Ballistocardiography and Seismocardiography: A Review of Recent Advances Inan, Omer T.; Migeotte, Pierre-Francois; Kwang-Suk Park ...
IEEE journal of biomedical and health informatics,
2015-July, 2015-Jul, 2015-7-00, 20150701, 2015-07-01, Letnik:
19, Številka:
4
Journal Article, Publication
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In the past decade, there has been a resurgence in the field of unobtrusive cardiomechanical assessment, through advancing methods for measuring and interpreting ballistocardiogram (BCG) and ...seismocardiogram (SCG) signals. Novel instrumentation solutions have enabled BCG and SCG measurement outside of clinical settings, in the home, in the field, and even in microgravity. Customized signal processing algorithms have led to reduced measurement noise, clinically relevant feature extraction, and signal modeling. Finally, human subjects physiology studies have been conducted using these novel instruments and signal processing tools with promising results. This paper reviews the recent advances in these areas of modern BCG and SCG research.
Treatment of ARDS With Prone Positioning Scholten, Eric L., MD; Beitler, Jeremy R., MD, MPH; Prisk, G. Kim, PhD, DSc ...
Chest,
01/2017, Letnik:
151, Številka:
1
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Prone positioning was first proposed in the 1970s as a method to improve gas exchange in ARDS. Subsequent observations of dramatic improvement in oxygenation with simple patient rotation motivated ...the next several decades of research. This work elucidated the physiological mechanisms underlying changes in gas exchange and respiratory mechanics with prone ventilation. However, translating physiological improvements into a clinical benefit has proved challenging; several contemporary trials showed no major clinical benefits with prone positioning. By optimizing patient selection and treatment protocols, the recent Proning Severe ARDS Patients (PROSEVA) trial demonstrated a significant mortality benefit with prone ventilation. This trial, and subsequent meta-analyses, support the role of prone positioning as an effective therapy to reduce mortality in severe ARDS, particularly when applied early with other lung-protective strategies. This review discusses the physiological principles, clinical evidence, and practical application of prone ventilation in ARDS.
Microgravity and the respiratory system PRISK, G. Kim
European respiratory journal/The European respiratory journal,
05/2014, Letnik:
43, Številka:
5
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The structure of the lung, with its delicate network of airspaces and capillaries, means that gravity has a profound influence on its function. Studies of lung function in the absence of gravity ...provide valuable insight into how, for we Earth-bound individuals, its unavoidable effects shape our lung function. Gravity causes uneven ventilation in the lung through the deformation of lung tissue (the so-called Slinky effect), and uneven perfusion through a combination of the Slinky effect and the zone model of pulmonary perfusion. Both ventilation and perfusion exhibit persisting heterogeneity in microgravity, indicating important other mechanisms. However, gravity serves to maintain a degree of matching of these two processes, so that the ventilation/perfusion ratio, and thus gas exchange, remains efficient. Therefore, while both ventilation and perfusion are more uniform in spaceflight, gas exchange is seemingly no more efficient than on Earth. Despite the changes in lung function when gravity is removed, the lung continues to function well in weightlessness. Unlike many other organ systems, the lung does not appear to undergo structural adaptive changes when gravity is removed, and so there is no apparent degradation in lung function upon return to earth, even after 6 months in space.
Summary
Space flight presents a set of physiological challenges to the space explorer which result from the absence of gravity (or in the case of planetary exploration, partial gravity), radiation ...exposure, isolation and a prolonged period in a confined environment, distance from Earth, the need to venture outside in the hostile environment of the destination, and numerous other factors.
Gravity affects regional lung function, and the human lung shows considerable alteration in function in low gravity; however, this alteration does not result in deleterious changes that compromise lung function upon return to Earth.
The decompression stress associated with extravehicular activity, or spacewalk, does not appear to compromise lung function, and future habitat (living quarter) designs can be engineered to minimise this stress.
Dust exposure is a significant health hazard in occupational settings such as mining, and exposure to extraterrestrial dust is an almost inevitable consequence of planetary exploration. The combination of altered pulmonary deposition of extraterrestrial dust and the potential for the dust to be highly toxic likely makes dust exposure the greatest threat to the lung in planetary exploration.
The gravitational gradient of intrapleural pressure is suggested to be less in prone posture than supine. Thus the gravitational distribution of ventilation is expected to be more uniform prone, ...potentially affecting regional ventilation-perfusion (Va/Q) ratio. Using a novel functional lung magnetic resonance imaging technique to measure regional Va/Q ratio, the gravitational gradients in proton density, ventilation, perfusion, and Va/Q ratio were measured in prone and supine posture. Data were acquired in seven healthy subjects in a single sagittal slice of the right lung at functional residual capacity. Regional specific ventilation images quantified using specific ventilation imaging and proton density images obtained using a fast gradient-echo sequence were registered and smoothed to calculate regional alveolar ventilation. Perfusion was measured using arterial spin labeling. Ventilation (ml·min(-1)·ml(-1)) images were combined on a voxel-by-voxel basis with smoothed perfusion (ml·min(-1)·ml(-1)) images to obtain regional Va/Q ratio. Data were averaged for voxels within 1-cm gravitational planes, starting from the most gravitationally dependent lung. The slope of the relationship between alveolar ventilation and vertical height was less prone than supine (-0.17 ± 0.10 ml·min(-1)·ml(-1)·cm(-1) supine, -0.040 ± 0.03 prone ml·min(-1)·ml(-1)·cm(-1), P = 0.02) as was the slope of the perfusion-height relationship (-0.14 ± 0.05 ml·min(-1)·ml(-1)·cm(-1) supine, -0.08 ± 0.09 prone ml·min(-1)·ml(-1)·cm(-1), P = 0.02). There was a significant gravitational gradient in Va/Q ratio in both postures (P < 0.05) that was less in prone (0.09 ± 0.08 cm(-1) supine, 0.04 ± 0.03 cm(-1) prone, P = 0.04). The gravitational gradients in ventilation, perfusion, and regional Va/Q ratio were greater supine than prone, suggesting an interplay between thoracic cavity configuration, airway and vascular tree anatomy, and the effects of gravity on Va/Q matching.
The spatial/temporal dynamics of blood flow in the human lung can be measured noninvasively with magnetic resonance imaging (MRI) using arterial spin labeling (ASL). We report a novel data analysis ...method using nonlinear prediction to identify dynamic interactions between blood flow units (image voxels), potentially providing a probe of underlying vascular control mechanisms. The approach first estimates the linear relationship (predictability) of one voxel time series with another using correlation analysis, and after removing the linear component, it estimates the nonlinear relationship with a numerical mutual information approach. Dimensionless global metrics for linear prediction (
) and nonlinear prediction (
) represent the average amplitude of fluctuations in one voxel estimated by another voxel, as a percentage of the global average voxel flow. A proof-of-principle test of this approach analyzed experimental data from a study of high-altitude pulmonary edema (HAPE), providing two groups exhibiting known differences in vascular reactivity. Subjects were mountaineers divided into HAPE-susceptible (S,
= 4) and HAPE-resistant (R,
= 5) groups based on prior history at high altitudes. Dynamic ASL measurements in the lung in normoxia (N, Formula: see text = 0.21) and hypoxia (H, Formula: see text = 0.13 ± 0.01) were compared. The nonlinear prediction metric
decreased with hypoxia 7.4 ± 1.3 (N) vs. 6.3 ± 0.7 (H),
= 0.03 and was significantly different between groups 7.4 ± 1.2 (R) vs. 6.2 ± 14.1 (S),
= 0.03. This proof-of-principle test demonstrates that this nonlinear analysis approach applied to ASL data is sensitive to physiological effects even in small subject cohorts, and it potentially can be used in a wide range of studies in health and disease in the lung and other organs.
Pulmonary blood flow varies both spatially and temporally. We describe a novel technique to uncover nonlinear interactions in dynamic images of pulmonary blood flow measured using MRI, based on mutual information between the flow fluctuations in different imaging voxels. In a proof-of-principle study, we show that the proposed metric of nonlinear interactions was sufficiently sensitive to detect a difference between small cohorts of subjects susceptible to high-altitude pulmonary edema (HAPE) and subjects resistant to HAPE.
Measurement of ventilation heterogeneity with the multiple-breath nitrogen washout (MBW) is usually performed using controlled breathing with a fixed tidal volume and breathing frequency. However, it ...is unclear whether controlled breathing alters the underlying ventilatory heterogeneity. We hypothesized that the width of the specific ventilation distribution (a measure of heterogeneity) would be greater in tests performed during free breathing compared with those performed using controlled breathing. Eight normal subjects (age range = 23-50 yr, 5 female/3 male) twice underwent MRI-based specific ventilation imaging consisting of five repeated cycles with the inspired gas switching between 21% and 100% O
every ~2 min (total imaging time = ~20 min). In each session, tests were performed with free breathing (FB, no constraints) and controlled breathing (CB) at a respiratory rate of 12 breaths/min and no tidal volume control. The specific ventilation (SV) distribution in a mid-sagittal slice of the right lung was calculated, and the heterogeneity was calculated as the full width at half max of a Gaussian distribution fitted on a log scale (SV width). Free breathing resulted in a range of breathing frequencies from 8.7 to 15.9 breaths/min (mean = 11.5 ± 2.2,
= 0.62, compared with CB). Heterogeneity (SV width) was unchanged by controlled breathing (FB: 0.38 ± 0.12; CB: 0.34 ± 0.09,
= 0.18, repeated-measures ANOVA). The imposition of a controlled breathing frequency did not significantly affect the heterogeneity of ventilation in the normal lung, suggesting that MBW and specific ventilation imaging as typically performed provide an unperturbed measure of ventilatory heterogeneity.
By using MRI-based specific ventilation imaging (SVI), we showed that the heterogeneity of specific ventilation was not different comparing free breathing and breathing with the imposition of a fixed breathing frequency of 12 breaths/min. Thus, multiple-breath washout and SVI as typically performed provide an unperturbed measure of ventilatory heterogeneity.
The common pulmonary consequence of SARS-CoV-2 infection is pneumonia, but vascular clot may also contribute to COVID pathogenesis. Imaging and hemodynamic approaches to identifying diffuse pulmonary ...vascular obstruction (PVO) in COVID (or acute lung injury generally) are problematic particularly when pneumonia is widespread throughout the lung and hemodynamic consequences are buffered by pulmonary vascular recruitment and distention. Although stimulated by COVID-19, we propose a generally applicable bedside gas exchange approach to identifying PVO occurring alone or in combination with pneumonia, addressing both its theoretical and practical aspects. It is based on knowing that poorly (or non) ventilated regions, as occur in pneumonia, affect O
more than CO
, whereas poorly (or non) perfused regions, as seen in PVO, affect CO
more than O
. Exhaled O
and CO
concentrations at the mouth are measured over several ambient-air breaths, to determine mean alveolar Po
and Pco
. A single arterial blood sample is taken over several of these breaths for arterial Po
and Pco
. The resulting alveolar-arterial Po
and Pco
differences (AaPo
, aAPco
) are converted to corresponding physiological shunt and deadspace values using the Riley and Cournand 3-compartment model. For example, a 30% shunt (from pneumonia) with no alveolar deadspace produces an AaPO
of almost 50 torr, but an aAPco
of only 3 torr. In contrast, a 30% alveolar deadspace (from PVO) without shunt leads to an AaPO
of only 12 torr, but an aAPco
of 9 torr. This approach can identify and quantify physiological shunt and deadspace when present singly or in combination.
Identifying pulmonary vascular obstruction in the presence of pneumonia (e.g., in COVID-19) is difficult. We present here conversion of bedside measurements of arterial and alveolar Po
and Pco
into values for shunt and deadspace-when both coexist-using Riley and Cournand's 3-compartment gas exchange model. Deadspace values higher than expected from shunt alone indicate high ventilation/perfusion ratio areas likely reflecting (micro)vascular obstruction.
We thank M. Ackermann and co-workers for their interest in our recent publication 1. These authors highlight our report of persistent increased alveolar dead space in 30% of 17 patients studied ...within ∼2 months after an acute episode of mild–moderate COVID-19. After outlining their own work, demonstrating secondary pulmonary lobule pathologies found in the lungs of deceased COVID-19 patients, they then hypothesise that secondary lobular micro-ischaemia may be responsible for the elevated alveolar dead space found in our study.
Increased dead space following COVID-19 may be due to microvascular injury or secondary micro-ischaemia
https://bit.ly/3Fypdwz
Intestinal epithelial cell (IEC) junctions constitute a robust barrier to invasion by viruses, bacteria and exposure to ingested agents. Previous studies showed that microgravity compromises the ...human immune system and increases enteropathogen virulence. However, the effects of microgravity on epithelial barrier function are poorly understood. The aims of this study were to identify if simulated microgravity alters intestinal epithelial barrier function (permeability), and susceptibility to barrier-disrupting agents. IECs (HT-29.cl19a) were cultured on microcarrier beads in simulated microgravity using a rotating wall vessel (RWV) for 18 days prior to seeding on semipermeable supports to measure ion flux (transepithelial electrical resistance (TER)) and FITC-dextran (FD4) permeability over 14 days. RWV cells showed delayed apical junction localization of the tight junction proteins, occludin and ZO-1. The alcohol metabolite, acetaldehyde, significantly decreased TER and reduced junctional ZO-1 localization, while increasing FD4 permeability in RWV cells compared with static, motion and flask control cells. In conclusion, simulated microgravity induced an underlying and sustained susceptibility to epithelial barrier disruption upon removal from the microgravity environment. This has implications for gastrointestinal homeostasis of astronauts in space, as well as their capability to withstand the effects of agents that compromise intestinal epithelial barrier function following return to Earth.
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