Dan Stieper Karbing

A decision support system for suggesting ventilator settings: Retrospective evaluation in cardiac surgery patients ventilated in the ICU

Selecting appropriate ventilator settings decreases the risk of ventilator-induced lung injury. A decision support system (DSS) has been developed based on physiological models, which can advise on setting of tidal volume (Vt), respiratory frequency (f) and fraction of inspired oxygen (FiO2). The aim of this study is to assess the feasibility of the DSS by comparing its advice with the values used in clinical practice. Data from 20 patients following uncomplicated coronary artery bypass grafting (CABG) with cardiopulmonary bypass was used to test the DSS. Ventilator settings suggested by the DSS were compared to the settings selected by the clinician. When compared to the clinician the DSS suggested: lowering FiO2 (by median 7%, range 2-17%) at high SpO2 and increasing FiO2 (by median 2%, range 1-5%) at low SpO2; lowering ventilation volume (by median 0.57 l min(-1), range 0.2-1.1 l min(-1)) at high pHa and increasing ventilation volume (by median 0.4 l min(-1), range 0.1-0.9 l min(-1)) at low pHa. Suggested changes in ventilation volume were such that simulated values of PIP were < or = 22.9 cmH2O and respiratory frequency < or = 18 breaths min(-1). In all cases, computer suggested values of FiO2, Vt or f were consistent with maintaining sufficient oxygenation, normalising pH and obtaining low values of PIP.

A model of ventilation of the healthy human lung

This paper presents a model of the lung mechanics which simulates the pulmonary alveolar ventilation. The model includes aspects of: the alveolar geometry; pressure due to the chest wall; pressure due to surface tension determined by surfactant activity; pressure due to lung tissue elasticity; and pressure due to the hydrostatic effects of the lung tissue and blood. The cross-sectional area of the lungs in the supine position derived from computed tomography is used to construct a horizontally layered model, which simulates heterogeneous ventilation distribution from the non-dependent to the dependent layers of the lungs. The model is in agreement with experimentally measured hysteresis of the pressure-volume curve of the lungs, static lung compliance, changes in lung depth during breathing and density distributions at total lung capacity (TLC) and residual volume (RV). In the dependent layers of the lungs, alveolar collapse may occur at RV, depending on the assumptions concerning lung tissue elasticity at very low alveolar volumes. The model simulations showed that ventilation increased with depth in the lungs, although not as pronounced as observed experimentally. The model simulates alveolar ventilation including all of the mentioned components of the respiratory system and to be validated against all the above mentioned experimental data.

The effect of tissue elastic properties and surfactant on alveolar stability

This paper presents a novel mathematical model of alveoli, which simulates the effects of tissue elasticity and surfactant on the stability of human alveoli. The model incorporates a spherical approximation to the alveolar geometry, the hysteretic behavior of pulmonary surfactant and tissue elasticity. The model shows that the alveolus without surfactant and the elastic properties of the lung tissue are always at an unstable equilibrium, with the capability both to collapse irreversibly and to open with infinite volume when the alveolus has small opening radii. During normal tidal breathing, the alveolus can becomes stable, if surfactant is added. Including the passive effect of tissue elasticity stabilizes the alveolus, further allowing the alveoli to be stable, even for lung volumes below residual volume. The model is the first to describe the combined effects of tissue elasticity and surfactant on alveolar stability. The model may be used as an integrated part of a more comprehensive model of the respiratory system, since it can predict opening pressures of alveoli.

Prospective evaluation of a decision support system for setting inspired oxygen in intensive care patients

PURPOSE The aim of the study was to prospectively evaluate a decision support system for its ability to provide appropriate suggestions of inspired oxygen fraction in intensive care patients comparing with levels used by clinicians in attendance. MATERIALS AND METHODS Thirteen mechanically ventilated patients were studied in an intensive care unit where up to 4 experiments were performed during 2 consecutive days. Inspired oxygen fraction was selected in each experiment by both the decision support system and attending clinicians, and each selection was evaluated by measuring arterial oxygen saturation. RESULTS Median (interquartile range [range]) changes in inspired oxygen fraction from baseline level by attending clinicians and the decision support system were 0.00 (-0.05 to 0.00 [-0.10 to 0.05]) and -0.03 (-0.07 to 0.01 [-0.16 to 0.12]), respectively. Clinician ranges of inspired oxygen fraction and arterial oxygen saturation were 0.25 to 0.70 and 0.92 to 0.99, respectively. Decision support system ranges of inspired oxygen fraction and arterial oxygen saturation were 0.26 to 0.54 and 0.94 to 0.99, respectively. CONCLUSIONS The decision support system selects appropriate levels of inspired oxygen fraction in intensive care patients and could be used for automatic frequent assessment of patients, freeing the focus of clinicians to concentrate on more challenging therapy.

A model of perfusion of the healthy human lung

This study presents a model that simulates the pulmonary capillary perfusion. The model describes the lungs as divided into horizontal layers and includes: capillary geometry; capillary wall elasticity; pressure at the pulmonary artery; blood viscosity; the effect of the chest wall; the change in lung height and hydrostatic effects of the lung tissue and of the blood during breathing. The model simulates pulsatile blood perfusion with an increasing blood distribution down the lungs, in agreement with previous experimental studies. Moreover the model is in agreement with experimentally measured total capillary perfusion, total capillary volume, total capillary surface area and transition time of red blood cells passing through the pulmonary capillary network. The presented model is the first to be validated against the mentioned experimental data and to model the link between airway pressure, lung volume and perfusion.

Retrospective evaluation of a decision support system for controlled mechanical ventilation

Management of mechanical ventilation in intensive care patients is complicated by conflicting clinical goals. Decision support systems (DSS) may support clinicians in finding the correct balance. The objective of this study was to evaluate a computerized model-based DSS for its advice on inspired oxygen fraction, tidal volume and respiratory frequency. The DSS was retrospectively evaluated in 16 intensive care patient cases, with physiological models fitted to the retrospective data and then used to simulate patient response to changes in therapy. Sensitivity of the DSS’s advice to variations in cardiac output (CO) was evaluated. Compared to the baseline ventilator settings set as part of routine clinical care, the system suggested lower tidal volumes and inspired oxygen fraction, but higher frequency, with all suggestions and the model simulated outcome comparing well with the respiratory goals of the Acute Respiratory Distress Syndrome Network from 2000. Changes in advice with CO variation of about 20% were negligible except in cases of high oxygen consumption. Results suggest that the DSS provides clinically relevant and rational advice on therapy in agreement with current ‘best practice’, and that the advice is robust to variation in CO.

The role of community in the development of elite handball and football players in Denmark

Abstract The primary purpose of this study was to investigate the effect of the place of early development in a sample of Danish male elite and youth handball and football players. The sample included 366 handball and football players from the elite Danish league in the season 2011–2012 and a comparison sample of youth players under the age of 12 from 2003, including 147,221 football and 26,290 handball players. Odds ratio analysis showed that both population size and density significantly affected the proportional number of youth players per community and the odds of athletes reaching an elite level in football and handball. The odds for youth player registrations in both handball and football increased in rural in contrast to urban communities. However, elite football players primarily came from communities of high density (>1000 pop./km2), whereas elite handball players primarily came from less densely populated communities (100 to <250 pop./km2). Furthermore, there seems to be a relation between representation of elite and talent clubs in different communities and the probability of becoming an elite player in both sports. The limited number of elite players in both sports from rural communities may be due to national talent development strategies that do not incorporate development support for clubs in rural areas. Additionally, the results of the study clearly suggest the need to include the youth player population to advance research findings in birthplace effect studies.

A mathematical physiological model of the pulmonary ventilation

Abstract This paper presents a model of the lung mechanics and simulates the pulmonary alveolar ventilation. The model includes the alveolar geometry and distribution and pressures exerted by the chest wall, due to surface tension affected by surfactant activity, due to lung tissue elasticity and due to the hydrostatic effects of the lung tissue and blood utilizing a stratified subdivision of the lungs. The model simulates a heterogenous ventilation distribution down the lungs in agreement with experimental studies. Furthermore the model is in agreement with experimentally measured hysteresis, static lung compliance, lung volumes and density distribution at different lung volumes. The presented model is the first to simulate alveolar ventilation including all of the above mentioned components of the respiratory system.

Decision support of inspired oxygen fraction using a model of oxygen transport

Abstract Setting inspired oxygen fraction (FiO 2 ) is a complicated balance between ensuring adequate oxygenation and minimizing the risk of lung damage. This paper presents a retrospective test of a model-based decision support system (INVENT) for advising on FiO 2 levels in intensive care patients. Clinically determined FiO 2 levels and the resulting blood oxygenation are compared with INVENT determined FiO levels and model simulated blood oxygenation. The results indicate that INVENT can maintain an acceptable level of oxygenation using similar or more appropriate levels of FiO compared to clinical practice.

Mathematical modelling of pulmonary gas exchange

This chapter describes mathematical models used to quantify abnormalities of pulmonary gas exchange (i.e., abnormalities of diffusion, ventilation, and perfusion). It begins by deriving the standard equations of pulmonary gas exchange, then showing how these equations can be used to obtain more complex models of ventilation–diffusion and ventilation–perfusion mismatch in the lungs. The application of these models is then reviewed in both experimental and clinical environments.