Advancing orthostatic hypotension diagnostics

This thesis investigated the diagnostics of orthostatic hypotension (OH). OH is defined as a sustained systolic/diastolic blood pressure (BP) drop larger than 20/10 mmHg within 3 minutes after standing up. OH is common among older adults aged above 65 years (6 – 31%) and geriatric outpatients (22-56%), sometimes accompanied by orthostatic intolerance (dizziness, light-headedness and blurry vision) and associated with poor clinical outcome (cardiovascular diseases, impaired cognitive performance and mortality). Current OH diagnostics is limited due to 1) contradictory evidence on the association between the OH definition and physical functioning and falls; 2) the uncertainty of the clinical value of continuous BP measurements, which may in contrast to intermittent sphygmomanometer measurements reflect the challenge posed to compensation systems and brain exposure to low perfusion pressures; and 3) the lack of assessment of systems compensating for orthostatic BP drops such as baroreflex sensitivity (i.e., heart rate increase in response to a BP drop to stabilize BP), peripheral vasoconstriction (i.e., narrowing of peripheral artery diameter in response to a BP drop to increase peripheral resistance and stabilize BP) and cerebral autoregulation (i.e., dilation of cerebral arterioles in response to a BP drop to keep cerebral blood flow constant). In conclusion, the currently used OH definition was found to be clinically valuable as patients diagnosed according to this definition are at increased risk of impaired physical functioning and falls. BP drop rate and BP recovery derived from continuous BP measurements were found to have added clinical value by their association with clinical outcome and may after confirmation of the results in further studies have to be incorporated in a new OH definition for continuous orthostatic BP measurements to better identify individuals with clinical consequences due to OH. Parameters expressing baroreflex sensitivity, cerebral oxygenation and cerebral autoregulation were by their sensitivity, test-retest reliability and validity in younger and older adults demonstrated to be potentially valuable, supporting further study on the clinical value of these parameters

Photoplethysmography-Based Biomedical Signal Processing

In this dissertation, photoplethysmography-based biomedical signal processing methods are developed and analyzed. The developed methods solve problems concerning the estimation of the heart rate during physical activity and the monitoring of cardiovascular health. For the estimation of heart rate during physical activity, two methods are presented that are very accurate in estimating the instantaneous heart rate at the wrist and, at the same time, are computationally efficient so that they can easily be integrated into wearables. In the context of cardiovascular health monitoring, a method for the detection of atrial fibrillation using the video camera of a smartphone is proposed that achieves a high detection rate of atrial fibrillation (AF) on a clinical pre-study data set. Further monitoring of cardiovascular parameters includes the estimation of blood pressure (BP), pulse wave velocity (PWV), and vascular age index (VAI), for which an approach is presented that requires only a single photoplethysmographic (PPG) signal. Heart rate estimation during physical activity using PPG signals constitutes an important research focus of this thesis. In this work, two computationally efficient algorithms are presented that estimate the heart rate from two PPG signals using a three axis accelerometer. In the first approach, adaptive filters are applied to estimate motion artifacts that severely deteriorate the signal quality. The non-stationary relationship between the measured acceleration signals and the artifacts is modeled as a linear system. The outputs of the adaptive filters are combined to further enhance the signal quality and a constrained heart rate tracker follows the most probable high energy continuous line in the spectral domain. The second approach is modest in computational complexity and very fast in execution compared to existing approaches. It combines correlation-based fundamental frequency indicating functions and spectral combination to enhance the correlated useful signal and suppress uncorrelated noise. Additional harmonic noise damping further reduces the impact of strong motion artifacts and a spectral tracking procedure uses a linear least squares prediction. Both approaches are modest in computational complexity and especially the second approach is very fast in execution, as it is shown on a widely used benchmark data set and compared to state-of-the-art methods. The second research focus and a further major contribution of this thesis lies in the monitoring of the cardiovascular health with a single PPG signal. Two methods are presented, one for detection of AF and one for the estimation of BP, PWV, and VAI. The first method is able to detect AF based on a smartphone filming the finger placed on the video camera. The algorithm transforms the video into a PPG signal and extracts features which are then used to discriminate between AF and normal sinus rhythm (NSR). Perfect detection of AF is already achieved on a data set of 326 measurements (including 20 with AF) that were taken at a clinical pre-study using an appropriate pair of features whereby a decision is formed through a simple linear decision equation. The second method aims at estimating cardiovascular parameters from a single PPG signal without the conventional use of an additional electrocardiogram (ECG). The proposed method extracts a large number of features from the PPG signal and its first and second order difference series, and reconstructs missing features by the use of matrix completion. The estimation of cardiovascular parameters is based on a nonlinear support vector regression (SVR) estimator and compared to single channel PPG based estimators using a linear regression model and a pulse arrival time (PAT) based method. If the training data set contains the person for whom the cardiovascular parameters are to be determined, the proposed method can provide an accurate estimate without further calibration. All proposed algorithms are applied to real data that we have either recorded ourselves in our biomedical laboratory, that have been recorded by a clinical research partner, or that are freely available as benchmark data sets

Investigação dos efeitos de anestesia sobre a variabilidade cardíaca

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2012Dada a grande variabilidade da resposta fisiológica, um determinado volume de anestésico pode ser insuficiente para determinado indivíduo e ser excessivo para outro. Estudos realizados em vários países relatam uma taxa de 0,1% a 0,2% de retomada da consciência com lembranças de eventos durante cirurgia sob anestesia geral. O despertar peroperatório pode provocar síndrome pós-traumática, com graves sequelas psicológicas para o paciente. Existem também, os casos opostos, onde o excesso de anestésico, tardiamente percebido, acarreta dano cerebral. Pacientes excessivamente anestesiados demoram mais para receber alta, aumentando assim, o custo da internação hospitalar. Um crescente número de estudos vem sendo realizado para avaliar as alterações na variabilidade do ritmo cardíaco (VRC) durante anestesia. Estes estudos utilizam diferentes anestésicos, procedimentos, métodos de processamento e análise de sinais. A finalidade é obter índices que possam determinar o nível de profundidade anestésica. No entanto, os resultados obtidos ainda não são conclusivos. Este trabalho investiga a VRC em 11 pacientes anestesiados com o nível de profundidade anestésica monitorada por meio do índice BIS. Para tal, utiliza medidas de defasamento entre a série RR e volume pulmonar, bem como realiza modelamento multivariáveis da VRC. A partir dos resultados obtidos para esta pequena amostra, observou-se que a estabilidade do defasamento indica que o sistema nervoso autônomo não se encontra bloqueado. A extensão deste estudo para um maior número de pacientes pode permitir que a medida de defasamento seja incorporada a monitores de profundidade anestésica como um índice auxiliar de analgesia.Abstract : Due to the large variability of physiological responses, a given quantity of anesthetic may be insufficient for some individuals and ex-cessive for others. During surgery under general anesthesia, studies carried out in several countries reported a rate of consciousness recov-ery, in which the patients had memories of the events, between 0.1% and 0.2%. The per-operative wakeup may cause post-traumatic syn-drome with serious psychological consequences for the patients. There are also opposite cases when the excess of anesthetic causes brain dam-ages. Patients who receive anesthetics in excess remain longer under medical care, increasing the hospitalization costs. Recent studies have assessed changes of the heart rate variability (HRV) during anesthesia. These works employed different anesthetics, procedures and methods for signal processing and data analysis. Their purpose was to obtain indexes that could determine the level of anesthet-ic depth. However, the results obtained so far are not conclusive. This work investigated the HRV of 11 patients who had their an-esthetic depth monitored by the BIS index. Phase shift measurements between the RR and lung volume waveform and multivariate modeling of the HRV were carried out. From the obtained results for this small number of subjects, it was found that the phase shift stability between the RR and lung volume waveform points out that the autonomic nerv-ous system is not blocked. The extension of this study to a larger num-ber of patients may allow the monitoring of such phase shift to be used as an anesthetic index of analgesia

Life Sciences Program Tasks and Bibliography for FY 1997

This document includes information on all peer reviewed projects funded by the Office of Life and Microgravity Sciences and Applications, Life Sciences Division during fiscal year 1997. This document will be published annually and made available to scientists in the space life sciences field both as a hard copy and as an interactive internet web page

Patient Safety and Quality: An Evidence-Based Handbook for Nurses

Compiles peer-reviewed research and literature reviews on issues regarding patient safety and quality of care, ranging from evidence-based practice, patient-centered care, and nurses' working conditions to critical opportunities and tools for improvement