Modulation of platelet membrane function via exogenous lipid moiety exposure alters platelet responsiveness to shear.

Shear-induced platelet activation may cause life-threatening thrombosis, particularly in patients with mechanical support devices or coronary atherosclerosis. The majority of present anti-platelet agents target or interfere with biochemical, rather than physical mechanisms of platelet activation. Less data and understanding exists with regard to pharmacologic modulation of shear-mediated platelet activation. In this work, we hypothesized that modulating cell membrane properties, via alteration of membrane composition through addition of exogenous lipid moieties, would alter platelet responsiveness to shear. Here we tested fatty acids, lecithin and cholesterol as additive lipid compounds. We demonstrated that incorporation of fatty acids (DHA/EPA) or lecithin into the platelet membrane triggered enhanced sensitivity of platelets to shear-mediated activation. On the other hand, cholesterol incorporation provides significant protection, limiting the effect of shear on platelet activation. These findings provide valuable insight for the development of therapeutic strategies that can modulate shear-mediated platelet activation.

Effects of multiple injections of HCG on testis blood flow.

In attempting to determine whether or not multiple injections of human chorionic gonadotropin (hCG) augment testis blood flow, adult male rats were injected with three doses of 10 IU of hCG every other day and testis blood flow was determined on day 5, the day of the final injection. Testis blood flow (mL/100 g testis tissue/min +/- SEM) as measured by the 133Xe washout method increased from 10.8 +/- 1.3 to 20.4 +/- 4.5 (p less than 0.05) after the three doses of hCG. These observations suggest that multiple injections of hCG appear to have the same effect as a single dose of hCG in increasing testis blood flow. This supports the hypothesis that hCG should be administered to all patients undergoing orchiopexy in the hope that the increased perfusion of the gonad will make it less susceptible to ischemia during the surgical procedure.

The effect of varying degrees of stenosis on the characteristics of turbulent pulsatile flow through heart valves.

Many problems and complications associated with heart valves are related to the dynamic behavior of the valve and the resultant unsteady flow patterns. An accurate depiction of the spatial and temporal velocity and rms distributions imparts better understanding of flow related valve complications, and may be used as a guideline in valve design. While the generalized correlation between increased turbulence level and the severity of the stenosis is well established, few studies addressed the issue of the intermittent nature of turbulence and its timing in the cardiac cycle, and almost none assessed the effect of a progressive stenosis on the flow characteristics through heart valves. In this experimental work we simulated the type of flow which is present in normal and stenosed valves and conducted a comprehensive investigation of valve hemodynamics, valvular turbulence and morphology under varying degrees of stenosis. The characteristics of valves and stenoses were simulated closely, to achieve the flow conditions that initiate turbulent flow conditions. Laser Doppler anemometry (LDA) measurements were carried out in a pulse duplicator system distal to trileaflet polyurethane prosthetic heart valves, installed at mitral and aortic positions. The effect of the degree of the stenosis was comparatively studied through the structure of the turbulent jets emerging from normal and stenotic heart valves. Maximum turbulence level was achieved during the decelerating phase and correlated to the severity of the stenosis, followed by relaminarization of the flow during the acceleration phase. The intermittent nature of the turbulence emphasized the importance of realizing the timing of the turbulence production and its spatial location for optimizing current valve designs. The plug flow through the normal aortic valve prosthesis was replaced by jet like behavior for a 65% stenosis, with the jet becoming narrower and stronger for a 90% stenosis. The morphology of the velocity and turbulence waveforms was found to be governed by the stenosis geometry and the valve position (aortic, mitral).

Free emboli formation in the wake of bi-leaflet mechanical heart valves and the effects of implantation techniques.

The high incidence of thromboembolic complications of mechanical heart valves (MHV), primarily due to platelet activation by contact with foreign surfaces and by non-physiological flow patterns past the valve, still limits their success as permanent implants. The latter include elevated shear and turbulent stresses and shed vortices formed in the wake of the valve's leaflets during the deceleration phase, potentially entrapping activated and aggregated platelets. It is hypothesized that these flow patterns induce the formation of free emboli which are the source of cerebrovascular microemboli associated with MHV. Implicit to this hypothesis is that free emboli formation will be affected by the implantation technique employed and the valve orientation, as those will alter the flow characteristics past the valve and the interaction of the platelets with the flow. In this study, numerical simulations of turbulent pulsatile flow past a St. Jude Medical bi-leaflet MHV were conducted. Platelet shear histories were calculated along pertinent turbulent platelet trajectories, and the effect of a misaligned valve on platelet activation was quantified and compared to that of an aligned valve. It demonstrated that the combination of a tilted valve and subannularly sutured pledgets had an explicit detrimental effect on platelet activation, with the following entrapment of the platelets within the shed vortices of the wake leading to a significant increase of the thromboembolic potential of the valve. This numerical model depicted a viable course for free emboli formation, and indicated how the implantation technique may enhance the risk of cardioembolism.

A squeeze flow phenomenon at the closing of a bileaflet mechanical heart valve prosthesis.

In vivo cavitation in cardiovascular flow fields may occur under very unusual circumstances as a localized transient phenomenon which are confined to very small regions in the vicinity of the valve body or leaflet surface. The violent collapse of cavitation bubbles induces local erosion that may lead to structural damage. The fluid mechanical factors that may cause in vivo cavitation inception in mechanical heart valve (MHV) prostheses are investigated. It is established that the closing velocity of the leaflet holds the key to MHV cavitation. During the final phase of valve closing, the fluid mass in the gap space between the closing occluder and the valve's body is squeezed into motion by the rapidly approaching boundaries. The flow pattern created by this motion (termed 'squeeze flow'), is found to be related to the valve geometry, and the impact velocity of the closing leaflet. Given the closing velocity of the leaflet and the geometry of the MHV, computational flow dynamics (CFD) are made to determine the velocity distributions in the gap flow field of a bileaflet MHV in the mitral position. A two dimensional, time dependent model of the gap space show that flow velocity in the gap space can reach values as high as 30 ms-1 in regions near the edge of the inflow surface of the Edwards Duromedics (ED) MHV leaflet. This high speed stream ejected from the gap channel can create the conditions that characterize cavitation. The location of the isolated high speed region corresponds to the surface erosion that was observed in a number of damaged ED-MHV explants.

Closing behavior of a new bileaflet mechanical heart valve.

Recently, the in vivo cavitation potential has become a primary concern among manufacturers of new mechanical heart valves (MHV). An experimental/computational program was designed to investigate each of the flow parameters involved. It was established that the closing velocity of the leaflet holds the key to MHV cavitation. One of the novel concepts of the new bileaflet mechanical heart valve (1205-MHV) was its ability to operate with a relatively small angular excursion that led to a much smaller closure velocity at impact (as compared with control valves). This is believed to significantly reduce the cavitation potential. The 1205-MHV is characterized by a longer valve body, with the hinges protruding further upstream. The unique design allows the valve the freedom to open as much as 90 degrees. The closure velocities are reduced by a smaller leaflet excursion (50 degrees), combined with a floating hinge that allows absorption of part of the impact energy at closure. The impact velocities of the 1205-MHV leaflets at closure were measured by a laser sweeping technique that monitored the leaflet closing motion with a precision of 5 microseconds within the last 3 degrees before impact. The 27 mm 1205-MHV (the largest size) was tested in the program by mounting the valve in the mitral position of a physiologic mock circulatory loop. The valve was tested at 70, 90, and 120 bpm. The results were compared with those of a St. Jude Medical 29 mm MHV. The closure velocities measured with the 1205-MHV were significantly lower than those measured with the control valve.(ABSTRACT TRUNCATED AT 250 WORDS)

Symptom reporting in wanted and unwanted pregnancies.

This study examined the association between unwanted pregnancy and the reporting of pregnancy symptoms in a sample of 99 pregnant women drawn from an urban, medical school based family practice residency. Of these women, 51 had unwanted pregnancies, and 48 had wanted pregnancies. Women with wanted pregnancies were more likely than women with unwanted pregnancies to report three pregnancy symptoms (amenorrhea, breast tenderness, and morning sickness). This association of symptoms with a wanted pregnancy persisted after controlling for age, race, marital status, contraceptive use, menstrual irregularity, and days since last menses through multiple logistic regression. Findings suggest that symptoms may be underreported by women with unwanted pregnancies.

Psychosocial determinants of late prenatal care: the Health Belief Model.

This paper presents a theoretical framework for investigating psychosocial determinants of delayed prenatal care among disadvantaged women. This framework is based on the Health Belief Model (HBM), which postulates that beliefs concerning prenatal care are modified by psychological and social attributes and may predispose one to delay prenatal care enrollment. The HBM has a number of advantages for family medicine researchers in comparison to other models; its use in future investigations can provide the understanding necessary for overcoming psychosocial deterrents to entry into prenatal care.

Ethnic differences in patient requests for pregnancy testing.

This study identifies a black-white difference in pregnancy test requests and in factors predicting such requests among 324 women tested at an academic family practice in 1986. Data were obtained from encounter sheets filled out by clinicians at the time tests were ordered. Analysis of variance revealed that blacks requested fewer pregnancy tests than whites, and that this finding remained significant (P less than .01) after controlling for the effects of gestational status and other clinical and sociodemographic factors. Blacks were less likely to be married or possess health insurance, but more likely to have been pregnant before. Logistic regressions indicated that factors predicting test requests differed by ethnicity, with symptoms and age predicting test requests among whites, and pregnancy the only significant predictor among blacks. Explanations consistent with these findings include possible ethnic differences in reactions to symptoms and economic factors. Further refinement of these hypotheses and consideration of other alternatives will advance understanding of ethnicity as a factor in test-requesting behavior, and enable clinicians to communicate with and care for black women more effectively.

Knowledge of pregnancy symptoms among abortion patients: is race a predictor?

This cross-sectional study characterizes first-trimester abortion patients who perceived inadequate knowledge of pregnancy symptoms and identifies net predictors of inadequate symptom knowledge. Data were collected at an abortion facility in Hampton Roads, Virginia. Study subjects were women surveyed on the day of their abortions, prior to termination procedures. Self-reported knowledge of pregnancy symptoms was the study's dependent variable. Of 342 women, 120 (35%) perceived inadequate symptom knowledge. These women more often were young, black, single, and poorly educated. Only black race was a net predictor of inadequate symptom knowledge when study variables were entered into a multiple logistic regression. Black race was the only net predictor of inadequate symptom knowledge among first-trimester abortion patients. This racial difference was not explained by socioeconomic or access factors. Future research should consider an alternative hypothesis, the possibility that more effective communications with black abortion patients are needed. Additionally, health-care providers should not presume that first-trimester abortion patients are familiar with pregnancy symptoms and should not stereotype patients who perceive knowledge limitations with regard to socioeconomic status.

Should I trust office pregnancy tests?

Pregnancy tests have become quite reliable since the introduction of monoclonal antibody procedures. Even home kits use this technology and are greatly improved over earlier versions. However, as Dr Bluestein explains, use of these tests must be accompanied by an understanding of factors that can cause false results. He describes these factors and points out the need for further testing and obstetric consultation in some situations.

Determinants of delayed pregnancy testing among adolescents.

BACKGROUND: Pregnant teenagers often prolong the interval between suspecting and confirming that they are pregnant. Prior studies suggest a number of potential determinants for this delay but do not specify which ones are most salient. METHODS: In a cross-sectional survey, 123 pregnant teenagers, 64 of whom maintained their pregnancies and 59 of whom had abortions, completed a short version of the Center for Epidemiologic Studies Depression Scale, the Family APGAR test, and a study-specific questionnaire. RESULTS: Significant bivariate determinants of delayed pregnancy testing included young maternal age, black race, lower educational attainment, lack of pregnancy symptoms, continuing the pregnancy, and denial. Only denial, however, retained a significant net effect on delayed testing (P < .05) when the effects of these six variables were modeled using multiple linear regression. CONCLUSIONS: These results suggest that psychological barriers are the most salient determinants of delayed pregnancy testing among the teenagers surveyed in this study. Some teenagers may not volunteer information about a suspected pregnancy. Providers, therefore, should directly question teenagers about sexual activity and discuss the importance of early testing when pregnancy is suspected. Findings also suggest further research that would increase understanding of adolescent health behavior in pregnancy and identify effective clinical and educational interventions.

The sensitivity, specificity and predictive value of diagnostic information: a guide for clinicians.

Nurse practitioners and other clinicians use laboratory studies and ancillary tests to confirm or rule out suspected conditions. Deciding which tests to use and interpreting results are essential to the practice of high-quality, cost-effective primary care. A working knowledge of test characteristics and performance facilitates these decisions. This article illustrates how a conceptual understanding of sensitivity, specificity and predictive value applies to daily practice. In addition, the article explains how to evaluate the quality and relevance of literature that reports test performance. While discussion focuses on laboratory tests, the same principles may be applied to the history and physical examination, and to other types of diagnostic data.

Towards non-thrombogenic performance of blood recirculating devices.

Implantable blood recirculating devices have provided life saving solutions to patients with severe cardiovascular diseases. However, common problems of hemolysis and thromboembolism remain an impediment to these devices. In this article, we present a brief review of the work by several groups in the field that has led to the development of new methodologies that may facilitate achieving the daunting goal of optimizing the thrombogenic performance of blood recirculating devices. The aim is to describe work which pertains to the interaction between flow-induced stresses and the blood constituents, and that supports the hypothesis that thromboembolism in prosthetic blood recirculating devices is initiated and maintained primarily by the non-physiological flow patterns and stresses that activate and enhance the aggregation of blood platelets, increasing the risk of thromboembolism and cardioembolic stroke. Such work includes state-of-the-art numerical and experimental tools used to elucidate flow-induced mechanisms leading to thromboembolism in prosthetic devices. Following the review, the paper describes several efforts conducted by some of the groups active in the field, and points to several directions that should be pursued in the future in order to achieve the goal for blood recirculating prosthetic devices becoming more effective as destination therapy in the future.

The unanticipated pregnancy: a preliminary study.

To guide clinical judgements regarding possible pregnancy in women seen for nonpregnancy concerns, 75 pregnant women tested for pregnancy confirmation were compared to 31 women with pregnancies diagnosed when tested to clarify undifferentiated symptoms. Symptom clarification patients were more often unmarried (74.2% vs 37.3%, P less than 0.001), unemployed (54.8% vs 14.7%, P less than 0.0001), uninsured (54.8% vs 25.3%, P less than 0.004), black (67.8% vs 45.3%, P less than 0.04), using contraception (45.2% vs 22.7%, P less than 0.02), and carrying unwanted gestations (77.4% vs 34.7%, P less than 0.0001). Symptom clarification patients had a median 2 pregnancy symptoms versus 3 for pregnancy confirmation patients (P less than 0.001), less often reported amenorrhea (25.8% vs 6.7%, P less than 0.01) or breast tenderness (38.7% vs 66.7%, P less than 0.01), but more often experienced abdominal pain (45.2% vs 17.3%, P less than 0.003). Thus, symptom clarification patients are often earlier in gestation with fewer pregnancy symptoms, or may differ in how they perceive and interpret such symptoms when present, findings consistent with a tentative hypothesis that symptom clarification patients may not have anticipated being pregnant.