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Biomedical subjects

A T Dinh Xuan

Publications and source records attributed to A T Dinh Xuan.

At least 19 recordsLinked to original sources
PubMed1991

Endothelium-derived relaxing factor and the pulmonary circulation.

Endothelium-derived relaxing factor (EDRF) is probably identical to nitric oxide (NO) and is released by the vascular endothelium both in the basal unstimulated state and in response to a wide range of physical and chemical stimuli. Since it was first described 10 years ago, evidence is accumulating that it is an important modulator of vascular smooth muscle tone. EDRF acts on the pulmonary vascular bed as on the systemic circulation. EDRF release to pharmacologic stimuli is impaired in pulmonary arteries from patients with chronic hypoxemia. This impairment is associated with severity of respiratory failure and of structural change of vessel walls. Disturbance of EDRF activity may be important in the pathophysiology of pulmonary vascular disease. This brief review describes the current status of experimental studies concerning the possible role of EDRF on the pulmonary circulation in normal conditions and in the pathogenesis of pulmonary hypertension.

Animals↗
PubMed1991

The alpha 1-adrenergic agonist methoxamine and the "loop" diuretic frusemide reduce nasal potential difference.

Pretreatment by inhalation with the alpha 1-adrenergic agonist methoxamine and the "loop" diuretic frusemide reduces the bronchial response to certain airway challenges in asthma. To test whether these drugs may act by altering airway epithelial ion and water transport, their effect on nasal potential difference (PD) when applied topically in eight normal volunteers was measured. For comparison, the effect of the Na(+)-channel blocking drug amiloride and the beta 2-adrenergic agonist salbutamol was also tested. Both methoxamine and frusemide significantly reduced PD: at the highest concentration given (10(-3) mol.l-1), there was a mean drop in PD from baseline of 39.5% following methoxamine treatment (p less than 0.05) and a mean drop of 30.2% following frusemide (p less than 0.05). Neither drug was as effective as amiloride, which caused a mean drop in PD of 27.5% from baseline at 10(-6) mol.l-1 and a drop of 71.6% at 10(-3) mol.l-1 (p less than 0.01 for each concentration). Salbutamol had no significant effect on PD (p greater than 0.05). We conclude that methoxamine and frusemide may derive their protective effect on some bronchial challenge, at least in part, from their effect on airway epithelial ion flux.

Adult↗
PubMed1990

Validation of impedance cardiography measurements of cardiac output during limited exercise in heart transplant recipients.

Twenty-one patients were studied at rest and during exercise after heart transplantation to compare cardiac output measured by thermodilution and impedance cardiography. Exercise was performed on a bicycle ergometer over a limited range of work load (25 and 50 watt) whilst metabolic gas exchange was recorded. One patient was studied at rest whilst his circulation was maintained by a Jarvik-7 artificial heart. The values of cardiac output measured by impedance cardiography corresponded closely with the flow rate from the artificial heart. There was also close agreement between the impedance and thermodilution measurements of cardiac output at rest and during exercise. Both measurements followed the changes in heart rate and oxygen consumption. Both thermodilution and impedance cardiography methods elicited good reproducibility of cardiac output measurements at rest and during exercise. These observations suggest that the noninvasive and continuous record of cardiac output obtained by impedance cardiography can be used for the postoperative monitoring of heart transplant recipients.

Adult↗
PubMed1990

Effects of SK&F 104353, a leukotriene receptor antagonist, on the bronchial responses to histamine in subjects with asthma: a comparative study with terfenadine.

We compared the effects of pretreatment of 800 micrograms of inhaled Smith Kline & French (SK&F) 104353, a leukotriene receptor antagonist, and 120 mg of oral terfenadine on the bronchial responses to inhaled histamine in 12 subjects with asthma. The study took place on 3 different days and was conducted according to a double-blind, crossover, double-dummy, randomized, and placebo-controlled design. There was no difference in baseline and prechallenge FEV1 after placebo, SK&F 104353, and terfenadine administration. The median ratio of the provocative dose causing a 20% fall in FEV1 from baseline (PD20) with terfenadine over PD20 with placebo was 12.36 (range, 3.2 to 30.3; p less than 0.01) and that of PD20 with SK&F 104353 over PD20 with placebo was 1.51 (range, 0.8 to 5.9; not significant). Analysis of individual results demonstrated a shift toward the right of the dose-response curves to histamine with SK&F 104353 compared to that with placebo in three subjects, whereas the active compound did not exhibit any protective effect against histamine in the remaining nine subjects. We conclude that there is a leukotriene component to the bronchial responses to histamine in some, but not all, subjects. This component remains, however, small and does not appear to be clinically important in the population of subjects with asthma that was studied.

Adult↗
PubMed1990

Bronchial blood flow and microvascular permeability in the pathophysiology of asthma.

Bronchial smooth muscle contraction is not the only causative factor of airway narrowing in asthma. Other components, such as mucosal and submucosal oedema and mucosal inflammation, also intervene in the processes leading to bronchial obstruction. Re-analyzing the role of the tracheo-bronchial circulation is therefore necessary, since participation of the latter, through modification of bronchial blood flow and/or alteration of microvascular permeability, very likely modifies mucosal thickness of the bronchial wall and/or clearance of bronchoactive substances from the airways. This also implies that more attention should be paid on the vascular actions of compounds which are either currently prescribed or under development for future treatment of asthma.

Asthma↗
PubMed1990

Primary pulmonary hypertension: diagnosis, medical and surgical treatment.

Primary pulmonary hypertension continues to present both diagnostic and therapeutic challenges to the physician, reflecting the lack of understanding about the basic mechanism of the disease. The natural history of the condition has been described only recently, and this has allowed a reasonably accurate prognosis for the individual patient to be determined. New treatments have been found effective, including heart-lung transplantation, which can now offer improved survival. Long-term intravenous infusion of prostacyclin has a place in the treatment of severely affected patients awaiting heart-lung transplantation. However, the major impact of prostacyclin has been, perhaps, to concentrate research upon the role of the endothelial cell in the development of this disorder, in particular the potential role of an impairment of release of the recently described endothelium-derived relaxing factor in certain forms of pulmonary hypertension. We have attempted in this review to focus on the problems of diagnosis and treatment together with current developments in the understanding of primary pulmonary hypertension.

Heart-Lung Transplantation↗
PubMed1990

Impairment of pulmonary endothelium-dependent relaxation in patients with Eisenmenger's syndrome.

A comparison has been made between the endothelium-dependent relaxation of pulmonary arteries (PA) obtained at heart-lung transplantation from 4 patients with Eisenmenger's syndrome and secondary pulmonary hypertension, and PA obtained at lobectomy from 4 patients with lung carcinoma, the controls. All vascular rings were studied immediately after lung excision. PA rings from control patients dose-dependently relaxed to cumulative doses of acetylcholine (ACh, 10(-10) to 10(-5) M), achieving a maximal relaxation of 80 +/- 5% (mean +/- s.e. mean) from precontraction with phenylephrine. By contrast, PA rings from Eisenmenger's syndrome patients achieved a maximal relaxation of only 34 +/- 12% (P less than 0.05, unpaired t test), with even paradoxical contraction at high doses of ACh (10(-6) to 10(-5) M). Sodium nitroprusside (10(-4) M) relaxed all PA rings, with and without endothelium (carefully removed before study), obtained from both control and Eisenmenger's syndrome patients. These results provide the first evidence that endothelium-dependent relaxation of PA mediated by endothelium-derived relaxing factors is impaired in Eisenmenger's syndrome patients with secondary pulmonary hypertension.

Acetylcholine↗
PubMed1990

Inflation of antishock trousers increases bronchial response to methacholine in healthy subjects.

We studied changes in lung volumes and in bronchial response to methacholine chloride (MC) challenge when antishock trousers (AST) were inflated at venous occlusion pressure in healthy subjects in the standing posture, a maneuver known to shift blood toward lung vessels. On inflation of bladders isolated to lower limbs, lung volumes did not change but bronchial response to MC increased, as evidenced by a greater fall in the forced expiratory volume in 1 s (FEV1) at the highest dose of MC used compared with control without AST inflation (delta FEV1 = 0.94 +/- 0.40 vs. 0.66 +/- 0.46 liter, P less than 0.001). Full inflation of AST, i.e., lower limb and abdominal bladder inflated, significantly reduced vital capacity (P less than 0.001), functional residual capacity (P less than 0.01), and FEV1 (P less than 0.01) and enhanced the bronchial response to MC challenge compared with partial AST inflation (delta FEV1 = 1.28 +/- 0.47 liter, P less than 0.05). Because there was no significant reduction of lung volumes on partial AST inflation, the enhanced bronchial response to MC cannot be explained solely by changes in base-line lung volumes. An alternative explanation might be a congestion and/or edema of the airway wall on AST inflation. Therefore, to investigate further the mechanism of the increased bronchial response to MC, we pretreated the subjects with the inhaled alpha 1-adrenergic agonist methoxamine, which has both direct bronchoconstrictor and bronchial vasoconstrictor effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

[Vasomotor tonus and non-prostanoid endothelium-derived vasoactive factors].

There are two types of non-prostanoid endothelium-derived vasoactive factors, one which relaxes and the other which contracts the vascular smooth muscle (EDRF and EDCF). These factors are released in response to stimulation of specific membrane receptors of the vascular endothelium by a large number of agonist substances and in response to physical stimuli to the vascular wall. It has been shown that EDRF is nitric oxide (NO) and EDCF has recently been identified as a peptide composed of 21 amino acids called endothelin. Other compounds may also act as EDRF or EDCF. EDRF (NO) induces relaxation of the underlying vascular smooth muscle by increasing intracellular concentration of cyclic guanosine monophosphate. The mechanisms of action of endothelin have not yet been clearly defined. It would seem that they depend, at least partially, on influx of extracellular calcium. The recent discovery of endothelin and the increased knowledge of the mode of action of EDRF on vascular smooth muscle has led to the suggestion that, vasomotor tone in humans is probably the result of an equilibrium between these two factors, each of which play a fundamental role, and very likely interact with each other in maintaining and regulating vascular tone in man.

Animals↗
PubMed1990

Pulmonary hypertension in a lupus clinic: experience with twenty-four patients.

The clinical and serological findings on 24 patients with pulmonary hypertension (PHT) seen at the Lupus Clinic of St. Thomas' Hospital, London are presented. Twenty-two patients had systemic lupus erythematosus (SLE), one other a primary antiphospholipid syndrome and another an SLE/progressive systemic sclerosis (PSS) overlap syndrome. In 21 of the 24 patients, the disease resembled the primary idiopathic variety with clear lung fields and no clinical evidence of pulmonary thromboembolism, although angiography and nuclear perfusion scans were not performed. Two patients clearly suffered from thromboembolic PHT, one with SLE and one with an antiphospholipid syndrome. One patient with SLE/PSS overlap syndrome developed pulmonary fibrosis. The frequency of antiphospholipid antibodies (lupus anticoagulant and antibodies to cardiolipin was 68% which appears to be higher than generally found in patients with SLE, and the clinical significance of this finding is unknown. Other associated features of the antiphospholipid syndrome in this group were uncommon. Death occurred in 13 of the 24 patients, 4 were lost to followup and 7 are known to be alive. The cause of death was circulatory failure in the majority; sudden death once this complication occurred was particularly common. One patient died from adult respiratory distress syndrome and one from hemorrhagic shock while undergoing heart/lung transplantation. Two patients underwent successful heart/lung transplantation. One, however, died of a mesenteric occlusion and bowel infarction following a second lung transplantation because of rejection of the first heart/lung transplantation after one year. The other patient is alive and well 2 years later.

Adult↗
PubMed1990

[Respiratory function in cardiopulmonary transplantation].

Today heart-lung transplantation (HLT) probably provides the best means of studying the role of pulmonary innervation in human respiratory physiology. Outside the periods of postoperative complications ventilatory function, blood gases and exercise tolerance of HLT recipients are compatible with a normal sedentary life. Control of breathing in the waking state at rest, and when asleep, in HLT subject is not different from that of the healthy subject, which suggests that the pulmonary afferents play a negligible role in the control of breathing of adult humans at rest. The results of the ventilatory response to carbon dioxide and to exercise in HLT subjects are contradictory and do not enable any conclusion about the role of pulmonary innervation in these types of integrated responses. On the other hand, the existence of bronchial hyperreactivity to cholinergic stimulation is well established, and is attributed to an upregulation of bronchial muscarinic receptors. An increase in the bronchial response to distilled water observed in some HLT subjects seems on the other and related to episodes of lung rejection. The reflex theory of cough is supported by studies of HLT subjects. Results of studies of the effect of a deep inspiration on bronchomotor tone are far from concordant. Other studies including a large number of subjects and looking at the presence or the absence of reinnervation after transplantation are perhaps two supplementary means to further investigate the respiratory function of HLT patients. Knowledge of the latter would equally enable a better understanding of control mechanisms of human respiratory physiology.

Biomechanical Phenomena↗
PubMed1990

Acetylcholine and adenosine diphosphate cause endothelium-dependent relaxation of isolated human pulmonary arteries.

Endothelium-dependent vasorelaxation mediated by endothelium-derived relaxing factors (EDRF) has been extensively studied in animals but only limited studies in man are available. Demonstration of EDRF-mediated dilatation of human vessels is fundamental for understanding the mechanisms of vascular diseases in man. We have investigated endothelium-dependent relaxation of isolated human pulmonary arteries. Vascular segments, taken from uninvolved regions of resected lung from eight patients undergoing lobectomy for lung carcinoma, were cut into rings. In rings precontracted with phenylephrine, both acetylcholine (ACh) and adenosine diphosphate (ADP) induced dose-dependent relaxation in the presence of endothelium but not when the endothelium had been carefully removed. The rings without endothelium relaxed completely with sodium nitroprusside, a vasodilator agent acting directly on vascular smooth muscle. Pre-incubation with indomethacin, a cyclo-oxygenase inhibitor which blocks production of prostacyclin, did not alter the vasorelaxant responses to ACh and ADP, suggesting that one (or several) non-prostanoid EDRF(s) are responsible for the endothelium-dependent relaxation of isolated human pulmonary arteries.

Acetylcholine↗
PubMed1989

Bronchial effects of alpha 2-adrenoceptor agonists and of other antihypertensive agents in asthma.

The respective prevalence of hypertension and asthma is sufficient for their combined existence to be far from rare. The effects of certain antihypertensive drugs, e.g., alpha 2-adrenoceptor agonists, on the bronchi may be either harmful or beneficial. When inhaled, alpha 2-agonists reduce the immediate bronchial response to allergens, whereas when ingested they aggravate the bronchial response to histamine and all the more so when their effect on the central nervous system is greater. Therefore, there has been much interest in agents such as the new oxazoline derivative, rilmenidine, which has less central effects than clonidine, an imidazoline compound of reference. Calcium antagonists inhibit smooth muscle contraction and release of mast cell inflammatory mediators. In asthmatic subjects, their short-term administration leads to a modest improvement in spontaneous bronchial obstruction, has only a partial protective action against various nonspecific or allergenic stimuli, and slightly reinforces the beneficial effect of beta 2-agonists. Beta-adrenoceptor antagonists aggravate bronchial obstruction and nonspecific bronchial hyperreactivity in asthmatic subjects. These harmful effects are dose-dependent, have even been reported after the administration of eyedrops, and are common to all beta-blockers. Angiotensin-converting enzyme inhibitors increase bronchial hyperreactivity in patients who develop cough during treatment and may, in certain cases, worsen or even induce asthma, probably by opposing inactivation by hydrolysis of tachykinins and of bradykinins.

Adrenergic alpha-Agonists↗