Biomedical subjects

B R Wilcox

Publications and source records attributed to B R Wilcox.

At least 55 records · Page 3Linked to original sources

PubMed1988

A clinical review of patients undergoing resection for pulmonary hamartoma.

Both the radiology and surgery literature mention "popcorn calcification" as a diagnostic aid in identifying pulmonary hamartomas. Nineteen patients underwent resection of pulmonary hamartomas at North Carolina Memorial Hospital between January 1969 and February 1983, representing 1.9 per cent of all thoracotomies performed for pulmonary disease. Of the 19 patients, there were 12 men (63%) and 7 women (37%), and most were asymptomatic. Chest x-ray demonstrated 12 right-sided and 7 left-sided lesions. All masses were located peripherally in the lung parenchyma and in no instance was calcification present. Fourteen wedge resections and 5 lobectomies were performed. Pathologic examination confirmed the absence of calcification; however, in two cases (11%) an associated malignancy was present. There were no operative deaths and only minor postoperative complications. All problems resolved without difficulty. These data show that pulmonary hamartomas are not commonly associated with calcification, and there may be an increased association with carcinoma of the lung. Excision can be performed with minimal morbidity and is necessary to distinguish hamartomas from malignant lesions.

Adult↗

PubMed1987

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.

Animals↗

PubMed1987

Thoracic surgery manpower: the fourth manpower study of thoracic surgery: 1985 report of the Ad Hoc Committee on Manpower of The American Association for Thoracic Surgery and The Society of Thoracic Surgeons.

Responding to a survey about their practice in 1985, 2,969 (70%) Board-certified thoracic surgeons provided data that were compared with data from manpower surveys in 1980 and 1976. (table; see text) Thoracic surgeons were most active between ages 35 and 54 years when they accomplished 61% of all general thoracic and 85% of cardiac operations. Surgeons older than 50 years performed significantly more general thoracic operations than younger surgeons, and the younger group performed significantly more cardiac operations than their older counterparts. Solo practice continued to decline. In smaller referral areas, the number of general thoracic procedures per surgeon increased, but the number of cardiac operations have decreased compared with 1980. Overall, general thoracic and cardiac operations increased, but peripheral vascular procedures and pacemaker insertions decreased in almost all nine census regions. Fewer general thoracic and cardiac operations were performed per thoracic surgeon in the western United States than in central and eastern regions. In response to questions about work load, 55% believed that their clinical activity was satisfactory, 42% operated too little, and 3% operated too much. The 363 non-Thoracic Board-certified surgeons who responded performed 14% of general thoracic and 8% of cardiac surgery in 1985. During the first half of the 1980s, our specialty certified an average of 134 thoracic surgeons annually, which is higher than the 120 surgeons per year estimated to meet the projected demand.

Adult↗

PubMed1987

Continuous measurement of pulmonary blood flow using a retractable pulsed Doppler probe.

The feasibility of measuring pulmonary blood flow (PAQ) continuously using a removable, extraluminal 20 MHz pulsed Doppler probe, which has been used successfully to measure aortic blood flow, was assessed in seven anesthetized mongrel dogs. Simultaneous recordings were made from the Doppler probe (range-gated 5-6 mm from the anterior wall of the main pulmonary artery) and an electromagnetic flow probe (encircling the aorta) over cardiac outputs (CO) ranging from 0.2 to 5.5 L/min. Assuming a flat velocity profile and a fixed cross-sectional area, PAQ was initially calculated as the product of area and mean velocity. Regression analyses (PAQ = a + b X CO) indicated good intraanimal linear correlations in six animals (r greater than or equal to 0.84) and no correlation in one animal (r = 0.003); however, PAQ was consistently higher than CO and interanimal variability was marked, as suggested by large deviations in mean intercept and slope values (a = 1.67 +/- 1.09 L/min and b = 0.70 +/- 0.33). Results improved (r greater than or equal to 0.79 in all animals, a = 0.47 +/- 0.52 L/min, and b = 0.77 +/- 0.21) when the method to estimate PAQ was altered to assume that the starting cross-sectional area was the area that would make baseline PAQ and CO agree, and that the area during each subsequent CO level changed as a function of pulmonary artery pressure and an estimate of pulmonary artery compliance. Results of this study imply that it will be more difficult to use this Doppler probe to monitor CO from the pulmonary artery than it was from the aorta due to the elliptical, more compliant pulmonary vessel walls and the irregular pulmonary artery velocity profile.

Animals↗

PubMed1987

The use of angiodynography to quantify blood flow in the canine aorta.

Previous attempts to quantify blood flow by means of ultrasound have been hampered by inaccurate diameter measurements and failure to account for the parabolic nature of the cross-sectional velocity profile. Angiodynography (ADG) provides a B-mode image of vessel walls, and the outer flow envelope is constantly monitored to provide phasic diameter measurements throughout the cardiac cycle. Frequency shifts are color-coded to provide a real-time visual display of varying velocity patterns across the vessel lumen throughout the cardiac cycle as well as calculation of average flow velocity and mean blood flow. Simultaneous flow values obtained with ADG were compared with electromagnetic flow probe (EMF) measurements in 12 open-chest dogs. Flow was varied with volume administration and exsanguination, and 201 data points were obtained. The average flow determined by EMF was 2.0 +/- 0.9 L/min compared with 2.04 +/- 0.71 L/min for ADG. The correlation coefficient was 0.88, the y-intercept was close to zero, and the slope approached unity, confirming the ability of ADG to accurately determine volume blood flow rather than merely to establish a flow trend. It is concluded that ADG offers an accurate way of quantifying volume blood flow.

Animals↗

PubMed1987

Constant postoperative monitoring of cardiac output after correction of congenital heart defects.

A new method has been developed that permits constant postoperative monitoring of mean and phasic cardiac output in patients after correction of congenital heart defects. A miniature ultrasound probe is attached to the adventitia of the ascending aorta at the conclusion of the operative procedure. This is connected to the monitoring equipment by means of polyurethane-covered wires that exit the chest wall through a small stab wound. The probe can easily be removed by gentle traction when the patient's condition is stable. The technique was developed, validated, and refined in extensive animal studies, and this report describes the first series of 20 consecutive human implants, performed between August 1984 and September 1985, in which the absolute cardiac output determination obtained with the ultrasound probe at the time of its application was correlated with cardiac output as measured with a standard electromagnetic flow probe. Fourteen male and six female patients (mean age 5.5 years) were studied. Operations performed included eight atrial septal defect repairs, four procedures for tetralogy of Fallot, three ventricular septal defect repairs, three stenotic valve corrections, and two Senning operations. One operative death occurred, but no complications were related to probe application or removal. The average cardiac output in the 20 patients as measured with the ultrasound probe was 2.2 +/- 1.1 L/min (range 0.67 to 5.27 L/min). This is nearly identical to the results noted with the electromagnetic flow probe, where the mean cardiac output was 2.3 +/- 1.2 L/min (range 0.7 to 6 L/min). Regression analysis revealed a high linear correlation (r = 0.9) between the two techniques. A monitor can display the cardiac output trend with 1 minute updates, which greatly enhance management of intravenous drug therapy and volume administration. In conclusion, this new extraluminal removable probe allows virtually continuous monitoring of the postoperative cardiac output after correction of congenital heart defects and should become a standard technique in the postoperative care of these patients.

Adolescent↗

PubMed1986

Maturation of pulmonary input impedance spectrum in infants and children with ventricular septal defect.

To determine whether pulmonary vascular disease can be detected in infants with ventricular septal defect (VSD) by the presence of an increase in the frequency of the impedance modulus minimum of the pulmonary input impedance spectrum, as has been implied for older children, spectra of 25 infants (2 years or younger) (group 1) were compared with spectra of 20 children (ages 2 to 7 years) (group 2). Groups were subdivided according to mean pulmonary artery (PA) pressure: those with moderate pressure levels (35 mm Hg or less, groups 1A and 2A) and those with high pressure levels (at least 40 mm Hg, groups 1B and 2B). Pulmonary vascular resistance, characteristic impedance and frequency of the modulus minimum were significantly lower in group 2A than in group 1A. The decrease in pulmonary vascular resistance and characteristic impedance with increasing age was consistent with body surface area increases; however, the shift in frequency of the modulus minimum could be more easily related to a decrease in the pulse wave velocity than to a shift in the primary reflection site. Pulmonary vascular resistance, characteristic impedance and the frequency of the first modulus minimum were comparable in groups 1B and 2B; however, none of the patients in group 1B had evidence of pulmonary damage, whereas 3 of 4 group 2B patients had microscopically apparent pulmonary vascular disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

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

Surgical management of symptomatic pulmonary aspergilloma.

Pulmonary aspergilloma is a potentially life-threatening disease resulting from the colonization of lung cavities by the ubiquitous fungus Aspergillus fumigatus. Complex aspergilloma, characterized by thick-walled cavities with surrounding parenchymal inflammation, is a risk factor for increased morbidity and mortality. Fifteen patients with symptomatic aspergilloma underwent major thoracic procedures at North Carolina Memorial Hospital between January 1, 1972, and December 31, 1983. Twelve of the patients had hemoptysis; in 7 it was recurrent and in 5, life threatening. Tuberculosis and sarcoidosis were the most common underlying causes of lung disease, and more than half of the patients had other coexistent serious medical illness. Eleven of the 15 patients were seen with complex aspergilloma; all of the 4 major complications and the 2 deaths occurred in these patients. Bronchopleural fistula with persistent air space was the most common serious complication, and required thoracoplasty in 3 patients. Nine patients, including 5 with complex aspergilloma, had no postoperative complications, and there were no recurrent symptoms in any of the 13 operative survivors over a mean follow-up of five years. It is concluded that aggressive pulmonary resection can provide effective long-term palliation in critically ill patients with symptomatic pulmonary aspergilloma.

Adult↗

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↗

PubMed1984

Selective application of fundoplication in achalasia.

Although esophagomyotomy alone may effectively relieve dysphagia in patients with achalasia, utilization of a complementary fundoplication procedure should be considered for selected patients. Fundoplication is a sensible addition to myotomy in circumstances that suggest high risk for the development of reflux esophagitis. Also, in complicated achalasia, relief of esophageal obstruction by simple myotomy may not be achieved safely. Identification of those pathological features associated with achalasia that merit consideration of fundoplication should improve operative results and reduce morbidity. This paper examines the application of a complementary fundoplication procedure in the operative management of 21 patients with achalasia over a ten-year period.

Adolescent↗

PubMed1984

Major pulmonary resection for suspected but unconfirmed malignancy.

Thoracotomy is not infrequently performed in patients with suspected pulmonary carcinoma but with no histological or cytological confirmation of malignancy. The intraoperative decision to proceed with major pulmonary resection (lobectomy or pneumonectomy) is difficult if a large or central lesion precludes total excisional biopsy. Incisional or needle biopsies violate the principles of good cancer surgery, and the results may be inconclusive if the tumor is missed and areas of associated inflammation or necrosis are sampled. Between January 1, 1970, and December 31, 1980, 303 patients underwent thoracotomy for suspected but unconfirmed malignancy. One hundred twenty-two had a minor resection only, 79 had a major resection (lobectomy or pneumonectomy) after a diagnosis was established by frozen section, and 102 had a major resection without a definitive diagnosis of cancer. Carcinoma subsequently was found in 68% (69) of this group of 102 patients, and benign lesions were identified in the remaining 32% (33), all of whom underwent lobectomy. The diagnoses in these 33 patients included seven granulomas, three hamartomas, nine instances of tuberculosis, and fourteen instances of fibrosis, inflammation, or cystic degeneration. The 2 thirty-day operative deaths in this group of 102 patients occurred among the 69 with malignant disease; 1 died of hemorrhage following pneumonectomy and 1, of respiratory insufficiency after lobectomy. In all 303 patients, there was no difference in operative mortality (p less than 0.01) between lobectomy (2%) and a lesser resection (1.6%). In a patient with a suspicious but inaccessible pulmonary lesion, lobectomy can be performed safely without violating the principles of cancer surgery. This recommendation should probably not be extended to lesions requiring pneumonectomy, because of the increased rates of morbidity and mortality associated with that procedure.

Diagnosis, Differential↗