Martin Smith - Academia.edu (original) (raw)

Papers by Martin Smith

Research paper thumbnail of Monitoring Cerebral Autoregulation After Brain Injury: Multimodal Assessment of Cerebral Slow-Wave Oscillations Using Near-Infrared Spectroscopy

Anesthesia and analgesia, Jan 19, 2015

Continuous monitoring of cerebral autoregulation might provide novel treatment targets and identi... more Continuous monitoring of cerebral autoregulation might provide novel treatment targets and identify therapeutic windows after acute brain injury. Slow oscillations of cerebral hemodynamics (0.05-0.003 Hz) are visible in multimodal neuromonitoring and may be analyzed to provide novel, surrogate measures of autoregulation. Near-infrared spectroscopy (NIRS) is an optical neuromonitoring technique, which shows promise for widespread clinical applicability because it is noninvasive and easily delivered across a wide range of clinical scenarios. The aim of this study is to identify the relationship between NIRS signal oscillations and multimodal neuromonitoring, examining the utility of near infrared derived indices of cerebrovascular reactivity. Twenty-seven sedated, ventilated, brain-injured patients were included in this observational study. Intracranial pressure, transcranial Doppler-derived flow velocity in the middle cerebral artery, and ipsilateral cerebral NIRS variables were cont...

Research paper thumbnail of Reduction of Cytochrome c Oxidase During Vasovagal Hypoxia-Ischemia in Human Adult Brain: A Case Study

Advances in Experimental Medicine and Biology, 2013

Research paper thumbnail of Modelling of Mitochondrial Oxygen Consumption and NIRS Detection of Cytochrome Oxidase Redox State

Advances in Experimental Medicine and Biology, 2009

Research paper thumbnail of Use of a Hybrid Optical Spectrometer for the Measurement of Changes in Oxidized Cytochrome c Oxidase Concentration and Tissue Scattering During Functional Activation

Oxygen Transport to Tissue Xxxiii, 2012

Research paper thumbnail of Investigation of frontal cortex, motor cortex and systemic haemodynamic changes during anagram solving

Advances in experimental medicine and biology, 2008

We have previously reported changes in the concentrations of oxy-(delta[HbO2]) deoxy- (delta[HHb]... more We have previously reported changes in the concentrations of oxy-(delta[HbO2]) deoxy- (delta[HHb]) and total haemoglobin (delta[HbT] = delta[HbO2] + delta[HHb]) measured using near infrared spectroscopy (NIRS) over the frontal cortex (FC) during an anagram solving task. These changes were associated with a significant increase in both mean blood pressure (MBP) and heart rate (HR). The aim of this study was to investigate whether the changes in MBP previously recorded during an anagram solving task produces associated changes in scalp blood flow (flux) measured by laser Doppler and whether any changes are seen in NIRS haemodynamic measurements over a control region of the brain (motor cortex: MC). During the 4-Letter anagram task significant changes were observed in the delta[HbO2], delta[HHb] and delta[HbT] in both the frontal and motor cortex (n = 11, FC p < 0.01, MC p < 0.01). These changes were accompanied by significant changes in both MBP (n = 11, p < 0.01) and scalp f...

Research paper thumbnail of Measurement of the absolute optical properties and cerebral blood volume of the adult human head with hybrid differential and spatially resolved spectroscopy

Physics in Medicine and Biology, 2006

Research paper thumbnail of Cytochrome c oxidase response to changes in cerebral oxygen delivery in the adult brain shows higher brain-specificity than haemoglobin

Research paper thumbnail of Multi-Wavelength, Depth Resolved, Scattering and Pathlength Corrected in vivo Near-Infrared Spectroscopy of Brain Tissue

Biomedical Optics and 3-D Imaging, 2010

Research paper thumbnail of Quantification of adult cerebral blood volume using the NIRS tissue oxygenation index

Advances in experimental medicine and biology, 2006

Research paper thumbnail of Cerebral blood flow assessment with indocyanine green bolus transit detection by near-infrared spectroscopy before and after acetazolamide challenge in humans

Biomedical Optics, 2006

ABSTRACT Cranial near-infrared spectroscopy and intravenous injection of indocyanine green were u... more ABSTRACT Cranial near-infrared spectroscopy and intravenous injection of indocyanine green were used to calculate the blood flow index during rest and after an induced increase in cerebral blood flow following acetazolamide administration.

Research paper thumbnail of Estimating a modified Grubb's exponent in healthy human brains with near infrared spectroscopy and transcranial Doppler

Physiological Measurement, 2008

The relationship between cerebral blood volume (CBV) and flow (CBF) has been widely studied. One ... more The relationship between cerebral blood volume (CBV) and flow (CBF) has been widely studied. One of the most significant early studies was by Grubb et al (1974 Stroke 5 630-9), who conducted hypercapnia studies in primates with positron emission tomography (PET) and empirically found CBV = 0.8 CBF 0.38. The exponent used here has since been known as the Grubb's exponent. In this paper, we define a similar exponent known as the modified Grubb's exponent, G , which is based on CBV and cerebral blood flow velocity (CBFV) estimated by near infrared spectroscopy (NIRS) and transcranial Doppler respectively, i.e. G = log(CBV/CBV 0)/log(CBFV/CBFV 0), where CBV 0 and CBFV 0 are baseline values. The aim of this study was to estimate the nominal value of the modified Grubb's exponent in healthy human brains. We conducted hypercapnia and hypocapnia studies on 14 healthy adult subjects. The correlation coefficient between log(CBV/CBV 0) and log(CBFV/CBFV 0) is 0.71 (p < 0.0001). We found a modified Grubb's exponent of 0.13 (the 95% confidence bounds are 0.10 and 0.17) which is expectedly lower than the conventional Grubb's exponents estimated by other techniques. The modified Grubb's exponent is a simple measure to quantify the hemodynamics between local CBV and global CBFV in the brain and as such may provide insight on brain physiology. Both NIRS and transcranial Doppler techniques are noninvasive and portable, facilitating future studies in other population groups such as brain-injured patients.

Research paper thumbnail of Cerebral microdialysis: research technique or clinical tool

British Journal of Anaesthesia, 2006

Cerebral microdialysis is a well-established laboratory tool that is increasingly used as a bedsi... more Cerebral microdialysis is a well-established laboratory tool that is increasingly used as a bedside monitor to provide on-line analysis of brain tissue biochemistry during neurointensive care. This review describes the principles of cerebral microdialysis and the rationale for its use in the clinical setting, including discussion of the most commonly used microdialysis biomarkers of acute brain injury. Potential clinical applications are reviewed and future research applications identified. Microdialysis has the potential to become an established part of mainstream multi-modality monitoring during the management of acute brain injury but at present should be considered a research tool for use in specialist centres.

Research paper thumbnail of Theoretical investigation of measuring cerebral blood flow in the adult human head using bolus Indocyanine Green injection and near-infrared spectroscopy

Applied Optics, 2007

To investigate the accuracy of measuring cerebral blood flow (CBF) using a bolus injection of ind... more To investigate the accuracy of measuring cerebral blood flow (CBF) using a bolus injection of indocyanine green (ICG) detected by near infrared spectroscopy in adult human heads, simulations were performed using a two layered model, representing the extracerebral and intracerebral layers. Modelled optical data were converted into tissue ICG concentration using either the one detector modified Beer Lambert law (MBLL) method, or the two detector partial pathlength (PPL) method. CBFs were estimated using deconvolution and blood flow index techniques respectively. Using the MBLL method, CBFs were significantly underestimated but the PPL method improved their accuracy and robustness, especially when used as relative measures. Dispersion of the arterial input function also affected the CBF estimates.

Research paper thumbnail of Crustal heterogeneity and basement influence on the development of the Kenya Rift, East Africa

Tectonics, 1993

Structural and metamorphic studies within the exposed Precambrian basement in Kenya indicate that... more Structural and metamorphic studies within the exposed Precambrian basement in Kenya indicate that a number of heterogeneities exist within the lithosphere beneath the line of the Kenya Rift. Of these, the most important is the mechanical and thermal contrast between thick, cold, and rigid Archean lithosphere and thinner anisotropic Proterozoic mobile belt crust/lithosphere. Structural, geophysical, and heat flow data indicate that during a late Proterozoic collisional event the margin of the Tanzanian Archean craton was reworked, overthrust, and effectively buried by tectonically emplaced “Mozambique Belt” rocks. Its position now lies some 100 km east and northeast of the exposed outcrop. These variations in crust/lithosphere type may be directly correlated with the morphotectonic and structural framework of the Kenya Rift and in particular are reflected in the spatial patterns of Cenozoic volcanism within the Gregory Rift zone. Along the craton margin and within the mobile belt a s...

Research paper thumbnail of Monitoring Cerebral Autoregulation After Brain Injury: Multimodal Assessment of Cerebral Slow-Wave Oscillations Using Near-Infrared Spectroscopy

Anesthesia and analgesia, Jan 19, 2015

Continuous monitoring of cerebral autoregulation might provide novel treatment targets and identi... more Continuous monitoring of cerebral autoregulation might provide novel treatment targets and identify therapeutic windows after acute brain injury. Slow oscillations of cerebral hemodynamics (0.05-0.003 Hz) are visible in multimodal neuromonitoring and may be analyzed to provide novel, surrogate measures of autoregulation. Near-infrared spectroscopy (NIRS) is an optical neuromonitoring technique, which shows promise for widespread clinical applicability because it is noninvasive and easily delivered across a wide range of clinical scenarios. The aim of this study is to identify the relationship between NIRS signal oscillations and multimodal neuromonitoring, examining the utility of near infrared derived indices of cerebrovascular reactivity. Twenty-seven sedated, ventilated, brain-injured patients were included in this observational study. Intracranial pressure, transcranial Doppler-derived flow velocity in the middle cerebral artery, and ipsilateral cerebral NIRS variables were cont...

Research paper thumbnail of Reduction of Cytochrome c Oxidase During Vasovagal Hypoxia-Ischemia in Human Adult Brain: A Case Study

Advances in Experimental Medicine and Biology, 2013

Research paper thumbnail of Modelling of Mitochondrial Oxygen Consumption and NIRS Detection of Cytochrome Oxidase Redox State

Advances in Experimental Medicine and Biology, 2009

Research paper thumbnail of Use of a Hybrid Optical Spectrometer for the Measurement of Changes in Oxidized Cytochrome c Oxidase Concentration and Tissue Scattering During Functional Activation

Oxygen Transport to Tissue Xxxiii, 2012

Research paper thumbnail of Investigation of frontal cortex, motor cortex and systemic haemodynamic changes during anagram solving

Advances in experimental medicine and biology, 2008

We have previously reported changes in the concentrations of oxy-(delta[HbO2]) deoxy- (delta[HHb]... more We have previously reported changes in the concentrations of oxy-(delta[HbO2]) deoxy- (delta[HHb]) and total haemoglobin (delta[HbT] = delta[HbO2] + delta[HHb]) measured using near infrared spectroscopy (NIRS) over the frontal cortex (FC) during an anagram solving task. These changes were associated with a significant increase in both mean blood pressure (MBP) and heart rate (HR). The aim of this study was to investigate whether the changes in MBP previously recorded during an anagram solving task produces associated changes in scalp blood flow (flux) measured by laser Doppler and whether any changes are seen in NIRS haemodynamic measurements over a control region of the brain (motor cortex: MC). During the 4-Letter anagram task significant changes were observed in the delta[HbO2], delta[HHb] and delta[HbT] in both the frontal and motor cortex (n = 11, FC p < 0.01, MC p < 0.01). These changes were accompanied by significant changes in both MBP (n = 11, p < 0.01) and scalp f...

Research paper thumbnail of Measurement of the absolute optical properties and cerebral blood volume of the adult human head with hybrid differential and spatially resolved spectroscopy

Physics in Medicine and Biology, 2006

Research paper thumbnail of Cytochrome c oxidase response to changes in cerebral oxygen delivery in the adult brain shows higher brain-specificity than haemoglobin

Research paper thumbnail of Multi-Wavelength, Depth Resolved, Scattering and Pathlength Corrected in vivo Near-Infrared Spectroscopy of Brain Tissue

Biomedical Optics and 3-D Imaging, 2010

Research paper thumbnail of Quantification of adult cerebral blood volume using the NIRS tissue oxygenation index

Advances in experimental medicine and biology, 2006

Research paper thumbnail of Cerebral blood flow assessment with indocyanine green bolus transit detection by near-infrared spectroscopy before and after acetazolamide challenge in humans

Biomedical Optics, 2006

ABSTRACT Cranial near-infrared spectroscopy and intravenous injection of indocyanine green were u... more ABSTRACT Cranial near-infrared spectroscopy and intravenous injection of indocyanine green were used to calculate the blood flow index during rest and after an induced increase in cerebral blood flow following acetazolamide administration.

Research paper thumbnail of Estimating a modified Grubb's exponent in healthy human brains with near infrared spectroscopy and transcranial Doppler

Physiological Measurement, 2008

The relationship between cerebral blood volume (CBV) and flow (CBF) has been widely studied. One ... more The relationship between cerebral blood volume (CBV) and flow (CBF) has been widely studied. One of the most significant early studies was by Grubb et al (1974 Stroke 5 630-9), who conducted hypercapnia studies in primates with positron emission tomography (PET) and empirically found CBV = 0.8 CBF 0.38. The exponent used here has since been known as the Grubb's exponent. In this paper, we define a similar exponent known as the modified Grubb's exponent, G , which is based on CBV and cerebral blood flow velocity (CBFV) estimated by near infrared spectroscopy (NIRS) and transcranial Doppler respectively, i.e. G = log(CBV/CBV 0)/log(CBFV/CBFV 0), where CBV 0 and CBFV 0 are baseline values. The aim of this study was to estimate the nominal value of the modified Grubb's exponent in healthy human brains. We conducted hypercapnia and hypocapnia studies on 14 healthy adult subjects. The correlation coefficient between log(CBV/CBV 0) and log(CBFV/CBFV 0) is 0.71 (p < 0.0001). We found a modified Grubb's exponent of 0.13 (the 95% confidence bounds are 0.10 and 0.17) which is expectedly lower than the conventional Grubb's exponents estimated by other techniques. The modified Grubb's exponent is a simple measure to quantify the hemodynamics between local CBV and global CBFV in the brain and as such may provide insight on brain physiology. Both NIRS and transcranial Doppler techniques are noninvasive and portable, facilitating future studies in other population groups such as brain-injured patients.

Research paper thumbnail of Cerebral microdialysis: research technique or clinical tool

British Journal of Anaesthesia, 2006

Cerebral microdialysis is a well-established laboratory tool that is increasingly used as a bedsi... more Cerebral microdialysis is a well-established laboratory tool that is increasingly used as a bedside monitor to provide on-line analysis of brain tissue biochemistry during neurointensive care. This review describes the principles of cerebral microdialysis and the rationale for its use in the clinical setting, including discussion of the most commonly used microdialysis biomarkers of acute brain injury. Potential clinical applications are reviewed and future research applications identified. Microdialysis has the potential to become an established part of mainstream multi-modality monitoring during the management of acute brain injury but at present should be considered a research tool for use in specialist centres.

Research paper thumbnail of Theoretical investigation of measuring cerebral blood flow in the adult human head using bolus Indocyanine Green injection and near-infrared spectroscopy

Applied Optics, 2007

To investigate the accuracy of measuring cerebral blood flow (CBF) using a bolus injection of ind... more To investigate the accuracy of measuring cerebral blood flow (CBF) using a bolus injection of indocyanine green (ICG) detected by near infrared spectroscopy in adult human heads, simulations were performed using a two layered model, representing the extracerebral and intracerebral layers. Modelled optical data were converted into tissue ICG concentration using either the one detector modified Beer Lambert law (MBLL) method, or the two detector partial pathlength (PPL) method. CBFs were estimated using deconvolution and blood flow index techniques respectively. Using the MBLL method, CBFs were significantly underestimated but the PPL method improved their accuracy and robustness, especially when used as relative measures. Dispersion of the arterial input function also affected the CBF estimates.

Research paper thumbnail of Crustal heterogeneity and basement influence on the development of the Kenya Rift, East Africa

Tectonics, 1993

Structural and metamorphic studies within the exposed Precambrian basement in Kenya indicate that... more Structural and metamorphic studies within the exposed Precambrian basement in Kenya indicate that a number of heterogeneities exist within the lithosphere beneath the line of the Kenya Rift. Of these, the most important is the mechanical and thermal contrast between thick, cold, and rigid Archean lithosphere and thinner anisotropic Proterozoic mobile belt crust/lithosphere. Structural, geophysical, and heat flow data indicate that during a late Proterozoic collisional event the margin of the Tanzanian Archean craton was reworked, overthrust, and effectively buried by tectonically emplaced “Mozambique Belt” rocks. Its position now lies some 100 km east and northeast of the exposed outcrop. These variations in crust/lithosphere type may be directly correlated with the morphotectonic and structural framework of the Kenya Rift and in particular are reflected in the spatial patterns of Cenozoic volcanism within the Gregory Rift zone. Along the craton margin and within the mobile belt a s...