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Biomedical subjects

G R Mason

Publications and source records attributed to G R Mason.

At least 55 records · Page 3Linked to original sources
PubMed1986

99mTc-DTPA aerosol deposition and clearance in COPD, interstitial disease, and smokers.

The application of 99mTc-DTPA radioaerosols to a variety of clinical disorders is described. With the development of simple equipment that can deliver very small droplets, this approach has become increasingly popular for measurements of the distribution of ventilation in patients with obstructive lung disease and suspected pulmonary embolism. In addition, by determining the rate at which the radionuclide is cleared from the lung, information has been obtained concerning the permeability of the pulmonary epithelium to extracellular indicators. Accelerated clearance rates have been found in patients with a variety of chronic interstitial lung diseases indicating that epithelial permeability is increased. Accelerated clearance rates have also been found with acute inflammation of the lung such as the adult respiratory distress syndrome and pneumocystis pneumonia. Furthermore, rapidly reversible increases in 99mTc-DTPA clearance occur in smokers and may be related to the inflammatory changes that contribute to the development of emphysema.

Aerosols↗
PubMed1986

Movement of ions and small solutes across endothelium and epithelium of perfused rabbit lungs.

In situ and isolated fluid-filled rabbit lungs were used to study the transport of indicators between the air space and vascular compartments. These indicators were placed in either the perfusate or air spaces and samples were collected from the perfusate at intervals during a 1-h perfusion period. At the end of the hour, fluid was pumped out of the air space compartment into serial tubes and indicator concentrations were determined in both the air space and perfusion fluids. One hour after introducing the indicators into the air space, the relative decreases in solute concentration were (arranged from the greatest to the least decline): [14C]urea greater than 36Cl- = 125I- greater than 22Na+ greater than [3H]mannitol. The relative rates at which the indicators appeared in the perfusate were similar. When the indicators were placed in the perfusate, a similar relationship was observed in the increase in air space concentrations, but the loss of 22Na+ from the perfusate was similar to those of 36Cl- and 125I-. Losses of all indicators from the perfusate were two or more times those from the air spaces, and although the loss of [3H]mannitol from the perfusate was similar to that of 22Na+ for about 30 min, subsequent loss was much slower. Very little 125I-albumin traversed the tissue barrier, and the small changes in the concentrations of 125I-albumin in the air spaces suggested that little fluid movement had occurred. These studies suggest that the epithelium is less permeable to solutes than the endothelium and permits passage of anions at a faster rate than 22Na+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Selective impairment of nutrient absorption from intestines with chronic venous hypertension.

Malnutrition is frequently associated with advanced cirrhosis. To investigate the role of portal hypertension in nutritional impairment, we developed an animal model to isolate and characterize the effects of chronic intestinal venous hypertension on intestinal nutrient absorption. We performed mesenteric arteriovenous anastomosis combined with portal vein banding in rats. Hepatic architecture and excretory function (bile flow and bile salt output) were unaltered, while severe and persistent intestinal venous hypertension was produced. We then measured in vivo absorption rates of three test nutrients (vitamin D3, valine, and tryptophan) and water. Vitamin D3 absorption was significantly impaired by intestinal congestion, while amino acid absorption was unaffected. Splanchnic hypertensive rats absorbed less water than controls. We conclude that chronic intestinal venous hypertension alone selectively impairs nutrient absorption.

Animals↗
PubMed1985

Evaluation of possible patient survival in a mock airplane disaster.

A mock disaster at Orange County's John Wayne Airport provided a basis for examining correct triage of patients and their arrival time for definitive care. The ability to triage critically injured patients in a timely fashion was found to be only slightly better than chance routing. For most of the seriously and critically injured patients, it took more than 1.5 hours to reach the hospital. Advanced life support with intravenous fluid resuscitation available on the scene would probably reduce the mortality of possible disaster victims by 50 percent. These problems are presently being addressed. In future disaster exercises, the present type of evaluation could be used to judge improvement in possible patient triage and survival.

Accidents, Aviation↗
PubMed1985

Diffusion of labeled water and lipophilic solutes in the lung.

A perfused, in situ rabbit lung preparation was used to study the diffusion of tritiated water and labeled lipophilic solutes from the airways into the pulmonary vasculature. Following instillation into the airways, initial concentrations of labeled ethanol and butanol in the left atrial outflow usually exceeded those of 3H2O when the lungs were perfused at 37 degrees. In contrast, initial concentrations of [14C]acetone equaled 3H2O concentrations, and those of [14C]antipyrine were below 3H2O concentrations. Increasing the rate of perfusion increased concentrations of the labeled butanol and acetone but decreased that of antipyrine relative to 3H2O. This suggests that the tissues separating the gaseous and vascular compartments of the lung are more permeable to 3H2O than to antipyrine but less permeable to 3H2O than to the alcohols and acetone. Cooling slowed permeation of ethanol and antipyrine relative to 3H2O but seemed to slow diffusion of butanol less than that of 3H2O. These differences cannot be related to movement in the aqueous phase and suggest that cooling slows solute diffusion through lipid membranes. This phenomenon appears to be related to the activation energy of each molecule between the aqueous and lipid phases rather than a phase change in the membrane. 3H2O seems to diffuse through aqueous regions of the air-perfusate barrier.

Acetone↗
PubMed1985

Pulmonary imaging in pregnancy. Maternal risk and fetal dosimetry.

A Tc-99m macroaggregated albumin (MAA) perfusion lung scan and a Tc-99m DTPA aerosol ventilation scan were performed for suspicion of pulmonary embolism (PE) in a patient who was ten weeks pregnant. There was considerable reluctance on the part of the obstetricians to permit this study. Standard MIRD dose estimates to the fetus were performed, which showed a maximum fetal exposure of about 50 mrem. It was concluded that the risk to mother and fetus from undiagnosed and untreated PE is much greater than the negligible risk to the fetus from the radiation exposure; fear of fetal radiation damage should not be a deterrent to performing these scans.

Adult↗
PubMed1985

Laser Doppler velocimetry as a monitor of cardiac output changes in dogs.

Cutaneous blood flow may be measured utilizing a continuous, noninvasive technique, laser Doppler velocimetry (LDV). Monitoring of cutaneous blood flow by LDV might be a useful method to monitor cardiac output. To test this hypothesis, sequential measurements of cardiac output, LDV, and transcutaneous oxygen (PtcO2) were made on 10 anesthetized dogs during experimental shock. There was significant correlation between LDV and cardiac output, while PtcO2 reflected cardiac output only at low flow states. These results show that, in the animal model, cutaneous LDV is a sensitive and specific method for monitoring cardiac output changes.

Animals↗
PubMed1985

Small solute clearance from the lungs of patients with cardiogenic and noncardiogenic pulmonary edema.

The regional clearance of 99mTc-diethylenetriamine penta-acetate (99mTc-DTPA) from the lungs was measured in 14 patients with noncardiogenic pulmonary edema, six patients with acute pulmonary edema secondary to heart failure, and 29 normal subjects. The radionuclide was delivered in an aerosol which was inhaled for 120 seconds, and the subsequent decline of radioactivity from the lungs was monitored for seven minutes over each of six peripheral regions of interest with a computerized scintillation camera. The average 99mTc-DTPA clearance of these regions was accelerated above the 98 percent confidence limits in all but three of the patients with noncardiogenic edema. The mean clearance value in this group of patients was significantly greater than those in normal subjects or patients with cardiogenic pulmonary edema. Clearances returned toward normal in each of seven subjects who improved clinically. Only one of the patients with cardiogenic pulmonary edema had an elevated average clearance rate, and the mean clearance for this population was not statistically greater than normal. This procedure appears to detect increased epithelial permeability caused by lung injury and may help distinguish between cardiogenic and noncardiogenic pulmonary edema.

Adult↗
PubMed1985

Blood and plasma substitutes--plasma expansion and oxygen transport properties.

Because of the risks and costs of blood and blood product infusion, developing blood and plasma substitutes is of significance. Two currently utilized substances, dextran and hydroxyethyl starch, are effective colloid plasma expanders. The dextrans have properties that improve microcirculatory blood flow but are associated with several possible adverse effects. Hydroxyethyl starch is a well-tolerated agent that has efficacy similar to albumin but at a lower cost. Two newer substances, perfluorocarbons and stroma-free hemoglobin, are being developed to improve oxygen transport as well as plasma expansion.

Blood Substitutes↗
PubMed1984

Perfluorocarbon infusion in bleeding patients refusing blood transfusions.

Six severely anemic surgical patients who refused blood products were treated with a perfluorochemical (PFC) emulsion (Fluosol-DA 20%). When these patients received high inspired oxygen concentrations, the emulsion resulted in moderate increases of arterial oxygen content but considerable increases of oxygen consumption, suggesting improved microcirculatory oxygen distribution. The mean +/- SD percentages of consumed oxygen transported by dissolved oxygen in PFC and PFC plus plasma emulsions were 22% +/- 5% and 60% +/- 12%, respectively. Several adverse clinical effects were seen, however, including transient decreases in leukocyte counts, hypotension, and abnormal hepatic and pulmonary function.

Anemia↗
PubMed1984

Laser photoradiation therapy of cancer: an update of the experience at the University of California, Irvine.

This update of the experience at the University of California at Irvine with laser photoradiation therapy (PRT) encompasses the period between May 1981 and June 1983. The results of treatment of 77 patients are reported (head and neck, 39; breast, 33; and lung 5). Head and neck cancer patients received treatment to 114 sites with a complete response (CR) in 28, partial response (PR) in 42, stable disease (SD) in three, and no response (NR) in 34, and an undetermined response in seven. Breast cancer patients were treated in 395 sites with CR in 222, PR in 74, SD in one, NR in 92, and undetermined response in six. The lung cancer patients in this series responded poorly, if at all. In addition to the above patient trials, we have investigated the interaction of laser hematoporphyrin derivative (HPD)-PRT with a chemotherapeutic agent, Cisplatin, against an experimental tumor (RIF-1) in an animal model. We have been unable to demonstrate an additive effect of laser HPD-PRT at total light doses of 25 J/cm2 and 75 J/cm2 with Cisplatin at a dose of 7 mg/kg. However, no additional toxicity was observed in combination therapy, suggesting that sequential application of laser HPD-PRT and Cisplatin may be safely employed in clinical situations. Another area of investigation has been the evaluation of the light-scattering characteristics of a lipid emulsion designed for laser HPD-PRT of bladder tumors. We have demonstrated that it is feasible to gain uniform illumination of the bladder surface with the use of this light-dispersing medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Evaluation of visual acuity during laser photoradiation therapy of cancer.

Visual function for ten patients undergoing HPD-PRT was tested using 1) the Graham Field Eye Chart for distance vision, 2) pseudo-isochromatic plates for color vision, and 3) Amsler grid for changes in macular function. Whereas some increases and decreases in ocular function were observed, no clear patterns or changes of significance were observed.

Adult↗
PubMed1984

Pancreaticogastrostomy: clinical experience with a direct pancreatic-duct-to-gastric-mucosa anastomosis.

The propensity for leakage and disruption at the site of the pancreaticojejunostomy is a major reason for morbidity and death after pancreaticoduodenal resection. Because it is less prone to leakage and disruption, pancreaticogastrostomy has been reintroduced as a possible alternative to pancreaticojejunostomy. Of four patients in whom the pancreas was simply implanted into the stomach and five patients in whom a direct pancreatic-duct-to-gastric-mucosa anastomosis was constructed, there was no morbidity or death related to the pancreatic anastomosis. Because of evidence that a direct pancreatic-duct-to-gastric-mucosa anastomosis has an increased incidence of patency and because it was successful in a clinical setting, it is recommended.

Aged↗
PubMed1984

Photoradiation therapy of head and neck cancer.

We have embarked upon a pilot study of photoradiation therapy (PRT) in the treatment of persistent or recurrent cancer of the head and neck, utilizing the photosensitizing agent, hematoporphyrin derivative (HPD). This treatment is based upon selective concentration of HPD within malignant tissue, with resultant necrosis upon illumination with light of the appropriate wavelength (640 nm). Patients entered in this trial have failed all forms of conventional therapy. Twenty-one patients with local recurrence were treated. Sites of recurrence were: tongue (9); nasopharynx (3); floor of mouth (2); soft palate (2); oropharynx (1); buccal mucosa (1); maxilla (1); larynx (1); and basal cell nevus (1). There were six complete responses and twelve partial responses (greater than 50% reduction). These responses are clinically significant, with some complete responses lasting over 1 year after a single course of therapy. Ten patients with cutaneous metastases from head and neck primary tumors were also treated. There were two complete responses and three partial responses. However, these patients rapidly developed new tumors in areas adjacent to those previously treated. Less than complete responses could be augmented by repeated applications of this technique. The success of this pilot study combined with the accessibility of head and neck primaries suggest that there should be a clinical trial of HPD-PRT in early mucosal cancer of the head and neck region.

Bronchoscopy↗
PubMed1984

Predictability and maintenance of portal flow patterns after small-diameter portacaval H-grafts in man.

Patients undergoing small-diameter (8, 10, 12, and 14 mm) portacaval H-grafts were followed up to 3.5 years. Eight- and 10-mm grafts maintained prograde portal perfusion in 50% of the patients. Follow-up studies performed from 6 to 36 months after surgery show late shunt patency to be 97%. Recurrent variceal hemorrhage has not occurred in any patients. Direction of portal flow after a shunt was related to the size of the portal vein and the size of the shunt. If the shunt diameter was less than 50% that of the portal vein measured on the preoperative angiogram, portal flow was prograde. Encephalopathy rates remained significantly lower in patients with prograde flow after small diameter (8 and 10 mm) portacaval H-graft (p = .0.1). If thrombosis and encephalopathy rates remain low, the small-diameter, polytetrafluoroethylene portacaval H-graft is an attractive alternative to standard portacaval and mesocaval shunts.

Blood Circulation↗