lowered from 30 degrees to0 degrees. No statistically signicantchanges were observed in nonaf-fected MCAs or MCAs with completerecanalization. The lack of a signi-cant orthostatic variation in bloodow velocity after CT angiographicevidence of recanalization suggestsintact autoregulation in the territory of the affected MCA. The lower

Table 1.Participant Demographics at Baseline and 24-Hour Follow-up a

ParticipantAge(y) Sex

Recanalizedat 24 h

ThrombolyticTherapy

Affected MiddleCerebral Artery

BaselineNIHSS Score

24-h NIHSSScore

Change inNIHSS Score

1 31 F No Yes Right 15 17 2


3 78 F No Yes Left 11 3 8


5 45 M Yes No Left 4 1 3

6 64 M Yes No Left 10 9 1

7 74 F Yes No Left 3 2 1

8 75 M Yes Yes Left 13 1 12

a Baseline at presentation to hospital within 6 hours of symptom onset. NIHSS National Institutes of Health Stroke Scale.

Table 2. Average Values a for Stroke-Affected and Nonaffected Middle Cerebral Arteries by Angle of Elevation of the Head of the Bed(HOB) and Recanalization Status at 24 Hours After Stroke

Parameter

Stroke Statusof Middle

Cerebral Artery

Mean Flow Velocity (cm/s) in Participants Showing:

Incomplete Recanalization at 24 h Complete Recanalization at 24 h

1 2 3 4 5 6 7 8

30 HOB elevation Affected by stroke 67 116 32 36 50 32 30 45

Not affected 76 91 54 45 46 43 34 35


Not affected 70 88 51 42 49 45 29 29


Not affected 66 89 60 38 48 44 30 32

Change from 30 to 0HOB elevation Affected by stroke 30 21 22 37

7 1 0

14Not affected 10 2 6 6 2 1 4 4

% change from 30 to0 HOB elevation

Affected by stroke 45 18 69 104 14 3 0 32

Not affected 13 2 11 14 4 2 12 10

a Over a 1-minute acquisition period.




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blood ow velocity with HOB eleva-tion in participants who did notshow CT angiographic evidence of recanalization raises the possibility that, in this situation, the affected

MCA territory may have had adecreased capacity to autoregulateand adapt to orthostatic stress. Theimplications for rehabilitation arethat the early use of upright posturesmay place greater orthostatic stresson circulating blood volumes inparticipants who show evidence of incomplete recanalization. The nd-ings suggest that implementing aroutine CT examination at 24 hoursafter stroke may improve clinical

decision making during early rehabilitation.

Interestingly, in our sample, 3 of the4 participants who showed completearterial recanalization did not receivethrombolytic therapy, whereas all par-ticipants in the incompletely recana-lized group retained partial arterialocclusion despite the administrationof thrombolytic therapy. Although these results are contrary to expec-

tations for thrombolytic therapy,our small sample suggests that they may not be inconsistent with docu-mented outcomes for this therapy in the literature. 25 The lack of recan-

alization in participants receivingthrombolytic therapy in the presentstudy probably reects individualresponses to treatment in our smallsample and does not represent a lim-itation to the external validity of thepresent study.

Comparisons With PreviousResearchFew studies have investigated theeffects of changing orthostatic posi-

tions on cerebral blood ow veloci-ties in acute ischemic stroke. Tworeports 9,21 documented the investi-gation of TCD ultrasoundmeasuredMFVs with variations in the angle of the HOB of 0 to 30 degrees. Both studies identied a greater MFV inthe stroke-affected MCA at 0 degreesof HOB elevation than at 30 degreesof HOB elevation, although impor-tant differences in patient selec-tion and study design limit compari-

sons with the present study. Oneof these studies, by Wojner- Alexandrov et al, 9 excluded patients who showed recanalization. This fac-tor limits the generalizability of their

ndings, particularly with regard tofuture populations, because con-tinued improvements in the efcacy of thrombolytic therapy are likely toincrease rates of arterial recanaliza-tion. In the other study, Schwarz etal21 used bilateral TCD ultrasoundmeasurements and identied a sig-nicant difference in blood ow velocities between affected and non-affected hemispheres but no signi-cant change in the nonaffected MCA.The ndings for the incompletely recanalized group in the presentstudy agree with the results of Schwarz et al, 21 suggesting that cere-bral perfusion may be impaired pre-dominantly in the stroke-affectedhemisphere. However, Schwarz etal21 did not categorize patientsaccording to arterial recanalization, afactor that limits comparisons with the present study. Interestingly, inthe present study, we identied nosignicant changes in MFVs with

orthostatic variations in either hemi-sphere in participants who showedcomplete recanalization, suggestinggreater stability of blood ow inthese participants.

Physiological RationaleIn the present study, we identiedlarge increases in MFVs in partici-pants with incompletely recanalizedarteries when the HOB was loweredto horizontal. This result suggests

that the vasodilatory responses nec-essary to maintain constant cerebralblood ow in body positions approx-imating horizontal were impairedin these participants. The clinicalimpact of MFVs that are greater thannormative values is uncertain.Increased MFVs beyond 48 hoursafter stroke onset are associated with hyperperfusion injury and hemor-rhagic transformation, whereashyperperfusion in the rst 48 hours

Figure 3.Box plots illustrating differences between affected and nonaffected middle cerebralarteries (MCAs) by group (recanalized or incompletely recanalized) in changes in meanblood ow velocities when the head of the bed was lowered from 30 degrees to 0degrees at 24 hours after ischemic stroke.




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appears to be associated with neuro-logical improvement withoutincreased risk of hemorrhage. 36 Fur-thermore, increased MFVs with thebed in the at position were previ-

ously associated with clinically sig-nicant neurological improvementin 3 of 20 patients who did not show recanalization. 9 Previous studies sug-gested that adopting a resting posi-tion of 0 degrees of HOB elevationmay be benecial for patients whodo not show recanalization, 9 as longas the intracranial pressure remainsstable. 21 In contrast, the effect oncerebral blood ow of raising theHOB above 30 degrees has not yetbeen studied. However, the associa-tion between body positions andMFVs in the acute phase after isch-emic stroke in patients whose arter-ies remain occluded supports thebiological rationale that orthostaticpositions closer to vertical may pres-ent a potential risk of cerebral hypo-perfusion. The clinical impact of large decreases in blood ow veloc-ity in patients with acute stroke isunknown. One report 37 documentedthat a decrease in blood ow velocity

of greater than 70% during carotidclamping for endarterectomy waspredictive of adverse clinical events,although other studies 38,39 identieddecrements of 85% occurring with-out clinical consequences.

Implications for RehabilitationPhysical therapy guidelines currently advocate early rehabilitation after ischemic stroke to facilitate the opti-mal recovery of physical func-

tion.10,11

However, the most appro-priate point at which to beginrehabilitation is not specied. Typi-cally, patients in the acute strokeunit where the present study wasconducted begin rehabilitation,including sitting, standing, and walk-ing, 4 or 5 days after stroke. Other authors 12 investigated the effects of very early rehabilitation, commenc-ing within 24 hours after stroke.Phase II of the AVERT (Very Early

Rehabilitation Trial for Stroke)study 40 identied similar numbersof deaths and levels of disability at 3,6, and 12 months of follow-up ingroups receiving either very early

rehabilitation (getting patients outof bed within the rst 24 hours) or standard care. However, the impactof rehabilitation on blood ow veloc-ities during this acute phase isuncertain.

In the present study, participants who showed recanalization early after stroke maintained greater stabil-ity of blood ow velocities duringorthostatic changes at low angles of HOB elevation than participants whoshowed incomplete recanalization.Participants who showed recanaliza-tion may have retained blood ow stability in orthostatic positionscloser to vertical. Conversely, in par-ticipants whose recanalization wasincomplete, blood ow velocities were sensitive to orthostatic changes,even at low angles of HOB elevation.Therefore, these participants may have been more vulnerable to cere-bral hypoperfusion in orthostatic

positions closer to vertical.Follow-up angiography to determinearterial recanalization after stroke isnot currently part of routine clinicalpractice. However, the apparentimpact that arterial recanalizationhas on blood ow responses toorthostatic changes suggests a poten-tial for imaging services to play agreater role in informing clinicaldecisions pertinent to rehabilitationin the future.

LimitationsThe sample size in the present study was small and limited the power of statistical calculations. Furthermore,1 participant in the incompletely recanalized group (participant 2,Tab. 2) displayed signicantly greater MFVs in the stroke-affectedhemisphere than did the other participants. The implications of increased MFVs are uncertain. Previ-

ous studies indicated the associationof positive neurological outcomes with increased MFVs with the bed inthe at position. 9 However, poten-tially detrimental effects of increased

MFVs in patients with impairedcerebral autoregulation cannot beexcluded. Thus, the inclusion of par-ticipant 2 in the present study meansthat the conclusions should be inter-preted with caution.

Another limitation of the presentstudy was the exclusion of patients who were unable to tolerate horizon-tal positioning because of symptom-atic orthopnea. This factor may limitthe generalizability of the ndings,but it was necessary to ensure thesafety of the participants. Addition-ally, TCD ultrasound may introducesome error because the measure-ments are operator dependent. How-ever, TCD ultrasound is widely accepted as a safe and reliable non-invasive technique for measuringcerebral blood ow velocity. Consis-tency and accuracy in the presentstudy were ensured by the use of oneexperienced neurosonographer.

Conclusion and FutureDirectionsIn the present study, when the HOB was lowered to horizontal, bloodow velocities in affected MCAs thathad not completely recanalizedincreased; there were no statistically signicant changes in arteries thathad completely recanalized. Partici-pants who showed complete recan-alization appeared to demonstrate

greater stability of blood ow veloc-ities, a result that may have beenrepresentative of a normalization of cerebral autoregulation. Participants who did not show complete recana-lization, however, displayed signi-cant changes in blood ow velocities with manipulation of the HOBbetween 0 and 30 degrees. Futurestudies with larger sample sizes areindicated to validate the ndings of the present study as well as to exam-




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ine the physiological effects and clin-ical implications of orthostatic posi-tions closer to vertical in the acutephase after ischemic stroke.

All authors provided concept/idea/researchdesign and consultation (including review of manuscript before submission). Ms Hunter and Dr Snodgrass provided writing. MsQuain and Dr Parsons provided data collec-tion. Ms Hunter, Dr Snodgrass, and Dr Par-sons provided data analysis. Dr Parsons pro-vided project management and institutionalliaisons. Dr Parsons and Dr Levi providedparticipants and facilities/equipment.

Approval for this study was granted by theHunter New England Area Health ServiceHuman Research Ethics Committee (ref:03/09/10/3.07).

An abstract presentation of this study wasgiven at Stroke 2011: the 22nd Annual Sci-entic Meeting of the Stroke Society of Aus-tralasia; September 14, 2011; Adelaide,South Australia, Australia.

DOI: 10.2522/ptj.20100271

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