Cerebral oxygenation responses to standing in elderly patients with predominantly diastolic dysfunction

Patients with left ventricular dysfunction may have different orthostatic responses of blood pressure (BP) and cerebral oxygenation than healthy elderly subjects. We investigated orthostatic changes in systemic haemodynamic variables and cerebral oxygenation in 21 elderly patients with heart failure New York Heart Association class I-III in stable condition (age 70-83 years) after withdrawal of furosemide and captopril for 2 weeks, and in 18 healthy elderly subjects (age 70-84 years). Frontal cortical concentration changes of oxyhaemoglobin ([O2Hb]) and deoxyhaemoglobin ([HHb]) were continuously measured by near-infrared spectrophotometry and BP changes by Finapres before and during 10 min of standing. Upon standing [O2Hb] reflecting blood flow, changed by -1.2 +/- 0.9 micromol L-1 (mean +/- SEM) in the patients, whereas it decreased by -4.5 +/- 0.6 micromol L-1 (P<0.01) in the healthy subjects after standing (P<0.05 between groups). [HHb] reflecting the sum of cerebral blood flow, arterial oxygen saturation and cerebral oxygen uptake, increased by 1.5 +/- 0.5 micromol L-1 (P<0.05) and 1.7 +/- 0.6 micromol L-1 (P<0.05), respectively. Compared with healthy elderly subjects, elderly patients with left ventricular dysfunction showed smaller orthostatic [O2Hb] decreases (P<0.01), in relation to higher orthostatic BP rises (P<0.05). These findings indicate that BP changes and an altered cardiovascular balance may influence orthostatic cortical haemodynamic responses in elderly subjects.     

Achieving haemodynamic baseline values with Finapres in elderly subjects during supine rest

Background: Clear guidelines for the resting time necessary to achieve stable blood pressure (BP) levels are scant in gerontology research. Therefore, we aimed to determine the minimum period required for obtaining haemodynamic baseline values in elderly subjects during supine rest. In addition, we evaluated the effect of cardiovascular morbidity, such as diastolic heart failure, and the effect of complex comorbidity of geriatric patients, on haemodynamic changes during supine rest. Methods: A total of 17 healthy subjects, 18 heart failure patients with normal systolic function and 24 geriatric patients, aged 70 years and more, participated. After an overnight fast, changes in systolic BP (SBP), diastolic BP (DBP), heart rate (HR), and stroke volume (SV) were determined by Finapres beat‐to‐beat non‐invasive BP monitoring during a 20‐min supine rest. The procedure was repeated in the healthy subjects and geriatric patients on a second day. Results: Complete BP stabilization was reached in each group within 5 min of supine rest, as SBP remained essentially unchanged and DBP did not change significantly anymore after the fourth minute. In the heart failure patients, HR decreased and SV increased until the twelfth minute of rest. The SBP, DBP, HR, and SV changes during supine rest showed good reproducibility. Conclusions: A span of 5 min of supine rest ensured achievement of reliable and reproducible baseline BP values by Finapres in elderly subjects. However, we recommend at least 12 min of rest to obtain full haemodynamic stability in elderly patients with diminished cardiac compliance and diastolic function.     

Well‐being and cerebral oxygen saturation during acute heart failure in humans

Cerebral symptoms and near‐infrared spectrophotometry‐determined cerebral oxygen saturation (ScO₂) were followed in patients treated for normotensive acute congestive heart failure. The reproducibility and normal range for ScO₂ were established from 39 resting subjects without cardio‐respiratory disease: the ScO₂ ranged from 55 to 78% with a coefficient of variation for triple determination of 6%. Patients rated cerebral symptoms on a scale with end‐points of 0 (best) and 10 (worst). In eight patients with acute heart failure, arterial oxygen tension increased during decongestive treatment, from 9·1 (4·9–10) to 10·4 kPa (7·3–17); median with range, as did arterial oxygen saturation, from 94 (48–97) to 97% (87–99) (P<0·02), whereas the mean arterial pressure, heart rate and arterial carbon dioxide tension remained unchanged. The cerebral symptom score improved from 8 (3–10) to 1 (1–9) and the ScO₂ increased from 34 (20–58) to 50% (19–91) (P<0·02). A ninth patient presented with a silent but massive myocardial infarction: she was cerebrally obtunded with a ScO₂ of 18% and soon died. In patients with normotensive acute heart failure and cerebral symptoms, cerebral oxygen saturation is low, and during successful treatment ScO₂ increases with the well‐being of the patient.     

The effect of phenylephrine on arterial and venous cerebral blood flow in healthy subjects

Aim: Sympathetic regulation of the cerebral circulation remains controversial. Although intravenous phenylephrine (PE) infusion reduces the near‐infrared spectroscopy (NIRS)‐determined measure of frontal lobe oxygenation (S_cO₂) and increases middle cerebral artery mean blood velocity (MCA V_mean), suggesting α‐adrenergic‐mediated cerebral vasoconstriction, this remains unconfirmed by evaluation of arterial and venous cerebral blood flow. Methods: We determined S_cO₂, MCA V_mean, and right internal carotid artery (ICA) and internal jugular venous (IJV) blood flow (duplex ultrasound) during infusion of PE in eight supine young healthy men [26 (3) years, 177 (7) cm and 74 (8) kg; mean (SD)]. Results: Compared with saline, during infusion of PE, mean arterial pressure increased 26 ± 3% (mean ± SE) and MCA V_mean by 4·8 ± 1·9% (P<0·05), while S_cO₂ decreased by 13·7 ± 3·7% (P<0·05) with no significant changes in the arterial oxygen or carbon dioxide tensions. ICA blood flow did not change significantly in response to PE administration (351 ± 12 versus 373 ± 21 ml min^?1; P = 0·236), while IJV blood flow increased (443 ± 57 versus 507 ± 58 ml min^?1; P = 0·023). Conclusions: These findings confirm that PE induces a reduction in S_cO₂ measured by NIRS and causes an increase in MCA V_mean indicative of cerebral arterial vasoconstriction, although ICA was preserved and IJV increased. These results suggest that a decrease in S_cO₂ during infusion of PE reflects an altered cerebral contribution of arterial versus venous blood to the NIRS signal, although we cannot rule out that an effect of PE on skin blood flow is important.     

中风后非流畅型失语症患者语言激活时左前额皮层血氧反应及血流动力学变化:NIRS的研究

目的：探讨NIRS检测认知激活状态大脑功能性变化的临床应用价值。方法：运用近红外光谱(near infrared spectroscopy，NIRS)技术监测脑血管病(CVD)失语症组、CVD非失语症组及正常人组共36名被试语言活动时大脑左前额氧代谢和血流动力学的相应变化，并将CVD合并非流畅性失语症患者的参数变化与正常的成年人及脑血管病未合并失语症患者的变化进行了比较。结果：①NIRS参数的变化在CVD非失语症组及正常人组中均各有50％被试呈现氧合血红蛋白和总血红蛋白同时上升。而还原血红蛋白无明显改变或稍有下降。②CVD失语症组中50％的被试、CVD非失语症组与正常人组各有16．7％被试显示随着氧合血红蛋白和总血红蛋白的增加，还原血红蛋白亦有所增加。结论：语言激活在各组被试的左前额皮层的脑血氧反应和血流动力学变化呈现多样性，失语症患者的还原血红蛋白随着氧合血红蛋白和总血红蛋白的增加亦有所增加，提示失语病人的左前额皮层在语言任务期间比非失语病人利用更多的氧。     

Reproducibility of the alterations in circulation and cerebral oxygenation from supine rest to head-up tilt

Cardiovascular stability, as affected by several diseases, may be assessed by head-up tilt testing. Follow-up studies are essential in both evaluating interventions and assessing progression. However, data on the reproducibility of the changes in circulatory status and cerebral oxygenation provoked by head-up tilt testing are fundamental to follow-up studies. The aim of this study was, therefore, to assess the reproducibility of the alterations in stroke volume (SV), mean arterial pressure (MAP), as well as oxygenated ([O₂Hb]) and deoxygenated haemoglobin ([HHb]) concentration in cerebral tissue from supine rest (SUP) to head-up tilt (HUT). SV was calculated by Modelflow, a pulse contour method, from the finger arterial pressure wave measured by Portapres, the portable version of Finapres. [O₂Hb] and [HHb] were measured using near-infrared spectroscopy (NIRS). Ten healthy individuals visited the laboratory on two different days. On both days, they underwent 10 min SUP followed by 10 min 70° HUT twice. SV decreased, which was (in part) compensated for by an increased heart rate, while MAP increased slightly during HUT compared with SUP. Although [HHb] increased during HUT, no presyncope symptoms were experienced. The circulatory variables (SV, HR and MAP) as well as [HHb] showed an acceptably small systematic and random error as well as reproducibility error compared with the observed difference between HUT and SUP and were similar between and within visits. Therefore, it is concluded that MAP measured by Portapres and SV calculated by Modelflow as well as HHb measured by NIRS seem to be reproducible and may therefore be used in follow-up studies.     

Effects of oxygen supplementation on cerebral oxygenation during exercise in chronic obstructive pulmonary disease patients not entitled to long-term oxygen therapy

Background: The rate of change (Δ) in cerebral oxygenation (COx) during exercise is influenced by blood flow and arterial O₂ content (CaO₂). It is currently unclear whether ΔCOx would (i) be impaired during exercise in patients with chronic obstructive pulmonary disease (COPD) who do not fulfil the current criteria for long‐term O₂ therapy but present with exercise‐induced hypoxaemia and (ii) improve with hyperoxia (FIO₂ = 0·4) in this specific sub‐population. Methods: A total of 20 non‐hypercapnic men (FEV₁ = 47·2 ± 11·5% pred) underwent incremental cycle ergometer exercise tests under normoxia and hyperoxia with ΔCOx (fold‐changes from unloaded exercise in O₂Hb) being determined by near‐infrared spectroscopy. Pulse oximetry assessed oxyhaemoglobin saturation (SpO₂), and impedance cardiography estimated changes in cardiac output (ΔQT). Results: Peak work rate and ΔCOx in normoxia were lower in eight O₂‘desaturators’ compared with 12 ‘non‐desaturators’ (P<0·05). Area under ΔCOx during sub‐maximal exercise was closely related to SpO₂ decrements in ‘desaturators’ (r = 0·92, P<0·01). These patients showed the largest improvement in peak exercise capacity with hyperoxia (P<0·05). Despite a trend to lower sub‐maximal ΔQT and mean arterial pressure with active intervention, ΔCOx was significantly improved only in this group (0·57 ± 0·20 versus 2·09 ± 0·42 for ‘non‐desaturators’ and ‘desaturators’, respectively; P<0·05). Conclusions: ΔCOx was impaired in non‐hypoxaemic patients with COPD who desaturated during exercise. Hyperoxic breathing was able to correct for these abnormalities, an effect related to enhanced CaO₂ rather than improved central haemodynamics. This indicates that O₂ supplementation ameliorates exercise COx in patients with COPD who are not currently entitled to ambulatory O₂ therapy.     

Prefrontal cortex oxygenation during incremental exercise in chronic fatigue syndrome

This study examined the effects of maximal incremental exercise on cerebral oxygenation in chronic fatigue syndrome (CFS) subjects. Furthermore, we tested the hypothesis that CFS subjects have a reduced oxygen delivery to the brain during exercise. Six female CFS and eight control (CON) subjects (similar in height, weight, body mass index and physical activity level) performed an incremental cycle ergometer test to exhaustion, while changes in cerebral oxy-haemoglobin (HbO2), deoxy-haemoglobin (HHb), total blood volume (tHb = HbO2 + HHb) and O2 saturation [tissue oxygenation index (TOI), %)] was monitored in the left prefrontal lobe using a near-infrared spectrophotometer. Heart rate (HR) and rating of perceived exertion (RPE) were recorded at each workload throughout the test. Predicted VO2peak in CFS (1331 +/- 377 ml) subjects was significantly (P < or = 0.05) lower than the CON group (1990 +/- 332 ml), and CFS subjects achieved volitional exhaustion significantly faster (CFS: 351 +/- 224 s; CON: 715 +/- 176 s) at a lower power output (CFS: 100 +/- 39 W; CON: 163 +/- 34 W). CFS subjects also exhibited a significantly lower maximum HR (CFS: 154 +/- 13 bpm; CON: 186 +/- 11 bpm) and consistently reported a higher RPE at the same absolute workload when compared with CON subjects. Prefrontal cortex HbO2, HHb and tHb were significantly lower at maximal exercise in CFS versus CON, as was TOI during exercise and recovery. The CFS subjects exhibited significant exercise intolerance and reduced prefrontal oxygenation and tHb response when compared with CON subjects. These data suggest that the altered cerebral oxygenation and blood volume may contribute to the reduced exercise load in CFS, and supports the contention that CFS, in part, is mediated centrally.     

Tissue oxygenation index measured using spatially resolved spectroscopy correlates with changes in cerebral blood flow in newborn lambs

Background/Objective  Abnormal cerebral haemodynamics in very preterm infants undergoing neonatal intensive care have been associated with adverse outcome, but cerebral blood flow (CBF) is difficult to assess at the cotside. Spatially resolved spectroscopy (SRS) continuously measures cerebral tissue oxygen saturation expressed as tissue oxygenation index (TOI, %), and TOI would reflect changes in CBF with constant cerebral metabolic demand. We aimed to evaluate the relationship between simultaneous measurements of CBF (Transonic System) and TOI (Hamamatsu NIRO-200) in newborn lambs (n = 8). We hypothesised that alterations in CBF of different magnitudes and frequencies would be reflected as changes of TOI in both time domain and frequency domain analyses. Methods  A silicon cuff positioned around the common brachiocephalic artery was inflated to induce 10–30% reductions in cerebral perfusion pressure so as to produce mild-to-moderate variations of CBF. Relationships between changes in CBF and TOI were evaluated in the time domain (Pearson correlation) and frequency domain (Coherence). Results  In time domain analysis, there was significant correlation between ΔTOI (%) and ΔCBF (%) (R ² = 0.69, P < 0.001). In frequency domain analysis, CBF-TOI coherence was ≥0.5 at frequencies below 0.1 Hz, but <0.5 at higher frequencies. Conclusions  We conclude that overall TOI changes are concordant with CBF variations, when arterial oxygen saturation and cerebral oxygen consumption are constant. While TOI reflects CBF, it is more sensitive to variations of CBF of low frequency (<0.1 Hz) than to more rapid, higher frequency changes.     

Long‐term changes in dynamic cerebral autoregulation: a 10 years follow up study

This study takes a novel approach to describing time‐related changes in dynamic cerebral autoregulation (dCA). It is well‐recognized that dCA exhibits both intra‐ and inter‐ subject variability, and this study seeks to characterize the extent to which intra‐subject variability occurs after a significant period of time by studying the same subjects 10 years apart, thus eliminating inter‐subject variability as a source of error. Ten healthy subjects were identified in 1998 and followed up in 2008. On each visit they underwent simultaneous recordings of right middle cerebral artery cerebral blood flow velocity (RMCA CBFV), blood pressure and heart rate. Data were analysed in the frequency domain using transfer function analysis and in the time domain using CBFV step response, from which the autoregulatory index (ARI) was calculated. Ten subjects of mean age 35·5 (range 24–51) years in 1998 (seven male) were studied. There was a significant fall in ARI from 1998–2008 (ΔARI = 1·1, P = 0·021), along with a significant rise in coherence in 2008 (at 0·05 Hz, P = 0·018). Difference in mean step response between 1998 and 2008 was also significant (P = 0·045). This is the first study to assess dCA in the same subjects 10 years apart, providing a novel opportunity to assess intra‐subject variation in dCA after a long time period has elapsed. A fall in frequency and time domain parameters was observed. This is important, and needs to be considered in future studies assessing long‐term changes in dCA, particularly given the body evidence which suggests that dCA is unaffected by ageing.     

近红外光谱技术用于运动和运动想象时大脑皮质血氧反应监测的研究

目的:使用近红外光谱技术监测运动和运动想象时大脑血氧反应的变化以探讨运动和运动想象运用于脑卒中偏瘫患者康复治疗和评价的理论依据。方法:选取64名健康大学生,随机分为两组:运动组32名,运动想象组32名。运用近红外光谱技术监测运动组受试者安静时和运动时大脑皮质的血氧代谢相应变化情况,以及运动想象组受试者安静时和运动想象时大脑皮质的血氧代谢相应变化情况,并将监测结果进行统计学比较和分析。结果:①运动时,大脑氧合血红蛋白和总血红蛋白明显增加,而还原血红蛋白下降。②运动想象时,也呈现大脑氧合血红蛋白和总血红蛋白增加,而还原血红蛋白下降。与安静时进行比较,差异均有显著性意义。结论:运动想象与实际运动同样会提高大脑皮质血氧饱和度,改善相应区域大脑皮质血氧供应。     

脑氧饱和度监测对老年肩关节镜手术患者控制性降压的影响

目的 探讨脑氧饱和度(rSCO2)监测对老年肩关节镜手术患者控制性降压的影响.方法 将60例肩关节镜手术患者随机分为对照组和观察组,每组30例.对照组采取传统的降压模式,观察组采用rSCO2监测下的控制性降压.比较2组患者的麻醉时间、手术时间、术中补液量和尿量、术中硝普钠用量、术后拔管时间、麻醉前后的简易智能精神状态量...     

Role of the renin-angiotensin system in systemic and regional vascular responses to orthostatic stress in healthy volunteers

Summary— The effects of a single oral dose (5 mg) of the angiotensin-converting enzyme (ACE) inhibitor, ramipril, on the systemic and regional vascular responses to simulated orthostatic stress by the lower body negative pressure (LBNP) technique were investigated in eight healthy volunteers, in a double-blind, placebo-controlled crossover study. Arterial blood pressure remained unchanged throughout the study. Ramipril increased significantly forearm (venous occlusion plethysmography, + 37% ± 4% from 1.98 ml±min⁻¹±100 ml⁻¹) and renal (PAH clearance, + 6 ± 2% from 1.20 1±min⁻¹) blood flows and decreased corresponding vascular resistances, 150 minutes after its administration and before LBNP. It also significantly reduced calculated filtration fraction and inhibited by approximately 86% plasma ACE activity. Lower body negative pressure at −10 and −20 mmHg induced a progressive and significant decrease in central venous pressure and significant increases in forearm, splanchnic (indocyanine green clearance) and total peripheral vascular resistances which were of the same magnitude after ramipril and placebo administrations. Ramipril blunted the LBNP-induced increase in renal vascular resistance observed at −20 mmHg after placebo but a similar increase in glomerular filtration rate (inulin clearance) was observed at LBNP-10 and −20 mmHg after ramipril and placebo. Calculated filtration fraction increased after placebo (LBNP-10 mmHg) and ramipril (LBNP-20 mmHg). Finally, LBNP-induced changes in biological parameters were similar after ramipril and placebo at all levels of LBNP. Thus, ramipril does not interfere with the adaptive forearm and splanchnic vascular responses and preserves renal hemodynamics during orthostatic stress simulated by LBNP in healthy volunteers.     

Cerebral oxygenation monitor during head-up and -down tilt using near-infrared spatially resolved spectroscopy

Reflectance near-infrared spectroscopy (NIRS) has become a suitable and easily manageable method to monitor cerebral oxygenation changes in presyncopal and syncopal symptoms caused by postural changing or standing. A new clinical tissue oxygenation monitor has been recently developed which measures absolute tissue haemoglobin saturation (Tissue Oxygenation Index, TOI) utilizing spatially resolved spectroscopy (SRS). The present study examined the effects of postural changes on cerebral oxygenation as reflected in SRS-NIRS findings. Cerebral oxyhaemoglobin (O2Hb), deoxyhaemoglobin (HHb), and the TOI were recorded from both sides of the forehead in five healthy male subjects (age range, 28-40 years) during 90 degrees head-up tilt (HUT) and -6 degrees head-down tilt (HDT). Three series of measurements were carried out on separate days. O2Hb was decreased during HUT. TOI was significantly lower in HUT than in the supine position (SUP). There was no significant change in TOI during HDT. A significant session effect was observed in the left forehead TOI during SUP, but not in the right. SRS-NIRS measurements confirmed sub-clinical alterations of cortical oxygenation during HUT. NIRS data from the left side of the forehead, which may vary with cognitive or emotional activation, were more variable than those from the right side.     

Improving the neurological prognosis following OHCA using real-time evaluation of cerebral tissue oxygenation

Background

The neurological prognosis is poor for patients suffering from out-of-hospital cardiac arrest (OHCA), in the absence of bystander cardio pulmonary resuscitation (CPR), and showing asystole as the initial waveform. However, such patients have the potential of resuming social activity if cerebral tissue oxygen saturation can be preserved.

The effect of circulating adenosine on cerebral haemodynamics and headache generation in healthy subjects

Adenosine is an endogenous neurotransmitter that is released from the brain during hypoxia and relaxes isolated human cerebral arteries. Many cerebral artery dilators cause migraine attacks. However, the effect of intravenous adenosine on headache and cerebral artery diameter has not previously been investigated in man and reports regarding the effect of intravenous adenosine on cerebral blood flow are conflicting. Twelve healthy participants received adenosine 80, 120 microg kg(-1) min(-1) and placebo intravenously for 20 min, in a double-blind, three-way, crossover, randomized design. Headache was rated on a verbal scale (0-10). Regional cerebral blood flow (rCBF) with 133Xe inhalation and single-photon emission computed tomography (SPECT) and MCA flow velocity (V(MCA)) with transcranial Doppler, were measured in direct sequence. Six participants developed headache during 80 microg kg(-1) min(-1) and six during 120 microg kg(-1) min(-1) compared with none on placebo (P = 0.006). The headache was very mild and predominantly described as a pressing sensation. When correcting data for adenosine-induced hyperventilation, no significant changes in rCBF (P = 0.22) or V(MCA) (P = 0.16) were found between treatments. A significant dilation of the superficial temporal artery (STA) was seen (P < 0.001). These results show that circulating adenosine has no effect on rCBF or V(MCA), while it dilates the STA and causes very mild headache.     

Responsiveness of cerebral vessels to changes of blood pressure and partial pressure of carbon dioxide after a transient period of cardiac arrest in dogs

Post-ischemic cerebral hypoperfusion supposedly due to constriction of cerebral vessels is considered to be one of the most important factors limiting the recovery of the brain after cerebral ischemia. An experimental study on dogs was carried out to determine the changes in the responsiveness of cerebral vessel to the dilating effects of increase of arterial pressure (AP) and of CO2 inhalation after 3-6 min of cardiac arrest. Responsiveness was measured by the ratio of change in intracranial pressure (ICP) to change in AP (delta ICP/delta AP) and to change in PCO2 (delta ICP/delta PCO2), since in a bony cranium the changes in cerebral vessel diameter are reflected by instantaneous ICP change. delta ICP/delta AP following the administration of intravenous epinephrine was 33%, 43%, 36%, 37% and 16% of pre-ischemic value 1 h, 2 h, 3 h, 4 h and 5 h after cerebral ischemia, respectively. delta ICP/delta PCO2 following 10% CO2 inhalation was 13%, 32%, 55%, 50%, 70% and 75% of pre-ischemic value 1/2 h, 1 h, 2 h, 3 h, 4 h and 5 h after cerebral ischemia, respectively. Normal delta ICP/central venous pressure (delta CVP) was observed during the post-ischemic period, although statistical analysis was not done. From this we concluded: After 3-6 min of cardiac arrest, cerebral arteries constricted for more than 5 h during post-ischemic period. These arteries did not respond well to the dilating effects of increased arterial pressure or CO2 inhalation, but after 3 h their responses to CO2 inhalation returned to their pre-ischemic levels. The intracranial pressure became more or less dependent on CVP during post-ischemic period.