Non-invasive hemodynamic monitoring by electrical impedance tomography

The monitoring of central hemodynamic parameters such as cardiac output (CO) and pulmonary artery pressure (PAP) is of paramount clinical importance to assess the health status of the cardiovascular system. However, their measurement requires the insertion of a pulmonary artery catheter, a highly invasive procedure associated with non-negligible morbidity and mortality rates. In this thesis, we investigated the clinical potential of electrical impedance tomography (EIT) - a radiation-free medical imaging technique - as a non-invasive alternative for the measurement of CO and PAP. In a first phase, we investigated the potential of EIT for the measurement of CO. This measurement is implicitly based on the hypothesis that the EIT heart signal (the ventricular component of the EIT signals) is induced by ventricular blood volume changes. This hypothesis has never been formally investigated, and the exact origins of the EIT heart signal remain subject to interpretation. Therefore, using a model, we investigated the genesis of this signal by identifying its various sources and their respective contributions. The results revealed that the EIT heart signal is dominated by cardioballistic effects (heart motion). However, although of prominently cardioballistic origin, the amplitude of the signal has shown to be strongly correlated to stroke volume (r = 0.996, p < 0.001; error of 0.57 +/- 2.19 mL). We explained these observations by the quasi-incompressibility of myocardial tissue and blood. We further identified several factors and conditions susceptible to affect the accuracy of the measurement. Finally, we investigated the influence of the EIT sensor belt position on the measured heart signal. We observed that small belt displacements - likely to occur in clinical settings during patient handling - can induce errors of up to 30 mL on stroke volume estimation. In a second phase, we investigated the feasibility of a novel method for the non-invasive measurement of PAP by EIT. The method is based on the physiological relation linking the PAP to the velocity of propagation of the pressure waves in the pulmonary arteries. We hypothesized that the variations of this velocity, and therefore of the PAP, could be measured by EIT. In a bioimpedance model of the human thorax, we demonstrated the feasibility of our method in various types of pulmonary hypertensive disorders. Our EIT-derived parameter has shown to be particularly well-suited for predicting early changes in pulmonary hemodynamics due to its physiological link with arterial compliance. Finally, we validated experimentally our method in 14 subjects undergoing hypoxia-induced PAP changes. Significant correlation coefficients (range: [0.70, 0.98], average: 0.89) and small standard errors of the estimate (range: [0.9, 6.3] mmHg, average: 2.4 mmHg) were found between our EIT-derived systolic PAP and reference systolic PAP values obtained by Doppler echocardiography. In conclusion, there is a promising outlook for EIT in non-invasive hemodynamic monitoring. Our observations provide novel insights for the interpretation and understanding of EIT heart signals, and detail the physiological and metrological requirements for an accurate measurement of CO by EIT. Our novel PAP monitoring method, validated in vivo, allows a reliable tracking of PAP changes, thereby paving the way towards the development of a new branch of non-invasive hemodynamic monitors based on the use of EIT

Non-invasive pulmonary artery pressure estimation by electrical impedance tomography in a controlled hypoxemia study in healthy subjects.

Pulmonary hypertension is a hemodynamic disorder defined by an abnormal elevation of pulmonary artery pressure (PAP). Current options for measuring PAP are limited in clinical practice. The aim of this study was to evaluate if electrical impedance tomography (EIT), a radiation-free and non-invasive monitoring technique, can be used for the continuous, unsupervised and safe monitoring of PAP. In 30 healthy volunteers we induced gradual increases in systolic PAP (SPAP) by exposure to normobaric hypoxemia. At various stages of the protocol, the SPAP of the subjects was estimated by transthoracic echocardiography. In parallel, in the pulmonary vasculature, pulse wave velocity was estimated by EIT and calibrated to pressure units. Within-cohort agreement between both methods on SPAP estimation was assessed through Bland-Altman analysis and at subject level, with Pearson's correlation coefficient. There was good agreement between the two methods (inter-method difference not significant (P > 0.05), bias ± standard deviation of - 0.1 ± 4.5 mmHg) independently of the degree of PAP, from baseline oxygen saturation levels to profound hypoxemia. At subject level, the median per-subject agreement was 0.7 ± 3.8 mmHg and Pearson's correlation coefficient 0.87 (P < 0.05). Our results demonstrate the feasibility of accurately assessing changes in SPAP by EIT in healthy volunteers. If confirmed in a patient population, the non-invasive and unsupervised day-to-day monitoring of SPAP could facilitate the clinical management of patients with pulmonary hypertension

Comparing belt positions for monitoring the descending aorta by EIT

In electrical impedance tomography, the impedance changes stemming from the descending aorta contain valuable information for haemodynamic monitoring. However, the low signal strength necessitates an optimal measurement setup. Among different belt positions investigated in this work, a transversal and low placement is the best choice for detecting signals of the descending aorta

Validation of an integrated pedal desk and electronic behavior tracking platform

Background This study tested the validity of revolutions per minute (RPM) measurements from the Pennington Pedal Desk™. Forty-four participants (73 % female; 39 ± 11.4 years-old; BMI 25.8 ± 5.5 kg/m2 [mean ± SD]) completed a standardized trial consisting of guided computer tasks while using a pedal desk for approximately 20 min. Measures of RPM were concurrently collected by the pedal desk and the Garmin Vector power meter. After establishing the validity of RPM measurements with the Garmin Vector, we performed equivalence tests, quantified mean absolute percent error (MAPE), and constructed Bland–Altman plots to assess agreement between RPM measures from the pedal desk and the Garmin Vector (criterion) at the minute-by-minute and trial level (i.e., over the approximate 20 min trial period). Results The average (mean ± SD) duration of the pedal desk trial was 20.5 ± 2.5 min. Measures of RPM (mean ± SE) at the minute-by-minute (Garmin Vector: 54.8 ± 0.4 RPM; pedal desk: 55.8 ± 0.4 RPM) and trial level (Garmin Vector: 55.0 ± 1.7 RPM; pedal desk: 56.0 ± 1.7 RPM) were deemed equivalent. MAPE values for RPM measured by the pedal desk were small (minute-by-minute: 2.1 ± 0.1 %; trial: 1.8 ± 0.1 %) and no systematic relationships in error variance were evident by Bland–Altman plots. Conclusion The Pennington Pedal Desk™ provides a valid count of RPM, providing an accurate metric to promote usage

Global biodiversity monitoring: From data sources to Essential Biodiversity Variables

Essential Biodiversity Variables (EBVs) consolidate information from varied biodiversity observation sources. Here we demonstrate the links between data sources, EBVs and indicators and discuss how different sources of biodiversity observations can be harnessed to inform EBVs. We classify sources of primary observations into four types: extensive and intensive monitoring schemes, ecological field studies and satellite remote sensing. We characterize their geographic, taxonomic and temporal coverage. Ecological field studies and intensive monitoring schemes inform a wide range of EBVs, but the former tend to deliver short-term data, while the geographic coverage of the latter is limited. In contrast, extensive monitoring schemes mostly inform the population abundance EBV, but deliver long-term data across an extensive network of sites. Satellite remote sensing is particularly suited to providing information on ecosystem function and structure EBVs. Biases behind data sources may affect the representativeness of global biodiversity datasets. To improve them, researchers must assess data sources and then develop strategies to compensate for identified gaps. We draw on the population abundance dataset informing the Living Planet Index (LPI) to illustrate the effects of data sources on EBV representativeness. We find that long-term monitoring schemes informing the LPI are still scarce outside of Europe and North America and that ecological field studies play a key role in covering that gap. Achieving representative EBV datasets will depend both on the ability to integrate available data, through data harmonization and modeling efforts, and on the establishment of new monitoring programs to address critical data gaps

Marine terrace staircases of western Iberia: uplift rate patterns from rocky limestone coasts of central Portugal (Cape Espichel and Raso)

The Western Iberian passive margin is under compressive tectonic reactivation resulting in spatial and temporal variations in surface uplift. This uplift can be quantified in coastal settings using staircases of wave-cut platforms developed onto rocky headlands. This study focuses on two marine terrace staircases of central Portugal: Cape Raso (west of Lisbon) and Cape Espichel (western Arrábida mountain chain). Geomorphic and stratigraphic analyses identified four marine terraces above sea level at Cape Raso area and twelve at Cape Espichel. ESR and pIRIR dating were used to develop a chronological framework for the staircases, from which uplift rates were calculated. Using the interaction between the global mean sea-level elevations in the Quaternary and the local uplift rate (Roberts et al., 2013) the marine terraces were correlated with Marine Isotope Stages (MIS). At Cape Raso, Tm1 (+38 m) corresponds to MIS 17 (712-676 ka), Tm2 (+34 m) corresponds to the MIS 15 (621-563 ka) and was reworked during the MIS 11 (399-408 ka), Tm3 (+ 22 m) correlates with MIS 13 (533-478 ka) and was reworked during the highstand of MIS 9 (330-316 ka) and Tm4 (+9 m) correlates with MIS 7 (243 -191 ka). At Cape Espichel, a correlation was found between the relative sea-level elevations of the eight lowest terraces with several MISs (MIS 5 until MIS 17). The correlation becomes unclear for terraces older than MIS 17, translating into an apparent decrease in uplift rate towards older times. Either in Cape Raso or Espichel, the terrace staircases do not correlate in all cases with sea level high stands sequentially. For instance, the palaeoshoreline elevation of MIS 11 is higher than the palaeoshoreline of MIS 13. This suggests that marine terraces have been formed by superposition of multiple sea-level fluctuations in a long-term uplift context, but with an uplift rate low enough to allow the reworking of older shorelines during subsequent MISs. At Cape Raso, the dating of Tm2 correlated with MIS 15 allows for an estimation of an uplift rate of ~0.07 m/ka for this coast, seemingly decreasing over the last ~125 ka. At Cape Espichel, the chronological framework of Tm5 and Tm6 allows associations with MIS 15 and MIS 11, respectively.The estimated mean uplift rate from MIS 5e to MIS 17 was ~0.14m/ka. For times older than MIS 17 (up to ca. 3.7 Ma) the uplift rate was lower than during the last ~125 ka (~0.04 m/ka). The present elevations of the late Zanclean wave-cut platform, represented by the Raso Cape Platform (~100 m) and the Cape Espichel (up to ~220 m) platforms, further express the differential uplift between the study areas for the last ~3.7 Ma. References: Roberts, G.P., Meschis, M., Houghton, S., Underwood, C., Briant R.M., 2013. The implications of revised Quaternary paleo-shoreline chronologies for the rates of active extension and uplift in the upper plate of subduction zones. Quaternary Science Reviews 78, 169-187

Discarding the Direct Component in Electrical Impedance Tomography

Several studies [1,2] have shown the potential of EIT to estimate cardiovascular parameters. To achieve this goal, EIT devices have to deal with small impedance variations. As a consequence, the high value of the direct component (DC) of the bio-impedance signal becomes an issue in terms of analog to digital converter resolution. With this research, we aim at demonstrating that the DC of the signal can be discarded before digitalization

A resposta da NATO à Nova Ordem Euro-Atlântica confrontacional

A Cimeira da NATO de Madrid foi uma cimeira histórica. A Aliança Atlântica adotou o seu novo conceito estratégico, num contexto radicalmente diferente do ambiente estratégico de há 12 anos atrás, quando, em 2010, o último conceito estratégico da Aliança tinha definido uma política de “reset” com a Rússia. Agora, a Aliança Atlântica depara-se, há cinco meses, com o regresso da guerra à Europa, com a invasão russa da Ucrânia a marcar a nova orientação estratégica da Aliança e a confirmar a deterioração de relações com a Rússia. Na definição do novo conceito estratégico, que decisões foram tomadas na cimeira de Madrid? Como responderam os principais Estados-membros europeus? E como se posicionam Lisboa, Madrid, Berlim, Paris e Varsóvia neste novo contexto estratégico? Este IDN Brief reúne um conjunto de especialistas, nacionais e estrangeiros, para responder a estas e outras questões.info:eu-repo/semantics/publishedVersio

Marine terrace staircases of western Iberia: uplift rate patterns from rocky limestone coasts of central Portugal (Cape Espichel and Raso)

The Western Iberian passive margin is under compressive tectonic reactivation resulting in spatial and temporal variations in surface uplift. This uplift can be quantified in coastal settings using staircases of wave-cut platforms developed onto rocky headlands. This study focuses on two marine terrace staircases of central Portugal: Cape Raso (west of Lisbon) and Cape Espichel (western Arrábida mountain chain). Geomorphic and stratigraphic analyses identified four marine terraces above sea level at Cape Raso area and twelve at Cape Espichel. ESR and pIRIR dating were used to develop a chronological framework for the staircases, from which uplift rates were calculated. Using the interaction between the global mean sea-level elevations in the Quaternary and the local uplift rate (Roberts et al., 2013) the marine terraces were correlated with Marine Isotope Stages (MIS). At Cape Raso, Tm1 (+38 m) corresponds to MIS 17 (712-676 ka), Tm2 (+34 m) corresponds to the MIS 15 (621-563 ka) and was reworked during the MIS 11 (399-408 ka), Tm3 (+ 22 m) correlates with MIS 13 (533-478 ka) and was reworked during the highstand of MIS 9 (330-316 ka) and Tm4 (+9 m) correlates with MIS 7 (243 -191 ka). At Cape Espichel, a correlation was found between the relative sea-level elevations of the eight lowest terraces with several MISs (MIS 5 until MIS 17). The correlation becomes unclear for terraces older than MIS 17, translating into an apparent decrease in uplift rate towards older times. Either in Cape Raso or Espichel, the terrace staircases do not correlate in all cases with sea level high stands sequentially. For instance, the palaeoshoreline elevation of MIS 11 is higher than the palaeoshoreline of MIS 13. This suggests that marine terraces have been formed by superposition of multiple sea-level fluctuations in a long-term uplift context, but with an uplift rate low enough to allow the reworking of older shorelines during subsequent MISs. At Cape Raso, the dating of Tm2 correlated with MIS 15 allows for an estimation of an uplift rate of ~0.07 m/ka for this coast, seemingly decreasing over the last ~125 ka. At Cape Espichel, the chronological framework of Tm5 and Tm6 allows associations with MIS 15 and MIS 11, respectively.The estimated mean uplift rate from MIS 5e to MIS 17 was ~0.14m/ka. For times older than MIS 17 (up to ca. 3.7 Ma) the uplift rate was lower than during the last ~125 ka (~0.04 m/ka). The present elevations of the late Zanclean wave-cut platform, represented by the Raso Cape Platform (~100 m) and the Cape Espichel (up to ~220 m) platforms, further express the differential uplift between the study areas for the last ~3.7 Ma. References: Roberts, G.P., Meschis, M., Houghton, S., Underwood, C., Briant R.M., 2013. The implications of revised Quaternary paleo-shoreline chronologies for the rates of active extension and uplift in the upper plate of subduction zones. Quaternary Science Reviews 78, 169-187