Application of a quantum cascade laser aperture scanning near-field optical microscope to the study of a cancer cell.

This work reports the first images obtained by combining an infrared aperture scanning near-field optical microscope (SNOM) with a quantum cascade laser (QCL). The future potential of this set-up is demonstrated by a preliminary study on an OE33 human oesophageal adenocarcinoma cell in which the cell is imaged at 1751 cm-1, 1651 cm-1, 1539 cm-1 and 1242 cm-1. In addition to the 1651 cm-1 image, three other images were acquired within the Amide I band (1689 cm-1, 1675 cm-1 and 1626 cm-1) chosen to correspond to secondary structures of proteins. The four images obtained within the Amide I band show distinct differences demonstrating the potential of this approach to reveal subtle changes in the chemical composition of a cell.

The Determinants of Medical Tourism Intentions: Applying the Theory of Planned Behavior.

This study introduces the theory of planned behavior to health care marketers by extending and replicating a prior study that predicted student's intention to engage in medical tourism. Based on a sample of 164 usable survey responses, our findings suggested that the MEDTOUR scale (developed and introduced a prior study) is robust and works reasonably well with a national sample. Based on these findings, MEDTOUR appears to be worthy of further consideration by health marketing scholars.

Point-of-care ultrasound in aerospace medicine: known and potential applications.

Since its initial introduction into the bedside assessment of the trauma patient via the Focused Assessment with Sonography for Trauma (FAST) exam, the use of point-of-care ultrasound has expanded rapidly. A growing body of literature demonstrates ultrasound can be used by nonradiologists as an extension of the physical exam to accurately diagnose or exclude a variety of conditions. These conditions include, but are not limited to, hemoperitoneum, pneumothorax, pulmonary edema, long-bone fracture, deep vein thrombosis, and elevated intracranial pressure. As ultrasound machines have become more compact and portable, their use has extended outside of hospitals to places where the physical exam and diagnostic capabilities may be limited, including the aviation environment. A number of studies using focused sonography have been performed to meet the diagnostic challenges of space medicine. The following article reviews the available literature on portable ultrasound use in aerospace medicine and highlights both known and potential applications of point-of-care ultrasound for the aeromedical clinician.

Jugular venous flow dynamics during acute weightlessness.

During spaceflight, fluids shift headward, causing internal jugular vein (IJV) distension and altered hemodynamics, including stasis and retrograde flow, that may increase the risk of thrombosis. This study's purpose was to determine the effects of acute exposure to weightlessness (0-G) on IJV dimensions and flow dynamics. We used two-dimensional (2-D) ultrasound to measure IJV cross-sectional area (CSA) and Doppler ultrasound to characterize venous blood flow patterns in the right and left IJV in 13 healthy participants (6 females) while 1) seated and supine on the ground, 2) supine during 0-G parabolic flight, and 3) supine during level flight (at 1-G). On Earth, in 1-G, moving from seated to supine posture increased CSA in both left (+62 [95% CI: +42 to 81] mm2, P < 0.0001) and right (+86 [95% CI: +58 to 113] mm2, P < 0.00012) IJV. Entry into 0-G further increased IJV CSA in both left (+27 [95% CI: +5 to 48] mm2, P = 0.02) and right (+30 [95% CI: +0.3 to 61] mm2, P = 0.02) relative to supine in 1-G. We observed stagnant flow in the left IJV of one participant during 0-G parabolic flight that remained during level flight but was not present during any imaging during preflight measures in the seated or supine postures; normal venous flow patterns were observed in the right IJV during all conditions in all participants. Alterations to cerebral outflow dynamics in the left IJV can occur during acute exposure to weightlessness and thus, may increase the risk of venous thrombosis during any duration of spaceflight.NEW & NOTEWORTHY The absence of hydrostatic pressure gradients in the vascular system and loss of tissue weight during weightlessness results in altered flow dynamics in the left internal jugular vein in some astronauts that may contribute to an increased risk of thromboembolism during spaceflight. Here, we report that the internal jugular veins distend bilaterally in healthy participants and that flow stasis can occur in the left internal jugular vein during acute weightlessness produced by parabolic flight.

Abdomen-high elastic gradient compression garments during post-spaceflight stand tests.

UNLABELLED: Space Shuttle astronauts wore an inflatable antigravity suit during reentry and landing, and astronauts and cosmonauts wear an elastic-compression garment (with lacing) during Soyuz re-entry and landings and in the first few days of recovery. However, neither garment is an ideal countermeasure to spaceflight-induced orthostatic intolerance. Our laboratory has been investigating an elastic graded compression garment (GCG) that applies graduated pressures from the feet to the abdomen for use following International Space Station missions and possibly during exploration missions. METHODS: Before and after Shuttle missions, 14 astronauts participated in a 3.5-min stand test. The stand test was conducted without garments preflight. On landing day, 7 astronauts wore the GCG while 7 astronauts did not (controls). Heart rate and blood pressure were measured in all astronauts during prone rest and standing. Stroke volume and cardiac output were measured only in GCG subjects. RESULTS: No astronauts in either group became presyncopal during the stand test preflight or postflight. The change in heart rate from prone to standing was lower in the GCG subjects on landing day than in the control subjects. Within the GCG subjects only, the increase in total peripheral resistance from prone to standing was higher after spaceflight. CONCLUSIONS: The GCG prevented tachycardia and increased total peripheral resistance with standing after spaceflight. The GCG shows promise as a countermeasure against post-spaceflight orthostatic intolerance, can be easily donned, and is relatively comfortable to wear, but has not been validated after long-duration spaceflight.

Virtual guidance as a tool to obtain diagnostic ultrasound for spaceflight and remote environments.

INTRODUCTION: With missions planned to travel greater distances from Earth at ranges that make real-time two-way communication impractical, astronauts will be required to perform autonomous medical diagnostic procedures during future exploration missions. Virtual guidance is a form of just-in-time training developed to allow novice ultrasound operators to acquire diagnostically-adequate images of clinically relevant anatomical structures using a prerecorded audio/visual tutorial viewed in real-time. METHODS: Individuals without previous experience in ultrasound were recruited to perform carotid artery (N = 10) and ophthalmic (N = 9) ultrasound examinations using virtual guidance as their only training tool. In the carotid group, each untrained operator acquired two-dimensional, pulsed and color Doppler of the carotid artery. In the ophthalmic group, operators acquired representative images of the anterior chamber of the eye, retina, optic nerve, and nerve sheath. Ultrasound image quality was evaluated by independent imaging experts. RESULTS: Of the studies, 8 of the 10 carotid and 17 of 18 of the ophthalmic images (2 images collected per study) were judged to be diagnostically adequate. The quality of all but one of the ophthalmic images ranged from adequate to excellent. DISCUSSION: Diagnostically-adequate carotid and ophthalmic ultrasound examinations can be obtained by previously untrained operators with assistance from only an audio/video tutorial viewed in real time while scanning. This form of just-in-time training, which can be applied to other examinations, represents an opportunity to acquire important information for NASA flight surgeons and researchers when trained medical personnel are not available or when remote guidance is impractical.

Outbound medical tourists: The interplay of perceived quality, length of stay, group-size, post-visit destination image and revisit intention.

Using halo effect as the underlying theory, we examined how perceived quality of medical care influenced components of post-visit destination image (infrastructure, attraction, value for money, and enjoyment) and how each component influenced Bangladeshi outbound medical tourists' revisit intentions. Additionally, we examined how these relationships varied based on their length of stay (LOS) and travel-group size (TGS). Results showed a significant positive effect of the perceived quality of medical care on all four components of the post-visit destination image. Except for enjoyment, all three components had a significant positive influence on revisit intentions. All the proposed relationships were supported for medical tourists with higher LOS and TGS. However, for medical tourists with low LOS, the perceived quality of medical care did not influence value for money. Furthermore, value for money and enjoyment did not significantly influence revisit intentions for medical tourists with low LOS and TGS.

Noninvasive indicators of intracranial pressure before, during, and after long-duration spaceflight.

Weightlessness induces a cephalad shift of blood and cerebrospinal fluid that may increase intracranial pressure (ICP) during spaceflight, whereas lower body negative pressure (LBNP) may provide an opportunity to caudally redistribute fluids and lower ICP. To investigate the effects of spaceflight and LBNP on noninvasive indicators of ICP (nICP), we studied 13 crewmembers before and after spaceflight in seated, supine, and 15° head-down tilt postures, and at ∼45 and ∼150 days of spaceflight with and without 25 mmHg LBNP. We used four techniques to quantify nICP: cerebral and cochlear fluid pressure (CCFP), otoacoustic emissions (OAE), ultrasound measures of optic nerve sheath diameter (ONSD), and ultrasound-based internal jugular vein pressure (IJVp). On flight day 45, two nICP measures were lower than preflight supine posture [CCFP: mean difference -98.5 -nL (CI: -190.8 to -6.1 -nL), P = 0.037]; [OAE: -19.7° (CI: -10.4° to -29.1°), P < 0.001], but not significantly different from preflight seated measures. Conversely, ONSD was not different than any preflight posture, whereas IJVp was significantly greater than preflight seated measures [14.3 mmHg (CI: 10.1 to 18.5 mmHg), P < 0.001], but not significantly different than preflight supine measures. During spaceflight, acute LBNP application did not cause a significant change in nICP indicators. These data suggest that during spaceflight, nICP is not elevated above values observed in the seated posture on Earth. Invasive measures would be needed to provide absolute ICP values and more precise indications of ICP change during various phases of spaceflight.NEW & NOTEWORTHY The current study provides new evidence that intracranial pressure (ICP), as assessed with noninvasive measures, may not be elevated during long-duration spaceflight. In addition, the acute use of lower body negative pressure did not significantly reduce indicators of ICP during weightlessness.

On-orbit prospective echocardiography on International Space Station crew.

OBJECTIVES: A prospective trial of echocardiography was conducted on six crew members onboard the International Space Station. The main objective was to determine the efficacy of remotely guided tele-echocardiography, including just-in-time e-training methods and determine what is "space normal" echocardiographic data. METHODS: Each crew member operator (n = 6) had 2-hour preflight training. Baseline echocardiographic data were collected 55-167 days preflight. Similar equipment was used in each 60-minute in-flight session (mean microgravity exposure--114 days [34--190]). On-orbit ultrasound (US) operators used an e-learning system within 24 hours of these sessions. Expert assistance was provided using US video downlink and two-way voice. Testing was repeated 5-16 days after landing. Separate ANOVA was used on each echocardiographic variable (n = 33). Within each ANOVA, three tests were made: (a) effect of mission phase (preflight, in-flight, postflight); (b) effect of echo technician (two technicians independently analyzed the data); (c) interaction between mission phase and technician. RESULTS: Eleven rejections of the null hypothesis (mission phase or technician or both had no effect) were found that could be considered for possible follow up. Of these, eight rejections were for significant technician effects, not space flight. Three rejections of the null hypothesis (aortic valve time velocity integral, mitral E-wave velocity, and heart rate) were attributable to space flight but determine to not be clinically significant. No rejections were due to the interaction between technician and space flight. CONCLUSION: Thus, we found no consistent clinically significant effects of long-duration space flight on echocardiographic variables of the given group of subjects.

Teleguided self-ultrasound scanning for longitudinal monitoring of muscle mass during spaceflight.

Loss of muscle mass is a major concern for long duration spaceflight. However, due to the need for specialized equipment, muscle size has only been assessed before and after spaceflight where ~20% loss is observed. Here, we demonstrate the utility of teleguided self-ultrasound scanning (Tele-SUS) to accurately monitor leg muscle size in astronauts during spaceflight. Over an average of 168 ± 57 days of spaceflight, 74 Tele-SUS sessions were performed. There were no significant differences between panoramic ultrasound images obtained by astronauts seven days prior to landing and expert sonographer after flight or between change in muscle size assessed by ultrasound and magnetic resonance imaging. These findings extend the current capabilities of ultrasound imaging to allow self-monitoring of muscle size with remote guidance.

Mechanical countermeasures to headward fluid shifts.

Head-to-foot gravitationally induced hydrostatic pressure gradients in the upright posture on Earth are absent in weightlessness. This results in a relative headward fluid shift in the vascular and cerebrospinal fluid compartments and may underlie multiple physiological consequences of spaceflight, including the spaceflight-associated neuro-ocular syndrome. Here, we tested three mechanical countermeasures [lower body negative pressure (LBNP), venoconstrictive thigh cuffs (VTC), and impedance threshold device (ITD) resistive inspiratory breathing] individually and in combination to reduce a posture-induced headward fluid shift as a ground-based spaceflight analog. Ten healthy subjects (5 male) underwent baseline measures (seated and supine postures) followed by countermeasure exposure in the supine posture. Noninvasive measurements included ultrasound [internal jugular veins (IJV) cross-sectional area, cardiac stroke volume, optic nerve sheath diameter, noninvasive IJV pressure], transient evoked otoacoustic emissions (OAE; intracranial pressure index), intraocular pressure, choroidal thickness from optical coherence tomography imaging, and brachial blood pressure. Compared with the supine posture, IJV area decreased 48% with application of LBNP [mean ratio: 0.52, 95% confidence interval (CI): 0.44-0.60, P < 0.001], 31% with VTC (mean ratio: 0.69, 95% CI: 0.55-0.87, P < 0.001), and 56% with ITD (mean ratio: 0.44, 95% CI: 0.12-1.70, P = 0.46), measured at end-inspiration. LBNP was the only individual countermeasure to decrease the OAE phase angle (Δ -12.9 degrees, 95% CI: -25 to -0.9, P = 0.027), and use of combined countermeasures did not result in greater effects. Thus, LBNP, and to a lesser extent VTC and ITD, represents promising headward fluid shift countermeasures but will require future testing in analog and spaceflight environments.NEW & NOTEWORTHY As a weightlessness-induced headward fluid shift is hypothesized to be a primary factor underlying several physiological consequences of spaceflight, countermeasures aimed at reversing the fluid shift will likely be crucial during exploration-class spaceflight missions. Here, we tested three mechanical countermeasures individually and in various combinations to reduce a posture-induced headward fluid shift as a ground-based spaceflight analog.

Ventricular chamber sphericity during spaceflight and parabolic flight intervals of less than 1 G.

INTRODUCTION: Pathology driven alterations in the geometric shape of the heart have been found to result in regional changes in ventricular wall stress and a remodeling of the myocardium. If reductions in the gravitational forces acting on the heart produce similar changes in the overall contour of the ventricles, this modification might also induce adaptations in the cardiac structure during long-term spaceflight. In this study we examined the changes in left ventricle (LV) shape in spaceflight and during parabolic flights. METHODS: The diastole dimensions of the human LV were assessed with echocardiography during spaceflight and in parabolic flights which replicated the gravity of the Moon, Mars, and spaceflight and were compared to findings in Earth's gravity. LV dimensions were translated into circularity indices and geometric aspect ratios and correlated with their corresponding gravitational conditions. RESULTS: During parabolic flight, a linear relationship (r = 0.99) was found between both the circularity index and geometric aspect ratio values and the respective gravitational fields in which they were measured. During spaceflight (N = 4) and parabolic flights (N = 3), there was an average 4.1 and 4.4% higher circularity index and a 5.3 and 8.1% lower geometric aspect ratio, respectively. CONCLUSIONS: A correlative trend was found between the degree of LV sphericity and the amount of gravitational force directed caudal to the longitudinal orientation of the body. The importance of this finding is uncertain, but may have implications regarding physiologic adaptations in the myocardial structure secondary to changes in LV wall stress upon prolonged exposure to microgravity.

Venous and Arterial Responses to Partial Gravity.

Introduction: Chronic exposure to the weightlessness-induced cephalad fluid shift is hypothesized to be a primary contributor to the development of spaceflight-associated neuro-ocular syndrome (SANS) and may be associated with an increased risk of venous thrombosis in the jugular vein. This study characterized the relationship between gravitational level (Gz-level) and acute vascular changes. Methods: Internal jugular vein (IJV) cross-sectional area, inferior vena cava (IVC) diameter, and common carotid artery (CCA) flow were measured using ultrasound in nine subjects (5F, 4M) while seated when exposed to 1.00-Gz, 0.75-Gz, 0.50-Gz, and 0.25-Gz during parabolic flight and while supine before flight (0-G analog). Additionally, IJV flow patterns were characterized. Results: IJV cross-sectional area progressively increased from 12 (95% CI: 9-16) mm2 during 1.00-Gz seated to 24 (13-35), 34 (21-46), 68 (40-97), and 103 (75-131) mm2 during 0.75-Gz, 0.50-Gz, and 0.25-Gz seated and 1.00-Gz supine, respectively. Also, IJV flow pattern shifted from the continuous forward flow observed during 1.00-Gz and 0.75-Gz seated to pulsatile flow during 0.50-Gz seated, 0.25-Gz seated, and 1.00-Gz supine. In contrast, we were unable to detect differences in IVC diameter measured during 1.00-G seated and any level of partial gravity or during 1.00-Gz supine. CCA blood flow during 1.00-G seated was significantly less than 0.75-Gz and 1.00-Gz supine but differences were not detected at partial gravity levels 0.50-Gz and 0.25-Gz. Conclusions: Acute exposure to decreasing Gz-levels is associated with an expansion of the IJV and flow patterns that become similar to those observed in supine subjects and in astronauts during spaceflight. These data suggest that Gz-levels greater than 0.50-Gz may be required to reduce the weightlessness-induced headward fluid shift that may contribute to the risks of SANS and venous thrombosis during spaceflight.

Arterial structure and function during and after long-duration spaceflight.

Spaceflight missions expose astronauts to increased risk of oxidative stress and inflammatory damage that might accelerate the development of asymptomatic cardiovascular disease. The purpose of this investigation was to determine whether long-duration spaceflight (>4 mo) results in structural and functional changes in the carotid and brachial arteries. Common carotid artery (CCA) intima-media thickness (cIMT), CCA distensibility and stiffness, and brachial artery endothelium-dependent and -independent vasodilation were measured in 13 astronauts (10 men, 3 women) ~180 and 60 days before launch, during the mission on ~15, 60, and 160 days of spaceflight, and within 1 wk after landing. Biomarkers of oxidative stress and inflammation were measured at corresponding times in fasting blood samples and urine samples from 24- or 48-h pools. Biomarkers of oxidative stress and inflammation increased during spaceflight, but most returned to preflight levels within 1 wk of landing. Mean cIMT, CCA stiffness, and distensibility were not significantly different from preflight at any time. As a group, neither mean endothelium-dependent nor -independent vasodilation changed from preflight to postflight, but changes within individuals in endothelial function related to some biomarkers of oxidative stress. Whereas biomarkers of oxidative stress and inflammation are elevated during spaceflight, CCA and brachial artery structure and function were not changed by spaceflight. It is unclear whether future exploration missions, with an extended duration in altered gravity fields and higher radiation exposure, may be problematic.NEW & NOTEWORTHY Carotid artery structure and stiffness did not change on average in astronauts during long-duration spaceflight (<12 mo), despite increased oxidative stress and inflammation. Most oxidative stress and inflammation biomarkers returned to preflight levels soon after landing. Brachial artery structure and function also were unchanged by spaceflight. In this group of healthy middle-aged male and female astronauts, spaceflight in low Earth orbit does not appear to increase long-term cardiovascular health risk.

Cardiovascular adaptations to long-duration head-down bed rest.

INTRODUCTION: Orthostatic hypotension is a serious risk for crewmembers returning from spaceflight. Numerous cardiovascular mechanisms have been proposed to account for this problem, including vascular and cardiac dysfunction, which we studied during bed rest. METHODS: Thirteen subjects were studied before and during bed rest. Statistical analysis was limited to the first 49-60 d of bed rest and compared to pre-bed rest data. Ultrasound data were collected on vascular and cardiac structure and function. Tilt testing was conducted for 30 min or until presyncopal symptoms intervened. RESULTS: Plasma volume was significantly reduced (15%) by day 7 of bed rest. Flow-mediated dilation in the leg was significantly increased at bed rest day 49 (6% from pre-bed rest). Arterial responses to nitroglycerin differed in the arm and leg, but did not change as a result of bed rest. Anterior tibial artery intimal-medial thickness markedly decreased at bed rest days 21 (21%), 35 (22%), and 49 (19%). Several cardiac functional parameters, including isovolumic relaxation time (73 ms to 85 ms at day 7) and myocardial performance index, were significantly increased (0.41 to 0.49 by day 7 of bed rest; indicating a decrease in cardiac function) during bed rest. There was a trend for decreased orthostatic tolerance following 60 d of bed rest (P = 0.1). DISCUSSION: Our data suggest that bed rest altered cardiovascular structure and function in a pattern similar to short-duration spaceflight. Additionally, the vascular alterations were primarily seen in the lower body, while vessels of the upper body were unaffected.

Self Injection of Topical Skin Preparation by Patient Seeking Facial Volume Enhancement: A Case Report.

A 25-year-old man seeking increased prominence of the cheeks self-injected a topical skin preparation containing hyaluronic acid into his malar soft tissues. Labeling and marketing of the product, which highlighted the hyaluronic acid as one of the ingredients, might have contributed to his misunderstanding of the intended use for the product. Additionally, a popular medical-based talk show and numerous videos online contributed to the errant belief that self-administration was a viable option. Complications from the injection of nonpharmaceutical substances of this type and implications for treatment in clinical practice are discussed.

Assessment of Jugular Venous Blood Flow Stasis and Thrombosis During Spaceflight.

Importance: Exposure to a weightless environment during spaceflight results in a chronic headward blood and tissue fluid shift compared with the upright posture on Earth, with unknown consequences to cerebral venous outflow. Objectives: To assess internal jugular vein (IJV) flow and morphology during spaceflight and to investigate if lower body negative pressure is associated with reversing the headward fluid shift experienced during spaceflight. Design, Setting, and Participants: This prospective cohort study included 11 International Space Station crew members participating in long-duration spaceflight missions . Internal jugular vein measurements from before launch and approximately 40 days after landing were acquired in 3 positions: seated, supine, and 15° head-down tilt. In-flight IJV measurements were acquired at approximately 50 days and 150 days into spaceflight during normal spaceflight conditions as well as during use of lower body negative pressure. Data were analyzed in June 2019. Exposures: Posture changes on Earth, spaceflight, and lower body negative pressure. Main Outcomes and Measures: Ultrasonographic assessments of IJV cross-sectional area, pressure, blood flow, and thrombus formation. Results: The 11 healthy crew members included in the study (mean [SD] age, 46.9 [6.3] years, 9 [82%] men) spent a mean (SD) of 210 (76) days in space. Mean IJV area increased from 9.8 (95% CI, -1.2 to 20.7) mm2 in the preflight seated position to 70.3 (95% CI, 59.3-81.2) mm2 during spaceflight (P < .001). Mean IJV pressure increased from the preflight seated position measurement of 5.1 (95% CI, 2.5-7.8) mm Hg to 21.1 (95% CI, 18.5-23.7) mm Hg during spaceflight (P < .001). Furthermore, stagnant or reverse flow in the IJV was observed in 6 crew members (55%) on approximate flight day 50. Notably, 1 crew member was found to have an occlusive IJV thrombus, and a potential partial IJV thrombus was identified in another crew member retrospectively. Lower body negative pressure was associated with improved blood flow in 10 of 17 sessions (59%) during spaceflight. Conclusions and Relevance: This cohort study found stagnant and retrograde blood flow associated with spaceflight in the IJVs of astronauts and IJV thrombosis in at least 1 astronaut, a newly discovered risk associated with spaceflight. Lower body negative pressure may be a promising countermeasure to enhance venous blood flow in the upper body during spaceflight.

North American Football Fans Show Neurofunctional Differences in Response to Violence: Implications for Public Health and Policy.

While social and behavioral effects of violence in the media have been studied extensively, much less is known about how sports affect perceptions of violence. The current study examined neurofunctional differences between fans and non-fans of North American football (a contact sport) while viewing violent imagery. Participants viewed images of violence in both football and non-football settings while high-resolution functional magnetic resonance imaging (fMRI) data were acquired from their brains. Neurological activation was compared between these violence types and between groups. Fans of football show diminished activation in brain regions involved in pain perception and empathy such as the anterior cingulate cortex, fusiform gyrus, insula, and temporal pole when viewing violence in the context of football compared to more broadly violent images. Non-fans of football showed no such effect for the types of violent imagery and had higher activation levels than fans of football for the specified brain regions. These differences show that fans of football may perceive violence differently when it is in the context of football. These fan attitudes have potential policy implications for addressing the issue of concussions in North American football.

Real-time monitoring of the development and stability of biofilms of Streptococcus mutans using the quartz crystal microbalance with dissipation monitoring.

Quartz crystal microbalance with dissipation monitoring (QCM-D) was used for continuous in-situ monitoring of cell attachment and growth of Streptococcus mutans as biofilms. Cell attachment and proliferation were monitored within an overnight period of 20 h. Biofilms generated using a 'continuous flow' method had a greater mass and were more dissipative (more viscoelastic) than those established using an 'attach and flow' strategy. Cell numbers (as colony forming units, c.f.u.) in biofilms formed inside the QCM-D device after a 2-h attachment phase and during a 20-h growth period could be related to frequency (f) changes. The percentage surface coverage on the QCM-D crystals by bacteria was estimated using the surface analysis features of the atomic force microscope and image analysis software. Both mean percentage coverage and c.f.u increased after growth of S. mutans. The energy losses displayed by the increases in the dissipative factor (D) indicated an increase in 'softness' of the attached cells. The ratio of D/f was used to provide information of the way in which viscoelasticity changed per unit mass. Flow conditions over the cells on the surface appeared to be important in creating biofilms of a greater complexity and stability and the QCM-D enabled properties of cells during attachment and binding, proliferation and removal to be monitored continuously.

Computer systems analysis of spaceflight induced changes in left ventricular mass.

Circulatory adaptations resulting in postflight orthostasis have frequently been observed in response to space travel. It has been postulated that a decrement in left ventricular mass (LVM) found after microgravity exposure may be the central component in this cardiovascular deconditioning. However, a physiologic mechanism responsible for these changes in the myocardium has not been determined. In this study, we examined the sequential alterations in echocardiographic measured LVM from preflight to landing day and 3 days into the postflight recovery period. In a previous study in returning astronauts we found a comparative 9.1% reduction in postflight LVM that returned to preflight values by the third day of recovery. This data was further evaluated in a systems analysis approach using a well-established advanced computer model of circulatory functioning. The computer model incorporates the physiologic responses to changes in pressures, flows and hydraulics within the circulatory system as affected by gravitational forces. Myocardial muscle progression to atrophy or hypertrophy in reaction to the circulatory load conditions is also included in the model. The integrative computer analysis suggests that these variations in LVM could be explained by simple fluid shifts known to occur during spaceflight and can reverse within a few days after reentry into earth's gravity. According to model predictions, the reductions in LVM found upon exposure to microgravity are a result of a contraction of the myocardial interstitial fluid space secondary to a loss in the plasma volume. This hypothesis was additionally supported by the published ground-based study in which we followed the alterations in LVM and plasma volume in normal subjects in which hypovolemia was induced by simple dehydration. In the hypovolemic state, plasma volume was reduced in these subjects and was significantly correlated with echocardiographic measurements of LVM. Based on these experimental findings and the performance of the computer systems analysis it appears that reductions in LVM observed after spaceflight may be secondary to fluid exchanges produced by common physiologic mechanisms. Reductions in LVM observed after microgravity exposure have been previously postulated to be a central component of spaceflight-induced cardiovascular deconditioning. However, a recent study has demonstrated a return of astronauts' LVM to preflight values by the third day after landing through uncertain mechanisms. A systems analysis approach using computer simulation techniques allows for a dissection of the complex physiologic control processes and a more detailed examination of the phenomena. From the simulation studies and computer analysis it appears that microgravity induced reductions in LVM may be explained by considering physiologic fluid exchanges rather than cardiac muscle atrophy.