Effects of elevated ICP on brain function: can the multiparametric monitoring system detect the 'Cushing Response'?

Behavioral and physiological monitoring for awake neurovascular coupling experiments: a how-to guide

Significance: Functional brain imaging in awake animal models is a popular and powerful technique that allows the investigation of neurovascular coupling (NVC) under physiological conditions. However, ubiquitous facial and body motions (fidgeting) are prime drivers of spontaneous fluctuations in neural and hemodynamic signals. During periods without movement, animals can rapidly transition into sleep, and the hemodynamic signals tied to arousal state changes can be several times larger than sensory-evoked responses. Given the outsized influence of facial and body motions and arousal signals in neural and hemodynamic signals, it is imperative to detect and monitor these events in experiments with un-anesthetized animals. Aim: To cover the importance of monitoring behavioral state in imaging experiments using un-anesthetized rodents, and describe how to incorporate detailed behavioral and physiological measurements in imaging experiments. Approach: We review the effects of movements and sleep-related signals (heart rate, respiration rate, electromyography, intracranial pressure, whisking, and other body movements) on brain hemodynamics and electrophysiological signals, with a focus on head-fixed experimental setup. We summarize the measurement methods currently used in animal models for detection of those behaviors and arousal changes. We then provide a guide on how to incorporate this measurements with functional brain imaging and electrophysiology measurements. Results: We provide a how-to guide on monitoring and interpreting a variety of physiological signals and their applications to NVC experiments in awake behaving mice. Conclusion: This guide facilitates the application of neuroimaging in awake animal models and provides neuroscientists with a standard approach for monitoring behavior and other associated physiological parameters in head-fixed animals.

Changes in Blood Pressure and Heart Rate during Decompressive Craniectomy

Objective

Rapid increase in intracranial pressure (ICP) can result in hypertension, bradycardia and apnea, referred to as the Cushing phenomenon. During decompressive craniectomy (DC), rapid ICP decreases can cause changes in mean atrial blood pressure (mABP) and heart rate (HR), which may be an indicator of intact autoregulation and vasomotor reflex.

Methods

A total of 82 patients who underwent DC due to traumatic brain injury (42 cases), hypertensive intracerebral hematoma (19 cases), or major infarction (21 cases) were included in this prospective study. Simultaneous ICP, mABP, and HR changes were monitored in one minute intervals during, prior to and 5–10 minutes following the DC.

Results

After DC, the ICP decreased from 38.1±16.3 mmHg to 9.5±14.2 mmHg (p<0.001) and the mABP decreased from 86.4±14.5 mmHg to 72.5±11.4 mmHg (p<0.001). Conversly, overall HR was no significantly changed in HR, which was 100.1±19.7 rate/min prior to DC and 99.7±18.2 rate/min (p=0.848) after DC. Notably when the HR increased after DC, it correlated with a favorable outcome (p<0.001), however mortality was increased (p=0.032) when the HR decreased or remained unchanged.

Conclusion

In this study, ICP was decreased in all patients after DC. Changes in HR were an indicator of preserved autoregulation and vasomotor reflex. The clinical outcome was improved in patients with increased HR after DC.

A novel technology to model pressure-induced cellular injuries in the brain

BACKGROUND

Elevated intracranial pressure (ICP) accompanying a number of neurological emergencies is poorly understood, and lacks a model to determine cellular pathophysiology. This limits our ability to identify cellular and molecular biomarkers associated with the pathological progression from physiologic to pathologic ICP.

NEW METHOD

We developed an ex vivo model of pressure-induced brain injury, which combines 3D neural cell cultures and a newly developed Pressure Controlled Cell Culture Incubator (PC³I). Human astrocytes and neurons maintained in 3D peptide-conjugated alginate hydrogels were subjected to pressures that mimic both physiologic and pathologic levels of ICP for up to 48h to evaluate the earliest impacts of isolated pressure on cellular viability and quantify early indicators of pressure-induced cellular injury.

RESULTS

Compared to control cell cultures grown under physiologic pressure, sustained pathologic pressure exposure increased the release of intracellular ATP in a cell-specific manner. Eighteen hours of sustained pressure resulted in increased ATP release from neurons but not astrocytes.

COMPARISON WITH EXISTING METHODS

Cell culture incubators maintain cultures at normal atmospheric pressure. Based on multiple literature searches, we are not aware of any other cell culture incubator systems that modify the pressure at which primary CNS cells are maintained.

CONCLUSION

This model simulates the clinical features of elevated ICP encountered in patients with hydrocephalus, and provides a first estimate of the pathological signaling encountered during the earliest perid of progression in neonatal hydrocephalus. This model should provide a means to better understand the pathological biomarkers associated with the earliest stages of elevated ICP.

Doppler Non-invasive Monitoring of ICP in an Animal Model of Acute Intracranial Hypertension

BACKGROUND

In many neurological diseases, intracranial pressure (ICP) is elevated and needs to be actively managed. ICP is typically measured with an invasive transducer, which carries risks. Non-invasive techniques for monitoring ICP (nICP) have been developed. The aim of this study was to compare three different methods of transcranial Doppler (TCD) assessment of nICP in an animal model of acute intracranial hypertension.

METHODS

In 28 rabbits, ICP was increased to 70-80 mmHg by infusion of Hartmann's solution into the lumbar subarachnoid space. Doppler flow velocity in the basilar artery was recorded. nICP was assessed through three different methods: Gosling's pulsatility index PI (gPI), Aaslid's method (AaICP), and a method based on diastolic blood flow velocity (FVdICP).

RESULTS

We found a significant correlation between nICP and ICP when all infusion experiments were combined (FVdICP: r = 0.77, AaICP: r = 0.53, gPI: r = 0.54). The ability to distinguish between raised and 'normal' values of ICP was greatest for FVdICP (AUC 0.90 at ICP >40 mmHg). When infusion experiments were considered independently, FVdICP demonstrated again the strongest correlation between changes in ICP and changes in nICP (mean r = 0.85).

CONCLUSIONS

TCD-based methods of nICP monitoring are better at detecting changes of ICP occurring in time, rather than absolute prediction of ICP as a number. Of the studied methods of nICP, the method based on FVd is best to discriminate between raised and 'normal' ICP and to monitor relative changes of ICP.

Shedding light on mitochondrial function by real time monitoring of NADH fluorescence: I. Basic methodology and animal studies

Normal mitochondrial function in the process of metabolic energy production is a key factor in maintaining cellular activities. Many pathological conditions in animals, as well as in patients, are directly or indirectly related to dysfunction of the mitochondria. Monitoring the mitochondrial activity by measuring the autofluorescence of NADH has been the most practical approach since the 1950s. This review presents the principles and technological aspects, as well as typical results, accumulated in our laboratory since the early 1970s. We were able to apply the fiber-optic-based NADH fluorometry to many organs monitored in vivo under various pathophysiological conditions in animals. These studies were the basis for the development of clinical monitoring devices as presented in accompanying article. The encouraging experimental results in animals stimulated us to apply the same technology in patients after technological adaptations as described in the accompanying article. Our medical device was approved for clinical use by the FDA.

Cushing's mechanism maintains cerebral perfusion pressure in experimental subarachnoid haemorrhage

Mortality following subarachnoid haemorrhage (SAH) is high, especially within the first 48 h. Poor outcome is predicted by high intracranial pressure which causes diminished cerebral perfusion pressure unless a compensatory increase in mean arterial blood pressure occurs. Therefore blood pressure elevation can be protective following subarachnoid haemorrhage despite the potential for rebleeding. This study investigated blood pressure responses to SAH and the impact on cerebral perfusion pressure and outcome, as demonstrated by two experimental models. Various blood pressure responses were demonstrated, both at the ictus and within the following 5h. Elevated MABP at the ictus and at 2h following experimental SAH was associated with maintenance of CPP in the presence of raised ICP. Poor outcome (arrest of the cerebral circulation) was predicted by failure of MABP to increase significantly above sham levels within 2h of SAH. Rat SAH provides relatively inexpensive models to investigate physiological mechanisms that maintain cerebral perfusion in the presence of intracranial hypertension.

Use of NADH fluorescence to determine mitochondrial function in vivo

Normal mitochondrial function is a critical factor in maintaining cellular homeostasis in various organs of the body. Due to the involvement of mitochondrial dysfunction in many pathological states, the real-time in vivo monitoring of the mitochondrial metabolic state is crucially important. This type of monitoring in animal models as well as in patients provides real-time data that can help interpret experimental results or optimize patient treatment. In this paper we are summarizing the following items: (1) presenting the solid scientific ground underlying nicotine amide adenine dinucleotide (NADH) NADH fluorescence measurements based on published materials. (2) Presenting NADH fluorescence monitoring and its physiological significance. (3) Providing the reader with basic information on the methodologies of the fluorometers reflectometers. (4) Clarifying various factors affecting the monitored signals, including artifacts. (5) Presenting the potential use of monitoring mitochondrial function in vivo for the evaluation of drug development. The large numbers of publications by different groups testify to the valuable information gathered in various experimental conditions. The monitoring of NADH levels in the tissue provides the most important information on the metabolic state of the mitochondria in terms of energy production and intracellular oxygen levels. Although NADH signals are not calibrated in absolute units, their trend monitoring is important for the interpretation of physiological or pathological situations. To better understand the tissue function, the multiparametric approach has been developed where NADH serves as the key parameter to be monitored.

Intraoperative jugular bulb desaturation during acute aneurysmal rupture

PURPOSE

To describe an episode of acute jugular venous desaturation during intraoperative rupture of a cerebral aneurysm.

CLINICAL FEATURES

A 57-yr-old patient was scheduled for clipping of a large unruptured basilar tip aneurysm. Abrupt bulging of the brain was observed after bone flap removal, but before dura was opened. This was associated with concurrent development of systemic hypertension to 200/120 mmHg and jugular venous bulb (S(jv)O(2)) desaturation to 13%. Rupture of aneurysm was confirmed by frank blood in cerebrospinal fluid drainage from the lumbar subarachnoid catheter.

CONCLUSIONS

Abrupt S(jv)O(2) desaturation prior to dural opening may suggest an acute increase in intracranial pressure, which in our case followed aneurysmal rupture; the systemic response to increased intracranial pressure (Cushing's response) may be ineffective in maintaining cerebral perfusion.