Use of the augmentation index to predict short-term outcome after acute ischemic stroke

Prognostic value of central blood pressure on the outcomes of embolic stroke of undetermined source

We investigated the prognostic impact of central blood pressure (BP) on outcomes in patients with embolic stroke of undetermined source (ESUS). The prognostic value of central BP according to ESUS subtype was also evaluated. We recruited patients with ESUS and data on their central BP parameters (central systolic BP [SBP], central diastolic BP [DBP], central pulse pressure [PP], augmentation pressure [AP], and augmentation index [AIx]) during admission. ESUS subtype classification was arteriogenic embolism, minor cardioembolism, two or more causes, and no cause. Major adverse cardiovascular event (MACE) was defined as recurrent stroke, acute coronary syndrome, hospitalization for heart failure, or death. Over a median of 45.8 months, 746 patients with ESUS were enrolled and followed up. Patients had a mean age of 62.8 years, and 62.2% were male. Multivariable Cox regression analysis showed that central SBP and PP were associated with MACE. All-cause mortality was independently associated with AIx. In patients with no cause ESUS, central SBP and PP, AP, and AIx were independently associated with MACE. AP and AIx were independently associated with all-cause mortality (all p < 0.05). We demonstrated that central BP can predict poor long-term prognosis in patients with ESUS, especially those with the no cause ESUS subtype.

Decrease in Pulse Wave Velocity is Associated with Clinical Improvement in Patients with Ischemic Stroke

BACKGROUND

Arterial stiffness is an independent determinant of cardiovascular and cerebrovascular risks. The relationship between the increase in arterial stiffness parameters and the severity of stroke has been shown in previous studies. We aimed to investigate the association between clinical improvement and changes in arterial stiffness parameters in patients presenting acute ischemic stroke.

METHODS

A total of 107 patients were enrolled in this study. On the first and seventh day of the hospitalization, 24 h non-invasive blood pressure was monitored and arterial stiffness parameters were measured. The National Institutes of Health Stroke Scale (NIHSS) was used to determine the severity of stroke, and the Modified Rankin Scale was used to determine dependency and to evaluate functional improvements.

RESULTS

Arterial stiffness parameters of augmentation index (AIx@75) and pulse wave velocity (PWV) were significantly higher in patients who died during hospitalization than patients who were discharged (respectively p <0.001, p = 0.04). In the group with clinical improvement, PWV values measured on the seventh day were significantly lower than PWV values measured on the first day (p = 0.032). When the changes in PWV value measured on the first and seventh day for both groups were analyzed using mixed ANOVA test, p value were significant (p = 0.033). Multivariate binary logistic regression analyses showed that negatively change in PWV and CDBP independently predicts the clinical improvement.

CONCLUSIONS

Increased AIx@75 and PWV appear to be associated with higher in-hospital mortality rates in patients with acute ischemic stroke. Additionally, clinical improvement in patients with ischemic stroke is associated with a decrease in PWV .

Changes of augmentation index early after ischaemic stroke predict functional outcome

Purpose: Outcome after ischaemic stroke (AIS) depends on multiple factors, including values of blood pressure (BP) and arterial stiffness (AS) in the early phase. It is also known that stroke outcome is affected by BP variability; however, the influence of AS oscillations in the early phase of stroke on its prognosis is unknown. The aim of our study was to assess the relationship between changes of AS markers and stroke outcome.Materials and methods: Baseline clinical data, BP parameters, and markers of AS (pulse wave velocity [PWV], augmentation index [AIx]) were assessed 1, 6, and >90 days after AIS. The outcomes were defined using modified Rankin scale (mRS) score: early favourable (EFO) and early poor (EPO), as mRS ≤1 and >2 points at discharge, respectively; late favourable (LFO) and late poor (LPO), as mRS ≤1 and >2 points on day >90, respectively.Results: In the recruited 50 patients (62.2 ± 12.1 years, 68% males), BP and PWV decreased while AIx did not change within 90 days after AIS. Twenty-eight patients (56%) had EFO, 10 (20%) - EPO, 29 (58%) - LFO, and 9 (18%) - LPO. In univariate analysis, rise in AIx in days 1-6 was associated with EFO (odds ratio [OR] = 1.09, 95% confidence interval [CI] = 1.02-1.17, p = 0.01) and LFO (OR = 1.08; 95%CI = 1.01-1.14, p = 0.02), whereas decrease in AIx in days 1-6 was associated with EPO (OR = 1.07, 95%CI = 1.00-1.15, p = 0.05). For EFO and LFO, the relationships remained significant after including confounders (p = 0.03 and p = 0.03, respectively).Conclusions: Rise in AIx within one week after ischaemic stroke may be of additional importance in determining better early and late favourable functional outcome.

Augmentation index in the assessment of wave reflections and systolic loading

BACKGROUND

Augmentation index (AI_x) is used to quantify the augmented systolic aortic pressure that impedes ventricular ejection. Its use as an index of wave reflections is questionable. We hypothesize that AI_x is quantitatively different from the reflection coefficient under varied physiological conditions.

METHODS

42 datasets of aortic pressure and flow waveforms were obtained during induced hypertension (methoxamine infusion) and vasodilation (nitroprusside infusion) in our mongrel dog experiments (n = 5) and from Mendeley data during various interventions (vasoconstrictors, vasodilators, pacing, stimulation, hemorrhage and hemodilution). Wave reflections and principal components of reflection coefficients were computed for comparison to AI_x and heart rate normalized AI_x. RESULTS: Principal reflection coefficient, Γ₁, increased in hypertension and decreased in vasodilation, hemorrhage and hemodilution. AI_x followed the trend in many cases but was consistently lower than Γ₁ in almost all the subjects. The Bland-Altman analysis also showed that both AI_x and normalized AI_x underestimated Γ₁. The relationship between augmentation index and reflection coefficient was explained by a linear regression model (r² = 0.23, p < 0.01) in which AI_x followed directional changes in Γ₁ and the normalization of AI_x resulted in a linear model that explained less variation in the relationship between AI_x and Γ₁.

CONCLUSION

AI_x is a reasonable clinical trend indicator, albeit not an accurate surrogate measure of the amount of wave reflections.

Chlorthalidone Plus Amiloride Reduces the Central Systolic Blood Pressure in Stage 1 Hypertension Patients

BACKGROUND

Hypertension reduction strategies use blood pressure in the brachial artery as the primary endpoint. Individuals who achieve the target blood pressure reduction with antihypertensive treatment have residual cardiovascular risk attributed to the difference in pressure between the aorta and brachial artery. Antihypertensive treatment affects the intrinsic properties of the vascular wall and arterial stiffness markers and consequently the central pressure. Recent publications stress the importance of adequate control of the central compared to peripheral blood pressure. Related clinical implications suggest that individuals with normal peripheral but high central blood pressure should not receive antihypertensive drugs that act on the central pressure. Therefore, they are at greater cardiovascular risk. The aim of the study was to evaluate the effect of treatment with a thiazide diuretic versus losartan on the central blood pressure in stage 1 hypertensive patients.

METHODS

Twenty-five patients were randomized to the chlorthalidone 25 mg/amiloride 5 mg group (q.d.) and 25 patients received losartan 50 mg (b.i.d). The central systolic blood pressure (CSBP) and augmentation index (AIx 75) were assessed using applanation tonometry. The paired t-test was used to compare the systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), pulse pressure (PP), CSBP and AIx 75 between the thiazide and losartan groups at baseline and after 6 months of treatment.

RESULTS

Significant reductions in CSBP (123.3 ± 14.2 vs. 113.4 ± 111.4, P = 0.0103) and AIx 75 (87.7 ± 9.6 vs. 83.8 ± 8.9, P = 0.0289) were observed after 6 months of drug treatment with chlorthalidone 25 mg/amiloride 5 mg (q.d.). The administration of losartan 50 mg (b.i.d) did not reduce the CSBP and there were insignificant changes in the AIx 75.

CONCLUSIONS

Six-month treatment of chlorthalidone/amiloride but not losartan reduces the CSBP and AIx 75 in adults with stage 1 hypertension.

Principles of cerebral hemodynamics when intracranial pressure is raised: lessons from the peripheral circulation

Background: The brain is highly vascular and richly perfused, and dependent on continuous flow for normal function. Although confined within the skull, pressure within the brain is usually less than 15 mmHg, and shows small pulsations related to arterial pulse under normal circumstances. Pulsatile arterial hemodynamics in the brain have been studied before, but are still inadequately understood, especially during changes of intracranial pressure (ICP) after head injury.

Method: In seeking cohesive explanations, we measured ICP and radial artery pressure (RAP) invasively with high-fidelity manometer systems, together with middle cerebral artery flow velocity (MCAFV) (transcranial Doppler) and central aortic pressure (CAP) generated from RAP, using a generalized transfer function technique, in eight young unconscious, ventilated adults following closed head trauma. We focused on vascular effects of spontaneous rises of ICP (‘plateau waves’).

Results: A rise in mean ICP from 29 to 53 mmHg caused no consistent change in pressure outside the cranium, or in heart rate, but ICP pulsations increased in amplitude from 8 to 20 mmHg, and ICP waveform came to resemble that in the aorta. Cerebral perfusion pressure (=central aortic pressure – ICP), which equates with transmural pressure, fell from 61 to 36 mmHg. Mean MCAFV fell from 53 to 40 cm/s, whereas pulsatile MCAFV increased from 77 to 98 cm/s. These significant changes (all P < 0.01) may be explained using the Monro–Kellie doctrine, because of compression of the brain, as occurs in a limb when external pressure is applied.

Conclusion: The findings emphasize importance of reducing ICP, when raised, and on the additional benefits of reducing wave reflection from the lower body.

Acute passive vibration reduces arterial stiffness and aortic wave reflection in stroke survivors

PURPOSE

Impaired leg arterial stiffness (pulse wave velocity, PWV) and vasodilatory function are found after stroke. Acute passive vibration (PV) decreases leg PWV (legPWV) and pressure wave reflection (aortic augmentation index, aAIx) in healthy men. Our objective was to evaluate the effects of acute PV on aAIx and PWV in the paretic and non-paretic sides in stroke survivors.

METHODS

Eleven stroke survivors (4 females) were randomized to either no-PV (control) or PV (25 Hz and 2 mm amplitude) trials on two separated visits. Following 20 min of supine rest with legs on a vibration platform, blood pressure, PWV, and aAIx were gathered before 10 continuous minutes of control or PV. Measurements were repeated at post-5, post-15, and post-30 min after control or PV.

RESULTS

LegPWV and brachial-ankle PWV (baPWV, systemic stiffness) in paretic and non-paretic sides along with aAIx were significantly (P < 0.05) decreased from baseline at post-5 min after PV compared with control. At post-15 min, paretic and non-paretic legPWV remained significantly lower than baseline, but only non-paretic legPWV was different from control. We noted correlations between changes in paretic legPWV and changes in paretic baPWV (r = 0.47, P = 0.028) and aAIx (r = 0.51, P = 0.017) at post-5 min.

CONCLUSIONS

Acute PV applied to the legs of stroke survivors reduces systemic arterial stiffness and aortic wave reflection due to a reduction in leg arterial stiffness, which last longer in the non-paretic than in the paretic leg.