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Biomedical subjects

L Beydon

Publications and source records attributed to L Beydon.

At least 73 records · Page 4Linked to original sources
PubMed1996

Respiratory mechanics in patients ventilated for critical lung disease.

Respiratory mechanics, using flow interruption, was previously studied during the complete breath in healthy ventilated man, numerical techniques relieving constraints regarding flow pattern. The classical linear model of non-Newtonian behaviour was found to be valid. The present study was extended to subjects with critical lung disease. Subjects with acute lung injury (ALI; n = 2), acute respiratory distress syndrome (ARDS; n = 4), and chronic obstructive pulmonary disease (COPD; n = 3) were studied with and without positive end-expiratory pressure (PEEP). Functional residual capacity (FRC) was measured with sulphur hexafluoride (SF6) wash-out. The static pressure-volume (P-V) curve was linear at zero end-expiratory pressure (ZEEP), but nonlinear at PEEP. Its hysteresis was nonsignificant. In ALI/ARDS, PEEP increased lung volume by distension and recruitment, but only by distension in COPD. In ALI/ARDS, resistance was increased, at ZEEP. In COPD, resistance became extremely high during expiration at ZEEP. In ALI/ARDS at ZEEP, non-Newtonian behaviour, representing tissue stress relaxation and pendel-luft, complied with the classical linear model. At PEEP, the non-Newtonian compliance became volume-dependent to an extent correlated to the nonlinearity of the static P-V curve. In COPD, non-Newtonian behaviour was adequately explained only with a model with different inspiratory and expiratory behaviour. The classical model of the respiratory system is valid in ALI/ARDS at ZEEP. More advanced models are needed at PEEP and in COPD.

Adult↗
PubMed1996

A new correction technique for measuring respiratory impedance through an endotracheal tube.

Measurement of respiratory impedance (Zrs) in intubated patients requires corrections for flow-dependent resistance and air compression inside the endotracheal tube (ET). The purpose of this study was to test a new correction technique for these effects. We therefore studied 110 patients in two conditions: breathing normally (C1), or breathing through an ET placed at the mouth (C2). In C1, we measured pressure and flow signals at the mouth, and in C2, at the ET inlet, during application of a pseudorandom forced excitation (4-32 Hz). In C1, respiratory impedance was calculated directly as Z1. In C2, pressure data were first corrected for the flow-dependent resistance of the ET, and respiratory impedance was then corrected both for gas compression inside the set-up and ET inertance (impedance Z2). Strong linear relationships were found between the reference and corrected estimates of the resistance at 6 Hz, the frequency dependence of resistance and the resonant frequency. The mean normalized distance between Z1 and Z2 observed in the patients over the 4-32 Hz frequency range was about 14% for resistance and 12% for reactance (-9% and -4%, respectively, when considering the algebraic value of the distance). This slight underestimation of both components of impedance might be due to an overcorrection of pressure for the flow-dependent resistance of the ET. We conclude that, in intubated patients, newly tested corrections for the mechanical contribution of the endotracheal tube may yield a fair estimate of respiratory impedance when pressure is measured at the inlet of the endotracheal tube.

Airway Resistance↗
PubMed1995

Contribution of bronchoalveolar lavage to the diagnosis of posttraumatic pulmonary fat embolism.

OBJECTIVE: To verify whether the determination of the percentage of cells recovered by bronchoalveolar lavage and containing fat inclusions is a useful diagnostic tool of posttraumatic pulmonary fat embolism. DESIGN: Prospective study. SETTING: Surgical Intensive Care Units in two university hospitals. PATIENTS: 56 successive trauma patients needing prolonged postinjury mechanical ventilation, including 4 with clinical definite fat embolism syndrome, 5 in whom the diagnosis had been clinically suspected but was impossible to confirm or exclude before bronchoscopy, and 47 with no clinical evidence of the syndrome. Control groups included 8 patients without previous trauma who developed ARDS and 6 healthy surgical patients. METHODS: Bronchoalveolar lavage was performed within the first post-traumatic 3 days in trauma patients, at the beginning of the pulmonary disease in non trauma ARDS patients and just after anesthesic induction in healthy ortopedic patients. The magnitude of lipid content in alveolar cells was compared with the clinical pattern of the pulmonary fat embolism syndrome retrospectively evaluated at the seventh day postinjury in trauma patients. RESULTS: All the patients with definite fat embolism syndrome had more than 70% of lavage cells containing fat droplets. The group of patients in whom the diagnosis of the fat embolism syndrome was suspected had percentages of fat cells above 30% in 4 out of 5 patients. A percentage of fat cells above 30% was only observed in 7 out of the 47 patients without clinical evidence of the syndrome. The percentage varied between 0% to 35% in the group of non trauma ARDS patients and between 0 to 5% in healthy surgical patients. CONCLUSION: Lipid inclusions in alveolar cells are common during traumatic and non-traumatic respiratory failure. Determination of the percentage of cells recovered by bronchoalveolar lavage and containing fat droplets may contribute to the diagnosis of the fat embolism syndrome in mechanically-ventilated trauma patients with respiratory failure provided that the significant threshold would be 30%.

Adult↗
PubMed1995

Topical upper airway anaesthesia with lidocaine increases airway resistance by impairing glottic function.

OBJECTIVE: To assess if two different forms of upper airway topical anaesthesia induce similar changes in airway flow resistance (Rrs). DESIGN: Serial measurements of Rrs before and after topical anaesthesia with acqueous or paste lidocaine. SETTING: Lung function test laboratory. PARTICIPANTS: 9 normal men with documented normal lung function tests. INTERVENTIONS: 2 different session of topical upper airway anaesthesia with 100 mg of liquid 5% lidocaine and 100 mg of 2% lidocaine paste, respectively. MEASUREMENTS AND RESULTS: Rrs was measured by the random noise forced oscillation technique. Fiberoptic upper airway examination was performed in two subjects. Rrs increased on average by 81% after lidocaine spray and by 68% after lidocaine paste (p < 0.005, respectively) with no difference in the magnitude of Rrs increase between the two modes of anaesthesia studied. This increase lasted 13 +/- 3 min (spray) and 12 +/- 3 min (paste), respectively (p = ns). Fiberoptic examination of the two most responders showed inspiratory laryngeal collapse. CONCLUSIONS: Topical upper airway anaesthesia transiently increases Rrs with no specific effects regarding the drug presentation. Laryngeal dysfunction may be one mechanisms involved in Rrs increase following upper airway topical anaesthesia. Such findings may explain some poor respiratory tolerance reported during endoscopy.

Adolescent↗
PubMed1995

Systematic transesophageal echocardiography for detection of mediastinal lesions in patients with multiple injuries.

A prospective study assessing the interest in and the results of systematic transesophageal echocardiography (TEE) examination in nonselected intubated multiple injury patients was carried out from January 1992 through June 1993. Seventy patients were included and divided into two groups according to the results of admission screening, including clinical examination, EKG, CK-MB and chest radiograph. Group 1 (60 patients) had abnormalities on initial screening, while group 2 (10 patients) had no symptom of thoracic or mediastinal injury. TEE was performed within 48 hours following admission and its results were compared with those of the initial screening. TEE usefulness was evaluated on a score grade from 0 (no interest) to 4 (outstanding interest). Myocardial contusion was suspected in 25 patients. TEE invalidated 18 suspected and found 5 unsuspected myocardial contusions. Pericardial effusion was suspected in only one case, while TEE documented 13 additional cases. A mediastinal enlargement was seen in 13 patients, but TEE invalidated aortic lesions in all these cases and made an unsuspected diagnosis of aortic tears. Eight cases of severe hypovolemia and seven cases of left ventricle dysfunction were detected by TEE. The score of interest showed that TEE allowed new interesting diagnoses in 70% of group I patients and in 33% of group II patients. TEE is of utmost importance in multiple injury patients, with or without any evidence of thoracic or mediastinal injury, providing a safe and rapid examination of the mediastinal structures and an evaluation of the hemodynamic status.

Adult↗
PubMed1995

Titration of tidal volume and induced hypercapnia in acute respiratory distress syndrome.

Mechanical ventilation may promote overdistension-induced pulmonary lesions in patients with acute respiratory distress syndrome (ARDS). The static pressure-volume (P-V) curve of the respiratory system can be used to determine the lung volume and corresponding static airway pressure at which lung compliance begins to diminish (the upper inflection point, or UIP). This fall in compliance may indicate overdistension of lung units. We prospectively studied 42 patients receiving mechanical ventilation with an FIO2 of 0.5 or more for at least 24 h. According to the Lung Injury Score (LIS), 25 patients were classified as having ARDS (LIS > 2.5), while 17 patients constituted a non-ARDS control group. The P-V curve was obtained every 2 d. Mechanical ventilation initially used standard settings (volume-control mode, a positive end-expiratory pressure [PEEP] adjusted to the lower inflection point on the P-V curve, and a tidal volume [VT] of 10 ml/kg). The end-inspiratory plateau pressure (Pplat) was compared to the UIP, and VT was lowered when the Pplat was above the UIP. In the range of lung volume studied on the P-V curves (up to 1600 ml), a UIP could be shown in only one control patient (at 23 cm H2O). By contrast, a UIP was present on the P-V curve obtained from all patients with ARDS, corresponding to a mean airway pressure of 26 +/- 6 cm H2O, a lung volume of 850 +/- 200 ml above functional residual capacity and 610 +/- 235 ml above PEEP.(ABSTRACT TRUNCATED AT 250 WORDS)

Case-Control Studies↗
PubMed1994

Transesophageal echocardiographic assessment of left ventricular function during apnea testing for brain death.

The effects of apnea testing-induced respiratory acidosis on left ventricular function (LVF) are still controversial. The aim of the study was to assess LVF during apnea testing using transesophageal echocardiography (TEE). Twenty consecutive patients suspected of brain death, hemodynamically stable, and considered as potential organ donors were prospectively studied. A 20-min apnea test was performed after obtaining a PaCO2 > 35 mmHg and 20 min of FIO2 1 ventilation. LVF was assessed using TEE with a CFM 750 (Diasonic) connected to a 5 MHz probe. Heart rate (HR), mean arterial pressure (MAP), left ventricle end-diastolic and systolic area (LVEDA, LVESA), and LVF assessed by fractional area changes (FAC), systolic wall motion (SWM) scores, and blood gases were recorded at baseline, and after 5, 10, 15, and 20 min of apnea testing. In 19 patients, no spontaneous respiratory movement occurred during the standard 20-min period. In one patient (No. 15), the apnea test had to be stopped after 10 min because of hypoxia. HR, LVEDA, LVESA, and SWM were not significantly modified during the study. There was a progressive statistically significant decrease in MAP during apnea (from 77 +/- 10 to 63 +/- 11 mmHg), associated with a statistically significant increase in FAC at 20 min (from 48 +/- 13 to 56 +/- 8%). PaCO2 progressively rose (from 40 +/- 3 to 95 +/- 11 mmHg), associated with a decrease in pH (from 7.42 +/- 0.06 to 7.09 +/- 0.08). At the same time, PaO2 decreased slightly in all patients, but values remained well above hypoxic levels, except for one patient. Despite severe respiratory acidosis the increase in FAC suggests that apnea testing is well tolerated for brain death assessment.

Acidosis, Respiratory↗
PubMed1994

[Survey of the quality of sleep during the perioperative period. Study of factors predisposing to insomnia].

In order to assess the quality of sleep in surgical patients the amount of self-rated postoperative insomnia and its predisposing factors, we conducted a three-fold questionnaire * survey in 176 consecutive patients undergoing elective orthopaedic, vascular or abdominal surgery. The first questionnaire was completed the day preceding surgery, the second at the day of discharge and the third two weeks later. This survey concerned the patient's general status, his usual sleep profile and factors which could interfere with sleep (hypnotics, pain, environmental factors) throughout the study period. It allowed quantification of these parameters and the assessment of their time-course. Perioperative insomnia appeared to be a long-lasting phenomenon which persisted after discharge. Factor analysis and multiple regression models showed that postoperative, self-rated insomnia was multifactorial and mainly explained by the amount of postoperative pain (p = 0.035).

Adult↗
PubMed1994

[A study of 3 new ventilators for anesthesia: a series of tests].

We report the bench testing of three new anaesthesia ventilators: Flexima (Datex), SA2/RA2 and Cato (Dräger). The test circuit included a two compartment lung model, a pneumotachograph and a pressure gauge. Volume was integrated from flow signal. The tidal volume delivered by the Flexima and SA2/RA2 ventilators decreased with increasing mechanical work load contrarily to the Cato. Moreover, the tidal volume of the Flexima increased with the fresh gas flow. In spontaneous ventilation inspiratory resistance were low.

Anesthesia, Inhalation↗
PubMed1994

Acoustic method to estimate the longitudinal area profile of endotracheal tubes.

A problem in mechanical ventilation is the accumulation of mucus secretions in the endotracheal tube (ETT), which tends to reduce the patent cross-sectional area. Here we characterized the extent and locus of the ETT obstruction using an acoustic reflection method recently modified to be applied at bedside. Experiments were conducted both in vivo in 10 intubated patients and in vitro in ETT with or without known constrictions of 1 to 3 mm over 5 cm, located at various distances from the ETT entry: 5, 10, 15, and 20 cm. Acoustic results were compared with the results obtained by an hydraulic reference method, which was the only method available to measure ETT obstruction in mechanically ventilated patients. In vivo acoustic results showed that area reductions were maximal near the tracheal extremity of the ETT, with a range from 2 to 36% (mean value 13 +/- 10%), when estimated relative to the area measured in an unused ETT of the same inner diameter (7 to 9 mm). Statistical analysis of the differences between acoustic reflection data and hydraulic data showed that the two methods did not differ significantly. In vitro acoustic results obtained in constricted ETT showed a highly significant correlation with the actual area (r = 0.97, p = 0.0001). Thus, reductions in ETT area may be detected, quantified, and located by the present acoustic reflection method, which therefore provides a means to avoid emergency extubation because of ETT obstruction.

Acoustics↗
PubMed1993

Clonidine comparably decreases the thermoregulatory thresholds for vasoconstriction and shivering in humans.

BACKGROUND: Clonidine stops postoperative shivering, but its underlying mechanism of action is unknown. Clonidine may impair central control of thermoregulation or act on peripheral receptors. Accordingly, the authors tested the hypothesis that clonidine reduces both the vasoconstriction and shivering thresholds, a pattern consistent with central thermoregulatory impairment. METHODS: Seven healthy volunteers participated in the study. Thermoregulatory vasoconstriction was evaluated using forearm minus fingertip, skin-temperature gradients; values exceeding 4 degrees C were considered to be significant vasoconstriction. Systemic oxygen consumption (VO2) was measured with a canopy system. In addition, shivering was qualitatively evaluated using a simple scale, graduated from 0 (no shivering) to 2 (intense shivering). The tympanic membrane temperatures triggering significant vasoconstriction and grade 1 shivering were considered to be the thresholds for the two thermoregulatory responses. Measurements were performed after a 10-min steady state period and during cooling by central venous infusion of Ringer's lactate solution at 4 degrees C. Each subject was evaluated at two sessions, separated by at least 48 h. They were randomly and blindly assigned to received either an intravenous bolus of 75 micrograms clonidine or a placebo before cooling. When the shivering score equaled 2, 75 micrograms clonidine was injected intravenously, and repeated if necessary, to completely stop shivering.

Adult↗
PubMed1993

Mechanics of respiratory system in healthy anesthetized humans with emphasis on viscoelastic properties.

The classic model of the respiratory system (RS) is comprised of a Newtonian resistor in series with a capacitor and a viscoelastic unit including a resistor and a capacitor. The flow interruption technique has often been used to study the viscoelastic behavior under constant inspiratory flow rate. To study the viscoelastic behavior of the RS during complete respiratory cycles and to quantify viscoelastic resistance (Rve) and compliance (Cve) under unrestrained conditions, we developed an iterative technique based on a differential equation. We, as others, assumed Rve and Cve to be constant, which concords with volume and flow dependency of model behavior. During inspiration Newtonian resistance (R) was independent of flow and volume. During expiration R increased. Static elastic recoil showed no significant hysteresis. The viscoelastic behavior of the RS was in accordance with the model. The magnitude of Rve was 3.7 +/- 0.7 cmH2O.l-1 x s, i.e., two times R. Cve was 0.23 +/- 0.051 l/cmH2O, i.e., four times static compliance. The viscoelastic time constant, i.e., Cve.Rve, was 0.82 +/- 0.11s. The work dissipated against the viscoelastic system was 0.62 +/- 0.13 cmH2O x 1 for a breath of 0.56 liter, corresponding to 32% of the total energy loss within the RS. Viscoelastic recoil contributed as a driving force during the initial part of expiration.

Adult↗
PubMed1992

Test of 20 similar intensive care ventilators in daily use conditions--evaluation of accuracy and performances.

Infrequent control, aging of components, may compromise the accuracy of ICU ventilators. In order to assess the reliability of ventilators during their clinical use, we bench tested a group of 20 CPU1 ventilators (Ohmeda) sampled at random in several ICU units. We found major leaks in 5 ventilators, attributable to the disposable tubings used in these systems. Mean error in expired tidal volume and corresponding standard deviation (precision) were greater than 100 ml in two. Positive end expiratory pressure measurement comprised a mean error higher than 2 cm H2O in 40% of the ventilators tested. The valve opening pressure threshold was correlated to the inspiratory flow (r = 0.81) contrary to the valve opening delay (average 138 +/- 40 ms). These two parameters did not correlate with the age of the ventilator. Our study addresses the need for periodic control of ventilator performance in order to minimize the risks of errors and malfunctions.

Age Factors↗
PubMed1992

[A study of 11 ventilators for anesthesia: laboratory testing].

Eleven anaesthesia ventilators were instrumentally tested under various conditions. They included: Excel and Modulus II Plus (Ohmeda); 710 and Servo anaesthesia circle 985 (Siemens); Jollytronic (Soxil) and Elsa (Engström); SA2 and Cicero (Dräger); ABT 4,300 (Kontron); Monnal A and the prototype Alys (Taema). The test circuit comprised a two compartment model lung, a pneumotachograph, a pressure gauge in the "airway". The volume was calculated as the integral of flow rate. Each machine was calibrated by the firms' technicians. Before each test, the pneumotachograph was calibrated using a 11 air syringe and the pressure gauge with a 5 cm water column. Each machine ventilated the model lung for 30 min before starting the tests. There were five tests: 1) reliability of the machine's spirometer, 2) reliability of the ventilation rate, 3) reliability of pressure measurements, 4) effect of increasing fresh gas flow on spirometry, 5) effect of increasing downstream resistances. In usual simulated ventilatory conditions, all the machines accurately delivered the setted ventilation and spirometric measurements were with minimal error only. Several ventilators (SA2, Excel, 710, Elsa, ABT 4,300) did not succeed in maintaining their performances when compliance was strongly decreased or resistance of the test lung notably increased. Resistance in the circuit during simulated spontaneous ventilation was < 3.6 cmH2O.l-1.s-1. Increasing fresh gas flow raised the minute volume delivered in six ventilators. It is concluded that, during extreme ventilatory conditions, the inspired volume must be adjusted so as to maintain the inspired tidal volume. However, ventilators which increase inspiratory time in response to an increased mechanical load cannot be adjusted by this way.

Anesthesia, Closed-Circuit↗
PubMed1992

[Carotid artery injury: value of Doppler screening in head injured patients].

A case is reported of a patient with a traumatic aneurysm of the intracranial part of the carotid artery occurring after a traffic accident. The patient was admitted in coma (Glasgow score 5), and presented with a depressed fracture of the frontal and parietal bones, a fracture of the left petrous pyramid and of the left anterior clinoid process, as well as of the right tympanic bone and temporomandibular joint. The borders of the left carotid canal seemed unaltered. Despite the lack of localised neurological signs, cervical and transcranial Doppler ultrasonography was carried out. Intracranial carotid blood flow was found to be altered on both sides. Angiography showed a false carotid aneurysm on the left side (carotid siphon portion C3), and a moderate irregular stenosis of the C2 part on the right. There were no brain lesions on the CT scan. Prophylactic treatment with heparin was started. The patient recovered normal consciousness within a fortnight. The false aneurysm increased in volume and was treated by embolisation. Flow speeds in the carotid siphons also returned to normal. The usefulness of routine screening of patients with petrous bone fractures with Doppler ultrasound is discussed.

Adult↗
PubMed1992

Risk factors for oxygen desaturation during sleep, after abdominal surgery.

The postoperative period after major abdominal surgery is known to be a period of increased episodic oxygen desaturation. In order to assess the risk factors for episodic desaturation, we have studied 29 surgical patients using pulse oximetry during the preoperative night (Npre) when they received benzodiazepine premedication and breathed air, and also during the first three nights after operation when they received nasal oxygen supplementation. Modal oxygen saturation (SpO2) exceeded 95% during all nights studied. The time spent at less than 90% (t90) and 85% (t85) SpO2 and the average SpO2 nadir (SpO2, nadir) did not differ each night. Heart rate was greater (mean 90.1 (SD 16.6) vs 68.2 (12.0) beat min-1, P < 0.001) during the second night after operation (N2) than during Npre. Before operation, the number of desaturations, t90 and t85 correlated with pharyngeal hypertrophy (P = 0.003, P = 0.002, P = 0.001, respectively). At the same time, t90 and t85 correlated with body mass index (P = 0.02 and P = 0.05, respectively). During N2, t90 correlated with radiological lung consolidation (P = 0.05) and SpO2, nadir correlated with FEV1 (P = 0.03). We conclude that there are several mechanisms responsible for oxygen desaturation and that these mechanisms differ before and after surgery.

Abdomen↗