The effect of diabetes on the interrelationship between jugular venous oxygen saturation responsiveness to phenylephrine infusion and cerebrovascular carbon dioxide reactivity

Chronic hyperglycemia before acute ischemic stroke impairs the bilateral cerebrovascular response to exercise during the subacute recovery period

BACKGROUND AND PURPOSE

Chronic hyperglycemia contributes to cerebrovascular dysfunction by damaging blood vessels. Poor glucose control has been tied to impairments in cerebral blood flow, which may be particularly detrimental for people recovering from major cerebrovascular events such as acute ischemic stroke. In this secondary analysis, we explore for the first time the connection between chronic hyperglycemia before acute stroke and the cerebrovascular response (CVR) to exercise 3 and 6 month into the subacute recovery period.

METHODS

We recorded middle cerebral artery velocity (MCAv) using transcranial Doppler ultrasound bilaterally at rest and during moderate-intensity exercise in stroke patients at 3 (n = 19) and 6 (n = 12) months post-stroke. We calculated CVR as the difference between MCAv during steady-state exercise and resting MCAv. We obtained hemoglobin A1c levels (HbA1c; a measure of blood glucose over the prior 3 months) from the electronic medical record (EMR) and divided participants by HbA1c greater or less than 7%.

RESULTS

Participants with high HbA1c (>7%) at the time of acute stroke had significantly lower CVR to exercise for both the stroke-affected (p = .009) and non-affected (p = .007) hemispheres at 3 months post-stroke. These differences remained significant at 6 months post-stroke (stroke-affected, p = .008; non-affected, p = .016).

CONCLUSIONS

Patients with chronic hyperglycemia before acute ischemic stroke demonstrated impaired cerebrovascular function during exercise months into the subacute recovery period. These findings highlight the importance of maintaining tight glucose control to reduce morbidity and improve recovery post-stroke and could have implications for understanding cerebrovascular pathophysiology.

Forbidden word entropy of cerebral oximetric values predicts postoperative neurocognitive decline in patients undergoing aortic arch surgery under deep hypothermic circulatory arrest

Purpose:

Up to 53% of cardiac surgery patients experience postoperative neurocognitive decline. Cerebral oximetry is designed to detect changes in cerebral tissue saturation and therefore may be useful to predict which patients are at risk of developing neurocognitive decline.

Methods:

This is a retrospective analysis of a prospective study originally designed to determine if treatment of cerebral oximetry desaturation is associated with improvement in postoperative cognitive dysfunction in patients undergoing aortic reconstruction under deep hypothermic circulatory arrest. Cognitive function was measured, preoperatively and 3 months postoperatively, with 15 neuropsychologic tests administered by a psychologist; the individual test scores were summed and normalized. Bilateral cerebral oximetry data were stored and analyzed using measures of entropy. Cognitive decline was defined as any decrease in the summed normalized score from baseline to 3 months.

Results:

Seven of 17 (41%) patients suffered cognitive decline. There was no association between baseline cerebral oximetry and postoperative cognitive dysfunction. Nor were changes in oximetry values associated with cognitive decline. However, cognitive decline was associated with loss of forbidden word entropy (FwEn) (correlation: Rho ρ = 0.51, P = 0.037 for left cerebral oximetry FwEn and ρ = 0.54, P = 0.025 for right cerebral oximetry FwEn).

Conclusion:

Postoperative cognitive decline was associated with loss of complexity of the time series as shown by a decrease in FwEn from beginning to end of the case. This suggests that regulation of cerebral oximetry is different between those who do and those who do not develop cognitive decline.

Arterial wall function is associated with cognitive performance primarily in elderly with type 2 diabetes

Regression analyses compared 41 type 2 diabetes (T2D) and 131 non-T2D cognitively normal elderly males on the associations of arterial wall function measures [large artery elasticity index (LAEI), small artery elasticity index (SAEI), systemic vascular resistance (SVR), and total vascular impedance (TVI)] with cognitive performance (memory, language, and executive functions), controlling for socio-demographic and cardiovascular factors. Higher LAEI and lower TVI were significantly associated with better executive functions performance in T2D but not in non-T2D subjects. Lower TVI was more associated with better language performance in T2D. Results suggest that arterial wall function is associated with cognition in T2D.

Assessment of dynamic cerebral autoregulation and cerebral carbon dioxide reactivity during normothermic cardiopulmonary bypass

Despite increased risk of neurological complications after cardiac surgery, monitoring of cerebral hemodynamics during cardiopulmonary bypass (CPB) is still not a common practice. Therefore, a technique to evaluate dynamic cerebral autoregulation and cerebral carbon dioxide reactivity (CO2R) during normothermic nonpulsatile CPB is presented. The technique uses continuous recording of invasive arterial blood pressure, middle cerebral artery blood flow velocity, absolute cerebral tissue oxygenation, in-line arterial carbon dioxide levels, and pump flow measurement in 37 adult male patients undergoing elective CPB. Cerebral autoregulation is estimated by transfer function analysis and the autoregulation index, based on the response to blood pressure variation induced by cyclic 6/min changes of indexed pump flow from 2.0 to 2.4 up to 2.8 L/min/m(2). CO2R was calculated from recordings of both cerebral blood flow velocity and cerebral tissue oxygenation. Cerebral autoregulation and CO2R were estimated at hypocapnia, normocapnia, and hypercapnia. CO2R was preserved during CPB, but significantly lower for hypocapnia compared with hypercapnia (p < 0.01). Conversely, cerebral autoregulation parameters such as gain, phase, and autoregulation index were significantly higher (p < 0.01) during hypocapnia compared with both normocapnia and hypercapnia. Assessing cerebral autoregulation and CO2R during CPB, by cyclic alteration of pump flow, showed an impaired cerebral autoregulation during hypercapnia.

Cognition and Hemodynamics

The relationship between cerebral hemodynamics and cognitive performance has increasingly become recognized as a major challenge in clinical practice for older adults. Both diabetes and hypertension worsen brain perfusion and are major risk factors for cerebrovascular disease, stroke and dementia. Cerebrovascular reserve has emerged as a potential biomarker for monitoring pressure-perfusion-cognition relationships. Endothelial dysfunction and inflammation, microvascular disease, and mascrovascular disease affect cerebral hemodynamics and play an important role in pathohysiology and severity of multiple medical conditions, presenting as cognitive decline in the old age. Therefore, the identification of cerebrovascular vascular reactivity as a new therapeutic target is needed for prevention of cognitive decline late in life.

Assessment of moderate to severe abdominal blood loss using peripheral to central blood oxygen saturation

PURPOSE

There are various definitions and monitoring modalities for hemodynamic status. Each of them has its own advantages and shortcomings. A new hemodynamic index is proposed in this study. This index can be calculated by placing the measured hemoglobin saturation in a formula. Blood samples for this measurement are taken from arterial, antecubital and central venous blood.

MATERIAL AND METHODS

We calculated this index in three different groups undergoing laparatomy. The control group consisted of patients who underwent elective surgery. The case group with acute internal abdominal bleeding was divided into two groups. Those with more than 20 ml/kg of blood in their abdominal cavity were designated as the severe case group, while those bleeding less were categorized as moderate. Blood samples were taken from ten patients in each group in stable and unstable conditions.

RESULTS

This index differed significantly between dissimilar hemodynamic conditions. The pre-anesthesia value of this index in the control group showed a mean +/- SD of 8.5 +/- 3.2 vs. 1.6 +/- 0.4 in the moderate case group vs. 0.7 +/- 0.08 in the case group with severe hemodynamic changes (p < .001). The index approximated to the control values as the circumstances improved. After compensation for volume loss, pre-extubation values were not significantly different. These were 9.6 +/- 2 in the control group vs. 8 +/- 2 in the case group with moderate hemodynamic change vs. 8 +/- 1.8 in the severe case group. The likelihood ratio of bleeding increased as this index decreased.

CONCLUSION

As the hemodynamic condition deteriorates, this index decreases significantly. This index is an accurate indicator for predicting hemodynamic changes compared to some other modalities. Further investigations are needed into the prognostic and therapeutic advantages of this index.

Effects of nicardipine-induced hypotension on cerebrovascular carbon dioxide reactivity in patients with diabetes mellitus under sevoflurane anesthesia

PURPOSE

The purpose of this study was to examine the effects of nicardipine-induced hypotension on cerebrovascular CO2 reactivity in patients with diabetes mellitus under sevoflurane anesthesia.

METHODS

Nineteen diabetic patients, and 11 nondiabetic patients (serving as controls), undergoing elective orthopedic, cardiovascular, or thoracic surgery were included in the study. The diabetic patients were divided into three groups according to the antidiabetic therapy they were receiving, i.e., diet therapy (n = 6), oral antidiabetic drugs (n = 7), and insulin (n = 6). Anesthesia was maintained with 1.0 minimum alveolar concentration of sevoflurane. Absolute and relative cerebrovascular CO2 reactivity was calculated using a 2.5-MHz pulsed transcranial Doppler (TCD) probe for the continuous measurement of mean blood flow velocity in the middle cerebral artery (Vmca). The cerebrovascular CO2 reactivity was measured both at baseline and during hypotension by increasing the ventilatory frequency by 4 to 7 breaths.min(-1). Nicardipine was used to induce hypotension.

RESULTS

We found that values for the Bispectral index (BSI), baseline mean blood pressure, endtidal CO2 (Pet(CO2)), and Vmca were essentially identical in all patients, irrespective of the type of antidiabetic treatment being taken. Values for absolute and relative CO2 reactivity in insulin-dependent patients, at both baseline blood pressure and during hypotension, were lower than those in patients in the antidiabetic drug, diet, and control groups (during hypotension, absolute CO2 reactivity: diet group: 3.2 +/- 0.9; oral antidiabetic drug group: 3.2 +/- 0.7; insulin group: 1.5 +/- 0.6; control group: 3.4 +/- 0.8 cm.s(-1).mmHg(-1), [P < 0.05 insulin group vs the other groups]; relative CO2 reactivity: diet group, 6.3 +/- 1.0; oral antidiabetic drug group, 6.5 +/- 0.8; insulin group, 3.5 +/- 0.8; control group, 6.5 +/- 0.7%.mmHg(-1), [P < 0.05 insulin group vs the other groups].

CONCLUSION

We concluded that cerebrovascular CO2 reactivity in insulin-dependent patients is impaired during nicardipine-induced hypotension under sevoflurane anesthesia.

Global and regional effects of type 2 diabetes on brain tissue volumes and cerebral vasoreactivity

OBJECTIVE

The aim of this study was to evaluate the regional effects of type 2 diabetes and associated conditions on cerebral tissue volumes and cerebral blood flow (CBF) regulation.

RESEARCH DESIGN AND METHODS

CBF was examined in 26 diabetic (aged 61.6 +/- 6.6 years) and 25 control (aged 60.4 +/- 8.6 years) subjects using continuous arterial spin labeling (CASL) imaging during baseline, hyperventilation, and CO2 rebreathing. Regional gray and white matter, cerebrospinal fluid (CSF), and white matter hyperintensity (WMH) volumes were measured on a T1-weighted inversion recovery fast-gradient echo and a fluid attenuation inversion recovery magnetic resonance imaging at 3 Tesla.

RESULTS

The diabetic group had smaller global white (P = 0.006) and gray (P = 0.001) matter and larger CSF (36.3%, P < 0.0001) volumes than the control group. Regional differences were observed for white matter (-13.1%, P = 0.0008) and CSF (36.3%, P < 0.0001) in the frontal region, for CSF (20.9%, P = 0.0002) in the temporal region, and for gray matter (-3.0%, P = 0.04) and CSF (17.6%, P = 0.01) in the parieto-occipital region. Baseline regional CBF (P = 0.006) and CO2 reactivity (P = 0.005) were reduced in the diabetic group. Hypoperfusion in the frontal region was associated with gray matter atrophy (P < 0.0001). Higher A1C was associated with lower CBF (P < 0.0001) and greater CSF (P = 0.002) within the temporal region.

CONCLUSIONS

Type 2 diabetes is associated with cortical and subcortical atrophy involving several brain regions and with diminished regional cerebral perfusion and vasoreactivity. Uncontrolled diabetes may further contribute to hypoperfusion and atrophy. Diabetic metabolic disturbance and blood flow dysregulation that affects preferentially frontal and temporal regions may have implications for cognition and balance in elderly subjects with diabetes.

Cerebral blood flow velocity and periventricular white matter hyperintensities in type 2 diabetes

OBJECTIVE

Diabetes increases the risk for cerebromicrovascular disease, possibly through its effects on blood flow regulation. The aim of this study was to assess the effects of type 2 diabetes on blood flow velocities (BFVs) in the middle cerebral arteries and to determine the relationship between white matter hyperintensities (WMHs) on magnetic resonance imaging (MRI) and BFVs.

RESEARCH DESIGN AND METHODS

We measured BFVs in 28 type 2 diabetic and 22 control subjects (aged 62.3 +/- 7.2 years) using transcranial Doppler ultrasound during baseline, hyperventilation, and CO(2) rebreathing. WMHs were graded, and their volume was quantified from fluid-attenuated inversion recovery images on a 3.0 Tesla MRI.

RESULTS

The diabetic group demonstrated decreased mean BFVs and increased cerebrovascular resistance during baseline, hypo- and hypercapnia (P < 0.0001), and impaired CO(2) reactivity (P = 0.05). WMH volume was negatively correlated with baseline BFV (P < 0.0001). A regression model revealed that baseline BFVs were negatively associated with periventricular WMHs, HbA(1c) (A1C), and inflammatory markers and positively associated with systolic blood pressure (R(2) = 0.86, P < 0.0001).

CONCLUSIONS

Microvascular disease in type 2 diabetes, which manifests as white matter abnormalities on MRI, is associated with reduced cerebral BFVs, increased resistance in middle cerebral arteries, and inflammation. These findings are clinically relevant as a potential mechanism for cerebrovascular disease in elderly with type 2 diabetes.

The Comparative Effects of Sevoflurane Versus Isoflurane on Cerebrovascular Carbon Dioxide Reactivity in Patients with Diabetes Mellitus

The use of volatile anesthetics has been reported to alter cerebrovascular carbon dioxide (CO2) reactivity. We examined the comparative effects of sevoflurane versus isoflurane on cerebrovascular CO2 reactivity in 40 patients with diabetes mellitus. Anesthesia was maintained with either 1.0 minimum alveolar anesthetic concentration of sevoflurane or 1.0 minimum alveolar anesthetic concentration of isoflurane in 33% oxygen and 67% nitrous oxide. A 2.5-MHz pulsed transcranial Doppler probe was attached to the patient's head at the right temporal window for continuous measurement of mean blood flow velocity in the middle cerebral artery. After establishing baseline middle cerebral artery velocity values and cardiovascular hemodynamics, we increased end-tidal CO2 by decreasing ventilatory frequency by 2-5 breaths/min and repeated the measurements. These were then used to calculate absolute and relative CO2 reactivity. Absolute CO2 reactivity was less in insulin-treated patients with either sevoflurane or isoflurane compared with those patients on oral antidiabetic drugs or dietary therapy (sevoflurane group: diet = 2.6 +/- 0.6; oral antidiabetic drug = 2.5 +/- 0.8; insulin = 1.6 +/- 0.8*; isoflurane group: diet = 3.3 +/- i0.7; oral antidiabetic drug = 3.4 +/- 0.7; insulin = 1.9 +/- 0.7* cm.s(-1).mm Hg(-1); *P < 0.05, respectively). Relative CO2 reactivity showed a similar pattern in the diet-controlled and oral antidiabetic groups, absolute and relative CO2 reactivities were lower with sevoflurane versus isoflurane. Hence, we conclude that cerebrovascular CO2 reactivity in insulin-dependent patients is impaired under both sevoflurane and isoflurane anesthesia.

Cerebrovascular Reserve Capacity Is Preserved in a Population-Based Sample of Patients with Type 2 Diabetes Mellitus

BACKGROUND AND PURPOSE

Type 2 diabetes mellitus (DM2) is associated with an increased risk of stroke. DM2 is also associated with cognitive impairments. Vascular dysfunction, such as impaired cerebrovascular reserve capacity (CVR), may be a determinant of these changes, but previous studies on CVR in DM2 have provided variable results in selected populations of patients. We aimed to examine CVR in a population-based sample of DM2 patients.

METHODS

The CO(2) reactivity of the middle cerebral artery was examined using transcranial Doppler ultrasonography in 81 DM2 patients and 38 controls. In DM2 patients CVR was correlated with diabetic parameters, vascular risk factors and cognitive functioning.

RESULTS

CVR was similar in patients and controls (51 vs. 49%). Within the DM2 group, there was no statistically significant relationship between CVR and DM duration, HbA(1c), albuminuria, blood pressure, intima-media thickness and cognition. CVR tended to be lower in diabetic patients with retinopathy [46 vs. 55%, mean difference: -7.9 (confidence interval -18.0, 2.2)].

CONCLUSION

We conclude that CVR is not impaired in unselected patients with DM2 and probably does not, therefore, play a major role in the aetiology of cognitive impairment.