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Biomedical subjects

C L Lucas

Publications and source records attributed to C L Lucas.

At least 37 records · Page 2Linked to original sources
PubMed1986

Cardiopulmonary hypoxic response 5 years postpneumonectomy in beagles.

Ventilatory hypoxia was used to study the effects on pneumonectomy on the right heart and pulmonary vascular bed in purebred beagle dogs. Operated animals underwent pneumonectomy at 6 to 10 weeks of age (six, group I) or at 1 year (eight, group II). Eight unoperated adult beagles served as controls (group III). Five years following pneumonectomy, exposure to 10% O2 ventilation indicated that group I animals were more reactive to hypoxia than either group II or III. Increases in pulmonary flow were recorded as group I, 0.79 +/- 0.58 liter/min; II, 0.32 +/- 0.54 liter/min; III, 0.04 +/- 0.24 liter/min (P = 0.006, I vs III, two-tailed test). Also, the peak first derivatives of power and blood flow and the external work of the right ventricle increased significantly in group I compared to group III but not in group II compared to group III. On the contrary, hypoxic stress produced similar changes in pulmonary vascular resistance and characteristic impedance in all groups. It is concluded that the hyperdynamic response of the group I animals, those undergoing pneumonectomy as puppies, can be attributed to a primary change in pump characteristics.

Age Factors↗
PubMed1986

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.

Animals↗
PubMed1985

Infant pulmonary vascular model based on the pulmonary input impedance spectrum.

A mathematical model of the infant pulmonary vascular system was developed by altering an adult model to fit the hemodynamic properties of an infant pulmonary vascular bed. The model was designed for infants between the ages of 1 and 2 years with both normal and high mean pulmonary artery pressures (PAPs). The resulting infant model was evaluated on the basis of the computed parameters of cumulative length, volume and resistance of the pulmonary vascular bed, as well as on the basis of comparisons of the model spectra with actual computed spectra for ventricular septal defect patients who were of comparable age, had comparable mean PAPs and were not diagnosed as having pulmonary vascular disease. It was observed that the first minimum and first maximum in the modulus of the input impedance spectrum of the infant model for both normal and high mean PAPs occurred at a higher frequency than in the adult model. These observations led to the conclusion that there is a natural, age-related shift in the input impedance spectrum of infants which is not necessarily indicative of pulmonary impairment.

Blood Pressure↗
PubMed1985

Changes in ventricular hemodynamics caused by a systemic-pulmonary shunt.

Systemic pulmonary shunts are both surgically created (Blalock-Taussig anastomosis) and obliterated (patent ductus arteriosus), but the effects of such a vascular communication on left ventricular hemodynamics have not been examined quantitatively. To study these effects, innominate arterial allografts were sutured between the descending thoracic aorta and the left main pulmonary artery in nine mongrel dogs. Left ventricular output (LVO) and shunt flow (SF) were monitored with electromagnetic flow probes while simultaneous phasic and mean pressures were recorded from the right atrium, aorta (AOP), and pulmonary artery. Data points (192) were analyzed while SF was varied between 0.02 and 5.5 liters/min using a variable-sized constricting band. Regression analysis showed increases (P less than 0.01) in LVO, stroke work (SW), and stroke volume (SV) in all dogs which were linearly related to SF (r = 0.64-0.99). Increasing SF was also associated with decreases (P less than 0.01, r = 0.61-0.99) in resistance (RES) facing the left ventricle and in diastolic (D) AOP. To compensate for differences in allograft size and to quantify the effects of a patent shunt, the regression equations were used to compare the percentage change in all parameters at SF = 0 and SF = 1.5 liters/min. Increases occurred in SV (46 +/- 21%), SW (32 +/- 14%), and LVO (48 +/- 21%), and decreases were present in DAOP (15 +/- 12%) and RES (32 +/- 13%). These data show that despite the decreases in pressure or the decreases in resistance facing the left ventricle in the presence of a systemic pulmonary shunt, a substantial increase in stroke work occurs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

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)

Age Factors↗
PubMed1985

Cardiovascular effects of positive end-expiratory pressure (PEEP) after pneumonectomy in dogs.

Little is known regarding the hemodynamic effect of positive end-expiratory pressure (PEEP) following pneumonectomy. To investigate this, 9 mongrel dogs underwent PEEP before and after lung resection. With the chest closed, the dog anesthetized, and partial pressure of carbon dioxide constant, PEEP was added in increments of 2 mm Hg until the animal's condition became hemodynamically unstable. At each level of PEEP, aortic, pulmonary, left atrial, and central venous pressures were monitored while aortic flow (cardiac output) was determined with an electromagnetic probe and airway pressure was measured with a Millar catheter in the respiratory tubing. Pneumonectomy was then performed, PEEP was again sequentially added, and the same measurements were recorded. Both before and after pneumonectomy, a strong positive linear correlation exists between the level of PEEP and pulmonary vascular resistance (PVR) (r greater than 0.74; p less than 0.05). Also, there is a high negative linear correlation between the level of PEEP and cardiac output (r greater than -0.76; p less than 0.05). At 0 mm Hg of PEEP, the PVR is higher after pneumonectomy than before (p less than 0.02). The incremental elevation in PVR persists after pneumonectomy at each level of PEEP, and in 5 of the 9 dogs the slope of the linear regression line relating PVR to PEEP was steeper following resection (p less than 0.05), thereby demonstrating an exaggerated effect of PEEP on PVR. In addition, all animals had a lower cardiac output at each comparable level of PEEP following pneumonectomy (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Two-dimensional in vivo pressure/diameter relationships in the canine main pulmonary artery.

Ultrasonic measurement of blood flow within the main pulmonary artery (MPA) requires a precise knowledge of the mean blood velocity within this vessel and the cross-sectional area (CSA). Small conformational changes in the elliptical shape of the MPA have substantial effects on the calculation of CSA and, subsequently, flow. We examined the extent of these changes by measuring the pulsatile and mean elliptical dimensions of the MPA in nine anaesthetised, open-chested, mechanically ventilated mongrel dogs using two pairs of 10 MHz ultrasonic, piezoelectric crystals. These custom-made devices were sutured to the PA adventitia along the long and short cross-sectional axes 2 cm distal to the pulmonary valve. Axial dimensions were collected during normal, elevated (via noradrenaline and fluid additions) and reduced (via exsanguination) PA pressures. We confirmed the linear pressure/diameter response in 15/18 axial data sets (r greater than 0.80). Further, the linear axial responses of the long and short diameters were parallel (7/9, p less than 0.05) and have different zero-pressure intercepts (7/9, p less than 0.0001). A mathematical consequence of this parallelism is predictable, although non-constant, eccentricity. Finally, error analysis of multi-axial measurement techniques were shown to improve CSA accuracy by as much as 50% when compared with uni-axial determinations.

Animals↗
PubMed1985

Ultrasound detection and quantitation of left to right aortopulmonary shunt flow in a canine model.

To test the sensitivity and accuracy of pulsed Doppler ultrasonography to detect and quantitate left to right aortopulmonary shunt flow, an arterial allograft aortopulmonary anastomosis was constructed in nine adult mongrel dogs. Cardiac output and allograft flow were measured as the diameter of the allograft was varied. Piezoelectric crystals attached to the carotid artery and proximal descending aorta were energized with 20 MHz pulsed Doppler signals. Negative Doppler shift and negative Doppler shift/positive Doppler shift were calculated for seven dogs. All dogs exhibited negative Doppler shift in the carotid artery at zero allograft flow; five of the seven dogs exhibited a similar pattern in the descending aorta. Increasing negative Doppler shift was measured in all dogs from both sites as the allograft flow increased. Excellent linear correlation existed between allograft flow and negative Doppler shift and negative Doppler shift/positive Doppler shift for each dog from both sampling sites. However, marked interanimal variation in the slopes of the linear regression lines existed, making the composite linear correlation very poor. Detection of small left to right aortopulmonary shunting and single measurements to quantitate accurately left to right aortopulmonary shunting introduce errors due to intersubject variation. However, these results suggest that serial ultrasound measurements made over a short time can accurately predict changes in left to right aortopulmonary shunting.

Animals↗
PubMed1985

Viscous factors in peripheral tissue perfusion.

To ascertain the relative importance of the factors that influence blood viscosity (VIS), we measured hematocrit (HCT), filterability index, fibrinogen level (FIB), and Ektacytometer indices at osmolarities of both 290 (EI 290) and 200 (EI 200) in 21 diabetic patients with peripheral vascular disease (DPVDs) and 11 healthy volunteers (HVs). Stepwise multiple regression analyses generated a formula based on three of the independent variables (FIB, HCT, EI 200) that accurately predicted VIS (r = 0.79, p less than 0.01). Based on the beta coefficients and F statistics, HCT and FIB were the most important elements in the linear regression equation. Compared with HVs the total group of DPVDs had lower HCT (36.5% vs. 42.4%) and higher FIB (661 vs. 276 mg/dl, p less than 0.01) values. When all HVs were compared with a subgroup of DPVDs with similar HCT (n = 10), both FIB and VIS were higher (p less than 0.001) in the DPVD than in the HV group. We conclude that the most important of the multiple factors that influence VIS are HCT and FIB. The finding of increased FIB in DPVDs could have important implications for drug and surgical therapy in this group of patients.

Blood Circulation↗
PubMed1984

Velocity profile in the main pulmonary artery in a canine model.

The velocity profile of the main pulmonary artery was determined in nine adult, open-chested, mechanically ventilated mongrel dogs using an intraluminal, needle-mounted, range-gated, pulsed Doppler technique. Mean phasic point velocities were determined at 2 mm intervals across the lumen of the vessel, 2 cm above the pulmonary valve, by recording the Doppler shift of an activated 20 MHz piezoelectric crystal, range-gated 3.5 mm in the direction of the pulmonary valve. Mean Reynolds numbers from the main pulmonary artery ranged from 275 to 1140. Radially normalised intraluminal distance versus mean phasic point velocity plots were constructed which demonstrated a curved profile in all 9 dogs. First order regression analysis demonstrated a poor fit (r: 0.05-0.68). Second order (r:0.61-0.97) and third order (r:0.72-0.99) regression analyses markedly improved the fit, confirming the non-linear nature of the velocity profile. Step-wise third order regression analysis to determine the importance of the entry sequence demonstrated that the most important term for determining the regression coefficient was the X2 term in six dogs. In addition, the velocity profile was noted to be shifted, with the highest velocities recorded between the centre of the vessel and the anterior wall in eight of nine dogs (location of highest velocity: +0.26 radius +/- 0.25 (mean +/- SD).

Animals↗
PubMed1984

The velocity profile in the canine ascending aorta and its effects on the accuracy of pulsed Doppler determinations of mean blood velocity.

The velocity profile in the ascending aorta, which has been variously reported as parabolic, skewed or flat, was measured using an intraluminal probe equipped with a miniature piezoelectric crystal activated by a 20 MHz pulsed Doppler with a 1 mm3 sample volume size. Phasic velocities, determined via spectral analyses, were obtained at 2 mm intervals across the aortic lumen of anaesthetised open-chest dogs by sequentially moving the crystal between posterior and anterior walls, maintaining the ultrasound beam parallel to the flow axis. Range-gating allowed data acquisition 3.5 mm proximal to the crystal, thus eliminating probe induced turbulence. Time and spatial distributions of velocities over the cross-section were computed. Expected errors in vessel mean velocity estimates based on point measurements were calculated. Analysis of phasic waveforms showed increased posterior velocities during systole but third order regression analysis of normalised point mean velocities across the lumen showed the best fit was a statistically flat straight line. Centreline referenced analyses indicated the expected difference between point mean velocity and vessel mean velocity was maximal (19.3 +/- 10.1%) 4 mm toward the posterior wall and minimal (4.7 +/- 9.1%) 5 mm toward the anterior wall. Anterior posterior wall referenced analyses indicated the most reliable position for estimating vessel mean velocity from point mean velocity along this axis was 5 mm from the anterior wall.

Animals↗
PubMed1984

Fluid mechanics of the pulmonary circulation.

Assessment of the fluid mechanics of the pulmonary circulation has been hindered by the relative inaccessibility of the pulmonary vascular bed. Current understanding is based largely on analyses of mathematical models which have been used to simulate hemodynamic characteristics within an architectural representation of that bed. These representations have ranged from simple, lumped parameter structures to anatomically realistic structures based on measurements of casts of the irregular branching network of pulmonary arteries and veins. Nonlinear models have been studied to determine the effects of vessel taper and within beat geometrical variations as cross-sectional shapes change from circular to elliptical and small vessels undergo recruitment, distention, and collapse as a result of the shifting balance in alveolar, pleural, and capillary pressures. This article reviews current concepts of pulmonary circulatory fluid mechanics focusing on mathematical models and relevant hemodynamic studies.

Adolescent↗
PubMed1983

Identification of internal carotid artery stenosis in coronary artery bypass candidates.

Identification of stenotic internal carotid arteries in neurologically asymptomatic coronary artery bypass candidates is difficult. We correlated carotid arteriograms with carotid bruits in 422 vessels and demonstrated a sensitivity of 79% and a specificity of 65% with regard to the bruit's identification of vessels with a 50% or more reduction in angiographic diameter. The noninvasive duplex scan, used in conjunction with Fast Fourier Transform spectral analysis, had a sensitivity and a specificity of 90% in this same regard. Since there is only a 6% incidence of significant internal carotid stenosis in bypass candidates, Bayes' theorem used in conjunction with our findings showed that a carotid bruit was an incorrect predictor of internal carotid stenosis 87% of the time. The duplex scan was somewhat better, but still inaccurate 64% of the time. Thus neither parameter alone has a high enough predictive value to determine whether preoperative carotid angiography is necessary. However, if one limits duplex scanning to patients with a carotid bruit, the predictive value is raised to 92%. At the same time, there is minimal increase in the number of undiagnosed patients. Thus far this combined approach is recommended for preoperative evaluation of patients scheduled for coronary artery bypass.

Angiography↗
PubMed1983

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.

Animals↗
PubMed1983

Effects of pneumonectomy on pulmonary input impedance.

The long-term effects of pneumonectomy on the pulmonary circulation quantifiable through pulmonary input impedance analysis were studied. Excision of the left lung was performed in purebred beagle dogs aged 6 to 10 weeks (n = 6 group I) or 1 year (n = 8 group II). Unoperated beagles served as controls (n = 8 group III). When the dogs were 5 years of age, pulmonary pressure and flow were measured and the impedance spectra calculated. Characteristic impedance (Zo) (indicative of changes in proximal vessel physical properties) and pulmonary vascular resistance (PVR) (indicative of the distal response) were estimated. In group III the cardiac output (CO) was 1.7 +/- 0.4 L/min, mean pressure 16 +/- 5 mm Hg, PVR 605 +/- 448 dyne-sec/cm, and Zo 204 +/- 76 dyne-sec/cm. Group I results exhibited bimodal distributions that were not statistically different from results of groups II or III; four dogs had spectra comparable to those of group III, while two dogs had developed moderate hypertension and high PVR and Zo. Group II results were more normally distributed, and comparison with group III indicated statistically significant differences (P less than 0.05) in CO (1.1 +/- 2 L/min), PVR (1396 +/- 573 dynes-sec/cm), and Zo (543 +/- 273 dynes-sec/cm). Doubling of PVR and Zo in group II indicated that proximal vessel compliance and peripheral perfusion radius had not increased following pneumonectomy in adult beagles. Group I results indicate that marked facilitory adaptation can occur when pneumonectomy is performed in puppies; however, the adaptation may not be based on true lung growth and, therefore, may not be sustained indefinitely.

Adaptation, Physiological↗
PubMed1981

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.

Aortic Dissection↗
PubMed1976

Contrasting pulmonary blood flow profiles in children with atrial and ventricular septal defects.

Instantaneous pulmonary blood flow profiles and other measures of haemodynamic functioning were studied in children with atrial septal defects (ASD) and children with ventricular septal defects (VSD) and normal pulmonary pressures and resistance at the time of defect closure. Though most parameters measured were comparable in the patient populations, several significant differences were found in the shape of the flow profile.

Blood Flow Velocity↗