Incomplete functional reverse remodelling of the left ventricle one year after bariatric surgery. Insights from the prospective FatWest study

Background

Patients with severe obesity are predisposed to development of left ventricular (LV) hypertrophy with subsequent increased myocardial oxygen demand and impaired myocardial function. Bariatric surgery leads to rapid weight loss and improves cardiovascular risk profile.

Purpose

To assess whether LV systolic function, wall mechanics, and cardiac power improve 1 year after bariatric surgery.

Methods

91 severely obese patients (43±10 years, 70% women, body mass index [BMI] 41.7±4.9 kg/m2, 55% with hypertension, 17% with diabetes mellitus) underwent echocardiography before, 6 and 14 months after Roux-en-Y gastric bypass surgery in the prospective FatWest (Bariatric Surgery on the West Coast of Norway) study. We assessed LV systolic function by biplane ejection fraction (EF), LV wall mechanics by midwall shortening (MWS) and global longitudinal strain (GLS), and cardiac power normalized for LV mass by 0.222 x cardiac output x mean blood pressure (BP)/LV mass.

Results

Surgery induced a significant reduction in BMI, heart rate, systolic BP, and LV mass (Figure 1). Prevalence of LV hypertrophy fell from 34 to 20% 14 months after surgery (p<0.001), while that of concentric geometry remained stable: 8 vs 10% (p=0.36). GLS improved by 28%, however LV EF and MWS did not change (Figure 2). LV power at rest decreased postoperatively, reflecting the lower BP and heart rate, but was unaltered when normalized for LV mass (Figure 2). In backward stepwise multivariate regression analyses, 1 year improvement in GLS was predicted by the systolic BP reduction (p<0.05) (R2 0.73, p<0.001), while low 1-year MWS was independently associated with female gender, concentric geometry and higher myocardial oxygen demand (all p<0.01) (Nagelkerke R2 0.44, p<0.001), and lower 1-year LV power-mass with female gender and LV hypertrophy (p<0.01) (R2 0.24, p<0.001).

Conclusion

In severely obese patients, LV longitudinal function normalizes 1 year after bariatric surgery, mainly due to the BP reduction. LV midwall mechanics and power do not improve, especially in women and patients with persistent LV geometric abnormalities.

Funding Acknowledgement

Type of funding sources: None. Figure 1Figure 2

Does number of volumes affect regional deformation measurements when using volume stitched 3D speckle tracking?

Funding Acknowledgements

Type of funding sources: None.

Background

Optimal 3D speckle tracking echocardiography (STE) requires volume stitching, a technique prone to errors, such as patient movements, respiration and arrhythmias. With different resolution at different depths (Figure 1A), such errors may cause stitching artefacts that affect STE derived deformation measurements at different levels of the left ventricle.

Methods

In this cross-sectional study, 62 patients with variable degree of aortic stenosis participated. 3D images were recorded using 3 different methods (2-, 4- and 6-beat volume stitching at 22 ± 2, 29 ± 4 and 36 ± 6 volumes per second, respectively). Strain, rotation and torsion were analyzed at 3 different levels (basal, mid and apical) (Figure 1B). Results were compared using one-way analysis of variance between methods. Inter-segmental variation was estimated using the coefficient of variation (CV) of the segments involved for each level. Results were interpreted as more accurate if low values of inter-segmental variation between segments in a level was present.

Results

Neither longitudinal strain (LS) nor circumferential strain (CS) showed any difference between methods in the basal level (Table 1). LS was higher in mid and apical level for 2-beat, while CS was higher only in apical level for 2-beat.

Inter-segmental CV showed no significant difference between methods for LS and CS. Between levels, both had higher CV in basal than apical level, but CS had much higher values, indicating lower accuracy in basal level.

Rotation measurements showed negative values in basal level and positive in apical level. None of the methods differed significantly. Torsion showed higher values for 2 beat images only.

Conclusion

3D STE from both 4- and 6 beat images have insignificant differences for strain, as well as low inter-segmental variability. LS is accurate in all levels while CS has high accuracy in apical, and poor in basal level. Both rotation and torsion differ insignificantly when using 4- and 6-beat images.

Table 1 Level Mean ± SD ANOVA P CV 2-beat 4-beat 6-beat 2-beat 4-beat 6-beat Longitudinal strain (%) Basal -17.82 ± 4.83 -16.81 ± 4.48 -17.05 ± 3.56 0.402 34.5 34.9 31.5 Mid -16.34 ± 4.30 -14.91 ± 3.62 -14.46 ± 3.53 0.019 31.4 29.9 29.9 Apical -16.80 ± 4.33 -15.06 ± 3.12 -15.09 ± 3.02 0.008 30.6 28.5 24.9 Circumferential strain (%) Basal -12.93 ± 4.42 -14.16 ± 4.21 -13.05 ± 3.24 0.168 106.7 71.7 74.4 Mid -17.59 ± 3.86 -16.73 ± 3.56 -16.98 ± 3.51 0.406 43.0 36.9 30.3 Apical -22.14 ± 6.20 -19.04 ± 4.81 -20.32 ± 5.40 0.008 26.8 29.4 23.4 Abstract Figure 1

P1514 Increased myocardial oxygen demand is associated with impaired left ventricular strain in patients with morbid obesity referred for bariatric surgery

Background

Obesity predisposes for left ventricular (LV) hypertrophy and systolic dysfunction. Higher myocardial oxygen demand in LV hypertrophy is associated with higher risk for cardiovascular events, while the association with LV systolic function has been less explored.

Purpose

To assess the association of myocardial oxygen demand with LV systolic function in morbidly obese subjects without known heart disease.

Methods

Clinical and echocardiographic data from 110 obese subjects referred for gastric bypass surgery (mean age 42 ± 11 years, 74% women, mean body mass index [BMI] 41.9 ± 4.8 kg/m², 33% with hypertension, 15% with diabetes) in the prospective FatWest (Bariatric Surgery on the West Coast of Norway) study was used. LV function was assessed by ejection fraction (EF) by Simpson"s biplane method and endocardial global longitudinal strain (GLS) by 2D vector velocity imaging using a 16-segment model (Image Arena 4.6, Tomtec, Unterschleissheim, Germany). Myocardial oxygen demand was estimated from LV mass - wall stress - heart rate product according to a previously validated formula.

Results

Myocardial oxygen demand was higher in men (1884 vs. 1579 x 10³ g x kdyne/cm² x bpm, p < 0.05), and associated with higher BMI (r = 0.24) and pulse pressure (r = 0.28), and with lower EF (r = -0.22) and lower GLS (r = 0.26, all p < 0.05). In multiple regression analysis, higher myocardial oxygen demand was associated with lower LV GLS (Beta = 0.21, p < 0.05) independent of age, gender, BMI, pulse pressure, diabetes, and EF (Table).

Conclusion

In obese patients without known heart disease referred for bariatric surgery, higher myocardial oxygen demand was associated with lower LV systolic function measured by GLS independent of confounders.

Covariates of lower GLS in multivariable Variable β correlation coefficient p LV mass - wall stress - heart rate product (g x kdyne/cm² x bpm x 10³) 0.21 0.04 Age (years) -0.12 0.22 Gender 0.34 <0.01 BMI (kg/m²) 0.25 <0.01 Pulse pressure (mmHg) -0.04 0.71 Diabetes -0.17 0.09 LV EF (%) -0.01 0.90

Effect of fitness on cardiac structure and function in overweight and obesity (the FATCOR study)

BACKGROUND AND AIMS

Obesity is associated with reduced left ventricular (LV) systolic myocardial function. We aimed to explore by means of a cross-sectional study whether this effect is offset in the presence of good fitness.

METHODS AND RESULTS

We studied clinical and echocardiographic data from 469 overweight (body mass index [BMI] >27 kg/m²) and obese (BMI ≥30 kg/m²) women and men without known cardiovascular (CV) disease in the FAT associated CardiOvasculaR dysfunction (FATCOR) study. The participants were grouped according to obesity and sex- and age adjusted peak oxygen uptake, obtained by ergospirometry. LV systolic myocardial function was assessed by peak systolic global longitudinal strain (GLS) measured by speckle tracking echocardiography. The association of fitness with GLS was tested in logistic regression analyses and reported as odds ratio (OR) with 95% confidence interval (CI). In the total study population, participants were 47 years old, 60% were women, and mean BMI was 32.0 kg/m². GLS did not differ between fit and unfit subjects within the overweight and obese groups (both p > 0.05), but the overweight fit group had higher GLS (more negative value) compared to the obese unfit group (-20.1 ± 2.6 vs. -19.0 ± 3.0, p < 0.05). In obese subjects, fitness was associated with higher GLS (OR 0.88 [95% CI 0.79-0.99, p < 0.05) in multivariable logistic regression analysis, independent of significant associations with higher arterial stiffness and lower fat percentage (all p < 0.05). In the overweight group, fitness was not significantly associated with GLS.

CONCLUSION

In obesity, fitness was independently associated with higher GLS, while no association was found in overweight.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.govNCT02805478.

Measured acoustic intensities for clinical diagnostic ultrasound transducers and correlation with thermal index

OBJECTIVES

To investigate if the thermal index for bone (TIB) displayed on screen is an adequate predictor for the derated spatial-peak temporal-average (I_SPTA.3 ) and spatial-peak pulse-average (I_SPPA.3 ) acoustic intensities in a selection of clinical diagnostic ultrasound machines and transducers.

METHODS

We calibrated five clinical diagnostic ultrasound scanners and 10 transducers, using two-dimensional grayscale, color Doppler and pulsed-wave Doppler, both close to and far from the transducer, with a TIB between 0.1 and 4.0, recording 103 unique measurements. Acoustic measurements were performed in a bespoke three-axis computer-controlled scanning tank, using a 200-μm-diameter calibrated needle hydrophone.

RESULTS

There was significant but poor correlation between the acoustic intensities and the on-screen TIB. At a TIB of 0.1, the I_SPTA.3 range was 0.51-50.49 mW/cm² and the I_SPPA.3 range was 0.01-207.29 W/cm² . At a TIB of 1.1, the I_SPTA.3 range was 19.02-309.44 mW/cm² and the I_SPPA.3 range was 3.87-51.89 W/cm² .

CONCLUSIONS

TIB is a poor predictor for I_SPTA.3 and I_SPPA.3 and for the potential bioeffects of clinical diagnostic ultrasound scanners. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Authors' reply Cobb correspondence re: J-E. Gjertsen, S. A. Lie, T. Vinje, et al. More re-operations after uncemented than cemented hemiarthroplasty used in the treatment of displaced fractures of the femoral neck: An observational study of 11 116 hemiarthroplasties from a national register. J Bone Joint Surg [Br] 2012;94-B:1113-1119

We welcome letters to the Editor concerning articles that have recently been published. Such letters will be subject to the usual stages of selection and editing; where appropriate the authors of the original article will be offered the opportunity to reply.

Rome III subgroups of functional dyspepsia exhibit different characteristics of antral contractions measured by strain rate imaging - a pilot study

PURPOSE

Rome III defines two distinct entities of functional dyspepsia (FD), namely epigastric pain syndrome (EPS) and postprandial distress syndrome (PDS). We aimed at studying these subgroups of FD by simultaneously assessing antral strain, gastric accommodation and emptying and visceral hypersensitivity.

MATERIALS AND METHODS

Strain during antral contractions was assessed by ultrasound strain rate imaging in 15 controls and 19 FD patients (8 EPS patients and 11 PDS patients). Gastric accommodation and emptying were assessed using B-mode ultrasonography. Symptoms were assessed by visual analogue scale (VAS).

RESULTS

During fasting, antral strain in EPS patients (mean±SEM) was 61.4 ± 6.4 %, significantly higher than in controls (47.5 ± 3.3 %; p = 0.042) and in PDS patients (28.6 ± 1.7 %; p = 0.001). PDS patients had lower strain than controls (p < 0.001). Postprandially, EPS patients had higher strain than both controls and PDS patients (p < 0.01) but no difference was found between controls and PDS patients. Compared with controls, PDS patients had significantly larger fasting proximal area than controls (14.9 ± 1.6 cm2 vs. 7.8 ± 0.2 cm2; p < 0.001), whereas EPS patients did not differ (12.1 ± 1.9 cm2; p = 0.057). Gastric emptying fraction (1 - proximal area at 40 min postprandially/area at 1 min postprandial × 100) at 40 min postprandially in EPS patients 46.4 ± 6.6 % was lower than in controls (62.9 ± 1.3 %; p = 0.032), but higher than PDS patients (27.4 ± 5.3 %; p = 0.018).

CONCLUSION

Anterior radial strain measured by ultrasound strain rate imaging may discriminate between subgroups of FD and healthy controls. This study supports the Rome III classification of FD into EPS and PDS groups.

More re-operations after uncemented than cemented hemiarthroplasty used in the treatment of displaced fractures of the femoral neck

Using data from the Norwegian Hip Fracture Register, 8639 cemented and 2477 uncemented primary hemiarthroplasties for displaced fractures of the femoral neck in patients aged > 70 years were included in a prospective observational study. A total of 218 re-operations were performed after cemented and 128 after uncemented procedures. Survival of the hemiarthroplasties was calculated using the Kaplan-Meier method and hazard rate ratios (HRR) for revision were calculated using Cox regression analyses. At five years the implant survival was 97% (95% confidence interval (CI) 97 to 97) for cemented and 91% (95% CI 87 to 94) for uncemented hemiarthroplasties. Uncemented hemiarthroplasties had a 2.1 times increased risk of revision compared with cemented prostheses (95% confidence interval 1.7 to 2.6, p < 0.001). The increased risk was mainly caused by revisions for peri-prosthetic fracture (HRR = 17), aseptic loosening (HRR = 17), haematoma formation (HRR = 5.3), superficial infection (HRR = 4.6) and dislocation (HRR = 1.8). More intra-operative complications, including intra-operative death, were reported for the cemented hemiarthroplasties. However, in a time-dependent analysis, the HRR for re-operation in both groups increased as follow-up increased.

This study showed that the risk for revision was higher for uncemented than for cemented hemiarthroplasties.

Ultrasound safety in early pregnancy: reduced energy setting does not compromise obstetric Doppler measurements

OBJECTIVES

We hypothesized that first-trimester Doppler ultrasonography can be carried out at lower output energies than the currently advocated limits without compromising clinically important information.

METHODS

We recruited 42 pregnant women for an ultrasound examination at 12 weeks' gestation. Twenty-one women were examined with a transvaginal transducer, the rest with a transabdominal transducer. We used pulsed Doppler to measure pulsatility index (PI) and peak systolic velocity (PSV) in five clinically relevant fetal and maternal blood vessels. The energy indicator thermal index for bone (TIb) was set at 1.0, 0.5 and 0.1. Each measurement was repeated three times. A mixed linear regression model accounting for correlation between measurements was used to assess the effect of different TIb levels and transducers.

RESULTS

We were able to visualize the vessels by color Doppler and measure PI and PSV in all vessels at all energy levels in all the participants with the exception of the ductus venosus in two participants, yielding 1872 recordings for statistical analysis. A reduction in TIb from 1.0 to 0.5 and 0.1 had no effect on the PI or PSV values, nor was there any trend towards higher parameter variance with decreasing TIb. There was no difference between measured values of PI and PSV between the transducers, but the transabdominal technique was associated with a greater parameter variance.

CONCLUSION

Reliable first-trimester Doppler data can be obtained with output energy reduced to a TIb of 0.5 or 0.1.

Strain measurement during antral contractions by ultrasound strain rate imaging: influence of erythromycin

Strain rate imaging (SRI) is a non-invasive ultrasound (US) modality that enables the study of mechanical deformation (strain) with high spatial and temporal resolution. A total of 244 contractions in seven healthy volunteers were studied by SRI on two separate days to characterize radial strain of antral contractions in the fasting and fed states and to assess the influence of intravenous erythromycin. Gastric accommodation and emptying were assessed by 2D ultrasonography. The perception of hunger was registered by the participants. The strain increased from early to late phase II and phase III activity by (median) 18%, 58% and 82%, respectively, P < 0.05. Erythromycin infusion in phase I induced contractions with median strain of 35%, but did not increase postprandial strain. Both fasting and postprandially, lumen-occlusive contractions with erythromycin were more frequent than in naturally occurring contractions, 69%vs 48%, P = 0.036 and 40%vs 5%, P < 0.001 respectively. All subjects had rumbling in their abdomens when intraluminal air was detected sonographically (85% of all phase III contractions) and that rumbling was perceived by the participant as maximal awareness of hunger. SRI enabled detailed strain measurement of individual antral contractions. Erythromycin initiated fasting antral contractions and increased the number of lumen-occlusive contractions.

A multimodal laser Doppler and endosonographic distension device for studying mechanosensation and mucosal blood flow in the oesophagus

We describe the development of a multimodal device combining bag distension, manometry, high frequency intraluminal ultrasound, laser Doppler flowmetry and symptom registration. Bench tests showed that the different modalities did not influence each other. During bag distension we obtained high quality images of the oesophageal wall for computing biomechanical parameters, and laser Doppler signals showing variation in mucosal perfusion. We conclude that the principle of measurement is sound and that the device can provide a basis for further studies.

An anaesthetic protocol in the young domestic pig allowing neuromuscular blockade for studies of cardiac function following cardioplegic arrest and cardiopulmonary bypass

BACKGROUND

Neuromuscular blockade should, for ethical reasons, not be allowed in animal experiments unless the use is strongly motivated. Beforehand, the anaesthetic protocol must be documented without muscle relaxation in the species studied. Documentation is difficult to obtain from the scientific literature. When focusing on cardiac function over time, in particular, the ideal anaesthetic protocol should cause no or minor alterations in cardiac variables.

METHODS

We intended to document an anaesthetic protocol involving ventilation with N(2)O combined with loading doses and continuous infusions of pentobarbital, fentanyl and midazolam in seven pigs by applying potentially painful stimuli every 15 min for 7 h. Subsequently, left ventricular global and regional function was studied with conductance catheter and strain rate imaging by echocardiography in eight pigs with pancuronium included.

RESULTS

Pigs without pancuronium were completely immobilized and unresponsive to potentially painful stimuli and sternotomy, with no accumulation or degradation of anaesthetic agents. With pancuronium included, left ventricular preload gradually decreased together with reduction of cardiac index from 3.52 +/- 0.14 at 2 h to 2.84 +/- 0.11 L min(-1). m(-2) (+/-SEM) after 7 h of observation. Preload recruitable stroke work decreased after 7 h, whereas peak systolic strain in the anterior left ventricular wall and load-independent indices of diastolic function were not significantly altered.

CONCLUSION

In specific experimental protocols, the anaesthetic protocol described could allow the use of muscular paralysis in young domestic pigs, for instance when involving hypothermic cardiopulmonary bypass, cardioplegic arrest and reperfusion.

The effect of body weight on the degree of blood velocity profile skewness in the aortic annulus in domestic pigs

We investigated the blood velocity profile in the aortic annulus (AA) in two groups of domestic pigs using epicardial Doppler echocardiography. The velocity profile skewness in terms of max/mean TVI (the ratio of maximal to cross-sectional mean time-velocity integral along the diameter) was 1.107 +/- 0.01 in the small pigs (n = 10; body weight: 24.6 +/- 0.8 kg) and 1.216 +/- 0.026 in the large pigs (n = 8; body weight: 50.6 +/- 2.5 kg) (P = 0.002). The velocity profile in the AA is more skewed in large animals than in small animals and the skewness in the larger animals is similar to that in normal adult humans. This study shows the importance of choosing animals of sufficient size if flow method investigations are to be performed. This is particularly important for ultrasound Doppler investigations based on a limited sample of velocities across the flow channel.

Mechanical properties in the human gastric antrum using B-mode ultrasonography and antral distension

The aims of this study were to investigate gastric antral geometry and stress-strain properties by using transabdominal ultrasound scanning during volume-controlled distensions in the human gastric antrum. Seven healthy volunteers underwent stepwise inflation of a bag located in the antrum with volumes up to 60 ml. The stretch ratio and Cauchy stress and strain were calculated from measurements of pressure, diameter, and wall thickness. A second distension series was conducted in three volunteers during administration of the anticholinergic drug butylscopolamine. Analysis of stretch ratios demonstrated positive strain in the circumferential direction, negative strain in the radial direction, and no strain in the longitudinal direction. The stress-strain relation was exponential and did not differ without or with the administration of butylscopolamine. The wall stress was decomposed into its active and passive components. The well-known length-tension diagram from in vitro studies of smooth muscle strips was reproduced. The maximum active tension appeared at a volume of 50 ml, corresponding to a stretch ratio of 1.5. We conclude that the method provides measures of antral biomechanical wall properties and can be used to reproduce the muscle length-tension diagram in humans.

Determination of plasma volume in anaesthetized piglets using the carbon monoxide (CO) method

Based on measurements of the circulating red blood cell volume (V(RBC)) in seven anaesthetized piglets using carbon monoxide (CO) as a label, plasma volume (PV) was calculated for each animal. The increase in carboxyhaemoglobin (COHb) concentration following administration of a known amount of CO into a closed circuit re-breathing system was determined by diode-array spectrophotometry. Simultaneously measured haematocrit (HCT) and haemoglobin (Hb) values were used for PV calculation. The PV values were compared with simultaneously measured PVs determined using the Evans blue technique. Mean values (SD) for PV were 1708.6 (287.3)ml and 1738.7 (412.4)ml with the CO method and the Evans blue technique, respectively. Comparison of PVs determined with the two techniques demonstrated good correlation (r = 0.995). The mean difference between PV measurements was -29.9 ml and the limits of agreement (mean difference +/-2SD) were -289.1 ml and 229.3 ml. In conclusion, the CO method can be applied easily under general anaesthesia and controlled ventilation with a simple administration system. The agreement between the compared methods was satisfactory. Plasma volume determined with the CO method is safe, accurate and has no signs of major side effects.

Velocity distribution in the ascending aorta in pigs during chronotropic and inotropic stimulation

The influence of heart rate, stroke volume and myocardial contractility on temporal and spatial velocity distribution in the ascending aorta was investigated in 10 pigs. A pulsed Doppler ultrasound technique with intraluminal probe and a single crystal connected to a position-sensitive device was used to measure blood velocity. After baseline registration, the heart rate was increased in two discrete steps of 20 beats/min by right atrial pacing. Isoproterenol infusion was given to increase contractility. Finally, without isoproterenol, the heart rate was again raised to the values found during inotropic stimulation. The first three measuring situations did not differ haemodynamically, apart from increased heart rate and reduced stroke volume. Increased heart rates were not associated with significant change in the parameters for skewness of velocity distribution (peak systolic slope and ratio, maximum skewness slope and ratio). During inotropic stimulation the peak left ventricular dP/dt, aortic systolic pressure, cardiac output and stroke volume were greater than at comparable paced heart rate, and the peak systolic slope of velocity distribution was significantly increased. Velocity distribution in the ascending aorta thus was not altered by increased heart rate alone, whereas skewness of distribution was enhanced by increased inotropic drive of the myocardium and the concomitant central and peripheral vascular changes.

In vitro volume estimation of kidneys using three-dimensional ultrasonography and a position sensor

OBJECTIVE

A new 3D ultrasound system using a position sensor based on magnetic scanhead tracking and new software utilising automatic contour tracing between manually traced contours was tested for volume estimation of kidneys in vitro.

METHODS

Kidneys from piglets and pigs were fixed in formaldehyde. A reservoir with 0.9% saline kept at 37 degrees C was used. The kidneys were scanned either by a linear translational movement along the organ or by a tilting movement. The outer contour of the kidneys was traced manually, by two independent investigators. The volume of each kidney was also measured using the Archimedes principle (true volumes).

RESULTS

Good agreement between 3D ultrasound volume estimates and true volumes was found for both probe movements. For translational movement of the transducer, the mean errors between the methods were 4.17 and 4.31 ml for the two independent investigators, and the volume range was 96-203 ml. The corresponding error values for tilting movement were 1.10 and 0.19 ml. The interobserver variation was also small, there was no difference in the volumes obtained by the two investigators, or by the two scanning movements.

CONCLUSION

Volume estimates using this 3D ultrasound method showed very good agreement with true volumes, both mean errors and interobserver variation were low.

In vitro evaluation of three-dimensional ultrasonography based on magnetic scanhead tracking

The objective of this study was to evaluate the accuracy and precision of a magnetic position sensor system for acquisition of three-dimensional (3D) ultrasound images in volume estimation of phantoms in vitro. Installation of either 0.9% solution of saline at 37 degrees C or distilled water at 20 degrees C to a condom was performed. Scanning was performed either by a continuous or stepwise acquisition. This 3D ultrasound system demonstrated good correlation (r = 0.99-1.0, n = 8) between estimated (EV) and true volumes (TV). The errors were in the range 1.3%+/-0.3% (SEM) to 1.9%+/-0.6%, independent of sound velocity. Scanning through a porcine abdominal wall positioned at the fluid surface yielded a systematic underestimation of the volume: mean (EV - TV) = -7.2+/-0.8 ml. Eight repeated scans of the same volume yielded a coefficient of variation of 1.1%. Interobserver error of the tracing procedure was 2.6%+/-0.9%. This 3D ultrasound system gave high accuracy and precision in volume estimation in vitro, and yielded low interobserver error. A change in ultrasound velocity of approximately 60 m/s did not influence the accuracy significantly. Scanning through an abdominal wall underestimated volumes slightly.

Resetting of renal blood autoregulation during acute blood pressure reduction in hypertensive rats

Decrease in systemic blood pressure, duration of pressure decrease, and change in the activity of the renin or the sympathetic nervous system may represent mechanisms involved in resetting the renal blood flow (RBF) autoregulation found in hypertensive rats. Autoregulation of RBF, plasma renin concentration (PRC), and the time needed for resetting to take place were studied in the nonclipped kidney before and after removal of the clipped kidney of two- kidney, one-clip (2K1C) hypertensive rats and before and after mechanical reduction of the renal arterial pressure (RAP) for 10 min in the spontaneously hypertensive rat (SHR) and in the nonclipped kidney of 2K1C hypertensive rats with and without renal denervation. Mean arterial pressure (MAP) fell from 147 to 107 mmHg 30 min after removal of the clipped kidney, and the lower pressure limit of RBF autoregulation decreased from 113 to 90 mmHg (P < 0.01); PRC fell. Mechanical reductions of RAP from 161 to 120 mmHg in the nonclipped kidney for 10 min did not change RBF, but at 120 mmHg, the lower pressure limit of RBF autoregulation was reduced from 115 mmHg before pressure reduction to 96 mmHg afterwards (P < 0.02). In SHR, similar pressure reduction for 10 min decreased the lower pressure limit of RBF autoregulation from 106 to 86 mmHg (P < 0.01). PRC was unchanged in both models, and denervation did not change RBF autoregulation. When RAP was reduced below the lower pressure limit of RBF autoregulation, RBF decreased approximately 20%; the lower pressure limit of RBF autoregulation remained unchanged. In normotensive Wistar-Kyoto rats, pressure reduction did not change the range of RBF autoregulation. These results indicate that acute normalization of the pressure range of RBF autoregulation in hypertensive rats is dependent on the degree of pressure reduction of RAP, whereas renal innervation and PRC do not play a major role. We propose that the mechanism of resetting is due to afterstretch of noncontractile elements of the vessel wall or is caused by pure myogenic mechanisms. An effect of intrarenal angiotensin cannot be excluded.

Dieulafoy's vascular malformation: role of endoscopic ultrasonography in therapeutic decision-making

BACKGROUND

Dieulafoy's vascular malformation may cause severe, potentially life-threatening gastrointestinal bleeding. Endoscopic diagnosis may be difficult because of minute mucosal lesions, and additional intramural abnormalities are usually not encountered. Endoluminal high-frequency ultrasonography is a new modality for imaging intramural and perivisceral structures.

METHODS

We report two cases of recurrent severe gastric bleeding in which different endosonographic modalities were used in the diagnosis of Dieulafoy's malformation, and the impact of endosonography on therapeutic strategy is discussed. In the first case a radial-scanning 7.5/12-MHz echoendoscope and a linear 20-MHz miniature probe were applied for B-mode imaging in a stable-state patient who had undergone previous endoscopic sclerotherapy, and arterial flow signals from the small intramural lesion were recorded using a 10-MHz transendoscopic pulsed Doppler probe. In the other case urgent endosonography was performed shortly after a bleeding episode, disclosing an aberrant large-calibre artery entering the gastric wall with a long submucosal branch.

RESULTS

Both patients were successfully operated on with a transabdominal approach.

CONCLUSION

Endosonography is a quick and safe diagnostic method and should be considered when vascular malformations are suspected as the cause of gastric bleeding.

Effects of velocity distribution, diameter measurement and velocity tracing on the accuracy of cardiac output measurement by pulsed Doppler echocardiography in the aortic annulus of pigs

The accuracy of cardiac output measurement by pulsed Doppler echocardiography can be affected by several factors, such as the velocity distribution, the measurement of diameter and the method of tracing the pulsed Doppler flow spectrum. This experimental study was designed to find the most accurate way of measuring cardiac output in consideration of all these factors. In 10 open-chest normal piglets (24 +/- 1 kg), the velocity distribution in the aortic annulus was evaluated using Doppler colour flow mapping. Cardiac output was measured by pulsed Doppler echocardiography in the aortic annulus by a number of different ways and compared to the simultaneous result of the thermodilution method. All measurements were made at baseline, after intravenous injection of esmolol and during infusion of dobutamine.

RESULTS

(1) the velocity distribution in the aortic annulus in the piglets was just slightly skewed during all three haemodynamic situations; (2) The in vivo measurements of the diameter of the aortic annulus varied throughout the ejection period, but the average of the three largest diameter measurements was almost identical with the diameter measured in vitro (18.5 +/- 0.3 mm vs. 18.6 +/- 0.2 mm; p = NS); (3) Tracing the maximal velocity of the pulsed Doppler flow spectrum produced a cardiac output that was 18%-21% higher than that measured by the thermodilution method, while tracing the brightest part (modal velocity) of the pulsed Doppler flow spectrum yielded a cardiac output very close to the thermodilution measurement.

CONCLUSION

The velocity distribution in the aortic annulus in the piglet has little effect on cardiac output measurement by pulsed Doppler. Using the maximal measurable diameter of the aortic annulus and tracing the brightest part of the pulsed Doppler flow spectrum yielded the cardiac output closest to that measured by the thermodilution method.

Three-dimensional cross-sectional velocity distribution in the ascending aorta in cardiac patients

Knowledge of the distribution of velocities across the ascending aorta is important for measurements of cardiac output; for understanding the function of normal and diseased valves and for the evaluation of prosthetic valves. The aim of this study was to investigate, in detail, the spatial distribution of axial velocities in the human ascending aorta, covering a nearly complete cross-section of the lumen in a time continuous modus. During open-heart surgery, blood velocities in the ascending aorta were mapped in 10 patients. All patients had aortic valves with no significant clinical evidence of disease. Pulsed Doppler ultrasound technique was used to measure blood velocity using an intraluminal probe with a 1 mm, 10 MHz crystal connected to a position-sensitive device. The distribution of blood velocity in the aorta 6-8 cm above the valve was characterized by a skewed and irregular peak systolic flow, with maximum velocity posteriorly. There was a positive correlation (r=0.854, P<0.002) between the maximum skewness slope and the stroke volume. Significant retrograde flow was recorded in all patients in the left posterior part of aorta in late systole and early diastole. The rotation of the point of maximal velocity was anticlockwise in six patients, clockwise in three and alternating in one. The present study shows that there is a considerable individual variation in the velocity distribution in the ascending aorta, with no plane symmetric features, and that large sampling volumes are required for reliable estimates of mean velocity.

The velocity distribution in the aortic annulus at different times during systole is mainly determined by the pattern of flow convergence in the left ventricular outflow tract--an experimental study using Doppler colour flow mapping

An experimental study in 10 open chest normal pigs (body weight: 24 +/- 1 kg) was carried out to explore the relationship between the velocity distribution in the aortic annulus and the pattern of flow convergence in the left ventricular outflow tract. The cross-sectional velocity profiles in the aortic annulus were constructed by using Doppler colour flow mapping with a previously validated time-interpolation method. The pattern of flow convergence in the left ventricular outflow tract was quantified by measuring the colour flow areas on the anterior and posterior sides of the central axis of the aortic annulus, and calculating their difference. The dynamic changes of the velocity distribution, the pattern of flow convergence and the septal angle throughout systole were observed. The velocity distribution in the aortic annulus changed according to the pattern of flow convergence in the left ventricular outflow tract. During early systole, the pattern of flow convergence was most asymmetrical. With the central longitudinal axis of the aortic annulus as a reference, the main part of the converging flow was along the anterior wall of the left ventricular outflow tract. Consequently, the velocity profile in the aortic annulus was most skewed during the early systole, with the highest velocity along the anterior wall. Towards late systole, the pattern of flow convergence became more and more symmetrical, and the velocity distribution in the aortic annulus gradually became flat. A significant correlation was found between the extent of asymmetry of the pattern of flow convergence in the left ventricular outflow tract and the extent of skewness of the velocity distribution in the aortic annulus (r = 0.69, P < 0.001). Throughout systole, septal angle increased very slightly (from 35 +/- 3 to 38 +/- 3 degrees, P < 0.01). The pattern of flow convergence in the left ventricular outflow tract is a major determinant of the velocity distribution in the aortic annulus in pigs.

Velocity distributions in the left ventricular outflow tract in patients with valvular aortic stenosis. Effect on the measurement of aortic valve area by using the continuity equation

The cross-sectional velocity distribution in the left ventricular outflow tract was studied in 40 patients with valvular aortic stenosis. Doppler colour flow mapping and a time-interpolation method were used to construct the cross-sectional velocity and time-velocity integral (TVI) profiles at different levels. By using pulsed Doppler, the subaortic flow velocity was sampled from the anterior, middle and posterior regions along the diameter of the left ventricular outflow tract (at 0.5 to 1.0 cm proximal to the aortic anulus) in the apical long axis view. Thus, for each patient, three aortic valve areas were calculated by using the continuity equation. Each patient was assigned to one of three subgroups according to the left ventricular ejection fraction (EF): subgroup I with EF < or = 25% (n = 10), subgroup II with 25% < EF < or = 50% (n = 17) and subgroup III with EF > 50% (n = 13). Velocity distributions in the three subgroups were compared to each other.

RESULTS

(1) The velocity distribution in the left ventricular outflow tract was skewed with the highest velocities and TVIs along the anterior wall and septum. The skewness of the velocity distribution was more pronounced in the apical long axis view than in the four chamber view (P < 0.05). The extent of skewness of the TVI profile was positively correlated to the left ventricular EF both in the long axis view (r = 0.63; P < 0.001) and in the four chamber view (r = 0.57; P < 0.001). (2) Pulsed Doppler sampling from different regions along the diameter produced different TVIs, and therefore yielded significantly different calculated aortic valve areas, especially in subgroup III. Due to the skewness of the velocity distribution in the left ventricular outflow tract, location of the pulsed Doppler sample volume significantly affects the accuracy of aortic valve area calculation by using the continuity equation, especially in patients with relatively high left ventricular EF. In patients with low EF, selection of pulsed Doppler sampling site is less important.

In vivo comparison of 3D ultrasonography and magnetic resonance imaging in volume estimation of human kidneys

The objective of this study was to evaluate the accuracy of a three-dimensional ultrasound system (3D-US) compared with Magnetic Resonance Imaging (MRI) in volume estimation of human kidneys in vivo. Twenty healthy volunteers were scanned fasting in supine position with MRI and with a 3D-US. An ultrasound sector scanner with a mechanical transducer coupled to a tilting motor provided images of multiple sections of kidneys. A 3.25-MHz transducer was tilted through 88 degrees yielding 81 frames, and volume estimation was performed on a Unix workstation after manual contour indication. Data acquisition with MRI was performed by using a 1-T magnet. Eighteen included kidneys [mean +/- standard deviation (SD)] measured 155.7 +/- 26.4 mL (range 110.0-205.0 mL) by 3D ultrasound and 171.8 +/- 24.6 mL (range 127.5-211.0 mL) by MRI, yielding a good correlation (r = 0.82, p < 0.001) between the two methods. The mean difference was -16.1 +/- 15.6 mL (SD) and the limits of agreement were -49.0 mL. We conclude that this 3D-US is accurate in volume estimation of human kidneys in vivo.

Volume measurements of gastric antrum by 3-D ultrasonography and flow measurements through the pylorus by duplex technique

We present a method for estimating volumes of abdominal organs using 3-D ultrasonography. In vitro validation experiments demonstrated excellent agreement between estimated and true volumes. In vivo estimations after ingestion of 500 ml meat soup showed greater antral filling and poorer emptying of the gallbladder in patients with functional dyspepsia (FD) than in healthy controls. Abnormal antral filling was associated with dyspeptic symptoms. The relationship between motility and transpyloric movements of luminal contents after ingestion of 500 ml meat soup was studied in healthy subjects by duplex technique. Accurate timing of antegrade and retrograde flow were recorded using bidirectional velocity curves. Mid-cycle and end-cycle reflux were often observed; end-cycle reflux was more frequent in conjunction with coordinated than with uncoordinated antroduodenal contractions. The peristaltic closure of the pylorus was normally preceded by a short gush of duodenogastric reflux.

Intraluminal recording of cross-sectional blood velocity distribution of human ascending aorta by ultrasound Doppler technique

A pulsed Doppler ultrasound technique was used for mapping two-dimensional blood velocity profiles in the human ascending aorta during open-heart surgery. An electronic position-sensitive device was constructed and linked to an intraluminal 10 MHz Doppler ultrasound probe. From a plane perpendicular to the central direction of blood flow, velocity mapping was performed covering the entire cross-section of the ascending aorta 6-7 cm above the valve. This method is based on a sequential sampling of velocity from continuously changing locations during a stable haemodynamic period; typically velocity points are recorded from 150-300 beats. Further processing transformed data to suit a previously developed velocity distribution model for normal blood flow in the human ascending aorta, based on multi-regression analyses. In this model, the time series of data from consecutive beats were computed into an average two-dimensional profile described through one cardiac cycle. This method allows high spatial resolution (1.5 mm), in addition to the high-frequency response (200 Hz) of the modified ultrasound Doppler meter. Together with the advantage of velocity directionality and minimal time interventions, this makes the method well suited for studies on normal flow conditions as well as flow velocity distribution distal to different heart valve prostheses.

Comparison of transit-time and Doppler ultrasound methods for measurement of flow in aortocoronary bypass grafts during cardiac surgery

To evaluate the accuracy of flow measurements in aortocoronary bypass grafts with the ultrasound transit-time method, an in vitro and in vivo comparison was carried out. The in vitro comparison with evaluation against both true flow and the ultrasound Doppler method, was carried out with a fresh saphenous vein mounted in a pulsatile flow rig. The two flow probes were placed on the graft 4-5 cm apart to avoid acoustic interference, and blood was pumped through the system at different flow rates. The comparison between the methods showed excellent agreement with a linear correlation coefficient of 0.996, and a mean error of -2.9 ml/min with limits of agreement +/- 13.1 ml/min (+/- 2 SD = 95% of measured differences between these limits). However, against true flow, both methods overestimated flow slightly with mean error 4.4 and 7.3 ml/min for the transit-time and Doppler, respectively. Both methods showed excellent correlation with true flow (correlation coefficient 0.998 for the transit-time and 0.997 for the Doppler method). The in vivo accuracy was evaluated by comparison of the two methods in 9 patients. The two probes were placed on the same saphenous vein grafts 4-5 cm apart, and a total of 34 measurements in 17 grafts were carried out including measurements at baseline and after papaverine injection. The correlation coefficient was 0.990 and linear regression analysis gave the equation: Transit-time flow = 1.00 x Doppler flow + 1.3. In terms of flow, the mean error was 1.5 ml with limits of agreement +/- 17.2 ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial contraction patterns in non-ischaemic and ischaemic regions during acute coronary insufficiency

The effect of coronary insufficiency on the myocardial contraction pattern was studied in 11 thoracotomized cats using apical long axis echocardiograms and cross-oriented segments in the anterior midwall. Myocardial tissue blood flow was studied using radiolabelled microspheres. After circumflex coronary artery occlusion, ejection shortening increased on average 17% for circumferential segments (P < 0.05) and 61% for longitudinal segments (P < 0.001). Hyperkinesis was also validated as augmented anterior endocardial wall motion and wall thickening. Circumflex occlusion increased end-systolic sphericity of the left ventricle (P < 0.05). Subsequent underperfusion of the left coronary artery, in two discrete steps, decreased subendocardial blood flow by, on average, 36% (P < 0.001) and 75% (P < 0.001) vs the post-occlusion value, while subepicardial flow did not change. While subendocardial blood flow decreased by 36%, systolic shortening of the global major axis decreased, by, on average, 77% (P < 0.001), shortening of the longitudinal segments by 36% (P < 0.001), and systolic shortening of the minor axis by 18% (P < 0.05), whereas shortening of midwall circumferential segments did not change. This study shows that changes in myocardial contraction in both non-ischaemic and ischaemic regions during coronary insufficiency are most pronounced in the direction of the cardiac major axis.

In vitro evaluation of three-dimensional ultrasonography in volume estimation of abdominal organs

The purpose of this study was to evaluate the accuracy and precision of a three-dimensional (3D) ultrasound system in volume estimation of abdominal organs in vitro. A mechanical sector scanner coupled to a stepping motor recorded images of porcine stomach and kidneys. The transducer was tilted through 88 degrees yielding 81 frames, and volume estimation was performed digitally after interactive manual contour indication and organ reconstruction in 3 dimensions. This 3D system showed good correlation (r = 0.998) between estimated and true volumes. Volume estimation of stomach and kidneys using 3.25 MHz probe demonstrated limits of agreement of 0.877 to 1.146 and 1.007 to 1.125, respectively, depicting estimated volumes as a proportion of true volumes in 95% of the examinations. Intra- and interobserver variation of the tracing procedure revealed low values. We conclude that this 3D ultrasound system performs high accuracy and precision in volume estimation.

Velocity distributions in the left ventricular outflow tract and the aortic anulus measured with Doppler colour flow mapping in normal subjects

This study was designed to investigate the velocity distributions in the left ventricular outflow tract and aortic anulus. In 18 out of 22 healthy male individuals, instantaneous cross-sectional flow velocity profiles were constructed at different levels of the left ventricular outflow tract and aortic anulus by time interpolation of digital velocity data from sequentially delayed Doppler colour flow maps. The results showed that: (1) the velocity distributions in the left ventricular outflow tract and the aortic anulus were skewed with the highest velocities along the anterior and septal parts of the flow channel; (2) based on the time-velocity integral profiles in the aortic anulus, which were also skewed with the highest integrals along the anterior and septal parts, the maximal time-velocity integrals were higher than the mean cross-sectional time-velocity integrals by approximately 30% in the four chamber view and 40% in the long axis view. However, the time-velocity integrals at the middle point of the diameter correlated significantly with the mean cross-sectional time-velocity integrals in the four chamber view (10.3 +/- 0.8 vs 9.9 +/- 0.9 cm; r = 0.95) and in the long axis view (12.5 +/- 0.9 vs 11.8 +/- 0.8 cm; r = 0.95). Therefore, it can be concluded that: (1) the velocity distributions in the left ventricular outflow tract and the aortic anulus are skewed; (2) if the aortic anulus is used for cardiac output measurement by pulsed Doppler echocardiography in normal subjects, the middle point of its diameter is the best sampling site.

Non-uniformity of two-dimensional myocardial deformation in response to chronotropic and inotropic stimulation in cats

The degree of uniformity of myocardial deformation for cross-oriented segments in the anterior wall of the left ventricle is influenced both by loading conditions and by infusion of isoprenaline. The aim of this study was to clarify the chronotropic influence (atrial pacing) compared to the combined inotropic and chronotropic effects of isoprenaline on uniformity of contraction. In eight open-chest pentobarbitone-anaesthetized cats segment performance was measured by orthogonal sonomicrometry. Heart rate (HR) increased from control state, 199 +/- 5 (mean +/- SEM) beats min-1, to 224 +/- 6 and 227 +/- 7 beats min-1 during atrial pacing and isoprenaline infusion, respectively (P < 0.0005). Circumferential segment shortening remained unchanged during pacing but increased with isoprenaline (P < 0.0005). Longitudinal segments showed reduced shortening during pacing (P < 0.05), whereas shortening during isoprenaline infusion did not differ from control shortening. The ratio between shortening of longitudinal and circumferential segments, long/circ ratio, changed from 0.52 +/- 0.13 in the control state to 0.36 +/- 0.10 during pacing and 0.39 +/- 0.11 with isoprenaline (P < 0.05). End-systolic pressure-length relations were unchanged by atrial pacing but showed leftward shifts during isoprenaline infusion. Myocardial tissue blood flow (microspheres) was unchanged during interventions. We conclude that both atrial pacing and isoprenaline infusion lead to a more non-uniform deformation in the anterior wall. However, non-uniformity during atrial pacing was primarily related to reduced longitudinal shortening whereas the non-uniformity during isoprenaline infusion was due to increased circumferential shortening.

Coronary artery stenosis provokes non-uniformity of two-dimensional deformation in the anterior wall of the feline left ventricle

The effect of coronary stenosis on the uniformity of local left ventricular contraction was studied in 11 open-chest cats. Coronary artery stenosis was established by controlled constriction of a shunt line from the right subclavian artery to the left main coronary artery. Two pairs of ultrasonic crystals were placed in the midwall of the anterior left ventricular wall; one pair, circumferential (Circ), aligned with midwall and subepicardial fibres; the other, longitudinal (Long), aligned with subendocardial fibres. Three steps of coronary perfusion pressure (poststenotic) were studied; open shunt line (140 +/- 4 mmHg), light stenosis (94 +/- 2 mmHg), and severe stenosis (70 +/- 3 mmHg). Subendocardial tissue blood flow showed the most pronounced reduction (from 1.87 +/- 0.11 to 1.43 +/- 0.10 and 0.86 +/- 0.12 ml min-1 g-1, respectively) with coronary stenosis whereas subepicardial flow remained unchanged. Maximal systolic shortening deteriorated for both segments. However, it was most pronounced for longitudinal segments. Duration of shortening decreased in longitudinal segments during severe stenosis to 62% of duration with open shunt (P less than 0.05), but was unchanged in circumferential segments. Long/Circ ratio of maximal systolic shortening declined by 50% (P less than 0.05) with reduction of coronary perfusion pressure. The reduced uniformity of segment shortening, caused by a marked reduction of longitudinal segment shortening, may support the notion that the longitudinal segment reflects performance of subendocardial fibres. This study demonstrates local non-uniformity of two-dimensional deformation during coronary artery stenosis and subendocardial hypoperfusion.

Antroduodenal motility and movements of luminal contents studied by duplex sonography

The motility of the gastroduodenal wall, movement of gastric contents, and velocity curves of transpyloric flow can be synchronously visualized by duplex sonography. In eight healthy individuals, 18 +/- 6 (mean +/- SD) peristaltic cycles per person in response to the ingestion of 500 mL of meat soup were recorded. Coordinated antroduodenal contractions were seen in 67% of the cycles. Two types of duodenogastric reflux were observed. One type occurred in the middle of the peristaltic cycle (midcycle reflux), whereas the other followed immediately after antegrade flow at the end of the cycle (end-cycle reflux). End-cycle reflux was significantly more frequent in conjunction with coordinated (70%) than with uncoordinated (17%) antroduodenal contractions (P less than 0.005). Thus, in the fed state, a short gush of duodenogastric reflux normally precedes the peristaltic closure of the pylorus.

Effect of mesangiolysis on autoregulation of renal blood flow and glomerular filtration rate in rats

Interlobular arteries and afferent arterioles are involved in autoregulation of renal blood flow (RBF) and glomerular filtration rate (GFR). The question of whether the contractile mesangial cells are also involved in autoregulation was investigated in Wistar rats. Autoregulation of RBF was examined before and 1 h after infusion of antithymocyte (anti-Thy 1-1) antibodies, and both RBF and GFR autoregulation were examined 30 h after the infusion of antibodies. Mesangial cell destruction was present 30 h after the infusion of antibodies. The angiotensin II-induced contraction of isolated glomeruli (70% of control volume, P less than 0.001) was abolished after the glomeruli had been exposed to anti-Thy 1-1 in vitro. RBF, as well as the lower limit of RBF autoregulation, were not different from control 30 h after the infusion (82 +/- 5 vs. 79 +/- 4 mmHg, P greater than 0.10). Autoregulation of GFR was maintained in the control group but was restricted in the experimental group (autoregulatory index: 0.71 +/- 0.42 for left kidney, 0.02 +/- 0.35 for control; P less than 0.05). The afferent arteriolar diameter was unchanged 30 h after the infusion of antibodies (17.8 +/- 0.8 vs. 17.6 +/- 0.4 microns, P greater than 0.10). One hour after infusion of the antibodies, RBF autoregulation was normal. It is concluded that mesangial cells do not seem to be involved in RBF autoregulation, but may in part influence autoregulation of GFR during pressure reduction.

Dyssynchrony of segment shortening in the anterior wall of the feline left ventricle

Non-uniformity of regional contraction may be both spatial and temporal. This study was undertaken to deal with the temporal aspects of shortening and to quantify non-uniformity with regard to timing. Nine cats were anaesthetized and artificially ventilated. Two pairs of ultrasonic crystals were situated in the anterior midwall of the left ventricle to measure regional shortening. One pair, longitudinal segment, was oriented to align with midwall fibres. The other pair, transverse segment, was placed perpendicular to the first one. Registrations in control state, during caval occlusion, and during aortic constriction were carried out with and without isoprenaline infusion. Cyclic events were analysed in terms of phase angle, 0-2 pi representing one heart cycle. Transverse segments showed marked shift of duration of shortening, from 1.19 pi +/- 0.06 pi (mean +/- SEM) in the control state to 0.40 pi +/- 0.14 pi during caval occlusion with isoprenaline infusion. Duration of shortening of longitudinal segments showed less prominent shift with mean values between 1.38 pi and 1.11 pi. Regional uniformity of timing, expressed as synchronization index, varied markedly with interventions (P less than 0.0005). Dyssynchrony was most prominent during caval occlusion with mean values less than 0.6. A simple model of force generation for the two segments visualizes that segment shortening of the transverse segment is of shorter duration than the longitudinal segment and a common mechanism for temporal and spatial non-uniformity within a region could be elaborated. This study quantifies both the time course of shortening and temporal non-uniformity of two cross-oriented segments within the same myocardial region.

Non-uniform and non-linear end systolic pressure-length relations at low left ventricular pressures in anaesthetised cats

STUDY OBJECTIVE

The aims were (1) to establish a basis for measurements of regional inotropy using the slope (E) of the linear part of the end systolic pressure-length relation; (2) to investigate the range of end systolic pressure where linearity is valid, and particularly its lower pressure limit, called turning point pressure; (3) to determine whether local myocardial inotropy measured by normalised slope, E(n), varies with segment orientation

DESIGN

Pressure and two cross oriented segment lengths were measured in the left ventricle. One pair of crystals measured a longitudinal segment, aligned with anterior midwall fibre direction; another pair measured a transverse segment, aligned with endocardial and epicardial fibre direction. Temporary obstruction of the inferior caval vein and descending aorta were performed to produce a wide pressure range of end systolic pressure-length relations during basal as well as high inotropic states (isoprenaline).

SUBJECTS

Seven open chest cats anaesthetised with sodium pentobarbitone and nitrous oxide were used. MEASUREMENTS AND MAIN RESULTS - Turning point pressure for longitudinal segments showed lower values than for transverse segments (p less than 0.05). With isoprenaline, turning point pressure increased for all transverse segments, at 103(SEM 8) v 153(19) mm Hg (p less than 0.05), whereas no change occurred for longitudinal segments, at 82(4) v 87(7) mm Hg. In the basal state, E(n) showed lower values in all longitudinal segments compared to transverse segments, except for one pair. E(n) of all segments increased during isoprenaline infusion, except in one segment where no change occurred. CONCLUSIONS - There is a lower limit for linearity of end systolic pressure-length relations; this is affected by segment orientation as well as by the inotropic state of the heart. E(n) as a measure of regional inotropy varies with segment orientation, but offers a local measure of changes in inotropic state.

Transmural fibre direction in the anterior wall of the feline left ventricle: theoretical considerations with regard to uniformity of contraction

Previous studies of non-uniform performance of a myocardial region have indicated that measurement of local contraction is vectorial. Myocardial performance in one direction mainly, but not exclusively, depends on performance of the wall fibres in this same direction irrespective of wall depth. In this study we therefore determined fibre direction across the anterior wall of the left ventricle in twelve cats. Based on the fibre configuration a simple model is developed to analyse and predict the degree of uniformity of contraction. Fibre direction shifted continuously across the wall, from almost alignment with global apex-to-base axis in the endocardium (90 degrees), to close to the equatorial direction (0 degrees) in the midwall, and finally to about -50 degrees in the epicardial layer. The model predicts less uniformity with reduction of preload, and in the event of subendocardial ischaemia, which fits well with experimental data. Analysis of uniformity based on the integrated vectorial contribution of all myocardial layers thus provides a way to quantify regional uniformity/non-uniformity as a regulatory mechanism of cardiac function.

Endoscopic ultrasound Doppler probes for velocity measurements in vessels in the upper gastrointestinal tract using a multifrequency pulsed Doppler meter

To quantify flow velocity in vascular structures in the upper gastrointestinal tract, prototype ultrasound Doppler transducers having frequencies of 5 and 10 MHz were designed. Connected to an advanced pulse ultrasound Doppler meter via an isolation transformer for patient safety, these transducers enabled the recording of flow velocity in vessels within an surrounding the wall of the GI tract. This set up improves the endoscopic ultrasound Doppler method by extending the measurable depth-range by using two frequencies, permitting independent selection of measuring depth and sample volume length, and giving an output format which includes full spectral analysis, simultaneous ECG and capabilities of displaying two additional signals.

Instantaneous cross-sectional flow velocity profiles: a comparative study of two ultrasound Doppler methods applied to an in vitro pulsatile flow model

Two methods based on different techniques for construction of cross-sectional flow velocity profiles from Doppler ultrasound signals were compared: an intraluminal method using pulsed-wave Doppler echocardiography and an extraluminal method using two-dimensional (color) Doppler ultrasound. The methods were applied to an in vitro pulsatile flow model. With the intraluminal method, pulsed Doppler recordings obtained throughout several flow pulses at different positions across a tube were digitized, and cross-sectional flow velocity profiles were obtained by matching the onset of flow velocity at the various positions. With the extraluminal method, cross-sectional flow velocity profiles were obtained by time interpolation between the digital flow velocity data obtained from several flow velocity maps. The first flow velocity map was recorded at onset of flow and the following maps were incrementally delayed with 20 msec from one flow pulse to the next. The time lag caused by the time needed to update each of the flow velocity maps was compensated for by time interpolation between the sequentially recorded flow velocity maps. The cross-sectional flow velocity profiles obtained with the two methods were compared at identical positions within the tube model at equal flow settings and throughout the pulsatile flow periods. At three different flow settings with peak flow velocity of 0.3, 0.5, and 0.7 m/sec, the difference (mean +/- SD) between the obtained velocities were 0.01 +/- 0.04, -0.01 +/- 0.05, and -0.03 +/- 0.07 m/sec, respectively. The findings suggest that cross-sectional flow velocity profiles from pulsatile flow velocity recordings can be obtained equally well with both methods.

Gradual reduction of coronary perfusion pressure in cats: changes in transmural distribution of blood flow

We evaluated a model for regional myocardial hypoperfusion in cats with an extracorporeal shunt line to the left main coronary artery, and investigated the effects of reduced coronary perfusion pressure on the transmural distribution of left ventricular blood flow measured with radioactive microspheres. Shunt establishment did not alter cardiac function, myocardial tissue blood flow, or its transmural distribution. An artificial shunt stenosis, which clearly reduced coronary perfusion pressure without changing cardiac function, caused reduced endocardial blood flow, slight flow reduction in mid-myocardium, and no flow change in the epicardium. When a severe stenosis was applied, causing increased end-diastolic pressure and reduced shunt flow, endocardial and mid-myocardial flow further decreased whereas epicardial blood flow remained essentially unchanged. These results demonstrate a transmural profile of the coronary autoregulation capacity.

Nonuniform shortening of the anterior wall of feline left ventricles

Recorded performance of segments between implanted ultrasonic crystals placed at midwall position of the left ventricle reportedly depends almost exclusively on midwall function and alignment with fibers. Accordingly, one would expect the ratio between performance of a segment perpendicular to midwall fiber direction (transverse) and a parallel segment (longitudinal) to be constant and independent of changes in preload, afterload, and the inotropic state. We tested this hypothesis by implanting cross-oriented crystal pairs in nine open-chest cats and studied their performance during preload and afterload changes with and without isoproterenol infusion. Fiber orientation across the ventricular wall was determined by serial histological sectioning. The ratio between performance of transverse and longitudinal segments (trans/long) changed with interventions. Increased end-diastolic pressure leads to increased segment performances as well as trans/long. Inotropic stimulation produced increased sensitivity to preload changes both for individual segment performances and for trans/long. These results suggest that longitudinal segments represent the function of midwall fibers, whereas transverse segments may well represent the function of sub-endocardial fibers, which run closer to this orientation. Thus trans/long provides a way to quantify nonuniformity of local myocardial contraction.