Brain tissue pH in severely head-injured patients: a report of three cases

The spectrum of acute and chronic consequences of neurotrauma in professional and amateur boxing - A call to action is advocated to better understand and prevent this phenomenon

Introduction

Despite changes in regulations, boxing-related injuries and fatalities are still occurring. The numbers available in the literature regarding mortality and long-term consequences may not accurately represent the actual situation. Indeed, the real extent of this phenomenon remains poorly known.

Research question

Delineating the spectrum of acute and chronic consequences of boxing-related traumatic brain injuries (TBI).

Material and methods

Narrative review of the literature concerning acute and chronic boxing-related TBI. Keywords such as mortality, boxing, subdural hematoma were used to search in PubMed and Google scholar. An updated analysis of the Velazquez fatalities collection in boxing was undertaken.

Results

The Velazquez collection includes 2076 fatalities from 1720 to the present with a death rate of 10 athletes per year. More than half of the deaths (N = 1354, 65.2%) occurred after a knock-out, and nearly 75% happened during professional bouts. In Australia, from 1832 to 2020, 163 fatalities were recorded (75% professional). In Japan, from 1952 to 2016, 38 deaths were recorded with a mean age of 23.9 years. Up to 40% of retired professional boxers in the United States were diagnosed with symptoms of chronic brain injury. Clinical dementia is far more prevalent among professional boxers than in amateurs with an incidence of 20%.

Discussion and conclusions

A concerted effort to raise awareness and shed light on boxing-related neuro-trauma is required. Similar considerations can be made for other combat sports or contact sports. A call to action to address this knowledge gap, decrease and prevent this phenomenon is advocated.

1H-MR spectroscopy in traumatic brain injury

Traumatic brain injury (TBI) is a common cause of neurological damage and disability. Conventional imaging (CT scan or MRI) is highly sensitive in detecting lesions and provides important clinical information regarding the need for acute intervention. However, abnormalities detected by CT scan or conventional MRI have limited importance in the classification of the degree of clinical severity and in predicting patients' outcome. This can be explained by the widespread microscopic tissue damage occurring after trauma, which is not observable with the conventional structural imaging methods. Advances in neuroimaging over the past two decades have greatly helped in the clinical care and management of patients with TBI. The advent of newer and more sensitive imaging techniques is now being used to better characterize the nature and evolution of injury and the underlying mechanisms that lead to progressive neurodegeneration, recovery or subsequent plasticity. This review will describe the role of proton magnetic resonance spectroscopic (MRS), an advanced MRI technique as related to its use in TBI. Proton MRS is a noninvasive approach that acquires metabolite information reflecting neuronal integrity and function from multiple brain regions and allows to assess clinical severity and to predict disease outcome.

Evidence of "regional hyperemia" in patients with severe closed head injury using single-photon emission computed tomography

Regional cerebral blood flow (rCBF) was assessed in 32 patients with acute/subacute (n = 18) or chronic (n = 14) head injury using single-photon emission computed tomography (SPECT) and (99m)Tc-hexamethylpropylenenamine oxime (HMPAO) (n = 20) or (123)I-IMP (n = 12). Twelve of the 18 patients with acute/subacute head injury were studied with a high-resolution three-head camera and (99m)Tc-HMPAO. Twenty-eight SPECT studies showed regional abnormalities of tracer uptake. In all cases in which computed tomography (CT) and/or magnetic resonance imaging (MRI) (n = 30) were available for comparison, SPECT showed similar or more extensive abnormalities with high agreement on the laterality of the lesions. Particularly in the 18 patients with acute/subacute head injury, SPECT revealed more and larger lesions than the anatomical scans. In 9 of the 12 patients, at least one region with increase in HMPAO uptake reflecting "hyperemia" was detected (mean study time after injury, 6.3 ± 2.7 days). Follow-up SPECT scans in two patients showed decreased tracer uptake in the previous hyperemic regions and encephalomalacia in the anatomical scan. Thus, hyperemia may reflect "luxury perfusion" in early phases of head injury. In three patients with diffuse axonal injury, a generalized reduction in cortical tracer activity, especially in occipital/parietal regions, was observed. The typical finding in chronic head injury was observation of lesions of similar sizes and high agreement in focal abnormalities between SPECT and CT and/or MRI. However, in nine patients with behavioral disturbances, a decrease in the cortical/basal ganglia was detected. Thus, our study confirms the presence of hyperemia in acute/subacute head injury and demonstrates the value of SPECT for assessing functional impairment in these patients.

Examining lactate in severe TBI using proton magnetic resonance spectroscopy

PRIMARY OBJECTIVE

Clinical management of acute traumatic brain injury (TBI) has emphasized identification of secondary mechanisms of pathophysiology. An important objective in this study is to use proton magnetic resonance spectroscopy (pMRS) to examine early metabolic disturbance due to TBI.

RESEARCH DESIGN

The current design is a case study with repeated measures.

METHOD AND PROCEDURE

Proton magnetic resonance imaging was used to examine neurometabolism in this case of very severe brain trauma at 9 and 23 days post-injury. MRI was performed on a clinical 1.5 Tesla scanner.

MAIN OUTCOMES AND RESULTS

These data also reveal that pMRS methods can detect lactate elevations in an adult surviving severe head trauma and are sensitive to changes in basic neurometabolism during the first month of recovery.

CONCLUSIONS

The current case study demonstrates the sensitivity of pMRS in detecting metabolic alterations during the acute recovery period. The case study reveals that lactate elevations may be apparent for weeks after severe neurotrauma. Further work in this area should endeavour to determine the ideal time periods for pMRS examination in severe TBI as well as the ideal locations of data acquisition (e.g. adjacent or distal to lesion sites).

Acute metabolic brain changes following traumatic brain injury and their relevance to clinical severity and outcome

BACKGROUND

Conventional MRI can provide critical information for care of patients with traumatic brain injury (TBI), but MRI abnormalities rarely correlate to clinical severity and outcome. Previous magnetic resonance spectroscopy studies have reported clinically relevant brain metabolic changes in patients with TBI. However, these changes were often assessed a few to several days after the trauma, with a consequent variation of the metabolic pattern due to temporal changes.

METHODS

Proton magnetic resonance spectroscopic imaging (1H-MRSI) examinations were performed in 10 patients with TBI 48-72 h after the trauma, to obtain early measurements of central brain levels of N-acetylaspartate (NAA), choline (Cho), creatine (Cr) and lactate (La). Metabolite values were expressed as ratios to (1) a metabolic pattern, given by the sum of the resonance intensities of all metabolites detected in the same voxel and (2) intravoxel Cr.

RESULTS

NAA ratios were found to be significantly lower in patients with TBI than in normal controls. In contrast, Cho ratios were significantly higher in patients with TBI than in normal controls. Increased La levels were found in 5 of 10 patients with TBI. Both NAA and La values correlated closely with those of the Glasgow Coma Scale at presentation (r = 0.73 and -0.62, respectively; p<0.01 for both) and the Glasgow Outcome Scale at 3 months (r = -0.79 and 0.79, respectively; p<0.01 for both).

CONCLUSION

Spectroscopic measures of neuro-axonal damage occurring soon after a brain trauma are clinically relevant. Significant increases in cerebral La level also may be detected when 1H-MRSI is performed early after the trauma and, at this stage, can represent a reliable index of injury severity and disease outcome in patients with TBI.

Spatiotemporal pH dynamics following insertion of neural microelectrode arrays

Insertion trauma is a critical issue when assessing intracortical electrophysiological and neurochemical recordings. Previous reports document a wide variety of insertion techniques with speeds ranging from 10 microm/s to 10 m/s. We hypothesize that insertion speed has an effect on tissue trauma induced by implantation of a neural probe. In order to monitor the neural interface during and after probe insertion, we have developed a silicon-substrate array with hydrous iridium oxide microelectrodes for potentiometric recording of extracellular pH (pH(e)), a measure of brain homeostasis. Microelectrode sites were sensitive to pH in the super-Nernstian range (-85.9 mV/pH unit) and selective over other analytes including ascorbic acid, Na(+), K(+), Ca(2+), and Mg(2+). Following insertion, arrays recorded either triphasic or biphasic pH(e) responses, with a greater degree of prolonged acidosis for insertions at 50 microm/s than at 0.5 mm/s or 1.0 mm/s (p<0.05). Spatiotemporal analysis of the recordings also revealed micro-scale variability in the pH(e) response along the array, even when using the same insertion technique. Implants with more intense acidosis were often associated histologically with blood along the probe tract. The potentiometric microsensor array has implications not only as a useful tool to measure extracellular pH, but also as a feedback tool for delivery of pharmacological agents to treat surgical brain trauma.

Cerebral acid—base homeostasis after severe traumatic brain injury

Object. Brain tissue acidosis is known to mediate neuronal death. Therefore the authors measured the main parameters of cerebral acid—base homeostasis, as well as their interrelations, shortly after severe traumatic brain injury (TBI) in humans.

Methods. Brain tissue pH, PCO2, PO2, and/or lactate were measured in 151 patients with severe head injuries, by using a Neurotrend sensor and/or a microdialysis probe. Monitoring was started as soon as possible after the injury and continued for up to 4 days.

During the 1st day following the trauma, the brain tissue pH was significantly lower, compared with later time points, in patients who died or remained in a persistent vegetative state. Six hours after the injury, brain tissue PCO2 was significantly higher in patients with a poor outcome compared with patients with a good outcome. Furthermore, significant elevations in cerebral concentrations of lactate were found during the 1st day after the injury, compared with later time points. These increases in lactate were typically more pronounced in patients with a poor outcome. Similar biochemical changes were observed during later hypoxic events.

Conclusions. Severe human TBI profoundly disturbs cerebral acid—base homeostasis. The observed pH changes persist for the first 24 hours after the trauma. Brain tissue acidosis is associated with increased tissue PCO2 and lactate concentration; these pathobiochemical changes are more severe in patients who remain in a persistent vegetative state or die. Furthermore, increased brain tissue PCO2 (> 60 mm Hg) appears to be a useful clinical indicator of critical cerebral ischemia, especially when accompanied by increased lactate concentrations.

Cerebral concussion in athletes: evaluation and neuropsychological testing

OBJECTIVE

To conduct a topic review of studies related to cerebral concussion in athletes, as an aid to improving decision-making and outcomes.

METHODS

We review the literature to provide an historical perspective on the incidence and definition of and the management guidelines for mild traumatic brain injury in sports. In addition, metabolic changes resulting from cerebral concussion and the second-impact syndrome are reviewed, to provide additional principles for decision-making. Neuropsychological testing, as it applies to athletes, is discussed in detail, to delineate baseline assessments, the characteristics of the neuropsychological evaluation, the neuropsychological tests used, and the methods for in-season identification of cerebral concussion. Future directions in the management of concussions are presented.

RESULTS

The incidence of cerebral concussions has been reduced from approximately 19 per 100 participants in football per season to approximately 4 per 100, i.e., 40,000 to 50,000 concussions per year in football alone. The most commonly used definitions of concussion are those proposed by Cantu and the American Academy of Neurology. Each has associated management guidelines. Concussion or loss of consciousness occurs when the extracellular potassium concentration increases beyond the upper normal limit of approximately 4 to 5 mmol/L, to levels of 20 to 50 mmol/L, inhibiting the action potential and leading to loss of consciousness. This phenomenon helps to explain the delayed effects of symptoms after trauma.

CONCLUSION

Neuropsychological testing seems to be an effective way to obtain useful data on the short-term and long-term effects of mild traumatic brain injury. Moreover, knowledge of the various definitions and management strategies, as well as the utility of neuropsychological testing, is essential for those involved in decision-making with athletes with mild traumatic brain injuries.

Continuous monitoring of cerebrospinal fluid acid-base balance and oxygen metabolism in patients with severe head injury: pathophysiology and treatments for cerebral acidosis and ischemia

INTRODUCTION

Continuous monitoring of cerebral acid-base balance and oxygen metabolism has been introduced in neurointensive care settings. The hypothesis of this study utilizing multimodal neuromonitoring modalities is that hyperventilation and hypothermia improve cerebral acidosis through prevention of cerebral ischemia aggravation in patients with severe head injury.

PATIENTS AND METHODS

Continuous monitoring of cerebrospinal fluid (CSF) pH, PCO2, HCO3-, base excess (BE), PO2, SO2, temperature, lactate and pyruvate (La and Py) measurements were conducted in 8 patients with severe head injury. Temperature-corrected CSF parameters were correlated with those in the jugular blood including oxygen saturation (SjO2), regional oxygen saturation (rSO2), intracranial pressure (ICP) and cerebral perfusion pressure (CPP), jugular blood temperature (Tjb), and endtidal PCO2 (PetCO2). Therapeutic significance of hyperventilation and hypothermia was evaluated.

RESULTS

1) CSF acidosis was observed in all cases (minimum pH 6.59-7.17) due to increased CSF PCO2 and/or decreased CSF HCO3- and tended to associate with abnormal ICP and/or CPP or ischemic episodes indicated by CSF PO2 and SO2, rSO2, and/or SjO2 during monitoring. 2) It was more obvious in CSF than in jugular blood that increased PCO2, La and Py, and/or decreased HCO3- resulted in decreased BE and pH. 3) Decreased CSF PO2 and SO2 only correlated with severe CSF acidosis. 4) Hyperventilation: Decreased PetCO2 did not always closely correlate with CSF PCO2 decrease and CSFpH increase. 5) Hypothermia: There were negative correlations of Tjb with CSF pH and SO2 in all cases, though correlation coefficients were not always high.

CONCLUSIONS

CSF acidosis caused by increased CSF PCO2, La and Py, and/or decreased HCO3- tended to associate with abnormal ICP and CPP, and desaturation indicated by CSF SO2, rSO2, and/or SjO2. Hypothermia rather than hyperventilation tends to improve cerebral acidosis and ischemia.

Modulatory activity of extracellular H+ and Zn2+ on ATP-responses at rP2X1 and rP2X3 receptors

1 The modulatory activity of extracellular H+ and Zn2+ was examined on ATP-responses at rat P2X1 (rP2X1) and rat P2X3 (rP2X3) receptors expressed in Xenopus oocytes and studied under voltage-clamp conditions. 2 Superfused ATP (0.03-30 microM, at pH 7.5) evoked inward currents at rP2X1 receptors (EC50 value, 300+/-7 nM). ATP potency was reduced 2 fold at pH 6.5, and 6 fold at pH 5.5, without altering the maximum ATP effect. Alkaline conditions (pH 8.0) did not alter ATP activity. 3 Superfused ATP (0.01 - 300 microM, at pH 7. 5) evoked inward currents at rP2X3 receptors (EC50 value, 1.8+/-0.3 microM). ATP activity was affected only at pH 5.5, reducing agonist potency 15 fold without altering the maximum ATP effect. 4 Extracellular Zn2+ inhibited ATP-responses at rP2X1 receptors in a time-dependent manner, a 20 min pre-incubation being optimal (IC50 value, 1.0+/-0.2 microM). However, the Zn2+ effect was pH-independent, suggesting Zn2+- and H+-inhibition of ATP-responses occur through independent processes. 5 Extracellular Zn2+ weakly potentiated ATP-responses at rP2X3 receptors (EC50 value, 11+/-1 microM). The Zn2+ effect was dependent on pre-incubation time and, with 20 min pre-incubation periods, Zn2+ potentiated then inhibited ATP-responses in a concentration-dependent, but pH-independent, manner. 6 In summary, ATP activity at rP2X1 receptors was decreased by both extracellular H+ and Zn2+ and their effects were additive. ATP activity at rP2X3 receptors was less sensitive to H+-inhibition and, in contrast, was potentiated by Zn2+ in a pH-independent manner. These differential effects may help distinguish P2X1 and P2X3 receptors in whole tissues.

Modulation of ATP-responses at recombinant rP2X4 receptors by extracellular pH and zinc

The modulatory effects of extracellular H+ and Zn2+ were tested against ATP-responses at rat P2X4 (rP2X4) receptors expressed in Xenopus oocytes under voltage-clamp conditions. ATP (0.1-100 microM, at pH 7.5), evoked inward currents via rP2X4 receptors (EC50 value, 4.1+/-0.98 microM; nH, 1.2+/-0.1). ATP potency was reduced 2 fold, at pH 6.5, without altering maximal activity. ATP potency was reduced by a further 4 fold, at pH 5.5, and the maximal activity of ATP was also reduced. Alkaline conditions (pH 8.0) had no effect on ATP-responses. Zn2+ (100 nM - 10 microM) potentiated ATP-responses at the rP2X4 receptor by 2 fold, whereas higher concentrations (30 microM - 1 mM) inhibited ATP-responses. Zn2+ potentiation was due to an increase in ATP potency, whereas its inhibitory action was due to a reduction in ATP efficacy. Zn2+ modulation of ATP-responses was pH-dependent. At pH 6.5, the bell-shaped curve for Zn2+ was shifted to the right by 1 log unit. At pH 5.5, Zn2+ potentiation was abolished and its inhibitory effect reduced considerably. Suramin (50 microM) also potentiated ATP-responses at rP2X4 receptors. Neither H+ (pH 6.5 and 5.5), Zn2+ (10-100 microM) or a combination of both failed to reveal an inhibitory action of suramin at rP2X4 receptors. In conclusion, H+ and Zn2+ exerted opposite effects on the rP2X4 receptor by lowering and raising agonist potency, respectively. H+ (> or = 3 microM) and Zn2+ (> or = 30 microM) also reduces agonist efficacy by lowering the number of rP2X4 receptors available for activation. The striking differences between the modulatory actions of H+ and Zn2+ at rP2X4 and rP2X2 receptors are discussed.

Early 1H magnetic resonance spectroscopy of acute head injury: four cases

In an attempt to examine in vivo the early metabolic consequences of severe acute head injury, 1H MRS was performed in four patients from 8 to 25 h (mean 15 h) following trauma. In three of these patients, decompressive surgery was performed 4-5 h prior to the MRS. High levels of lactate (area of lactate peak >50% of the mean areas of the NAA, choline-containing, and creatine-containing compound peaks) were found at 8 h posttrauma in the one patient who was not operated on and at 10 h posttrauma in one of the patients who underwent surgery. In the other two postoperative patients, at 18 and 25 h after trauma, lactate levels were found to be low (lactate peak <20% of the mean area of the other three peaks). In the one patient who had a follow-up at 6 days and who had the largest initial lactate levels, these remained high. These findings suggest that high levels of lactate may not be an inevitable consequence of severe head injury and that similar MRS studies should be performed on each individual patient before therapies to reduce lactate are considered. There appeared to be no correlation between the relative amounts of lactate and outcome.

Effects of extracellular pH on agonism and antagonism at a recombinant P2X2 receptor

1. Under voltage-clamp conditions, the activity of agonists and antagonists at a recombinant P2X2 receptor expressed in Xenopus oocytes was examined at different levels of extracellular pH (pHe). 2. In normal Ringer (Mg2+ ions absent), the amplitude of submaximal inward currents to ATP was increased by progressively lowering pHe (8.0-5.5). ATP-responses reached a maximum at pH 6.5 with a 5 fold increase in ATP-affinity; the apparent pKa was 7.05 +/- 0.05. 3. Receptor affinity for ATP was lowered when extracellular Ca2+ ions were replaced with equimolar Mg2+ ions. However, the amplitude of the ATP-responses was still enhanced under acidic conditions, reaching maximal activity at pH 6.5 with a 5 fold increase in ATP-affinity; the apparent pKa was 7.35 +/- 0.05. 4. ATP species present in the superfusate (for the above ionic conditions and pH levels) were calculated to determine the forms of ATP which activate P2X2 receptors: possible candidates include HATP, CaHATP and MgHATP. However, levels of these protonated species increase below pH 6.5, suggesting that receptor protonation rather than agonist protonation is more important. 5. The potency order for agonists of P2X2 receptors was: ATP> 2-MeS-ATP ATPgammaS> ATPalphaS> >CTP >BzATP, while other nucleotides were inactive. EC50 and nH values for full agonists were determined at pH 7.4 and re-examined at pH 6.5. Extracellular acidification increased the affinity by approximately 5 fold for full agonists (ATP, 2-MeSATP, ATPyS and ATP alpha S), without altering the potency order. 6. The potency order for antagonists at P2X2 receptors was: Reactive blue-2 >trinitrophenol-ATP > or = Palatine fast black > or = Coomassie brilliant blue > or = PPADS>suramin (at pH 7.4). IC50 values and slopes of the inhibition curves were re-examined at different pH levels. Only blockade by suramin was affected significantly by extracellular acidification (IC50 values: 10.4 +/- 2 microM, at pH 7.4; 78 +/- 5 nM, at pH 6.5; 30 +/-6 nM, at pH 5.5). 7 In summary, a lowered pHe enhanced the activity of all agonists at P2X2 receptors but, with the exception of suramin, not antagonists. Since a lowered pHe is also known to enhance agonist activity at P2x receptors on sensory neurones containing P2X2 transcripts, the sensitization by metabolic acidosis of native P2x receptors containing P2X2 subunits may have a significant effect on purinergic cell-to-cell signalling.

Brain injury and repair mechanisms: the potential for pharmacologic therapy in closed-head trauma

Rotational acceleration from closed-head trauma produces shear-strain brain injury at the interface of gray and white matter. The initial injury is followed by progressive damage involving three key phenomena: progression of subtle focal axonal damage to axonal transection between six and 12 hours after injury, progressive development of tissue microhemorrhages between 12 and 96 hours after injury, and development of tissue and cerebral spinal fluid lactic acidosis that does not appear to be explained by trauma-induced tissue depolarization, activation of phospholipases and the release of free arachidonic acid, radical generation by metabolism of arachidonate, and lipid peroxidation with consequent membrane degradation and partial mitochondrial uncoupling. Because of terminal differentiation, neurons may have a limited membrane repair capability that might be stimulated by growth factors. Other potential therapeutic interventions include calmodulin inhibitors, iron chelators, and free radical scavengers.

On-line monitoring of cerebral pH by microdialysis

An on-line pH meter that can be mounted in microdialysis systems is described. The pH monitoring system was tested in rat cortex before and after middle cerebral artery occlusion (focal ischemia model). After probe implantation, pH values in the dialysate quickly reached a stable level that depended on perfusion medium (6.72, Ringer; 6.47, 0.9% saline) and flow rate (2 microliters/min). During ischemia, pH values sank rapidly and significantly, whereas lactic and ascorbic acid levels in the dialysate increased 9- to 12-fold. The pH of the dialysate is lower than that of the extracellular fluid because the relative recovery of carbon dioxide is about twice that of bicarbonate at the flow rate used, as shown in in vitro experiments. The pH meter would provide useful additional information during monitoring for ischemia, not only in experimental situations but also during neurosurgical intensive care. In the latter case, the on-line pH value would be a bedside parameter enabling fast feedback for setting analytical priorities and making therapeutical decisions.

Brain pH in head injury: an image-guided 31P magnetic resonance spectroscopy study

It has been suggested that brain acidosis may follow head trauma, and therapies aimed at correcting acidosis have been proposed. Direct measurements of intracellular pH, however, have thus far not been possible in clinical situations. We have studied the intracellular brain pH in 22 patients after head injury (mean Glasgow Coma Score 6.1). Patients were investigated by a combined approach of phosphorus 31 magnetic resonance spectroscopy and magnetic resonance imaging (overall examination time 50-75 min) at a mean time of 11 days after injury (36 hours to 24 days). 31P spectra were obtained in 11 patients on assisted ventilation and in 11 patients on spontaneous ventilation. These spectra were analyzed to yield the pH in the regions studied in all the patients. All pH values were in the normal or alkalotic range when compared with 6 age-matched normal controls. No differences were found between patients on assisted ventilation and patients on spontaneous ventilation. When analyzed as a group, the brain pH in the focal lesions appeared to increase in the first days, to reach a peak in the alkalotic range in the second week, and to return toward normal within 3 weeks from acute injury. Our results suggest that there is no evidence of posttraumatic intracellular brain acidosis in recent human head injury, and therefore, therapies aimed at alkalinizing brain cells need to be reconsidered.

Persistent metabolic sequelae of severe head injury in humans in vivo

Six patients who had suffered severe non-penetrating high velocity head injuries were investigated with phosphorus (31P) magnetic resonance spectroscopy (MRS) to determine, non-invasively, long-term alteration in intracellular biochemistry. The normal subjects were found to have a constant intracellular pH (pHi, 7.03 +/- 0.03) with depth into the brain. The adenosine triphosphate (ATP, 3.46 +/- 0.66 mmol/L of brain tissue), inorganic phosphate (Pi, 1.15 +/- 0.41 mmol/L) and phosphomonester (PME, 2.76 +/- 1.0 mmol/L) tissue concentrations did not alter significantly with depth into normal brain. The phosphocreatine (PCr, 2 cm = 5.21 +/- 1.25, 5 cm = 4.85 +/- 1.49 mmol/L) was slightly reduced, whilst phosphodiesters (PDE, 2 cm = 9.53 +/- 2.6, 5 cm = 14.41 +/- 4.2 mmol/L) rose significantly between tissue comprising mainly of gray (2 cm) and white matter (5 cm). In comparison the contra-lateral hemisphere to the side of worst spasticity showed significant changes a considerable time after injury (6-18 months). The intracellular metabolite tissue concentrations were all reduced by 30% (ATP 2.53 +/- 1.0 mmol/L, PCr 3.44 +/- 0.8 mmol/L) with PDE reduced most significantly at depth (5 cm = 8.4 +/- 3.4 mmol/L), compatible with the cerebral atrophy seen in these patients. In white matter the pHi also decreased with depth (2 cm = 7.03 +/- 0.03, 5 cm = 6.89 +/- 0.05). The reduction in pHi so long after injury is difficult to explain in these steady-state conditions. A structural abnormality, such as a disorder in the blood brain barrier or accumulation of large acidic lysosomes, could cause these pHi changes. There may also be a failure in blood flow regulation, with near critical fluctuations in blood flow both with time and space.

Evaluation of the 11CO2 positron emission tomographic method for measuring brain pH. II. Quantitative pH mapping in patients with ischemic cerebrovascular diseases

A practical method has been developed that, using 11CO2 and positron emission tomography (PET), computes and maps (a) "effective pH" (pHt), a weighted average of intra- and extracellular pH, and (b) "clearance" (K1), product of blood flow and 11CO2 extraction. This method, together with measurements of cerebral blood flow (CBF) and oxygen extraction fraction (OEF), was applied to 12 patients with cerebral ischemia or stroke. The regional K1 was positively correlated with CBF (n = +0.78). The k1/CBF ratio, representing the extraction fraction ratio of 11CO2 to H2 15O, was negatively correlated with CBF (r = -0.54), suggesting that 11CO2 extraction decreases as flow increases. In five acute stroke patients within 2 days of onset, the injured cortex had lower CBF (20.6 ml/min/100 g), higher OEF (78.1%), and lower pHt (6.96) than the contralateral cortex (CBF = 41.4 ml/min/100 g, OEF = 53.3%, pHt = 7.00), suggesting intracellular acidosis with intact cell membranes. In three stroke patients 5-8 days after onset, the injured cortex had higher CBF (60.9 ml/min/100 g), lower OEF (32.0%), and higher pHt (7.12) than the contralateral cortex (CBF = 45.3 ml/min/100 g, OEF = 58.0%, pHt = 7.06), which suggested an increase in extracellular volume compartment reflecting loss of cell membrane integrity. This method provides information on the regional tissue acid-base status and cell membrane integrity, which may be prognostic of tissue viability.