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

Skeletal Muscle Pump Drives Control of Cardiovascular and Postural Systems

The causal interaction between cardio-postural-musculoskeletal systems is critical in maintaining postural stability under orthostatic challenge. The absence or reduction of such interactions could lead to fainting and falls often experienced by elderly individuals. The causal relationship between systolic blood pressure (SBP), calf electromyography (EMG), and resultant center of pressure (COPr) can quantify the behavior of cardio-postural control loop. Convergent cross mapping (CCM) is a non-linear approach to establish causality, thus, expected to decipher nonlinear causal cardio-postural-musculoskeletal interactions. Data were acquired simultaneously from young participants (25 ± 2 years, n = 18) during a 10-minute sit-to-stand test. In the young population, skeletal muscle pump was found to drive blood pressure control (EMG → SBP) as well as control the postural sway (EMG → COPr) through the significantly higher causal drive in the direction towards SBP and COPr. Furthermore, the effect of aging on muscle pump activation associated with blood pressure regulation was explored. Simultaneous EMG and SBP were acquired from elderly group (69 ± 4 years, n = 14). A significant (p = 0.002) decline in EMG → SBP causality was observed in the elderly group, compared to the young group. The results highlight the potential of causality to detect alteration in blood pressure regulation with age, thus, a potential clinical utility towards detection of fall proneness

Non-linear Heart Rate and Blood Pressure Interaction in Response to Lower-Body Negative Pressure

Early detection of hemorrhage remains an open problem. In this regard, blood pressure has been an ineffective measure of blood loss due to numerous compensatory mechanisms sustaining arterial blood pressure homeostasis. Here, we investigate the feasibility of causality detection in the heart rate and blood pressure interaction, a closed-loop control system, for early detection of hemorrhage. The hemorrhage was simulated via graded lower-body negative pressure (LBNP) from 0 to -40 mmHg. The research hypothesis was that a significant elevation of causal control in the direction of blood pressure to heart rate (i.e., baroreflex response) is an early indicator of central hypovolemia. Five minutes of continuous blood pressure and electrocardiogram (ECG) signals were acquired simultaneously from young, healthy participants (27 ± 1 years, N = 27) during each LBNP stage, from which heart rate (represented by RR interval), systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) were derived. The heart rate and blood pressure causal interaction (RR SBP and RR MAP) was studied during the last 3 min of each LBNP stage. At supine rest, the non-baroreflex arm (RR SBP and RR MAP) showed a significantly (p \u3c 0.001) higher causal drive toward blood pressure regulation compared to the baroreflex arm (SBP RR and MAP RR). In response to moderate category hemorrhage (-30 mmHg LBNP), no change was observed in the traditional marker of blood loss i.e., pulse pressure (p = 0.10) along with the RR SBP (p = 0.76), RR MAP (p = 0.60), and SBP RR (p = 0.07) causality compared to the resting stage. Contrarily, a significant elevation in the MAP RR (p = 0.004) causality was observed. In accordance with our hypothesis, the outcomes of the research underscored the potential of compensatory baroreflex arm (MAP RR) of the heart rate and blood pressure interaction toward differentiating a simulated moderate category hemorrhage from the resting stage. Therefore, monitoring baroreflex causality can have a clinical utility in making triage decisions to impede hemorrhage progression

Joint symbolic dynamics for the assessment of cardiovascular and cardiorespiratory interactions

Beat-to-beat variations in heart period provide information on cardiovascular control and are closely linked to variations in arterial pressure and respiration. Joint symbolic analysis of heart period, systolic arterial pressure and respiration allows for a simple description of their shared short-term dynamics that are governed by cardiac baroreflex control and cardiorespiratory coupling. In this review, we discuss methodology and research applications. Studies suggest that analysis of joint symbolic dynamics provides a powerful tool for identifying physiological and pathophysiological changes in cardiovascular and cardiorespiratory control.Mathias Baumert, Michal Javorka and Muammar Kabi

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

Life Sciences Program Tasks and Bibliography

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 1995. Additionally, this inaugural edition of the Task Book includes information for FY 1994 programs. 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 pag

Assessment of the autonomic nervous system through the study of cardiovascular autonomic reflexes and their association with inflammation in three clinical settings.

Heart Rate Variability describes the beat-to-beat variation in heart rate arising from activity of the sympathetic and parasympathetic branches of the Autonomic Nervous System (ANS). Reduced ANS tone measured by reduced heart rate variability (HRV) is a powerful predictor of adverse diagnosis in patients and is associated with increased mortality. Published research suggests that inflammation has a deleterious effect on Autonomic Nervous System tone. This study aimed to: establish if mild inflammatory conditions are associated with changes in autonomic tone as defined by heart rate variability studies in the following conditions: a. Influenza vaccination b. Reduction in oesophageal inflammation c. Reduction in weight The aim of the first study was to assess the link between inflammation resulting from the influenza vaccination and the associated changes on heart rate variability. 71 healthy volunteers opting to have a routine influenza vaccination were investigated for potential changes in cardiovascular autonomic tone associated with the temporary inflammatory effects of an Influenza vaccination. A number of temporal and frequency domain parameters of heart rate and breathing were assessed 2-5 days prior to vaccination and 1-4 days post vaccination. A sub-group of 15 volunteers who reported significant symptomatic reaction to the vaccination for at least 24 hours following vaccination displayed a statistically significant (p=<0.02) reduction in five of the six HRV parameters obtained during metronome-guided breathing. There was no evidence of significant reduction in autonomic tone following vaccination in the full sample of 71 volunteers. The aim of the second study was to establish whether inflammation resulting from erosive or non-erosive oesophagitis caused by gastro-oesophageal reflux disease had any association with changes in heart rate variability. 12 volunteers with non-erosive oesophageal reflux disease (NERD) and 8 with erosive oesophageal reflux disease (ERD) were investigated for HRV after initial diagnosis under gastroscopy. HRV assessment was repeated following 8 weeks of treatment with a proton-pump inhibitor (PPI). Initial reflux symptoms and response to PPI treatment were assessed using the GERD Impact Scale questionnaire. All participants had effective symptom response to treatment and there was no significant difference insymptoms score between NERD and ERD groups. There was a small but statistically significant increase in HRV detected following PPI treatment in the ERD group (p=0.05). The aim of the third study was to assess the link between obesity / pro-inflammatory adiposity, weight loss and the associated changes in heart rate variability. 38 clinically obese volunteers (BMI 30-39) with a family history of diabetes were reviewed for HRV prior to and following a lifestyle intervention designed to reduce body weight and BMI. Volunteers underwent repeated HRV studies after 4 months and 8 months of treatment. Volunteers on average achieved a weight loss of 11.5% (±6.0). There were statistically significant changes in HRV parameters in sub-group A (BMI ≥36) and correlation of biochemical measures with weight loss. These results further elucidate the effect of mild inflammatory triggers on autonomic tone as measured by HRV. These effects and their significance are discussed in detail in this document. The significance of the ‘cholinergic anti-inflammatory pathway’ is discussed with respect to the inflammatory conditions investigated. Suggestions for further work are proposed. In conclusion it is entirely possible to measure subtle changes in heart rate variability associated with mild inflammation and that on the evidence presented here these changes in heart rate variability are hypothesised to be reversible. My original contribution to knowledge is: 1. Changes in heart rate variability are associated with low grade inflammation resulting from the Influenza vaccination, erosive oesophagitis and increased adiposity. 2. Measurement of subtle changes in autonomic tone, associated with inflammatory challenges is possible and concurs with other published research. 3. The level of HRV attenuation does appear to be linked to those with a higher level of inflammation. In each study the most significant results came from subgroups of volunteers either demonstrating: a higher level of symptom severity, erosive oesophagitis or were in a subgroup of participants with the highest BMI / adipose tissue. 4. In the early stages of reduced heart rate variability we see that concurrent reduction in inflammation is associated with an increase in autonomic tone

Muscle activation patterns in shoulder impingement patients

Introduction: Shoulder impingement is one of the most common presentations of shoulder joint problems 1. It appears to be caused by a reduction in the sub-acromial space as the humerus abducts between 60o -120o – the 'painful arc'. Structures between the humeral head and the acromion are thus pinched causing pain and further pathology 2. Shoulder muscle activity can influence this joint space but it is unclear whether this is a cause or effect in impingement patients. This study aimed to observe muscle activation patterns in normal and impingement shoulder patients and determine if there were any significant differences. Method: 19 adult subjects were asked to perform shoulder abduction in their symptomatic arm and non-symptomatic. 10 of these subjects (age 47.9 ± 11.2) were screened for shoulder impingement, and 9 subjects (age 38.9 ± 14.3) had no history of shoulder pathology. Surface EMG was used to collect data for 6 shoulder muscles (Upper, middle and lower trapezius, serratus anterior, infraspinatus, middle deltoids) which was then filtered and fully rectified. Subjects performed 3 smooth unilateral abduction movements at a cadence of 16 beats of a metronome set at 60bpm, and the mean of their results was recorded. T-tests were used to indicate any statistical significance in the data sets. Significance was set at P<0.05. Results: There was a significant difference in muscle activation with serratus anterior in particular showing a very low level of activation throughout the range when compared to normal shoulder activation patterns (<30%). Middle deltoid recruitment was significantly reduced between 60-90o in the impingement group (30:58%).Trends were noted in other muscles with upper trapezius and infraspinatus activating more rapidly and erratically (63:25%; 60:27% respectively), and lower trapezius with less recruitment (13:30%) in the patient group, although these did not quite reach significance. Conclusion: There appears to be some interesting alterations in muscle recruitment patterns in impingement shoulder patients when compared against their own unaffected shoulders and the control group. In particular changes in scapula control (serratus anterior and trapezius) and lateral rotation (infraspinatus), which have direct influence on the sub-acromial space, should be noted. It is still not clear whether these alterations are causative or reactionary, but this finding gives a clear indication to the importance of addressing muscle reeducation as part of a rehabilitation programme in shoulder impingement patients