Assessment Of Blood Pressure Regulatory Controls To Detect Hypovolemia And Orthostatic Intolerance

Regulation of blood pressure is vital for maintaining organ perfusion and homeostasis. A significant decline in arterial blood pressure could lead to fainting and hypovolemic shock. In contrast to young and healthy, people with impaired autonomic control due to aging or disease find regulating blood pressure rather demanding during orthostatic challenge. This thesis performed an assessment of blood pressure regulatory controls during orthostatic challenge via traditional as well as novel approaches with two distinct applications 1) to design a robust automated system for early identification of hypovolemia and 2) to assess orthostatic tolerance in humans. In chapter 3, moderate intensity hemorrhage was simulated via lower-body negative pressure (LBNP) with an aim to identify moderate intensity hemorrhage (-30 and -40 mmHg LBNP) from resting baseline. Utilizing features extracted from common vital sign monitors, a classification accuracy of 82% and 91% was achieved for differentiating -30 and -40 mmHg LBNP, respectively from baseline. In chapter 4, cause-and-effect relationship between the representative signals of the cardiovascular and postural systems to ascertain blood pressure homeostasis during standing was performed. The degree of causal interaction between the two systems, studied via convergent cross mapping (CCM), showcased the existence of a significant bi-directional interaction between the representative signals of two systems to regulate blood pressure. Therefore, the two systems should be accounted for jointly when addressing physiology behind fall. Further, in chapter 5, the potential of artificial gravity (2-g) induced via short-arm human centrifuge at feet towards evoking blood pressure regulatory controls analogous to standing was investigated. The observation of no difference in the blood pressure regulatory controls, during 2-g centrifugation compared to standing, strongly supported the hypothesis of artificial hypergravity for mitigating cardiovascular deconditioning, hence minimizing post-flight orthostatic intolerance

Assessment of trends in the cardiovascular system from time interval measurements using physiological signals obtained at the limbs

Cardiovascular diseases are an increasing source of concern in modern societies due to their increasing prevalence and high impact on the lives of many people. Monitoring cardiovascular parameters in ambulatory scenarios is an emerging approach that can provide better medical access to patients while decreasing the costs associated to the treatment of these diseases. This work analyzes systems and methods to measure time intervals between the electrocardiogram (ECG), impedance plethysmogram (IPG), and the ballistocardiogram (BCG), which can be obtained at the limbs in ambulatory scenarios using simple and cost-effective systems, to assess cardiovascular intervals of interest, such as the pulse arrival time (PAT), pulse transit time (PTT), or the pre-ejection period (PEP). The first section of this thesis analyzes the impact of the signal acquisition system on the uncertainty in timing measurements in order to establish the design specifications for systems intended for that purpose. The minimal requirements found are not very demanding yet some common signal acquisition systems do not fulfill all of them while other capabilities typically found in signal acquisition systems could be downgraded without worsening the timing uncertainty. This section is also devoted to the design of systems intended for timing measurements in ambulatory scenarios according to the specifications previously established. The systems presented have evolved from the current state-of-the-art and are designed for adequate performance in timing measurements with a minimal number of active components. The second section is focused on the measurement of time intervals from the IPG measured from limb to limb, which is a signal that until now has only been used to monitor heart rate. A model to estimate the contributions to the time events in the measured waveform of the different body segments along the current path from geometrical properties of the large arteries is proposed, and the simulation under blood pressure changes suggests that the signal is sensitive to changes in proximal sites of the current path rather than in distal sites. Experimental results show that the PAT to the hand-to-hand IPG, which is obtained from a novel four-electrode handheld system, is correlated to changes in the PEP whereas the PAT to the foot-to-foot IPG shows good performance in assessing changes in the femoral PAT. Therefore, limb-to-limb IPG measurements significantly increase the number of time intervals of interest that can be measured at the limbs since the signals deliver information from proximal sites complementary to that of other measurements typically performed at distal sites. The next section is devoted to the measurement of time intervals that involve different waves of the BCG obtained in a standing platform and whose origin is still under discussion. From the relative timing of other physiological signals, it is hypothesized that the IJ interval of the BCG is sensitive to variations in the PTT. Experimental results show that the BCG I wave is a better surrogate of the cardiac ejection time than the widely-used J wave, which is also supported by the good correlation found between the IJ interval and the aortic PTT. Finally, the novel time interval from the BCG I wave to the foot of the IPG measured between feet, which can be obtained from the same bathroom scale than the BCG, shows good performance in assessing the aortic PAT. The results presented reinforce the role of the BCG as a tool for ambulatory monitoring since the main time intervals targeted in this thesis can be obtained from the timing of its waves. Even though the methods described were tested in a small group of subjects, the results presented in this work show the feasibility and potential of several time interval measurements between the proposed signals that can be performed in ambulatory scenarios, provided the systems intended for that purpose fulfill some minimal design requirements.Les malalties cardiovasculars són una tema de preocupació creixent en societats modernes, degut a l’augment de la seva prevalença i l'elevat impacte en les vides dels pacients que les sofreixen. La mesura i monitoratge de paràmetres cardiovasculars en entorns ambulatoris és una pràctica emergent que facilita l’accés als serveis mèdics i permet reduir dràsticament els costos associats al tractament d'aquestes malalties. En aquest treball s’analitzen sistemes i mètodes per la mesura d’intervals temporals entre l’electrocardiograma (ECG), el pletismograma d’impedància (IPG) i el balistocardiograma (BCG), que es poden obtenir de les extremitats i en entorns ambulatoris a partir de sistemes de baix cost, per tal d’avaluar intervals cardiovasculars d’interès com el pulse arrival time (PAT), pulse transit time (PTT) o el pre-ejection period (PEP). En la primera secció d'aquesta tesi s’analitza l’impacte del sistema d’adquisició del senyal en la incertesa de mesures temporals, per tal d’establir els requeriments mínims que s’han de complir en entorns ambulatoris. Tot i que els valors obtinguts de l’anàlisi no són especialment exigents, alguns no són assolits en diversos sistemes habitualment utilitzats mentre que altres solen estar sobredimensionats i es podrien degradar sense augmentar la incertesa en mesures temporals. Aquesta secció també inclou el disseny i proposta de sistemes per la mesura d’intervals en entorns ambulatoris d’acord amb les especificacions anteriorment establertes, a partir de l’estat de l’art i amb l’objectiu de garantir un correcte funcionament en entorns ambulatoris amb un nombre mínim d’elements actius per reduir el cost i el consum. La segona secció es centra en la mesura d’intervals temporals a partir de l’IPG mesurat entre extremitats, que fins al moment només s’ha fet servir per mesurar el ritme cardíac. Es proposa un model per estimar la contribució de cada segment arterial per on circula el corrent a la forma d’ona obtinguda a partir de la geometria i propietats físiques de les artèries, i les simulacions suggereixen que la senyal entre extremitats és més sensible a canvis en arteries proximals que en distals. Els resultats experimentals mostren que el PAT al hand-to-hand IPG, obtingut a partir d’un innovador sistema handheld de quatre elèctrodes, està fortament correlacionat amb els canvis de PEP, mentre que el PAT al foot-to-foot IPG està correlat amb els canvis en PAT femoral. Conseqüentment, l’ILG entre extremitats augmenta de manera significativa els intervals d’interès que es poden obtenir en extremitats degut a que proporciona informació complementària a les mesures que habitualment s’hi realitzen. La tercera secció està dedicada a la mesura d’intervals que inclouen les ones del BCG vertical obtingut en plataformes, de les que encara se’n discuteix l’origen. A partir de la posició temporal relativa respecte altres ones fisiològiques, s’hipostatitza que l’interval IJ del BCG es sensible a variacions del PTT. Els resultats experimentals mostren que la ona I del BCG és un millor indicador de l’ejecció cardíaca que el pic J, tot i que aquest és el més utilitzat habitualment, degut a la bona correlació entre l’interval IJ i el PTT aòrtic. Finalment, es presenta un mètode alternatiu per la mesura del PTT aòrtic a partir de l’interval entre el pic I del BCG i el peu del foot-to-foot IPG, que es pot obtenir de la mateixa plataforma que el BCG i incrementa la robustesa de la mesura. Els resultats presentats reforcen el paper del BCG com a en mesures en entorns ambulatoris, ja que els principals intervals objectiu d’aquesta tesi es poden obtenir a partir de les seves ones. Tot i que els mètodes descrits han estat provats en grups petits de subjectes saludables, els resultats mostren la viabilitat i el potencial de diversos intervals temporals entre les senyals proposades que poden ésser realitzats en entorns ambulatoris, sempre que els sistemes emprats compleixin els requisits mínims de disseny.Postprint (published version

Evidence Report: Risk of Spaceflight Associated Neuro-ocular Syndrome (SANS)

A subset of astronauts develop neuro-ocular structural and functional changes during prolonged periods of spaceflight that may lead to additional neurologic and ocular consequences upon return to Earth

Workplace Standing Desks and Arterial Stiffness

Many jobs in today’s society require sitting at a desk with little physical activity. Individuals who engage in ten hours of sedentary behavior per day double their CVD risk. Standing desks are thought to decrease sedentary time and improve cardiovascular health. Acute use of standing desks is shown to lower PWV. However, chronic effects remain unknown. Forty eight participants qualified as seated (19 females, 5 males: age 41 ± 2 years, BMI 25 ± 1 kg/m2) or standing (21 females, 3 males: age 45 ± 2 years, BMI 25 ± 1 kg/m2) groups based on habitual workplace use. Arterial stiffness was assessed as pulse wave velocity (PWV) by using applanation tonometry in conjunction with electrocardiography. No differences were detected in carotid-femoral PWV (cfPWV) between seated and standing groups (p = 0.47). However, age (p \u3c 0.01), aerobic fitness (p \u3c 0.01), and fat percentage (p = 0.02) classifications revealed significant differences between groups. Standing for 50% of a workday does not affect cfPWV. Although, cardiorespiratory fitness and healthy body composition are associated with less arterial stiffness

The Effect of Spironolactone on Cerebral Blood Flow and Cognition

Hypertension and arterial stiffness are associated with structural and functional changes in cerebral circulation and cognitive function, but based on existing evidence the effects are potentially reversible by spironolactone (Spiro) reducing blood pressure (BP) and arterial stiffness. This thesis consisted of a double-blind, controlled trial with older hypertensive adults (OA) who were receiving stable treatment with centrally acting angiotensin converting enzyme inhibitors randomly assigned to Spiro or placebo to test the hypothesis that reductions in BP and arterial stiffness would be associated with improved anterior cerebral blood flow (aCBF) and cognitive function. Secondary objectives were to investigate how Spiro would affect cerebrovascular autoregulation and to conduct a supplementary experimental study in younger adults (YA) comparing blood pressure and arterial stiffness to OA; and to determine how induced acute small changes in BP could impact interpretation of the chronic changes in BP and arterial stiffness associated with Spiro therapy. The pooled data from the randomized, controlled trial (RCT) in OA (n=18) showed that age, mean arterial pressure (MAP), systolic (SBP), diastolic (DBP) and pulse pressure (PP) were 65±3 years, 97±9 mmHg, 142±16 mmHg, 75±8 mmHg, and 66±13 mmHg respectively. There was a significant association between age and carotid distensibility coefficient (r= - 0.51, P<0.05). Six months of Spiro significantly reduced SBP and PP by 14±14 mmHg and 12±14 mmHg respectively. However arterial stiffness estimated by regional indicator carotid-femoral pulse wave velocity (cfPWV), or local indicators carotid distensibility coefficient and β-stiffness index, remained unchanged. Spiro did not significantly improve aCBF or cognitive function scores. Cerebrovascular autoregulation response to standing upright remained unchanged after Spiro compared to placebo. Mean adherence to study-drug was at least 95% for both groups. The calculated Cohen’s d effect size for Spiro was 0.3 from this thesis RCT data; much smaller than the desired Cohen’s d effect size of 1.0 that was derived from observational data used to calculate sample size for the RCT. The supplementary experimental study in YA (n=14) demonstrated that OA in the RCT had greater MAP (97±9 mmHg vs 86±9 mmHg, P<0.01), SBP (142±16 mmHg vs 124±12 mmHg, P<0.01), DBP (75±8 mmHg vs 67±9 mmHg, P<0.05), PP (66±13 mmHg vs 57±7 mmHg, P<0.05), and arterial stiffness was greater as indicated by faster cfPWV (7.22±1.09 m/s vs 5.43±1.13 m/s, P<0.001), smaller carotid distensibility coefficient (0.0014±0.0006 mmHg-1 vs 0.0031±0.0008, P<0.001), and greater β-stiffness index (8.78±3.53 a.u. vs 3.74±0.91, P<0.001). Application of lower body negative pressure to induce acute hemodynamic changes in these YA reduced stroke volume (P<0.001) and cardiac output (P<0.001); and increased total peripheral resistance (P<0.001) while MAP remained unchanged. There were also small acute decreases in both SBP (P<0.05) and PP (P<0.001) in these YA that were concurrent with a non-significant increase in arterial stiffness (cfPWV increase, carotid distensibility coefficient decrease, β-stiffness index increase). Transit times from R-peak of QRS complex to foot of aortic velocity pulse, carotid artery, or finger artery significantly increased with progressively increasing LBNP as a consequence of longer pre-ejection period (P<0.001). In conclusion for the main thesis objective, Spiro safely and effectively reduced BP while arterial stiffness, aCBF, cognitive function, and cerebrovascular autoregulation remained unchanged. OA, compared to YA, had greater blood pressure and arterial stiffness for all measures. In YA, acute reductions in systolic and pulse pressure affected stiffness indicators, in contrast to unchanged stiffness indicators observed in OA. These limited data should be interpreted with caution given the small sample size in the RCT, small effect size of Spiro and that acute reductions in SBP and PP may affect arterial stiffness

새로운 심탄도 계측 시스템의 응용 -연속혈압 추정과 생체인식

학위논문 (박사)-- 서울대학교 대학원 : 협동과정 바이오엔지니어링전공, 2014. 8. 김희찬.심탄도 (Ballistocardiogram)는 심박에 동기되어 발생하는 우리 몸의 미세한 진동을 측정한 신호이다. 비침습적으로 심혈관계의 활동을 관찰할 수 있다는 장점 때문에, 20세기 초반에 심탄도의 해석에 대한 많은 연구가 이루어졌다. 그러나 초음파 기기 등 심혈관계 관련 질병들을 진단할 수 있는 새로운 기술들이 개발되면서 상대적으로 실용적이지 못한 특성을 가진 심탄도에 대한 관심은 1970년대 이후에 급격히 줄어들었다. 새로운 센서들의 등장과 마이크로프로세서, 신호처리 기술들의 발전에 힘입어 심탄도 연구는 다시 활기를 띠고 있다. 그러나 이러한 발전들에도 불구하고 심탄도는 의자나 침대 등 상당한 부피를 차지하는 사물을 이용하여 계측되고, 분석을 위해서는 동기화 된 심전도가 동시에 측정되어야 하는 등 측정상의 번거로움이 있다. 또한, 심탄도는 개인 간에는 물론 한 개인에게서도 파형에 많은 변이를 보여 신호의 일관된 해석에 어려움이 있다. 본 학위논문에서는, 이러한 측정 측면과 신호처리 측면에서 현 심탄도 응용의 한계점을 극복할 수 있는 방안을 마련하여, 심탄도의 실질적인 활용 범위를 더욱 확장할 수 있는 방안에 대해 연구하였다. 우선, 심탄도를 심전도와 동시에 무구속적으로 잴 수 있는 필름기반의 패치타입 센서를 개발하였다. 압전소자의 양면에 복수개의 전극을 패터닝하고 각각의 전극에 독립된 기능을 부여해 회로에 연결함으로써 필름 한 장으로 물리적인 신호 (심탄도)와 전기적인 신호(심전도)의 동시 측정이 가능하게 하였다. 센서를 가슴에 부착하였을 때 심전도의 특징적인 R 피크과 심탄도의 특징적인 J 피크를 확인하여 기능을 확인할 수 있었으며, 추가적으로 R-J 간격이 수축기 혈압과 음의 상관관계를 가짐을 이용하여 개발된 센서로 혈압을 추정할 수 있었다. 센서를 통해 예측한 수축기 혈압 오차의 평균값과 표준편차는 각각 -0.16 mmHg와 4.12mmHg으로, 미국과 영국의 혈압계 가이드라인을 모두 만족시킬 수 있었다. 다음으로, 심탄도의 변이적 특성을 새로운 생체인식 기법으로 발전시키는 방안에 대한 연구를 진행하였다. 이를 위하여 심탄도 한 파형 내의 특이점들을 기반으로 특징 벡터를 추출하고 기계학습을 통해 특징들의 변이를 개인들 간의 변이와 한 개인 내에서의 변이로 구분 하였다. 추출된 특징들을 이용하여 35명의 피험자들에게 실험해 본 결과, 단일 심박신호로는 90.20%의 확률로 개개인을 구분할 수 있었으며 7개의 연속된 심박신호로는 98%이상의 성능을 낼 수 있었다. 또한 약 일주일 간격을 두고 반복하여 측정한 데이터와 운동을 통해 심박수가 변화된 데이터의 적용을 통해서 심탄도를 이용한 생체인식 방법의 재현성을 확인할 수 있었다.Ballistocardiogram (BCG) is a recording of body movement, which is generated in synchronous with the heartbeats. Studies on BCG were a field of intense research in the past decades, since it could provide a non-invasive means to monitor cardiovascular activities. However, such interests have slowly diminished after 1970s due to its impractical characteristics compared to the new technologies (i.e. echocardiography) that diagnose cardiovascular system. Studies on BCG are now on its resurgence era, with advent of new sensors, microprocessor, and the signal processing techniques. Notable differences of todays BCG researches, compared to the past ones, are on the emergence of non-diagnostic applications of BCG. Sleep analysis, heartbeat detection and the estimation of pre-ejection time are the few examples of BCG applications that were previously non-existent. Despite these advancements, however, practical usage of BCG has yet to become reality. One reason for this is in its difficulties in instrumentation. In a number of researches, BCGs are often recorded with a sensor attached to bulky objects, for example bed or chair. Also, a synchronously measured electrocardiogram (ECG) is required for the accurate analysis of BCG, therefore, increases the system complexity. Morphological variability of BCG is another limiting factor. Waveforms of BCG are reported to vary among subjects and even in a same person. Such characteristics of BCG impose difficulties in its consistent interpretation and in drawing meaningful information. In this dissertation, we first propose a sensor, namely BE-patch, which can record both the BCG and ECG using a ferro-electret film. As the sensor is thin and flexible and features reduced complexity, it suits for wearable applications in terms both of user compliance and power consumption. The fabrication method of BE-patch and its application in blood pressure estimation is reported in Chapter 2. Using the time delay of R-peak of ECG and J-peak of BCG (so-called, R-J interval), which showed the negative relationship with changes in blood pressure, the beat-by-beat systolic blood pressure (SBP) is estimated. The mean error of the estimated SBP and its standard deviation were ?0.16 and 4.12 mm Hg, respectively and their performance met both the Association for the Advancement of Medical Instrumentation and the British Hypertension Society guidelines. In Chapter 3, the variable aspect of BCG is re-analyzed to develop a biometric application. Waveforms of BCG were described using features and their variability was separated to the inter-individual and the intra-individual variations by applying supervised learning algorithms. The result showed the potential utility of BCG as biometric signal, by achieving identification accuracy of 90.20% using only a cycle of BCG. Then identification increased to 98% when multiple beats were used, and reproducible with time and changes in heart-rates. In Chapter 4, the thesis work is summarized, and future directions to further develop the proposed sensor and applications are discussed.Abstract i List of Tables v List of Figures vi 1. Introduction １ 1.1. History of BCG Research １ 1.2. Recent Advances ７ 1.3. Goal of Thesis Work ９ 2. Blood Pressure Estimation １３ 2.1. Introduction １３ 2.2. Principles of BP Estimation １６ 2.3. Methods ２１ 2.4. Results and Discussions ２６ 2.5. Conclusion ２８ 3. Biometric Application ２９ 3.1. Introduction ２９ 3.2. Methods ３９ 3.3. Results and Discussions ４８ 3.4. Conclusion ５６ 4. Conclusions and Discussions ５７ Bibliography ６５ 국문초록 ７１Docto

Analysis of Transcranial Doppler Ultrasound Waveform Morphology for the Assessment of Cerebrovascular Hemodynamics

The use of transcranial Doppler (TCD) ultrasound for the assessment of cerebral blood flow velocity (CBFV) provides an indication of cerebral blood flow assuming the diameter of the insonated vessel remains constant. Studies using TCD have traditionally described cerebrovascular hemodynamics with respect to CBFV and cerebrovascular resistance (CVRi); however, a more complete assessment of the cerebral circulation can be gleaned from the analysis of within beat characteristic of the TCD velocity waveform for the determination of cerebrovascular tone. Therefore, the general purpose of the presented studies was to assess CBFV responses and within beat characteristic for the description of cerebrovascular hemodynamics after long duration spaceflight, with sustained orthostasis, in response to changes in the partial pressure of end tidal carbon dioxide (PETCO2), and with NG stimulation. After long duration spaceflight, cerebrovascular autoregulation was found to be impaired along with a reduction in cerebrovascular CO2 reactivity (Study 1). Additionally, critical closing pressure (CrCP) was found to be increased suggesting potential remodelling of the cerebrovasculature contributing to an increase in cerebrovascular tone (Study 2). With sustained orthostasis, CBFV was found to progressively decrease and to be related to reductions in PETCO2 and increases in CrCP suggesting the contribution of changes in cerebrovascular tone leading to the development of syncope (Study 4). The CBFV reduction with the progression towards syncope was also associated with changes in waveform morphology such that the dicrotic notch point was less than the end diastolic value (Study 3). Mathematical modelling (RCKL) was used to further assess changes in cerebrovascular hemodynamics for physiological interpretation of changes in CBFV waveform morphology and found that the amplitude of the dicrotic notch and the calculation of the augmentation index were both significantly related to vascular compliance before and after stimulation with NG (Study 5). The use of quantitative assessments of common carotid artery (CCA) blood flow as an indicator of cerebral blood flow suggested the dilation of the middle cerebral artery (MCA) with NG (Study 5 and 6) and changes in MCA diameter with acute alterations in PETCO2 (Study 6). CCA and MCA velocity wave morphology were assessed showing that with changes in PETCO2, changes in CBFV velocity wave were not reflected in the CCA trace (Study 7). In addition, further assessment of the CBFV velocity trace and the calculation of CrCP and the augmentation index suggested that with changes in PETCO2 cerebrovascular compliance and cerebrovascular tension, both thought to be components of cerebrovascular tone, change independently (Study 7). Combined, the results of the presented studies suggest that changes in cerebrovascular hemodynamics can be determined from alterations in the CBFV velocity waveform morphology. However, further work is required to determine how these variations relate to specific components of cerebrovascular tone, including alterations in cerebrovascular compliance and vascular tension, and how these variables change with acute and chronic alterations in cerebrovascular hemodynamics

Quantifying the Effects of Altered-Gravity and Spaceflight Countermeasures on Acute Cardiovascular and Ocular Hemodynamics

The cardiovascular system is strongly dependent on the gravitational environment. Gravitational changes cause mechanical fluid shifts and, in turn, autonomic effectors influence systemic circulation and cardiac control. For future long-duration spaceflight, these gravitational effects could be related to decreased cardiovascular performance, the pathoetiology of spaceflight associated neuro-ocular syndrome (SANS), and increased venous thromboembolism (VTE) risk. The development of novel countermeasure protocols using, for example, lower body negative pressure (LBNP) or short-radius centrifugation (SRC) requires a full understanding of the detailed cardiovascular response to gravity and to different levels of countermeasure intervention. In this research effort, we use a complementary experimental and modeling approach to generate acute dose-response curves for systemic, autonomic, and cephalad parameters of the cardiovascular system in graded tilt (as an analog for altered-gravity), graded LBNP, and graded SRC. In the experimental approach, 24 subjects (12 male and 12 female) experienced 1) a graded tilt profile in the range of 45° head-up tilt to 45° head-down tilt in 15° increments; and 2) a graded LBNP profile from 0 mmHg to –50 mmHg in 10 mmHg increments. Using two different statistical techniques (mixed-effects modeling and Bayesian hierarchical multivariate modeling) we generate dose-response curves for the cardiovascular and ocular response. In the computational approach, we further develop an existing lumped-parameter model of the cardiovascular system to incorporate cephalad hemodynamics and the effects of body tissue weight. In addition, we also further develop a complementary lumped-parameter model of the eye. We simulate the same tilt and LBNP profiles, along with a graded SRC profile and a gravitational field change using simulated 50th percentile male and female subjects. The quantification of cardiovascular hemodynamics as a function of changes in the gravitational vector or the presence of countermeasure interventions presented here provides a terrestrial model to reference spaceflight-induced changes, contributes to the assessment of the pathogenesis of SANS and spaceflight VTE events, and informs the development of countermeasures

Kreislaufregulation bei Lagewechsel mit echokardiografischer Untersuchung

Die Kreislaufregulation beim Lagewechsel vom Liegen zum Stehen (Orthostase) ist ein wichtiges Thema der Kreislaufphysiologie, aber quantitative Angaben in Lehrbüchern zur Änderung der Kreislaufparameter sind uneinheitlich. Diese wurden an 20 Probanden während des Liegens und der passiven Orthostase auf einem Kipptisch (Kippwinkel 70°) nichtinvasiv gemessen. In einer ersten Messreihe wurden Änderungen des Unterschenkelvolumens mit Dehnungsmessstreifen und die Herzfrequenz und der aus der Laufzeit der Pulswelle errechnete Blutdruck mit einem SOMNOtouch-Gerät ermittelt. Im Vergleich zum Liegen stiegen Herzfrequenz (+38%) und Beinvolumen (ca. +1%) während der Orthostase signifikant an (t-Tests, p<0,01) an, während systolischer, diastolischer und mittlerer Blutdruck um etwa 4% fielen (p<0,01). Dabei ließen sich drei typische zeitliche Verlaufsmuster der Herzfrequenz identifizieren. In einer zweiten Messreihe erfolgten dopplerechokardiografische Messungen der Schlagvolumina und des Herzzeitvolumens. Das Schlagvolumen war während des Stehens kleiner als im Liegen (-20%, p<0,01), was jedoch durch den gleichzeitigen Anstieg der Herzfrequenz um +31% kompensiert wurde. Daher änderte sich das Herzzeitvolumen während der Orthostase, anders als in Lehrbüchern angegeben, nicht wesentlich. Zusatzmessungen in Kopftieflage ergaben keine signifikanten Änderungen von Kreislaufparametern. Die Messmethoden sind für Versuche in Praktika der Physiologie prinzipiell geeignet

Life Sciences Program Tasks and Bibliography for FY 1996

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 1996. 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