Systems analysis of cerebrovascular pressure transmission: an observational study in head-injured patients

1990 ◽  
Vol 73 (6) ◽  
pp. 871-880 ◽  
Author(s):  
Ian R. Piper ◽  
J. Douglas Miller ◽  
N. Mark Dearden ◽  
James R. S. Leggate ◽  
Ian Robertson
Keyword(s):  
Transfer Function ◽  
Frequency Response ◽  
Response Curve ◽  
Frequency Response Curve ◽  
Content Type ◽  
High Frequency Response ◽  
Curve Type ◽  
Head Injured ◽  
Pressure Transmission ◽  
Injured Patients

✓ In an observational study in head-injured patients, cerebrovascular pressure transmission was investigated using a systems analysis approach whereby the blood pressure (BP) waveform was used as a measure of an input stimulus to the cerebrovascular bed (CVB) and the intracranial pressure (ICP) waveform as the response to that stimulus. The transfer function is a measure of how much pressure is transmitted through the CVB at a given frequency and is calculated using Fourier analysis of the pressure waveforms. The transfer function allows quantification of the pressure transmission performance of the CVB, thus providing a basis for comparison between normal and abnormal function. Fifteen hundred samples of ICP and BP waveforms were collected from 30 head-injured patients via microcomputer. Off-line spectral analysis of the waveform database revealed four main classes of transfer function: those with an overall flat transfer function (curve type 1); those with an elevated low-frequency response (curve type 2); those with an elevated high-frequency response (curve type 3); and those exhibiting both an elevated low- and high-frequency response (curve type 4). Curve types 2 and 4 were most often associated with raised ICP (> 20 mm Hg), whereas curve types 1 and 3 were most often affiliated with ICP less than 15 mm Hg. Studies of this type may provide insight into the pathophysiology of the CVB and ultimately aid in the prediction and treatment of raised ICP.

A Method of Model Reduction

1986 ◽  
Vol 108 (4) ◽  
pp. 368-371 ◽  
Author(s):  
Jium-Ming Lin ◽  
Kuang-Wei Han
Keyword(s):  
Transfer Function ◽  
Frequency Response ◽  
Model Reduction ◽  
Control Systems ◽  
Response Curve ◽  
Nonlinear Control Systems ◽  
Frequency Response Curve ◽  
Stability Boundaries ◽  
Parameter Variations ◽  
The Stability

In this brief note, the effects of model reduction on the stability boundaries of control systems with parameter variations, and the limit-cycle characteristics of nonlinear control systems are investigated. In order to reduce these effects, a method of model reduction is used which can approximate the original transfer function at S=0, S=∞, and also match some selected points on the frequency response curve of the original transfer function. Examples are given, and comparisons with the methods given in current literature are made.

Verbal learning deficits following severe head injury: heterogeneity in recovery over 1 year

1991 ◽  
Vol 75 (Supplement) ◽  
pp. S50-S58 ◽  
Author(s):  
Ronald M. Ruff ◽  
David Young ◽  
Theresa Gautille ◽  
Lawrence F. Marshall ◽  
Jeff Barth ◽  
...  
Keyword(s):  
Memory Performance ◽  
Verbal Learning ◽  
Data Bank ◽  
Learning Deficits ◽  
Content Type ◽  
Recovery Curve ◽  
Recovery Curves ◽  
Head Injured ◽  
Injured Patients ◽  
Case Basis

✓ A total of 40 severely head-injured patients were selected from the Traumatic Coma Data Bank, supported by the National Institute of Neurological Disorders and Stroke, to analyze the recovery of verbal learning across baseline and 6- and 12-month evaluations postinjury. During the initial 6 months, the group demonstrated marked recovery, followed by an absence of improvement over the latter part of the year. Analysis of this recovery curve on a case by case basis revealed three recovery subtypes: namely, a flat curve, a peak-drop curve, or an improvement curve. These three subtypes proved to have concurrent validity when compared with another memory test. Adding 19 new patients to the sample cross-validated the subtypes. However, the memory performance of the 59 patients was dissociated from other neuropsychological tests which showed recovery at more equivalent rates across the subtypes. Analysis of the demographic and neurological characteristics disclosed that the group with a peak-drop recovery curve was less well educated and the group with a flat curve demonstrated a trend toward higher levels of hypoxia. Moreover, the three subgroups were rated by their relatives to have equivalent levels of depression at baseline and at 6 months, but only the improved subgroup demonstrated reduced depression at 1 year. The clinical relevancy of these differential recovery curves is discussed.

Contribution of CSF and vascular factors to elevation of ICP in severely head-injured patients

1987 ◽  
Vol 66 (6) ◽  
pp. 883-890 ◽  
Author(s):  
Anthony Marmarou ◽  
Angelo L. Maset ◽  
John D. Ward ◽  
Sung Choi ◽  
Danny Brooks ◽  
...  
Keyword(s):  
Severe Head Injury ◽  
Ventricular Catheter ◽  
Outflow Resistance ◽  
Content Type ◽  
Relative Contribution ◽  
Temporal Course ◽  
Head Injured ◽  
Predominant Factor ◽  
Injured Patients ◽  
Fine Print

✓ The authors studied the relative contribution of cerebrospinal fluid (CSF) and vascular parameters to the level of intracranial pressure (ICP) in 34 severely head-injured patients with a Glasgow Coma Scale score of less than 8. This was accomplished by first characterizing the temporal course of CSF formation and outflow resistance during the 5-day period postinjury. The CSF formation and outflow resistance were obtained from pressure responses to bolus addition and removal of fluid from an indwelling ventricular catheter. The vascular contribution to the level of ICP was assessed by withdrawing fluid at its rate of formation and observing the resultant change in equilibrium ICP level. It was found that, with the exception of patients with subarachnoid hemorrhage, CSF parameters accounted for approximately one-third of the ICP rise after severe head injury, and that a vascular mechanism may be the predominant factor in elevation of ICP.

Outcome from head injury related to patient' age

1988 ◽  
Vol 68 (3) ◽  
pp. 409-416 ◽  
Author(s):  
Thomas G. Luerssen ◽  
Melville R. Klauber ◽  
Lawrence F. Marshall
Keyword(s):  
Mortality Rate ◽  
Pediatric Population ◽  
Adult Population ◽  
Content Type ◽  
Head Injured ◽  
Injured Patients ◽  
Age Range ◽  
Relationship Of ◽  
The Relationship ◽  
Pupillary Reactivity

✓ A series of 8814 head-injured patients admitted to 41 hospitals in three separate metropolitan areas were prospectively studied. Of these, 1906 patients (21.6%) were 14 years of age or less. This “pediatric population” was compared to the remaining “adult population” for mechanism of injury, admission Glasgow Coma Scale score, motor score, blood pressure, pupillary reactivity, the presence of associated injuries, and the presence of subdural or epidural hematoma. The relationship of each of these factors was then correlated with posttraumatic mortality. Except for patients found to have subdural hematoma and those who were profoundly hypotensive, the pediatric patients exhibited a significantly lower mortality rate compared to the adults, thus confirming this generally held view. This study indicates that age itself, even within the pediatric age range, is a major independent factor affecting the mortality rate in head-injured patients.

Adverse effects of prolonged hyperventilation in patients with severe head injury: a randomized clinical trial

1991 ◽  
Vol 75 (5) ◽  
pp. 731-739 ◽  
Author(s):  
J. Paul Muizelaar ◽  
Anthony Marmarou ◽  
John D. Ward ◽  
Hermes A. Kontos ◽  
Sung C. Choi ◽  
...  
Keyword(s):  
Cerebral Ischemia ◽  
Control Group ◽  
Content Type ◽  
Cerebral Vasoconstriction ◽  
Number Of Patients ◽  
Severity Of Injury ◽  
Head Injured ◽  
Injured Patients ◽  
To Receive

✓ There is still controversy over whether or not patients should be hyperventilated after traumatic brain injury, and a randomized trial has never been conducted. The theoretical advantages of hyperventilation are cerebral vasoconstriction for intracranial pressure (ICP) control and reversal of brain and cerebrospinal fluid (CSF) acidosis. Possible disadvantages include cerebral vasoconstriction to such an extent that cerebral ischemia ensues, and only a short-lived effect on CSF pH with a loss of HCO3− buffer from CSF. The latter disadvantage might be overcome by the addition of the buffer tromethamine (THAM), which has shown some promise in experimental and clinical use. Accordingly, a trial was performed with patients randomly assigned to receive normal ventilation (PaCO2 35 ± 2 mm Hg (mean ± standard deviation): control group), hyperventilation (PaCO2 25 ± 2 mm Hg: HV group), or hyperventilation plus THAM (PaCO2 25 ± 2 mm Hg: HV + THAM group). Stratification into subgroups of patients with motor scores of 1–3 and 4–5 took place. Outcome was assessed according to the Glasgow Outcome Scale at 3, 6, and 12 months. There were 41 patients in the control group, 36 in the HV group, and 36 in the HV + THAM group. The mean Glasgow Coma Scale score for each group was 5.7 ± 1.7, 5.6 ± 1.7, and 5.9 ± 1.7, respectively; this score and other indicators of severity of injury were not significantly different. A 100% follow-up review was obtained. At 3 and 6 months after injury the number of patients with a favorable outcome (good or moderately disabled) was significantly (p < 0.05) lower in the hyperventilated patients than in the control and HV + THAM groups. This occurred only in patients with a motor score of 4–5. At 12 months posttrauma this difference was not significant (p = 0.13). Biochemical data indicated that hyperventilation could not sustain alkalinization in the CSF, although THAM could. Accordingly, cerebral blood flow (CBF) was lower in the HV + THAM group than in the control and HV groups, but neither CBF nor arteriovenous difference of oxygen data indicated the occurrence of cerebral ischemia in any of the three groups. Although mean ICP could be kept well below 25 mm Hg in all three groups, the course of ICP was most stable in the HV + THAM group. It is concluded that prophylactic hyperventilation is deleterious in head-injured patients with motor scores of 4–5. When sustained hyperventilation becomes necessary for ICP control, its deleterious effect may be overcome by the addition of THAM.

Impairment of helper T-cell function and lymphokineactivated killer cytotoxicity following severe head injury

1991 ◽  
Vol 75 (5) ◽  
pp. 766-773 ◽  
Author(s):  
Keith B. Quattrocchi ◽  
Edmund H. Frank ◽  
Claramae H. Miller ◽  
Asim Amin ◽  
Bernardo W. Issel ◽  
...  
Keyword(s):  
T Cell ◽  
Head Injury ◽  
Severe Head Injury ◽  
Cell Cytotoxicity ◽  
Content Type ◽  
Lak Cell ◽  
Head Injured ◽  
Injured Patients ◽  
Fine Print

✓ Infection is a major complication of severe head injury, occurring in 50% to 75% of patients who survive to hospitalization. Previous investigations of immune activity following head injury have demonstrated suppression of helper T-cell activation. In this study, the in vitro production of interferon-gamma (INF-γ), interleukin-1 (IL-1), and interleukin-2 (IL-2) was determined in 25 head-injured patients following incubation of peripheral blood lymphocytes (PBL's) with the lymphocyte mitogen phytohemagglutinin (PHA). In order to elucidate the functional status of cellular cytotoxicity, lymphokine-activated killer (LAK) cell cytotoxicity assays were performed both prior to and following incubation of PBL's with IL-2 in five patients with severe head injury. The production of INF-γ and IL-2 by PHA-stimulated PBL's was maximally depressed within 24 hours of injury (p < 0.001 for INF-γ, p = 0.035 for IL-2) and partially normalized within 21 days of injury. There was no change in the production of IL-1. When comparing the in vitro LAK cell cytotoxicity of PBL's from head-injured patients and normal subjects, there was a significant depression in LAK cell cytotoxicity both prior to (p = 0.010) and following (p < 0.001) incubation of PBL's with IL-2. The results of this study indicate that IL-2 and INF-γ production, normally required for inducing cell-mediated immunity, is suppressed following severe head injury. The failure of IL-2 to enhance LAK cell cytotoxicity suggests that factors other than decreased IL-2 production, such as inhibitory soluble mediators or suppressor lymphocytes, may be responsible for the reduction in cellular immune activity following severe head injury. These findings may have significant implications in designing clinical studies aimed at reducing the incidence of infection following severe head injury.

The metabolic response to severe head injury

1984 ◽  
Vol 60 (4) ◽  
pp. 687-696 ◽  
Author(s):  
Guy L. Clifton ◽  
Claudia S. Robertson ◽  
Robert G. Grossman ◽  
Susan Hodge ◽  
Richard Foltz ◽  
...  
Keyword(s):  
Body Surface ◽  
Nitrogen Balance ◽  
Metabolic Response ◽  
The Body ◽  
Nitrogen Excretion ◽  
Content Type ◽  
Head Injured ◽  
The Mean ◽  
Metabolic Expenditure ◽  
Injured Patients

✓ Caloric expenditure and nitrogen balance were measured in 14 steroid-treated comatose head-injured patients acutely and up to 28 days after injury. During this period patients were fed with a continuous enteral infusion of a formula containing 2 Kcal/cc and 10 gm nitrogen/liter. Indirect calorimetry was carried out for 102 patient-days. The mean resting metabolic expenditure (RME) for nonsedated nonparalyzed patients was 138% ± 37% of that expected for an uninjured resting person of equivalent age, sex, and body surface area. Nitrogen excretion was measured for 135 patient-days. The mean excretion was 20.2 ± 6.4 gm/day. The mean protein caloric contribution was 23.9% ± 6.7% and was greater than 25% for six patients, compared to normal values of 10% to 15%. Despite hyperalimentation, positive nitrogen balance for any 3-day period was achieved in only seven patients, and required replacement of 161% to 240% of RME with enterally administered formula. Head-injured patients had a metabolic response similar to that reported for patients with burns of 20% to 40% of the body surface.

Mechanisms and implications of hypoalbuminemia in head-injured patients

1988 ◽  
Vol 69 (3) ◽  
pp. 386-392 ◽  
Author(s):  
Craig J. McClain ◽  
Bernhard Hennig ◽  
Linda G. Ott ◽  
Simeon Goldblum ◽  
A. Byron Young
Keyword(s):  
Endothelial Cell ◽  
Acute Phase ◽  
Nutritional Support ◽  
Cell Injury ◽  
Acute Phase Proteins ◽  
Interleukin 1 ◽  
Endothelial Permeability ◽  
Content Type ◽  
Head Injured ◽  
Injured Patients

✓ Severely head-injured patients are hypermetabolic/hypercatabolic and exhibit many aspects of the postinjury acute-phase response. These patients have hypoalbuminemia, hypozincemia, hypoferremia, hypercupria, fever, and increased synthesis of acute-phase proteins such as ceruloplasmin and higher C-reactive protein levels. It has been suggested that increased interleukin-1 (IL-1) in the ventricular fluid may be responsible, at least in part, for these metabolic abnormalities. In the present study, serum albumin levels were evaluated throughout an 18-day study period in 62 head-injured patients receiving aggressive nutritional support. Hypoalbuminemia (mean ± standard error of the mean 3.10 ± 0.2 gm/dl; normal value 3.5 to 5 gm/dl) was observed upon hospital admission; these albumin levels continued to decrease until 2 weeks postinjury, despite aggressive nutritional support. This hypoalbuminemia may be mediated via altered endothelial permeability properties due to endothelial cell dysfunction caused by cytokines such as IL-1. Transendothelial movement of albumin was assayed using a pulmonary artery endothelial cell culture system. Both a crude macrophage supernatant derived from a murine P388D cell line having IL-1 activity (mIL-1) and human recombinant IL-1 (rIL-1) were tested. The amount of albumin transferred was time- and concentration-dependent, with maximal transfer at 24 hours and 20 U of mIL-1 per 0.5 ml of culture medium. Endothelial permeability changes observed after incubation with mIL-1 were confirmed using rIL-1. Compared to control cultures, 20 U of rIL-1 and 20 U of mIL-1 increased albumin transfer across endothelial monolayers 205% and 459%, respectively. These findings suggest that the mechanism of hypoalbuminemia seen after severe head trauma can be explained in part by IL-1-induced endothelial cell injury, resulting in enhanced endothelial permeability to albumin.

Prediction tree for severely head-injured patients

1991 ◽  
Vol 75 (2) ◽  
pp. 251-255 ◽  
Author(s):  
Sung C. Choi ◽  
Jan P. Muizelaar ◽  
Thomas Y. Barnes ◽  
Anthony Marmarou ◽  
Danny M. Brooks ◽  
...  
Keyword(s):  
Prognostic Factors ◽  
Predictive Accuracy ◽  
Head Injuries ◽  
Pupillary Response ◽  
Prognostic Indicators ◽  
Critical Threshold ◽  
Content Type ◽  
Intermediate Outcomes ◽  
Head Injured ◽  
Injured Patients

✓ Prediction tree techniques are employed in the analysis of data from 555 patients admitted to the Medical College of Virginia hospitals with severe head injuries. Twenty-three prognostic indicators are examined to predict the distribution of 12-month outcomes among the five Glasgow Outcome Scale categories. A tree diagram, illustrating the prognostic pattern, provides critical threshold levels that split the patients into subgroups with varying degrees of risk. It is a visually useful way to look at the prognosis of head-injured patients. In previous analyses addressing this prediction problem, the same set of prognostic factors (age, motor score, and pupillary response) was used for all patients. These approaches might be considered inflexible because more informative prediction may be achieved by somewhat different combinations of factors for different patients. Tree analysis reveals that the pattern of important prognostic factors differs among various patient subgroups, although the three previously mentioned factors are still of primary importance. For example, it is noted that information concerning intracerebral lesions is useful in predicting outcome for certain patients. The overall predictive accuracy of the tree technique for these data is 77.7%, which is somewhat higher than that obtained via standard prediction methods. The predictive accuracy is highest among patients who have a good recovery or die; it is lower for patients having intermediate outcomes.

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