E. Negri

Relationship between oxygen supply and cerebral blood flow assessed by transcranial Doppler and near – infrared spectroscopy in healthy subjects during breath – holding

BackgroundBreath – holding (BH) is a suitable method for inducing cerebral vasomotor reactivity (VMR). The assessment of VMR is of clinical importance for the early detection of risk conditions and for the follow-up of disabled patients. Transcranial Doppler ultrasonography (TCD) is used to measure cerebral blood flow velocity (CBFV) during BH, whereas near-infrared spectroscopy (NIRS) measures the concentrations of the oxygenated (O2Hb) and reduced (CO2Hb) hemoglobin. The two techniques provide circulatory and functional-related parameters. The aim of the study is the analysis of the relationship between oxygen supply and CBFV as detected by TCD and NIRS in healthy subjects performing BH.Methods20 healthy subjects (15 males and 5 females, age 33 ± 4.5 years) underwent TCD and NIRS examination during voluntary breath – holding. VMR was quantified by means of the breath-holding index (BHI). We evaluated the BHI based on mean CBFV, O2Hb and CO2Hb concentrations, relating the baseline to post-stimulus values. To quantify VMR we also computed the slope of the linear regression line of the concentration signals during BH. From the NIRS signals we also derived the bidimensional representation of VMR, plotting the instantaneous O2Hb concentration vs the CO2Hb concentration during the BH phase. Two subjects, a 30 years old current smoker female and a 63 years old male with a ischemic stroke event at the left middle cerebral artery, were tested as case studies.ResultsThe BHI for the CBFV was equal to 1.28 ± 0.71 %/s, the BHI for the O2Hb to 0.055 ± 0.037 μ mol/l/s and the BHI for CO2Hb to 0.0006 ± 0.0019 μ mol/l/s, the O2Hb slope was equal to 0.15 ± 0.09 μ mol/l/s and the CO2Hb slope to 0.09 ± 0.04 μ mol/l/s. There was a positive correlation between the CBFV and the O2Hb increments during BH (r = 0.865). The bidimensional VMR pattern shows common features among healthy subjects that are lost in the control studies.ConclusionWe show that healthy subjects present a common VMR pattern when counteracting cerebral blood flow perturbations induced by voluntary BH. The proposed methodology allows for the monitoring of changes in the VMR pattern, hence it could be used for assessing the efficacy of neurorehabilitation protocols.

Why do we need NIRS in migraine

Migraine patients may present altered values of the parameters related to their cerebral circulation. The non-invasive assessment of the autoregulation of such patients can be helpful in investigating the causes of migraine. We developed a joint analysis protocol based on transcranial Doppler (TCD) and near-infrared spectroscopy (NIRS) for assessing cerebral autoregulation. We tested 30 healthy subjects and 30 patients suffering from migraine without aura. We measured the baseline values of cerebral blood flow velocity (CBFV) in the middle cerebral arteries and the concentration of oxygenated (oxy-Hb) and reduced (deoxy-Hb) haemoglobin in brain tissue. Afterwards, the subjects performed a breath-holding (BH) task. In baseline conditions, we did not find significant difference between the CBFVs of healthy subjects and of migraineurs, even though the latter group showed a greater dispersion of the velocities (healthy: 70.6±6.8 cm/s; migraine: 71.5±14.4 cm/s). Strong differences in the CBFV were observable during the BH task: migraineurs showed a smaller BH index than controls (0.83±0.55% vs. 1.29±0.71%; p<0.005) and a reduced increase of the oxy-Hb (migraineurs: 0.033±0.019 μmol/l/s; healthy: 0.055±0.037 μmol/l/s; p<0.01). Also, we found a different haemoglobin balancing during the BH phase between migraineurs and controls, revealing that migraineurs do not show a marked vasodilation as functional response to the CO2 increase.We propose this joint analysis protocol to assess cerebral autoregulation of migraine patients, and suggest NIRS as a low-cost, easy, reliable and fast technique to deeply investigate cerebral coupling deregulations.

Follow-up of residual shunt after patent foramen ovale closure.

Orzan F, Liboni W, Bonzano A, Molinari F, Ribezzo M, Rebaudengo N, Grippi G, Negri E. Follow‐up of residual shunt after patent foramen ovale closure.
Acta Neurol Scand: 2010: 122: 257–261.
© 2009 The Authors Journal compilation

Patent foramen ovale detected by near-infrared spectroscopy in patients suffering from migraine with aura

There is an increased prevalence of patent foramen ovale (PFO) in women with migraine with aura (MwA) compared to controls, but the role of PFO in triggering aura is still debated. The aim of this study was to test a group of women suffering from MwA with nearinfrared spectroscopy (NIRS), to assess the NIRS capability of discriminating between subjects with and without PFO. Eighty-eight MwA patients (mean age 37.4±10.7 years, range 16–62 years) underwent NIRS measurement of the cerebral variations of the oxygenated (O2Hb) and reduced haemoglobin (HHb) during breath-holding. The prevalence of O2Hb vs. HHb was used to assess the presence of PFO. As a gold standard, the presence of PFO was assessed by transcranial Doppler sonography (TCD). At the TCD analysis 48 patients (55%) showed PFOs, 32 of which were permanent. NIRS correctly detected 36 subjects out of 40 without PFO, and 38 subjects out of 48 having PFO: sensitivity was 79%; specificity was 90%. All the false negatives were permanent shunts. MwA patients with PFO showed a delayed increase in the O2Hb concentration and a reduced oxygenation with respect to subjects without PFO. NIRS is effective in identifying the presence of PFO in a MwA population, but TCD achieves better diagnostic performances. The NIRS provides additional information about the cerebral vasoreactivity and highlights substantial differences between patients with latent and permanent shunts that warrant further studies.

The diagnostic iter of patent foramen ovale in migraine patients: an update

Patent foramen ovale (PFO) is a frequent finding in migraine patients. The standard technique for PFO diagnosis is actually trans-oesophageal echocardiography (TEE). It requires the injection of a contrast agent unable to pass the pulmonary filter; hence, it is possible to detect a right-to-left shunt by observing the presence of the contrast medium in the cardiac left compartment. The transcranial Doppler (TCD) device accurately measures the blood flow velocities in different cerebral arteries. It can record microembolic signals (MES) backscattered by microbubbles travelling in the cerebral circulation, and distinguish cardiac shunts from pulmonary shunts. The number of MES is correlated to the entity of the shunt. The near-infrared spectroscopy (NIRS) technique tracks the changes in the concentration of oxygenated and reduced haemoglobin in the brain tissue. PFO is revealed by an alteration of the normal vasoreactivity pattern of the subject during functional stimuli. Magnetic resonance imaging (MRI) provides, at the same time, detailed anatomical information and functional measurements. MRI dynamic perfusion sequences can be used to reliably detect PFO either by visual assessment or by signal-time curves in the pulmonary artery and in the left atrium. A good correlation between TEE and MRI grading scores has been demonstrated, even though the interindividual variability of performing the Valsalva manoeuvre could greatly reduce the sensitivity of the method. Further prospective studies are needed to confirm the PFO MRI grading and to assess the sensitivity and specificity of the method.

Cerebral Hemodynamics Assessed by means of Transcranial Doppler and Near - Infrared Spectroscopy in Healthy Smokers and non-Smokers

The assessment of cerebral vasomotor reactivity (VMR) is a valuable tool for the early detection of risk condition in healthy subjects and for the non-invasive bedside evaluation of patients. Typically, cerebral hemodynamics assessment is performed in correspondence of CO2 reactivity. We studied the VMR of a population of young healthy non-smokers (n=10, age 27 plusmn 4.1) and healthy smokers (n=4, age 28 plusmn 4.5) using a joint approach based on transcranial Doppler ultrasonography and near-infrared spectroscopy, to monitor cerebral blood flow velocity (CBFV) and concentrations of oxygenated (O2Hb) and reduced (CO2Hb) haemoglobin. VMR was induced by means of voluntary breath-holding (BH). We quantified VMR using the breath-holding index (BHI). Smokers BH duration was significantly lower than that of non-smokers (p < 10-4; their BHI did not significantly differ from that of non-smokers in terms of CBFV, but differed in terms of O2Hb and CO2Hb concentrations changes. Specifically, with respect to non-smokers, smokers presented a delayed VMR that took place only around 60% of the apnoea phase. This delayed response could reveal an impaired autoregulatory mechanism and could be a risk condition when the subjects need to compensate an abrupt change in the cerebral blood flow