LDA measurements of mean velocity and Reynolds stress fields within an artificial heart ventricle

Laser Doppler Anemometry measurements of mean (ensemble average) velocities and turbulent (Reynolds) stresses at 140 locations within the left ventricle of the Penn State 70 cc electric artificial heart/ventricular assist device are reported at 8 times during the cardiac cycle. Mean velocity patterns indicate that the surfaces of the blood sac and valve tracts are exposed to significant levels of wall shear stress (good wall washing) during some portion of the flow cycle, and there is no location where the flow is stagnant over the entire flow cycle. This implies that thrombus deposition within the artificial heart should be suppressed. Turbulent stresses in the main pumping chamber and the outflow tracts of the tilting disk valves do not exceed 2000 dynes/cm2. The highest turbulent stresses (20,000 dynes/cm2) and smallest turbulent microscales (6 microns) are found in the regurgitant jets on the minor orifice side of the aortic valve during diastole and the mitral valve during systole. Taken together, the data suggest that improvements in artificial heart fluid mechanics will come through valve design and pump operating conditions, not pumping chamber design.

An in-vitro investigation of prosthetic heart valve cavitation in blood

Vapor cavities produced by low pressure fluid flow conditions have been observed in the vicinity of mechanical heart valves for many years. As cavities collapse during pressure recovery, they can produce stresses large enough to cause pitting of the valve occluders and lysing or activation of blood cells. To date, no method has been presented for the quantification of mechanical heart valve cavitation in blood because it has only been detected optically in transparent blood analog fluids. This paper describes a novel method for quantifying cavitation intensities in opaque fluids such as blood. It is based on the detection of high frequency pressure oscillations (35-350 kHz) at a location 4.5 cm proximal to a Björk-Shiley monostrut mitral valve in a mock circulatory loop driven by a Penn State Electric Ventricular Assist Device. The pressure oscillations which result from cavity collapse are used to quantify cavitation intensities in blood. One time domain and three frequency domain parameters have been developed to quantify cavitation intensity during a single valve closure event and over an ensemble of closure events. The time domain parameter is the Root Mean Squared (RMS) value of the pressure signal after it has been high-pass filtered at 35 kHz. The other three parameters are derived from the power spectrum of the pressure signal. One is the maximum value of the power spectrum between 100 and 200 kHz, another is the area under the power spectrum between 35 and 400 kHz, and the last is the volume under a 3-dimensional time vs. frequency vs. power spectrum plot. The parameters are averaged over a random sample of pressure traces to determine an average cavitation intensity for each operating condition studied. In addition, cavitation pressure fluctuations and hemolysis rates were determined simultaneously at several different mock flow loop operating conditions using porcine blood, and the relationships between various measures of cavitation intensity and the associated index of hemolysis have been established. Hemolysis was shown to increase with cavitation intensity.

Hormone production by the postmenopausal ovary in cases of benign ovarian neoplasia

OBJECTIVE

The objective of this study was to determine whether hormone production by postmenopausal ovaries containing benign ovarian tumors differed from that of normal postmenopausal ovaries.

STUDY DESIGN

The sera of 32 postmenopausal patients were assayed before and after bilateral oophorectomy for estrone, 17 beta-estradiol, androstenedione, testosterone, and dehydroepiandrosterone sulfate. The data from all patients as a group were analyzed, followed by analysis of the data from 15 patients with normal ovaries separately from the remaining 17 patients who had nonfunctioning, benign ovarian tumors.

RESULTS

For patients with benign ovarian tumors there was a statistically significant drop in estrone (from a presurgical level of 55.8 +/- 46.3 pg/ml to a postoperative level of 29.9 +/- 10.2 pg/ml, p < 0.03) and 17 beta-estradiol (from 18.6 +/- 14.1 pg/ml preoperatively to 9.8 +/- 3.8 pg/ml postoperatively, p < 0.02). For postmenopausal woman with normal ovaries there was no significant drop in estrone or 17 beta-estradiol after bilateral oophorectomy. There was a statistically significant drop in testosterone and androstenedione after bilateral oophorectomy both for women with normal ovaries and for those with benign tumors. No significant differences in dehydroepiandrosterone sulfate were noted in either group.

CONCLUSIONS

These data suggest that, although normal postmenopausal ovaries have not been demonstrated to secrete clinically significant amounts of estrogen, those that contain benign ovarian tumors do secrete small but significant amounts of estrone and 17 beta-estradiol. Both tumor-containing and normal ovaries secrete the androgens androstenedione and testosterone, this secretion not being significantly influenced by the presence of a tumor.

Determination of principal reynolds stresses in pulsatile flows after elliptical filtering of discrete velocity measurements

The purpose of this study was to develop a method to accurately determine mean velocities and Reynolds stresses in pulsatile flows. The pulsatile flow used to develop this method was produced within a transparent model of a left ventricular assist device (LVAD). Velocity measurements were taken at locations within the LVAD using a two-component laser Doppler anemometry (LDA) system. At each measurement location, as many as 4096 realizations of two coincident orthogonal velocity components were collected during preselected time windows over the pump cycle. The number of realizations was varied to determine how the number of data points collected affects the accuracy of the results. The duration of the time windows was varied to determine the maximum window size consistent with an assumption of pseudostationary flow. Erroneous velocity realizations were discarded from individual data sets by implementing successive elliptical filters on the velocity components. The mean velocities and principal Reynolds stresses were determined for each of the filtered data sets. The filtering technique, while eliminating less than 5 percent of the original data points, significantly reduced the computed Reynolds stresses. The results indicate that, with proper filtering, reasonable accuracy can be achieved using a velocity data set of 250 points, provided the time window is small enough to ensure pseudostationary flow (typically 20 to 40 ms). The results also reveal that the time window which is required to assume pseudostationary flow varies with location and cycle time and can range from 100 ms to less than 20 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Excessive estradiol secretion in polycystic ovarian disease

Polycystic ovarian disease is both a hyperestrogenic and a hyperandrogenic syndrome, and all studies have shown that hyperestrogenemia is the result of an elevation of estrone with plasma estradiol levels in the normal follicular range. Because a literature search failed to reveal any report of polycystic ovarian disease with significantly elevated estradiol levels, we report a case in which the plasma estradiol was so massively elevated as to mimic an estrogen-producing neoplasm. This case also suggests that although polycystic ovarian disease is a very rare cause of such excessive estradiol production, it should be included in the differential diagnosis of estrogen-producing neoplasms.

Relative blood damage in the three phases of a prosthetic heart valve flow cycle

Blood flow through a prosthetic heart valve operating in a ventricular assist device can be subdivided into three phases: a) forward flow through an open valve, b) rapid valve closure, and c) regurgitant back flow through a closed valve. Recent studies of fluid stresses in the Penn State Electric Left Ventricular Assist Device (PS LVAD) operating under physiologic conditions indicate that Reynolds stresses of possibly hemolytic magnitude may exist in the valve area. Although several studies have been made of the fluid stresses seen in forward flow through an open valve, few have looked at valve closure or backflow, and none have related these stresses directly to blood damage. In this study, novel in vitro blood flow loops were developed to allow for the separate analysis of the three flow phases of a Bjork-Shiley monostrut Delrin disk valve operating in a PS LVAD. Forward flow through fully open aortic and mitral valves and backflow through closed valves are studied separately in flow loops driven by a roller pump with the LVAD acting as a valve housing and compliance vessel. Valve closure is investigated with a PS LVAD operating in a low volume mock circulatory loop characterized by cavitation potential through stroboscopic videography of this mock loop, using saline as the working fluid. Rate of hemolysis, characterized by the index of hemolysis, IH, is determined for each of the three flow loops charged with fresh porcine blood.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration of serum pituitary hormone levels in postmenopausal women with stroke

BACKGROUND AND PURPOSE

The aim of this study was to determine if circulating levels of pituitary hormones are altered by stroke and, if so, whether these alterations offer insight into specific neurochemical pathways in the region of the central nervous system injury.

METHODS

Twenty-eight consecutive postmenopausal women undergoing computed tomographic imaging of the brain for evaluation of clinical evidence of stroke underwent blood sampling for determination of serum levels of luteinizing hormone, follicle-stimulating hormone, thyroid-stimulating hormone, triiodothyronine, prolactin, estradiol, and sex hormone--binding globulin.

RESULTS

In stroke involving the caudate, serum levels of luteinizing hormone and follicle-stimulating hormone were reduced to 16% and 24% of concentrations found in those with stroke outside of the basal ganglia (p < 0.03 and p < 0.01, respectively). Levels of estradiol, sex hormone-binding globulin, thyroid-stimulating hormone, and prolactin were similar in all stroke groups. Nonspecific biochemical effects of stress that might influence hormone concentrations were assessed by measurement of serum triiodothyronine, the level of which is a sensitive biochemical correlate of disease severity. These levels were not different between stroke groups.

CONCLUSIONS

Stroke involving the caudate nucleus may interrupt neurotransmitter pathways involved in control of secretion of gonadotropins. Peripheral levels of these hormones may serve as a marker for central neurochemical disturbances associated with stroke in specific brain regions.

Comparison of the adrenocorticotropic hormone stimulation test in the follicular and luteal phases of the menstrual cycle

A comparison was made of the ACTH stimulation test in the proliferative and luteal phases of the menstrual cycle in 13 subjects, each of whom served as her own control. The test yielded a 53.9% false-positive rate in the luteal phase. The study, therefore, clearly shows that from a practical, clinical point of view, the test is completely unreliable in the luteal phase, and is only valid when carried out in the follicular phase of the cycle.

Mean velocities and Reynolds stresses within regurgitant jets produced by tilting disc valves

Fluid velocities were measured with a two-component laser Doppler anemometry system in the regurgitant jet regions of Bjork-Shiley Delrin monostrut tilting disc valves mounted within a Plexiglas model of the 70 cm3 Penn State electric left ventricular assist device. At each measurement location, 250 instantaneous velocity realizations were collected at times when regurgitation through the valves occurred. The maximum Reynolds shear and normal stresses were calculated after filtering the data. Results show that Reynolds shear and normal stresses proximal to the mitral valve were elevated to magnitudes of 9,000 dynes/cm2 and 20,000 dynes/cm2, respectively. The peak Reynolds stresses near the mitral valve occurred during early systole, when regurgitant jet velocities reached magnitudes as high as 440 cm/sec. The Reynolds shear and normal stresses proximal to the aortic valve reached magnitudes of 9,900 dynes/cm2 and 20,500 dynes/cm2, respectively. The peak Reynolds stresses near the aortic valve occurred during early diastole, when regurgitant jet velocities were as high as 280 cm/sec. These high Reynolds stresses created by turbulent regurgitant flow have the potential to cause significant blood damage.

Real-time in vitro observation of cavitation in a prosthetic heart valve

A technique for real-time in vitro observation of cavitation on a prosthetic heart valve operating in a ventricular assist device under normal physiologic conditions has been developed. Considering the documented observation of cavitation erosion in heart valve components from human explants, and the potential risk of blood damage that cavitation presents, the technique developed in this study may prove useful in the design of prosthetic heart valves and ventricular assist devices. Cavitation of a glycerol blood analog fluid has been documented for a Medtronic/Hall prosthetic heart valve operating in a Penn State Electric Ventricular Assist Device. The ventricular assist device was operated in a mock circulatory system under normal physiologic conditions. The valve was located in the mitral position, with the cavitation occurring on the inlet side after valve closure. Bubble cavitation was seen on the valve occluder face, and vortex cavitation was observed at two locations in the vicinity of the valve occluder and housing. The cavity growth and collapse cycle for these forms of vaporous cavitation was less than 1 msec. Stroboscopic photography and stroboscopic videography with frame grabbing were used to document the cavity life cycle. With beat rate held constant, the cavity duration time was found to decrease with increasing mean venous return pressure.

Serum estradiol as an aid in the diagnosis of ectopic pregnancy

The value of serum beta-hCG measurement in the diagnosis of ectopic pregnancy is well established, and there have been recent studies on the use of serum progesterone levels. However, we have been unable to find any reports on the potential application of serum estradiol (E2) assays in the diagnosis of ectopic pregnancy. We therefore concurrently measured serum E2, progesterone, and beta-hCG in 100 women with ectopic pregnancies, as well as in 69 controls with normal intrauterine pregnancies and 36 women with threatened abortion. The mean (+/- standard deviation) E2 levels for ectopic-pregnancy patients, the normal controls, and the women with threatened abortion were 281.1 +/- 115.6, 788.2 +/- 45.5, and 788.8 +/- 40.6 pg/mL, respectively; the mean levels in the ectopic group were significantly different (P less than .0001) from those of the other two groups. All but one of the ectopic pregnancies had values below 650 pg/mL for E2 and 23 ng/mL for progesterone, and all but one of the normal intrauterine pregnancies had values above these levels. Our data suggest that the addition of the estradiol assay, with or without progesterone, to the early evaluation of patients suspected of having an ectopic pregnancy may be helpful in diagnosis.

Estimation of Reynolds stresses within the Penn State left ventricular assist device

Fluid velocities were measured using a two-component laser Doppler anemometery (LDA) system at 129 locations within a Plexiglas model of a 70 cm3 Penn State electric Left Ventricular Assist Device (LVAD). The LVAD was driven by a pulsatile piston pump acting on an attached segmented polyurethane diaphragm. Bjork-Shiley tilting disc valves were used to provide unidirectional flow through the inlet and outlet ports. A seeded blood analog fluid, which matched the kinematic viscosity of blood at high shear rates and the refractive index of Plexiglas, was used to make the measurements. At each location, 250 instantaneous velocity realizations were collected at eight instances during the pump cycle. The maximum Reynolds shear and normal stresses were calculated for each pump cycle time and location after filtering the data. The results reveal that the highest Reynolds shear and normal stresses occur in the near wall region just proximal to the aortic valve during diastole, and reach values of 5,300 dynes/cm2 and 10,800 dynes/cm2, respectively. The elevated turbulent stresses are observed during the period of regurgitant flow through the aortic valve, with peak stress values arising during the period of peak regurgitant flow. This supports the hypothesis that a regurgitant turbulent jet is formed near the wall of the prosthetic aortic valve and may be contributing to blood damage.

On the determination of input sound frequencies by the auditory central processor

There are two schools of thought with regard to how the auditory central processor achieves good frequency resolution. The first is based on the steep 300 dB/oct rolloff; the second on the fact that the action potential (AP) output of neurons associated with hair cells is partially synchronized to the incoming fin or its subharmonics. The main objection to this proposal is that synchronization seems to fail for high-frequency audio inputs. It is shown that this failure may be due to experimental difficulties. It is impossible to avoid trauma to the cochlea and/or auditory nerve. To study synchronization at 10,000 Hz, the interspike-interval (ISI) histogram requires a timing accuracy of 4 microseconds or better despite input AP's that have a rise time of 200 microseconds. Synthetic AP ISI histograms are derived for a) unstimulated; b) fully synchronized; c) low-frequency; and d) high-frequency audio input conditions. The latter are compared with typical experimentally derived data. Hypothetical processing by reverberatory neurons is also considered.

First prenatal visit glucose screening

In order to determine the benefit of glucose screening at different stages of pregnancy, a prospective study of 999 patients was performed. All the patients underwent a nonfasting glucose screen at their first prenatal visit. This screen consisted of an oral 50 gm glucose load followed by a 1 hour serum glucose determination. If the glucose result was 130 mg/dl or higher, a 3-hour oral glucose tolerance test was performed at that time. There were 228, 354, 122, and 295 patients with gestational ages less than 14 weeks, 14 to 23 weeks, 24 to 28 weeks, and more than 28 weeks, respectively. The group less than 24 years of age had a significantly lower mean screening glucose value (106.1 +/- 35.9 mg/dl) than the group whose age was 24 years or older (117.4 +/- 35.9 mg/dl). There were significantly fewer patients with elevated screening glucose values when the patients were less than 24 years of age. Nevertheless, in the final analysis, 13% of the gestational diabetics diagnosed were in the age group younger than 24 years. Although the majority of the diagnosed gestational diabetic had elevated screening glucose values after 23 weeks of gestation, 33% had positive screening tests before 24 weeks. Earlier glucose screening, regardless of maternal age or gestational age, can lead to an earlier diagnosis of gestational diabetes. Cost of universal screening, regardless of maternal age, is only slightly more expensive than a screening protocol with a minimum age limit.

Hot-film wall shear probe measurements inside a ventricular assist device

Wall shear rates at eleven sites within the Penn State Electric Ventricular Assist Device (EVAD) were determined with the pump operating under conditions of 30 and 50 percent systolic duration and a mean flow rate of 5.8 L/min using a flush-mounted hot-film probe. Probe calibrations were performed with the hot-film in two orientations relative to the flow direction: a standard orientation and an orientation in which the hot-film was rotated by 90 deg from the standard orientation. The magnitude and direction of the wall shear stress at each site within the EVAD were estimated from ensemble averaged voltage data recorded for similar standard and rotated film orientations. The results indicate that, during diastole the wall shear stress direction around the pump's periphery for both operating conditions is predominantly perpendicular to the inflow-outflow plane (in the direction of the pusher plate motion) and reaches a peak value of approximately 350 dynes/cm2. The highest wall shear stresses were found near the prosthetic aortic valve (inside the EVAD) under the 30 percent systolic duration condition and are estimated to be as high as 2700 dynes/cm2. Peak shear stress values of 1400 dynes/cm2 were observed in the vicinity of the prosthetic mitral valve under both operating conditions. The results suggested that the valve regions are substantially more hemolytic than other wall regions of the EVAD; the magnitudes of the wall shear stresses are sensitive to operating conditions; and that wall shear in the direction of pusher plate motion can be significant.

Workplace democracy and worker health: strategies for implementation

A large body of literature documents that increased worker participation leads to improvements in the working environment. This article identifies the Swedish and Norwegian sources of some of this research and notes the link with social policy, namely, legislative reform in those countries. In contrast, the United States has resisted legislative solutions, but that may be changing. New strategies to democratize the workplace are a result of global economic competition, desire to reduce job stress and compensation costs, and more successful application of new technologies at work. These are examined and some conclusions are drawn about next stages in the reform efforts.

Comparison of the adrenocorticotropic hormone stimulation test with and without prior dexamethasone suppression in the diagnosis of congenital adrenal hyperplasia

A comparison was made of the ACTH stimulation test with and without prior dexamethasone suppression in 10 patients, each of whom served as her own control. It was found that it is not necessary to administer DEX before the test, the specificity and sensitivity of both tests being the same in the diagnosis of CAH, although the calculated values are lower when DEX is given. Further investigation with HLA typing and ACTH stimulation testing is necessary to establish whether either or both types of ACTH stimulation tests are capable of discriminating between the heterozygotic and homozygotic varieties of CAH.