Increasing pressure of external counterpulsation augments blood pressure but not cerebral blood flow velocity in ischemic stroke

Cerebral multi-autoregulation model based enhanced external counterpulsation treatment planning for cerebral ischemic stroke

Enhanced external counterpulsation (EECP) treatment for cerebral ischemic stroke patients with differing severity of stenosis, is subject to uncertainties due to the varying effects of the cerebral autoregulation mechanism on haemodynamics. The current study reports the development of a cerebral multi-autoregulation (MR) mathematical model, based on cerebral arteriole regulation of neurogenic, vascular smooth muscle reflex and shear stress mechanisms which takes into account the severity of stenosis. The model was evaluated by comparison to authentic clinical measurements of cerebral autoregulatory efficiency. Then it was applied to a 0D/3D geometric multi-scale haemodynamic model of a cerebral artery. Haemodynamic indicators were calculated under different pressurization durations of EECP to evaluate the efficacy for different stenosis lesions. Moderate stenosis of 50% to 60% produced excessive time-averaged wall shear stress in the distal area of the stenosis (>7 Pa) during prolonged pressurization and may result in damage to vascular endothelial cells. However, prolonged pressurization did not result in haemodynamic risk for severe stenosis of 70% to 80%, indicating that the duration of pressurization may be extended with increasing severity of stenosis. The current MR model accurately simulated cerebral blood flow and has relevance to the simulation of cerebral haemodynamics in a clinical setting.

Hemodynamic Responses in Carotid Bifurcation Induced by Enhanced External Counterpulsation Stimulation in Healthy Controls and Patients With Neurological Disorders

Enhanced external counterpulsation is a Food and Drug Administration–approved, non-invasive, assisted circulation therapy for ischemic cardiovascular and cerebrovascular diseases. Previous studies have confirmed that EECP stimulation induces largely different cerebral hemodynamic responses in patients with ischemic stroke and healthy controls. However, the underlying mechanisms remain uncertain. We hypothesize that different blood redistributions at the carotid bifurcation may play a key role. Ten subjects were enrolled in this study, namely, five patients with neurological disorders and five young healthy volunteers as controls. Magnetic resonance angiography (MRA) was performed on the carotid artery. All the subjects received a single session of EECP treatment, with external cuff pressures ranging from 20 to 40 kPa. Vascular ultrasound measurements were taken in the common carotid artery (CCA), external carotid artery (ECA) and internal carotid artery (ICA). Three-dimensional patient-specific numerical models were developed to calculate the WSS-derived hemodynamic factors. The results indicated that EECP increased CCA and ECA blood flow in both groups. The ICA blood flow in the patient group exhibited a mean increase of 6.67% during EECP treatment compared with the pre-EECP condition; a mean decrease of 9.2% was observed in the healthy control group. EECP increased the averaged wall shear stress (AWSS) throughout the carotid bifurcation in the patient group; the ICA AWSS of the healthy group decreased during EECP. In both groups, the oscillatory shear index (OSI) in the ICA increased proportionally with external cuff pressure. In addition, the relative resident time (RRT) was constant or slightly decreased in the CCA and ECA in both groups but increased in the ICA. We suggest that the benefits of EECP to patients with neurological disorders may partly result from blood flow promotion in the ICA and increase in WSS at the carotid bifurcation. In the healthy subjects, the ICA blood flow remained constant during EECP, although the CCA blood flow increased significantly. A relatively low external cuff pressure (20 kPa) is recommended as the optimal treatment pressure for better hemodynamic effects. This study may play an important role in the translation of physiological benefits of EECP treatment in populations with or without neurological disorders.

Intermittent Sequential Pneumatic Compression Improves Coupling between Cerebral Oxyhaemoglobin and Arterial Blood Pressure in Patients with Cerebral Infarction

This study aims to explore the effect of intermittent sequential pneumatic compression (ISPC) intervention on the coupling relationship between arterial blood pressure (ABP) and changes in oxyhaemoglobin (Δ [O₂Hb]). The coupling strength between the two physiological systems was estimated using a coupling function based on dynamic Bayesian inference. The participants were 22 cerebral infarction patients and 20 age- and sex-matched healthy controls. Compared with resting state, the coupling strength from ABP to Δ [O₂Hb] oscillations was significantly lower in the bilateral prefrontal cortex (PFC), sensorimotor cortex (SMC), and temporal lobe cortex (TLC) during the ISPC intervention in cerebral infarction patients in interval II. Additionally, the coupling strength was significantly lower in the bilateral SMC in both groups in interval III. These findings indicate that ISPC intervention may facilitate cerebral circulation in the bilateral PFC, SMC, and TLC in cerebral infarction patients. ISPC may promote motor function recovery through its positive influences on motor-related networks. Furthermore, the coupling between Δ [O₂Hb] and ABP allows non-invasive assessments of autoregulatory function to quantitatively assess the effect of rehabilitation tasks and to guide therapy in clinical situations.

Hemodynamics in acute stroke: Cerebral and cardiac complications

Hemodynamics is the study of blood flow, where parameters have been defined to quantify blood flow and the relationship with systemic circulatory changes. Understanding these perfusion parameters, the relationship between different blood flow variables and the implications for ischemic injury are outlined in the ensuing discussion. This chapter focuses on the hemodynamic changes that occur in ischemic stroke, and their contribution to ischemic stroke pathophysiology. We discuss the interaction between cardiovascular response and hemodynamic changes in stroke. Studying hemodynamic changes has a key role in stroke prevention, therapeutic implications and prognostic importance in acute ischemic stroke: preexisting hemodynamic and autoregulatory impairments predict the occurrence of stroke. Hemodynamic failure predisposes to the formation of thromboemboli and accelerates infarction due to impairing compensatory mechanisms. In ischemic stroke involving occlusion of a large vessel, persistent collateral circulation leads to preservation of ischemic penumbra and therefore justifying endovascular thrombectomy. Following thrombectomy, impaired autoregulation may lead to reperfusion injury and hemorrhage.

Expert consensus on the clinical application of enhanced external counterpulsation in elderly people (2019)

Enhanced external counterpulsation (EECP) is a non-invasive assisted circulation technique and a rich pool of evidence has accumulated for its clinical application in the prevention and management of multiple comorbidities in the elderly population, including angina, heart failure, ischemic cerebrovascular diseases, neurodegenerative diseases, sleep disorder, diabetes and its complications, ischemic eye diseases, sudden hearing loss and erectile dysfunction, as well as various psychological and psychiatric conditions. When applying EECP to elderly patients, emphasis should be placed on issues such as safety assessment, risk management and protocol individualization, as well as the monitoring of efficacy during and after treatment.

Long-term hemodynamic mechanism of enhanced external counterpulsation in the treatment of coronary heart disease: a geometric multiscale simulation

Enhanced external counterpulsation (EECP) is a noninvasive treatment method for coronary artery atherosclerosis that acts on the vascular endothelial cells. The intracoronary hemodynamic parameters that influence long-term treatment effect are the fundamental factors for the inhibition of intimal hyperplasia, which cannot be measured in real time. In order to optimize the long-term treatment effect of coronary heart disease, it is necessary to establish a method for quantified calculation of intracoronary hemodynamic parameters during counterpulsation to research the long-term hemodynamic mechanism of EECP. A geometric multiscale model coupled by the zero-dimensional (0D) lumped parameter model and the three-dimensional (3D) model of narrow coronary artery was established for the simulation of intracoronary hemodynamic environment. The 3D model was used to calculate the hemodynamic parameters such as wall shear stress (WSS) and oscillatory shear index (OSI), while the 0D model was used to simulate the blood circulatory system. Sequential pressure was applied to calves, thighs, and buttocks module in 0D model with the consideration of vessel collapse. Hemodynamic performance was compared with clinical reports to verify the effectiveness of the method. There were significant increases of the diastolic blood pressure (DBP), coronary flow, and the area-averaged WSS during application of EECP, while OSI behind stenosis has some decrease. The waveforms of coronary flow has good similarity with the clinical measured waveforms, and the differences between calculated mean arterial pressures (MAPs) and clinical measurements were within 1%. The fundamental factor in the cure of coronary heart disease by EECP is the improvement of WSS and the decrease of OSI. Comparing with the clinical reports, the immediate hemodynamic changes demonstrate the effectiveness of model. Intracoronary hemodynamic parameters during EECP could be acquired and the method could be used to simulate the long-term treatment effect of EECP. Graphical abstract.

Hemodynamic effects of enhanced external counterpulsation on cerebral arteries: a multiscale study

Background

Enhanced external counterpulsation (EECP) is an effective method for treating patients with cerebral ischemic stroke, while hemodynamics is the major contributing factor in the treatment of EECP. Different counterpulsation modes have the potential to lead to different acute and long-term hemodynamic changes, resulting in different treatment effects. However, various questions about appropriate counterpulsation modes for optimizing hemodynamic effects remain unanswered in clinical treatment.

Methods

A zero-dimensional/three-dimensional (0D/3D) geometric multiscale model of the cerebral artery was established to obtain acute hemodynamic indicators, including mean arterial pressure (MAP) and cerebral blood flow (CBF), as well as localized hemodynamic details for the cerebral artery, which includes wall shear stress (WSS) and oscillatory shear index (OSI). Counterpulsation was achieved by applying pressure on calf, thigh and buttock modules in the 0D model. Different counterpulsation modes including various pressure amplitudes and pressurization durations were applied to investigate hemodynamic responses, which impact acute and long-term treatment effects. Both vascular collapse and cerebral autoregulation were considered during counterpulsation.

Results

Variations of pressure amplitude and pressurization duration have different impacts on hemodynamic effects during EECP treatment. There were small differences in the hemodynamics when similar or different pressure amplitudes were applied to calves, thighs and buttocks. When increasing pressure amplitude was applied to the three body parts, MAP and CBF improved slightly. When pressure amplitude exceeded 200 mmHg, hemodynamic indicators almost never changed, demonstrating consistency with clinical data. However, hemodynamic indicators improved significantly with increasing pressurization duration. For pressurization durations of 0.5, 0.6 and 0.7 s, percentage increases for MAP during counterpulsation were 1.5%, 23.5% and 39.0%, for CBF were 1.2%, 23.4% and 41.6% and for time-averaged WSS were 0.2%, 43.5% and 85.0%, respectively.

Conclusions

When EECP was applied to patients with cerebral ischemic stroke, pressure amplitude applied to the three parts may remain the same. Patients may not gain much more benefit from EECP treatment by excessively increasing pressure amplitude above 200 mmHg. However, during clinical procedures, pressurization duration could be increased to 0.7 s during the cardiac circle to optimize the hemodynamics for possible superior treatment outcomes.

Short-term external counterpulsation augments cerebral blood flow and tissue oxygenation in chronic cerebrovascular occlusive disease

Background and purpose

External counterpulsation improves cerebral perfusion velocity in acute stroke and may stimulate collateral artery growth. However, whether (non‐acute) at‐risk patients with high‐grade carotid artery disease may benefit from counterpulsation needs to be validated.

Methods

Twenty‐eight patients (71 ± 6.5 years, five women) with asymptomatic unilateral chronic severe internal carotid artery stenosis (>70%) or occlusion were randomized to receive 20 min active counterpulsation followed by sham treatment or vice versa. Cerebral blood flow velocity (CBFV) (measured bilaterally by transcranial middle cerebral artery Doppler), tissue oxygenation index (TOI) (measured over the bilateral prefrontal cortex by near‐infrared spectroscopy) and cerebral hemodynamic parameters, such as relative pulse slope index (RPSI), were monitored.

Results

Ipsilateral mean CBFV (ΔV_mean +3.5 ± 1.2 cm/s) and tissue oxygenation (ΔTOI +2.86 ± 0.8) increased significantly during active counterpulsation compared to baseline, whilst the sham had little effect (ΔV_mean +1.13 ± 1.1 cm/s; ΔTOI +1.25 ± 0.65). On contralateral sides, neither counterpulsation nor sham control had any effect on either parameter. During counterpulsation, early dynamic changes in ΔRPSI of the ipsilateral CBFV signal predicted improved tissue oxygenation during counterpulsation (odds ratio 1.179, 95% confidence interval 1.01–1.51), whilst baseline cerebrovascular reactivity to hypercapnia failed to show an association.

Conclusions

In patients with high‐grade carotid disease, ipsilateral cerebral oxygenation and blood flow velocity are increased by counterpulsation. This is a necessary condition for the stimulation of regenerative collateral artery growth and thus a therapeutic concept for the prevention of cerebral ischaemia. This study provides a rationale for further clinical investigations on the long‐term effects of counterpulsation on cerebral hemodynamics and collateral growth.

The potential synergism by combining external counterpulsation with intermittent theta burst stimulation in post-stroke motor function recovery

Upper limb weakness and incoordination is a common disability following ischemic stroke. Previous studies have showed that the single application of external counterpulsation (ECP) and intermittent theta burst stimulation (iTBS) can effectively enhance the cortical motor excitability and facilitate recovery. However, it remains uncertain if sequential application of these therapies would further augment the recovery. We hypothesize a synergistic effect of ECP followed by iTBS to upper limb function may happen through improvements in both cerebral perfusion and neuron excitability.

Enhancing cerebral perfusion with external counterpulsation after ischaemic stroke: how long does it last?

OBJECTIVE

External counterpulsation (ECP) is a non-invasive method used to augment cerebral perfusion in ischaemic stroke. We aimed to investigate time-course effects on blood pressure elevation and cerebral blood flow augmentation induced by ECP in ischaemic stroke.

METHODS

Patients with acute unilateral ischaemic stroke and large artery occlusive disease were recruited to receive 35 daily 1 h ECP treatment sessions. Serial transcranial Doppler monitoring of bilateral middle cerebral arteries was performed on days 3, 5, 7, 10, 14, 21, 28 and 35 after stroke onset. Flow velocity changes before, during and after ECP and continuous beat-to-beat blood pressure data were recorded. The cerebral augmentation index (CAI) is the increase in the percentage of the middle cerebral artery mean flow velocity during ECP compared with baseline.

RESULTS

The CAI in patients with stroke was significantly higher on the ipsilateral side and on the contralateral side on day 3 (ipsilateral CAI, 9.3%; contralateral CAI, 7.2%), day 5 (7.0%; 6.7%), day 7 (6.8%; 6.0%), day 10 (6.0%; 5.1%), day 14 (4.7%; 2.6%) and day 21 (4.1%; 2.2%) after stroke onset than that in controls (-2.0%) (all p<0.05). There was a significant trend of decreasing CAI on the ipsilateral and contralateral sides over time after a stroke. Differences in the percentage increase in the mean blood pressure did not change significantly over time in patients with stroke.

CONCLUSIONS

Blood pressure elevation persists throughout ECP treatment, which consists of 35 sessions. However, cerebral blood flow augmentation may last at least 3 weeks and then appears to return to baseline 1 month after acute stroke onset.

A retrospective pilot study of correlation of cerebral augmentation effects of external counterpulsation with functional outcome after acute ischaemic stroke

OBJECTIVE

External counterpulsation (ECP) is a non-invasive method used to augment cerebral blood flow of patients with ischaemic stroke via induced hypertension. We aimed to explore the correlation between the cerebral blood flow augmentation effects induced by ECP and clinical outcome after acute ischaemic stroke.

METHODS

We retrospectively analysed our ECP registry of patients with ischaemic stroke who were enrolled within 7 days after stroke onset. Bilateral middle cerebral arteries of patients were monitored using transcranial Doppler (TCD). Flow velocity changes before, during and after ECP were, respectively, recorded for 3 min. The cerebral augmentation index (CAI) was the increase in percentage of the middle cerebral artery mean flow velocity during ECP compared with baseline. TCD data were analysed based on the side ipsilateral or contralateral to the infarct. The modified Rankin Scale (mRS) (good outcome: mRS 0∼2; poor outcome: mRS 3∼6) was evaluated 6 months after the index stroke.

RESULTS

72 patients were included (mean age, 63.8±10.7 years; 87.5% males). At month 6 after stroke onset, univariate analysis showed that the National Institutes of Health Stroke Scale at recruitment was significantly higher and ECP therapy duration was longer in the poor outcome group, while the ipsilateral CAI was significantly lower in the good outcome group than that in the poor outcome group (3.71±4.94 vs 7.73±7.66, p=0.044). Multivariate logistic regression showed that ipsilateral CAI was independently correlated with an unfavourable functional outcome after adjusting for confounding factors.

CONCLUSIONS

The higher degree of cerebral blood flow velocity augmentation on the side ipsilateral to the infarct induced by ECP is independently correlated with an unfavourable functional outcome after acute ischaemic stroke.

Feasibility and Safety of Using External Counterpulsation to Augment Cerebral Blood Flow in Acute Ischemic Stroke-The Counterpulsation to Upgrade Forward Flow in Stroke (CUFFS) Trial

BACKGROUND

External counterpulsation (ECP) increases perfusion to a variety of organs and may be helpful for acute stroke.

METHODS

We conducted a single-blinded, prospective, randomized controlled feasibility and safety trial of ECP for acute middle cerebral artery (MCA) ischemic stroke. Twenty-three patients presenting within 48 hours of symptom onset were randomized into one of two groups. One group was treated with ECP for 1 hour at a pressure of up to 300 mmHg ("full pressure"). During the procedure, we also determined the highest possible pressure that would augment MCA mean flow velocity (MFV) by 15%. The other group was treated with ECP at 75 mmHg ("sham pressure"). Transcranial Doppler MCA flow velocities and National Institutes of Health Stroke Scale (NIHSS) scores of both groups were checked before, during, and after ECP. Outcomes were assessed at 30 days after randomization.

RESULTS

Although the procedures were feasible to implement, there was a frequent inability to augment MFV by 15% despite maximal pressures in full-pressure patients. In sham-pressure patients, however, MFV frequently increased as shown by increases in peak systolic velocity and end diastolic velocity. In both groups, starting ECP was often associated with contemporaneous improvements in NIHSS stroke scores. There were no between-group differences in NIHSS, modified Rankin Scale Scores, and Barthel Indices, and no device or treatment-related serious adverse events, deaths, intracerebral hemorrhages, or episodes of acute neuro-worsening.

CONCLUSIONS

ECP was safe and feasible to use in patients with acute ischemic stroke. It was associated with unexpected effects on flow velocity, and contemporaneous improvements in NIHSS score regardless of pressure used, with a possibility that even very low ECP pressures had an effect. Further study is warranted.