Proximal Aortic Compliance in Young Male Endurance Athletes: An MRI Study.

INTRODUCTION: High-intensity endurance training can elicit profound cardiac adaptations; however, the current evidence as to its impact on the proximal aorta is limited. The purpose of this study was to investigate the morphological and functional characteristics of the proximal aorta in endurance athletes. METHODS: Fifteen young male middle- and long-distance runners were compared with 19 age- and sex-matched sedentary control participants. CINE phase-contrast magnetic resonance imaging was used to measure blood flow velocities and cross-sectional areas of the ascending and proximal descending aorta. Aortic blood pressure was measured simultaneously during the phase-contrast magnetic resonance imaging scan using a generalized transfer function. Maximal oxygen uptake (V˙O2max) was measured in the athletes. Left ventricular morphology was assessed in a subgroup of participants (n = 16) with cardiac magnetic resonance imaging. RESULTS: The athlete group exhibited an average V˙O2max of 69.5 ± 3.1 mL·kg-1⋅min-1, which is above the 90th percentile of men with similar age according to the American College of Sports Medicine guideline. The athletes had significantly higher stroke volume and slower heart rate at rest and greater left ventricular end-diastolic volume and mass than the sedentary participants. Significantly larger cross-sectional areas and higher compliance of the ascending and proximal descending aorta were also found in the athletes, independently of body surface area. Moreover, higher compliance of the ascending aorta was associated with greater stroke volume (r = 0.382, P = 0.026) and slower heart rate (r = -0.442, P = 0.009) across all participants. CONCLUSIONS: The proximal aorta of young male endurance athletes undergoes morphological and functional adaptations that may be resulting from the significant hemodynamic alterations associated with their cardiac function.

Urinary TIMP-2 and MMP-2 are significantly associated with poor bladder compliance in adult patients with spina bifida.

AIMS: To assess the predictive values of six urinary markers (nerve growth factor [NGF], brain-derived neurotrophic factor [BDNF], matrix metalloproteinase 2 [MMP-2], tissue inhibitor metalloproteinase 2 [TIMP-2], transformation growth factor ß-1 [TGF-B1], and prostaglandin 2 [PGE2]) for adverse urodynamic features and for upper urinary tract damage in adult patients with spina bifida. MATERIALS AND METHODS: A single-center prospective trial was conducted from March 2015 to March 2017 including all consecutive adult patients with spina bifida seen for urodynamic testing. The urine was collected and stored at -80°C. A urodynamic and an upper urinary tract were systematically performed. At the end of the inclusion period, urines were defrosted and urinary nerve growth factor, BDNF, TIMP-2, and TGF-B1 were assessed using validated ELISA kits. The urinary markers levels were adjusted on the urinary creatinine level. Urinary MMP-2 levels were assessed by zymography. RESULTS: Fourty patients were included. Only TIMP-2 and MMP-2 were significantly associated with poor bladder compliance (P = .043 and P = .039, respectively). TIMP-2 was also the only urinary marker significantly associated with upper urinary tract damage on imaging (OR = 19.81; P = .02). Of all urodynamic parameters, bladder compliance and maximum detrusor pressure were the only ones associated with upper urinary tract damage on imaging (P = .01 and P = .02), The diagnostic performances of urinary TIMP-2 for upper urinary tract damage were slightly superior to PdetMax and bladder compliance with an area under the curve of 0.72. CONCLUSION: Urinary TIMP-2 and MMP-2 were significantly associated with poor bladder compliance and urinary TIMP-2 was significantly associated with upper urinary tract damage. These findings support a pathophysiological role of extracellular matrix remodeling in poor bladder compliance of adult patients with spina bifida.

Hybrid mediated blood flow investigation for atherosclerotic bifurcated lesions with slip, convective and compliant wall impacts.

OBJECTIVE: The present investigation is concerned with hybrid mediated blood flow model through atherosclerotic bifurcated artery with slip effects by considering the properties of compliant walls. DESIGN/APPROACH: In human body, the circulatory system is made up of a network of blood vessels that include the bifurcation therefore the influence of hybrid nanoparticles on parent artery with mild stenosis, at apex and in the region of daughter arteries (after being bifurcated) is observed. Blood streaming along the segment of vessel is considered to be Newtonian. The compliant nature of the atherosclerotic artery wall is also considered to create association with permeability aspects for the thickness of arterial wall. Property of heat transfer with convective impacts is taken into account to weaken the stenotic lesions. Through phase flow model approach, a mathematical model is develop with the phenomena of hybrid nanofluid. FINDINGS: For theoretical research of designed equations experimentally determined values of nanoparticles and base fluid are used. Further, flow configurations of hemodynamics are figure out to analyze the blood flow through bifurcated stenotic artery. The comparison in parent and daughter artery is plotted for velocity profile. These patterns provide us a graphical way to recognize the importance of theoretical assistance of this model to biomedical field. At the end, it is concluded from graphical results that slip to the boundary reduces the resistance to flow for atherosclerotic bifurcated artery. CONCLUSIONS: In bifurcated artery, blood circulation is assumed due to difference of pressure between atherosclerotic and non-atherosclerotic portions. Slip impacts are more effective to reduce the hemodynamics effects of stenosis for bifurcated artery. Bifurcation angle reduces the shear stress for daughter artery whereas opposite behavior is observed for parent artery. Compliant wall parameters reduces the inner bolus size in stenotic region while number of bolus increases in bifurcated region. Reduction in the amplitude of shear stress for convective parameter is more prominent in the parent artery as compared to daughter artery.

Periodicity, time constants of drainage, and the mechanical determinants of peak cardiac output during exercise.

To analyze mechanical adaptations that must occur in the cardiovascular system to reach the high cardiac outputs known to occur at peak aerobic performance, we adapted a computational model of the circulation by adding a second parallel venous compartment as proposed by August Krogh in 1912. One venous compartment has a large compliance and slow time constant of emptying; it is representative of the splanchnic circulation. The other has a low compliance and fast time constant of emptying and is representative of muscle beds. Fractional distribution between the two compartments is an important determinant of cardiac output. Parameters in the model were based on values from animal and human studies normalized to a 70 kg male. The baseline cardiac output was set at 5 L/min, and we aimed for 25 L/min at peak exercise with a fractional flow to the peripheral-muscle region of 90%. Finally, we added the equivalent of a muscle pump. Adjustments in circuit and cardiac parameters alone increased cardiac output to only 15.6 L/min because volume accumulated in the muscle compartment and limited a higher cardiac output. Addition of muscle contractions decompressed the muscle region and allowed cardiac output to increase to 23.4 L/min. The pulsatility of blood flow imposes important constraints on the adaptations of cardiac and circulatory functions because it fixes the times for filling and emptying. Flow is further limited by the limits of cardiac filling on each beat. Muscle contractions play a key role by decompressing volume that would otherwise accumulate in the muscle vasculature and by decreasing the time for stroke return to the right ventricle.NEW & NOTEWORTHY We used a computational model of the circulation and previous human and animal data to model mechanical changes in the heart and circulation that are needed to reach the known high cardiac output at peak aerobic exercise. Key points are that time constants of drainage of circulatory compartments put limits on peak flow in a pulsatile system. Muscle contractions increase the rate of return to the heart and by doing so prevent accumulation of volume in the muscle compartment and greatly increase circulatory capacity.

Trabecular cutting: a novel surgical therapy to increase diastolic compliance.

Heart failure with preserved ejection fraction (HFpEF) is a common cause of hospital admission in patients over 65 yr old and has high mortality. HFpEF is characterized by left ventricular (LV) hypertrophy that reduces compliance. Current HFpEF therapies control symptoms, but no existing medications or therapies can sustainably increase LV compliance. LV trabeculae develop hypertrophy and fibrosis that contribute to reduced LV compliance. This study expands our previous results in ex vivo human hearts to show that severing LV trabeculae increases diastolic compliance in an ex vivo working rabbit heart model. Trabecular cutting was performed in ex vivo rabbit hearts set up in a working heart perfusion system perfused with oxygenated Krebs-Henseleit buffer. A hook was inserted in the LV to cut trabeculae. End-systolic and end-diastolic pressure-volume relationships during transient preload reduction were recorded using an admittance catheter in the following three groups: control (no cutting; n = 9), mild cutting (15 cuts; n = 5), and aggressive cutting (30 cuts; n = 5). In a second experiment, each heart served as its own control. Hemodynamic data were recorded before and after trabecular cutting (n = 10) or sham cutting (n = 5) within the same heart. In the first experiments, trabecular cutting did not affect systolic function (P > 0.05) but significantly increased overall diastolic compliance (P = 0.009). Greater compliance was seen as trabecular cutting increased (P = 0.002, r2 = 0.435). In the second experiment, significant increases in systolic function (P = 0.048) and diastolic compliance (P = 0.002) were seen after trabecular cutting compared with baseline. In conclusion, trabecular cutting significantly increases diastolic compliance without reducing systolic function.NEW & NOTEWORTHY We postulate that, in mammalian hearts, free-running trabeculae carneae exist to provide tensile support to the left ventricle and minimize diastolic wall stress. Because of hypertrophy and fibrosis of trabeculae in patients with left ventricular hypertrophy, this supportive role can become pathologic, worsening diastolic compliance. We demonstrate a novel operation involving cutting trabeculae as a method to acutely increase diastolic compliance in patients presenting with heart failure and diastolic dysfunction to improve their left ventricle compliance.

Interactive Compliance Control of a Wrist Rehabilitation Device (WReD) with Enhanced Training Safety.

Interaction control plays an important role in rehabilitation devices to ensure training safety and efficacy. Compliance adaptation of interaction is vital for enabling robot movements to better suit the patient's requirements as human joint characteristics vary. This paper proposes an interactive compliance control scheme on a wrist rehabilitation device (WReD) for enhanced training safety and efficacy. This control system consists of a low-level trajectory tracking loop and a high-level admittance loop. Experiments were conducted with zero load and human interaction, respectively. Satisfactory trajectory tracking responses were obtained, with the normalized root mean square deviation (NRMSD) values being 1.08% with zero load and the NRMSD values no greater than 1.4% with real-time disturbance and interaction from human users. Results demonstrate that such an interactive compliance control method can adaptively adjust the range of training motions and encourage active engagement from human users simultaneously. These findings suggest that the proposed control method of the WReD has great potentials for clinical applications due to enhanced training safety and efficacy. Future work will focus on evaluating its efficacy on a large sample of participants.

Effects of vibrotactile feedback and grasp interface compliance on perception and control of a sensorized myoelectric hand.

Current myoelectric prosthetic limbs are limited in their ability to provide direct sensory feedback to users, which increases attentional demands and reliance on visual cues. Vibrotactile sensory substitution (VSS), which can be used to provide sensory feedback in a non-invasive manner has demonstrated some improvement in myoelectric hand control. In this work, we developed and tested two VSS configurations: one with a single burst-rate modulated actuator and another with a spatially distributed array of five coin tactors. We performed a direct comparative assessment of these two VSS configurations with able-bodied subjects to investigate sensory perception, myoelectric control of grasp force and hand aperture with a prosthesis, and the effects of interface compliance. Six subjects completed a sensory perception experiment under a stimulation only paradigm; sixteen subjects completed experiments to compare VSS performance on perception and graded myoelectric control during grasp force and hand aperture tasks; and ten subjects completed experiments to investigate the effect of mechanical compliance of the myoelectric hand on the ability to control grasp force. Results indicated that sensory perception of vibrotactile feedback was not different for the two VSS configurations in the absence of active myoelectric control, but it was better with feedback from the coin tactor array than with the single actuator during myoelectric control of grasp force. Graded myoelectric control of grasp force and hand aperture was better with feedback from the coin tactor array than with the single actuator, and myoelectric control of grasp force was improved with a compliant grasp interface. Further investigations with VSS should focus on the use of coin tactor arrays by subjects with amputation in real-world settings and on improving control of grasp force by increasing the mechanical compliance of the hand.

Venous and autonomic function in formerly pre-eclamptic women and controls matched for body mass index.

OBJECTIVE: Prepregnancy reduced plasma volume (PV) increases the risk of subsequent pre-eclamptic pregnancy. Reduced PV is thought to reflect venous reserve capacity, especially when venous vasculature is constricted and sympathetic tone is elevated. As obesity might affect these variables, and is associated with pre-eclampsia, increased body weight may underlie these observations. The aim of this study was to determine whether the relationship between reduced venous reserve and pre-eclampsia is independent of body mass index (BMI). METHODS: This was an observational case-control study in which venous reserve capacity in 30 formerly pre-eclamptic, but currently non-pregnant, women divided equally into three groups based on BMI (BMI 19.5-24.9, 25.0-29.9 or ≥ 30.0 kg/m2 ), was compared with that in 30 healthy parous, non-pregnant controls. Cases and controls were matched for BMI, age and parity. Venous reserve capacity was quantified by assessing PV and venous compliance (VeC). The autonomic nervous system regulating venous capacitance was evaluated using heart rate (HR) variability analysis, with the women in a resting supine position and during positive head-up tilt (HUT). RESULTS: Compared with controls, formerly pre-eclamptic women had, when in a resting supine position, lower PV (1339 ± 79 vs 1547 ± 139 mL/m2 (P < 0.0001)), lower VeC (0.04 ± 0.02 vs 0.07 ± 0.02 mL/dL/mmHg (P < 0.0001)), higher sympathetic tone (1.9 ± 1.1 vs 1.2 ± 0.7 (P = 0.002)) and lower baroreceptor sensitivity (BRS; 8.7 ± 3.8 vs 19.0 ± 1.7 ms/mmHg (P < 0.0001)). During HUT, women with a history of pre-eclampsia had less modulatory capacity over VeC and BRS, while HR and sympathetic tone remained consistently higher. CONCLUSIONS: Women with a history of pre-eclampsia had reduced venous reserve capacity compared with that in BMI-matched controls. This is reflected by lower PV and VeC, with the autonomic balance being shifted towards sympathetic dominance and lower BRS. This suggests that underlying reduced venous reserve, but not BMI, relates to pre-eclampsia. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Tympanometric evaluation of Eustachian tube function in Polish scuba divers.

BACKGROUND: Scuba divers are subjected to relatively high ambient pressures while descending. Equalizing maneuvers (e.g., Valsalva) are necessary to open the Eustachian tube (ET) and allow air into the middle ear (ME) cavity. Insufficient opening of the ET leads to ME barotrauma, which is the most common injury related to scuba diving. The study aims were to assess the incidence of ME barotrauma and to compare tympanometric parameters and stapedial reflexes in scuba divers and non-diving individuals. MATERIAL AND METHODS:: 60 scuba divers participated in the study; control consisted of 90 non-diving volunteers without a history of otolaryngologic problems. All participants were examined with the use of otoscopy and tympanometry with evaluation of ipsilateral stapedial reflexes. The group studied was surveyed regarding occurrence of ME barotrauma and diving competence. RESULTS: 51.7% of the divers experienced ME barotrauma, the most common symptoms being earache and hearing loss. Comparison of the group studied and control revealed significantly lower ME pressure and compliance in scuba divers. In scuba divers with ME barotrauma, longer time from injury correlates directly with greater ME pressure and compliance, indicating tissue recovery. At 4,000Hz 100dB percentage of present stapedial reflexes among scuba divers was significantly lower than in controls; moreover, a greater number of dives correlated inversely with percentage of present stapedial reflexes at 4000Hz 100dB. The reduced thresholds at high intensities suggest a negative effect of scuba diving on hearing. CONCLUSIONS: ME pressure and compliance, however still within the norm, are significantly lower in scuba divers than in non-diving healthy volunteers. This may be attributed to a subclinical form of barotrauma.

Comparación del efecto del aliskireno frente a controles negativos en la rigidez aórtica de los pacientes con síndrome de Marfan tratados con atenolol / Comparison of the effect of aliskiren versus negative controls on aortic stiffness in patients with Marfan Syndrome under treatment with atenolol

Introducción y objetivos: El objetivo del estudio es evaluar el efecto de aliskireno en la rigidez aórtica del paciente con síndrome de Marfan (SM). Métodos: Se reclutó a 28 pacientes con SM (media ± desviación estándar de edad, 32,6 ± 10,6 años) entre noviembre de 2009 y octubre de 2014. Todos estaban tratados con atenolol como terapia estándar con bloqueadores beta. Mediante un proceso prospectivo de aleatorización, se asignó a los participantes a tratamiento con aliskireno (150-300 mg/día vía oral) o sin tratamiento con aliskireno (controles negativos) en un diseño de etiquetado abierto. Se examinaron al inicio y a las 24 semanas la distensibilidad aórtica central y la velocidad de la onda de pulso (PWV) cuantificadas con resonancia magnética (RM), la PWV periférica, la presión aórtica central y el índice de aumento medidos por tonometría y la dilatación aórtica por ecocardiografía. El objetivo primario fue la distensibilidad aórtica central por RM. Resultados: En el análisis de la diferencia entre el examen basal y a las 24 semanas en el grupo tratado frente a los controles negativos, la distensibilidad aórtica central (general; p = 0,26) y la PWV central (0,2 ± 0,9 frente a 0,03 ± 0,7 m/s; p = 0,79) medidas con RM no fueron significativas. La presión sistólica central en la aorta era de 14 mmHg, menor en los pacientes tratados que en los controles (p = 0,09). Se observó una reducción significativa de la PWV periférica (brazo-tobillo) en el grupo tratado (-1,6 m/s) respecto a los controles (+0,28 m/s; p = 0,005). Conclusiones: En los pacientes con SM, la incorporación de aliskireno a los bloqueadores beta no mejora la rigidez de la aorta central a las 24 semanas de tratamiento

Introduction and objectives: The aim of this study was to evaluate the effect of aliskiren on aortic stiffness in patients with Marfan syndrome (MS). Methods: Twenty-eight MS patients (mean age ± standard deviation: 32.6 ± 10.6 years) were recruited from November 2009 to October 2014. All patients were receiving atenolol as standard beta-blocker therapy. A prospective randomization process was performed to assign participants to either aliskiren treatment (150-300 mg orally per day) or no aliskiren treatment (negative control) in an open-label design. Central aortic distensibility and central pulsed wave velocity (PWV) by magnetic resonance imaging (MRI), peripheral PWV, central aortic blood pressure and augmentation index by peripheral tonometry, and aortic dilatation by echocardiography were examined initially and after 24 weeks. The primary endpoint was central aortic distensibility by MRI. Results: In analyses of differences between baseline and 24 weeks for the aliskiren treatment group vs the negative control group, central distensibility (overall; P = .26) and central PWV (0.2 ± 0.9 vs 0.03 ± 0.7 [m/s]; P = .79) by MRI were not significantly different. Central systolic aortic blood pressure tended to be lower by 14 mmHg in patients in the aliskiren treatment group than in the control group (P = .09). A significant decrease in peripheral PWV (brachial-ankle PWV) in the aliskiren treatment group (-1.6 m/s) compared with the control group (+0.28 m/s) was noted (P = .005). Conclusions: Among patients with MS, the addition of aliskiren to beta-blocker treatment did not significantly improve central aortic stiffness during a 24-week period

Aqueous volume loss associated with occlusion break surge in phacoemulsifiers from 4 different manufacturers.

PURPOSE: To evaluate aqueous volume losses associated with occlusion breaks at varying vacuum limits in phacoemulsification systems from 4 different manufacturers. SETTING: Alcon Research Ltd., Lake Forest, California, USA. DESIGN: Experimental study. METHODS: The anterior chamber was modeled using the spring eye model. Systems tested included the Centurion, Whitestar Signature, Stellaris PC, and EVA. Occlusion breaks were actuated at vacuum limits of 200, 300, 400, 500, and 600 mm Hg and a target intraocular pressure of 55 mm Hg. RESULTS: The model eye piston reached its measurement limit just below 600 mm Hg on the EVA and just above 400 mm Hg on the Stellaris PC. Higher vacuum limits could not be tested on these 2 units. Surge volumes varied from 17 to 77 µL on the Centurion, 30 to 103 µL on the Whitestar Signature, 67 µL to 163 µL on the Stellaris PC, and 47 to 165 µL on the EVA. Assuming an average phakic eye aqueous volume of 250 µL, these µL values correspond to percent aqueous volume losses of 7% to 31% on the Centurion, 12% to 41% on the Whitestar Signature, 27% to 65% on the Stellaris PC, and 19% to 66% on the EVA. Surge responses increased on all machines with each increment in vacuum limit. The Centurion had the lowest surge volumes across all vacuum limits. CONCLUSIONS: Occlusion break surge volumes vary considerably across phacoemulsification platforms. Severe chamber shallowing might occur if an occlusion break occurs under high vacuum on some systems.

Training children aged 5-10 years in compliance control: tracing smaller figures yields better learning not specific to the scale of drawn figures.

Previously we developed a method that supports active movement generation to allow practice with improvement of good compliance control in tracing and drawing. We showed that the method allowed children with motor impairments to improve at a 3D tracing task to become as proficient as typically developing children and that the training improved 2D figure copying. In this study, we expanded the training protocol to include a wider variety of ages (5-10-year-olds) and we made the figures traced in training the same as in figure copying, but varied the scale of training and copying figures to assess the generality of learning. Forty-eight children were assigned to groups trained using large or small figures. All were tested before training with a tracing task and a copying task. Then, the children trained over five sessions in the tracing task with either small or large figures. Finally, the tracing and copying tasks were tested again following training. A mean speed measure was used to control for path length variations in the timed task. Performance on both tasks at both baseline and posttest varied as a function of the size of the figure and age. In addition, tracing performance also varied with the level of support. In particular, speeds were higher with more support, larger figures and older children. After training, performance improved. Speeds increased. In tracing, performance improved more for large figures traced by children who trained on large figures. In copying, however, performance only improved significantly for children who had trained on small figures and it improved equally for large and small figures. In conclusion, training by tracing smaller figures yielded better learning that was not, however, specific to the scale of drawn figures. Small figures exhibit greater mean curvature. We infer that it yielded better general improvement.

Pulse wave velocity in the microcirculation reflects both vascular compliance and resistance: Insights from computational approaches.

OBJECTIVE: PWV is the speed of pulse wave propagation through the circulatory system. mPWV emerges as a novel indicator of hypertension, yet it remains unclear how different vascular properties affect mPWV. We aim to identify the biomechanical determinants of mPWV. METHODS: A 1D model was used to simulate PWV in a rat mesenteric microvascular network and, for comparison, in a human macrovascular arterial network. Sensitivity analysis was performed to assess the relationship between PWV and vascular compliance and resistance. RESULTS: The 1D model enabled adequate simulation of PWV in both micro- and macrovascular networks. Simulated arterial PWV changed as a function of vascular compliance but not resistance, in that arterial PWV varied at a rate of 0.30 m/s and -6.18 × 10-3  m/s per 10% increase in vascular compliance and resistance, respectively. In contrast, mPWV depended on both vascular compliance and resistance, as it varied at a rate of 2.79 and -2.64 cm/s per 10% increase in the respective parameters. CONCLUSIONS: The present study identifies vascular compliance and resistance in microvascular networks as critical determinants of mPWV. We anticipate that mPWV can be utilized as an effective indicator for the assessment of microvascular biomechanical properties.

ICP Monitoring and Phase-Contrast MRI to Investigate Intracranial Compliance.

OBJECTIVE: The amplitude of intracranial pressure (ICP) can be measured by ICP monitoring. Phase-contrast magnetic resonance imaging (PCMRI) can quantify blood and cerebrospinal fluid (CSF) flows. The aim of this work was to investigate intracranial compliance at rest by combining baseline ICP monitoring and PCMRI in hydrocephalus patients. MATERIALS AND METHODS: ICP monitoring was performed before infusion testing to quantify ΔICP_rest at the basal condition in 33 suspected hydrocephalus patients (74 years). The day before, patients had had a PCMRI to assess total cerebral blood flow (tCBF), intracranial blood volume change (stroke volume SVblood), and cervical CSF volume change (the stroke volume CSV). Global (blood and CSF) intracranial volume change (ΔIVC) during each cardiac cycle (CC) was calculated. Finally, Compliance: C_rest = ΔIVC/ΔICP_rest was calculated. The data set was postprocessed by two operators according to blind analysis. RESULTS: Bland-Altman plots showed that measurements presented no significant difference between the two operators. ΔICP_rest = 2.41 ± 1.21 mmHg, tCBF = 469.89 ± 127.54 mL/min, SVblood = 0.82 ± 0.32 mL/cc, CSV = 0.50 ± 0.22 mL/cc, ΔIVC = 0.44 ± 0.22 mL, and C_rest = 0.23 ± 0.15 mL/mmHg. There are significant relations between SVblood and CSV and also SVblood and tCBF. CONCLUSIONS: During "basal" condition, the compliance amplitude of the intracranial compartment is heterogeneous in suspected hydrocephalus patients, and its value is lower than expected! This new parameter could represent new information, complementary to conventional infusion tests. We hope that this information can be applied to improve the selection of patients for shunt surgery.

Mechanical model of human eye compliance for volumetric occlusion break surge measurements.

PURPOSE: To develop a mechanical model of human eye compliance for volumetric studies. SETTING: Alcon Research, Ltd., Lake Forest, California, USA. DESIGN: Experimental study. METHODS: Enucleated human eyes underwent pressurization and depressurization cycles with peak intraocular pressures (IOPs) of 60 to 100 mm Hg; anterior chamber pressure and volume changes were measured. Average net volume change curves were calculated as a function of IOP for each eye. Overall mean volumes were computed from each eye's average results at pressure points extrapolated over the range of 5 to 90 mm Hg. A 2-term exponential function was fit to these results. A fluid chamber with a displaceable piston was created as a mechanical model of this equation. A laser confocal displacement meter was used to measure piston displacement. A test bed incorporated the mechanical model with a mounted phacoemulsification probe and allowed for simulated occlusion breaks. Surge volume was calculated from piston displacement. RESULTS: An exponential function, V = C1 × exp(C2 × IOP) + C3 × exp(C4 × IOP) - V0, where V, the volume, was fit to the final depressurization curve obtained from 15 enucleated human eyes. The C1 through C4 values were -0.07141, -0.23055, -0.14972, and -0.02006, respectively. The equation was modeled using a piston system with 3 parallel springs that engaged serially. The mechanical model mimicked depressurization curves observed in human cadaver eyes. CONCLUSION: The resulting mechanical compliance model measured ocular volumetric changes and thus would be helpful in characterizing the postocclusion break surge response.

Effects of flexibility and aspect ratio on the aerodynamic performance of flapping wings.

In the current study, we experimentally investigated the flexibility effects on the aerodynamic performance of flapping wings and the correlation with aspect ratio at angle of attack α = 45°. The Reynolds number based on the chord length and the wing tip velocity is maintained at Re = 5.3 × 103. Our result for compliant wings with an aspect ratio of 4 shows that wing flexibility can offer improved aerodynamic performance compared to that of a rigid wing. Flexible wings are found to offer higher lift-to-drag ratios; in particular, there is significant reduction in drag with little compromise in lift. The mechanism of the flexibility effects on the aerodynamic performance is addressed by quantifying the aerodynamic lift and drag forces, the transverse displacement on the wings and the flow field around the wings. The regime of the effective stiffness that offers improved aerodynamic performance is quantified in a range of about 0.5-10 and it matches the stiffness of insect wings with similar aspect ratios. Furthermore, we find that the aspect ratio of the wing is the predominant parameter determining the flexibility effects of compliant wings. Compliant wings with an aspect ratio of two do not demonstrate improved performance compared to their rigid counterparts throughout the entire stiffness regime investigated. The correlation between wing flexibility effects and the aspect ratio is supported by the stiffness of real insect wings.

Enhancement of muscle and locomotor performance by a series compliance: A mechanistic simulation study.

The objective was to better understand how a series compliance alters contraction kinetics and power output of muscle to enhance the work done on a load. A mathematical model was created in which a gravitational point load was connected via a linear spring to a muscle (based on the contractile properties of the sartorius of leopard frogs, Rana pipiens). The model explored the effects of load mass, tendon compliance, and delay between onset of contraction and release of the load (catch) on lift height and power output as measures of performance. Series compliance resulted in increased lift height over a relatively narrow range of compliances, and the effect was quite modest without an imposed catch mechanism unless the load was unrealistically small. Peak power of the muscle-tendon complex could be augmented up to four times that produced with a muscle alone, however, lift height was not predicted by peak power. Rather, lift height was improved as a result of the compliance synchronizing the time courses of muscle force and shortening velocity, in particular by stabilizing shortening velocity such that muscle power was sustained rather than rising and immediately falling. With a catch mechanism, enhanced performance resulted largely from energy storage in the compliance during the period of catch, rather than increased time for muscle activation before movement commenced. However, series compliance introduced a trade-off between work done before versus after release of the catch. Thus, the ability of tendons to enhance locomotor performance (i.e. increase the work done by muscle) appears dependent not only on their established role in storing energy and increasing power, but also on their ability to modulate the kinetics of muscle contraction such that power is sustained over more of the contraction, and maximizing the balance of work done before versus after release of a catch.

Carotid ß-stiffness index is associated with slower processing speed but not working memory or white matter integrity in healthy middle-aged/older adults.

Aging is associated with increased carotid artery stiffness, a predictor of incident stroke, and reduced cognitive performance and brain white matter integrity (WMI) in humans. Therefore, we hypothesized that higher carotid stiffness/lower compliance would be independently associated with slower processing speed, higher working memory cost, and lower WMI in healthy middle-aged/older (MA/O) adults. Carotid ß-stiffness (P < 0.001) was greater and compliance (P < 0.001) was lower in MA/O (n = 32; 64.4 ± 4.3 yr) vs. young (n = 19; 23.8 ± 2.9 yr) adults. MA/O adults demonstrated slower processing speed (27.4 ± 4.6 vs. 35.4 ± 5.0 U/60 s, P < 0.001) and higher working memory cost (-15.4 ± 0.14 vs. -2.2 ± 0.05%, P < 0.001) vs. young adults. Global WMI was lower in MA/O adults (P < 0.001) and regionally in the frontal lobe (P = 0.020) and genu (P = 0.009). In the entire cohort, multiple regression analysis that included education, sex, and body mass index, carotid ß-stiffness index (B = -0.53 ± 0.15 U, P = 0.001) and age group (B = -4.61 ± 1.7, P = 0.012, adjusted R2 = 0.4) predicted processing speed but not working memory cost or WMI. Among MA/O adults, higher ß-stiffness (B = -0.60 ± 0.18, P = 0.002) and lower compliance (B = 0.93 ± 0.26, P = 0.002) were associated with slower processing speed but not working memory cost or WMI. These data suggest that greater carotid artery stiffness is independently and selectively associated with slower processing speed but not working memory among MA/O adults. Carotid artery stiffening may modulate reductions in processing speed earlier than working memory with healthy aging in humans.NEW & NOTEWORTHY Previously, studies investigating the relation between large elastic artery stiffness, cognition, and brain structure have focused mainly on aortic stiffness in aged individuals with cardiovascular disease risk factors and other comorbidities. This study adds to the field by demonstrating that the age-related increases in carotid artery stiffness, but not aortic stiffness, is independently and selectively associated with slower processing speed but not working memory among middle-aged/older adults with low cardiovascular disease risk factor burden.

A cross-sectional study of physical activity and arterial compliance: the effects of age and artery size.

Our study examined the relationship between habitual high levels of vigorous physical activity on large and small artery compliance via radial artery pulse wave analysis. Eighty-three healthy men (n = 44) and women (n = 39), aged 18-78 years, were recruited as habitually less active (light-to-moderate exercise ≤3 times/wk) or habitually highly active (vigorous exercise ≥5 times/wk). A multivariate analysis of variance revealed a significant interaction of age and activity level; habitual vigorous activity was associated with greater compliance in large and small arteries in older adults (40-78 years) and younger adults (18-22 years). In the large and small arteries, we observed an age-associated decrease in arterial compliance (aged ≥ 40 years), though it appears to be less pronounced in the large artery among habitually highly active subjects. This study suggests that aging may be associated with declines in large and small artery compliance that can be attenuated by habitual vigorous activity.

The influence of race length on arterial compliance following an ultra-endurance marathon.

There is inconclusive evidence concerning the effects of routine participation in ultra-endurance events on cardiovascular disease (CVD) risk. Arterial compliance is a reliable, non-invasive, and effective tool for evaluating CVD risk. The purpose of this research was to examine if race length influences acute changes in arterial compliance following an ultra-marathon event. A total of 46 ultra-marathon runners were recruited including 21 participants (39.8 ± 8.3 years, 6 females) in the 80-km event and 25 participants (43.7 ± 9.8 years, 3 female) in the 195-km event. Arterial compliance was measured via radial applanation tonometry (CR-2000, HDI) for diastolic pulse contour analysis before and following the race. Significant between-group differences were found for changes in large arterial compliance with a decrease (increase in stiffness) following the 195-km event and an increase following the 80-kilometre event (p < .05). Longer race lengths are associated with greater reductions in large arterial compliance following recreational ultra-marathon running. Assessment of arterial compliance might be a useful prognostic tool to assess the long-term risk of CVD among ultra-marathon runners.