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 147,016 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In this study, we have investigated how enhanced total flight force production compromises steering performance in tethered flying fruit flies, Drosophila melanogaster. The animals were flown in a closed-loop virtual-reality flight arena in which they modulated total flight force production in response to vertically oscillating visual patterns. By simultaneously measuring stroke amplitude and stroke frequency, we recorded the ability of each fly to modulate its wing kinematics at different levels of aerodynamic force production. At a flight force that exactly compensates body weight, the temporal deviations with which fruit flies vary their stroke amplitude and frequency are approximately 2.7 degrees and 4.8 Hz of their mean value, respectively. This variance in wing kinematics decreases with increasing flight force production, and at maximum force production fruit flies are restricted to a unique combination of stroke amplitude, stroke frequency and mean force coefficient. This collapse in the kinematic envelope during peak force production could greatly attenuate the manoeuvrability and stability of animals in free flight.
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PMID:The production of elevated flight force compromises manoeuvrability in the fruit fly Drosophila melanogaster. 1117 45

The study is retrospective review of the demographic, clinical, angiographic, and operative data of the first 205 consecutive CABG operations performed by Caribbean Heart Care at the Eric Williams Medical Sciences Complex (EWMSC), Trinidad and Tobago, between November 1993 and December 1997. The aim of the study was to determine the in-hospital and intermediate-term follow-up results. The mean age of patients was 59 +/- 10 years and 78% were male. Sixty-four per cent were of East Indian descent, whereas 16% were of African descent. Forty-eight per cent of the patients were hypertensive, 46% were diabetic, 33% had hyperlipidaemia, 20% had a recent history of cigarette smoking and 16% were obese. Sixty-five per cent had a positive family history of ischaemic heart disease. The average time interval between angiography and surgery was 2.3 months. At the time of angiography, 63.5% of patients had Canadian Cardiac Society (CCS) class 3 or 4 angina. The mean ejection fraction was 61 +/- 15%. Wall motion abnormalities were seen in 67% of patients. Significant stenoses of the left anterior descending artery, right circumflex artery, circumflex and ramus coronary arteries were present in 91%, 78%, 54% and 5%, respectively. Many patients (67%) had severe diffuse disease on angiography. The mean intensive care stay was 2.2 +/- 0.8 days. In-hospital mortality was 3.9% (8/205). The most frequent post-operative complication was haemorrhage (2.6%). Acute renal failure occurred in 2.1%; pulmonary collapse, 1.6%; stroke, 1% and cardiac arrest, 1%. Both sternal wound infections and systemic sepsis occurred in 0.5%. Intermediate-term follow-up data were obtained for 92% (189/205). The duration of follow-up ranged from 1 to 5 years (mean 3.7 years). During the follow-up period, 7 patients (3.4%) died. Angina severity was reduced from a mean CCS score of 2.61 +/- 0.95 before CABG to 1.22 +/- 0.55 at the time of follow-up (p < 0.0001). Overall 4-year mortality compared favourably with data from international studies. Among survivors, quality of life improved as evidenced by the reduction in the mean angina score.
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PMID:Coronary artery bypass graft outcome: the Trinidad and Tobago experience. 1121 37

Pulmonary embolism (PE) represents the third more frequent cardiovascular disease following the acute coronary artery disease and stroke. The most important predisposing clinical condition for PE is represented by the deep-vein thrombosis. The clinical diagnosis of PE has a very low accuracy; so the clinical suspect has to be necessarily directed towards the performance of diagnostic procedures. Among the most used procedures, the echocardiography has a diagnostic role but also a prognostic one. Moreover, it offers precious informations useful to perform the most suitable treatment. The echocardiography features which suggest the presence of pulmonary embolism are: right ventricle and atrium dilatation, right ventricular hypokinesia, systolic flattening of the interventricular septum, tricuspid regurgitation, pulmonary artery dilatation, disappearance or reduction of the inspiratory collapse of the inferior vena cava and presence of eventual embolic sources. According to the involvement degree of right ventricular function, it is generally possible to identify a different survival. The subgroup of patients with moderate or severe right ventricular dysfunction shows a high in hospital and within 1 year death rate. For this reason the right ventricular dysfunction degree together with the hemodynamic stability, are the most important parameters in the therapeutic choice. If there is no right ventricular dysfunction a treatment with heparin is indicated. In presence of right ventricular dysfunction and hemodynamic instability, the thrombolytic treatment is necessary. If the patient is hemodynamically stable, a transesophageal echocardiography is recommended; in case of central thrombosis the thrombolytic therapy or surgery are needed, while if no embolic material is shown the heparin treatment is advisable.
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PMID:[Cardiologic diagnosis of pulmonary embolism: echocardiography]. 1125 35

The novel cyclic undecapeptide human urotensin-II (hU-II) and its high-affinity G-protein-coupled receptor, GPR14, are both expressed within the human cardiovasculature (vascular smooth muscle, endothelium, myocardium, coronary atheroma, etc.) and may, therefore, contribute to the (patho)physiological regulation of cardiovascular homeostasis in humans. Indeed, hU-II is an efficacious, sustained spasmogen of mammalian isolated blood vessels including those from rats, rabbits, dogs, pigs, non-human primates and humans (where it is one to two orders of magnitude more potent than endothelin(ET)-1). In vivo, hU-II markedly alters systemic hemodynamics in the anesthetized primate (increase cardiac contractility [dP/dt], increase stroke volume, decrease total peripheral resistance) ultimately resulting in fatal cardiovascular collapse. As such, the development of selective hU-II receptor antagonists may be of utility in the management of cardiovascular disorders characterized by aberrant vasoconstriction, myocardial dysfunction and/or cardiac remodeling (e.g., myocardial infarction, congestive heart failure).
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PMID:Human urotensin-II, the most potent mammalian vasoconstrictor identified to date, as a therapeutic target for the management of cardiovascular disease. 1128

This study was proposed to define early and long-term results of coronary artery bypass grafting (CABG) in dialysis-dependent renal failure (RF) patients, and preoperative patient characteristics. This study included 105 patients (87 males and 18 females; mean age 60.0 +/- 9.0 years, range 39-79) with RF on maintenance dialysis (hemodialysis 100, peritoneal dialysis 5) who underwent isolated CABG between August 1985 and April 2000. Postoperative follow-up was completed in 100% and averaged 3.1 years. There were 22 emergency and 2 re-CABG cases. Previous myocardial infarction (MI) was found in 55 patients (52%), and unstable angina was noted in 53 patients (50%). Diabetes mellitus was the cause of RF in 50 patients (48%; 24 patients required insulin). There was 1 case of single vessel disease, 31 cases of double vessel disease, 54 cases of triple vessel disease, and 19 cases of left main disease. Preoperative left ventriculography was performed in 92 patients (88%). Left ventricular ejection fraction (LVEF) was 48.3 +/- 15.8% (range 11-74%) and was 40% or less in 25 patients (27%). The mean number of distal anastomoses was 2.5 (range 1-5). Three patients received only vein grafts, but all were cases of emergency CABG. The remaining 102 patients (97%) received at least 1 arterial conduit. Among them, 64 patients received only arterial conduits, and 72 patients received 2 or more distal anastomoses with arterial conduits. Five patients (4.8%) died within 30 days after CABG (2 cardiac deaths and 3 noncardiac deaths), and 8 patients (7.6%) died beyond 30 days after CABG before discharge (all noncardiac deaths). The cause of 2 cardiac deaths was abrupt circulatory collapse during or after hemodialysis in patients with severe left ventricular dysfunction (LVEF; 11% and 28%) in the early postoperative period. The causes of 8 noncardiac deaths included infection in 4 and rupture of aortic aneurysm, stroke, sleep apnea syndrome, and mesenteric infarction. During the follow-up period, there were 29 late deaths (8 cardiac, 13 noncardiac, and 8 sudden death), 6 MIs, 13 percutaneous transluminal coronary angioplasty, and 1 re-CABG. The 5-year actuarial survival rate was 59.8%, the cardiac death-free rate was 83.0%, and the cardiac event-free rate was 62.4%. Although CABG in patients on hemodialysis is associated with high early and long-term mortality in terms of both cardiac and noncardiac deaths in proportion to the severity of the preoperative condition, long-term survival was still better than that of general dialysis patients. Meticulous perioperative management may be the key factor in the improvement of early results.
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PMID:Coronary artery bypass grafting in 105 patients with hemodialysis-dependent renal failure. 1131 55

Ventricular interdependence is that property of the normal heart such that distension of one ventricle alters the distensibility and filling pressure of the other. This phenomenon coupled with reciprocal changes in right and left heart venous return during normal quiet respiration results in minor decreases in left ventricular stroke volume, systolic blood pressure, pulse pressure, total electromechanical systole (Q-A2), left ventricular ejection time and mitral e-wave velocity during inspiration and minor increases in these parameters during expiration. Opposite changes in these parameters occur in the right heart with increases occurring during inspiration and decreases during expiration. Exaggerated ventricular interdependence occurs in cardiac tamponade when the pericardial constraint limits the total contents in the pericardial sac. This, together with the decreased effective left ventricular filling pressure which occurs during inspiration, is responsible for the exaggerated decrease in stroke volume, blood pressure, pulse pressure, left ventricular ejection time and mitral e-wave velocity in this condition. These observations, together with the echocardiographic findings of right atrial collapse, right ventricular collapse, and inferior vena cava plethora constitute the noninvasive diagnosis of pericardial tamponade. The utility of these noninvasive tests in detecting both the presence and degree of increased pericardial pressure was evaluated in 33 invasively studied patients with pericardial effusion. In Group 1 (n = 13) intrapericardial pressure was elevated but less than both right atrial pressure and pulmonary wedge pressure, in Group 2 (n = 10) intrapericardial pressure equaled right atrial pressure but was less than pulmonary wedge pressure, and in Group 3 (n = 10) intrapericardial pressure equaled right atrial pressure and pulmonary wedge pressure. From these data it is concluded that right atrial and right ventricular collapse are highly sensitive techniques for predicting increased intrapericardial pressure in all three groups, but fail to predict the level of intrapericardial pressure and the severity of hemodynamic compromise. However, the absence of inferior vena cava plethora helped separate Group 1 patients from Groups 2 and 3 patients, thereby aiding in distinguishing a group of patients with severe hemodynamic derangement requiring urgent intervention. Exaggerated reciprocal changes in mitral and tricuspid e-wave velocity is a very sensitive finding for increased intrapericardial pressure. However, its presence correlates poorly with the severity of tamponade. Acute pericardial tamponade is a clinical diagnosis determined by the integration of the history, physical exam and appropriate noninvasive physiologic and imaging techniques.
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PMID:Noninvasive/invasive correlates of exaggerated ventricular interdependence in cardiac tamponade. 1143 31

During ultra-endurance exercise, both increase in body temperature and dehydration due to sweat losses, lead to a decrease in central blood volume. The heart rate drift allows maintaining appropriate cardiac output, in order to satisfy both muscle perfusion and heat transfer requirements by increasing skin blood flow. The resulting dehydration can impair thermal regulation and increase the risks of serious accidents as heat stroke. Endurance events, lasting more than 8 hours, result in large sweat sodium chloride losses. Thus, ingestion of large amounts of water with poor salt intake can induce symptomatic hyponatremia (plasma sodium < 130 mEq/L) which is also a serious accident. Heat environment increases the thermal constraint and when the air humidity is high, evaporation of sweat is compromise. Thus, thermal stress becomes uncompensable which increases the risk of cardiovascular collapse. Cold exposure induces physiological responses to maintain internal temperature by both limiting thermal losses and increasing metabolic heat production. Cold can induce accidental hypothermia and local frost-bites; moreover, it increases the risk of arrhythmia during exercise. Some guidelines (cardiovascular fitness, water and electrolyte intakes, protective clothing) are given for each extreme condition.
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PMID:[Sports and extreme conditions. Cardiovascular incidence in long term exertion and extreme temperatures (heat, cold)]. 1150 64

Cardiac function is determined by preload, afterload, heart rate and contractility. During orthostatic stress, the footward blood shift is compensated for by an increase of afterload. LBNP is widely used to analyze effects of volume displacement during orthostatic stress. Comparisons of invasive (right heart catheterization) and non-invasive approach (echocardiography) yielded similar changes. Preload and afterload change with graded LBNP, heart rate increases, and stroke volume and cardiac output decrease. Thus, the working point on the left ventricular function curve is shifted to the left and downward, similar to hypovolemia. However, position on the Frank-Starling curve, the unchanged ejection fraction, and the constant Vcf indicate a normal contractile state during LBNP. A decrease of arterial oxygen partial pressure during LBNP shows impaired ventilation/ perfusion ratio. Finally, LBNP induced cardiac and hemodynamic changes can be effectively countermeasured by dihydroergotamine, a potent venoconstrictor. Comparison of floating catheter data with that of echocardiography resulted in close correlation for cardiac output and stroke volume. In addition, cardiac dimensions changed in a similar way during LBNP. From our findings, echocardiography as a non-invasive procedure can reliably used in LBNP and orthostatic stress tests. Some information can be obtained on borderline values indicating collapse or orthostatic syncope. Early fainters can be differentiated from late fainters by stroke volume changes.
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PMID:Cardiac factors in orthostatic hypotension. 1153 5

Arguably a seminal event in most trauma and disease is the breakdown of the cell membrane. In most cells, this is first observed as a collapse of the axolemmas barrier properties allowing a derangement of ions to occur, leading to a progressive dissolution of the cell or its process. We have shown that an artificial sealing of mechanically damaged membranes by topical application of hydrophilic polymers such as polyethylene glycol (PEG) immediately restores variable levels of nerve impulse conduction through the lesion. This was documented by a rapid recovery of somatosensory evoked potential (SSEP) conduction, and by recovery of the cutaneous trunchi muscle (CTM) reflex in PEG-treated animals. The CTM reflex is a sensorimotor behavior dependent on an intact (and identified) white matter tract within the ventrolateral funiculus of the spinal cord, and is thus an excellent index of white matter integrity. We show that PEG can be safely introduced into the bloodstream by several routes of administration. Using a fluorescein decorated PEG, we demonstrate that the polymer specifically targets the hemorrhagic contusion of the adult guinea pig spinal cord when administered through the vasculature, but not intact regions of the spinal cord. A single subcutaneous injection (30% weight by weight in sterile saline) made 6 hr after a standardized spinal cord contusion in adult guinea pigs was sufficient to produce a rapid recovery of SSEP propagation through the lesion in only PEG-treated animals, accompanied by a statistically significant recovery of the CTM reflex. These data suggest that parenterally administered PEG may be a novel treatment for not only spinal injury, but head injury and stroke as well.
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PMID:Rapid recovery from spinal cord injury after subcutaneously administered polyethylene glycol. 1174 51

Severe stenosis may cause critical flow and wall mechanical conditions related to artery fatigue, artery compression, and plaque rupture, which leads directly to heart attack and stroke. The exact mechanism involved is not well understood. In this paper a nonlinear three-dimensional thick-wall model with fluid-wall interactions is introduced to simulate blood flow in carotid arteries with stenosis and to quantify physiological conditions under which wall compression or even collapse may occur. The mechanical properties of the tube wall were selected to match a thick-wall stenosis model made of PVA hydrogel. The experimentally measured nonlinear stress-strain relationship is implemented in the computational model using an incremental linear elasticity approach. The Navier-Stokes equations are used for the fluid model. An incremental boundary iteration method is used to handle the fluid-wall interactions. Our results indicate that severe stenosis causes considerable compressive stress in the tube wall and critical flow conditions such as negative pressure, high shear stress, and flow separation which may be related to artery compression, plaque cap rupture, platelet activation, and thrombus formation. The stress distribution has a very localized pattern and both maximum tensile stress (five times higher than normal average stress) and maximum compressive stress occur inside the stenotic section. Wall deformation, flow rates, and true severities of the stenosis under different pressure conditions are calculated and compared with experimental measurements and reasonable agreement is found.
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PMID:Steady flow and wall compression in stenotic arteries: a three-dimensional thick-wall model with fluid-wall interactions. 1178 25


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