| 1. |
- Shahsavari, Sima, 1976, et al.
(författare)
-
A comparison between the transfer function of ABP to ICP and compensatory reserve index in TBI
- 2008
-
Ingår i: Acta Neurochirurgica, Supplement. - Vienna : Springer Vienna. - 0065-1419. - 9783211855775 ; 102:102, s. 9-13
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The transfer functions which map the arterial blood pressure to the intracranial pressure and the compensatory reserve index have been investigated by various groups to evaluate the brain compliance of patients with traumatic brain injury. The focus of this study has been to assess the capability of both the above mentioned methods to monitor the intracranial compliance in patients suffering from brain swelling. MATERIALS AND METHODS: Clinical data was collected from sixteen traumatic brain injury patients and split into 4 min segments. For each segment, both the magnitude of the empirical transfer function at the fundamental cardiac frequency and the compensatory reserve index were extracted. FINDINGS: The mean values of the compensatory reserve index and the magnitude of the transfer function which scored higher than 0.7 and 0.1 respectively were recorded for all patients suffering from brain swelling. By comparing the histogram of the magnitude of the transfer function at the fundamental cardiac frequency with the histogram of the compensatory reserve index for all patients, a positive correlation between the mean values and a negative correlation among their variances were observed. The linear correlation between the mean values was estimated at r = 0.82 (p
|
|
| 2. |
- Shahsavari, Sima, 1976
(författare)
-
Cerebral Hemodynamics through Intracrnial Pressure
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Traumatic Brain Injury (TBI) continues to be a major problem worldwide. Today, intensive care of patients with TBI is mainly focused on preventing and treating secondary brain injuries. High pressure inside the intracranial cavity has been found to be an important feature of disturbed cerebral dynamics and secondary injuries. Thus, invasive measurement of intracranial pressure (ICP) is today a well established routine in modern neuro-intensive care. Variations in ICP can be regarded as a response of the cerebrospinal system to different stimuli, including homeostatic mechanisms which attempt to maintain the cerebral equilibrium. Nevertheless, the autoregulatory processes and their functionality may also be affected by ICP.This study is an attempt to investigate the cerebral hemodynamics through analysis of ICP and other biomedical measurements available, such as arterial blood pressure and electrocardiography. The study is mainly conducted by analysing biomedical data through mathematical modelling, model-based frameworks, and simulations. This thesis focuses on the dynamics of intracranial pressure in either presence or absence of cerebral autoregulation. A model-based framework which describes the relationship between arterial distensibility and compliance was developed to study variations in the mechanical properties of distant cerebral artries/arteriols. The measurements of pulse wave propagation velocity as well as transfer function between arterial blood pressure and intracranial pressure were utilized as the key elements of the study. Using the aforementioned model, it was shown that variations in the level of ICP may arise from different states of cerebral autoregulation and the associated regime within the cerebral vasculature.The state of Cerebral Blood Flow (CBF) autoregulation during plateau waves of ICP was taken as a subsequent focus of the study. The investigation was conducted by applying the mathematical models of cerebral hemodynamics to the measurements from a TBI patient. Considering the mechanical properties of the cerebrovascular system, the study examined models of impaired as well as intact CBF autoregulation as the possible options. Although the intact autoregulatory mechanism could simulate elevated ICP waves, a large time constant of regulation far from the reported response times in human was needed. The assumption of an exhausted autoregulatory mechanism, however, led to the results pointing to a partial collapse within the cerebral arterial-arteriolar path.Finally, the origin of plateau waves of ICP was investigated by reviewing the phenomenon from a new perspective. The estimation of the baroreceptor reflex index was utilised to locate the source of bradycardia during ICP plateau waves. The result suggested that an activation of the Cushing reflex when the cerebral arterial-arteriolar segment suffers from a partial collapse may lead to the generation of these waves. Furthermore, a negative correlation between cerebral perfusion pressure (CPP) and CBF was recognised associated to this circumstance. It is concluded that a CPP-oriented treatment of TBI patients who demonstrate ICP plateau waves may not lead to the expected regulation of CBF.
|
|
| 3. |
- Shahsavari, Sima, 1976, et al.
(författare)
-
Cerebrovascular Mechanical Properties and Slow Waves of Intracranial Pressure in TBI Patients
- 2011
-
Ingår i: IEEE Transactions on Biomedical Engineering. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9294 .- 1558-2531. ; 58:7, s. 2072-2082
-
Tidskriftsartikel (refereegranskat)abstract
- Myogenic autoregulation of cerebral blood flow is one of the mechanisms affecting cerebral hemodynamics. Short or long-lasting changes in intracranial pressure (ICP) are believed to reveal the responses of the cerebral system to myogenic stimuli. Through the incorporation of a theoretical model into the experimental measurements of cerebrovascular distensibility and compliance in patients with traumatic brain injury (TBI), the current study is an attempt to explain ICP dynamics in either presence or absence of cerebral autoregulation. The pulse wave velocity and transfer function between arterial blood pressure and ICP were utilized as the major tools to reflect variations in the mechanical properties of distant cerebral artries/arteriols. The results imply that different states of cerebral autoregulation and associated regimes within the cerebrovascular system can lead to different types of interrelationship between the slow variations of ICP, cerebral arterial distensibility, and compliance. Consequently, each of these classes may require different types of treatment on patients with TBI.
|
|
| 4. |
- Shahsavari, Sima, 1976, et al.
(författare)
-
Frequency Interpretation of Tidal Peak in Intracranial Pressure Wave
- 2008
-
Ingår i: 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS'08; Vancouver, BC; Canada; 20 August 2008 through 25 August 2008. - : IEEE. - 9781424418152 ; , s. 2689-2692
-
Konferensbidrag (refereegranskat)abstract
- A new approach to locate different components of ICP signal for each cardiac induced ICP beat is presented. In this method an initial timing map is used to define the appropriate part of the ICP wave which should be searched for the specific component. In parallel a recently proposed method was used to decompose the ICP wave to its different frequency harmonics. This algorithm, which is based on tracking the amplitude of the harmonic components using Kalman filtering, brings both heart rate variability and cardiorespiratory interaction into account and provides good time and frequency resolution. Comparing the results of two methods for seventeen ICP records, each one hour long, it has been observed that the fundamental cardiac component has the most significant contribution in the construction of the tidal peak in ICP and therefore tracking of this harmonic could be informative of the tidal peak evolution over the time.
|
|
| 5. |
|
|
| 6. |
- Shahsavari, Sima, 1976
(författare)
-
Intracranial Pressure in Traumatic Brain Injury
- 2009
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Traumatic Brain Injury (TBI) continues to be a major problem worldwide. Today, intensive care of patients with TBI is mainely focused on preventing and treating secondary brain injuries. High pressure inside the intracranial cavity (ICP) has been found to be an important feature of disturbed cerebral dynamics and secondary injuries. Thus, invasive measurement of ICP has been turned into a well established routine in modern neuro-intensive care. ICP can be regarded as a response of the cerebrospinal system to different stimuli. Within this system, parameters are affected by each other, often through complex nonlinear relationships. An evaluation of the brain state is often performed using the time average of the ICP signal. Although this feature provides important information, it is far too simple to grasp and reflect the complete picture.The development of more informative features through ICP signal processing has been the center of attention in many TBI-related investigations as well as in this thesis. This study considers the ICP signal as a composed wave, which contains contributions by circulatory and respiratory mechanisms. By this we avail ourself of studying the cerebrospinal system through its dynamic response upon circulatory and respiratory excitations. Such study is conducted through two different methods. First, arterial blood pressure (ABP) and ICP is defined as the cerebrospinal system input and output, respectively. The associated transfer function is empirically estimated and its amplitude at the fundamental cardiac frequency is compared to the index of compensatory reserve. Linear correlation between two estimates is approximately 0.82, suggesting that the transfer function between ABP and ICP conveys the same sort of information as the index of compensatory reserve. The second method is more concerned with morphology aspects of the ICP. A harmonic model is proposed to decompose the pressure signals of human body to the cardiac and respiratory components. Both linear and nonlinear approaches to the problem are discussed. Results then are compared to the tidal component of ICP, tracked over time. In this study, the fundamental cardiac component is found to have the most significant contribution in the construction of the tidal peak, implying that time evolution of this component can be tracked by tracking the fundamental cardiac component in ICP.
|
|
| 7. |
- Shahsavari, Sima, 1976, et al.
(författare)
-
Linear and Non-linear Approaches to Decomposition of human Body Pressure Signals
- 2009
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Pressure signals, collected from a human body, include responses to different excitations such as respiratory and circulatory mechanisms. In a frequency decomposition of pressure signals, this may be an important piece of information to be incorporated into the procedure. In this paper an alternative parametric approach to frequency decomposition of pressure signals is presented. The decomposition scheme employs a harmonic model based on a Volterra series representation of a non-linear system. Both linear and non-linear strategies to estimate the parameters are applied and discussed.
|
|
| 8. |
- Shahsavari, Sima, 1976, et al.
(författare)
-
Normalized Power Transmission between ABP and ICP in TBI
- 2009
-
Ingår i: Proceedings of the 31st Annual International Conference of the IEEE. Engineering in Medicine and Biology Society. - 9781424432967 ; , s. 4699-4703
-
Konferensbidrag (refereegranskat)abstract
- A new approach to study the pulse transmission between the cerebrovascular bed and the intracranial space is presented. In the proposed approach, the normalized power transmission between ABP and ICP has got the main attention rather than the actual power transmission. Evaluating the gain of the proposed transfer function at any single frequency can reveal how the percentage of contribution of that specific frequency component has been changed through the cerebrospinal system. The gain of the new transfer function at the fundamental cardiac frequency was utilized to evaluate the state of the brain in three TBI patients. Results were assessed using the reference evaluations achieved by a novel CT scanbased scoring scheme. In all three study cases, the gain of the transfer function showed a good capability to follow the trend of the CT scores and describe the brain state. Comparing the new transfer function with the traditional one and also the index of compensatory reserve, the proposed transfer function was found more informative about the state of the brain in the patients under study.
|
|
| 9. |
- Shahsavari, Sima, 1976, et al.
(författare)
-
Plateau Waves and Baroreflex Sensitivity in Patients with Head Injury: A Case Study
- 2011
-
Ingår i: Proceedings of the 33rd Annual International Conference of the IEEE. Engineering in Medicine and Biology Society. - 1557-170X. ; , s. 3792-3795
-
Konferensbidrag (refereegranskat)abstract
- The study aimed to investigate baroreceptor reflex sensitivity in a patient with head injury for whom plateau waves of intracranial pressure (ICP) were recorded. Baroreflex sensitivity index was separately estimated on top of plateau waves and during intermediate intervals between two consecutive waves. The EuroBaVar data set was utilized to verify and validate the results. A very high baroreflex sensitivity associated with dominant parasympathetic activity was observed spontaneous to the acute elevations of ICP. The high vagal afferent discharge was found to be suggestive for the high firing rate of carotid baroreceptors and probably an active Cushing reflex mechanism during plateau waves.
|
|
| 10. |
- Shahsavari, Sima, 1976, et al.
(författare)
-
Pulse Wave Velocity in Patients with Severe Head Injury: A Pilot Study
- 2010
-
Ingår i: Proceedings of the 32nd Annual International Conference of the IEEE. Engineering in Medicine and Biology Society. - 9781424441235 ; , s. 5277-5281
-
Konferensbidrag (refereegranskat)abstract
- The study aimed to determine the potential of pulse wave velocity measurements to reflect changes in compliant cerebral arteries/arterioles in head injured patients. Theapproach utilizes the electrocardiogram and intracranial pressure signals to measure the wave transit time between heart and cranial cavity. Thirty five clinical records of nineteen head injured patients, with different levels of cerebrovascular pressurereactivity response, were investigated through the study. Results were compared with magnitude of normalized transfer function at the fundamental cardiac frequency. In patients with intact cerebrovascular pressure-reactivity, magnitude of normalized transfer function at the fundamental cardiac component was found to be highly correlated with pulse wave transit time.
|
|
