Modulation of pulse travel and blood flow during cuff inflation- An experimental case study.

The blood pressure (BP) cuff can be used to modulate blood flow and propagation of pressure pulse along the artery. In our previous work, we researched methods to adapt cuff modulation techniques for pulse transit time vs. BP calibration and for measurement of other hemodynamic indices of potential interest to critical care, such as arterial compliance. A model characterized the response of the vasculature located directly under the cuff, but assumed that no significant changes occur in the distal vasculature.This study has been tailored to gain insights into the response of distal BP and pulse transit time to cuff inflation. Invasive BP data collected downstream from the cuff demonstrates that highly dynamic processes occur in the distal arm during cuff inflation. Mean arterial pressure increases in the distal artery by up to 20 mmHg, leading to a decrease in pulse transit time of up to 20 ms. Clinical Relevance: Such significant changes need to be taken into account in order to improve non-invasive BP estimations and to enable inference of other hemodynamic parameters from vasculature response to cuff inflation. A simple model is developed in order to reproduce the observed behaviors. The lumped-parameter model demonstrates opportunities for cuff modulation measurements which can reveal information on parameters such as systemic resistance, distal arterial, venous compliances and artery-vein interaction.

Modulation of Pulse Propagation and Blood Flow via Cuff Inflation-New Distal Insights.

In standard critical care practice, cuff sphygmomanometry is widely used for intermittent blood pressure (BP) measurements. However, cuff devices offer ample possibility of modulating blood flow and pulse propagation along the artery. We explore underutilized arrangements of sensors involving cuff devices which could be of use in critical care to reveal additional information on compensatory mechanisms. In our previous work, we analyzed the response of the vasculature to occlusion perturbations by means of observations obtained non-invasively. In this study, our aim is to (1) acquire additional insights by means of invasive measurements and (2) based on these insights, further develop cuff-based measurement strategies. Invasive BP experimental data is collected downstream from the cuff in two patients monitored in the OR. It is found that highly dynamic processes occur in the distal arm during cuff inflation. Mean arterial pressure increases in the distal artery by 20 mmHg, leading to a decrease in pulse transit time by 20 ms. Previous characterizations neglected such distal vasculature effects. A model is developed to reproduce the observed behaviors and to provide a possible explanation of the factors that influence the distal arm mechanisms. We apply the new findings to further develop measurement strategies aimed at acquiring information on pulse arrival time vs. BP calibration, artery compliance, peripheral resistance, artery-vein interaction.

Surrogate based continuous noninvasive blood pressure measurement.

Arterial blood pressure is one of the most often measured vital parameters in clinical practice. State-of-the-art noninvasive ABP measurement technologies have noticeable limitations and are mainly based on uncomfortable techniques of complete or partial arterial occlusion by cuffs. Most commonplace devices provide only intermittent measurements, and continuous systems are bulky and difficult to apply correctly for nonprofessionals. Continuous cuffless ABP measurements are still an unmet clinical need and a topic of ongoing research, with only few commercially available devices. This paper discusses surrogate-based noninvasive blood pressure measurement techniques. It covers measurement methods of continuously and noninvasively inferring BP from surrogate signals without applying external pressures, except for reference or initialization purposes. The BP is estimated by processing signal features, so called surrogates, which are modulated by variations of BP. Discussed techniques include well-known approaches such as pulse transit time and pulse arrival time techniques, pulse wave analysis or combinations thereof. Despite a long research history, these methods have not found widespread use in clinical and ambulatory practice, in part due to technical limitations and the lack of a standardized regulatory framework. This work summarizes findings from an invited workshop of experts in the fields covering clinical expertise, engineering aspects, commercialization and standardization issues. The goal is to provide an application driven outlook, starting with clinical needs, and extending to technical actuality. It provides an outline of recommended research directions and includes a detailed overview of clinical use case scenarios for these technologies, opportunities, and limitations.

Hybrid in-phase and continuous auditory stimulation significantly enhances slow wave activity during sleep.

Recent evidence has shown that enhancing slow-wave activity (SWA) during sleep has positive effects on cognitive, metabolic, and autonomic function. We have developed a consumer, integrated device that automatically detects sleep stages from a single electroencephalogram (EEG) signal and delivers auditory stimulation in a closed-loop manner. The stimulation was delivered in 15-auditory tone blocks separated from each other by at least 15 seconds. The first tone in a block was synchronized to the up-state of a detected slow-wave while subsequent ones were separated from each other by a constant 1-second inter-tone interval. The system was tested in a study involving 22 participants and SWA enhancement (average 45.8%; p=0.0027) was found in 19/22 participants.

Recurrent Deep Neural Networks for Real-Time Sleep Stage Classification From Single Channel EEG.

Objective: We investigate the design of deep recurrent neural networks for detecting sleep stages from single channel EEG signals recorded at home by non-expert users. We report the effect of data set size, architecture choices, regularization, and personalization on the classification performance. Methods: We evaluated 58 different architectures and training configurations using three-fold cross validation. Results: A network consisting of convolutional (CONV) layers and long short term memory (LSTM) layers can achieve an agreement with a human annotator of Cohen's Kappa of ~0.73 using a training data set of 19 subjects. Regularization and personalization do not lead to a performance gain. Conclusion: The optimal neural network architecture achieves a performance that is very close to the previously reported human inter-expert agreement of Kappa 0.75. Significance: We give the first detailed account of CONV/LSTM network design process for EEG sleep staging in single channel home based setting.

Calibration of Contactless Pulse Oximetry.

BACKGROUND: Contactless, camera-based photoplethysmography (PPG) interrogates shallower skin layers than conventional contact probes, either transmissive or reflective. This raises questions on the calibratability of camera-based pulse oximetry. METHODS: We made video recordings of the foreheads of 41 healthy adults at 660 and 840 nm, and remote PPG signals were extracted. Subjects were in normoxic, hypoxic, and low temperature conditions. Ratio-of-ratios were compared to reference SpO2 from 4 contact probes. RESULTS: A calibration curve based on artifact-free data was determined for a population of 26 individuals. For an SpO2 range of approximately 83% to 100% and discarding short-term errors, a root mean square error of 1.15% was found with an upper 99% one-sided confidence limit of 1.65%. Under normoxic conditions, a decrease in ambient temperature from 23 to 7°C resulted in a calibration error of 0.1% (±1.3%, 99% confidence interval) based on measurements for 3 subjects. PPG signal strengths varied strongly among individuals from about 0.9 × 10 to 4.6 × 10 for the infrared wavelength. CONCLUSIONS: For healthy adults, the results present strong evidence that camera-based contactless pulse oximetry is fundamentally feasible because long-term (eg, 10 minutes) error stemming from variation among individuals expressed as A*rms is significantly lower (<1.65%) than that required by the International Organization for Standardization standard (<4%) with the notion that short-term errors should be added. A first illustration of such errors has been provided with A**rms = 2.54% for 40 individuals, including 6 with dark skin. Low signal strength and subject motion present critical challenges that will have to be addressed to make camera-based pulse oximetry practically feasible.

Cuff-pressure induced PAT changes - modelling and experimental verification towards calibration of blood pressure surrogates.

Arterial Blood Pressure (ABP) is one of the most often measured vital parameters in daily clinical practice. State-of-the-Art non-invasive ABP measurement technologies have obvious limitations and are still mainly based on uncomfortable techniques by complete or partial occlusions of arteries. Additionally, embodiments are bulky, difficult to apply for the layman, or provide only intermittent measurements. We have been investigating the pulse arrival time (PAT) and pulse transit time (PTT) methodology for unobtrusive blood pressure (BP) measurements. However, BP surrogates like PAT or PTT require a calibration step, which is currently an unresolved problem. In this paper we report on our investigations using cuff-pressure induced PAT changes in order to provide insights in the BP-PAT sensitivities for subjects at rest.

Comparison of pulse wave velocity derived from accelerometer and reflective photo-plethysmography signals placed at the carotid and femoral artery.

Carotid - femoral pulse wave velocity is an established measure to assess cardiovascular risk and an interesting surrogate parameter towards non-invasive continuous blood pressure inference. Due to progress in sensing technologies for wearable wrist worn sensors, there are low cost sensor combinations of photo-plethysmography and high fidelity accelerometers available offering access to pulse information from larger arteries complemented by blood volume changes in the superficial tissue. In this work we compare pulse wave velocities derived from accelerometer and reflective photo-plethysmography signals placed at the carotid and femoral artery. We discuss the different underlying physiological processes for the two sensing principles and present experimental results obtained in a study with healthy subjects.

Real-time magnetic resonance imaging and electromagnetic articulography database for speech production research (TC).

USC-TIMIT is an extensive database of multimodal speech production data, developed to complement existing resources available to the speech research community and with the intention of being continuously refined and augmented. The database currently includes real-time magnetic resonance imaging data from five male and five female speakers of American English. Electromagnetic articulography data have also been presently collected from four of these speakers. The two modalities were recorded in two independent sessions while the subjects produced the same 460 sentence corpus used previously in the MOCHA-TIMIT database. In both cases the audio signal was recorded and synchronized with the articulatory data. The database and companion software are freely available to the research community.

Paralinguistic mechanisms of production in human "beatboxing": a real-time magnetic resonance imaging study.

Real-time magnetic resonance imaging (rtMRI) was used to examine mechanisms of sound production by an American male beatbox artist. rtMRI was found to be a useful modality with which to study this form of sound production, providing a global dynamic view of the midsagittal vocal tract at frame rates sufficient to observe the movement and coordination of critical articulators. The subject's repertoire included percussion elements generated using a wide range of articulatory and airstream mechanisms. Many of the same mechanisms observed in human speech production were exploited for musical effect, including patterns of articulation that do not occur in the phonologies of the artist's native languages: ejectives and clicks. The data offer insights into the paralinguistic use of phonetic primitives and the ways in which they are coordinated in this style of musical performance. A unified formalism for describing both musical and phonetic dimensions of human vocal percussion performance is proposed. Audio and video data illustrating production and orchestration of beatboxing sound effects are provided in a companion annotated corpus.

Real-time magnetic resonance imaging investigation of resonance tuning in soprano singing.

This article investigates using real-time magnetic resonance imaging the vocal tract shaping of 5 soprano singers during the production of two-octave scales of sung vowels. A systematic shift of the first vocal tract resonance frequency with respect to the fundamental is shown to exist for high vowels across all subjects. No consistent systematic effect on the vocal tract resonance could be shown across all of the subjects for other vowels or for the second vocal tract resonance.

Analysis of pausing behavior in spontaneous speech using real-time magnetic resonance imaging of articulation.

It is hypothesized that pauses at major syntactic boundaries (i.e., grammatical pauses), but not ungrammatical (e.g., word search) pauses, are planned by a high-level cognitive mechanism that also controls the rate of articulation around these junctures. Real-time magnetic resonance imaging is used to analyze articulation at and around grammatical and ungrammatical pauses in spontaneous speech. Measures quantifying the speed of articulators were developed and applied during these pauses as well as during their immediate neighborhoods. Grammatical pauses were found to have an appreciable drop in speed at the pause itself as compared to ungrammatical pauses, which is consistent with our hypothesis that grammatical pauses are indeed choreographed by a central cognitive planner.

Region segmentation in the frequency domain applied to upper airway real-time magnetic resonance images.

We describe a method for unsupervised region segmentation of an image using its spatial frequency domain representation. The algorithm was designed to process large sequences of real-time magnetic resonance (MR) images containing the 2-D midsagittal view of a human vocal tract airway. The segmentation algorithm uses an anatomically informed object model, whose fit to the observed image data is hierarchically optimized using a gradient descent procedure. The goal of the algorithm is to automatically extract the time-varying vocal tract outline and the position of the articulators to facilitate the study of the shaping of the vocal tract during speech production.

Timing effects of syllable structure and stress on nasals: a real-time MRI examination.

The coordination of velum and oral gestures for English [n] is studied using real-time MRI movies to reconstruct vocal tract aperture functions. This technique allows for the examination of parts of the vocal tract otherwise inaccessible to dynamic imaging or movement tracking. The present experiment considers syllable onset, coda, and juncture geminate nasals and also addresses the effects of a variety of word stress patterns on segment internal coordination. We find a bimodal timing pattern in which near-synchrony of velum lowering and tongue tip raising characterizes the timing for onsets and temporal lag between the gestures is characteristic for codas, supporting and extending the findings of Krakow (1989), 1993) for [m]. Intervocalic word-internal nasals are found to have timing patterns that are sensitive to the local stress context, which suggests the presence of an underlying timing specification that can yield flexibly. We consider these findings in light of the gestural coupling structures described by Goldstein and colleagues (Goldstein, Byrd, & Saltzman 2006; Nam, Goldstein, and Saltzman in press; Goldstein, Nam, Saltzman, & Chitoran 2008).

Synchronized and noise-robust audio recordings during realtime magnetic resonance imaging scans.

This letter describes a data acquisition setup for recording, and processing, running speech from a person in a magnetic resonance imaging (MRI) scanner. The main focus is on ensuring synchronicity between image and audio acquisition, and in obtaining good signal to noise ratio to facilitate further speech analysis and modeling. A field-programmable gate array based hardware design for synchronizing the scanner image acquisition to other external data such as audio is described. The audio setup itself features two fiber optical microphones and a noise-canceling filter. Two noise cancellation methods are described including a novel approach using a pulse sequence specific model of the gradient noise of the MRI scanner. The setup is useful for scientific speech production studies. Sample results of speech and singing data acquired and processed using the proposed method are given.