Neurotensin-induced bursting of cholinergic basal forebrain neurons promotes gamma and theta cortical activity together with waking and paradoxical sleep.

Cholinergic basal forebrain neurons have long been thought to play an important role in cortical activation and behavioral state, yet the precise way in which they influence these processes has yet to be fully understood. Here, we have examined the effects on the electroencephalogram (EEG) and sleep-wake state of basal forebrain administration of neurotensin (NT), a neuropeptide that has been shown in vitro to potently and selectively modulate the cholinergic cells. Microinjection of (0.1-3.0 mm) NT into the basal forebrain of freely moving, naturally waking-sleeping rats produced a dose-dependent decrease in delta ( approximately 1-4 Hz) and increase in both theta ( approximately 4-9 Hz) and high-frequency gamma activity (30-60 Hz) across cortical, areas with no increase in the electromyogram. These EEG changes were accompanied by concomitant decreases in slow wave sleep (SWS) and transitional SWS (tSWS), increases in wake, and most remarkably, increases in paradoxical sleep (PS) and transitional PS (tPS), despite the virtual absence of SWS. The effects were attributed to direct action on cholinergic neurons as evidenced by selective internalization of a fluorescent ligand, Fluo-NT, in choline acetyltransferase (ChAT)-immunoreactive cells and stimulation by NT of bursting discharge in juxtacellularly recorded, Neurobiotin-labeled, ChAT-immunoreactive neurons. We conclude that NT-induced rhythmic bursting of cholinergic basal forebrain neurons stimulates rhythmic theta oscillations and gamma across the cerebral cortex. With the selective action of NT on the cholinergic cells, their bursting discharge promotes theta and gamma independent of motor activity and thereby also stimulates and enhances PS.

Effects of glutamate agonist versus procaine microinjections into the basal forebrain cholinergic cell area upon gamma and theta EEG activity and sleep-wake state.

Serving as the ventral, extra-thalamic relay from the brainstem reticular activating system to the cerebral cortex, basal forebrain neurons, including importantly the cholinergic cells therein, are believed to play a significant role in eliciting and maintaining cortical activation during the states of waking and paradoxical sleep. The present study was undertaken in rats to examine the effects upon electroencephalogram (EEG) activity and sleep-wake state of inactivating basal forebrain neurons with microinjections of procaine versus activating them with microinjections of agonists of glutamate, which is the primary neurotransmitter of the brainstem reticular activating system. Microinjections into the basal forebrain were performed using a remotely controlled device in freely moving, naturally sleeping/waking rats during the day when they are asleep the majority of the time. Procaine produced a decrease in gamma (30-60 Hz) and theta (4-8 Hz) EEG activities, and an increase in delta (1-4 Hz) associated with a loss of paradoxical sleep, despite the persistence of slow wave sleep. alpha-Amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and N-methyl-D-aspartate (NMDA) produced an increase in gamma and a decrease in delta, while eliciting waking. In addition, NMDA, which has been shown in vitro to induce rhythmic bursting in the cholinergic cells, significantly increased theta activity. Following the microinjections of NMDA, c-Fos protein, which has been shown to reflect neural activity, was found in numerous cholinergic, and also GABAergic (gamma-aminobutyric acid) and other non-cholinergic neurons, in the substantia innominata and magnocellular preoptic nucleus near the microinjection cannulae. These results substantiate the role of cholinergic, possibly together with other, basal forebrain neurons in cortical activation, including elicitation of gamma and theta activities that underlie cortical arousal during waking and paradoxical sleep.

Bidirectional superior cavopulmonary anastomosis improves mechanical efficiency in dilated atriopulmonary connections.

OBJECTIVE: Few therapeutic options exist for patients with failing dilated atriopulmonary connections. We addressed the hypothesis that a bidirectional superior cavopulmonary anastomosis will improve the hemodynamic efficiency of dilated atriopulmonary connections while maintaining physiologic pulmonary flow distributions. METHODS: Dilated atriopulmonary connections with and without a bidirectional superior cavopulmonary anastomosis were created in explanted sheep heart preparations and transparent glass models. A mechanical energy balance and flow visualization were performed for 6 flow rates (1-6 L/min), both with and without the bidirectional superior cavopulmonary anastomosis, and were then compared. A novel contrast echocardiographic technique was used to quantify inferior vena cava flow (hepatic venous return) distributions into the pulmonary arteries. RESULTS: The rate of fluid-energy dissipation was 52% +/- 14% greater in the dilated atriopulmonary anastomosis than in the bidirectional superior cavopulmonary anastomosis model over the range of flow rates studied (P = 6.3E(-3)). Total venous return passing to the right pulmonary artery increased from 41% +/- 2% to 47% +/- 3% (P = 9.7E(-3)) and that for inferior vena cava flow decreased from and 42% +/- 3% to 12% +/- 4% (P = 3.3E(-4)) after addition of the bidirectional superior cavopulmonary anastomosis. Flow visualization confirmed more ordered atrial flow in the bidirectional cavopulmonary anastomosis model, resulting from a reduction of caval flow stream collision and interaction. CONCLUSIONS: A bidirectional cavopulmonary anastomosis reduces fluid-energy dissipation in atriopulmonary connections, provides a physiologic distribution of total flow, and maintains some hepatic venous flow to each lung. This approach may be a technically simple alternative to atriopulmonary takedown procedures and conversions to total cavopulmonary connections in selected patients.

Effect of aortic compliance on Doppler diastolic flow pattern in coarctation of the aorta.

The spectral Doppler pattern at the site of an aortic coarctation (CoA) generally displays increased maximal velocity (Vmax) during systole with a slow velocity decay, resulting in the characteristic "sawtooth" pattern. If there is rapid velocity decay, the obstruction is often judged to be mild. The purpose of this study was to investigate if velocity decay is affected by proximal aortic compliance (C(p)). The relation between the velocity decay measured from the Doppler pattern and C(p) was studied with the use of an in vitro pulsatile flow model. The time (tau) between Vmax and 33% Vmax was the measure of velocity decay. The C(p) was varied from 0.7 to 2.6 mL/mm Hg for each of 4 levels of CoA severity. The various obstructions produced a Vmax range of 2.7 to 5.5 m/s. There was a positive linear relation between tau and C(p) (r(2) = 0.76). For a low C(p) (compliance = 0.7 mL/mm Hg), velocity decay was rapid (tau = 0.2 to 0.3 seconds) with no diastolic gradient. For equivalent obstructions, a high C(p) (2.6 mL/mm Hg) produced a persistent diastolic gradient and slow velocity decay (tau = 0.5 to 0.6 seconds). The Doppler pattern across a CoA is affected by C(p). Therefore, the absence of a sawtooth pattern should not exclude the diagnosis of significant CoA obstruction.

Insights into catheter/Doppler discrepancies in congenital aortic stenosis.

Despite inherent discrepancies between Doppler and catheter gradients in aortic stenosis, the simplified Bernoulli equation is still the accepted noninvasive technique to quantitate severity. The Reynolds number is a dimensionless parameter that characterizes the nature of flow as being viscous, turbulent, or transitional. Recently, in vivo and animal studies have successfully used a Reynolds number-based approach to reconcile Doppler-estimated and catheter-measured discrepancies. At the midrange of Reynolds number, pressure recovery effects are most evident, resulting in "overestimation" of catheter gradients by Doppler. At the lower range of the Reynolds number viscous effects are important, whereas at a higher range, turbulent factors are dominant; both result in a tendency toward agreement. We recorded 18 peak instantaneous gradients from dual left ventricular catheters (15 to 95 mm Hg), while simultaneously recording Doppler velocities before and after intervention in 11 pediatric patients (ages 0.5 to 16 years, mean 4.5). Doppler correlated but overestimated catheter-measured peak instantaneous gradients (y = 0.84x + 18.4, r = 0.8, SEE +/- 15.2 mm Hg, mean percent difference 29.9 +/- 36) over the range of catheter gradients measured. Accounting for the Reynolds number successfully collapsed data onto a single curve. Our study confirms in a clinical setting the importance of applying fluid dynamic principles such as the Reynolds number to explain apparent discrepancies between catheter and Doppler gradients. These principles provide a foundation for developing clinically appropriate correction factors.

Fluid dynamic comparison of intra-atrial and extracardiac total cavopulmonary connections.

OBJECTIVE: Extracardiac total cavopulmonary connection has recently been introduced as an alternative to intra-atrial procedures. The purpose of this study was to compare the hydrodynamic efficiency of extracardiac and intra-atrial lateral tunnel procedures in total cavopulmonary connections. METHODS: Intra-atrial lateral tunnel, extracardiac tunnel, and extracardiac conduit with and without caval vein offset were performed on explanted sheep heart preparations and studied in an in vitro flow loop. A rate of fluid-energy dissipation analysis was performed for each model using simultaneous measurement of pressure and flow at each inlet and outlet of the right side of the heart. Preparations were perfused by using a steady flow blood pump at 4 flow indices (1-6 L/min/m 2) with the inferior vena cava carrying 65% of the total venous return. RESULTS: Fluid-power losses were consistently lower for the extracardiac conduit procedure compared with the two tunnel configurations (P <.01). A further reduction in energy dissipation of up to 36% was noted in the extracardiac procedure, with 5 mm offset of the extracardiac conduit toward the distal right pulmonary. The intra-atrial and extracardiac tunnel procedures were least efficient, with losses 73% greater than the optimal extracardiac conduit procedure. CONCLUSIONS: The extracardiac conduit procedure provides superior hemodynamics compared with the intra-atrial lateral tunnel and extracardiac tunnel techniques. This hydrodynamic advantage is markedly enhanced by the use of conduit-superior vena cava offset, particularly at high physiologic flows that are representative of exercise. These data suggest additional rationale for the use of extracardiac conduit procedures for final-stage completion of the Fontan circulation.

REM sleep enhancement and behavioral cataplexy following orexin (hypocretin)-II receptor antisense perfusion in the pontine reticular formation.

Orexin (hypocretin)-containing neurons of the hypothalamus project to brainstem sites that are involved in the neural control of REM sleep, including the locus coeruleus, the dorsal raphe nucleus, the cholinergic zone of the mesopontine tegmentum, and the pontine reticular formation (PRF). Orexin knockout mice exhibit narcolepsy/cataplexy, and a mutant and defective gene for the orexin type II receptor is present in dogs with an inherited form of narcolepsy/cataplexy. However, the physiological systems mediating these effects have not been described. We reasoned that, since the effector neurons for the majority of REM sleep signs, including muscle atonia, were located in the PRF, this region was likely implicated in the production of these orexin-related abnormalities. To test this possibility, we used microdialysis perfusion of orexin type II receptor antisense in the PRF of rats. Ten to 24 hours after antisense perfusion, REM sleep increased two- to three-fold during both the light period (quiescent phase) and the dark period (active phase), and infrared video showed episodes of behavioral cataplexy. Moreover, preliminary data indicated no REM-related effects following perfusion with nonsense DNA, or when perfusion sites were outside the PRF. More work is needed to provide precise localization of the most effective site of orexin-induced inhibition of REM sleep phenomena.

In vitro Doppler assessment of pressure gradients across modified Blalock-Taussig shunts.

The relation between flow velocity and the pressure decrease is evaluated in Blalock-Taussig shunts used in congenital heart surgery and is related to the flow conditions and geometries of the shunts studied. The authors propose that the flow conditions within the shunt as well as shunt dimensions need to be taken into account when using Doppler velocimetry to predict pressure drops across these shunts.

Differential modulation of high-frequency gamma-electroencephalogram activity and sleep-wake state by noradrenaline and serotonin microinjections into the region of cholinergic basalis neurons.

Several lines of evidence indicate that cholinergic basalis neurons play an important role in cortical activation. The present study was undertaken to determine the effect of noradrenergic and serotonergic modulation of the cholinergic neurons on cortical EEG activity and sleep-wake states. The neurotransmitters were injected into the region of the basalis neurons by remote control in freely moving, naturally sleeping-waking rats during the day when the rats are normally asleep the majority of the time. Effects were observed on behavior and EEG activity, including high-frequency gamma activity (30-60 Hz), which has been demonstrated to reflect behavioral and cortical arousal in the rat. Noradrenaline, which has been shown in previous in vitro studies to depolarize and excite the cholinergic cells, produced a dose-dependent increase in gamma-EEG activity, a decrease in delta activity, and an increase in waking. Serotonin, which has been found in previous in vitro studies to hyperpolarize the cholinergic neurons, produced a dose-dependent decrease in gamma-EEG activity with no significant change in amounts of wake or slow wave sleep. Both chemicals resulted in a dose-dependent decrease in paradoxical sleep. These results demonstrate that noradrenaline and serotonin exert differential modulatory effects on EEG activity through the basal forebrain, the one facilitating gamma activity and eliciting waking and the other diminishing gamma activity and not significantly affecting slow wave sleep. The results also confirm that the cholinergic basalis neurons play an important role in cortical activation and particularly in the high-frequency gamma activity that underlies cortical and behavioral arousal of the wake state.

Simultaneous Doppler and catheter transvalvular pressure gradients across St Jude bileaflet mitral valve prosthesis: in vivo study in a chronic animal model with pediatric valve sizes.

A mixture of valve types has been used in previous in vivo studies to assess the accuracy of Doppler echocardiography compared with catheter-measured pressure gradients across prosthetic mitral valves. However, limited data exist regarding the most commonly used bileaflet mechanical valve. We studied 14 sheep with St Jude Medical mechanical mitral valves. Continuous wave Doppler data were obtained across each of the 3 valve orifices. Hemodynamic data were obtained simultaneously by direct measurements with catheters. Valve sizes commonly used in the pediatric population in the mitral position (23 mm, 25 mm, and 27 mm) were studied. Linear regression analyses of Doppler-predicted versus catheter-measured gradients provided correlation coefficients ranging from 0.75 to 0.91. Agreement analysis demonstrated a scatter of Doppler data about the regression line. Although a reasonably good correlation of Doppler-predicted peak and mean pressure gradients across bileaflet mechanical valves exists in the mitral position, caution is needed when this method is applied to patients. Doppler overestimation was greatest across the 23-mm valves. Analyses of the specific orifice interrogated demonstrated higher estimated pressure gradients across the central orifice compared with the side orifices.

Hemodynamic effect of progressive right atrial dilatation in atriopulmonary connections.

OBJECTIVE: Right atrial dilation occurring late after the modified Fontan procedure is frequently associated with low output states, supraventricular arrhythmias, and atrial thrombus formation. We addressed the hypothesis that progressive right atrial dilatation contributes to inefficient right heart flow dynamics. METHODS: Modified atriopulmonary connections were performed on explanted isolated sheep heart preparations with various degrees of surgically induced right atrial dilatation (right atrial volumes 6 to 55 cm3). Flow models were perfused in an in vitro flow loop with the use of a blood analog fluid. A fluid energy balance was performed for six flow rates (1.0 to 6.0 L/min) at each degree of right atrial dilatation, and the rate of total fluid energy loss was calculated and expressed as a function of right atrial volume and flow rate. Effective pressure drop and fluid resistance across the right atrial chamber were also determined for each flow condition. RESULTS: The rate of fluid energy loss increased with increasing right atrial dilatation and flow rate for all conditions studied (p < 0.001). Over the range of right atrial volumes and flow rates examined, the average increase in the rate of energy loss was 3.8- and 117-fold, respectively. Calculated fluid resistance through the right atrium also increased with increasing right atrial volume and flow rate (p < 0.001), exhibiting an average increase of 3.2- and 3.3-fold respectively. CONCLUSIONS: Right atrial dilatation in atriopulmonary connections causes fluid energy losses and increases the energy required to move blood from the venae cavae to the pulmonary arteries. These observations may help explain the progressive nature of late failures of atriopulmonary connections and provide additional rationale for conversion from atriopulmonary connections to lateral tunnel total cavopulmonary connections in selected patients.

Usefulness of combined color Doppler/contrast in providing complete delineation of left ventricular cavity.

Contrast-enhanced 2-dimensional echocardiography without color Doppler did not result in complete filling of the left ventricular cavity in 21 patients studied. However, contrast-enhanced color Doppler was very effective and provided complete opacification of the left ventricular cavity in 20 of these 21 patients.

Potential role of mechanical stress in the etiology of pediatric heart disease: septal shear stress in subaortic stenosis.

OBJECTIVES: The objective of this study was to show elevations in septal shear stress in response to morphologic abnormalities that have been associated with discrete subaortic stenosis (SAS) in children. Combined with the published data, this critical connection supports a four-stage etiology of SAS that is advanced in this report. BACKGROUND: Subaortic stenosis constitutes up to 20% of left ventricular outflow obstruction in children and frequently requires surgical removal, and the lesions may reappear unpredictably after the operation. The etiology of SAS is unknown. This study proposes a four-stage etiology for SAS that I) combines morphologic abnormalities, II) elevation of septal shear stress, III) genetic predisposition and IV) cellular proliferation in response to shear stress. METHODS: Morphologic structures of a left ventricular outflow tract were modeled based on measurements in patients with and without SAS. Septal shear stress was studied in response to changes in aortoseptal angle (AoSA) (120 degrees to 150 degrees), outflow tract convergence angle (45 degrees, 22.5 degrees and 0 degree), presence/location of a ventricular septal defect (VSD) (3-mm VSD; 2 and 6 mm from annulus) and shunt velocity (3 and 5 m/s). RESULTS: Variations in AoSA produced marked elevations in septal shear stress (from 103 dynes/cm2 for 150 degrees angle to 150 dynes/cm2 for 120 degrees angle for baseline conditions). This effect was not dependent on the convergence angle in the outflow tract (150 to 132 dynes/cm2 over full range of angles including extreme case of 0 degree). A VSD enhanced this effect (150 to 220 dynes/cm2 at steep angle of 120 degrees and 3 m/s shunt velocity), consistent with the high incidence of VSDs in patients with SAS. The position of the VSD was also important, with a reduction of the distance between the VSD and the aortic annulus causing further increases in septal shear stress (220 and 266 dynes/cm2 for distances of 6 and 2 mm from the annulus, respectively). CONCLUSIONS: Small changes in AoSA produce important changes in septal shear stress. The levels of stress increase are consistent with cellular flow studies showing stimulation of growth factors and cellular proliferation. Steepened AoSA may be a risk factor for the development of SAS. Evidence exists for all four stages of the proposed etiology of SAS.

Abnormalities of the left ventricular outflow tract associated with discrete subaortic stenosis in children: an echocardiographic study.

OBJECTIVES: The purpose of this study was to examine the echocardiographic abnormalities of the left ventricular outflow tract associated with subaortic stenosis in children. BACKGROUND: Considerable evidence suggests that subaortic stenosis is an acquired and progressive lesion, but the etiology remains unknown. We have proposed a four-stage etiologic process for the development of subaortic stenosis. This report addresses the first stage by defining the morphologic abnormalities of the left ventricular outflow tract present in patients who develop subaortic stenosis. METHODS: Two study groups were evaluated-33 patients with isolated subaortic stenosis and 12 patients with perimembranous ventricular septal defect and subaortic stenosis-and were compared with a size- and lesion-matched control group. Subjects ranged in age from 0.05 to 23 years, and body surface area ranged from 0.17 to 2.3 m2. Two independent observers measured aortoseptal angle, aortic annulus diameter and mitral-aortic separation from previously recorded echocardiographic studies. RESULTS: The aortoseptal angle was steeper in patients with isolated subaortic stenosis than in control subjects (p < 0.001). This pattern was also true for patients with ventricular septal defect and subaortic stenosis compared with control subjects (p < 0.001). Neither age nor body surface area was correlated with aortoseptal angle. A trend toward smaller aortic annulus diameter indexed to patient size was seen between patients and control subjects but failed to achieve statistical significance (p = 0.08). There was an excellent interrater correlation in aortoseptal angle and aortic annulus measurement. The mitral-aortic separation measurement was unreliable. Our results, specifically relating steep aortoseptal angle to subaortic stenosis, confirm the results of other investigators. CONCLUSIONS: This study demonstrates that subaortic stenosis is associated with a steepened aortoseptal angle, as defined by two-dimensional echocardiography, and this association holds in patients with and without a ventricular septal defect. A steepened aortoseptal angle may be a risk factor for the development of subaortic stenosis.

A new method for assessment of changes in retinal blood flow.

This study validates the use of residence time distribution (RTD) functions in human subjects to assess changes in retinal flow by using the widely recognized model of flow changes due to oxygen breathing. Changes in retinal blood flow may provide important information for clinical decision-making in several populations, including those with diabetic retinopathy, sickle cell disease and retinitis pigmentosa. Normal volunteer subjects were studied before and after oxygen breathing. After i.v. injection, relative fluorescence was obtained using scanning laser ophthalmoscopy/image processing in all vessel branches (average, 17). For each experiment, 64 frames (2/s) were digitized and were normalized using the RTD method. Vessel diameters were measured using densitometry techniques on fundus photos, where the diameter data made it possible to weight each vessel according to relative cross-sectional area to obtain a true mean circulation time (MCT). MCT increased for the group of subjects when breathing oxygen compared to normal air (P = 0.001), representing a decrease in retinal blood flow. Average MCT increased 2.82 +/- 2.51 s for all subjects, with an increase of 2.93 +/- 2.26 s in repeat trials for one subject. The proposed method uses information from all retinal vessels and allows the assessment of overall, as well as selected, regional retinal flow. It is more comprehensive than previous methods analysing single vessel flow. This method will be potentially useful for assessing hemodynamic changes in the retina associated with a wide range of eye disease.

High-frequency gamma electroencephalogram activity in association with sleep-wake states and spontaneous behaviors in the rat.

The occurrence of high-frequency gamma activity (30-60 Hz) and its relationship to other frequency band activities were examined by spectral analysis of the electroencephalogram in association with sleep wake states and spontaneous behaviors in the rat. In the electroencephalogram, gamma wave activity was evident in unfiltered and high-frequency filtered recordings, in which it was prominent during attentive or active Wake episodes and during Paradoxical Sleep, when theta-like activity was also apparent. In amplitude spectra from these episodes, multiple peaks were evident within the gamma frequency band, indicating broad-band high-frequency activity, in association with a single low-frequency peak in the theta band. gamma peaks were attenuated during quiet Waking, in association with a low-frequency peak between theta and delta, and during Slow Wave Sleep, in association with a low-frequency peak in the delta band. In coherence spectra from ipsilateral cortical leads, peaks were also present within the gamma range and were significantly higher in Waking moving and Paradoxical Sleep than in Waking quiet and Slow Wave Sleep. In measures of frequency band amplitude, gamma activity (30.5-58.0 Hz) varied significantly across the sleep waking cycle, being similarly high during Wake and Paradoxical Sleep and lowest during Slow Wave Sleep. Across these states, gamma was negatively correlated with delta (1.5-4.0 Hz). In contrast, high beta (19.0-30.0 Hz) was significantly lower in Wake than in Slow Wave Sleep and was positively correlated with delta. gamma differed significantly across specific behaviors, being highest in Paradoxical Sleep with twitches and during Waking eating and moving behaviors, slightly lower in Waking attentive, lower in Waking grooming and as low in Waking quiet as during Slow Wave Sleep. These results indicate that the reciprocal variation of high-frequency gamma activity (and not beta) with low-frequency delta activity reflects the sleep waking cycle of the rat. Moreover, gamma activity reflects the degree of behavioral arousal, since it is high during active Waking, when the electromyogram is high, and low during quiet Waking, when the electromyogram is low. It also reflects cortical arousal, independent of motor activity, since it attains high levels in association with attentive immobility and maximal levels only during particular active behaviors (eating and moving and not grooming), and it also attains maximal levels during Paradoxical Sleep, when the nuchal electromyogram is minimal, but small twitches evidence dreaming. The co-variation of gamma and a slow oscillation in the theta band across states and behaviors suggests that a common system may modulate these fast and slow electroencephalogram rhythms, and that such modulation, potentially emanating from the basal forebrain, could predominate during certain states or behaviors, such as Paradoxical Sleep.

Turbulent/viscous interactions control Doppler/catheter pressure discrepancies in aortic stenosis. The role of the Reynolds number.

BACKGROUND: Despite good correlation between Doppler and catheter pressure drops in numerous reports, it is well known that Doppler tends to apparently overestimate pressure drops obtained by cardiac catheterization. Neither (1) simplification of the Bernoulli equation nor (2) pressure recovery effects can explain this dilemma when taken alone. This study addressed the hypothesis that a Reynolds number-based approach, which characterizes (1) and (2), provides a first step toward better agreement of catheter and Doppler assessments of pressure drops. METHODS AND RESULTS: Doppler and catheter pressure drops were studied in an in vitro model designed to isolate the proposed Reynolds number effect and in a sheep model with varying degrees of stenosis. Doppler pressure drops in vitro correlated with the directly measured pressure drop for individual valves (r = .935, .960, .985, .984, .989, and .975) but with markedly different slopes and intercepts. A Bland-Altman type plot showed no useful pattern of discrepancy. The Reynolds number was successful in collapsing the data into the profile proposed in the hypothesis. Parallel results were found in the animal model. CONCLUSIONS: Apparent overestimation of net pressure drop by Doppler is due to pressure recovery effects, and these effects are countered by both viscous effects and inertial/turbulent effects. Only by reconciliation of discrepancies by use of a quantity such as Reynolds number that embodies the relative importance of competing factors can the noninvasive and invasive methods be connected. This study shows that a Reynolds number-based approach accomplishes this goal both in the idealized in vitro setting and in a biological system.

Insights from three-dimensional echocardiographic laser stereolithography. Effect of leaflet funnel geometry on the coefficient of orifice contraction, pressure loss, and the Gorlin formula in mitral stenosis.

BACKGROUND: Three-dimensional echocardiography can allow us to address uniquely three-dimensional scientific questions, for example, the hypothesis that the impact of a stenotic valve depends not only on its limiting orifice area but also on its three-dimensional geometry proximal to the orifice. This can affect the coefficient of orifice contraction (Cc = effective/anatomic area), which is important because for a given flow rate and anatomic area, a lower Cc gives a higher velocity and pressure gradient, and Cc, routinely assumed constant in the Gorlin equation, may vary with valve shape (60% for a flat plate, 100% for a tube). To date, it has not been possible to study this with actual valve shapes in patients. METHODS AND RESULTS: Three-dimensional echocardiography reconstructed valve geometries typical of the spectrum in patients with mitral stenosis: mobile doming, intermediate conical, and relatively flat immobile valves. Each geometry was constructed with orifice areas of 0.5, 1.0 and 1.5 cm2 by stereolithography (computerized laser polymerization) (total, nine valves) and studied at physiological flow rates. Cc varied prominently with shape and was larger for the longer, tapered dome (more gradual flow convergence proximal and distal to the limiting orifice): for an anatomic orifice of 1.5 cm2, Cc increased from 0.73 (flat) to 0.87 (dome), and for an area of 0.5 cm2, from 0.62 to 0.75. For each shape, Cc increased with increasing orifice size relative to the proximal funnel (more tubelike). These variations translated into important differences of up to 40% in pressure gradient for the same anatomic area and flow rate (greatest for the flattest valves), with a corresponding variation in calculated Gorlin area (an effective area) relative to anatomic values. CONCLUSIONS: The coefficient of contraction and the related net pressure loss are importantly affected by the variations in leaflet geometry seen in patients with mitral stenosis. Three-dimensional echocardiography and stereolithography, with the use of actual information from patients, can address such uniquely three-dimensional questions to provide insight into the relations between cardiac structure, pressure, and flows.

How sensitive are jet centerline velocities to an opposing flow? Implications for using the centerline method to quantify regurgitant jet flow.

A method for quantifying peak mitral and tricuspid regurgitant jet flow rate that utilizes a measure of jet orifice velocity (Uo, m s-1), a distal centerline velocity (Um, m s-1), and the intervening distance (X, cm) was recently developed. This method, however, modeled the regurgitant jet as a free jet, whereas many atrial jets are counterflowing jets because of jet opposing intra-atrial flow fields (counterflows). This study evaluated the feasibility of using the free jet quantification equation in the atrium where ambient flow fields may alter jet centerline velocities and therefore reduce the accuracy of jet flow rate calculations. A 4 cm wide chamber was used to pump counterflows of 0, 4, and 22 cm s-1 against jets of 2.3, 4.8, and 6.4 s-1 originating from a 2 mm diameter orifice. For each counterflow-jet combination, jet centerline velocities were measured using laser Doppler anemometry. For free jets (no counterflow), flow rate was calculated with 98% mean accuracy. For all jets in counterflow, the calculation was less accurate as (i) the ratio of jet orifice velocity to counterflow velocity decreased (Uo/Uc, where Uc is counterflow velocity), i.e. the counterflow was relatively more intense, an (ii) centerline measurements were mad further from the orifice. But although counterflow lowered jet centerline velocities beneath free jet values, it did so only significantly in the jet's distal portion, while the initial portion (X/D < 16, where D is jet orifice diameter) of a jet in counterflow behaved essentially as a free jet. Therefore, regurgitant jets, although not classically free because of systolic atrial inflow, will decay in their initial portions as free jets and hence are candidates for quantification with the centerline technique.

Influence of stenotic valve geometry on measured pressure gradients and ventricular work: the relationship between morphology and flow.

The physiologic impact of aortic valve stenosis is most directly reflected by an increased workload placed on the ventricle. In the pediatric population the morphology of aortic stenosis varies considerably. Fluid dynamic principles suggest that different morphologies may require the ventricle to accelerate blood to different maximal velocities for constant cardiac outputs and valve areas, resulting in different ventricular workloads. This study examined this important concept in in vitro models designed to isolate the effect of valve geometry on distal velocity, pressure gradients, and proximal work. Four stenotic valve morphologies were examined using a variable-voltage pump system. For constant orifice areas and flows, markedly different workloads were required by the pump, and this difference was reflected in direct measurements of pressure gradient and Doppler predictions of gradient. These fundamental fluid dynamic studies isolate the relationship between flow, work, and stenotic valve morphology. Different orifice geometries affect the value of the coefficient of contraction, which is reflected in different maximum velocity values for stenosis with constant anatomic areas and flows. The proximal pumping chamber must generate different levels of force to achieve these different velocities, and this variability is reflected in the clinically measured pressure gradient.