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Biomedical subjects

G Lister

Publications and source records attributed to G Lister.

At least 91 records · Page 5Linked to original sources
PubMed1984

Relationship between oxygen uptake and oxygen transport in stable patients with chronic obstructive pulmonary disease. Physiologic effects of nitroprusside and hydralazine.

This study was designed to determine whether alterations in systemic oxygen transport induced by the use of vasodilators for pulmonary hypertension would simultaneously affect oxygen uptake in patients with chronic obstructive pulmonary disease (COPD). Six stable patients with moderate to severe COPD were studied during resting conditions, nitroprusside infusion, a second control period, and after administration of hydralazine. Systemic oxygen transport fell with nitroprusside infusion (523 +/- 94 to 418 +/- 78 ml/min/m2, p less than 0.05). With this there was a fall in oxygen uptake (135 +/- 11 to 119 +/- 12 ml/min/m2, p less than 0.05), but only a minimal increase in oxygen extraction. In contrast, systemic oxygen transport was augmented in all patients when hydralazine was administered (444 +/- 121 to 840 +/- 157 ml/min/m2, p less than 0.05). There was also a net increase in oxygen uptake in these patients (122 +/- 19 to 148 +/- 21 ml/min/m2, p less than 0.05). We postulate that these clinically stable patients have a resting oxygen uptake that may become dependent on systemic oxygen transport whenever the latter decreases. This phenomenon has been described previously only in patients with adult respiratory distress syndrome, and it is important to consider when designing studies of pharmacologic therapy for COPD complicated by pulmonary hypertension.

Aged↗
PubMed1984

Oxygen transport in the intact hypoxic newborn lamb: acute effects of increasing P50.

We examined the acute effects of a change in hemoglobin oxygen affinity (P50) on systemic oxygen transport and oxygen consumption during hypoxia. Ten awake, intact, newborn lambs were studied during four consecutive conditions: normoxia (FIO2 = 0.21); hypoxia (FIO2 = 0.10); hypoxia after isovolemic exchange transfusion, raising P50 8 +/- 3 Torr without changing hematocrit; and normoxia after the exchange transfusion. With hypoxia, oxygen extraction rose, cardiac output increased minimally, and systemic oxygen transport and oxygen consumption fell. After exchange transfusion during hypoxia, oxygen consumption rose to resting levels due to a significant augmentation of systemic oxygen transport, which resulted from an increase in cardiac output. This change in cardiac output was due to an increased stroke volume, most likely due to an improved inotropic state. The above findings are consistent with observations in newborn infants with respiratory distress syndrome who underwent exchange transfusion.

Animals↗
PubMed1984

The effects of tolazoline on the distribution of cardiac output in normoxemic and hypoxemic lambs.

We measured cardiac output and its distribution (microspheres), blood gases and pH, heart rate, and pulmonary and aortic pressures in three groups of 1- to 3-day-old lambs. Group I consisted of six animals who had these measurements made during both control (normoxemic) and hypoxemic (PaO2 25 +/- 3 mm Hg) periods. Hypoxemia increased the pulmonary artery pressure 70% (p less than 0.01). This elevation in pulmonary arterial pressure lasted as long as the animals were hypoxemic (90 min). Hypoxemia had no effect on cardiac output, mean systemic arterial pressure, heart rate, or the rate-pressure product of the left ventricle. Blood flow to the heart increased an average of 228% (p less than 0.05); flow to the brain increased 233% (p less than 0.05); flow to the skin decreased 35% (p less than 0.05) after 60 and 90 min of hypoxemia. Blood flow to the remaining organs was uneffected by hypoxemia. Group II consisted of four animals who were given 1, 5, and 10 mg/kg/h of tolazoline (Priscoline) intravenously while normoxemic. There was no effect on the pulmonary arterial pressures or blood gases and pH. Tolazoline (5 and 10 mg/kg/h) reduced systemic arterial pressures an average of 22% (p less than 0.05). Tolazoline (1 mg/kg/h) reduced blood flow to the spleen 48% and that to the brain by 20% and increased flow to the body 32% (p less than 0.05). Five mg/kg/h of tolazoline decreased renal and brain blood flow 35 and 20%, respectively (p less than 0.05) while that to the body and liver increased 26 and 48% (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Functional assessment of the pulmonary microcirculation during postnatal development.

It has been well documented that the lungs are able to remove or metabolize several vasoactive substances passing through the pulmonary circulation. One such function, the conversion of angiotensin I to angiotensin II and hydrolysis of bradykinin to inactive peptide fragments is performed by angiotensin-converting enzyme (ACE). Although a precise role of these functions for systemic vasoregulation has not been defined, measurement of pulmonary metabolic capacity has the potential for providing substantial information about the integrity and physiology of the pulmonary microcirculation. Studies are described using 3H-benzoyl-phenylalanyl-alanyl-proline (a synthetic substrate for pulmonary ACE) in developing conscious lambs and older sheep. Outflow curves from indicator dilution measurements contain information regarding apparent kinetics of ACE activity. Using a nonlinear model for saturable pulmonary metabolic functions, the derived data demonstrate a) a marked increase in Vmax, the apparent maximal velocity of ACE, with age; and b) no significant change with age in apparent Km, the concentration at which the velocity of ACE is one-half Vmax. This approach has the potential for providing a biochemical tool for examining postnatal growth of the pulmonary microcirculation as well as functional integrity of the pulmonary endothelium during a variety of conditions.

Animals↗
PubMed1984

Effects of alterations of oxygen transport on the neonate.

In the foregoing discussion we have attempted to provide an overview of much of the information available on the effects of changes in systemic oxygen transport on the neonatal and young subject. Using data synthesized from both human and animal studies, we have described the normal developmental changes and the findings of studies in which oxygen transport has been acutely altered by experimental means. This was intended to highlight the potentially delicate balance that can occur between oxygen supply and utilization during the critical period of rapid growth after birth. Finally, using the left-to-right shunt as an example, we have tried to show how a common pathologic condition can impair oxygen transport at multiple sites, and how normal development can make matters worse. It is anticipated that from an understanding of both normal and abnormal physiology, we will be able to develop rational approaches to the management of infants in whom the oxygen transport system has been stressed beyond its reserve.

2,3-Diphosphoglycerate↗
PubMed1983

Precautions for measuring blood flow during anemia with the microsphere technique.

Preliminary data from a study of the effects of anemia on organ blood flow showed large discrepancies between cardiac output measured with the microsphere technique and simultaneous values calculated by the Fick principle. The most likely explanation was that the reference sample drawn according to our standard procedure underestimated the microsphere concentration in arterial blood, resulting in erroneously high blood flow values. In the present experiments we compared our usual reference sample, from a small catheter advanced from a peripheral artery into the brachiocephalic artery (withdrawal rate 1.3 ml/min), with a simultaneous sample from a larger catheter withdrawn at the much higher rate (7.89 ml/min). At hematocrits above 32%, microsphere concentrations from the two catheters were similar, but below 32% the concentration of microspheres in blood from the larger catheter was 30-50% more than from the smaller. The discrepancy was not altered by changing the injection site from left ventricle to left atrium and thus was probably not the result of poor mixing within the heart. It may have been the result of nonhomogeneous distribution of microspheres within larger vessels, perhaps as a consequence of laminar flow and axial streaming of both red blood cells and microspheres during anemia. Whatever the cause, it was possible to eliminate the difference by withdrawing from the smaller catheter at a more rapid rate (2.46 ml/min).

Anemia↗
PubMed1983

Pulmonary metabolic function in the awake lamb: effect of development and hypoxia.

The effect of postnatal development and acute alveolar hypoxia on pulmonary metabolic function was studied in conscious newborn lambs. Measurements of the ability of the lungs of these animals to metabolize [3H]benzoyl-L-phenyl-alanyl-L-alanyl-L-proline ([3H]BPAP; a synthetic substrate for angiotensin-converting enzyme, ACE) and to remove 5-hydroxy-[14C]tryptamine (5-[14C]HT) were made by modified indicator-dilution techniques during normoxic and hypoxic (fraction of inspired O2 = 0.10) conditions at 1 day, 1 wk, and 1 mo of age. Six additional sheep (8-23 wk old) were studied acutely as "adult" controls. BPAP metabolism in the 1-day-old group was 48 +/- 3% and increased slowly to 57 +/- 1% (P less than 0.05) at 1 mo of age and to 79 +/- 3% (P less than 0.01) by 23 wk of age. Pulmonary 5-[14C]HT removal was adultlike at birth (69 +/- 2%). Alveolar hypoxia significantly decreased BPAP only in the 1-day-old group (41 +/- 3%; P less than 0.05) and had no significant effect on 5-[14C]HT removal over the range of ages studied. These data demonstrate a selective and gradual postnatal development of pulmonary ACE which could be due to alterations in either the affinity or maximal capacity of pulmonary ACE, or increased endothelial cell surface area secondary to rapid growth of small blood vessels in this period. Alveolar hypoxia does not appear to closely regulate either ACE activity or 5-HT removal in conscious lambs greater than 1 day old when trace amounts of substrate are used.

Animals↗
PubMed1983

Epiglottitis--duration of intubation and fever.

The present study reviewed the clinical course of 23 pediatric patients with epiglottitis to define criteria for the length of time children require nasotracheal intubation for relief of airway obstruction. All patients had a nasotracheal tube placed in the operating room, were treated with ampicillin or chloramphenicol, and tracheal extubation was performed when the epiglottis was markedly reduced in size to a point where examiners estimated the thickness of the proximal portion of the epiglottis to be 3-4 mm or less. The mean duration of intubation was 36 +/- 14 h (+/- SD), but there was marked variation between patients. There was no significant relationship between reduction in the size of the epiglottis and the febrile nature of the disease. Based on these observations, it would be imprudent to time tracheal extubation by the absence of fever or to establish an arbitrary time period for maintenance of nasotracheal intubation in epiglottis. Direct observation of the epiglottis should determine when airway support is no longer needed.

Child, Preschool↗
PubMed1982

Physiologic effects of increasing hemoglobin concentration in left-to-right shunting in infants with ventricular septal defects.

We studied the acute effects of increasing hemoglobin concentration and hematocrit on the pulmonary and systemic circulations of nine infants with large left-to-right shunts. After isovolemic exchange transfusion, which was designed to raise hemoglobin but keep blood volume constant, a consistent rise in systemic and pulmonary vascular resistances occurred. This rise was comparable to those previously found in isolated circulations showing a linear relation between hematocrit and loge of the vascular resistance. These changes in resistance were accompanied by decreases in systemic and pulmonary blood flow and a marked decline in left-to-right shunt. Despite the decrease in systemic blood flow, there was no decline in systemic oxygen transport, and there may have been a marginal decrease in left ventricular stroke work. These observations help explain why the newborn with a large ventricular septal defect and a high hemoglobin concentration does not have clinical signs of a large left-to-right shunt, and also suggest that the postnatal decline in hematocrit has a substantial role in the normal fall in pulmonary vascular resistance after birth.

Blood Circulation↗
PubMed1981

The pathophysiology of disorders of oxygen transport in the infant.

The major attempt in this monograph has been to provide a systematic approach to OT in the infant under normal and abnormal conditions based on an appreciation of pathophysiologic mechanisms. This has included a consideration of oxygen uptake, gas transfer from the lungs to the circulation, oxygen delivery to the tissues, and various adaptive responses. We have discussed disorders involving the control of respiration, the upper and lower airways, lung parenchyma, pulmonary circulation, heart, and the oxygen carrier, hemoglobin, that may impair OT to tissues, and how compensation for these conditions can be achieved. The clinical presentation in each of these pathologic processes represents the net effect of the lesion on the multiple steps involved in the transport of oxygen to the tissues and the adaptation provided by the lungs, heart, circulation, and hematologic system. These must be taken into account in developing a plan for medical and/or surgical treatment that is focused on improving the supply of oxygen to the various organ systems of the body.

Heart Diseases↗
PubMed1981

Effect of physical training on exercise performance of children following surgical repair of congenital heart disease.

The effect of physical training on the exercise performance of 26 patients following surgical repair of tetralogy of Fallot (16 patients) and ventricular septal defect (ten patients) was evaluated. Base line exercise testing was performed on a bicycle ergometer using the technique of Godfrey. Patients were placed on a six-week alternate day submaximal interval home exercise program of varying duration and intensity. Work loads at 50%, 60%, and 70% maximum oxygen consumption were selected to maintain heart rates between 130 and 160 beats per minute. Subjects completed an average of 18 of the possible 21 training sessions (range 11 to 21). A 25% improvement (p less than .001) was noted in maximum work capacity (747 to 935 km). Sixty-five percent of the patients performed at less than expected maximum work capacity prior to training, but only 31% performed at less than expected maximum work capacity after training. Repeat testing at work loads of one-third, one-half, and two-thirds the original maximum work capacity revealed improved aerobic efficiency as manifested by significantly decreased oxygen consumption and heart rate at each level of work. No significant difference was noted in maximum oxygen consumption. It is concluded that physical training can improve the exercise performance of patients after surgical repair, permitting the individuals to function at levels of activity at, or closely approaching, normal.

Adolescent↗
PubMed1980

Changes in venous admixture with alterations of inspired oxygen concentration.

To assess the change in venous admixture during breathing of 100 per cent oxygen (FIO2 1.0), shunt fraction (Qs/Qt) was calculated at a maintenance FIO2 (FIO2m:0.27--0.70) and at FIO2 1.0 in 40 studies of 34 patients with acute respiratory failure. At FIO2 1.0 Qs/Qt increased in 26 studies, but did not increase in 14 studies. Patients in whom Qs/Qt increased during breathing of oxygen and mild respiratory failure, as indicated by low Qs/Qt values at FI02m and a low incidence of diffuse parenchymal infiltrates on chest roentgenograms. All patients who had recently had cardiovascular surgical procedures were in this group. Respiratory failure was more severe in those in whom Qs/Qt decreased with oxygen, as indicated by high Qs/Qt values at FIO2m, evidence of diffuse pulmonary disease by roentgenography, and signs of adult respiratory distress syndrome. The authors conclude that changes in Qs/Qt in response to FIO2 1.0 in acute respiratory failure are related to the severity of respiratory insufficiency.

Acute Disease↗
PubMed1980

Rhesus incompatibility and a survey of the care of rhesus negative pregnant women in one general practice.

I review some of the literature and developments in research concerning rhesus immunization and report on a small survey, carried out in a group practice with a list size of about 12,000, of women who were delivered during the first 10 months of 1977. There were 106 deliveries (including one set of twins), and 16 rhesus negative mothers (one of whom had the twins). Of 17 infants delivered to these mothers, eight were rhesus negative, seven rhesus positive, and two were not grouped. None of the mothers developed antibodies and all the rhesus negative mothers at risk received anti-D. However, the survey shows discrepancies between hospital and practice records and recommendations to improve this are suggested.

Erythroblastosis, Fetal↗