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Biomedical subjects

A Harf

Publications and source records attributed to A Harf.

At least 145 records · Page 8Linked to original sources
PubMed1992

Use of the Blasius resistance formula to estimate the effective diameter of endotracheal tubes.

To early detect mucus deposition in endotracheal tubes (ETT), we propose using a geometric, flow-independent parameter, i.e., diameter of the ETT, based on a precise knowledge of ETT flow regime, instead of using the classic flow-dependent ETT resistance based on the empirical, nonlinear Rohrer equation. From the estimated slope of -0.24 derived from Moody diagrams characterizing the pressure-flow relationship in ETT of various inner diameters (D), we first assessed that the Blasius resistance formula slope of -0.25 could be applied to adult-size ETT, meaning that flow remains fully developed, turbulent, and hydraulically smooth (0.5 L/s less than or equal to V less than or equal to 1.4 L/s). Insertion into the ETT of a pressure catheter (external diameter: d) to stimulate in vivo measurements did not modify these results, provided the hydraulic diameter, D* = D - d, was substituted for D in the Blasius formula. The Blasius formula was then used to determine, from in vitro pressure and flow measurements in ETT before intubation and in ETT lined with dry mucus secretions, the effective diameter, shown here to be highly correlated to the actual diameter measured by volumetric water displacement. The effective ETT diameter was measured in eight patients at different stages after oral or nasal intubation. Compared with the actual ETT diameter measured before insertion, the effective diameter was slightly reduced (2.6 +/- 2.5%) during the first week of intubation and was strongly reduced (12.2 +/- 2.8%) during the second week.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1992

Can portable chest x-ray examination accurately diagnose lung consolidation after major abdominal surgery? A comparison with computed tomography scan.

PURPOSE: To prospectively quantify the degree of accuracy of portable chest x-ray film examination in the detection of postoperative lung consolidations. STUDY: Nineteen patients had a chest x-ray film and computed tomography (CT) scan the day before and 48 h following elective abdominal aortic replacement. RESULTS: The diagnosis of lung consolidations by x-ray film examination showed sensitivity of between 0.33 and 1.00, depending on the lung zone considered (lower at the lung bases). Specificity always was greater than 0.79. Radiologic lung volume decreased 16 percent postoperatively (p < 0.01) on average and noninflated parenchyma increased by a factor of 3 (p < 0.0001). Postoperatively, PaO2 correlated with the amount of condensed lung by CT scan (p < 0.002). CONCLUSION: In postoperative conditions, x-ray film examination is a method which presents good specificity but poor sensitivity in the diagnosis of lung consolidations.

Abdomen↗
PubMed1992

Influence of posture on mechanical parameters derived from respiratory impedance.

The influence of posture on respiratory mechanics was investigated in 10 healthy volunteers, using the forced pseudorandom noise technique. Subjects were studied in four randomly selected positions: sitting; sitting with the head turned sideways; supine; and prone with the head turned sideways. Respiratory compliance (Crs), inertance (Irs) and resistance estimated at 4 Hz (R4), were calculated by fitting respiratory impedance by a 4 parameter model with a frequency dependent resistance. When subjects changed from sitting to lying, whilst maintaining the head in the same position in relation to the body, Irs increased and Crs decreased, probably due to gravitational effects. R4 was significantly higher in the supine position than in either of the sitting or the prone positions. These results demonstrate that changes in lung volume cannot completely explain the influence of posture on respiratory resistance, and indicate upper airway geometry as a determinant factor of respiratory resistance.

Adolescent↗
PubMed1991

Effects of platelet-activating factor on lung epithelial permeability in the guinea-pig.

We examined the effects of platelet-activating factor (PAF) on lung epithelial permeability by measuring the clearance of intratracheally administered 99m-technetium-labeled diethylene triamine penta-acetic acid (99mTc-DTPA) in guinea-pigs which were anaesthetised, paralysed and mechanically ventilated. The clearance of the radiolabeled tracer molecule 99mTc-DTPA from airways to the blood was expressed as changes in counts/min corrected for background. For each guinea-pig, 99mTc-DTPA clearance was assessed before and after i.v. PAF administration, when tracheal pressure had returned to near control values. Doses of 10, 50 and 100 ng/kg of PAF caused dose-dependent increases in 99mTc-DTPA clearance of 7 +/- 3%, 38 +/- 7% and 65 +/- 11% respectively. The respective effects of 0.5 mg/kg of the beta 2-adrenergic agonist salbutamol and 0.3 mg/kg of the alpha 1-adrenergic agonist methoxamine on the increase in lung epithelial permeability induced by 50 ng/kg PAF were also studied. Salbutamol significantly reduced the acute bronchoconstrictor effects of PAF, but did not affect the increase in lung epithelial permeability, which was 58 +/- 10%. Conversely, methoxamine significantly enhanced the bronchoconstrictor effects of PAF but inhibited the lung epithelial permeability increase, which was only 10 +/- 13%. In the absence of PAF, salbutamol significantly increased this permeability by 49 +/- 11%, whereas methoxamine alone slightly reduced, it by -11 +/- 4%. These results demonstrate that PAF increases lung epithelial permeability and suggest that vascular surface area recruitment may explain this increase.

Albuterol↗
PubMed1991

Pressure support ventilation using a new tracheal gas injection tube.

In order to explore new types of jet ventilation, we tested a tracheal gas injection tube (TGIT) which included six thin capillaries and provided high pressure injection. The driving pressure was chosen to yield a plateau of inspiratory tracheal pressure of 10 cm H2O. An original controller was built to monitor spirometry and trigger injection in order to deliver both pressure controlled ventilation (PCVTGIT) and a new mode of inspiratory pressure support jet ventilation (IPSTGIT). The PVCTGIT mode maintained the same end-tidal carbon dioxide concentration as conventional ventilation with the same tidal and minute ventilation. We studied 10 patients after abdominal surgery. During spontaneous breathing, the patients were allowed to breathe through the tube, successively with and without IPSTGIT. IPSTGIT, compared with spontaneous breathing increased minute ventilation (from 5.7 (SD 1.6) to 7.1 (1.7) litre min-1) (P less than 0.001). It reduced the total work of breathing (from 0.625 (0.223) to 0.263 (0.151) J litre-1, respectively) (P less than 0.01) and the occlusion pressure (from 2.62 (1.28) to 1.36 (0.74) cm H2O, respectively) (P less than 0.01). It is concluded that this TGIT used with a specific system for sensing and triggering ventilation allows inspiratory pressure support during low frequency jet ventilation.

Female↗
PubMed1991

Changes in the distribution of ventilation and perfusion associated with separation from mechanical ventilation in patients with obstructive pulmonary disease.

A trial of separation from mechanical ventilation may induce an abnormal respiratory pattern and a maldistribution of ventilation-to-perfusion ratios (VA/Q), especially in patients with chronic obstructive pulmonary disease. This study was designed to assess the effects of three different modes of ventilation on the distribution of global and also regional VA/Q in eight patients with chronic obstructive pulmonary disease recovering from acute respiratory failure who remained dependent on mechanical ventilation after more than 5 days of attempted separation from the ventilator. VA/Q distribution was assessed using the multiple inert gas and isotopic scanning methods after 30 min each of controlled mechanical ventilation (CMV), 10 cmH2O inspiratory pressure support, and spontaneous breathing (SB). Controlled ventilation was provided at a respiratory rate ranging from 12 to 18 breaths per min and a tidal volume of 8 ml.kg-1. In comparison to CMV, SB resulted in a decrease in tidal volume (from 512 +/- 144 to 301 +/- 102 ml, P less than 0.01), and an increase in respiratory rate (from 15.5 +/- 3.2 to 27.3 +/- 15.0 breaths per min, P less than 0.05), which increased dead space (+7.1% of minute ventilation), cardiac output (+36%), and the perfusion to areas of low VA/Q (+8.9% of cardiac output) (P less than 0.05, P less than 0.001, and P less than 0.05, respectively). Isotopic scans revealed a horizontal craniocaudal difference of VA/Q in all modes, with the lowest VA/Q zones at the basal part of the lungs (mean basal VA/Q 0.58 in SB and 1.05 in CMV).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1991

Inspiratory pressure support compensates for the additional work of breathing caused by the endotracheal tube.

Breathing through an endotracheal tube and a demand valve may increase the work performed by the respiratory muscles. Inspiratory pressure support (PS) is known to reduce this work and might therefore compensate for this increased requirement. To test this hypothesis, we measured the work of breathing (WOB) in 11 patients whose tracheas were intubated. Five had no intrinsic lung disease, but six had chronic obstructive lung disease. We compared WOB measurements taken under several sets of conditions: during assisted breathing at four levels of PS, during unassisted breathing and connection to a T-piece, and after extubation of the trachea. During unassisted breathing via the ventilator circuit (PS set at 0 cmH20), the WOB per minute was greater than that after extubation, with a mean increase (+/- standard deviation) of 68 +/- 38% (10.3 +/- 5.1 vs. 6.5 +/- 3.7 J.min-1, P less than 0.01). While breathing through the T-piece, the WOB was 27 +/- 18% greater than after tracheal extubation (8.2 +/- 5.1 vs. 6.5 +/- 3.7 J.min-1, P less than 0.05). The principal reason why inspiratory work decreased after extubation was that the ventilatory requirement decreased. For each patient, we determined retrospectively, after extubation, the level of PS that had reduced WOB to its postextubation value and obtained levels ranging from 3.4 to 14.4 cmH2O. The PS level at which additional WOB was compensated for, was greater in patients with chronic lung disease than in those free of lung disease (12.0 +/- 1.9 vs. 5.7 +/- 1.5 cm H2O, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

5-Hydroxytryptamine-induced bronchoconstriction in the guinea-pig: effect of 5-HT2 receptor activation on acetylcholine release.

1. The bronchoconstrictor responses to 5-hydroxytryptamine (5-HT) were studied in the guinea-pig to establish whether they are partly attributable to parasympathetic activation within the airways. 5-HT dose-response curves were constructed in anaesthetized and ventilated guinea-pigs pretreated with saline, or by bilateral cervical vagotomy or vagotomy plus atropine 3 mg kg-1, i.v. Vagotomy had no effect on 5-HT-induced bronchoconstriction but vagotomy plus atropine significantly reduced it. 2. To determine whether parasympathetic activation within the airways resulted from pre- or postganglionic stimulation, 5-HT dose-response curves were constructed for two groups of vagotomized guinea-pigs treated with hexamethonium 2 mg kg-1, or hexamethonium 2 mg kg-1, plus atropine 3 mg kg-1. Guinea-pigs treated with hexamethonium plus atropine experienced significantly less 5-HT-induced bronchoconstriction than those treated with hexamethonium alone. 3. To characterize the subtype of 5-HT receptors involved in the activation of the parasympathetic system by 5-HT, dose-response curves to 5-HT were constructed for four groups of vagotomized guinea-pigs treated with saline, 1 mg kg-1 of the 5-HT3 antagonist ICS 205-930, or either 0.01 or 0.1 mg kg-1 of the 5-HT2 antagonist ketanserin. ICS 205-930 enhanced 5-HT-induced bronchoconstriction but 0.01 mg kg-1 ketanserin inhibited it significantly and 0.1 mg kg-1 ketanserin abolished it. To confirm the involvement of 5-HT2 receptors in these responses, we studied the effects in vagotomized guinea-pigs of atropine on the bronchoconstriction induced by the 5-HT2 agonist,x alpha-methyl-5-HT, infused at rates of 40 and 80ngkg-1s-'. At both rates, atropine significantly reduced the bronchoconstrictor responses to alpha-methyl-5-HT. 4. The above results indicate that 5-HT-induced bronchoconstriction is indeed partly mediated by parasympathetic activation within the airways. This activation is mediated by stimulation of 5-HT2 receptors which are probably located on the postganglionic parasympathetic nerve endings.

Acetylcholine↗
PubMed1991

Shunt effect of gas compression inside pneumotachographs during forced oscillations.

Determination of the frequency response of pneumotachographs is needed whenever they are used to measure high-frequency flows, such as in the forced oscillation method. When screen and capillary pneumotachographs are calibrated using an adiabatic compression in a closed box as a reference impedance, they can be adequately described by a series of inertial-resistive elements. However, this type of reference impedance strongly differs from the actual respiratory impedance (ZL). We studied the frequency response of pneumotachographs up to 250 Hz in reference to the impedance of a compressible gas oscillating in a long tube, taken as a more generalizable model of actual ZL. We found that, with this device, the series resistance-inertance models fail to describe the frequency response of the pneumotachograph. However, when compressible effects in the pneumotachograph are taken into account by adding to the resistive models a compliance (Cpn) corresponding to the compression in half of the inner volume of the pneumotachograph, the agreement with experiments becomes satisfactory. Gas compression-related phenomena were demonstrated to be negligible only when the parameter omega Cpn magnitude of ZL is much smaller than 1 (omega pulsation). Results obtained in normal humans have shown that such a correction is required above 100 Hz. Similar correction at lower frequency might also be necessary in cases of large respiratory impedance (e.g., babies, subjects with pathological lungs, and intubated subjects).

Humans↗
PubMed1991

Effects of substance P and calcitonin gene-related peptide on the pulmonary circulation.

To assess the in vivo effects of the neuropeptides calcitonin gene-related peptide (CGRP) and substance P (SP) on the pulmonary vascular bed, the hemodynamic responses to both CGRP and SP were examined in the in situ-perfused lung lobe of open-chest anesthetized pigs. Peptides were infused into the lobar artery under conditions of elevated pulmonary vascular tone by prostaglandin F2 alpha (PGF2 alpha, 20 micrograms/min). Pulmonary airway lobar dynamic compliance (Cdyn) and airway resistance (Re) were computed from simultaneously measured airway pressure and airflow entering the lobe through a Carlens endobronchial divider. PGF2 alpha infusion slightly reduced Cdyn (-20%) and increased Re (+11%) while lobar arterial pressure rose from 14 +/- 1 to 31 +/- 2 mmHg (n = 12). In these conditions, lobar artery infusion of SP (0.5-50 pmol/min) or CGRP (15-5,000 pmol/min) produced a dose-dependent decrease in the pressor response to PGF2 alpha, reaching -54 +/- 3 and -64 +/- 7%, respectively, without alterations in lung mechanics. On a molar basis, SP was more effective than CGRP; its vasodilatory effect was more rapid and of shorter duration. Higher CGRP infusion rates were not studied because of marked systemic hypotension. SP infused at 150, 500, and 1,000 pmol/min significantly reduced Cdyn by 12 +/- 2, 24 +/- 4, and 62 +/- 7%, respectively, but also induced a rise in lobar arterial pressure and a fall in systemic arterial pressure. The results show that both SP and CGRP are potent pulmonary vasodilators. In contrast to CGRP, which did not affect lung mechanics, high infusion rates of SP decreased Cdyn and increased Re.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1991

Effects of albuterol inhalation on the work of breathing during weaning from mechanical ventilation.

The work of breathing is a major determinant of the success of weaning from mechanical ventilation. The aim of this study was to assess whether an inhaled bronchodilator could reduce the mechanical load on the respiratory muscles and diminish the work. For this purpose, 15 intubated patients in the process of weaning from mechanical ventilation inhaled the beta 2-agonist bronchodilator albuterol via a spacer device filled with 1 mg of the drug and connected to the endotracheal tube. During spontaneous breathing, the mean work of breathing diminished significantly after albuterol, from 9.35 +/- 1.05 to 8.33 +/- 1.13 J/min (p less than 0.01), and seven patients exhibited a decrease superior or equal to 15%. This decrease resulted from a marked reduction in lung and airway resistance, from 12.0 +/- 1.7 to 9.8 +/- 1.4 cm H2O.L-1.s (p less than 0.05). No significant changes were observed in the breathing pattern, intrinsic PEEP or arterial blood gas measurements after albuterol, and peripheral cardiovascular effects were not significant. In seven patients, we were able to compare the changes that occurred after albuterol in the work of breathing during weaning from mechanical ventilation with the changes in pulmonary function induced by albuterol after extubation, as assessed by the forced oscillation method. A close correlation was found between the two types of change, further indicating that the reduction in the work of breathing was more likely to occur in patients with the largest bronchodilating effect of albuterol at baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1991

Constant-flow insufflation prevents arterial oxygen desaturation during endotracheal suctioning.

In mechanically ventilated patients, disconnection from the ventilator and endotracheal suctioning can induce major arterial oxygen desaturation resulting from apnea, changes in inspired oxygen fraction, and decrease in lung volume. The aim of this study was to test the efficacy of a simple method of delivering oxygen and maintaining lung volume during this process. Our study was conducted in two parts. In the first part, constant-flow insufflation of oxygen (CFI) was used in seven patients ventilated for acute respiratory failure (PaO2/FlO2 = 347 +/- 33 mm Hg) as a means of maintaining arterial oxygenation during apnea and disconnection from the ventilator. CFI was administered via a modified endotracheal tube in which small capillaries allowed delivery of a high-velocity jet flow near the tracheal end of the tube during disconnection from the ventilator. In comparison to apnea alone, CFI prevented a fall in arterial oxygen tension (16 +/- 7 mm Hg during CFI versus 117 +/- 27 during apnea, after 90 s of disconnection in the two situations, p less than 0.001), whereas it did not reduce the development of hypercapnia. The efficacy of CFI resulted both from the injection of oxygen into the trachea and from the maintenance of positive alveolar pressure induced by air entrainment (mean 10.4 +/- 1.1 cm H2O), preventing a fall in lung volume usually occurring after disconnection (+338 +/- 88 ml during CFI versus -344 +/- 64 ml during apnea, p less than 0.01). In the second part of the study CFI was used to prevent arterial oxygen desaturation induced by endotracheal suctioning.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1991

Droperidol prevents serotonin-induced bronchospasm in the guinea pig.

The effects of droperidol on bronchoconstriction induced by serotonin (5-HT) were studied in mechanically ventilated, paralyzed guinea pigs that had been anesthetized with pentobarbital. Droperidol did not modify the resting bronchial tone but prevented the bronchoconstrictor effects of 5-HT in a dose-related manner. Pretreatment with propranolol, hexamethonium, or prazosin did not alter the protective effects of droperidol on 5-HT-induced bronchoconstriction. The bronchoconstrictor responses to histamine or acetylcholine were not affected by droperidol. These results suggest that the protective effects of droperidol on 5-HT-induced bronchoconstriction are mediated through 5-HT receptor blockade on bronchial smooth muscle.

Acetylcholine↗
PubMed1991

Prevention of leucocyte elastase-induced emphysema in mice by heparin fragments.

Heparin and its derivatives inhibit human leucocyte proteinases i.e. elastase and cathepsin G, but do not inhibit porcine pancreatic elastase and Pseudomonas aeruginosa elastase. In vitro experiments, reported here, also indicate that elastin, one of the physiological substrates of human leucocyte elastase (HLE), could decrease by 30-fold the inhibitory potential of an hexadecasaccharide heparin fragment (dp 16) isolated from CY 222. Nevertheless, the inhibitory capacity of the heparin fragment still remains elevated with IC50 = 2.7 x 10(-7) M and still inhibits HLE in its free and adsorbed state to elastin. These overall data prompted us to evaluate the influence of CY 222 in HLE-induced emphysema. Emphysema was induced in mice eight weeks old, following a single instillation of 200 micrograms of HLE. CY 222 treated animals received 2.5 mg.kg-1 subcutaneously once daily, 6 days per week during 4 weeks prior to HLE instillation, and for eight weeks following HLE instillation. The heparin fragment treatment of the mice halved the mortality rate observed early following HLE instillation. After 8 weeks, surviving animals were examined for lung histological and morphometrical changes: mean linear intercept (MLI) and internal alveolar area (ISA). The CY 222 heparin fragments exerted a protective effect against HLE-induced emphysema by decreasing by 70% the MLI; these heparin fragments exerted no effect on emphysema induced by pancreatic elastase in hamsters or mice. Heparin derivatives represent a new class of physiological HLE low molecular weight inhibitors capable of preventing HLE-induced emphysema.

Animals↗
PubMed1991

Influence of lung volume on histamine-induced bronchoconstriction in guinea-pigs.

The influence of lung volume on bronchopulmonary reactivity was investigated in 4 groups of 14 anaesthetized paralysed mechanically ventilated guinea-pigs: animals of group 1 served as control; in animals of group 2, the parasympathetic nervous system was blockaded with atropine; animals of group 3 were submitted to a bilateral cervical vagotomy; animals of group 4 were both vagotomized and pretreated with atropine. In each group, the animals were randomly divided into 2 subgroups: one was ventilated at zero end-expiratory pressure (ZEEP), the other with 0.2 kPa positive end-expiratory pressure (PEEP) resulting in a mean increase in lung volume of about 1 ml. Bronchopulmonary response to infused histamine was assessed by the respiratory conductance and compliance values measured during bronchoconstriction (respectively HGrs and HCrs). In the control group, animals exposed to PEEP were found significantly less reactive than those ventilated at ZEEP. In groups 2, 3 and 4, this difference was significantly reduced for HGrs and even abolished for HCrs. These results demonstrate that the effect of lung volume on moderate histamine-induced bronchoconstriction in guinea-pigs is not purely mechanical, but is partly vagally mediated. They also suggest that this vagally mediated inhibitory influence results from involvement of central reflexes evoked by stretch receptor stimulation.

Animals↗
PubMed1990

Reversal of acute exacerbations of chronic obstructive lung disease by inspiratory assistance with a face mask.

BACKGROUND: Patients with acute exacerbations of chronic obstructive pulmonary disease may require endotracheal intubation with mechanical ventilation. We designed, and here report on the efficacy of, a noninvasive ventilatory-assistance apparatus to provide inspiratory-pressure support by means of a face mask. METHODS: We assessed the short-term (45-minute) physiologic effects of the apparatus in 11 patients with acute exacerbations of chronic obstructive pulmonary disease and evaluated its therapeutic efficacy in 13 such patients (including 3 of the 11 in the physiologic study) who were treated for several days and compared with 13 matched historical-control patients. RESULTS: In the physiologic study, after 45 minutes of inspiratory positive airway pressure by face mask, the mean (+/- SD) arterial pH rose from 7.31 +/- 0.08 to 7.38 +/- 0.07 (P less than 0.01), the partial pressure of carbon dioxide fell from 68 +/- 17 mm Hg to 55 +/- 15 mm Hg (P less than 0.01), and the partial pressure of oxygen rose from 52 +/- 12 mm Hg to 69 +/- 16 mm Hg (P less than 0.05). These changes were accompanied by marked reductions in respiratory rate (from 31 +/- 7 to 21 +/- 9 breaths per minute, P less than 0.01). Only 1 of the 13 patients treated with inspiratory positive airway pressure needed tracheal intubation and mechanical ventilation, as compared with 11 of the 13 historical controls (P less than 0.001). Two patients in each group died. As compared with the controls, the treated patients had a more transient need for ventilatory assistance (3 +/- 1 vs. 12 +/- 11 days, P less than 0.01) and a shorter stay in the intensive care unit (7 +/- 3 vs. 19 +/- 13 days, P less than 0.01). CONCLUSIONS: Inspiratory positive airway pressure delivered by a face mask can obviate the need for conventional mechanical ventilation in patients with acute exacerbations of chronic obstructive pulmonary disease.

Acute Disease↗