Carol L. Lucas

Elective Pulmonary Lobectomy: Factors Associated with Morbidity and Operative Mortality

Periodic review of clinical results is essential to ensure that high-quality patient care is maintained. To that end, we reviewed the morbidity and operative mortality in a consecutive series of 369 pulmonary lobectomies performed between January 1, 1970, and December 31, 1983. There were 251 male and 118 female patients with a mean age of 50.6 years. The thirty-day operative mortality was 2.2% (8/369), with 6 of these deaths related primarily to respiratory insufficiency. Two hundred twenty-four postoperative management problems occurred in 151 patients and included arrhythmia, air leak, pneumothorax, respiratory difficulties, postoperative bleeding, pleural effusion, wound infection, myocardial infarction, pulmonary embolus, empyema, bronchial stump leak, and lobar gangrene. Multiple factors were related to the occurrence of postoperative morbidity and mortality using both chi-square analysis to examine each individual item and discriminant analysis to evaluate their interaction. Chi-square tabulation showed no difference in the occurrence of major postoperative complications (p greater than 0.05) related to the side of operation, an abnormal preoperative electrocardiogram, a forced vital capacity of 2.8 liters or less, a one-second forced expiratory volume (FEV1) of less than 1.7 liters, an oxygen tension of less than 60 mm Hg, or the seniority of the surgeon (resident versus attending). An increased number of complications (p less than 0.05) was found in male patients, in patients operated on for carcinoma, and in patients older than 60 years. Stepwise discriminant analysis included FEV1 as a significant predictor of postoperative complications.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of time domain algorithms for estimating aortic characteristic impedance in humans

Using data obtained intraoperatively from 134 patients (262 data sets), ten algorithms for estimating aortic characteristic impedance from the relative slopes of the aortic pressure and flow (electromagnetic flow probe) waveforms during early systole were compared to the estimate obtained by averaging input impedance modulus values for frequencies between 2 and 16 Hz (Zc). Results clearly confirmed the relationship between these slopes and Zc:r>or=0.80, y intercepts approximately=0.0 and slopes approximately=1.0 for all algorithms tested. However, four algorithms yielded estimates with r >or=0.95. The common trait of these four algorithms was their dependence on portions of the pressure and flow waveforms independently centered around peak derivatives. Results imply that Zc can be estimated successfully in real time, which would be advantageous in critical postoperative periods. Furthermore, cumbersome computational procedures can be eliminated whenever Zc is the only spectral-related parameter to be calculated.<<ETX>>

The effect of incorporating vessel compliance in a computational model of blood flow in a total cavopulmonary connection (TCPC) with caval centerline offset

BACKGROUND The total cavopulmonary connection (TCPC), a palliative correction for congenital defects of the right heart, is based on the corrective technique developed by Fontan and Baudet. Research into the TCPC has primarily focused on reducing power loss through the connection as a means to improve patient longevity and quality of life. The goal of our study is to investigate the efficacy of including a caval offset on the hemodynamics and, ultimately, power loss of a connection. As well, we will quantify the effect of vessel wall compliance on these factors and, in addition, the distribution of hepatic blood to the lungs. METHODS We employed a computational fluid dynamic model of blood flow in the TCPC that includes both the non-Newtonian shear thinning characteristics of blood and the nonlinear compliance of vessel tissue. RESULTS Power loss in the rigid-walled simulations decayed exponentially as caval offset increased. The compliant-walled results, however, showed that after an initial substantial decrease in power loss for offsets up to half the caval diameter, power loss increased slightly again. We also found only minimal mixing in both simulations of all offset models. CONCLUSIONS The increase in power loss beyond an offset of half the caval diameter was due to an increase in the kinetic contribution. Reduced caval flow mixing, on the other hand, was due to the formation of a pressure head in the offset region which acts as a barrier to flow.

The Acute Effects of Pneumonectomy on Pulmonary Vascular Impedance in the Dog

Pulmonary vascular impedance is a measure of the pulsatile characteristic of pressure and flow that occurs in the proximal pulmonary arteries. Pulmonary vascular resistance (PVR) is most influenced by the distal circulation of the lung. This study was performed to evaluate the changes that occurred in pulmonary vascular impedance, as well as in other hemodynamic variables, following pneumonectomy by a closed-chest method in 10 anesthetized dogs. The following observations were made (numbers compare mean values for the 10 dogs before and after pneumonectomy): (1) PVR increased from 447 to 761 dyne sec cm-5 (p = .02); (2) the oscillatory work of the right ventricle increased from 1.23 to 1.76 J/min (p = .006); (3) the mean pulmonary artery pressure increased from 14 to 18.8 mm Hg (p = .0001); and (4) cardiac output and heart rate remained unchanged. Surprisingly, the estimated characteristic impedance (the impedance to oscillatory flow in the proximal bed) did not change significantly (279 to 296 dyne sec cm-5). This observation cannot be explained by the usual lumped compartmental models classically used to characterize the pulmonary vascular bed.

Characteristics of blood flow velocity in the hypertensive canine pulmonary artery

Pulmonary artery blood flow velocity was measured in 15 dogs by a recently developed direct intraluminal pulsed Doppler technique. Changes in velocity characteristics under conditions of experimentally induced hypoxic pulmonary hypertension were observed. Experimental conditions (fractional inspired oxygen concentration = 0.10) produced significant increases in mean pulmonary artery pressure and pulmonary vascular resistance. Overall and maximal negative velocity increased with pulmonary hypertension. Negative velocity occurred predominantly in the posterior half of the pulmonary artery during both control and experimental conditions. With pulmonary hypertension, diastolic negative velocity increased only in the posterior half of the pulmonary artery and systolic negative velocity decreased only in the anterior half. More basic knowledge of pulmonary artery blood flow characteristics may facilitate an informed approach to noninvasive detection of pulmonary hypertension. Direct measurements by this recently developed intraluminal technique will be useful in studying various conditions with altered pulmonary blood flow.

Pulmonary blood velocity profile variability in open-chest dogs: Influence of acutely altered hemodynamic states on profiles, and influence of profiles on the accuracy of techniques for cardiac output determination

SummaryClinical investigations focused on finding characteristics of noninvasively obtained measurements of pulmonary blood velocity that can be used to quantitate pulmonary blood flow and/or pulmonary pressure have often yielded results whose imprecision has been attributed to flow pattern variability. To determine flow pattern variability in an in vivo animal model in varying hemodynamic states, main pulmonary artery blood velocity waveforms were recorded in 17 dogs at 2-mm intervals along an anterior to posterior wall-oriented axis using a 20-MHz pulsed Doppler needle probe. Control data were obtained before the animals were subjected to altered flow (atrial level shunts) and pressure (10% O2 inhalation) states. Instantaneous velocity profiles were computed throughout the cardiac cycle. Estimates of pulmonary blood flow were obtained assuming an elliptical model of the pulmonary artery which allowed computation of velocity at all points in the cross section, based on the measured values along the axis. Model-based estimates were compared to measured values and estimates obtained in the traditional fashion, i.e., the product of centerline velocity and cross-sectional area. Results clearly showed marked interanimal variability, even in control states. Reverse flow in the posterior half of the vessel, which tended to become more pronounced with increased pulmonary artery pressure, was observed during late systole and early diastole. Elevated pulmonary blood flow tended to increase the maximum velocities along the anterior wall relative to midline velocities. Neither estimate of cardiac output yielded consistently accurate results (r=0.77 for model-based method,r=0.80 for area times central velocity method). Findings of this study, which highlight the dependency of waveform characteristics on sampling site, the large degree of intersubject variability, and the need for large or multiple sample volumes for pulmonary blood flow determination, help clarify inconsistencies observed by clinicians and suggest that future work with animal models will facilitate a greater understanding of the determinants of human pulmonary velocity waveforms.

Clinical and Experimental Evaluation of Left Ventriculoiliac Shunt Bypass during Repair of Lesions of the Descending Thoracic Aorta

Temporary ventriculoiliac bypass with a tridodecylmethylammonium chloride-coated shunt has been used routinely at the University of North Carolina for the past seven years for repair of lesions of the descending thoracic aorta. Although the technic appears to be safe and reliable, the hemodynamic effects of prolonged nonvalved apical diversion on left ventricular function are not defined. To evaluate left ventricular performance during ventriculoiliac shunt bypass, the procedure was investigated in adult sheep. Systolic flow through the shunt was pulsatile and accounted for approximately 35% of the total cardiac output. Reversed flow was minimal. No significant change occurred in cardiac output, left ventricular end-diastolic pressure, or left atrial pressure. Perfusion of the abdominal viscera through the shunt was sufficient to prevent intestinal and renal ischemia. Our results indicate that the shunt provides left ventricular decompression without evidence of deterioration in left ventricular performance for up to three hours of apical bypass and aortic occlusion. It is included that bypass with a left ventriculoiliac shunt provides safe and effective diversion during repair of lesions of the descending thoracic aorta and offers and excellent alternative to methods involving greater technical hazard or requiring systemic anticoagulation.

High-resolution four-dimensional surface reconstruction of the right heart and pulmonary arteries

Determination of the surface of the heart is a challenging problem due to the hearts motion and the potential importance of subtle geometric features. The Meyer watershed has been shown to be an effective solution to this problem in images of the left ventricle in at least two medical image types. In this paper the technique is extended, first of all, by application to the right ventricle (RV) in an image from the Dynamic Spatial Reconstructor (DSR). Additionally, several important issues related to its general application are addressed including: (1)image anisotropy, (2)4D processing and (3) valve localization. The Meyer watershed model itself is also discussed in some detail with respect to its implementation and general properties. A simple by-product of surface reconstruction of the RV in the DSR images is that of the pulmonary arteries.

A LabVIEW™ Model Incorporating an Open-Loop Arterial Impedance and a Closed-Loop Circulatory System

While numerous computer models exist for the circulatory system, many are limited in scope, contain unwanted features or incorporate complex components specific to unique experimental situations. Our purpose was to develop a basic, yet multifaceted, computer model of the left heart and systemic circulation in LabVIEW™ having universal appeal without sacrificing crucial physiologic features. The program we developed employs Windkessel-type impedance models in several open-loop configurations and a closed-loop model coupling a lumped impedance and ventricular pressure source. The open-loop impedance models demonstrate afterload effects on arbitrary aortic pressure/flow inputs. The closed-loop model catalogs the major circulatory waveforms with changes in afterload, preload, and left heart properties. Our model provides an avenue for expanding the use of the ventricular equations through closed-loop coupling that includes a basic coronary circuit. Tested values used for the afterload components and the effects of afterload parameter changes on various waveforms are consistent with published data. We conclude that this model offers the ability to alter several circulatory factors and digitally catalog the most salient features of the pressure/flow waveforms employing a user-friendly platform. These features make the model a useful instructional tool for students as well as a simple experimental tool for cardiovascular research.

A removable extraluminal Doppler probe for continuous monitoring of changes in cardiac output.

To address the problem of monitoring cardiac output in postoperative cardiac patients, a removable, extraluminal pulsed Doppler probe has been constructed which continuously reflects changes in cardiac output by monitoring blood velocity in the ascending aorta. Velocity is related to the frequency of the Doppler shift and the angle at which the ultrasound beam intersects the vessel. A 1 mm2 piezoelectric crystal mounted at a 45 degree angle on the tip of the probe is activated with a 20‐MHz range‐gated pulsed Doppler, and velocity is determined from Fourier analysis of quadrature data using computer software with a 50‐KHz processing range. The device is designed for application to the ascending aorta at the conclusion of a cardiac surgical procedure; and, since mean diameter changes in the ascending aorta have been shown to be very small over a wide range of mean aortic pressures, cardiac output is linearly related to velocity. To test this technique, simultaneous recordings were made from the pulsed Doppler probe and an electromagnetic flow probe in five mongrel dogs over a range of cardiac outputs from 0.5 to 6 l/min for a total of 136 data points. Excellent correlation was found between the electromagnetic flow probe and pulsed Doppler probe data (average r = .98 +/‐ .006). Average slope between the two was 1.004 and average zero intercept was ‐0.025 l/min. The catheter is small, stable, has no baseline drift, and continuously and accurately reflects pulsatile changes at high and low flows.