Comparison of Aortic Annulus Diameter Measurement between Multi-Detector Computed Tomography and Echocardiography: A Meta-Analysis

Background and Purpose

Accurate measurement of aortic annulus diameter is crucial for choosing suitable prosthetic size for transcatheter aortic valve implantation (TAVI). Several imaging methods are available for the measurement, but significant variability between different modalities has been observed. The purpose of this study was to systematically compare the measurements of aortic annulus diameter between multi-detector computed tomography (MDCT), transthoracic echocardiography (TTE), and transesophegeal echocardiography (TEE).

Methods

PubMed and EMBASE databases between January 2000 and January 2012 were searched. We extracted data from eligible studies evaluating the aortic annulus diameter by MDCT and echocardiography (TTE, TEE, or both). We performed a random-effects meta-analysis to calculate the weighted mean differences of aortic annulus diameter measurement between MDCT, TTE, and TEE.

Results

A total of 10 eligible studies involving 581 subjects with aortic valve stenosis were included. Aortic annulus diameter measured on coronal view by MDCT (25.3±0.52 mm) was respectively larger than that measured on sagittal view by MDCT (22.7±0.37 mm), TTE (22.6±0.28 mm), and TEE (23.1±0.32 mm). The weighted mean difference of aortic annulus diameter between coronal view by MDCT and TTE these two methods was 2.97 mm, followed by the weighted mean difference of 2.53 mm between coronal view and sagittal view by MDCT, and the mean difference of 1.74 mm between coronal view on MDCT and TEE (P<0.0001 for all). The weighted mean difference of aortic annulus diameter measurement between TEE and TTE was significant but somewhat small (0.45 mm, P = 0.007).

Conclusion

Aortic annulus diameter measured on coronal view by MDCT was robustly and significantly larger than that obtained on sagittal view by MDCT, TTE, or TEE. Such variability of aortic annulus diameter measurement by different imaging modalities cannot be ignored when developing optimal strategies for selection of prosthetic valve size in TAVI.     

Respiratory variations of aortic VTI: a new index of hypovolemia and fluid responsiveness

In 12 mechanically ventilated and anesthetized rabbits, we investigated whether the magnitude of respiratory changes in the aortic velocity time integral (VTI(Ao)), recorded by transthoracic echocardiography (TTE) during a stepwise blood withdrawal and restitution, could be used as a reliable indicator of volume depletion and responsiveness. At each step, left and right ventricular dimensions and the aortic diameter and VTI(Ao) were recorded to calculate stroke volume (SV) and cardiac output (CO). Respiratory changes of VTI(Ao) (maximal - minimal values divided by their respective means) were calculated. The amount of blood withdrawal correlated negatively with left and right ventricular diastolic diameters, VTI(Ao), SV, and CO and correlated directly with respiratory changes of VTI(Ao). Respiratory VTI(Ao) variations (but not other parameters) at the last blood withdrawal step was also correlated with changes in SV after blood restitution (r = 0.83, P < 0.001). In conclusion, respiratory variations in VTI(Ao) using TTE appear to be a sensitive index of blood volume depletion and restitution. This dynamic parameter predicted fluid responsiveness more reliably than static markers of cardiac preload.     

Effects of isoflurane concentration on basic echocardiographic parameters of the left ventricle in rats

Transthoracic echocardiography (TTE) has become an important modality for the assessment of cardiac structure and function in animal experiments. The acquisition of echocardiographic images in rats requires sedation/anesthesia to keep the rats immobile. Commonly used anesthetic regimens include intraperitoneal or inhalational application of various anesthetics. Several studies have compared the effects of anesthetic agents on echocardiographic parameters in rats; however, none of them examined the effects of different concentrations of inhalational anesthetics on echocardiographic parameters. Accordingly, the aim of this study was to examine the effects of different concentrations of isoflurane used for anesthesia during TTE examination in rats on basic echocardiographic parameters of left ventricular (LV) anatomy and systolic function. TTE examinations were performed in adult male Wistar rats (n=10) anesthetized with isoflurane at concentrations of 1.5-3 %. Standard echocardiograms were recorded for off-line analysis. An absence of changes in basic echocardiographic parameters of LV anatomy and systolic function was found under isoflurane anesthesia using concentrations between 1.5-2.5 %. An isoflurane concentration of 3 % caused a small, but statistically significant, increase in LV chamber dimensions without a concomitant change in heart rate or fractional shortening. For the purpose of TTE examination in the rat, our results suggest that isoflurane concentrations 相似文献   

Comparison of Doppler flow Tei-indexes with pulmonary artery thermodilution measurement of cardiac output in an experimental porcine model

The objective of our study was to compare Doppler echocardiography imaging with pulmonary artery thermodilution measurement during mechanical ventilation. Total 78 piglets (6 weeks old, average weight 24 kg, under general anesthesia) were divided into 4 groups under different cardiac loading conditions (at rest, with increased left ventricular afterload, with increased right ventricular preload, and with increased afterload of both heart ventricles). At 60 and 120 min the animals were examined by echocardiography and simultaneously pulmonary artery thermodilution was used to measure cardiac output. Tei-indexes data were compared with invasively monitored hemodynamic data and cardiac output values together with calculated vascular resistance indices. A total of 224 parallel measurements were obtained. Correlation was found between values of right Tei-index of myocardial performance and changes in right ventricular preload (p<0.05) and afterload (p<0.01). Significant correlation was also found between left index values and changes of left ventricular preload (p<0.001), afterload (p<0.001), stroke volume (p<0.01), and cardiac output (p<0.01). In conclusion, echocardiographic examination and determination of the global performance selectively for the right and left ventricle can be recommended as a suitable non-invasive supplement to the whole set of methods used for monitoring of circulation and cardiac performance.     

Measuring stroke volume of the ascending aorta with an extravascular Doppler ultrasound probe in comparison with aortic thermodilution]

Currently, no reliable minimally invasive method of measuring cardiac output continuously in neonates and children undergoing cardiac surgery is available. An extravascular Doppler probe was used to measure cardiac output in 15 New Zealand White rabbits (average weight 3.5 kg, range 2.5-4.5 kg). The results obtained were compared with cardiac outputs determined using the aortic thermodilution principle. The mean cardiac outputs measured with the extravascular Doppler probe was 0.37 +/- 0.01 l/min as compared with 0.39 +/- 0.01 l/min with aortic thermodilution. Regression analysis revealed a close correlation (r = 0.973) between the two techniques. The extravascular Doppler techniques is an option for continuous and reliable cardiac output measurement in small animals used in surgical experiments (open chest models) and in neonates or children during surgical repair of complicated congenital heart conditions.     

Noninvasive Doppler determination of cardiac output during submaximal and peak exercise

We compared pulsed Doppler (PD) measurements of stroke volume (SV) and cardiac output (CO) as a function of work load with previously reported values that were obtained by standard invasive methods. Suprasternal notch measurements of Doppler-shifted frequency (delta f) were obtained from the ascending aorta and SV calculated with the Doppler equation and an independent measurement of aortic diameter. Motion artifacts were minimized with the aid of a restraining table cycle ergometer. Signal aliasing was accommodated with manual summation of delta f waveforms. A total of 207 determinations were made in 10 sitting subjects exercising to exhaustion. Linear regression analysis of CO vs. work load was significant (P less than 0.001). The correlation coefficient (r = 0.95) and standard error of estimate value (1.21 1/min) were similar to values from the literature. Absolute values of CO and SV underestimated the literature values across all work loads. Technical reproducibility was assessed by comparing with paired t tests the differences between 65 duplicate serial measurements of CO and SV at rest and exercise. No significant differences (P less than 0.001) were found. We concluded that PD-determined SV and CO are reproducible and correlate linearly with work load in a manner consistent with reported invasive techniques. Thus the PD method appears suitable for use during submaximal and peak exercise.     

Central nervous effects of CRF and angiotensin II on cardiac output in conscious rats

Studies were performed to determine whether the central nervous system actions of corticotropin-releasing factor (CRF) and angiotensin II (ANG II) on systemic arterial pressure are mediated, in part, through changes in cardiac output (CO). Changes in CO after intracerebroventricular administration of ANG II and CRF were assessed in conscious unrestrained rats bearing pulsed Doppler flow probes on the ascending aorta. Intracerebroventricular injection of CRF (0.15 nmol) increased arterial pressure (15-20 mmHg), heart rate (70-100 beats/min), and CO (25-35%) without significantly affecting total peripheral resistance. Intracerebroventricular injection of ANG II (0.1 nmol) produced similar elevations of arterial pressure (15-20 mmHg). However, the ANG II-induced pressor response was attended by significant decreases in heart rate (20 beats/min) and CO (10-15%) and significant increases in total peripheral resistance (30-40%). The results of these studies demonstrate that CO, as assessed by pulsed Doppler flow probe methodology, may be influenced significantly and differentially by central nervous system administration of CRF and ANG II.     

Echocardiographic assessment of age-associated changes in systolic and diastolic function of the female F344 rat heart.

Aging is associated with hypertrophy, dilatation, and fibrosis of the left ventricle (LV) of the heart. Advances in echocardiographic assessment have made it possible to follow changes in cardiac function in a serial, noninvasive manner. The purpose was to determine whether there is echocardiographic evidence of age-associated changes in chamber dimensions and systolic and diastolic properties of the female Fischer 344 (F344) rat heart. On the basis of previous invasive studies, it was predicted that echocardiographic assessment would detect age-associated changes in indexes of systolic and diastolic function. Rats were sedated with 1.5% isoflurane and placed in the supine position. Two-dimensional images and two-dimensionally guided M-mode, Doppler M mode, Doppler tissue, and pulsed-wave Doppler recordings were obtained from the parasternal long axis, parasternal short axis, and/or apical four-chamber views as per convention by using a 15-MHz linear array or 8-MHz phased-array transducer or a GE S10-MHz phased-array transducer. Compared with young adult 4-mo-old rats, there is a significant decrement in the resting systolic function of the LV in 30-mo-old female F344 rats as evidenced by declines in LV ejection fraction (80 +/- 9 vs. 89 +/- 5%; mean +/- SD), fractional shortening (43 +/- 9 vs. 54 +/- 8%) and velocity of circumferential fiber shortening (2.43 +/- 0.53 vs. 2.99 +/- 0.50 circ/s). Evidence for age-associated differences in diastolic function included an increase in isovolumic relaxation time (25.0 +/- 7.6 vs. 17.2 +/- 4.4 ms) and decreases in the tissue Doppler peak E waves at the septal annulus and at the lateral annulus of the mitral valve. The modest changes in systolic and diastolic LV function that occur with advancing age in the female F344 rat are likely to reduce the capacity of the heart to respond to hemodynamic challenges.     

Intraoperative intravascular volume optimisation and length of hospital stay after repair of proximal femoral fracture: randomised controlled trial.

OBJECTIVES: To assess whether intraoperative intravascular volume optimisation improves outcome and shortens hospital stay after repair of proximal femoral fracture. DESIGN: Prospective, randomised controlled trial comparing conventional intraoperative fluid management with repeated colloid fluid challenges monitored by oesophageal Doppler ultrasonography to maintain maximal stroke volume throughout the operative period. SETTING: Teaching hospital, London. SUBJECTS: 40 patients undergoing repair of proximal femoral fracture under general anaesthesia. INTERVENTIONS: Patients were randomly assigned to receive either conventional intraoperative fluid management (control patients) or additional repeated colloid fluid challenges with oesophageal Doppler ultrasonography used to maintain maximal stroke volume throughout the operative period (protocol patients). MAIN OUTCOME MEASURES: Time declared medically fit for hospital discharge, duration of hospital stay (in acute bed; in acute plus long stay bed), mortality, perioperative haemodynamic changes. RESULTS: Intraoperative intravascular fluid loading produced significantly greater changes in stroke volume (median 15 ml (95% confidence interval 10 to 21 ml)) and cardiac output (1.2 l/min (0.1 to 2.3 l/min)) than in the conventionally managed group (-5 ml (-10 to 1 ml) and -0.4 l/min (-1.0 to 0.2 l/min)) (P < 0.001 and P < 0.05, respectively). One protocol patient and two control patients died in hospital. In the survivors, postoperative recovery was significantly faster in the protocol patients, with shorter times to being declared medically fit for discharge (median 10 (9 to 15) days v 15 (11 to 40) days, P < 0.05) and a 39% reduction in hospital stay (12 (8 to 13) days v 20 (10 to 61) days, P < 0.05). CONCLUSIONS: Proximal femoral fracture repair constitutes surgery in a high risk population. Intraoperative intravascular volume loading to optimal stroke volume resulted in a more rapid postoperative recovery and a significantly reduced hospital stay.     

Effect of exercise on blood flow through the aortic valve: a combined clinical and numerical study

The aim of this study was to measure the cardiac output and stroke volume for a healthy subject by coupling an echocardiogram Doppler (echo-Doppler) method with a fluid–structure interaction (FSI) simulation at rest and during exercise. Blood flow through aortic valve was measured by Doppler flow echocardiography. Aortic valve geometry was calculated by echocardiographic imaging. An FSI simulation was performed, using an arbitrary Lagrangian–Eulerian mesh. Boundary conditions were defined by pressure loads on ventricular and aortic sides. Pressure loads applied brachial pressures with (stage 1) and without (stage 2) differences between brachial, central and left ventricular pressures. FSI results for cardiac output were 15.4% lower than Doppler results for stage 1 (r = 0.999). This difference increased to 22.3% for stage 2. FSI results for stroke volume were undervalued by 15.3% when compared to Doppler results at stage 1 and 26.2% at stage 2 (r = 0.94). The predicted mean backflow of blood was 4.6%. Our results show that numerical methods can be combined with clinical measurements to provide good estimates of patient-specific cardiac output and stroke volume at different heart rates.     

Simultaneous determination of the accuracy and precision of closed-circuit cardiac output rebreathing techniques.

Foreign and soluble gas rebreathing methods are attractive for determining cardiac output (Q(c)) because they incur less risk than traditional invasive methods such as direct Fick and thermodilution. We compared simultaneously obtained Q(c) measurements during rest and exercise to assess the accuracy and precision of several rebreathing methods. Q(c) measurements were obtained during rest (supine and standing) and stationary cycling (submaximal and maximal) in 13 men and 1 woman (age: 24 +/- 7 yr; height: 178 +/- 5 cm; weight: 78 +/- 13 kg; Vo(2max): 45.1 +/- 9.4 ml.kg(-1).min(-1); mean +/- SD) using one-N(2)O, four-C(2)H(2), one-CO(2) (single-step) rebreathing technique, and two criterion methods (direct Fick and thermodilution). CO(2) rebreathing overestimated Q(c) compared with the criterion methods (supine: 8.1 +/- 2.0 vs. 6.4 +/- 1.6 and 7.2 +/- 1.2 l/min, respectively; maximal exercise: 27.0 +/- 6.0 vs. 24.0 +/- 3.9 and 23.3 +/- 3.8 l/min). C(2)H(2) and N(2)O rebreathing techniques tended to underestimate Q(c) (range: 6.6-7.3 l/min for supine rest; range: 16.0-19.1 l/min for maximal exercise). Bartlett's test indicated variance heterogeneity among the methods (P < 0.05), where CO(2) rebreathing consistently demonstrated larger variance. At rest, most means from the noninvasive techniques were +/-10% of direct Fick and thermodilution. During exercise, all methods fell outside the +/-10% range, except for CO(2) rebreathing. Thus the CO(2) rebreathing method was accurate over a wider range (rest through maximal exercise), but was less precise. We conclude that foreign gas rebreathing can provide reasonable Q(c) estimates with fewer repeat trials during resting conditions. During exercise, these methods remain precise but tend to underestimate Q(c). Single-step CO(2) rebreathing may be successfully employed over a wider range but with more measurements needed to overcome the larger variability.     

Mouse heart valve structure and function: echocardiographic and morphometric analyses from the fetus through the aged adult

The purpose of this study is to provide standard echocardiographic and morphometric data for normal mouse valve structure and function from late fetal to aged adult stages. Cross-sectional, two-dimensional and Doppler transthoracic echocardiography was performed in C57BL6 mice anesthetized with 1% to 2% isoflurane at embryonic day 18.5 (late fetal), 10 days (neonate), 1 mo (juvenile), 2 mo (young adult), 9 mo (old adult), and 16 mo (aged adult). Normal annulus dimensions indexed to age or weight, and selected flow velocities, were established by echocardiography. After echocardiographic imaging, hearts were harvested and histological and morphometric analyses were performed. Morphometric analysis demonstrated a progressive valve thinning and elongation during the fetal and juvenile stages that plateaued during adult stages (ANOVA, P < 0.01); however, there was increased thickening of the hinge of the aortic valve with advanced age, reminiscent of human aortic valve sclerosis. There was no age-related calcification. The results of this study provide comprehensive echocardiographic and morphometric data for normal mouse valve structure and function from late fetal to aged adult stages and should prove useful as a reference standard for future studies using mouse models of progressive valve disease.     

Wall shear stress during pulsatile flow distal to a normal porcine aortic valve

The shear stress at the wall has been of interest as one of the possible fluid dynamic factors that may be damaging in the region of prosthetic valves. The purpose of this study was to measure the axial wall shear stresses in the region of a 29 mm tissue annulus diameter porcine stent mounted prosthetic aortic valve (Hancock, Model 242). Studies were performed in an in vitro pulse duplicating system. The axial wall shear stress was calculated from velocities obtained near the wall with a laser Doppler anemometer. The largest axial wall shear stress was 29 dyn cm-2 and it occurred at the highest stroke volume used (80 ml). At a stroke volume of 50 ml, the largest axial wall shear stress was 17 dyn cm-2 and at a stroke volume of 35 ml, it was 15 dyn cm-2. Stresses of these magnitudes are far below those reported to be damaging to the endothelial surface. These stresses may be high enough, however, to affect platelet function.     

Bioreactance Is Not Interchangeable with Thermodilution for Measuring Cardiac Output during Adult Liver Transplantation

BackgroundThermodilution technique using a pulmonary artery catheter is widely used for the assessment of cardiac output (CO) in patients undergoing liver transplantation. However, the unclearness of the risk-benefit ratio of this method has led to an interest in less invasive modalities. Thus, we evaluated whether noninvasive bioreactance CO monitoring is interchangeable with thermodilution technique.MethodsNineteen recipients undergoing adult-to-adult living donor liver transplantation were enrolled in this prospective observational study. COs were recorded automatically by the two devices and compared simultaneously at 3-minute intervals. The Bland–Altman plot was used to evaluate the agreement between bioreactance and thermodilution. Clinically acceptable agreement was defined as a percentage error of limits of agreement <30%. The four quadrant plot was used to evaluate concordance between bioreactance and thermodilution. Clinically acceptable concordance was defined as a concordance rate >92%.ResultsA total of 2640 datasets were collected. The mean CO difference between the two techniques was 0.9 l/min, and the 95% limits of agreement were -3.5 l/min and 5.4 l/min with a percentage error of 53.9%. The percentage errors in the dissection, anhepatic, and reperfusion phase were 50.6%, 56.1%, and 53.5%, respectively. The concordance rate between the two techniques was 54.8%.ConclusionBioreactance and thermodilution failed to show acceptable interchangeability in terms of both estimating CO and tracking CO changes in patients undergoing liver transplantation. Thus, the use of bioreactance as an alternative CO monitoring to thermodilution, in spite of its noninvasiveness, would be hard to recommend in these surgical patients.     

Effect of the mechanical ventilatory cycle on thermodilution right ventricular volumes and cardiac output.

The purpose of this study was to evaluate right ventricular (RV) loading and cardiac output changes, by using the thermodilution technique, during the mechanical ventilatory cycle. Fifteen critically ill patients on mechanical ventilation, with 5 cmH(2)O of positive end-expiratory pressure, mean respiratory frequency of 18 breaths/min, and mean tidal volume of 708 ml, were studied with help of a rapid-response thermistor RV ejection fraction pulmonary artery catheter, allowing 5-ml room-temperature 5% isotonic dextrose thermodilution measurements of cardiac index (CI), stroke volume (SV) index, RV ejection fraction (RVEF), RV end-diastolic volume (RVEDV), and RV end-systolic volume (RVESV) indexes at 10% intervals of the mechanical ventilatory cycle. The ventilatory modulation of CI and RV volumes varied from patient to patient, and the interindividual variability was greater for the latter variables. Within patients also, RV volumes were modulated more by the ventilatory cycle than CI and SV index. Around a mean value of 3.95 +/- 1.18 l. min(-1). m(-2) (= 100%), CI varied from 87.3 +/- 5.2 (minimum) to 114.3 +/- 5.1% (maximum), and RVESV index varied between 61.5 +/- 17.8 and 149.3 +/- 34.1% of mean 55.1 +/- 17.9 ml/m(2) during the ventilatory cycle. The variations in the cycle exceeded the measurement error even though the latter was greater for RVEF and volumes than for CI and SV index. For mean values, there was an inspiratory decrease in RVEF and increase in RVESV, whereas a rise in RVEDV largely prevented a fall in SV index. We conclude that cyclic RV afterloading necessitates multiple thermodilution measurements equally spaced in the ventilatory cycle for reliable assessment of RV performance during mechanical ventilation of patients.     

Validation of echocardiographic and Doppler indexes of left ventricular relaxation in adult hypertensive and normotensive rats

This study was performed to validate echocardiographic and Doppler techniques for the assessment of left ventricular (LV) diastolic function in spontaneously hypertensive rats (SHR) and normotensive Wistar rats. In 11 Wistar rats and 20 SHR, we compared 51 sets of invasive and Doppler LV diastolic indexes. Noninvasive indexes of LV relaxation were related to the minimal rate of pressure decline (-dP/dt(min)), particularly isovolumic relaxation time (IVRT), the Tei index, the early velocity of the mitral annulus (E(m)) using Doppler tissue imaging, and early mitral flow propagation velocity using M-mode color (r = 0.28-0.56 and P < 0.05-0.0001). When the role of systolic load was considered, the correlation between Doppler indexes of LV diastolic function and relaxation rate [(-dP/dt(min))/LV systolic pressure] improved (r = 0.48-0.86 and P = 0.004-0.0001, respectively). Similarly, Doppler indexes of LV diastolic function and the time constant of isovolumic LV relaxation (tau) correlated well (r = 0.50-0.84 and P = 0.0002-0.0001, respectively). In addition, eight SHR and eight Wistar rats were compared; their LV end-diastolic diameters were similar, whereas the SHR LV mass was greater. Furthermore, IVRT and Tei index were significantly higher and E(m) was lower in SHR. Moreover, tau was higher in SHR, demonstrating impaired LV relaxation. In conclusion, LV relaxation can be assessed reliably using echocardiographic and Doppler techniques, and, using these indexes, impaired relaxation was demonstrated in SHR.     

Volutrauma activates the clotting cascade in the newborn but not adult rat

Coagulopathy and alveolar fibrin deposition are common in sick neonates and attributed to the primary disease, as opposed to their ventilatory support. Hypothesizing that high tidal volume ventilation activates the extrinsic coagulation pathway, we air ventilated newborn and adult rats at low (10 ml/kg) or high (30 ml/kg) tidal volume and compared them with age-matched nonventilated controls. Blood was collected at the end of the experiment for measurement of clot time, tissue factor, and other coagulation factor content. Similar measurements were obtained from lung lavage material. The newborn clot time (44+/-1) was lower and plasma tissue factor content higher (103.4+/-0.4) than adults (88+/-4 s and 26.6+/-1.4 units; P<0.01). High, but not low, tidal volume ventilation of newborns for as little as 15 min significantly reduced clot time and increased plasma tissue factor content (P<0.01). High volume ventilation increased plasma factor Xa (0.1+/-0.1 to 1.6+/-0.4 nM; P<0.01) and thrombin (1.3+/-0.2 to 2.2+/-0.4 nM; P<0.05) and decreased antithrombin (0.12+/-0.01 to 0.05+/-0.01; P<0.01) in the newborn. Lung lavage material of high volume-ventilated newborns showed increased (P<0.01) factor Xa and thrombin. No changes in these parameters were observed in adult rats that were high volume ventilated for up to 90 min. Compared with adults, newborn rats have a greater propensity for volutrauma-activated intravascular coagulation. These data suggest that mechanical ventilation promotes neonatal thrombosis via lung tissue factor release.     

Buccal capnometry to guide management of massive blood loss.

In both clinical and experimental settings, tissue P(CO2) measured in the oral mucosa is a practical and reliable measurement of the severity of hypoperfusion. We hypothesized that a threshold level of buccal tissue P(CO2) (P(CO2) BU)) would prognosticate the effects of volume repletion on survival. Twenty pentobarbital-anesthetized Sprague-Dawley male breeder rats, each weighing approximately 0.5 kg, were randomly assigned to one of four groups. Animals were bled over an interval of 30 min in amounts estimated to be 25, 30, 35, or 40% of total blood volume. One-half hour after the completion of bleeding, each animal received an infusion of Ringer lactate solution over the ensuing 30 min in amounts equivalent to two times the volume of blood loss. P(CO2) BU) was measured continuously with an optical P(CO2) sensor applied noninvasively to the mucosa of the left cheek. Arterial pressure and end-tidal CO2 were measured over the same interval. Neurological deficit and 72-h survival were recorded. Aortic pressures were restored to near baseline values for each of the four groups after fluid resuscitation. This contrasted with the improvement of P(CO2) BU), which differentiated between animals with short and long durations of postintervention survival. After electrolyte fluid resuscitation in rats subjected to rapid bleeding, noninvasive measurement of P(CO2) BU) was predictive of outcomes. Neither noninvasive end-tidal P(CO2) nor invasive aortic pressure measurements achieved such discrimination. Accordingly, P(CO2) BU) fulfills the criterion of a noninvasive and reliable measurement to guide fluid management of hemorrhagic shock.     

Shear-layer detection in poststenotic flow by spectrum analysis of Doppler signals

Spectrum analysis of the Doppler signals was performed 0.5 tube diameters downstream from an axisymmetric constriction with an area reduction of 80 percent in steady flow at a jet Reynolds number of 2840. Both pulsed and continuous wave (CW) Doppler spectra showed significant reverse flow components in the separated flow. The pulsed Doppler spectra exhibited sudden changes when the sample volume crossed the shear layer between the center jet and the separated flow. A power spectrum equation was theoretically derived from continuity of flow to define the Doppler shift frequency for the shear layer velocity. The CW Doppler spectrum showed a minimum spectrum density at a frequency which equalled the shear layer Doppler shift frequency derived from the equation. The pulsed spectra exhibited the sudden changes at the same frequency as well.     

Postnatal lung function in the developing rat.

Little is known about lung function during early stages of postnatal maturation, although the complex structural changes associated with developing rat lung are well studied. We therefore analyzed corresponding functional (lung volume, respiratory mechanics, intrapulmonary gas mixing, and gas exchange) and structural (alveolar surface area, mean linear intercept length, and alveolar septal thickness) changes of the developing rat lung at 7-90 days. Total lung capacity (TLC) increased from 1.54 +/- 0.07 to 16.7 +/- 2.46 (SD) ml in proportion to body weight, but an increase in body weight exceeded an increase in lung volume by almost twofold. Series dead space volume increased from 0.21 +/- 0.03 to 1.38 +/- 0.08 ml but decreased relative to TLC from 14% to 8%, indicating that parenchymal growth exceeded growth of conducting airways. Diffusing capacity of CO (D(CO)) increased from 8.1 +/- 0.8 to 214.1 +/- 23.5 micromol min(-1) hPa(-1), corresponding to a substantial increase in surface area from 744 +/- 20 to 6,536 +/- 488 cm(2). D(CO) per unit of lung volume is considerably lower in the immature lung, inasmuch as D(CO)/TLC in 7-day-old rats was only 42% of that in adult (90 day-old) rats. In humans, however, infants and adults show comparable specific D(CO). Our functional and structural analysis shows that gas exchange is limited in the immature rat lung. The pivotal step for improvement of gas exchange occurs with the transition from bulk alveolarization to the phase of expansion of air spaces with septal reconstruction and microvascular maturation.