Blood Pressure Gradient Research Articles

Misrepresentation of left ventricular contractile function by endocardial indexes: Clinical implications after coarctation repair

Background Endocardial function indexes overestimate myocardial fiber shortening, a geometric effect proportional to wall thickness. We hypothesized that elevated endocardial indexes of left ventricular contractile function after repair of isolated coarctation of the aorta could be related to this effect. Methods Chamber dimensions and wall thickness were measured from 59 echocardiograms in 57 patients aged 1.2 to 32 years, 8.5 ± 5.6 years after coarctation repair, and in 305 normal controls aged 1 to 35 years. Midwall and endocardial shortening indexes and end-systolic fiber stress were calculated. The stress-velocity index (SVI), a load-independent index of contractility, was derived from these variables. All values were expressed as z scores. Results After coarctation repair, the midwall-derived SVI was elevated, but significantly less so than the endocardial-derived SVI (0.6 ± 1.6 vs 1.3 ± 2.6; P = .01). The endocardial-derived SVI correlated with the end-systolic thickness/dimension ratio (P < .0001), but the midwall-derived SVI did not. There was no linear relation between the midwall-derived SVI and the residual blood pressure gradient. The mean midwall-derived SVI was higher compared with the normal population in those with a minor residual blood pressure gradient (≤15 mm Hg) and in those with more significant obstruction (>15 mm Hg), but this achieved statistical significance only in the latter group (0.5 ± 1.6, P = .08; and 0.8 ± 1.7, P = .03, respectively). Conclusions Endocardial indexes of function and contractility overestimate fiber shortening after coarctation repair. Nevertheless, midwall shortening indexes demonstrate enhanced contractility, particularly in those with residual coarctation.

Helical CT angiography with maximum intensity projection in the assessment of aortic coarctation after surgery.

The value of CT angiography and three-dimensional (3D) reconstructions was investigated in the postoperative care after surgical repair of aortic coarctation and compared with conventional angiography. Twenty-five patients referred because of suspicion of stenosis in the area of former coarctation were prospectively studied with CT angiography and catheter angiography. We determined the morphometric and morphologic findings such as aortic diameter, stenosis, aneurysm, intimal flaps, circumscribed pouch, or arteriosclerotic plaques with 3D reconstructions, using maximum-intensity-projection (MIP) technique and catheter angiography. The results of both techniques were compared. The ratio of the narrowest diameters of the former coarctation and the descending aorta was correlated with the systolic pullback blood pressure gradient in all patients. The former coarctation was normal in 11 patients, (44%), group A; narrowed in 12 children (48%), group B; and dilated in two children (8%), group C. An intimal flap and a circumscribed pouch were delineated in four subjects. MIP reconstructions and catheter angiography revealed identical results regarding the classification into groups A, B, C; intimal flaps; and circumscribed pouches. Statistical analysis revealed good correlation between the narrowest aortic diameters measured on MIP reconstructions and catheter angiography, whereas no correlation between the systolic pullback blood pressure gradient and the diameter ratio of the former coarctation and the descending aorta was found. CT angiography and 3D reconstructions using MIP represent a reliable noninvasive technique to replace diagnostic catheter angiography in the postoperative care of patients with coarctation and provide the clinician with valuable information concerning further invasive procedures.

Relationship Between Preoperative Duplex Vein Mapping and Intraoperative Longitudinal Impedance in Infrainguinal Vein Grafts

The importance of favorable vein size, resistance, and impedance for the sustained success of infrainguinal vein grafting procedures has repeatedly been demonstrated. Estimating these properties preoperatively, however, has been problematic. Ultrasonic vein mapping is a reliable technique for measuring vein diameters at venous pressures, but it is unknown whether these data accurately assess the resistive potential of the conduit in the arterial circulation. The purpose of this study was to compare vein diameter measured preoperatively with vein graft longitudinal impedance measured intraoperatively. Patients who had undergone both preoperative vein mapping and intraoperative impedance studies at the time of infrainguinal bypass were included (December 1995-April 1999). Vein mapping was performed using B-mode ultrasound with a 10 MHz probe. The dimensions of the specific vein segment used for reconstruction were tabulated and its mean diameter (D̄) was calculated. At the time of operation, following reconstruction, transgraft blood pressure gradient (δP) and blood flow (Q) waveforms were recorded by using digital data acquisition. Longitudinal impedance (ZL) was calculated as δP/Q at each harmonic following Fourier transformation and the area under the curve from 0 to 4 Hz designated as ∫ZL. Twenty-three bypasses in 22 patients were studied (D̄ = 3.5 ±0.2 mm, range 1.6-5.5 mm; ∫ZL= 37 ±4 x 103 dyne cm-5, range 13-95 X 103 dyne cm-5). D̄ significantly correlated with ∫ZL (slope = -0.454, p &lt; 0.05), albeit with a fairly low correlation coefficient ( r2 = 0.23). D̄ &gt; 3.6 mm was predictive of graft patency at 12 months (D̄ &gt; 3.6 mm 100% vs D̄ &lt; 3.6 mm 57 ±20%; p = 0.02). Larger veins identified by preoperative mapping have, in general, more favorable intraoperative resistive characteristics as defined by a lower JZL. However, some veins thought to have small diameters (&lt; 3.6 mm) may still demonstrate sufficiently low ∫ZL when grafted to remain patent.

Early results and medium-term follow-up of stent implantation for mild residual or recurrent aortic coarctation

Background Optimal timing and mode of treatment for patients with aortic coarctation remains controversial, particularly when the degree of obstruction is mild. Surgery, balloon dilatation, and stent implantation have all proven effective in the treatment of moderate or severe obstruction. In this report, we describe the use of stents to treat coarctation in a heterogeneous population, including patients with relatively mild obstruction. Methods Retrospectively, we studied the results of stent implantation in 33 patients, children and young adults, who underwent catheterization for treatment of coarctation. Patients with isolated coarctation, as well as those with associated cardiac defects, were included. The median systolic pressure gradient of our patients was 25 mm Hg. Results Patients had an acute decrease in systolic blood pressure gradient (25 mm Hg to 5 mm Hg, P <.001) and an increase in lumen diameter (8 mm to 13 mm, P <.001). When 16 patients were recatheterized during the follow-up period, gradients remained decreased (30 mm Hg to 14 mm Hg, P <.001) compared with prestent values. Ventricular end-diastolic pressure, which was increased in 82% of patients at the time of initial catheterization, decreased from 17 mm Hg to 14 mm Hg (P =.002). Although the procedure was generally safe, serious complications did occur. Conclusions Stent implantation represents a therapeutic option that can safely and effectively reduce gradient in challenging patients with mild postoperative coarctation. Furthermore, our data suggest that aortic obstruction often coexists with ventricular diastolic dysfunction in these patients and that relief of obstruction may play a role in improvement of function. (Am Heart J 2000;139:1054-60.)

Angiotensin-converting Enzyme: Induction by Hypertension-induced Vessel Distension

Vascular angiotensin-converting enzyme (ACE) activity is increased in a variety of disorders representing both early and late stages of atherosclerosis. The factors governing the induction of vascular ACE are poorly understood. We hypothesized that vascular ACE activity might be increased by hypertension-induced vessel distension. Hypertension was induced in rats by suprarenal coarctation of the aorta. Analyses were performed 5 days and 4 weeks post-operation. ACE activity and ACE mRNA level were increased in thoracic aortae from coarctation hypertensive rats that had been exposed to elevated blood pressure, whereas they remained at normal level in abdominal aortae from those rats that had been exposed to normal blood pressure. The degree of aortic ACE induction correlated well with the degree of the trans-stenotic blood pressure gradient. An increase in ACE transcript level was also observed in carotid arteries from coarctation hypertensive rats that had been exposed to elevated blood pressure. In contrast, ACE activity and ACE mRNA expression were not altered in tissues that did not contain any large arteries from coarctation hypertensive rats, although these tissues had been exposed to elevated blood pressure. These results demonstrate an induction of ACE in large arteries that had been exposed to elevated blood pressure, and they imply that the induction of vascular ACE is due to hypertension-induced vessel distension.

Dobutamine stress Doppler hemodynamics in patients with aortic stenosis: Feasibility, safety, and surgical correlations

Objectives This study was designed to describe the experience of our center with the safety and feasibility of dobutamine stress echocardiography (DSE) in aortic stenosis (AS), to characterize the hemodynamic response to dobutamine infusion, and to examine the hemodynamic response in relation to the anatomic evaluation of the valve among patients who underwent valve replacement. Background The diagnosis of the hemodynamic severity of AS can be difficult when the cardiac output is reduced and the gradient is low, but the effective valve area calculates to be small. DSE has been proposed as a means of assessing the severity of AS in this setting. Methods We reviewed 27 patients (18 men, 9 women; mean age 71 ± 12 years) with AS who underwent DSE between 1991 and 1996. Results Fifteen (55%) patients were New York Heart Association class III or IV, 8 (30%) had angina Canadian class III or IV, and 3 (11%) syncope. Dobutamine peak dose was 27 ± 11 μg/kg/min. Sixteen (59%) patients had mild side effects. DSE resulted in a significant increase in the cardiac output from 4.1 ± 1.2 L/min at rest to 7.3 ± 1.9 L/min at peak dose, and in heart rate (76 ± 16 beats/min to 124 ± 20 beats/min), systolic blood pressure (128 ± 26 mm Hg to 137 ± 26 mm Hg), ejection fraction (38% ± 20% to 42% ± 20%), and transvalvular mean gradient (28 ± 10 mm Hg to 39 ± 9 mm Hg) ( P < .05). There was also a significant increase in the valve area from 0.77 ± 0.14 cm 2 at rest to 0.97 ± 0.21 cm 2 ( P < .001). Seven patients underwent surgery; all valves were severely calcified, confirming anatomic disease. In this group, an increase in the mean gradient but also a trend toward an increase in the valve area were noted in response to dobutamine: 33 ± 10 mm Hg to 47 ± 6 mm Hg and 0.79 ± 0.11 cm 2 to 0.95 ± 0.19 cm 2 , respectively. Conclusion Although more data are needed to fully establish the safety of the test in this indication, this study suggests that patients with AS can safely undergo DSE. Dobutamine results in an increase not only in the mean gradient, but also in the valve area. An increase in valve area with dobutamine was observed in some patients with anatomically confirmed severe AS and thus does not exclude fixed valve disease. (Am Heart J 1998;136:1010-6.)

Outcome of pregnancy following intervention for coarctation of the aorta

There are limited data regarding the outcome of pregnancy in women after intervention for coarctation of the aorta (CoA). The Texas Children’s Hospital Cardiac Database was used to identify female patients with CoA born before 1980 who had undergone balloon angioplasty or surgery. Patients with Turner’s syndrome and cyanotic congenital heart disease were excluded. A chart review and telephone interview were performed. Data collected included age at intervention, type of intervention, the need for reintervention, functional status, number of pregnancies, and pregnancy outcomes. Seventy-four patients met our criteria and we were able to contact 52. Eighteen patients (39%) were pregnant a total of 36 times. There were 3 spontaneous and 4 elective abortions. Preeclampsia complicated 4 pregnancies in 3 women (17% of primigravidas). One patient had systemic hypertension. Eleven infants were delivered by Cesarean section. There were 29 births, with an average weight of 3.0 kg. There were 5 preterm births, 4 to a teenage mother. Only 1 child (3%) had a congenital heart defect. Thus, in women with an arm-to-leg blood pressure gradient of <20 mm Hg after CoA repair, pregnancy is successful. The occurrence of congenital heart disease in the offspring was 3%. Preeclampsia was similar to that in the general population.

Congenital heart disease: Measuring physiology with MRI

Cine MRI and VEC MRI can be used to quantitate the physiology of the heart and great vessels in patients with CHD. This information can be a valuable adjunct to anatomical imaging for preoperative planning as well as postoperative monitoring. Some important clinical applications of quantitative cardiovascular functional MRI include measurement of ventricular masses, stroke volumes, and ejection fractions; estimation of shunts and valvular regurgitation; assessment of collateral blood flow and pressure gradients in aortic coarctation; and postsurgical evaluation of conduit blood flow and pressure gradients.

Coarctation Repair: Modification of End-to-End Anastomosis With Subclavian Flap Angioplasty

Background. Subclavian angioplasty and resection and end-to-end anastomosis for coarctation repair carry a substantial risk of recurrence of coarctation. The combined technique using both these methods has shown good results but requires a longer period of continuous cross-clamping of the aorta. Methods. A modified technique using intermittent cross-clamping with a period of reperfusion between cross-clamping periods was used. After the end-to-end anastomosis the clamps are released for 10 minutes and reapplied to do the subclavian angioplasty. Between 1991 and 1996 this was done in 26 infants (mean age, 5 weeks; range, 1 day to 6 months; median, 3 weeks). Mean weight was 3.85 kg (range, 1.5 to 8.4 kg). Mean length of follow-up was 23 months. Twenty-two patients (85%) had associated anomalies, excluding patent ductus arteriosus, and 5 patients (19%) had another procedure performed at the same time. Results. There was no mortality. The mean echocardiographic gradient was 4 mm Hg in the immediate postoperative period and 2.9 mm Hg during follow-up. Residual or recurrent coarctation as detected by significant echocardiography or blood pressure gradient did not develop in any infant. Conclusions. This modified technique of anastomosis is an effective way of relieving coarctation with excellent intermediate-term results.

Spiral CT angiography and 3D reconstruction in patients with aortic coarctation

The objective of this study was to assess the reliability of spiral CT angiography (CTA) and 3D reconstruction in patients with aortic coarctation (CoA). Eighteen patients with suspected or surgically proven coarctation were examined by spiral CT. In addition to the axial slices, 3D reconstructions, such as shaded surface display (SSD) and maximum intensity projection (MIP), were used to determine the diameters of the CoA and the pre- and poststenotic aorta and to visualise the collateral vessels. Diameters derived from cardiac catheterization were compared with those from CTA in 8 patients. The degree of aortic stenosis was correlated with blood pressure gradients (BPG) in 12 patients. The difference between the diameters of the CoA and the pre- and poststenotic aorta derived from MIP and angiography was not statistically significant (p = 0.69). With SSD the internal thoracic artery was detected in 16 and the posterior intercostal artery in 13 cases. The degree of aortic stenosis correlated poorly with the BPG (r = 0.51, r2 = 0.26). CTA with 3D reconstruction represents a reliable noninvasive technique for the assessment of the degree of CoA and the visualisation of collateral vessels. It may serve as a follow-up investigation after intervention or surgical treatment.

Effects of anatomic variability on blood flow and pressure gradients in the pulmonary capillaries.

A theoretical model is developed to simulate the flow of blood through the capillary network in a single alveolar septum. The objective is to study the influence of random variability in capillary dimension and compliance on flow patterns and pressures within the network. The capillary bed is represented as an interconnected rectangular grid of capillary segments and junctions; blood flow is produced by applying a pressure gradient across the network. Preferred flow channels are shown to be a natural consequence of random anatomic variability, the effect of which is accentuated at low transcapillary pressures. The distribution of pressure drops across single capillary segments widens with increasing network variability and decreasing capillary transmural pressure. Blockage of one capillary segment causes the pressure drop across that segment to increase by 60%, but the increase falls to < 10% at a distance of three segments. The factors that cause nonuniform capillary blood flow through the capillary network are discussed.

Validation of a new and specific intraoperative measurement of vein graft resistance.

Clinical studies have revealed that the most important predictor of successful bypass grafting is the origin and quality of the bypass conduit. Attempts at intraoperative evaluation of the hemodynamic properties of the conduit, including assessment of blood flow (Q), pressure gradients (delta P), and resistance (R), have not been useful. This is because each of these parameters measures the characteristics of the graft plus the outflow bed. To date, no specific measurement of the resistive properties of the conduit only is available. The purpose of this investigation was to evaluate longitudinal impedance (ZL) as a measure of conduit-specific resistance and to evaluate its potential in predicting the outcome of infrainguinal vascular reconstructions. ZL was measured during surgery in 73 infrainguinal autologous vein reconstructions performed in 68 patients in two separate institutions over a 21-month period. Vein graft ultrasonic transit time Q and delta P (from proximal to distal anastomosis) were measured at baseline and after maximal peripheral vasodilatation with an intraarterial injection of papaverine 30 mg. Waveforms were recorded for 10 seconds at 200 Hz using a digital acquisition system. R was calculated as proximal mean pressure divided by mean blood flow (Q). After Fourier transformation, ZL was calculated as delta P/Q at each harmonic and total ZL (integral of ZL) was defined as the integral of moduli from 0 to 4 Hz. All hemodynamic variables were significantly affected by papaverine vasodilatation (delta P, 3.9 +/- 0.5 vs 6.3 +/- 0.8 mm Hg; Q, 78.2 +/- 7.0 vs 126 +/- 11 ml/min; R, 134 +/- 17 vs 72.7 +/- 6.2 x 10(3) dyne.sec.cm-5; p < 0.0001), except integral of ZL, which remained constant (31.1 +/- 2.8 vs 30.8 +/- 2.8 x 10(3) dyne.cm-5; p = NS). After follow-up of 1 week to 17 months (median, 5 months), the 1-year primary, primary-assisted, and secondary patency rates were 72% +/- 7%, 77% +/- 6%, and 81% +/- 6%, respectively. Using Cox analysis, primary patency was significantly associated with decreased integral of ZL (p = 0.0001), but not with baseline or papaverine-stimulated delta P, Q, delta P/Q, or R integral of ZL > 47 x 10(3) dyne.cm-5 predicted primary failure with 90% positive and negative predictive value. Intraoperative measurement of integral of ZL in infrainguinal vein grafts is independent of outflow conditions (that is, does not change with papaverine), and hence describes the resistive properties of the conduit only. In addition, these preliminary data suggest that integral of ZL is predictive of short-term primary patency. integral of ZL is the first available hemodynamic measurement that is conduit-specific and may therefore be a better predictor of graft patency than currently available methods.

Comparison of pulsatile versus nonpulsatile perfusion on the postcardiopulmonary bypass aortic-radial artery pressure gradient

Objective: To investigate whether the type of perfusion, pulsatile (PP) or nonpulsatile (NP), has any effect on the pressure gradient that exists between the aortic root and the radial artery after cardiopulmonary bypass (CPB). Design: Prospective, randomized study. Setting: Tertiary care, university hospital. Participants: Eighty patients undergoing elective, hypothermic coronary artery bypass graft (CABG) surgery. Interventions: Pulsatile perfusion with a pulse pressure of 10 to 20 mmHg and a frequency of 60 to 80 beats/min was created during the hypothermic phase of CPB. Both the radial artery and aorta were cannulated and attached to separate transducers but displayed and analyzed on the same monitor. Measurements and Main Results: Simultaneous recordings of radial artery and aortic root blood pressure were made prebypass, during CPB, and after discontinuation of CPB at 2,5, and 10 minutes. During CPB, the PP group had a significantly higher mean pulse pressure measured at the aortic root than the NP group (15.5 ± 8.1 v 1.7 ± 2.7, p < 0.0001). The aortic-to-radial-artery gradient within both groups was significantly different after CPB for systolic (SBP), diastolic (DBP), and mean pressure (MAP) ( p < 0.0001). There were, however, no statistically significant differences between the PP and NP groups in the aortic-to-radial-artery gradient after CPB for either SBP, DBP, or MAP. Conclusions: Pulsatile perfusion had no effect on the aortic root radial artery blood pressure gradient after CPB in elective CABG surgery patients.

Effect of Suspended Red Blood Cells On Pressure Gradients Across Blalock-Taussig Shunts 151

It is generally assumed that blood behaves strictly as a particle-free fluid and not as a suspension in arterial sized vessels (> 1 mm). However, we have previously demonstrated a biphasic deviation of pressure gradients(PG) of blood from a particle-free fluid of equal viscosity in straight tubes, with the blood PG being greater than the particle-free fluid at low flowrates and lower at high flowrates. Since this behavior may affect velocity-derived PG, we addressed the hypothesis that PG across a BT shunt would show significant deviation from that of a particle-free blood analog fluid (BAF). Methods: The in vitro BT shunt model consisted of two arterial sections connected by a physiologically sized shunt (D = 5 mm, L = 9 cm). PG across the shunt were obtained by measuring pressure 10 cm proximal and distal to the inlet and outlet respectively. For a given flow rate the PG across the shunt was recorded for both blood and an equal viscosity BAF(aqueous glycerin solution, 3.8 cP). PG differences were plotted vs. Reynolds number (Re = ratio of inertial to viscous forces) and divided into laminar and turbulent flow regimes, with a transition Re of 2100 (the approximate transition from laminar to turbulent flow in tubes). Differences in PG between blood and BAF were considered significant at a level of 0.01 using a paired t-test for both the laminar and turbulent regimes. Results: For Re 0.5). However, for Re > 2100, the PG for blood were consistently lower than that of BAF and the differences were significant (mean difference = 9.9 mmHg, p < 0.01). Conclusions: Blood PG across BT shunts deviate from BAF PG. This effect is especially pronounced in the turbulent regime and is consistent with our previous investigations using straight tubes, suggesting Re-dependent phenomena may account for this behavior. These findings may have important implications in the noninvasive assessment of pulmonary artery pressure in patients with BT shunts.

Finite element analysis of blood flow through biological tissue

Quantitative analysis of blood perfusion has been performed with a hierarchical mixture model of blood perfused biological tissue, for low Reynolds steady state Poiseuillian flow through two-dimensional, computer generated, rigid, arterial vascular trees. The mixture model describes blood flow through the vasculature by spatial and hierarchical flow components, both related to the blood pressure gradient via an extended Darcy equation. The Darcy-permeability tensor is derived from the geometry of the vascular tree, the fluid viscosity, and the vascular hierarchy which is quantified by a dimensionless parameter xo. Finite element results of fluid pressure and flow on certain levels of the hierarchy are compared to correspondingly volume averaged pressures and flows calculated by hydraulic network analysis. The correspondence between the finite element results and the network results strongly depends on the quantification of the hierarchy, which should be closely related to the hierarchical fluid pressure. Two methods for hierarchical quantification have been used, one of which is based on the network fluid pressure and the other on the segment diameters. With the first method a good correlation between x0 and fluid pressure, and consequently a good correspondence between finite element and network results, are found. The second method yields a poor correlation between xo and fluid pressure. However, still satisfying correspondence between finite element and network results is found.

Doppler echocardiography during exercise to predict residual narrowing of the aorta after coarctation resection.

Blood pressure measurements and Doppler echocardiography at rest and during exercise were performed in 36 patients at an average 17 years after coarctation resection. Interest focused on the study of Doppler systolic and diastolic gradients and half-times during exercise. Blood pressure gradients and Doppler values were compared with the degree of narrowing at the site of the anastomosis measured by magnetic resonance imaging. A systolic half-time of >110 ms together with a diastolic gradient of >/=17 mmHg on exercise Doppler sonography predicted a residual isthmic narrowing of >30%. We propose the use of this noninvasive method for identifying patients with narrowing of >30% at the site of the anastomosis after coarctation resection. In these cases evaluation by an imaging technique is necessary to confirm the need for surgery.

Early Diagnosis of Coarctation of the Aorta in Children: A Continuing Dilemma

Because late repair of coarctation of the aorta (COA) is associated with premature cardiovascular disease in adult life, early detection and treatment is important. To determine the timing of referral to see whether early detection of COA has improved in the past decade, to evaluate the pattern of and reasons for medical center referral, and to assess the clinical signs relating to the diagnosis of COA. The records of 50 consecutive patients older than 1 year who had surgical repair of COA from 1980 to 1990 were reviewed. The age of referral, pattern of referral, and presence of standard clinical signs of COA were analyzed, and data were compared with those from the previous decade. The mean and median ages at referral were 8.4 and 5.8 years, respectively. Pediatricians accounted for 64% of the referrals. A specific diagnosis of COA was made in 2 (4%) of 50 patients before referral to a pediatric cardiologist. The most consistent clinical findings were a cardiac murmur and a systolic blood pressure gradient between the arms and legs of greater than 10 mm Hg, which were both present in all patients. Lower-extremity pulses were decreased in 37 (74%) and absent in 9 (18%). Forty-seven children (94%) had upper-extremity hypertension (> 95th percentile for age); 25 (50%) had systolic blood pressure higher than 140 mm Hg. COA would have been missed in 82% of children if absent lower-extremity pulses were required as a diagnostic feature. These findings were similar to those reported by our institution in the previous decade, suggesting that early detection has not improved. The timing of, reasons for, and sources of referral for COA in this study, compared with data from the previous decade, indicate no improvement in early detection of COA by pediatricians. Screening all children for COA by routinely measuring upper- and lower-extremity blood pressures during at least one physical examination after the newborn period is mandatory.

The Therapeutic Significance of Pulse Reverse Osmosis

Pulse reverse osmosis (1) is a new theory of fluid balance and exchange which suggests that the mean blood pressure and osmotic gradient control fluid balance and that the pulse controls fluid exchange. In vitro testing has confirmed some of the physico chemical principles underlying the theory (2). The hypothesis suggests a relationship between mean capillary blood pressure and osmotic gradient. Imbalance in this relationship can be related to the development of hypertension, hypotension, oedema and shock. In an attempt to test this concept mean blood pressures and colloid osmotic pressures were measured and compared in a group of 50 healthy human volunteers. The results suggest a curvilinear correlation between the mean blood pressure and the COP.

Isolated Aortic Coarctation in Neonates and Infants: Results of Resection and End-to-End Anastomosis

Operative resection is the treatment of choice for native aortic coarctation in most institutions. The ideal timing for elective repair is still a matter of debate. This study evaluated one institution's results with resection and end-to-end anastomosis in the first year of life. Between January 1987 and December 1993, 46 neonates and infants with functionally isolated aortic coarctation underwent operative resection and end-to-end anastomosis. For the patients included in the study, all hospital records, catheterization data, and operative protocols were evaluated for retrospective analysis. To obtain valid follow-up information, all patients were systematically seen on an outpatient basis during 1994. After a mean follow-up of 49 +/- 24 months (range, 13 to 95 months), recoarctation (arm-leg blood pressure gradient > 20 mm Hg) occurred in 5 of 26 patients with neonatal operations (19%) and in 1 of 20 patients with operations in infancy (5%, p = not significant). Four of these 6 children with recoarctation needed reintervention. The other 2 patients had only mild recoarctation (gradients of 22 and 30 mm Hg, respectively) and were not treated. In all 6 patients, recoarctation was diagnosed within the first 6 months postoperatively. During the whole follow-up period, right arm systolic blood pressures slightly above the 90th percentile of normal developed in 11 of the patients (24%) (7 in the group with neonatal operation and 4 after operation in infancy; p = not significant). Resection with end-to-end anastomosis was shown to be an adequate therapeutic strategy for isolated aortic coarctation in neonates and infants. The results indicate that already beyond the neonatal age, there is a relatively low incidence of recoarctation.

Intravascular Oxygenation

An extra corporeal venovenous bypass circuit (right atrium to pulmonary artery), including an intravascular gas exchanger in a blood chamber with a variable inner diameter, was developed for ex vivo evaluation of the host vessel diameter/intravascular oxygen transfer relationship. Three host vessel diameters mimicking different configurations of the caval axis were studied in three bovine experiments (body weight 82 +/- 3 kg). Blood flow was 3,000 ml/min and device oxygen inflow was 2,300 ml/min. Serial blood samples were taken for 26 mm, 23 mm, and 20 mm inner blood chamber diameters after hemodynamic stabilization before and after exposure of the circulating blood to the intravascular gas exchanger (sampling ports at blood chamber inlet and outlet). Measured oxygen saturation at the blood chamber inlet was 25.0 +/- 11.7% for the 26 mm diameter as compared to 31.7 +/- 12.6% for 23 mm, and 28.7 +/- 9.2% for 20 mm. At the outlet, the corresponding O2 saturations were 34.5 +/- 11.5% for 26 mm, 42.9 +/- 8.8% for 23 mm, and 43.2 +/- 6.2 for 20 mm. Total O2 transfer was 24.9 +/- 11.5 ml/min for 26 mm, 31.9 +/- 7.4 ml/min for 23 mm, and 35.9 +/- 12.2 ml/min for 20 mm (p < 0.05). Likewise, O2 transfer rate was 8.3 +/- 3.8 ml/L, 10.6 +/- 2.4 ml/L, and 12.0 +/- 4.0 ml/L (p < 0.05). Parallel analyses of total CO2 transfer and CO2 transfer rates provided less consistent findings. At 3 L/min, the pressure drop between the inlet and outlet of the blood chamber was 12 +/- 3 mmHg for 26 mm, 26 +/- 1 mmHg for 23 mm, and 38 +/- 2 mmHg for 20 mm diameters (p < 0.001). The authors conclude that oxygen transfer of a given intravascular gas exchanger appears to be indirectly proportional to the host vessel diameter. Increasing blood pressure gradient as a function of decreasing diameter has to be considered in clinical application.