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Biomedical subjects

B Jonson

Publications and source records attributed to B Jonson.

At least 73 records · Page 4Linked to original sources
PubMed1994

Dynamic properties of body plethysmographs and effects on physiological parameters.

A model incorporating compliance, resistance, inertia, and the thermal time constant of plethysmographs is used to describe the effect of its dynamic properties on measured respiratory parameters. Using numerical simulation we studied the effect of distortion of flow signals from 13 infants in whom flow and esophageal pressure had been recorded. The distortion in amplitude, shape, and timing of the recorded flow patterns was dependent on the dynamic properties of the plethysmograph. For constant-volume "pressure" plethysmographs, errors of derived parameters such as compliance and resistance are very important if the thermal time constant is short. These errors are not corrected by calibrating the plethysmograph at the breathing frequency. Time correction of the flow signals in volume-displacement plethysmographs gives accurate results when the plethysmograph resistance and compliance are low. Overall, a volume-displacement plethysmograph with moderately high resistance of the flowmeter, corrected for internal pressure and inertia, gives the best possible results.

Air Pressure↗
PubMed1994

Biexponential pulmonary clearance of 99mTc-DTPA induced by detergent aerosol.

We measured the pulmonary clearance of technetium-99m-labeled diethylenetriamine pentaacetatic acid (99mTc-DTPA) for 3 h after perturbation of the surfactant system by administration of the detergent dioctyl sodium sulfosuccinate in aerosol. Forty-two rabbits were anesthetized with pentobarbital sodium. Tracheostomies were performed, and the rabbits were mechanically ventilated. Increasing concentrations of detergent (0.125-2%) or vehicle were given for 5 min, and clearance measurements were performed immediately or 60 min after detergent administration. No animals developed respiratory distress. After vehicle, the clearance was monoexponential with a half-life of 153 min. Detergent induced a biexponential clearance with a rapidly clearing additional pool of radioactivity with a half-life of 5-15 min. The relative amount of radioactivity clearing rapidly increased with detergent concentration. The detergent effect was partly reversible. We conclude that detergent induces a biexponential clearance of 99mTc-DTPA by accelerating the transfer of tracer across the alveolocapillary barrier in a proportion of lung units in a dose-related manner.

Aerosols↗
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

Effect of inhaled terbutaline sulphate in relation to its deposition in the lungs.

We studied the effects of inhaled terbutaline on FEV1 and gas exchange, and the pattern of deposition within the lungs. To document this and to estimate the dose of terbutaline administered to the lungs, [99mTc]DTPA was added to nebulised terbutaline solution. The aerosol was deposited preferentially in large or small airways by using aerosols with different particle mass median diameters (1.5 and 4.8 microns) and different inhalation flow rates (0.25 and 1.0 l/s). The patients inhaled placebo and then three increasing doses of terbutaline (0.006, 0.02 and 0.08 mg to the lungs). Finally, 2 mg terbutaline was inhaled from a metered dose inhaler via a spacer. After each inhalation FEV1, PaO2 and PaCO2 was measured. The inhalation of small particles at a low flow resulted in a fairly uniform lung deposition, while larger particles at a higher flow resulted in heavy central deposition. Penetration index for small and large particles were 1.3 +/- 0.2 and 0.8 +/- 0.3 (P less than 0.001), respectively. In both groups FEV1 increased similarly with each dose, and at 0.02 and 0.08 mg the increase was significant (P less than 0.01). After eight metered doses of terbutaline sulphate (0.25 mg per dose) inhaled via a spacer, there was a further increase in FEV1 (P less than 0.001). Gas exchange did not differ between the two groups but if they were combined the DA-aO2 was significantly lower after metered doses than control (P less than 0.05). Thus, it appears that the site of deposition is not important for the bronchodilator effect of terbutaline, and gas exchange tended to improve with both modes of administration.

Adult↗
PubMed1991

Lung mechanics and gas exchange during exercise in pulmonary sarcoidosis.

To clarify how lung function at exercise is affected in sarcoidosis, and to analyze how exercise studies compare to testing measurements, 63 patients with pulmonary sarcoidosis were examined with lung mechanics and arterial blood gases during exercise. These findings were compared with simultaneously obtained, but previously reported results of the static lung pressure/volume curve and the lung resistance/static lung pressure curve. While mechanical variables at maximal exercise were as sensitive as those determined by measuring the PstL/V and RL/PstL curves, mechanics during spontaneous breathing at rest was less sensitive. The derangement of mechanics was more evident than that of arterial blood gases. No measurement at rest was a good predictor of working capacity or of arterial PaO2. A comprehensive exercise examination may be an alternative to resting investigations, which are either more elaborate or less sensitive.

Adult↗
PubMed1991

Lung mechanics and gas exchange in steroid treated pulmonary sarcoidosis. A seven year follow-up.

Fifteen patients with pulmonary sarcoidosis, representing the functionally most severely affected quartile of referred patients, were prescribed steroids during one year. During this period and after 7 years on average, measurements were made of lung volumes, the static elastic pressure/volume (PstL/V) curve and lung resistance (RL). Lung mechanics and arterial blood gases were studied at exercise. Within months static compliance (CstL) and the arterial partial pressure of oxygen improved along with radiography. A modest positive trend continued throughout the follow-up. The vital capacity followed CstL changes closer than did the total lung capacity, which remained low. Though CstL improved, transpulmonary pressure at maximal inspiration increased and the upper part of the PstL/V curve became flatter. RL remained moderately increased. The course of the physiologic findings may be explained by fairly stable parenchymal and peribronchial fibrosis after cessation of active inflammation, and by regress of reflex inhibition of inspiration. Thus most subjects showed modest improvement during and after treatment. The initial study of lung function provided important prognostic information. The study does not allow conclusive evidence with respect to long term benefit of treatment, but encourages continued use of steroids under the guidance of function tests.

Adult↗
PubMed1990

Quantitative SPECT by attenuation correction of the projection set using transmission data: evaluation of a method.

A method for measuring attenuation coefficients in single-photon emission tomography (SPECT) is described and evaluated, together with a method for attenuation correction using these measured attenuation coefficients. Build-up, caused by scattered photons, is corrected for by a simple substitution in the algorithms. Transmission studies are performed with a 99mTc- or 57Co flood source, and emission phantom studies with 99mTc line sources. The method is evaluated with variable but well-defined phantoms. The result is accurate attenuation coefficients for different densities, dimensions and geometries, and an accuracy of corrected emission activities of better than +/- 10% in most cases. The present limitations of the method for attenuation correction are discussed.

Algorithms↗
PubMed1990

Treatment of drug-induced agranulocytosis with recombinant GM-CSF.

A 53-year male patient, treated for rheumatoid arthritis with sulphasalazine, developed a total agranulocytosis. When this state had prevailed for at least 10 d no bone marrow granulocyte progenitor cells were detectable. Intravenous GM-CSF treatment was initiated 5 d later, and the patient recovered within the next 6 d. GM-CSF treatment for severe agranulocytosis deserves further investigation.

Agranulocytosis↗
PubMed1990

Pulmonary clearance of inhaled [99Tcm]DTPA: effects of ventilation pattern.

While a rise in lung volume is known to increase the pulmonary clearance of technetium-99m-labelled dietylene triamine pentaacetate ([99Tcm]DTPA), little interest has been focused on the effects of changes in ventilation frequency, tidal volume and airway pressure. We studied adult, anaesthetized and intubated rabbits during three ventilation patterns (VP) using pressure controlled ventilation (ServoVentilator 900C). VP was either deep slow (f = 20 min-1, tidal volume (VT) = 30 +/- 4 ml kg-1 and positive end-expiratory pressure (PEEP) = 0.2 kPa [VP 20/0.2, n = 8]) or rapid shallow (f = 80 min-1, VT = 11 +/- 2 ml kg-1 and PEEP = 0.2 or 0.4 kPa [VP 80/0.2, n = 6 and VP 80/0.4, n = 6]). The mean airway pressure was similar at VP 20/0.2 and VP 80/0.4. During administration of [99Tcm]DTPA aerosol all animals were ventilated under the same conditions (f = 40 min-1 and PEEP = 0.2 kPa). The pulmonary clearance rate expressed as the half-life time (T1/2) of [99Tcm]DTPA was at VP 80/0.2 = 113 +/- 31 min, at VP 80/0.4 = 70 +/- 24 min (P less than 0.01 compared to VP 80/0.2) and at VP 20/0.2 = 36 +/- 18 min (P less than 0.001 compared to VP 80/0.2 and P less than 0.01 compared to VP 80/0.4). We conclude that the pulmonary clearance of [99Tcm]DTPA increases (1) during rapid shallow ventilation when PEEP is increased from 0.2 to 0.4 kPa; (2) during deep slow ventilation relative to rapid shallow ventilation even when the mean airway pressure is similar.

Animals↗
PubMed1990

Expiratory flushing of airways: a method to reduce deadspace ventilation.

A jet of fresh gas entering the trachea during the last part of expiration, expiratory flushing of airways (EFA), may during mechanical ventilation bring the fresh gas interface into the trachea to reduce deadspace. EFA, delivered in a variety of modes, was tested in healthy dogs. EFA allowed tidal volume, peak and mean airway pressure to be reduced by about 25%. EFA was administered in the form of pulses with frequencies 2-8 Hz, and as a continuous flow. The mode was of little importance. EFA was found to be efficient and should be clinically tested.

Animals↗
PubMed1989

Potential of early chest roentgen examination in ventilator treated newborn infants to predict future lung function and disease.

The potentially of early chest X-ray to predict the risk of lung function abnormalities was studied prospectively in 40 preterm ventilator treated infants in a 8-10-year follow-up investigation. According to the findings at chest X-ray 3 to 10 days after completed ventilator treatment the infants were divided into 3 groups considered to represent increasing risk and severity of lung damage: 1) normal findings, 2) interstitial parenchymal abnormalities exclusively or 3) in combination with local or general hyperinflation. Lung function tests and chest x-ray were performed at the age of 8 to 10 years. A correlation was found between the findings at the early chest roentgen examination and the risk of abnormal lung function at the follow-up. Occurrence of focal or general hyperinflation or both were associated with a greater risk of airway obstruction. Infants with only interstitial abnormalities were, however, at a higher risk than those with normal chest examination to develop general hyperinflation and increased air way obstruction.

Bronchopulmonary Dysplasia↗
PubMed1989

Lung function in patients with systemic lupus erythematosus and persistent chest symptoms.

Twelve consecutive patients with systemic lupus erythematosus (SLE) and chest symptoms of at least 3 months' duration were investigated with spirometry, lung mechanics at rest and exercise, diffusion capacity and right heart catheterization. Vital capacity (88% of predicted, p less than 0.05), and FEV1 (84%, p less than 0.01) were decreased in the study group, but spirometric and diffusion capacity abnormalities were moderate compared with previous studies. The single breath CO2 test showed, in six patients, ventilation-perfusion mismatch with patterns typical for either bronchial obstruction or vascular disease. Non-respiratory factors were responsible for reduction of working capacity (on average 68% of predicted normal values (p less than 0.001]. Two patients with pulmonary hypertension were identified by right heart catheterization. One of them had overlap features with the CREST syndrome. Both these patients had abnormal SBT-CO2 test and diffusion capacity, along with diffuse perfusion defects on perfusion scintigraphy. The low frequency of pulmonary function abnormalities in this study suggests that irreversible pulmonary damage is uncommon in SLE.

Adult↗
PubMed1989

Setting and monitoring of high-frequency jet ventilation in severe respiratory distress syndrome.

High-frequency jet ventilation (HFJV) is used in respiratory distress syndrome (RDS) to avoid high airway pressures and barotrauma. This study was designed to find rational strategies to regulate oxygenation and alveolar ventilation at HFJV and to determine appropriate monitoring methods. Seven dogs were subjected to total lung lavage with saline to induce RDS. PEEP was increased at conventional intermittent positive-pressure ventilation until re-expansion was indicated by a PaO2 of 300 torr at an FIO2 of 1.0 HFJV at 4 and 15 Hz was each tried at 0 and 10 cm H2O PEEP. Intermittent low-frequency inflations were also added to HFJV at 0 PEEP. Lung expansion was maintained without circulatory depression by adjustment of minute ventilation (VE) delivered by the HFJ ventilator; external PEEP was a useful complement. PaCO2 was controlled by frequency adjustment. HFJV at 4 Hz resulted in hypocapnia; intermittent low-frequency inflations had no effect. VE monitoring, CO2 elimination monitoring, and PEEP adjustment was done with a standard ventilator during HFJV. This study illustrates that HFJV is efficient in RDS; VE and external PEEP strongly influence oxygenation and may be used to regulate this factor, and frequency affects CO2 elimination, thus suggesting a method of PaCO2 control.

Alkalosis, Respiratory↗
PubMed1989

Volume-controlled ventilation with superimposed high frequency ventilation during expiration in healthy and surfactant-depleted pig lungs.

In the healthy and surfactant-depleted lungs of five pigs the influence of different forms of high frequency ventilation superimposed on conventional mechanical ventilation during the expiratory phase of the ventilatory cycle (SHFVE) on gas exchange and cardiocirculatory parameters was investigated. Subsequently the effects of end-expiratory flushing (EF), i.e. cleaning the large airways and connecting tubes from the ventilator free from end-expiratory CO2, with a volume greater than the dead space of the large airways and connecting tubes was investigated. SHFVE and EF resulted in a significant improvement in CO2 elimination in both healthy and surfactant-depleted lungs. Furthermore, in stiff lungs, at a certain level of oxygenation and CO2 elimination, SHFVE produced the lowest peak and mean airway pressure without any additional depression of cardiocirculatory parameters.

Animals↗
PubMed1989

Monitoring of physiological parameters during high frequency ventilation (HFV).

Non-biological descriptors such as jet feeding pressure and oscillator stroke volume are often used to describe HFV. This results in confusion and hinders acceptance of HFV. The goal of this paper is to show how physiological parameters which are valid during HFV can be monitored. Airway pressure measured in narrow tubes with high linear flow rates is underestimated. A relevant airway pressure must be measured well below the tracheal tube. Pressure measured higher up should be validated against peripheral pressure measurements. Minute ventilation and expired CO2 concentration can be determined with a ServoVentilator and a CO2 analyzer arranged at its exit port. Minute ventilation and CO2 elimination can thereby be continuously monitored during high frequency jet ventilation or so-called "combined high frequency jet ventilation" to prevent undetected disturbance of ventilation and perfusion. Physiological dead space can be studied for optimization of ventilatory pattern. The principle of gas analysis at the exit port of the ventilator may be used for FRC determinations with sulfur-hexafluoride.

Animals↗