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Biomedical subjects

S Nava

Publications and source records attributed to S Nava.

At least 109 records · Page 6Linked to original sources
PubMed1993

Non-invasive mechanical ventilation in the treatment of acute respiratory failure in chronic obstructive pulmonary disease.

Acute respiratory failure is usually managed by means of mechanical ventilation via an endotracheal tube or tracheostomy, when conservative treatment fails. Invasive mechanical ventilation is associated with several complications. The recent development of non-invasive methods of ventilation, has led to an attempt to avoid the complications of invasive mechanical ventilation during episodes of acute respiratory failure, ensuring at the same time a similar degree of efficacy. Both intermittent negative pressure ventilation and positive pressure ventilation by face or nasal mask have recently been used for this purpose. Negative pressure ventilation by means of iron lung, cuirass or poncho-wrap ventilators, has never been used in place of endotracheal intubation, and studies of this kind of ventilation are inconclusive: as a consequence, there is, at the moment, no indication for the generalized use of negative pressure ventilation in acute respiratory failure. Intermittent positive pressure ventilation by facial or nasal masks, has recently been used in the treatment of respiratory failure in place of endotracheal intubation. The results are promising, but remain controversial. It may be attempted in selected patients with obstructive respiratory disorders, but the procedure is very time-consuming for nurses.

Humans↗
PubMed1992

Endometrial patterns during therapy with danazol or gestrinone for endometriosis: structural and ultrastructural study.

We treated 36 women with laparoscopically proven endometriosis with danazol 600 mg/d (n = 17) or gestrinone 5.0 mg/wk (n = 19) for 6 months. Endometrial samples were obtained before and at 3 and 6 months of treatment and were studied by light, scanning, and transmission electron microscopy. At 3 months of treatment, the endometria of the danazol-treated patients were more atrophic than those of the women who received gestrinone. Some cell organelle involution was evident in patients of both treatment groups. After 6 months of treatment, marked endometrial atrophy was observed in all the patients, including those in whom spotting had occurred. The ultrastructural investigation demonstrated complete involution of the cytoplasmic organelles with cytoplasmic collapse in glandular cells of patients treated with danazol, whereas in the gestrinone group degeneration phenomena were observed in both nucleus and cytoplasm. Irregular secretory transformation was seen in the endometria of patients in both groups. Long-term treatment with danazol caused endometrial atrophy similar to that induced by gestrinone, but it appeared earlier; thus, the former drug seems preferable in short-term treatment.

Adult↗
PubMed1992

Ultrastructural aspects of endometrial surface in Kartagener's syndrome.

The endometrium of an infertile patient with Kartagener's syndrome showed initial secretory phase characteristics at SEM, whereas TEM analysis demonstrated several alterations in the central and peripheral microtubular distribution in 87% of the cilia examined. Such aspects seemed appropriate for a normal implantation, but the ciliary immotility or dyskinesia could cause an altered flow of the endometrial secretions and compromise the upstream movement of the spermatozoa.

Adult↗
PubMed1992

Flow and volume dependence of respiratory system flow resistance in patients with adult respiratory distress syndrome.

Using a simple and rapid technique, we studied the flow and volume dependence of the total resistance of the respiratory system (Rrs) in six patients with ARDS. At any given inflation volume, Rrs decreased progressively with increasing flow (V) according to the following hyperbolic function: Rrs = a/V + b, where a and b are constants. At any fixed inflation flow, Rrs increased progressively with increasing inflation volume. The observed flow and volume dependence of Rrs is probably mainly due to the viscoelastic properties of the pulmonary and chest wall tissues. The flow and volume dependence of Rrs found in the patients with ARDS is qualitatively similar to that previously observed in normal anesthetized paralyzed subjects. In ARDS, however, Rrs was considerably greater than in the normal subjects, indicating that besides a low respiratory compliance ARDS is characterized by a high flow resistance. This mainly reflects increased effective flow resistance of the pulmonary and chest wall tissues, although airway resistance is also higher than normal.

Adult↗
PubMed1992

Evidence of acute diaphragmatic fatigue in a "natural" condition. The diaphragm during labor.

Acute diaphragmatic fatigue has been experimentally shown to occur in normal healthy subjects and in patients with chronic obstructive pulmonary disease by asking them to modify their pattern of breathing or to breathe against high inspiratory resistances. During the expulsive period of labor women are asked periodically to make strong expulsive efforts and to sustain them isometrically for many seconds; this is likely to produce "natural" diaphragmatic fatigue. To investigate whether this was the case, six women were studied in the delivery room from the moment of the rupture of the amnion until delivery of the infant occurred. The development of diaphragmatic fatigue was assessed both by measuring the static maximal inspiratory pressure (MIP) and by analyzing the electromyographic power spectrum of the diaphragm (H/L ratio). The majority of contractions were concentrated in the expulsive period of labor. MIP, recorded in the supine position, significantly decreased from 103.2 +/- 17.2 cm H2O (at the beginning of the expulsive period) to 73.8 +/- 10.1 cm H2O (after the delivery). The H/L ratio fell progressively during the expulsive period; after the delivery, it was 59.2 +/- 15.7% of the value recorded at the beginning of the expulsive period. This study demonstrates that (1) the diaphragm is active in the expulsive efforts during labor and (2) the tension developed and the time each contraction is maintained may lead to the development of diaphragmatic fatigue. Therefore, we provide evidence of acute diaphragmatic fatigue in a natural condition.

Acute Disease↗
PubMed1992

Effect of a beta 2-agonist (broxaterol) on respiratory muscle strength and endurance in patients with COPD with irreversible airway obstruction.

The effect of broxaterol, a new beta 2-agonist, on respiratory muscle endurance and strength was studied in a double-blind, placebo-controlled, randomized crossover clinical trial in 16 patients with chronic obstructive pulmonary disease (COPD) with irreversible airway obstruction (FEV1 = 57.1 percent of predicted). One patient withdrew from the study because of acute respiratory exacerbation. Inspiratory muscle strength was assessed by maximal inspiratory pressure (MIP) and endurance time was determined as the length of time a subject could breathe against inspiratory resistance (target mouth pressure = 70 percent of MIP, Ti/Ttot = 0.4). Broxaterol (B) or placebo (P) was given orally for seven days at the dose of 0.5 mg three times a day with a washout period of 72 h between study treatments. Measurements were performed before administration of B or P and 2 h (six patients) or 8 h (nine patients) after the end of each treatment. No significant changes in FEV1 or FRC were observed after B or P suggesting that diaphragmatic length was maintained constant with each treatment. The MIP did not significantly change, while endurance time increased after B in the patients tested at 2 h (from 234.8 +/- 48.1 s to 284.0 +/- 48.0 s, p less than 0.05) and at 8 h (from 187.2 +/- 31.1 s to 258.2 +/- 40.4 s, p less than 0.005). No changes were observed after P. Minute ventilation, airway occlusion pressure (P0.1), integrated electromyographic activities of the diaphragm (Edi), and intercostal parasternals (Eic) (normalized to the value obtained during MIP) showed no change during the endurance run with different treatments. We conclude that in a group of COPD patients with irreversible airway obstruction, B significantly improves respiratory muscle endurance, and that this does not arise as a result of an effect on neuromuscular drive or pulmonary mechanics, but may be mediated by peripheral factors.

Adrenergic beta-Agonists↗
PubMed1992

Physiologic evaluation of pressure support ventilation by nasal mask in patients with stable COPD.

We evaluated the physiologic effects of pressure support ventilation by nasal route (NPSV) in eight patients with severe stable COPD and chronic hypercapnia who were randomly submitted to 2-h sessions of NPSV both with a portable ventilator (Respironics BIPAP device) and with a standard ventilator (Bird 6400ST device) at an inspiratory airway pressure of 22 cm H2O. Two sessions with each ventilator were performed using an FIO2 of 0.21 in each patient on two consecutive days. One patient did not tolerate either form of ventilation. Comparison of spontaneous with BIPAP ventilation showed a significant improvement in pH, PaCO2, and PaO2. Ventilatory pattern assessed by a respiratory inductive plethysmograph showed a significant increase in minute ventilation (VE), VT, and Ttot. Integrated surface diaphragmatic EMG activity measured only during BIPAP device ventilation decreased from that measured during spontaneous breathing. Similar changes in blood gases and ventilatory pattern were observed during ventilation by the Bird 6400ST except for VT/Ti ratio, which significantly increased. Comparison of baseline with measurements performed 12 h after the whole cycle of treatment showed a significant increase in pH and VE and a decrease in PaCO2. We conclude that short-term NPSV may be useful in improving respiratory pattern and blood gases in stable COPD patients with chronic hypercapnia.

Humans↗
PubMed1992

Respiratory muscle fatigue does not limit exercise performance during moderate endurance run.

The role of respiratory muscle fatigue in limiting exercise performance in well-trained subjects is still controversial, especially as far as relatively short runs are concerned. To determine the occurrence of respiratory muscle impairment, we studied six well-trained athletes before, during (middle of the run) and after a 17 km run. They were all asked to produce the maximum effort they could during the race. Strength was assessed by measuring maximal inspiratory mouth pressure against close airways (MIP), dynamic lung volumes were monitored using a spirometer. No changes in forced vital capacity (FVC), maximal expiratory flow (PEF) and forced expiratory volume in 1 sec (FEV1) were observed throughout the experiment. This suggested that functional residual capacity and subsequently the initial length of respiratory muscle were unchanged. Respiratory muscle strength did not significantly vary at the different time of measurements (154.8 +/- 20.9 cm H2O at the beginning, 157.5 +/- 23.7 cm H2O after 7.5 km, 155.8 +/- 22.5 cm H2O at the end and 152.3 +/- 17.6 cm H2O after 30 min of recovery). We therefore conclude that respiratory muscle fatigue does not impair the exercise performance of well-trained athletes in a relatively short race. The difference between these results and others reported in literature, could be explained by the different degree of training of the subjects performing the race.

Adult↗
PubMed1992

[A comparison between amiodarone and disopyramide in a delayed-release formulation in the prevention of recurrences of symptomatic atrial fibrillation].

In order to compare the efficacy in preventing recurrencies of symptomatic atrial fibrillation of amiodarone (A.) and slow release disopyramide (D.RET.), 76 consecutive patients with recent onset atrial fibrillation (1 to 24 hrs.) were enrolled. In 20 (26%) conversion to sinus rhythm was obtained by electrical cardioversion, and in 56 (74%) by oral quinidine loading. Forty-one patients (group A) were assigned at random to treatment with D.RET. (250 mg twice daily) and 35 patients (group B) to amiodarone treatment (1200 mg daily for 10 days, and subsequently 200 mg daily). The two groups were similar as to age, sex and cardiac pathology. Patients were followed as to clinical condition, standard and dynamic ECG after one and three months and every three months subsequently for an average of 13.2 months (group A) and 14.1 months (group B). Six group A patients (14%) were excluded from follow-up on account of side effects which arose during the first week of treatment. Crises of symptomatic atrial fibrillation occurred in 20 patients of group A (57%) and in 11 (32%) group patients; this difference is statistically significant (p less than 0.05). Four (10%) group A patients stopped taking the drug due to side effects of an anticholinergic type, and three (8.5%) patients developed hyperthyroidism during follow-up. The authors therefore come to the conclusion that amiodarone is more effective than slow-release disopyramide in preventing recurrencies of atrial fibrillation; besides untoward side effects are less frequent with amiodarone.

Amiodarone↗
PubMed1991

Expression of angiotensin converting enzyme mRNA in rat brain.

Using molecular genetic approaches, two forms of angiotensin-converting enzyme (ACE) have so far been identified; a pulmonary form and a testicular form. This study utilized both northern blot analysis and in-situ hybridization to examine the expression of ACE mRNA in the rat brain. Northern blot analysis using oligonucleotide probes specific to the testicular or pulmonary forms of ACE demonstrated expression of a 4-5kb mRNA doublet in the rat brain, identical in size to pulmonary ACE mRNA. No expression of the testicular form of ACE mRNA was detected in the brain. In situ hybridization demonstrated that ACE mRNA was expressed in the choroid plexus, caudate putamen and cerebellum. A weak signal was also observed in the hippocampus. This distribution correlated well with the expression of ACE mapped by radioligand binding and autoradiography.

Amino Acid Sequence↗
PubMed1991

Interspecies and interstrain studies on the increased susceptibility to metrazol-induced convulsions in animals given aspartame.

The ability of aspartame (APM) to increase the susceptibility to metrazol-induced convulsions was studied in two strains of mice (CD1 and DBA/2J) and in guinea-pigs. Rats were included as known positive controls. Plasma and brain levels of phenylalanine (Phe) and tyrosine (Tyr) were measured in CD1 mice and guinea-pigs at various intervals after a dose of 1 g APM/kg body weight (administered orally to mice and ip to guinea-pigs). In mice, peak levels of Phe and Tyr were observed in plasma after 30 min and in brain after 60 min. In guinea-pigs peak plasma levels of Phe and Tyr occurred 30 min after treatment. Phe was at a maximum in guinea-pig brain after 30 min, while Tyr levels reached a peak at 120 min. In further experiments Phe and Tyr levels were measured 1 hr after APM doses of 0.5, 0.75 or 1 g/kg. In CD1 mice, plasma Phe and Tyr levels were increased significantly only at the highest dose, whereas in brain, Tyr concentrations were significantly increased by 0.75 or 1 g APM/kg and Phe was significantly increased by all three doses. In the guinea-pig, plasma Phe and Tyr were increased significantly only by 1 g APM/kg and in brain this dose significantly raised only the Phe levels. Monoamine and metabolite levels were determined in the brain striata of CD1 and DBA/2J mice 1 hr after the oral administration of 1 or 2 g APM/kg body weight; no differences from control values were found in either strain. The studies of potentiation of metrazol-induced convulsions showed that APM, at doses of up to 2 g/kg body weight, had no such effect in mice or guinea-pigs. In contrast, as expected, the potentiation was significant in the rat at 1 g/kg.

Animals↗
PubMed1991

Subclinical cardiac dysfunction in sarcoidosis.

Clinically apparent myocardial disease is infrequent in sarcoidosis. However, autopsy data show myocardial involvement in up to 30 percent of patients. Unexplained exertional symptomatology is a common complaint in patients with sarcoidosis. In this study, we investigated whether abnormal cardiac function might limit exercise performance in patients with sarcoidosis without overt cardiac involvement. We studied exercise responses in 35 patients with sarcoidosis and compared them with 28 untrained controls. Seventy-seven percent of the patients were symptomatic. Pulmonary function test results were lower in the group with sarcoidosis than normal controls, but they were within normal range. Only one patient had evidence of ventilatory limitation to exercise. Sixteen (46 percent) patients had abnormally increased heart rates (HRs) at rest prior to exercise testing and/or with exercise. Rapid HRs were confirmed during daily activities by continuous ambulatory electrocardiographic (ECG) monitoring. Left ventricular ejection fraction (LVEF) was measured to determine if systolic dysfunction could account for abnormal HR responses. Of patients with abnormally increased HRs, five had LVEFs less than 50 percent, and eight had normal LVEFs, of whom 75 percent had tachycardia at rest. Retrospective comparison of HR responses and LVEF between patients who did or did not receive corticosteroids revealed no significant differences between groups. We conclude that abnormal HR responses in patients without evident cardiac sarcoidosis are common and exertional symptoms in this population are often associated with chronotropic abnormalities. The exact mechanisms underlying the chronotropic abnormalities are unclear, but they likely include ventricular systolic dysfunction, sinus node dysfunction from granulomatous infiltration, or combinations of the two.

Adult↗
PubMed1990

Atrioventricular canal in Down syndrome. Prevalence of associated cardiac malformations compared with patients without Down syndrome.

The atrioventricular canal is the "classic" congenital heart anomaly in Down syndrome. We may learn more of the nature of this disorder by careful study of the anatomic characteristics of the cardiac lesions and by comparing these lesions in patients with and patients without Down syndrome. We reviewed the clinical characteristics (echocardiographic and angiocardiographic) of 220 patients with atrioventricular canal and compared the prevalence of anatomic types and associated cardiac malformations in children with (105) and without (115) Down syndrome. In patients with Down syndrome, the complete form of atrioventricular canal was prevalent, with a high frequency of associated Fallot's tetralogy. Partial atrioventricular canal and left-sided anomalies were more common in patients without Down syndrome. Down syndrome is associated with a simpler type of atrioventricular canal when compared with patients with a normal chromosome configuration.

Coronary Circulation↗
PubMed1990

Systemic atrioventricular conduit for extracardiac bypass of hypoplastic systemic atrioventricular valve.

The management of severe congenital mitral stenosis in infants and children is still controversial. We describe our experience with the use of a systemic atrioventricular (SAV) extracardiac conduit to bypass a hypoplastic systemic atrioventricular valve. An SAV extracardiac conduit has been used in six patients (left atrium--left ventricle in five, right atrium--right ventricle in one). One hospital death occurred due to mediastinitis and there were two late deaths, one due to progressive subaortic stenosis and one sudden, possibly due to arrhythmia. Postoperative cardiac catheterization performed in five patients showed reduction of the transmitral gradient from a mean of 16 mmHg to a mean of 5 mmHg. Calcification of the bioprosthetic valve occurred in two patients 3 1/2 years and 2 years respectively after the operation; one died from concomitant subaortic stenosis and one underwent conduit replacement. Although its long-term efficacy is limited, the SAV conduit seems the most reliable surgical option for infants and children with hypoplastic systemic atrioventricular valves unsuited to conventional surgery.

Aortic Coarctation↗