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(Stroke. 1998;29:1305-1310.)
© 1998 American Heart Association, Inc.

Original Contributions

Bilateral Hemispheric Activation in the Early Recovery of Motor Function After Stroke

Mauro Silvestrini, MD; Letizia M. Cupini, MD; Fabio Placidi, MD; Marina Diomedi, MD; Giorgio Bernardi, MD

From the Clinic of Neurology (M.S., L.M.C., F.P., M.D., G.B.), "Tor Vergata" University of Rome, and IRCCS "S. Lucia" (M.S., G.B.), Rome, Italy.

Correspondence to Mauro Silvestrini, MD, Clinica Neurologica-Ospedale S Eugenio, Universitá di Roma "Tor Vergata," P.le dell'Umanesimo 10, 00144 Roma, Italy.

	Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Background and Purpose—Functional recovery after cerebral infarction is a complex phenomenon that depends on various factors. The aim of this study was to investigate changes in cerebral perfusion during motor activity in stroke patients with very early recovery of motor function.

Methods—We included 9 consecutive patients hospitalized for acute-onset hemiparesis who showed complete functional recovery within 24 hours. CT of the brain showed an ischemic or hemorrhagic cerebral lesion in areas compatible with the symptomatology. Within 36 hours (range, 28 to 36) all patients were examined for the effects of a thumb-to-finger opposition task on cerebral blood flow in the middle cerebral arteries, evaluated by means of bilateral transcranial Doppler ultrasonography. Data were compared with those of 9 healthy subjects matched for age and sex. In patients, the evaluation was repeated 2 to 4 months later.

Results—A comparable increase in flow velocity (% mean±SD) was observed with respect to baseline in the contralateral middle cerebral artery during motor activity with patients' normal (8.8±2.0%) and recovered hand (9.7±4.1%) and with both hands of control subjects (10.6±1.4%). In the middle cerebral artery ipsilateral to the hand performing the motor task, the increase in flow velocity was significantly higher (P<0.0001) during movement of the recovered hand in patients (8.6±2.7%) than during movement of the normal hand in both patients (2.6±1.6%) and control subjects (1.4±0.7%). In patients, pattern of changes in flow velocity during motor performance remained the same in the second evaluation.

Conclusions—These observations suggest that areas of the healthy hemisphere can be activated soon after a focal injury and contribute to the positive evolution of a functional deficit in some patients. This phenomenon of ipsilateral activation cannot be considered transient because it is evident months after stroke onset.

Key Words: motor function • recovery • stroke • ultrasonography, Doppler, transcranial

	Introduction

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Plastic functional changes in the brain play a role in recovery after cerebral injuries.¹ In recent years, activation of areas of the hemisphere contralateral to the lesion has received increasing attention. Studies with emission tomography techniques,^{2 3 4} with transcranial Doppler,⁵ and with neurophysiological investigation of motor pathways^{6 7} have shown the involvement of the healthy hemisphere in control of some neurological functions physiologically linked to the injured hemisphere. This recovery mechanism has been described months after cerebral injury, and some observations suggest that brain plasticity is more effective when the brain is damaged early in life.⁸

The aim of this study was to evaluate, by means of transcranial Doppler ultrasonography (TCD), the effect of a motor task on cerebral hemodynamics in patients who had very early motor recovery after stroke. We used bilateral TCD to simultaneously assess flow velocity changes in the right and left hemispheres.

	Subjects and Methods

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We considered all consecutive patients admitted to our ward between January 1996 and July 1997 for acute-onset hemiparesis that was fully reversible within 24 hours and in which brain CT scans performed within 36 hours after the onset of symptoms and repeated after 20 to 30 days showed signs of a single vascular lesion compatible with the previous neurological deficit. Lesion volume, calculated in milliliters (centimeter lengthxdepthxheight), ranged from 9.6 to 15.3. Exclusion criteria were multiple lesions, a history of previous neurological deficit and lacunar infarction, and significant stenosis or occlusion in extracranial vessels as demonstrated by color-coded Duplex scan. Nine patients (7 men, 2 women) were included in the study. They were submitted to a study of the effect of a sequential thumb-to-finger opposition test (alternatively performed with the normal and with the previously hemiparetic hand at a rate of 3 oppositions every 2 seconds) on flow velocity in the middle cerebral arteries (MCAs). Mean flow velocity (MFV) of right and left MCAs was continuously and simultaneously monitored by means of a Multi-Dop X/TCD 7 instrument (DWL Elektronische Systeme GmbH). Two dual 2-MHz transducers fitted on a headband and placed on the temporal bone window were used to obtain a bilateral continuous measurement. The highest signal was sought at a depth ranging from 46 to 52 mm. This unit allows for continuous-wave Doppler recording of the intracranial artery with on-line calculation of mean flow velocity in centimeters per second. Moreover, it is possible to save the Doppler spectra during the entire period of each study and then to calculate the MFV of any test period (rest phase and activation phase). In all subjects, recordings were made during a 2-minute rest phase and during a 2-minute motor task. Data were compared with those of 9 healthy subjects matched for age and sex. All study subjects were right-handed.⁹ Half of the patients performed the task with the hand of the recovered side first and half with the hand of the asymptomatic side first. Half of the control subjects began the task with the right hand and half with the left hand. Before the second recording, return to flow velocity baseline values was documented. Before proceeding to the study protocol, a normal direction of flow in the large intracranial arteries and their patency was evaluated by a complete TCD investigation including compression tests. Moreover, to exclude the possible presence of alterations in vasomotility, after fixing the transducers on the headband and obtaining a stable signal from the MCAs, patients were submitted to a breath-holding test.¹⁰ This consisted of recording the percentage change of mean flow velocity with respect to baseline values after 25 to 30 seconds of breath-holding after a normal inspiration. All patients showed normal intracranial flow in the large arterial vessels and a symmetric increase of flow velocity in the MCAs after breath-holding. This increase ranged from 24% to 38% without significant differences between lesion side and contralateral side. TCD investigations were performed by the same two operators, who were unaware of the clinical status of the study subjects. To check the possible effects of changing PCO₂ on vessel diameter, end-tidal CO₂ was monitored during the study by means of a CO₂ analyzer (Normocap-oxy, Datex). Mean blood pressure (MBP) and heart rate (HR) were continuously monitored by means of a blood pressure monitor (2300 Finapress Ohmeda). The study was approved by the local ethics committee, and all subjects gave informed consent to participate.

To evaluate whether the pattern of hemodynamic changes observed during motor activation could be considered a transient or a stable phenomenon, patients were submitted to the same investigation protocol with TCD 2 to 4 months after the first investigation.

The mean values of MFV during the rest phase and during motor activity were computed. Because there was considerable interindividual variability in basal MFV, we considered the percentage of change from rest to motor task as data for analysis.

Data were analyzed by means of a two-way analysis of variance with group (control subjects; patients, recovered hand; patients, normal hand) as the between factor and side of recording (contralateral and ipsilateral MCA with respect to the hand performing the motor task) as the within factor. Post hoc comparisons were performed by means of Scheffé's test. Because no difference was detected between right and left MCA flow velocity changes in healthy control subjects, ipsilateral and contralateral values were derived from the average of right and left MCA values. To compare patients' MFV changes in the first and second evaluation, a 3-way analysis of variance was performed with group (patients, recovered hand; patients, normal hand) as the between factor and time of recording (first, second evaluation) and side of recording (contralateral and ipsilateral MCA with respect to the hand performing the motor task) as the within factors.

Finally, to evaluate the possible influence of size and location of cerebral lesion on pattern of recovery, we selected all patients hospitalized during the same period with cerebrovascular lesions comparable in location and size to those of the patients included in our study. The clinical evolution of these patients was established by considering their scores on the Canadian Neurological Scale (CNS) performed every day for the first week after stroke and then at day 15 and day 30. The results of this kind of evaluation were not the primary findings of our study; they were only intended to rule out the possibility that the favorable and very early evolution of the motor deficit observed in a group of stroke patients was linked to the characteristics of their anatomic lesion. For this reason we limited ourselves to providing a brief description of these data in the "Results" section without performing any particular statistical analysis.

	Results

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Clinical presentation and patients' neuroradiological findings are reported in Table 1. End-tidal CO₂, HR, and MBP values in basal condition and after the 2-minute motor task in patients and control subjects are reported in Table 2. None of the basal values of these variables were significantly different. HR and MBP increased slightly during task performance. These changes were comparable in control subjects and in patients, regardless of the hand performing the movement. End-tidal CO₂ did not show significant changes from baseline to task performance. Basal mean values of MFV were not significantly different in patients: 58.5±12 cm/s for the lesioned side, 56.0±10 cm/s for the unlesioned side and control subjects: 56.5±10 cm/s for the left side, 54.5±15 cm/s for the right side.

View this table: [in this window] [in a new window]   Table 1. Clinical and Anatomic Features of Stroke Patients With Early Recovery of Motor Function

View this table: [in this window] [in a new window]   Table 2. Basal Mean Blood Pressure, Heart Rate, and End-Tidal CO2 Values During Rest Phase and During Execution of Motor Task in Control Subjects and in Patients

The Figure shows the percentage changes of MFV in the MCA ipsilateral and contralateral to the hand performing the motor task. Regarding the comparison between control subjects and patients at the first examination, the group effect was significant (F=10.0; P<0.001, df=2,24). A post hoc comparison revealed that the MFV increase, considering both contralateral and ipsilateral MCA, was significantly greater (P<0.01) during movement of the recovered hand in patients (9.2%) than during movement of the normal hand in either patients (5.7%) or control subjects (6.0%). The side of recording effect was also significant (F=83.7; P<0.0001, df=1,24). In this case, the effect was caused by the fact that considering all subjects, the increase of MFV during the motor task was significantly higher (P<0.0001) in the contralateral (9.7%) than in the ipsilateral (4.2%) MCA. Finally, the groupxside of the recording interaction was significant (F=15.5; P<0.0001, df=2,24). In fact, as shown in the Figure, a significant increase in MFV in the ipsilateral MCA was detected only in patients during the movement of the recovered hand. The post hoc comparison revealed that in the MCA ipsilateral to the hand performing the motor task, the increase in MFV was significantly greater during movement of the recovered hand in patients than during movement of the normal hand in patients and control subjects (P<0.0001).

View larger version (54K): [in this window] [in a new window]   Figure 1. Percentage of mean flow velocity (MFV) changes during performance of a 2-minute thumb-to-finger opposition in the ipsilateral and contralateral middle cerebral artery (MCA) of control subjects and patients. In control subjects, the effects of movement of the right and left hand are considered together; in patients the effects of movement of the normal and recovered hand are separated. In patients, the evaluation was performed early after stroke onset (T1) and 2 to 4 months after (T2). During movement of the normal hand, a nearly selective increase of MFV in the contralateral MCA occurred in both control subjects and patients. When the recovered hand was engaged in the motor task, a bilateral increase of MFV occurred in patients. No significant difference in MFV changes was detected in patients between T1 and T2.

When comparing the first and second examinations in patients, the time effect was not significant. In fact, as shown in the Figure, the percentage changes of MFV observed in patients at the second evaluation were very similar to those observed at the first one during movement of both the normal and the recovered hand.

During the study period, 18 patients were hospitalized with TCD findings similar to those observed in our study subjects. The neuroradiological characteristics and clinical findings of these patients are shown in Table 3. On the basis of the CNS score performed at different time intervals, 6 patients had very slight or no improvement 1 month after stroke, and 12 had complete or nearly complete recovery after the same period. In this case, the favorable clinical evolution became evident at least 15 days after onset of symptoms.

View this table: [in this window] [in a new window]   Table 3. Neuroradiological and Canadian Neurological Scale Score at Different Time Intervals in Patients With Stable Deficit or Late Recovery

	Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

 
We described some patients with cerebral ischemic or hemorrhagic lesions showing a transient neurological deficit with full recovery within 24 hours from the onset of symptoms. This is an unusual clinical course in this kind of patient in whom functional improvement, if it occurs, may require days or months to reach definitive levels. In this respect, we verified that the clinical evolution in these patients could not be simply ascribed to particular characteristics in location and size of cerebral lesion. In fact, we compared the outcome of our patients with that of patients hospitalized in the same period with identical volume and location of ischemic or hemorrhagic cerebral lesion and showed that the clinical evolution in subjects with vascular subcortical lesion with a volume ranging from 9 to 15.5 mL can cover all the possibilities from no significant recovery to complete recovery of function. Our investigation showed that in the patients selected for an early complete functional recovery of motor function, the favorable clinical evolution is associated with a simultaneous and symmetrical increase of flow velocity in both MCAs during motor performance involving the recovered hand. It should be mentioned that if vessel diameter and its perfusion area do not change during measurement, changes in flow velocity in the cerebral arteries are related to the caliber of the microcirculation bed.¹¹ The latter is in turn related to the metabolic level of the corresponding cerebral area. This means that an increase in cerebral activity and then of metabolism would lead to arteriocapillary dilatation and then to an increase in flow velocity in the cerebral artery supporting this area.^{12 13} For this reason, our results can be interpreted as the sign of a bilateral increase in cerebral activity during motor performance of a previously hemiparetic hand. This conclusion is supported by the concept that changes in flow velocity detected by TCD are reliable indicators of rapid flow changes, and then of activity, in the area supplied by the large intracerebral arteries.¹⁴ Moreover, the technique is able to discriminate the differential activation of the two hemispheres.^{15 16 17} This is also confirmed by the fact that in our study the movement of the normal hand in both control subjects and patients was associated with a selective increase in flow velocity in the contralateral MCA. The observed changes in flow velocity during the motor performance cannot be reasonably attributed to possible confounding factors such as alteration of vascular motility or presence of intracranial stenosis or occlusion with consequent activation of collateral pathways. In fact, in all the study patients, an accurate TCD investigation was performed to exclude abnormalities in intracranial arterial flow. In particular, the presence of a normal symmetric cerebrovascular reactivity to hypercapnia induced by a period of apnea demonstrated the absence of vasoparalysis or other phenomena able to influence the response of the vascular system to changes in cerebral activation.

Our finding of bilateral increase in flow velocity in the MCAs during the movement of the recovered hand supports the hypothesis that in the patients in this study, recovery of motor function was, at least in part, due to the activity of homolateral structures. This observation obviously does not prove that the rapid, favorable clinical course of the patients was due to a preexisting anatomic or functional situation of motor control. However, the very early functional recovery, despite the presence of a cerebral anatomic lesion, suggests that in these cases the reorganization mechanism and, in particular, the possibility of areas contralateral to the lesion assuming control of motor function of the homolateral limb was predisposed to sudden development. In this respect, studies investigating changes of cerebral blood flow and metabolism of motor cortices during the execution of motor tasks in normal subjects have led to conflicting results. A selective contralateral activation,¹⁸ a trend for bilateral activation in only some subjects,¹⁹ and a significant bilateral activation²⁰ have all been described. This fact suggests that the degree of lateralization of the motor system may be different in normal subjects. In patients, previous evidence of bilateral control of motor function by one corticospinal system refers to a chronic situation in which functional recovery was achieved months after cerebral damage.^{2 3 4 5} Another possible explanation of our findings is that the observed changes in cerebral activation may be due to the phenomenon of diaschisis. It is well known that unilateral lesions, such as those present in our patients, can cause a reduction in brain functioning involving both ipsilateral and contralateral structures.^{21 22} However, contralateral effects of brain lesions can be excitatory as well as inhibitory.²³ Even if there is considerable uncertainty about the pathophysiological significance of these effects in term of recovery of function, it has been recently suggested that hyperexcitability in the contralateral hemisphere may contribute to functional reorganization after stroke.²⁴ In our patients we did not find any sign of inhibition in the hemisphere ipsilateral to the lesion. In fact, during the performance of the motor task with the recovered hand, the increase of MFV was also present in the side of the lesion and the extent of this increase was comparable to that observed in the contralateral MCA during movement of the normal hand. It is of interest that the bilateral activation was not a transient phenomenon but persisted in the months after stroke onset. Obviously, TCD findings cannot provide information about the mechanism of activation nor the exact localization of changes in cerebral activity responsible for the recovery of function after a lesion. For this reason, the integration of our findings with those deriving from other techniques of cerebral blood flow and metabolism able to exactly define regional modification of cerebral activity seems to be very promising for improving our knowledge about the pathophysiology of recovery of neurological functions. In particular, this kind of information could be very useful for understanding whether different degrees of improvement are linked to a different modality of activation in cerebral areas contralateral or ipsilateral to the lesion or whether the possibility of recruiting different cerebral areas for the execution of some performances can be evidenced even before the occurrence of a lesion in some subjects. The response to these questions could have important practical implications when planning therapy for patients with brain lesions or when monitoring the evolution of a deficit.

Received January 6, 1998; revision received March 5, 1998; accepted April 7, 1998.

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