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Biomedical subjects

I R Piper

Publications and source records attributed to I R Piper.

At least 19 recordsLinked to original sources
PubMed2005

Assessment of different data representations and averaging methods on the Spiegelberg compliance device.

The Spiegelberg Compliance Device (Spiegelberg KG, Hamburg, Germany) has been available for the automated measurement and calculation of minute by minute intracranial compliance. Widespread practical use has been somewhat limited by the instability of values: especially at low intracranial pressures. We looked at two aspects of a methodology in an attempt to increase the value of the Spiegelberg device in the clinical setting. Firstly, we discussed the difference in representing measured values as elastance (dp/dv) instead of compliance (dv/dp); and secondly we proposed the use of an averaging algorithm called the Exponentially Weighted Moving Average (ewma), which could be applied as a flexible method to follow trends and rapid changes in the elastance (or compliance). Clinical data from sixteen patients were gathered and statistical analysis was focused on three particular aspects, the coefficient of variation which indicates the variability of data values, the correlation between the elastance (or compliance) time series and the underlying ICP signal and the percentage of outliers greater than 2.5 standard deviations from the mean. Our results showed that expressing elastance (dp/dv) instead of compliance (dv/dp) yielded fewer outliers and had a better correlation to ICP, and the ewma method had a better correlation to ICP than the Spiegelberg method.

Adult↗
PubMed2002

Clinical experience in the use of the Spiegelberg automated compliance device in the assessment of patients with hydrocephalus.

Deciding upon shunting in patients with hydrocephalus with possibly related symptomatology, is difficult. The Spiegelberg automated device allows continuous measurements of intracranial compliance. We aimed to evaluate the added information that this new technology can provide, in addition to standard continuous ICP monitoring. Thirty-three patients with hydrocephalus were continuously monitored for ICP and compliance. Patients with abnormal ICP or compliance profiles were selected for shunting. Thirteen patients underwent ventriculo-peritoneal shunting on this basis, with 12 obtaining benefit and one dying as a complication of shunt-related sepsis. The 13 patients undergoing shunting had abnormalities in either intracranial pressure or compliance or both. Only 1 patient had normal ICP, but abnormal compliance and so the true complementary role of continuous compliance measurements cannot be determined. It is proposed that further recruitment be on a larger multi-centre basis. Determination of benefit is required, particularly as a possible time lag of abnormal ICP abnormal compliance over appearing during monitoring can be demonstrated.

Adolescent↗
PubMed2002

An experimental evaluation of a new intraparenchymal continuous compliance probe: preliminary studies.

The Spiegelberg automated compliance device offers practical benefits over the standard manual injection techniques for assessing volume-pressure status. Currently, however, the system relies on the insertion of an intraventricular catheter. If automated continuous measurement of intraparenchymal compliance could be achieved, then this would be a further practical advance. Automated measurements of compliance using a prototype intraparenchymal probe were assessed in comparison with the current intraventricular probe in a sheep model of diffusely raised ICP. The results show poor correlation between intraventricular compliance (IVC) and intraparenchymal compliance (IPC) at low levels of cerebral perfusion pressure (CPP). The IPC response to decreasing CPP beyond probable levels of blood flow autoregulation suggest that IPC is more dependent on local tissue perfusion factors, rather than overall physical compliance. Further evaluation of compliance in the intraparenchymal compartment versus intraventricular compliance will be needed before adaptation of the automated system for clinical application.

Animals↗
PubMed2001

Transcranial Doppler identification of changing autoregulatory thresholds after autoregulatory impairment.

OBJECTIVE: Transcranial Doppler (TCD) flow velocity (FV) assessment may provide a useful index of autoregulatory impairment after severe head injury. It may define a therapeutic end point against which cerebral perfusion pressure (CPP) can be titrated. This study examines the relationship between cerebral blood flow (CBF) and TCD FV indices in a laboratory model before and after autoregulatory impairment. METHODS: CPP, CBF, and middle cerebral artery TCD FV were measured continuously in nine anesthetized and ventilated sheep. CPP was decreased by hemorrhagic hypotension. The process was repeated after impairment of autoregulation by cisternal infusion, which maintained CPP at 0 mm Hg for 15 minutes. Points of significant change (i.e., breakpoints) from baseline values for each of the measured flow parameters were identified by using a ratio of variance technique. RESULTS: Before any significant change in CBF or systolic TCD, diastolic TCD FV decreased (mean breakpoint, 69 mm Hg; range, 56-78 mm Hg) as CPP was reduced. This divergence of diastolic and systolic TCD FV, which occurred before autoregulatory failure, was associated with an increasing TCD pulsatility index (mean breakpoint, 63 mm Hg; range, 53-70 mm Hg). At diastolic TCD FV congruent with 10 cm/s, systolic TCD FV (mean breakpoint, 48 mm Hg; range, 46-53 mm Hg) and CBF (mean breakpoint, 49 mm Hg; range, 47-51 mm Hg) decreased rapidly, indicating autoregulatory failure. After autoregulatory impairment, the breakpoints for all four indices shifted to higher CPP values (mean, 16 mm Hg). CONCLUSION: TCD FV assessment identified two CPP thresholds of autoregulatory loss. Before autoregulatory failure, an earlier phase of autoregulatory disturbance may be detected by divergent systolic and diastolic TCD FVs. It is important to note that this phase may be detected before CBF decreases. These TCD FV breakpoints depend on the state of autoregulatory impairment and may provide potential targets for CPP-directed therapy.

Animals↗
PubMed2000

A study of the effects of using different cerebral perfusion pressure (CPP) thresholds to quantify CPP "secondary insults" in children.

Little is known about the incidence of secondary insults, particularly cerebral perfusion pressure insults, in children. The objectives of this study were to assess the duration of CPP insults at three different thresholds in children and to relate CPP insults to outcome. Eighteen children (age < 16, median & mean 8 years) admitted to the Neurointensive Care Unit who had ICP, MAP and CPP continuously monitored were studied. Using the Edinburgh secondary insult analysis program, data was scanned for CPP insults at three different thresholds: CPP < 70 mmHg, < 60 mmHg and < 50 mmHg. Outcome was assessed using the Glasgow Outcome Scale. Thirty percent of the time CPP was between 60 and 70 mmHg, 21% of the time CPP was between 50 and 60 mmHg and 8% of the time the CPP was less than 50 mmHg. Compared with adults, there was more than twice the incidence of CPP insults in all threshold groups. BP remained relatively stable above 70 mmHg across all three CPP threshold groups. However, ICP increased slightly on average from about 13-->17 mmHg when CPP decreased from the < 70 to < 60 mmHg group (p < 0.001). There was a marked increase in ICP to greater than 30 mmHg on average in the CPP < 50 mmHg group (p < 0.001). CPP insults less than 70, 60 and 50 mmHg do occur commonly in children, a larger dataset and possibly longer term follow up measures will be needed to identify potentially treatable physiological factors most effecting the outcome of children.

Adolescent↗
PubMed2000

Cerebral blood flow and metabolism in severe brain injury: the role of pressure autoregulation during cerebral perfusion pressure management.

OBJECTIVE: To ascertain if norepinephrine can be used as part of the cerebral perfusion pressure (CPP) management to increase arterial blood pressure (MAP) without causing cerebral hyperemia after severe head injury (HI). DESIGN: Prospective, interventional study. SETTING: Intensive care unit in a university hospital. PATIENTS: Twelve severely HI patients; median Glasgow Coma Scale was 6 (range 3-8). INTERVENTIONS: CPP management ( = 70 mmHg). Pressure autoregulation (assessed by norepinephrine infusion) was defined intact if % CPP/%CVR < or = 2. RESULTS: Cerebral blood flow (CBF: Xe133 inhalation technique), jugular bulb oxygen saturation (SjO2) and transcranial Doppler (TCD) were recorded during the test. Norepinephrine increased CPP by 33 % (+/- 4). Autoregulation was found to be intact in ten patients and defective in two. In the ten patients with preserved autoregulation, CBF decreased from 31 +/- 3 to 28 +/- 3 ml/ 100 g/min; in the two patients with impaired autoregulation CBF increased respectively from 16 to 35 and from 21 to 70 ml/100 g/min. SjO2 did not change significantly from baseline. TCD remained within the normal range. CONCLUSIONS: During CPP management norepinephrine can be used to increase MAP without potentiating hyperemia if pressure autoregulation is preserved. The assessment of pressure autoregulation should be considered as a guide for arterial pressure-oriented therapy after HI.

Adolescent↗
PubMed2000

Experimental evaluation of the Spiegelberg intracranial pressure and intracranial compliance monitor. Technical note.

The goal of this study was to compare the Spiegelberg intraventricular intracranial pressure (ICP)/intracranial compliance monitoring device, which features an air-pouch balloon catheter, with existing gold-standard methods of measuring ICP and intracranial compliance. A Spiegelberg intraventricular catheter, a standard intraventricular catheter, and a Codman intraparenchymal ICP microsensor were placed in five sheep, which previously had been given anesthetic and paralytic agents, to allow comparative measurement of ICP at incremental levels (range 5-50 mm Hg). Intracranial pressure measured using the Spiegelberg intraventricular air-pouch balloon catheter displayed a linear correlation with ICP measured using the standard intraventricular fluid-filled catheter (r2 = 0.9846, p < 0.001; average bias -0.74 mm Hg), as well as with ICP measured using the Codman intraparenchymal strain-gauge sensor (r2 = 0.9778, p < 0.001; average bias 0.01 mm Hg). Automated measurements of intraventricular compliance obtained using the Spiegelberg compliance device were compared with compliance measurements that were made using the gold-standard manual cerebrospinal fluid bolus injection technique at ICPs ranging from 5 to 50 mm Hg, and a linear correlation was demonstrated between the two methods (r2 = 0.7752, p < 0.001; average bias -0.019 ml/mm Hg). The Spiegelberg air-pouch ICP/compliance monitor provides ICP and compliance data that are very similar to those obtained using both gold-standard methods and an intraparenchymal ICP monitor over a range of pathophysiological ICPs. The automated closed Spiegelberg system offers practical advantages for the measurement of intraventricular compliance. Assessment of the clinical utility and robustness of the Spiegelberg system, together with the development of an intraparenchymal device, would enhance the clinical utility of automated compliance measurement and expand the range of its applications.

Animals↗
PubMed1999

Brain TXA(2) and PGI(2) levels in impact acceleration diffuse brain injury coupled with secondary insults.

OBJECTIVE: To study the changes of brain TXA(2) and PGI(2) levels in a new rodent model of impact acceleration diffuse brain injury with hypotention and hypoxia and the effect of diaspirin cross linked hemoglobin solution (DCLHb) on brain TXA(2) and PGI(2) levels. METHODS: Thirty-two male SD rats were randomized into sham, head injury alone, head injury with secondary insults and injury with insults followed by DCLHb administration groups. Animals were physiologically monitored throughout the experiment and the prostanoids were measured via radioimmunoassay (RIA). RESULTS: There were no changes in TXB(2) and 6-keto-PGF1alpha (stable metabolites of TXA(2) and PGI(2)) levels in injury alone group while TXB(2) level in secondary insults group elevated significantly and both TXB(2) and 6-keto-PGF1alpha levels in injury with insults followed by DCLHb administration augmented significantly in comparison with the corresponding value of sham at 4 h postimpact. CONCLUSIONS: The only increase in TXA(2) level in secondary insults rats suggests that there may be both thrombotic episodes and vasoconstriction leading to focal increase in micro-circulatory resistance which contributes to a decreased focal cerebral blood flow (CBF). And it is hypothesed that DCLHb may exert its protective properties through increasing PGI(2) production in injured brain by affecting CBF and cerebral perfusion pressure (CPP).

Journal Article↗
PubMed1999

The role of endothelin-1 in pressure autoregulation of cerebral blood flow in rats.

OBJECTIVE: To investigate the role of the endothelin system in pressure autoregulation of cerebral blood flow (CBF) in rats. DESIGN: We tested pressure autoregulation by increasing cerebral perfusion pressure (CPP; mean arterial pressure-intracranial pressure) with norepinephrine (0.08 microgram.kg-1.min-1 for 30 min) twice in ten anesthetized normocapnic rats. The first test was performed without (control test) and the second test after administration of the combined endothelin ETA/B receptor antagonist, bosentan, i.v. (30 mg/kg; drug test). CBF was measured by the hydrogen clearance technique. RESULTS: During the control test, norepinephrine infusion increased CPP by 21 +/- 2 (23 +/- 2%) mmHg (mean +/- SEM; p < 0.001) and CBF by 3.6 +/- 3.1 (6 +/- 8%) ml/100 g/min (p = 0.5, Fig. 1); during the drug test, norepinephrine infusion increased CPP by 18 +/- 1 (20 +/- 2%) mmHg (p < 0.001) and CBF by 15.8 +/- 4.1 (46 +/- 13%) ml/100 g/min (p = 0.004). Mean arterial pressure was not affected by bosentan infusion (p = 0.2). PaCO2 levels were stable during the tests (40.2 +/- 1.4 mmHg). CONCLUSIONS: The endothelin system is involved in cerebral pressure autoregulation in a rodent model in vivo. The role of this system under pathophysiologic conditions such as subarachnoid hemorrhage, where basal vascular tone and its regulation may be altered, remains to be defined.

Analysis of Variance↗
PubMed1999

Neuropathologic characterization of a rodent model of closed head injury--addition of clinically relevant secondary insults does not significantly potentiate brain damage.

We have characterized the early brain pathology in Sprague-Dawley rats subjected to a modified Richmond impact acceleration model of closed head injury (CHI). This model was modified to produce maximal traumatic brain injury (TBI) in the absence of skull fracture, extracerebral or intracerebral hemorrhage, or brain contusion. We then used this model to assess the neuropathologic effects of superimposed secondary insults, which were designed to reflect a clinically relevant combination of hypotension and pyrexia. Acute neuronal injury, blood-brain barrier (BBB) integrity, axonal injury (AI), and glial activation were studied 4 1/2 hours following either CHI (group A), CHI plus secondary insults (group B), secondary insults alone (group C), or sham control injury (group D). There was evidence of limited AI following CHI in the lower medulla and upper cervical cord region, which was not modified by addition of secondary insult. Loss of dendritic microtubule-associated protein MAP2 immunoreactivity proved a reliable marker of acute neuronal damage, which was confined to subimpact and inferolateral cortical locations following CHI and was widespread after secondary insult. The pattern of plasma protein extravasation paralleled that of acute neuronal injury. We found no evidence of microglial activation, either local or generalized, by 4 1/2 hours. However, by this time CHI and secondary insults had combined to produce evidence of subimpact astrocyte activation, which was not apparent with either insult or injury alone. We conclude that in this modified Richmond model of CHI, when combined with secondary insults, there is no convincing potentiation of brain damage with the minor exception of astrocyte activation.

Animals↗
PubMed1998

Brain TXA(2) and PGI(2) levels after head injury with secondary insults.

OBJECTIVE: The brain TXA(2) and PGI(2) levels in a new rodent model of impact acceleration diffuse brain injury alone and with hypotention and hyperthermia in combination were observed to look into the relationship between TXA(2), PGI(2) levels and different types of head injury. METHODS: Thirty-two SD rats were randomized into sham, head injury alone, secondary insult alone and head injury with secondary insult groups. At 4 hours after injury or experiment, all the rats were decapitated and their brains were sampled for radioimmunoassay (RIA) measurement. RESULTS: Compared with that of sham group there were no changes in TXA(2) and PGI(2) levels in injury alone group while there was a significant augmentation in PGI(2) level in insult alone group. Both TXA(2) and PGI(2) level in injury with secondary insult group increased significantly in comparison with that of sham at 4 hours postimpact. CONCLUSIONS: PGI(2) providing energy and precursors to the injured tissue and producing some vasoactive arachidonic products, especially TXA(2), is closely connected to the severity of brain damage.

Journal Article↗
PubMed1998

A clinical evaluation of the Codman MicroSensor for intracranial pressure monitoring.

The strain-gauge Codman MicroSensor intracranial pressure (ICP) transducer has shown consistently good laboratory performance. To assess the practical performance of the system in patients following acute brain injury, 10 patients were fitted with a MicroSensor and a second ICP monitor. In five cases this was a fibre-optic transducer and in five cases an intraventricular fluid-filled device. Paired ICP values were recorded every 5 min. ICP values ranged from 0 to 31 mmHg. Altman-Bland plots showed that individual readings could differ by as much as 9 mmHg. Further analysis showed that much of this disagreement could be explained by a constant offset on each occasion. Comparison traces of ICP in individual patients show high agreement in timing and size of changes. The unexplained constant offset leads to uncertainty about the true ICP. Treatment decisions are often based upon absolute levels of ICP and patient care may therefore differ depending upon the monitor used.

Brain Injuries↗
PubMed1998

Effects of diaspirin cross-linked haemoglobin on post-traumatic cerebral perfusion pressure and blood flow in a rodent model of diffuse brain injury.

Diaspirin cross-linked haemoglobin (DCLHb) is a new oxygen carrying blood substitute with vasoactive properties. Vasoactive properties may be mediated via high affinity binding of nitric oxide by the haem moiety. Using a rodent model of head injury combined with ischaemia, we studied the effects of DCLHb on cerebral blood flow (CBF) and intracranial pressure (ICP). Twenty anaesthetized rats were allocated randomly to receive treatment with DCLHb 400 mg kg-1 i.v. or placebo (oncotically matched plasma protein substitute 4.5% i.v.). To produce diffusely increased ICP, after a severe weight drop injury, all animals underwent a 30-min period of bilateral carotid ligation combined with a period of induced hypotension. After reperfusion, DCLHb or placebo was infused and the animals instrumented for measurement of intraventricular ICP and CBF in the region of the sensorimotor cortex using the hydrogen clearance technique. Mean arterial pressure (MAP), ICP, cerebral perfusion pressure (CPP) (CPP = MAP - ICP) and CBF were measured 4 h after injury in all animals. DCLHb significantly reduced ICP from mean 13 (SEM 2) to 3 (1) mm Hg (P < 0.001), increased CPP from 52 (8) to 95 (6) mm Hg (P < 0.001) and increased CBF from 21 (2) to 29 (2) ml 100 g-1 min-1 (P = 0.032). We conclude that DCLHb improved CPP without a reduction in CBF in a rodent model of post-traumatic brain swelling.

Animals↗
PubMed1997

Effects of alfentanil on cerebral haemodynamics in an experimental model of traumatic brain injury.

Alfentanil is reported to increase intracranial pressure (ICP) after neurotrauma. A direct cerebral vasodilator effect has been postulated. We studied 17 Sprague-Dawley rats allocated to one of three groups. Animals were anaesthetized and their lungs ventilated, and arterial pressure, ICP and/or regional cerebral blood flow (CBF) measurements were undertaken. Group 1 (n = 6) received a severe closed head injury while group 2 (n = 5) received no injury. ICP and mean arterial pressure (MAP) were measured before, during and after rapid infusion of alfentanil 250, 500 and 750 micrograms kg-1. CBF was measured by hydrogen clearance before rapid infusions and at 30-min intervals after starting a subsequent slow infusion of alfentanil 500 micrograms kg-1 h-1. Group 3 (n = 6) underwent CBF measurement only, for comparison with those of groups 1 and 2. They received an injury but no alfentanil. ICP or MAP values did not differ significantly between groups 1 and 2. Rapid i.v. doses of alfentanil produced increases in ICP and reductions in MAP. ICP changes were consistent with a drug effect (P < 0.001) but were small. Reductions in MAP were significant (P < 0.05) and preceded changes in ICP. CBF values were similar and unaffected by slow alfentanil infusion in groups 1 and 2, and did not differ significantly between groups 1 and 3. We conclude that alfentanil did not appear to exert a direct effect on the cerebral circulation. Changes in ICP after rapid infusion were secondary to reductions in SAP. Slow infusion did not cause such changes.

Alfentanil↗
PubMed1997

Importance of textual data in multimodality monitoring.

OBJECTIVES: The use of multimodality monitoring of patients in the intensive care unit (ICU) and the subsequent collection and analysis of such data are increasing. The aim of this work was to assess the importance of recording complementary textual data referring to patient care maneuvers, calibrations, and other incidents, in addition to the raw numerical values. DESIGN: A retrospective analysis of multimodality monitoring data, which included comments entered concurrently at the bedside, collected from head-injured patients admitted to an ICU. PATIENTS: One hundred forty-seven patients with a postresuscitation Glasgow Coma Scale score of < or = 12 were monitored for a total of nearly 1 million minutes on up to eight commonly used channels. MEASUREMENTS AND MAIN RESULTS: Approximately 13,000 comments were added to the raw data at the time of collection. The data were subsequently validated using these comments as indicators of artifactual values. The comments were classified into a surprisingly small number of important categories, with the most frequent referring to monitor calibrations and regular ICU care maneuvers. The difference between validated and unvalidated data on the quantity of secondary insult observed was in some cases nearly 50%. CONCLUSIONS: This work demonstrates that such textual information should be recorded concurrently with the raw monitoring values to ensure proper interpretation of the data in any retrospective analysis. Furthermore, it also suggests that a small number of prespecified categories could be used in the on-line validation of such data.

Craniocerebral Trauma↗
PubMed1996

Monitoring weight drop velocity and foam stiffness as an aid to quality control of a rodent model of impact acceleration neurotrauma.

Since the publication by Marmarou of a new rodent model of head injury, an increasing number of centres are adopting the model for use in a variety of paradigms. We report on two simple methods we have applied which allows us to monitor weight drop velocity and foam stiffness, both of which are critical factors for producing repeatable closed head injury with this model. We hope the application of these methods will assist in the standardisation of this model between centres.

Animals↗
PubMed1995

The evaluation of the wave-form analysis capability of a new strain-gauge intracranial pressure MicroSensor.

Both laboratory and clinical trials have indicated the reliability of a new catheter-tip, strain-gauge intracranial pressure transducer. We report on the results of bench tests comparing the wave-form analysis capabilities of the new Codman intracranial pressure MicroSensor and a similar strain-gauge transducer. Good agreement was found between the two sensors with no significant nonlinearity or hysteresis over a measured pressure range from 0 to 100 mg Hg. Under "fluid-filled" conditions, the MicroSensor showed good reproduction of an arterial pressure wave form; when spectral analysis was used to analyze the two sensor types and break them down into harmonic components, no significant differences could be found for any of the first 10 amplitude and phase harmonics. If proven to stay robust after long-term clinical use, this sensor may be a useful alternative to the existing transducer systems for routinely monitoring the intracranial pressure and its wave form.

Catheters, Indwelling↗