Open(G)PIAS: An Open-Source Solution for the Construction of a High-Precision Acoustic Startle Response Setup for Tinnitus Screening and Threshold Estimation in Rodents

The modulation of the acoustic startle reflex (ASR) by a pre-stimulus called pre-pulse inhibition (PPI, for gap of silence pre-stimulus: GPIAS) is a versatile tool to, e.g., estimate hearing thresholds or identify subjective tinnitus percepts in rodents. A proper application of these paradigms depends on a reliable measurement of the ASR amplitudes and an exact stimulus presentation in terms of frequency and intensity. Here, we introduce a novel open-source solution for the construction of a low-cost ASR setup. The complete software for data acquisition and stimulus presentation is written in Python 3.6 and is provided as an Anaconda package. Furthermore, we provide a construction plan for the sensor system based on low-cost hardware components. Exemplary GPIAS data from two animal models (Mus musculus, Meriones unguiculatus) show that the ratio histograms (1-GPIAS) of the gap-pre-stimulus and no pre-stimulus ASR amplitudes can be well described by a log-normal distribution being in good accordance to previous studies with already established setups. Furthermore, it can be shown that the PPI as a function of pre-stimulus intensity (threshold paradigm) can be approximated with a hard-sigmoid function enabling a reproducible sensory threshold estimation. Thus, we show that the open-source solution could help to further establish the ASR method in many laboratories and, thus, facilitate and standardize research in animal models of tinnitus and/or hearing loss.

Broadband multizone sound rendering by jointly optimizing the sound pressure and particle velocity

In this paper, a recently proposed approach to multizone sound field synthesis, referred to as joint pressure and velocity matching (JPVM), is investigated analytically using a spherical harmonics representation of the sound field. The approach is motivated by the Kirchhoff-Helmholtz integral equation and aims at controlling the sound field inside the local listening zones by evoking the sound pressure and particle velocity on surrounding contours. Based on the findings of the modal analysis, an improved version of JPVM is proposed, which provides both better performance and lower complexity. In particular, it is shown analytically that the optimization of the tangential component of the particle velocity vector, as is done in the original JPVM approach, is very susceptible to errors and thus not pursued anymore. Furthermore, the analysis provides fundamental insights as to how the spherical harmonics used to describe three-dimensional sound fields translate into two-dimensional basis functions as observed on the contours surrounding the zones. By means of simulations, it is verified that discarding the tangential component of the particle velocity vector ultimately leads to an improved performance. Finally, the impact of sensor noise on the reproduction performance is assessed.

The spatial coherence of noise fields evoked by continuous source distributions

In this work, analytic expressions for the spatial coherence of noise fields are derived in the modal domain with the aim of providing a sparse representation. For this purpose, the sound field in a region of interest is expressed in terms of a given pressure distribution on a virtual surrounding cylindrical or spherical surface. According to the Huygens-Fresnel principle, the sound pressure on this surface is represented by a continuous distribution of elementary line or point sources, where orthogonal basis functions characterize the spatial properties. To describe spatially windowed pressure distributions with arbitrary angular extensions, orthogonal basis functions of limited angular support are proposed. As special cases, circular and spherical pressure distributions with uncorrelated source modes of equal power are investigated. It is shown that these distributions result, respectively, in cylindrically isotropic and spherically isotropic, i.e., diffuse noise fields. The analytic expressions derived in this work allow for a prediction of the spatial coherence between arbitrary positions within the region of interest, such that no microphones need to be placed at the actual points of interest. Simulation results are presented to validate the derived relations.

Acoustic reciprocity: An extension to spherical harmonics domain

Acoustic reciprocity is a fundamental property of acoustic wavefields that is commonly used to simplify the measurement process of many practical applications. Traditionally, the reciprocity theorem is defined between a monopole point source and a point receiver. Intuitively, it must apply to more complex transducers than monopoles. In this paper, the authors formulate the acoustic reciprocity theory in the spherical harmonics domain for directional sources and directional receivers with higher order directivity patterns.

A model for the temporal evolution of the spatial coherence in decaying reverberant sound fields

Reverberant sound fields are often modeled as isotropic. However, it has been observed that spatial properties change during the decay of the sound field energy, due to non-isotropic attenuation in non-ideal rooms. In this letter, a model for the spatial coherence between two sensors in a decaying reverberant sound field is developed for rectangular rooms. The modeled coherence function depends on room dimensions, surface reflectivity, and orientation of the sensor pair, but is independent of the position of source and sensors in the room. The model includes the spherically isotropic (diffuse) and cylindrically isotropic sound field models as special cases.

Room geometry inference based on spherical microphone array eigenbeam processing

The knowledge of parameters characterizing an acoustic environment, such as the geometric information about a room, can be used to enhance the performance of several audio applications. In this paper, a novel method for three-dimensional room geometry inference based on robust and high-resolution beamforming techniques for spherical microphone arrays is presented. Unlike other approaches that are based on the measurement and processing of multiple room impulse responses, here, microphone array signal processing techniques for uncontrolled broadband acoustic signals are applied. First, the directions of arrival (DOAs) and time differences of arrival (TDOAs) of the direct signal and room reflections are estimated using high-resolution robust broadband beamforming techniques and cross-correlation analysis. In this context, the main challenges include the low reflected-signal to background-noise power ratio, the low energy of reflected signals relative to the direct signal, and their strong correlation with the direct signal and among each other. Second, the DOA and TDOA information is combined to infer the room geometry using geometric relations. The high accuracy of the proposed room geometry inference technique is confirmed by experimental evaluations based on both simulated and measured data for moderately reverberant rooms.

Localization of distinct reflections in rooms using spherical microphone array eigenbeam processing

This paper presents an experimental and comparative study of several spherical microphone array eigenbeam (EB) processing techniques for localization of early reflections in room acoustic environments, which is a relevant research topic in both audio signal processing and room acoustics. This paper focuses on steered beamformer-based and subspace-based localization techniques implemented in the spherical EB domain, including the plane-wave decomposition, eigenbeam delay and sum, eigenbeam minimum variance distortionless response, eigenbeam multiple signal classification (EB-MUSIC), and eigenbeam estimation of signal parameters via rotational invariance techniques (EB-ESPRIT) methods. The directions of arrival of the original sound source and the associated reflection signals in acoustic environments are estimated from acoustic maps of the rooms, which are obtained using a spherical microphone array. The EB-domain-based frequency smoothing and white noise gain control techniques are derived and employed to improve the performance and robustness of reflection localization. The applicability of the presented methods in practice is confirmed by experiments carried out in real rooms.

Real time heart ischemia detection in the smart home care system

In this paper, a novel real-time algorithm for detecting ischemia in the ECG signal is proposed. The goal of this research is to meet the requirements of some smart cardiac home care devices, which can automatically diagnose the ECG and detect the heart risks outside the hospital, especially heart ischemia without symptoms in their early stages. The algorithm is developed based on a real time R peak detector, time domain traditional ECG parameters, the advanced morphologic parameters from Karhunen-Loève transform, and the adaptive neurofuzzy logic classification. Besides, in order to improve the reliability of our algorithm, several significant constraints of the ECG signal are considered. As a result, the ischemia episodes can be detected if the ischemic alteration persists longer than one minute in the ECG signal.

[Preoperative ECG in routine preoperative assessment of children]

OBJECTIVE

The aim of this study is to examine whether a routine preoperative ECG is necessary in children to assess the risks in anaesthesia and surgery.

METHODS

We examined the records of 3030 children anaesthetized in our hospital in 1990 and compared records of complications with preoperative ECGs. We also evaluated questionnaires on this subject which we had sent to 51 large pediatric hospitals in Germany in 1991.

RESULTS

During 3030 anaesthetic procedures there were 93 complications, 67 of which were not of cardiac origin. Of the 26 cardiac complications only 4 needed therapy (AV-Block 2 degrees, fall in blood pressure). Preoperative ECGs were recorded in 180 cases: 152 were normal, 8 showed harmless deviations from normal and 16 were recorded because of known cardiac defects. None of the 180 children developed complications during anaesthesia. Our questionnaire was returned completed carefully by 36 of the 51 hospitals. In most hospitals a preoperative ECG is only recorded when heart disease is known or suspected.

CONCLUSION

Routine preoperative ECGs are unnecessary in children unless there are clinical symptoms of heart diseases or heart disease is suspected.

Reducing pain during propofol injection: the role of the solvent

We hypothesized that the concentration of propofol in the aqueous phase may be the most important variable responsible for the pain experienced during injection of the drug. The concentration of propofol in the aqueous phase (18.57 micrograms/mL) can be decreased by increasing the fat content of the solvent. To test this hypothesis, 36 patients were randomly allocated to one of three groups, each receiving a different formulation of propofol. Group A received 20 mL of propofol alone in a commercial preparation (Diprivan(R) with 10 mL of saline); Group B, 20 mL of propofol to which 5 mL of long-chain triglyceride (LCT) fat emulsion and 5 mL of saline and been added; and Group C, 20 mL of propofol and 10 mL of LCT fat emulsion. The propofol emulsion was injected over 30-60 s into a dorsal vein of the hand. Patients reported pain during injection as none, mild, moderate, or severe (almost intolerable). In Group A, 8 of 12 patients reported moderate or severe pain upon injection whereas in Group C only mild pain was reported by 6 of 12 patients. Our results suggest that a smaller concentration of propofol in the aqueous phase of the emulsion reduces pain on injection. With the addition of more lipid (10 mL), a higher percentage of propofol is absorbed by fat particles. If solvents that permit a smaller concentration of the drug in the aqueous phase of oil-in-water emulsions were used for propofol and other drugs that cause pain on injection, pain would be reduced and patient satisfaction may be increased.

A multicenter study of phospholipase A2 in patients in intensive care units

BACKGROUND

Multiple organ failure (MOF) is becoming the most common cause of death in patients in surgical intensive care units. In this respect, a multicenter study in four different groups of patients in surgical intensive care units was done to evaluate the role of phospholipase A2 (PLA2) in comparison with C-reactive protein (CRP) and polymorphonuclear (PMN) elastase.

STUDY DESIGN

A total of 223 patients entered the study: 73 patients with multiple injuries, 46 patients with diffuse peritonitis, 52 patients with sepsis, and 52 patients in a control group who were at a higher risk for postoperative sepsis after defined surgical interventions. The patients underwent a daily monitoring of PLA2, CRP, and PMN elastase for seven days.

RESULTS

Phospholipase A2 activity remained within the normal range in patients with multiple injuries and patients in the control group, indicating that this parameter is not influenced by the postaggression metabolism. In contrast, in patients with peritonitis, high PLA2 values were found from the beginning. The efficiency for predicting a lethal MOF was 85 percent for PLA2 (cut-off 80 U/L) in patients if determined at the day of operation. A comparably favorable efficiency (84 percent) was demonstrated for PMN elastase in patients with multiple injuries (cut-off 205 micrograms/L) measured at day one.

CONCLUSIONS

These efficiency rates of PLA2 in peritonitis and PMN elastase in multiple injuries were comparable or even better than multifactorial scoring systems used in the study. C-reactive protein did not contribute to an early estimation of the prognosis in all groups analyzed. Therefore, the measurement of PLA2 in patients with diffuse peritonitis and PMN elastase in patients with multiple injuries, as single parameters, is recommended to estimate the individual risk for the occurrence of lethal MOF.

Low-dose hydrocortisone infusion attenuates the systemic inflammatory response syndrome. The Phospholipase A2 Study Group

There is increasing evidence that the hypercortisolemia in inflammatory diseases suppresses the elaboration of proinflammatory cytokines, thus protecting the host from its own defence reactions. In severe sepsis and septic shock cortisol levels are usually elevated, but some patients may have relative adrenal insufficiency. This may contribute to the overwhelming systemic inflammatory response syndrome. We evaluated the impact of low-dose hydrocortisone infusion (10 mg/h) on the course of the systemic inflammatory response syndrome. This dose corresponds to a maximum secretory rate of cortisol achieved in corticotropin-stimulated healthy humans. In a prospective observational study 57 surgical patients with severe sepsis or septic shock were studied, of which in addition to the conventional treatment 12 patients were infused with low-dose hydrocortisone, and 45 were treated without any corticosteroid. In the longitudinal analysis the systemic inflammatory response--as judged by body temperature, cardiovascular response, and kinetics of inflammatory mediators such as phospholipase A2, C-reactive protein, and neutrophil elastase--started to differ in favor of the hydrocortisone-treated patients after 2 days of treatment (P < 0.05, Mann-Whitney U test). The difference disappeared after withdrawal of exogenous cortisol. Shock reversal was achieved in all patients treated with low-dose hydrocortisone. The data provide evidence that low-dose hydrocortisone infusion attenuates the systemic inflammatory response in human septic shock. From an immunological point of view a relative cortisol deficiency may contribute to the amplified immune response in systemic inflammatory diseases. A randomized clinical trial must clarify the impact of low-dose hydrocortisone infusion on the clinical course and outcome of septic shock patients.

[Diagnosis of phlebothrombosis using color-coded duplex sonography. A prospective comparison with phlebography]

In a prospective study the reliability of colour-coded duplex-sonography (CCDS) and phlebography in the diagnosis of deep leg and pelvic vein thrombosis was compared. In 82 consecutive in- or out-patients (42 men, 40 women; mean age 53 [19-86] years) with clinically suspected leg or pelvic vein thrombosis the results of 275 phlebographies (reference method) and 275 CCDS were compared on admission and during follow-up. The two methods were performed less than 6 hours apart. In the diagnosis of thrombosis the sensitivity of CCDS was 99%, specificity 80%. In 88% of all tests, the different thrombosis levels, as diagnosed by phlebography, were also demonstrated by CCDS. These data indicate that, if the clinical picture of suspected deep leg or pelvic vein thrombosis is unclear, CCDS should be done first. Phlebography should be performed only if the results of the former are inconclusive.

Heparin reversal by protamine in humans--complement, prostaglandins, blood cells, and hemodynamics

Fourteen noncardiac surgical patients received heparin (10,000 IU), which was neutralized by 100 mg protamine injected within 2 min during steady-state anesthesia. After protamine application, plasma complement C3a, thromboxane B2 (TxB2), prostaglandin F2 alpha (PGF2 alpha) and KH2PGF2 alpha increased significantly, whereas prostacyclin (6-keto-PGF2 alpha) levels did not change. This mediator response was associated with transient leukopenia and thrombocytopenia. Arterial pressure, pulmonary arterial pressure, and transpulmonary pressure gradient increased significantly. Heart rate, cardiac output, pulmonary capillary wedge pressure, and arterial PO2 remained constant. Positive correlations of plasma C3a were observed with pulmonary leukosequestration and plasma TxB2. Inverse correlations of C3a were noted with the counts of leukocytes and of platelets. A positive correlation was found between TxB2 and pulmonary arterial pressure. Our results indicate that marked activation of the complement system and the cyclooxygenase pathway is common after heparin reversal by protamine in anesthetized patients. This is in contrast to previous human studies performed after cardiopulmonary bypass but agrees well with results obtained in animal experiments. The mediator response in our patients, however, was not accompanied by hemodynamic instability, suggesting appropriate compensatory mechanisms.

Relationship between angiotensinogen, alpha 1-protease inhibitor elastase complex, antithrombin III and C-reactive protein in septic ARDS

The time-course of plasma angiotensinogen (Ao), elastase-alpha 1-protease inhibitor complex (EL alpha 1PI), antithrombin III (AT III) and C-reactive protein (CRP) have been investigated of six patients suffering from adult respiratory distress syndrome (ARDS). The total plasma Ao level (active and inactive Ao) varied in individuals but was increased up to five-fold. An increasing amount of inactive Ao is found. From the beginning of their stay in the intensive care unit up to five days half of the patients displayed a positive correlation between the plasma CRP and Ao level. The CRP and Ao values were either not or were negatively correlated with the AT III values. In contrast plasma Ao and AT III levels in all patients were positively correlated during a particular period in the subsequent phase of the disease, where there was no or a negative correlation with CRP. The two acute phase reactants CRP and EL alpha 1PI were only correlated in two patients at the beginning of the disease. The markedly increased plasma level at the beginning of the inflammatory disease indicates that Ao is an acute phase reactant, and this is supported by the parallel changes in plasma CRP and Ao levels during the early days of ARDS. The relationship between the plasma levels of Ao and AT III for more than fourteen days suggests similar regulation of these members of the serpin family after termination of the acute-phase.

Flow cytometric parameters of neutrophil function as early indicators of sepsis- or trauma-related pulmonary or cardiovascular organ failure

Flow cytometric parameters of neutrophil function, such as phagocytosis and degradation of Escherichia coli, intracellular pH value, esterase activity, and cell volume, were evaluated as risk indicators for sepsis- and trauma-related pulmonary and cardiovascular organ failure in intensive care patients. Serial blood samples (n = 201) were obtained from 47 prospectively identified patients. Each patient's condition was classified daily within four categories: post-traumatic (n = 22) or septic (n = 28) organ failure, transition state (n = 119), and stable organ function after recovery (n = 27). Thirty-two parameters of neutrophil function were automatically calculated for each blood sample from several flow cytometric list mode measurements of cell samples vitally stained with acridine orange for intact and denatured DNA or with 1,4-diacetoxy-2,3-dicyanobenzene for intracellular pH and esterase activity. The DNA of dead cells was simultaneously counterstained with propidium iodide. The cell biochemical parameter pattern was significantly different among samples of patients from the four clinical categories (p less than 0.05). Hyperergic phagocytosis was observed after trauma, in contrast to hypoergic phagocytosis, increased neutrophil cell volume, and elevated intracellular pH during sepsis. The clinical categories were correctly identified in 82% of the samples by automated classification with the DIAGNOS1/SPSS program system from the flow cytometrically determined cell functions. The course of the disease was correctly predicted 3 days in advance to the clinical manifestation of pulmonary or cardiovascular organ failure in 92% of the samples. The multifunctional analysis of neutrophils by flow cytometry seems of interest for early medical intervention in preseptic and preshock patients.

Phospholipase A in acute lung injury after trauma and sepsis: its relation to the inflammatory mediators PMN-elastase, C3a, and neopterin

Inflammatory mediators involved in the pathogenesis of the adult respiratory distress syndrome (ARDS) are products of the humeral cascade systems like the complement cascade and substances released from neutrophil granulocytes and macrophages like proteases, O2-radicals and arachidonate products. Phospholipase A2 (PLA) was shown by Vadas et al. to be correlated with circulatory shock in the sepsis syndrome, the probably most important underlying disease of ARDS. In a clinical study in 48 patients at risk for ARDS after trauma and sepsis we found plasma PLA elevated (52 +/- 5 U/l) in sepsis, with a positive correlation to the complement split product C3a (r = 0.42, p less than 0.01) and neopterin (r = 0.49, p less than 0.05), which serves as a marker of macrophage stimulation. Elastase-alpha 1PI and C3a showed higher plasma levels in patients with ARDS compared with non-ARDS patients, whereas the neopterin and PLA concentrations were not different with regard to ARDS. The relation between PLA and neopterin shown in the study is consistent with the possibility of macrophages being a source of the plasma PLA, as reported in experimental studies.

[The equilibrium of nitrogen, potassium and phosphate and renal excretion of creatinine and creatinine over the course of 3 weeks following severe trauma]

In 19 patients after accidental trauma and with intact renal function during an observation time of 21 days we found a cumulated negative balance of nitrogen (N), phosphate (P) and potassium (K) amounting to a mean of 214g, 357 and 447 mmol, respectively. Median daily potassium balance was positive on day 2 to 5 and this was interpreted as an increased extrarenal potassium deposition due to increased levels of circulating catecholamines. Median renal creatinine excretion was about 120% of predicted normal till day 10 and continuously decreased thereafter to values lower than predicted normal. Three patients did not show creatinuria (greater than 200 mg/day) during the whole observation time. In 15 patients after a "free interval" with a mean duration of 7 days creatinuria frequently developed rather quickly and maximal excretion of creatine was as high as 4 g/day. In 7 patients creatinuria persisted to the end of the 21 days observation time. During the phase of creatinuria the median cumulated excretion of creatine amounted to 14.4 g. The "free interval" of creatinuria after severe trauma is remarkable. Most of the N, K and P, which is lost from the body during this time obviously stems from tissues other than sceletal muscle. During the phase of creatinuria, however, the negative balance of N, K and P seems to be mainly due to muscle wasting. Hypophosphatemia was prominent during the first 5 days after trauma and obviously was caused by a decrease in renal phosphate threshold (TmPO4/GFR). The underlying mechanism of this primary change in renal function after severe trauma could not yet be identified.

Renin-angiotensin system in sepsis

The time course of the components of the renin-angiotensin system was investigated in the plasma of three patients on the intensive care unit. Two of them, which were both polytraumatized, suffered from adult respiratory distress syndrome (ARDS). All patients had sepsis and impaired pulmonary and renal function. Plasma samples were investigated for up to two weeks, in which time all three patients showed a decrease in their angiotensin converting enzyme (ACE) plasma concentration. Two of the patients with deteriorating renal function had three to four times elevated angiotensinogen (Ao) plasma levels, which were measured by both the direct and indirect radioimmunoassay. The ratio of the mean values between both assays was 1:1 in two patients and shifted to higher values in the direct assay in the third patient. This suggests that higher amounts of des-AngI-angiotensinogen were present in the latter patient, because "inactive" Ao is also detected by the direct assay. The decrease in active Ao may be caused by an up to twenty times elevated plasma renin activity (PRA). The PRA was correlated with the angiotensin I (AngI) plasma levels. However, at PRA values higher than 200 pmol AngI/ml/h this correlation decreased because of the rapid substrate consumption. In addition there was a good correlation between AngI and AngII plasma levels in two patients which could not be observed in the patient with the highest PRA and AngII values. A relationship between plasma ACE concentration and AngII formation could not be observed. Thus in two of the three septic patients the components of the renin angiotensin system were extremely stimulated at very low blood pressure values. These data show, that it is reasonable to follow the time course of the components of the renin angiotensin system in single patients. In addition it is demonstrated that the direct measurement of Ao is a valid supplement in the diagnosis of the renin angiotensin system.

[Work of breathing in spontaneous respiration with continuous positive airway pressure]

In postoperative respiratory failure continuous positive airway pressure (CPAP), besides improving pulmonary gas exchange, influences respiratory mechanics. Elastic and flowresistive components of respiratory work were measured in intensive care patients being weaned from the respirator. Measured values during breathing with a continuous-flow CPAP system with elastic reservoir were compared with those for O2 breathing via T-tube. Under CPAP total breathing work and resistance were reduced. Compliance, tidal volume and respiratory frequency did not change significantly. The reduction in respiratory work was primarily due to decreased nonelastic work associated with a decrease in resistance. Thus, on weaning from mechanical ventilation using a reservoir-CPAP system, the respiratory work was reduced in comparison to O2 breathing via T-tube.

Metabolism of phosphate and calcium after severe accidental trauma

Hypophosphatemia is a common finding during the first 4-5 days after severe accidental trauma. We demonstrated that hypophosphatemia after trauma is caused by a definite decrease in renal phosphate threshold (TmPO4/GFR), that is the theoretical plasma phosphate concentration at which all of the filtered phosphate is reabsorbed by the renal tubules and renal excretion of phosphate is close to zero. We speculated that the decrease in renal phosphate threshold could be due to an increased activity of PTH which in turn could be the result of ionized hypocalcemia. In 7 patients with severe and in 8 patients with moderate trauma, however, we found ionized calcium and PTH levels to be within normal limits. Total plasma calcium was below normal (1.90-2.00 mmol/l) up to 20 days after trauma, probably due to a decreased plasma albumin concentration (25-30 g/l). We conclude, that ionized hypocalcemia and consecutive stimulation of PTH is not the cause of decreased renal phosphate threshold after severe accidental trauma.

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH)--treatment with lithium

Two patients with SIADH after brain trauma are described. Features of SIADH are "inappropriate" antidiuresis and excessive natriuresis with negative sodium balance resulting in hyponatremia and plasma hypoosmolality which may lead to cerebral dysfunction. Oral lithium carbonate was beneficial in both patients. With plasma levels of lithium around 1 mmol/l a temporary impairment of renal concentrating ability and antinatriuresis with normalization of plasma sodium and plasma osmolality was observed. The SIADH subsided about 4 months after the original trauma, long after gross neurological symptoms had resolved.