Ulrika Bitzén

Retinyl palmitate is a reproducible marker for chylomicron elimination from blood

To study the individual variation in chylomicron clearance rate, young healthy volunteers were given a p.o. dose of 50,000 IU retinyl palmitate in the morning to label their chylomicrons. Serial blood samples were then obtained in the time interval 4-8 h after retinyl palmitate intake, to closely monitor the clearance of retinyl ester from the blood. The procedure was repeated in an identical way two days later. The calculated individual halflives for retinyl palmitate clearance ranged from 1.54 to 9.90 h, i.e. a more than five-fold variation. The intraindividual variation was much less (relative SD 11%). Retinyl palmitate clearance (and probably chylomicron clearance) is, thus, relatively constant within the same individual on different occasions but varies considerably between individuals.

Protective ventilation in experimental acute respiratory distress syndrome after ventilator-induced lung injury: a randomized controlled trial

BACKGROUND Low tidal volume (V(T)), PEEP, and low plateau pressure (P(PLAT)) are lung protective during acute respiratory distress syndrome (ARDS). This study tested the hypothesis that the aspiration of dead space (ASPIDS) together with computer simulation can help maintain gas exchange at these settings, thus promoting protection of the lungs. METHODS ARDS was induced in pigs using surfactant perturbation plus an injurious ventilation strategy. One group then underwent 24 h protective ventilation, while control groups were ventilated using a conventional ventilation strategy at either high or low pressure. Pressure-volume curves (P(el)/V), blood gases, and haemodynamics were studied at 0, 4, 8, 16, and 24 h after the induction of ARDS and lung histology was evaluated. RESULTS The P(el)/V curves showed improvements in the protective strategy group and deterioration in both control groups. In the protective group, when respiratory rate (RR) was ≈ 60 bpm, better oxygenation and reduced shunt were found. Histological damage was significantly more severe in the high-pressure group. There were no differences in venous oxygen saturation and pulmonary vascular resistance between the groups. CONCLUSIONS The protective ventilation strategy of adequate pH or PaCO2 with minimal V(T), and high/safe P(PLAT) resulting in high PEEP was based on the avoidance of known lung-damaging phenomena. The approach is based upon the optimization of V(T), RR, PEEP, I/E, and dead space. This study does not lend itself to conclusions about the independent role of each of these features. However, dead space reduction is fundamental for achieving minimal V(T) at high RR. Classical physiology is applicable at high RR. Computer simulation optimizes ventilation and limiting of dead space using ASPIDS. Inspiratory P(el)/V curves recorded from PEEP or, even better, expiratory P(el)/V curves allow monitoring in ARDS.

Multiple pressure-volume loops recorded with sinusoidal low flow in a porcine acute respiratory distress syndrome model.

Objectives:  To develop a method for automatic recording of multiple dynamic elastic pressure–volume (Pel/V) loops. To analyse the relationship between multiple dynamic Pel/V loops and static Pel/V loops in a porcine model of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). To test the hypothesis that increasing lung collapse and re‐expansion with decreasing positive end expiratory pressure (PEEP) can be characterized by hysteresis of the Pel/V loops.

Measurement and mathematical modelling of elastic and resistive lung mechanical properties studied at sinusoidal expiratory flow

Elastic pressure/volume (Pel/V) and elastic pressure/resistance (Pel/R) diagrams reflect parenchymal and bronchial properties, respectively. The objective was to develop a method for determination and mathematical characterization of Pel/V and Pel/R relationships, simultaneously studied at sinusoidal flow–modulated vital capacity expirations in a body plethysmograph. Analysis was carried out by iterative parameter estimation based on a composite mathematical model describing a three‐segment Pel/V curve and a hyperbolic Pel/R curve. The hypothesis was tested that the sigmoid Pel/V curve is non‐symmetric. Thirty healthy subjects were studied. The hypothesis of a non‐symmetric Pel/V curve was verified. Its upper volume asymptote was nearly equal to total lung capacity (TLC), indicating lung stiffness increasing at high lung volume as the main factor limiting TLC at health. The asymptotic minimal resistance of the hyperbolic Pel/R relationship reflected lung size. A detailed description of both Pel/V and Pel/R relationships was simultaneously derived from sinusoidal flow–modulated vital capacity expirations. The nature of the Pel/V curve merits the use of a non‐symmetric Pel/V model.

Clinical utility of lung mechanics measurements

Although routine lung function tests, such as spirometry, can be used to diagnose bronchial and parenchymal disease, lung mechanics studies are often required to differentiate between the two forms of disease. The flow regulator method allows analysis of parenchymal mechanics in terms of the elastic recoil pressure versus volume curve and of bronchial properties in terms of the elastic recoil pressure versus resistance curve. In this report the clinical utility of lung mechanics measurements is illustrated by means of two cases. A complete battery of lung function tests allows diagnosis and comprehension of the patients symptoms for many diseases which are difficult to diagnose using only spirometry.