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.

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.

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.

fusilli, an essential gene with a maternal role in Drosophila embryonic dorsal-ventral patterning.

The Drosophila fusilli (fus) gene was identified in a genetic screen for dominant maternal enhancers of an unusual dorsalizing mutation in the cactus gene, cact(E10). While females that are heterozygous for the cact(E10) allele produce embryos with wild-type dorsal-ventral patterning, more than 90% of the embryos produced by females that are heterozygous for both cact(E10) and the fus(1) mutation are weakly dorsalized. Loss of fusilli activity causes lethality during embryogenesis but not dorsal-ventral patterning defects, indicating that fusilli is important in more than one developmental process. The fusilli gene encodes a protein with RNA binding motifs related to those in mammalian hnRNP F and H, which play roles in regulated RNA splicing. The fusilli RNA is not present in the oocyte or early embryo, and germ-line clones of fusilli mutations have no maternal effect on dorsal-ventral patterning, indicating that the fusilli maternal effect does not depend on germ-line expression of the gene. Because the fusilli RNA is present in ovarian follicle cells, we propose that fusilli acts downstream of the Drosophila EGF receptor to control the biogenesis of follicle cell transcripts that control the initial dorsal-ventral asymmetry of the embryo.

Vortex shedding as a mechanism for free emboli formation in mechanical heart valves.

The high incidence of thromboembolic complications of mechanical heart valves (MHV) limits their success as permanent implants. The thrombogenicity of all MHV is primarily due to platelet activation by contact with foreign surfaces and by nonphysiological flow patterns. The latter include elevated flow stresses and regions of recirculation of blood that are induced by valve design characteristics. A numerical simulation of unsteady turbulent flow through a bileaflet MHV was conducted, using the Wilcox k-omega turbulence model for internal low-Reynolds-number flows, and compared to quantitative flow visualization performed in a pulse duplicator system using Digital Particle Image Velocimetry (DPIV). The wake of the valve leaflet during the deceleration phase revealed an intricate pattern of interacting shed vortices. Particle paths showed that platelets that were exposed to the highest flow stresses around the leaflets were entrapped within the shed vortices. Potentially activated, such platelets may tend to aggregate and form free emboli. Once formed, such free emboli would be convected downstream by the shed vortices, increasing the risk of systemic emboli.

Acetylated prothrombin as a substrate in the measurement of the procoagulant activity of platelets: elimination of the feedback activation of platelets by thrombin.

Human prothrombin was acetylated to produce a modified prothrombin that upon activation by platelet-bound prothrombinase generates a form of thrombin that does not activate platelets but retains its amidolytic activity on a chromogenic peptide substrate. If normal prothrombin is used in such an assay, the thrombin that is generated activates the platelets in a feedback manner, accelerating the rate of thrombin generation and thereby preventing accurate measurement of the initial platelet procoagulant activity. Acetylation of prothrombin was carried out over a range of concentrations of sulfo-N-succinimidyl acetate (SNSA). Acetylation by 3 mM SNSA at room temperature for 30 min at pH 8.2 in the absence of metal ions produced a modified prothrombin that has <0.1% clotting activity (by specific prothrombin clotting assay), but it is activated by factor Xa (in the presence of either activated platelets or factor Va + anionic phospholipid) to produce thrombin activity that is measurable with a chromogenic substrate. Because the feedback action on the platelets is blocked, thrombin generation is linear, allowing quantitative measurement of the initial platelet activation state.

Vortex shedding in steady flow through a model of an arterial stenosis and its relevance to mural platelet deposition.

In this study, the development of unsteady vortical formations in the separated flow region distal to a stenosis throat is presented and compared with the platelet deposition measurements, to enhance our understanding of the mechanisms involved in platelet kinetics in flowing blood. Qualitative and quantitative flow visualization and numerical simulations were performed in a model of a streamlined axisymmetric stenosis with an area reduction of 84% at the throat of the stenosis. Measurements were performed at Reynolds numbers (Re), based on upstream diameter and average velocity, ranging from 300 to 1,800. Both the digital particle image visualization method employed and the numerical simulations were able to capture the motion of the vortices through the separated flow region. Periodic shedding of vortices began at approximately Re=375 and continued for the full range of Re studied. The locales at which these vortices are initiated, their size, and their life span, were a function of Re. The numerical simulations of turbulent flow through the stenosis model entailed a detailed depiction of the process of vortex shedding in the separated flow region downstream of the stenosis. These flow patterns were used to elucidate the mechanisms involved in blood platelet kinetics and deposition in the area in and around an arterial stenosis. The unsteady flow development in the recirculation region is hypothesized as the mechanism for observed changes in the distribution of mural platelet deposition between Re =300, 900, and 1,800, despite only a marginal variation in the size and shape of the recirculation zone under these flow conditions.

Fluid mechanics of arterial stenosis: relationship to the development of mural thrombus.

In this study, we analyzed blood flow through a model stenosis with Reynolds numbers ranging from 300 to 3,600 using both experimental and numerical methods. The jet produced at the throat was turbulent, leading to an axisymmetric region of slowly recirculating flow. For higher Reynolds numbers, this region became more disturbed and its length was reduced. The numerical predictions were confirmed by digital particle image velocimetry and used to describe the fluid dynamics mechanisms relevant to prior measurements of platelet deposition in canine blood flow (R.T. Schoephoerster et al., Atherosclerosis and Thrombosis 12:1806-1813, 1993). Actual deposition onto the wall was dependent on the wall shear stress distribution along the stenosis, increasing in areas of flow recirculation and reattachment. Platelet activation potential was analyzed under laminar and turbulent flow conditions in terms of the cumulative effect of the varying shear and elongational stresses, and the duration platelets are exposed to them along individual platelet paths. The cumulative product of shear rate and exposure time along a platelet path reached a value of 500, half the value needed for platelet activation under constant shear (J.M.. Ramstack et al., Journal of Biomechanics 12: 113-125, 1979).

Steady flow in an aneurysm model: correlation between fluid dynamics and blood platelet deposition.

Laminar and turbulent numerical simulations of steady flow in an aneurysm model were carried out over Reynolds numbers ranging from 300 to 3600. The numerical simulations are validated with Digital particle Image Velocimetry (DPIV) measurements, and used to study the fluid dynamic mechanisms that characterize aneurysm deterioration, by correlating them to in vitro blood platelet deposition results. It is shown that the recirculation zone formed inside the aneurysm cavity creates conditions that promote thrombus formation and the viability of rupture. Wall shear stress values in the recirculation zone are around one order of magnitude less than in the entrance zone. The point of reattachment at the distal end of the aneurysm is characterized by a pronounced wall shear stress peak. As the Reynolds number increases in laminar flow, the center of the recirculation region migrates toward the distal end of the aneurysm, increasing the pressure at the reattachment point. Under fully turbulent flow conditions (Re = 3600) the recirculation zone inside the aneurysm shrinks considerably. The wall shear stress values are almost one order of magnitude larger than those for the laminar cases. The fluid dynamics mechanisms inferred from the numerical simulation were correlated with measurements of blood platelet deposition, offering useful explanations for the different morphologies of the platelet deposition curves.

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).

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.

Transition to turbulence in pulsatile flow through heart valves--a modified stability approach.

The presence of turbulence in the cardiovascular system is generally an indication of some type of abnormality. Most cardiologists agree that turbulence near a valve indicates either valvular stenosis or regurgitation, depending on the phase of its occurrence during the cardiac cycle. As no satisfying analytical solutions of the stability of turbulent pulsatile flow exist, accurate, unbiased flow stability criteria are needed for the identification of turbulence initiation. The traditional approach uses a stability diagram based upon the stability of a plane Stokes layer where alpha (the Womersley parameter) is defined by the fundamental heart rate. We suggest a modified approach that involves the decomposition of alpha into its frequency components, where alpha is derived from the preferred modes induced on the flow by interaction between flow pulsation and the valve. Transition to turbulence in pulsatile flow through heart values was investigated in a pulse duplicator system using three polymer aortic valve models representing a normal aortic valve, a 65 percent stenosed valve and a 90 percent severely stenosed valve, and two mitral valve models representing a normal mitral valve and a 65 percent stenosed valve. Valve characteristics were closely simulated as to mimic the conditions that alter flow stability and initiate turbulent flow conditions. Valvular velocity waveforms were measured by laser Doppler anemometry (LDA). Spectral analysis was performed on velocity signals at selected spatial and temporal points to produce the power density spectra, in which the preferred frequency modes were identified. The spectra obtained during the rapid closure stage of the valves were found to be governed by the stenosis geometry. A shift toward higher dominant frequencies was correlated with the severity of the stenosis. According to the modified approach, stability of the flow is represented by a cluster of points, each corresponding to a specific dominant mode apparent in the flow. In order to compare our results with those obtained by the traditional approach, the cluster of points was averaged to collapse into a single point that represents the flow stability. The comparison demonstrates the bias of the traditional stability diagram that leads to unreliable stability criteria. Our approach derives the stability information from measured flow phenomena known to initiate flow instabilities. It differentiates between stabilizing and destabilizing modes and depicts an unbiased and explicit stability diagram of the flow, thus offering a more reliable stability criteria.

Helping pregnant teenagers.

Teenagers who are pregnant face many difficult issues, and counseling by physicians can be an important source of help. We suggest guidelines for this counseling, beginning with a review of the scope and consequences of adolescent pregnancy. Communication strategies should be aimed at building rapport with techniques such as maintaining confidentiality, avoiding judgmental stances, and gearing communication to cognitive maturity. Techniques for exploring family relationships are useful because these relationships are key influences on subsequent decisions and behaviors. We discuss topics related to abortion and childbearing, such as safety, facilitation of balanced decision making, the use of prenatal care, and the formulation of long-term plans. Physicians who can effectively discuss these topics can help pregnant teenagers make informed decisions and improve their prospects for the future.

PIP: Pregnant teenagers are burdened with many difficult issues. Effective physician-counseling can help them with abortion decisions, early prenatal care when a teenager chooses to continue the pregnancy, and positive goal setting after childbirth. Prerequisites to building trust are ensuring confidentiality, patience, and a nonjudgmental attitude. Counseling must be geared to emotional and intellectual development. For example, teens aged 14-17 often cannot make the connection between current actions and future consequences, so they need explicit guidance in the realities of pregnancy and parenthood. Physicians must avoid imposing their personal views on abortion and unwed parenthood. They must not be authoritarian. They should explore a teen's family and social environment without stereotypical preconceptions to determine risks. Nonthreatening and open-ended questions can help open the way for discussions on family involvement (e.g., Do you enjoy being with your family?). When a teen is thinking about an abortion, the physician should provide information on the legality, availability, and timing of abortion. They should address the generally low medical risks of first trimester abortion. They should also examine the issue of parenthood versus abortion with the pregnant teen. The decision should be made by the pregnant teen herself rather than by the family or the physician. Denial, continual family concerns, fear of labor and delivery, financial barriers, ignorance of where to obtain prenatal care, and not understanding the importance of prenatal care are reasons teens delay seeking prenatal care. Counseling interventions should address fears about childbirth and misconceptions.

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.

Eliminating the need for bilateral pelvic lymphadenectomy in select patients with prostate cancer.

To determine if the preoperative variables of serum prostate specific antigen (PSA), primary Gleason grade from the biopsy specimen and local clinical stage as determined from digital rectal examination can accurately predict the pelvic lymph node status in patients with clinically localized prostate cancer, we reviewed the medical records of 1,632 patients who underwent bilateral pelvic lymphadenectomy at our institution between January 1988 and December 1991. Using logistic regression analysis, serum PSA was found to be the best predictor of pelvic lymph node metastases (p < 0.0001). The predictive power of serum PSA could be enhanced considerably by taking into account the Gleason grade (p < 0.001) and local clinical stage (p < 0.001). A statistical model using all 3 variables was developed that allows the practicing urologist to estimate on an individual basis the probability of pelvic lymph node involvement. Using a conservative cutoff point of less than 3% as an acceptable false-negative rate, 61% of the patients with clinical stages T1a to T2b (A1 to B1) disease and 29% of those with clinical stages T1a to T2c (A1 to B2) prostate cancer may be spared an open or laparoscopic staging bilateral pelvic lymphadenectomy. As a result, patient morbidity can be decreased and a significant economic savings to the health care system can be realized. This observation has particular importance for prostate cancer patients being managed with radical perineal prostatectomy or definitive radiation therapy.

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)

Family relationships and depressive symptoms preceding induced abortion.

This study examines the association between depressive symptoms preceding induced abortion and dissatisfaction with family relationships. In a cross-sectional survey, 304 women undergoing a first-trimester abortion completed a short version of the Center for Epidemiologic Studies Depression Scale, the Family APGAR, and a researcher-designed questionnaire. Bivariate analyses revealed that depressive symptoms decreased as measures of age, educational attainment, Family APGAR scores, marriage, and subjective health increased. Depressive symptoms increased as measures of denial, difficulties communicating with male partners, pregnancy symptoms, contraceptive use, and dissatisfaction with choosing abortion increased. Controlling for the effects of these significant bivariate associations, increased depressive symptoms were independently predicted by Family APGAR scores, age, communications difficulties, pregnancy symptoms, contraceptive use, and denial. Low Family APGAR scores exhibited the strongest overall effect. Clinicians who encounter women experiencing depressive symptoms preceding abortion may wish to explore family relationships and the possibility of underlying family dysfunction.

PIP: A cross-sectional survey of 304 young women about to undergo a 1st-trimester abortion at a Virginia clinic revealed a significant association between a pre-abortion depressive response and dissatisfaction with family relationships. The mean age of study participants was 24.3 years (range: 14-43 years); 83% were unmarried and 41% were Black. Depressive symptoms were measured by an abbreviated version of the Center for Epidemiologic Studies-Depression Scale (CES-D), while dissatisfaction with family relationships was assessed through use of the Family APGAR test. A researcher-designed questionnaire provided data on sociodemographic factors. The mean CES-D score was 16.82 (maximum possible score, 36), and the mean Family APGAR score was 6.63 (maximum possible, 10). Bivariate analysis revealed highly significant (p 0.001) associations between CES-D scores and Family APGAR scores, young age, lower educational attainment, and denial regarding the reality of the pregnancy. Also significantly correlated (p 0.01) with depression were poor subjective physical health and being unmarried. Lesser but significant (p 0.05) associations were found between depression and problems communicating with one's male partner, contraceptive use, dissatisfaction with the abortion decision, and the experience of symptoms of pregnancy. Multiple regression analysis indicated that increased depressive symptoms were independently predicted by low Family AGAR scores, young age, communication problems with the male partner, pregnancy symptoms, contraceptive use, and denial. The variables analyzed explained 25% of the variance in CES-D scores. Although long-term psychological adjustment to induced abortion is generally positive, over 50% of women are estimated to experience depressive symptoms prior to the procedure--a phenomenon that has not received adequate attention from family practitioners. Since problematic family relationships are often concealed from physicians, supportive exploration of the possibility of underlying family dysfunction should become a part of pre-abortion health care.

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.

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.