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Biomedical subjects

M E Douglas

Publications and source records attributed to M E Douglas.

10 recordsLinked to original sources
PubMed1992

Origin of Gila seminuda (Teleostei: Cyprinidae) through introgressive hybridization: implications for evolution and conservation.

Morphological and genetic characters from cyprinid fishes of the genus Gila were examined to assess a hypothesized hybrid origin of Gila seminuda from the Virgin River, Arizona-Nevada-Utah. The presumed parents, Gila robusta robusta and Gila elegans, are clearly differentiated from one another based on morphology, allozymes, and mtDNA haplotypes. G. seminuda is morphologically intermediate and polymorphic at allozyme loci diagnostic for the parental species. Restriction endonuclease analysis of mtDNA showed G. seminuda nearly identical to G. elegans. These results support an origin of the bisexual taxon G. seminuda through introgressive hybridization. The Gila population in the Moapa River, Nevada, also appears to be of hybrid origin and is considered a distinctive population of G. seminuda. Inter-specific hybridization is potentially an important mode of evolution among western North American fishes, and valid species of hybrid origin may exist in other groups as well. Consideration of this mode of evolution argues for the need to conserve entire species complexes.

Animals↗
PubMed1979

Alteration of oxygen tension and oxyhemoglobin saturation. A hazard of sodium bicarbonate administration.

The administration of sodium bicarbonate solution, which has been advocated for the treatment of metabolic acidosis, may have detrimental side effects. We evaluated oxyhemoglobin saturation and oxygen tensions in eight anesthetized swine before and after freshwater near-drowning and after a rapid intravenous infusion of 7.5% sodium bicarbonate solution (8 mEq/kg). After freshwater aspiration, arterial and venous oxygen tensions and oxyhemoglobin saturation decreased. Administration of sodium bicarbonate resulted in decreased venous and increased arterial, oxygen tensions. Arterial, but not venous, oxyhemoglobin saturation increased. These findings suggest that sodium bicarbonate caused a distinct leftward shift in the oxyhemoglobin dissociation curve, which could impair tissue oxygenation. Therefore, to avoid detrimental effects, sodium bicarbonate should be administered slowly and in a dose sufficient just to correct metabolic acidosis.

Acidosis↗
PubMed1979

Lung expansion, airway pressure transmission, and positive end-expiratory pressure.

Transmission of airway pressure to the intrapleural space and change in functional residual capacity by positive end-expiratory pressure (PEEP) were measured in ten anesthetized swine. Measurements and calculations were performed with varying lung and chest wall compliances. When both compliances were normal, approximately half of the applied airway pressure was transmitted. Aspiration of hydrochloric acid reduced lung compliance approximately fourfold and decreased airway pressure transmission. Increased thoracic compliance also reduced airway pressure transmission. When acid aspiration reduced lung compliance and sternotomy simultaneously increased thoracic compliance, pressure transmission was maximally reduced. Decreases in either thoracic or lung compliance reduced the volume-expanding effects of PEEP. Positive end-expiratory pressure was least effective when thoracic and lung compliances were reduced simultaneously. Careful assessment of both lung and thoracic compliances may be helpful in treating patients requiring elevated airway pressure.

Animals↗
PubMed1979

Renal function and cardiovascular responses during positive airway pressure.

The authors determined cardiovascular, renal, and hormonal responses to increased airway pressure during continuous positive-pressure ventilation (CPPV) and continuous positive airway pressure (CPAP). Nine healthy, hydrated laboratory swine had appropriate catheters placed to allow for measurement of intrapleural, aortic, inferior vena caval, and left ventricular end-diastolic pressures; cardiac output; and urinary flow. Samples of arterial blood were analyzed for oxygen and carbon dioxide tensions, pH, plasma vasopressin, osmolality, and creatinine and sodium concentrations. Urine was analyzed for osmolality and creatinine and sodium concentrations, and volume was recorded. Intrapleural pressure was subtracted from left ventricular end-diastolic pressure to calculate transmural pressure, a reflection of left ventricular filling pressure. Glomerular filtration rate and urinary free-water and osmolal clearances were also calculated. Expiratory left ventricular filling pressure was decreased equally by CPAP and CPPV. However, inspiratory left ventricular filling pressure and cardiac output were decreased by CPPV only. Urinary flow and glomerular filtration rate were decreased equally by CPAP and CPPV. Sodium excretion was decreased and plasma vasopressin increased by CPPV, but not by CPAP. Urinary free water and osmolal clearances were not changed by either ventilatory pattern. Although many of the renal-function variables were affected similarly by CPPV and CPAP, these alterations were not influenced solely by cardiac output or vasopressin, because only CPPV depressed cardiac output and increased vasopressin levels.

Animals↗
PubMed1979

Comparison of assisted and controlled mechanical ventilation in anesthetized swine.

We compared assisted mechanical ventilation with controlled mechanical ventilation with and without PEEP in 10 anesthetized swine. Catheters were placed to measure airway, intrapleural, and blood pressure; PaO2 and PaCO2; arterial pH; total minute ventilation; and mixed exhaled oxygen and carbon dioxide tensions. We calculated the ratio of physiological dead space to tidal volume, alveolar minute ventilation, CO2 production, VO2, and RQ. We found no clinically or statistically significant difference between assisted and controlled ventilation.

Anesthesia↗
PubMed1977

Pulmonary function following severe acute respiratory failure and high levels of positive end-expiratory pressure.

In an 18-month period, we treated 561 patients with mechanical ventilation. Fifty-four (10 percent) of these patients had acute respiratory failure, requiring treatment with positive end-expiratory pressure (PEEP) in excess of 20 mm Hg (range, 20 to 40 mm Hg). All patients were allowed to breathe spontaneously between volume-limited mechanical breaths delivered at a rate sufficient to maintain an arterial pH greater than or equal to 7.35. PEEP was applied until calculated pulmonary venous admixture was minimized. Forty-three (80 percent) of these 54 patients were alive and asymptomatic three months after dischage from the hospital, and tests of pulmonary function were performed on ten patients within one year after hospitalization. Abnormalities in pulmonary function appeared to be reversible, and pulmonary function gradually approached normal within one year. It appears that neither acute respiratory failure nor exposure to high airway pressures caused significant permanent pulmonary damage in the ten patients studied.

Acute Disease↗
PubMed1976

Acute respiratory failure and intravascular coagulation.

The possible association between acute respiratory failure and disseminated intravascular coagulation was examined in eight patients with severe acute respiratory failure--a condition characterized by tachypnea, right to left intrapulmonary shunting of blood greater than 30 per cent of cardiac output, increased pulmonary artery pressure with low or normal pulmonary artery wedge pressure and roentgenologic interstitial pulmonary edema. Treatment consisted of mechanical ventilation with positive end expiratory pressure sufficient to minimize intrapulmonary shunting. There was no abnormality in platelet concentration fibrin split product concentration, fibrinogen concentration, prothrombin time or activated partial thromboplastin time during the period of most severe respiratory failure in any patient. However, mean platelet concentration fell to 90,000+/-9,000 per cubic millimeter, less than 0.001, and mean fibrin split product levels rose to 60+/-10 micrograms per milliliter, p less than 0.05, the fourth day after the onset of acute respiratory failure. No significant change occurred in other coagulation parameters. Disseminated intravascular coagulation developed in none of the patients nor was there any correlation between coagulation abnormalities and severity of acute respiratory failure that would suggest a cause and effect relationship.

Acute Disease↗
PubMedDate not supplied

Change in pulmonary venous admixture with varying inspired oxygen.

Pulmonary venous admixture (Qsp/Qt) was analyzed as a function of fractional concentration of inspired O2 (FIO2) in 30 patients who required postoperative mechanical ventilation. Pulmonary and radial artery blood-gas tensions and pH were measured and Qsp/Qt was calculated with FIO2 ranging from 0.21 to 1. In all patients, Qsp/Qt decreased when FIO2 was increased from 0.21 to 0.4 and then stabilized to an FIO2 of approximately 0.6. As the FIO2 was increased to 1, Qsp/Qt increased. Since the inhalation of gas mixture with FIO2 greater than or equal to 0.6 increased right-to-left intrapulmonary shunting of blood, we recommend respiratory function be evaluated during inhalation of a clinically useful concentration of O2 rather than at an FIO2 of 1.

Humans↗
PubMedDate not supplied

Ventilatory pattern, intrapleural pressure, and cardiac output.

Continuous positive-pressure ventilation may decrease cardiac output. However, a few reports have separated the effects of positive and end-expiratory pressure (PEEP) from those of mechanical ventilation. Ten surgical patients requiring mechanical ventilatory support had catheters inserted for measurement of right atrial pressure (RAP), pulmonary artery occlusion pressure (PAOP), intrapleural, radial artery, airway, and atrial filling pressures, and cardiac output. All patients breathed spontaneously between mechanical breaths delivered every 30 seconds by intermittent mandatory ventilation (IMV). Measurements were made with 0, 5, and 10 cm H2O PEEP, and during intermittent positive-pressure ventilation (IPPV) with 12 breaths/min without PEEP. Airway pressure (Paw), intrapleural pressure, RAP, and PAOP were increased by PEEP and IPPV. Intrapleural pressure increased most during IPPV (p less than 0.001). Atrial filling pressures and cardiac output were unaffected by PEEP but decreased during IPPV (p less than 0.001). Patients receiving IMV maintained negative intrapleural pressure, atrial filling pressure, cardiac output and, therefore, O2 delivery, regardless of PEEP level. The authors conclude that patients requiring mechanical respiratory support, with or without PEEP, may maintain better cardiopulmonary function when allowed some spontaneous ventilatory activity.

Blood Gas Analysis↗