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Biomedical subjects

M Demedts

Publications and source records attributed to M Demedts.

At least 163 records · Page 9Linked to original sources
PubMed1989

Effects of acute hyperinflation on the mechanical effectiveness of the parasternal intercostals.

We studied the mechanical effectiveness of the parasternal intercostals at FRC and near TLC in 14 supine, vagotomized, and anesthetized dogs. First, we determined the relationship between parasternal intramuscular pressure (Pps), measured with Gaeltec 12 CT-mini-transducers, and parasternal EMG activity (Eps) during breathing at FRC and near TLC. Second, we examined the changes in Pps and the changes in parasternal force (Fps) generated during bilateral parasternal stimulation at FRC and near TLC with a given supramaximal stimulus. Before phrenicotomy, the inspiratory increases in Pps remained relatively constant near TLC (FRC, 50.4 +/- 16.5 versus TLC, 48.7 +/- 13.3 cm H2O, NS), whereas the Eps clearly decreased (82.9 +/- 5.5% FRC, p less than 0.01). This indicates that the gain converting electrical activity into pressure for the parasternals is greater near TLC than at FRC. A similar pattern of changes in Pps and in Eps was observed during quiet inspiration at FRC and near TLC after phrenicotomy. During bilateral parasternal stimulation the increases in Pps near TLC tended to be greater than those at FRC (140.7 +/- 28.6 versus 100 +/- 28.3 cm H2O, NS), whereas the increases in Fps were significantly greater near TLC than at FRC (277.4 +/- 60.6 versus 214.2 +/- 47.1 g, p less than 0.05). Therefore, we conclude that the mechanical effectiveness of the parasternal contraction near TLC remains relatively unchanged and is even greater in relation to that at FRC.

Acute Disease↗
PubMed1989

Total respiratory resistance and reactance as a measurement of response to bronchial challenge with histamine.

The potential of the forced oscillation technique to detect the airway response on histamine bronchial challenge tests was compared with that of FEV1 and plethysmographic SGaw. In 53 subjects with a history of episodic wheezing and a normal baseline airway resistance, we carried out bronchial challenges with successively doubling concentrations of histamine until FEV1 had dropped by 15% or more or a concentration of 16 mg/ml histamine was reached. For the baseline values, a mean within-subject coefficient of variation was found of 2.8% for FEV1, 7.4% for SGaw, 8.7% for the oscillatory respiratory conductance at 6 Hz (1/Rrs6), and 7.7% for the mean oscillatory respiratory conductance (between 2 and 26 Hz) (1/Rrs). The latter coefficients allow the calculation of the following threshold values: PD15FEV1, PD40SGaw, PD47 1/Rrs6, and PD42 1/Rrs. The probability of exceeding these levels by chance is virtually zero. Histamine challenge caused significant absolute changes in Rrs at 6 Hz (Rrs6), in mean level of Rrs and of respiratory reactance (Xrs), in slope of Rrs and Xrs versus frequency, and in mean curvature of Rrs-frequency curve. A multivariate analysis of the differences between prechallenge and postchallenge values showed that the parameters with the best sensitivity to detect the effect of histamine were, in decreasing order: the relative change of SGaw, of 1/Rrs6, of 1/Rrs, of FEV1, of FVC, and of 1/Vtg, followed by the absolute change of Xrs and of the average slope of the Rrs-frequency relationship.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Preoperative and postoperative abnormalities in chest x-ray indices and in lung function in pectus deformities.

In 88 patients with pectus deformities radiologic chest indices and routine pulmonary function tests were measured before and 1 to 20 years after corrective surgery. A combination of anteroposterior indices at the upper and lower level of the chest were investigated to quantitate and to discriminate the different pectus deformities. The study comprised four groups: pectus excavatum, pectus carinatum, pectus deformatum and pectus excavatum with scoliosis. These indices were also assessed in 250 healthy males and females. Generally, several indices showed significant and discriminative changes in the different patient groups and improved again after surgery. Preoperative lung function was decreased in pectus excavatum only. In all groups lung function worsened after surgery. A stepwise discriminant analysis performed on the large group with pectus excavatum indicated that postoperative lung function was decreased if the preoperative value of FEV1 or VC was more than about 75 percent predicted and vice versa, but that it was not related to other factors such as radiologic indices, age at operation or time since operation.

Adolescent↗
PubMed1989

[The cobalt lung in diamond cutters: a new disease].

Although for forty years already broncho-pulmonary pathology has been described in workers exposed to hard-metal (i.e. alloys of tungsten carbide and cobalt) and although cobalt is considered the offending agent of this hazard, these abnormalities have almost not been found after exposure to cobalt alone except in animal experiments. Recently we detected clearcut broncho-pulmonary pathology in 48 diamond polishers (i.e. nearly 1% of those exposed) attributable to the ultrafine cobalt dust from the cutting surface of polishing disks, in which it was used as a cementing matrix for microdiamonds without any tungsten carbide. Nineteen of these patients presented with a fibrosing alveolitis documented in 6 by lung biopsy and in 12 by broncho-alveolar lavage, both of which revealed characteristic multinucleated giant cells. Thirteen suffered from asthma of occupational origin, in 9 proven by cobalt-inhalation tests, and in 5 by peak flow measurements at the workplace. Sixteen had mixed bronchial and alveolar pathology or were incompletely documented. A cross-sectional study in about 200 diamond polishers showed a significant correlation between exposure to cobalt and decrease in lung function. The strikingly harmful effects of cobalt can be explained by the chronic exposure to very small particles with markedly increased solubility. The pathogenesis of the broncho-pulmonary pathology may be attributed to the cytotoxic as well as to the sensitising (i.e. allergic and/or idiosyncratic) actions of cobalt.

Asthma↗
PubMed1989

[Pulmonary pathology due to cobalt and hard metals].

For forty years, cases of interstitial pneumonia and bronchial asthma have been described in hard metal workers (i.e., alloys of tungsten carbide and cobalt). Recently we have reported comparable pulmonary lesions in workers in the diamond industry who were exposed to cobalt unassociated with tungsten carbide. The exposure came from the diamond cobalt discs used for polishing diamonds, which had as the hard element microdiamonds, cemented in an alloy of pure cobalt. The hard metals on the other hand consisted of cobalt and tungsten carbide. Forty-seven diamond cutters (i.e., nearly 1% of those exposed) presented with broncho-pulmonary pathology due to cobalt. Nineteen had a fibrosing alveolitis, sometimes documented by a pulmonary biopsy and more often by a broncho-alveolar lavage which revealed characteristic multinucleated giant cells. Thirteen had occupational asthma, often proved by specific inhalation provocation tests to cobalt or by lung function measurements at the place of work. Two patients had mixed forms and in thirteen a probable diagnosis was suggested. The pathogenesis of cobalt might be explained by cytotoxic action such as has been demonstrated in animal experiments. Either results suggest a sensitising or allergic action. Tungsten carbide does not produce pulmonary lesions but its association with cobalt intensifies the effects of the latter.

Alloys↗
PubMed1989

The effect of breath size and posture on calibration of the respiratory inductive plethysmograph by multiple linear regression.

The accuracy of the respiratory inductive plethysmograph (Respitrace) for estimation of lung volume changes during quiet breathing and vital capacity (VC) manoeuvres was evaluated using a variant of the multiple linear regression (MLR) technique. We applied this technique successively on quiet breathing, on the whole VC, and on each of the four quarters of the VC separately. This was carried out in six body positions. The best estimation of tidal volumes was obtained when calibration factors calculated during quiet breathing were used. The best estimation of VC was obtained when the calibration factors were adapted to the level of lung inflation. These results indicate that, using a single position MLR calibration method, the Respitrace measures tidal and VC mouth volumes very accurately. The accuracy of this MLR method for estimation of the rib cage and abdominal contributions was validated by comparison with isovolume calibration factors. Both techniques gave very similar results during tidal breathing. However, the MLR calibration factors may have no physiological meaning (i.e. for volume partitioning) when they are calculated from VC manoeuvres, in which more than two degrees of freedom are involved.

Abdomen↗
PubMed1989

Pulmonary phospholipid accumulation distal to an obstructed bronchus. A morphologic study.

Alveolar proteinosis (AP) and postobstructive or endogenous lipid pneumonia (ELP) are two distinct morphologic types of phospholipid accumulation in the lung. In ELP, ultrastructurally amorphous fat accumulates in the cytoplasm of alveolar macrophages. In AP, lamellar surfactant bodies with an electron microscopic complex structure are stored within alveolar lumina. In contrast to ELP, AP has not been associated with bronchial obstruction. One case of postobstructive AP occurred distal to a central carcinoid tumor, and two cases of combined AP and ELP occurred next to a squamous cell carcinoma that obstructed a lobar bronchus. Results of histologic and ultrastructural studies were determined with regard to new insights into the physiology and biochemistry of pulmonary lipids. It was concluded that the morphology of accumulated fat in obstructed lung tissue may depend on local oxygen and carbon dioxide tensions.

Bronchial Neoplasms↗
PubMed1989

Total respiratory resistance and reactance in patients with diffuse interstitial lung disease.

In 54 patients with interstitial lung diseases and no signs of airway obstruction we measured lung volumes, maximal expiratory flows, diffusing capacity (DLCO), total respiratory resistance (Rrs) and reactance (Xrs) between 4 and 26 Hz by means of the forced oscillation technique. In all patients DLCO was less than 75% of the expected value. Patients were classified into two groups depending on total lung capacity (TLC): group A with TLC less than 80% of expected, and group B with TLC of 80% or more. Group A demonstrated a decrease of Xrs especially at low frequencies, with small, not significant changes in Rrs. In the patients in this group with the lowest values of TLC (less than 50%), we observed an increase of Rrs at low frequencies causing a negative frequency dependence of Rrs. In group B no distinct changes of Rrs and Xrs occurred. Canonical correlation analysis between routine lung function data and forced oscillation parameters, showed tight correlations between TLC in absolute value or VC in percent of the predicted value on the one hand and average level of Xrs and average slope of Xrs (and Rrs) vs frequency curves on the other hand. Measurements of lung mechanics in five additional patients and comparison with a model of the respiratory system suggest that the changes of Rrs and Xrs are not explained totally by the observed increase in lung tissue resistance and decrease in lung compliance. The observed changes in Rrs and Xrs are not specific for restrictive lung disorders; similar changes are met also in moderately advanced obstructive diseases.

Adult↗
PubMed1988

Ventilatory response to carbonic anhydrase inhibition in cats: effects of acetazolamide in intact vs peripherally chemodenervated animals.

Hyperventilation induced by red cell carbonic anhydrase inhibition (CAI) has been observed frequently; its mechanism, however, is still obscure. In the present study in anaesthetized cats, we have investigated the effect of 50 mg/kg acetazolamide, a carbonic anhydrase inhibitor, on ventilation. In order to determine the role of the peripheral chemoreceptors, we compared the response in peripherally chemodenervated and intact cats. Furthermore, in cats with intact peripheral chemoreceptors, we determined hypoxic sensitivity before and 2 h after i.v. infusion of the drug. In all animals, acetazolamide caused a large increase in ventilation. However, the peripherally chemodenervated animals developed a significantly larger response than the intact animals (respectively about 200 and 100% increases in ventilation). The first group also showed a significantly larger fall in PACO2. In the intact animals studied, acetazolamide virtually abolished the hypoxic sensitivity which existed before infusion of the drug. We conclude that acetazolamide, at the dose studied, causes a decrease in activity of the peripheral chemoreceptors, and also a decrease (c.q. removal) of their sensitivity to PaO2 changes. The increase in ventilation by acetazolamide is probably caused by an action of the drug on the central nervous system, possibly on the central chemoreceptors.

Acetazolamide↗
PubMed1988

Mechanical coupling of upper and lower canine rib cages and its functional significance.

We studied rib cage distortability and reexamined the mechanical action of the diaphragm and the rib cage muscles in six supine anesthetized dogs by measuring changes in upper rib cage cross-sectional area (Aurc) and changes in lower rib cage cross-sectional area (Alrc) and the respective pressures acting on them. During quiet breathing in the intact animal the rib cage behaved as a unit (Aurc: 14.6 +/- 7.9 vs. Alrc: 15.1 +/- 9.6%), whereas considerable distortions of the rib cage occurred during breathing after bilateral phrenicotomy (Aurc: 21.0 +/- 5.1 vs. Alrc: 7.0 +/- 4.8%). These distortions were even more pronounced during phrenic nerve stimulation and separate stimulation of the costal and crural parts of the diaphragm (e.g., phrenic nerve stimulation; Aurc: -7.1 +/- 5.1 vs. Alrc: 6.9 +/- 3.5%). During the latter maneuvers the upper rib cage deflated along the relationship between upper rib cage dimensions and pleural pressure obtained during passive deflation, whereas the lower rib cage inflated close to the relationship between lower rib cage dimensions and abdominal pressure obtained during passive inflation. The latter relationship is expected to differ between costal and crural stimulation, since costal action has both an appositional and insertional component and crural action only has an appositional component. The difference between costal and crural stimulation, however, was relatively small, and the slopes were only slightly steeper for the costal than for the crural stimulation (2.9 +/- 1.2 vs. 2.2 +/- 1.0%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Early emphysema. Ten years' evolution.

In this study, functional evolution over ten years was evaluated in 13 patients with early emphysema. The diagnosis was made on the basis of a decrease in single-breath DCO (55 +/- 14 percent predicted, mean +/- 1 SD), a loss of elastic recoil (CL,st = 0.76 +/- 0.25 L/cm H2O), and only minor airway obstruction (FEV1 = 87 +/- 13 percent predicted, Sgaw = 0.09 +/- 0.04 cm H2O-1.s-1), and compatible chest radiographs. During the ten years, there was a decrease in FEV1 of 0.89 +/- 0.40 L p less than 0.001), with a range of 0.20 to 1.55 L (which could not clearly be related to smoking habits or to initial lung function), a decrease in elastic recoil (p less than 0.05, with a decrease of Ptp, TLC by 6 +/- 7 cm H2O; p approximately equal to 0.05), an increase in TLC of 0.46 +/- 0.80 1 (p approximately equal to 0.05), and in RV/TLC of 9 +/- 3 percent (p less than 0.001). The resistance of the upstream segment (ratio Ptp/Vmax) increased slightly but generally remained within normal limits. In conclusion, patients with early emphysema resemble those with classic COPD, with a mean yearly decline in FEV1 similar to that in COPD.

Adult↗
PubMed1988

Broncho-oesophageal fistula with vascular malformation.

We present a patient with a type III congenital broncho-oesophageal fistula and a connection between the systemic and the pulmonary circulation. The congenital fistula caused chronic bronchopulmonary suppuration with bronchiectasis which in turn was the cause of a left-to-right shunt, probably through multiple precapillary or capillary anastomoses.

Arterio-Arterial Fistula↗
PubMed1988

Mechanism of pulmonary function changes after surgical correction for funnel chest.

In 24 subjects with pectus excavatum we evaluated whether the previously detected unfavourable effects of corrective surgery on the ventilatory capacity were attributable to pulmonary or to chest wall factors. We found that 12.2 +/- 3.7 yrs postoperatively (i.e. at the age of 23.3 +/- 5.4 yrs) the vital capacity was decreased from 89 +/- 10% predicted (pred) preoperatively to 64 +/- 6% pred (p less than 0.001) and forced expiratory volume in one second from 88 +/- 17 to 66 +/- 11% pred (p less than 0.001). At total lung capacity (TLC; 69 +/- 5% pred) we found an obvious reduction in transpulmonary pressure (59 +/- 23% pred) and in transdiaphragmatic pressure (30 +/- 17 cmH2O) postoperatively. This indicated an extrapulmonary cause of the restrictive defect, attributable to abnormal chest wall mechanics secondary to the extensive surgery on the sternum and parasternal zones.

Adolescent↗