Probing the energetic particle environment near the Sun.

NASA's Parker Solar Probe mission1 recently plunged through the inner heliosphere of the Sun to its perihelia, about 24 million kilometres from the Sun. Previous studies farther from the Sun (performed mostly at a distance of 1 astronomical unit) indicate that solar energetic particles are accelerated from a few kiloelectronvolts up to near-relativistic energies via at least two processes: 'impulsive' events, which are usually associated with magnetic reconnection in solar flares and are typically enriched in electrons, helium-3 and heavier ions2, and 'gradual' events3,4, which are typically associated with large coronal-mass-ejection-driven shocks and compressions moving through the corona and inner solar wind and are the dominant source of protons with energies between 1 and 10 megaelectronvolts. However, some events show aspects of both processes and the electron-proton ratio is not bimodally distributed, as would be expected if there were only two possible processes5. These processes have been very difficult to resolve from prior observations, owing to the various transport effects that affect the energetic particle population en route to more distant spacecraft6. Here we report observations of the near-Sun energetic particle radiation environment over the first two orbits of the probe. We find a variety of energetic particle events accelerated both locally and remotely including by corotating interaction regions, impulsive events driven by acceleration near the Sun, and an event related to a coronal mass ejection. We provide direct observations of the energetic particle radiation environment in the region just above the corona of the Sun and directly explore the physics of particle acceleration and transport.

B-type natriuretic peptide concentrations and myocardial dysfunction in critical illness.

B-type natriuretic peptide (BNP) is the first biomarker of proven value in screening for left ventricular dysfunction. The availability of point-of-care testing has escalated clinical interest and the resultant research is defining a role for BNP in the investigation and treatment of critically ill patients. This review was undertaken with the aim of collecting and assimilating current evidence regarding the use of BNP assay in the evaluation of myocardial dysfunction in critically ill humans. The information is presented in a format based upon organ system and disease category. BNP assay has been studied in a spectrum of clinical conditions ranging from acute dyspnoea to subarachnoid haemorrhage. Its role in diagnosis, assessment of disease severity, risk stratification and prognostic evaluation of cardiac dysfunction appears promising, but requires further elaboration. The heterogeneity of the critically ill population appears to warrant a range of cut-off values. Research addressing progressive changes in BNP concentration is hindered by infrequent assay and appears unlikely to reflect the critically ill patient's rapidly changing haemodynamics. Multi-marker strategies may prove valuable in prognostication and evaluation of therapy in a greater variety of illnesses. Scant data exist regarding the use of BNP assay to alter therapy or outcome. It appears that BNP assay offers complementary information to conventional approaches for the evaluation of cardiac dysfunction. Continued research should augment the validity of BNP assay in the evaluation of myocardial function in patients with life-threatening illness.

Prospective independent validation of APACHE III models in an Australian tertiary adult intensive care unit.

Evaluation of the performance of the APACHE III (Acute Physiology and Chronic Health Evaluation) ICU (intensive care unit) and hospital mortality models at the Princess Alexandra Hospital, Brisbane is reported. Prospective collection of demographic, diagnostic, physiological, laboratory, admission and discharge data of 5681 consecutive eligible admissions (1 January 1995 to 1 January 2000) was conducted at the Princess Alexandra Hospital, a metropolitan Australian tertiary referral medical/surgical adult ICU ROC (receiver operating characteristic) curve areas for the APACHE III ICU mortality and hospital mortality models demonstrated excellent discrimination. Observed ICU mortality (9.1%) was significantly overestimated by the APACHE III model adjusted for hospital characteristics (10.1%), but did not significantly differ from the prediction of the generic APACHE III model (8.6%). In contrast, observed hospital mortality (14.8%) agreed well with the prediction of the APACHE III model adjusted for hospital characteristics (14.6%), but was significantly underestimated by the unadjusted APACHE III model (13.2%). Calibration curves and goodness-of-fit analysis using Hosmer-Lemeshow statistics, demonstrated that calibration was good with the unadjusted APACHE III ICU mortality model, and the APACHE III hospital mortality model adjusted for hospital characteristics. Post hoc analysis revealed a declining annual SMR (standardized mortality rate) during the study period. This trend was present in each of the non-surgical, emergency and elective surgical diagnostic groups, and the change was temporally related to increased specialist staffing levels. This study demonstrates that the APACHE III model performs well on independent assessment in an Australian hospital. Changes observed in annual SMR using such a validated model support an hypothesis of improved survival outcomes 1995-1999.

Kinetics of absorption atelectasis during anesthesia: a mathematical model.

Recent computed tomography studies show that inspired gas composition affects the development of anesthesia-related atelectasis. This suggests that gas absorption plays an important role in the genesis of the atelectasis. A mathematical model was developed that combined models of gas exchange from an ideal lung compartment, peripheral gas exchange, and gas uptake from a closed collapsible cavity. It was assumed that, initially, the lung functioned as an ideal lung compartment but that, with induction of anesthesia, the airways to dependent areas of lung closed and these areas of lung behaved as a closed collapsible cavity. The main parameter of interest was the time the unventilated area of lung took to collapse; the effects of preoxygenation and of different inspired gas mixtures during anesthesia were examined. Preoxygenation increased the rate of gas uptake from the unventilated area of lung and was the most important determinant of the time to collapse. Increasing the inspired O2 fraction during anesthesia reduced the time to collapse. Which inert gas (N2 or N2O) was breathed during anesthesia had minimal effect on the time to collapse.

Permissive hypercapnia and gas exchange in lungs with high Qs/Qt: a mathematical model.

Low volume ventilation with permissive hypercapnia is becoming widely used in the treatment of acute respiratory distress syndrome. A mathematical model was developed to examine the effects of hypoventilation on pulmonary gas exchange in lungs with a range of shunt fractions. Hypoventilation did not worsen gas exchange, provided the inspired oxygen concentration was high enough to maintain PAO2 at an adequate level. In lungs with a high shunt fraction, some improvement in gas exchange may result, but these effects are small. A rightwards shift of the oxygen-haemoglobin dissociation curve induced by hypercapnia, is likely to be beneficial rather than detrimental in patients with acute respiratory distress syndrome. This analysis was limited to the direct effects of hypoventilation in lungs with constant shunt fractions, and did not encompass a number of possible secondary effects such as changes in cardiac output with PaCO2, changes in shunt fraction associated with a reduction in mean airway pressure and possible direct effects of hypercapnia on the pulmonary vasculature or airways.

Nitrous oxide and the rate of gas uptake from an unventilated lung in dogs.

We have studied the effect of FIO2 of a nitrous oxide-oxygen mixture on the rate of gas uptake from an unventilated lung. Nine anaesthetized dogs were studied, each breathing four nitrous oxide-oxygen mixtures (FIO2 0.3, 0.5, 0.75 and 1.0) in random order. A double-lumen endobronchial tube separated lung ventilation. Both lungs were given the nitrous oxide-oxygen mixture for an equilibration period. Then the right lung was connected to a spirometer containing the same gas, and gas uptake measured. In every dog, gas uptake was faster with an FIO2 of 0.5 or 0.75 than with an FIO2 of 1.0. When breathing a nitrous oxide-oxygen mixture with FIO2 > 0.3, the rate of gas uptake from the unventilated lung was faster than with 100% oxygen.

What is the role of absorption atelectasis in the genesis of perioperative pulmonary collapse?

During anaesthesia the combination of breathing at low lung volume, the administration of nitrous oxide and high inspired oxygen concentrations produces conditions that favour absorption atelectasis. Measures such as adding nitrogen to the inspired mixture and avoiding high inspired oxygen concentrations would reduce the amount of perioperative atelectasis if gas absorption was important in the genesis of perioperative pulmonary collapse. Experimental results demonstrate that these measures do not protect against atelectasis. This indicates that absorption atelectasis does not play a significant role in the genesis of perioperative pulmonary collapse. Compression atelectasis may be the underlying mechanism.

Effects of inspired gas composition during anaesthesia for abdominal hysterectomy on postoperative lung volumes.

We have studied 51 patients who were allocated randomly and prospectively to receive either 100% oxygen (n = 16), 70% nitrous oxide in oxygen (n = 18) or 30% oxygen in nitrogen (n = 17) as the inspired gas during anaesthesia for abdominal hysterectomy. Lung volumes were measured before and after surgery. TLC, VC, FVC and FEV1 but not RV or FRC were reduced after surgery. There were no significant differences between the three treatment groups in any of the lung volumes measured. We conclude that absorption atelectasis during anaesthesia is not the main cause of perioperative changes in lung volume after abdominal hysterectomy. Any effect of the inspired gas is likely to be of limited clinical significance.

Influence of inspired nitrogen concentration during anaesthesia for coronary artery bypass grafting on postoperative atelectasis.

Pulmonary collapse is a common problem after coronary artery bypass graft surgery (CABG). If absorption atelectasis during anaesthesia is an important mechanism in the genesis of pulmonary collapse after CABG, the addition of nitrogen to the inspired gas during anaesthesia should reduce the amount of postoperative collapse. We studied 30 patients who were allocated randomly and prospectively to receive either 100% oxygen or an oxygen-air mixture as the inspired gas during anaesthesia for CABG. Lung volumes, PaO2, and an x-ray atelectasis score were measured before and after surgery to assess the degree of atelectasis. There were no significant differences between the two treatment groups in any of these measurements.

Gas uptake from an unventilated area of lung: computer model of absorption atelectasis.

A computer model of gas uptake from an area of nonventilated lung, such as a pulmonary lobe with an occluded bronchus or an alveolus with an occluded airway, is presented. Previous analyses have assumed that when an inert gas is present, equilibration of O2 and CO2 with mixed venous blood is sufficiently rapid to be treated as instantaneous. This is valid for insoluble gases such as N2 or He when the fractional concentration of inspired O2 (FIO2) is < or = 0.6 but is invalid for a relatively soluble gas such as N2O. When a mixture of O2 and an inert gas is breathed, the time for an area of unventilated lung to collapse depends on the solubility of the inert gas and FIO2. When the solubility is low (N2 or He), collapse takes longer than when 100% O2 is breathed, and the lower the FIO2 the longer the time to collapse. When the gas is more soluble (N2O) and FIO2 is > 0.3, collapse is more rapid than when 100% O2 is breathed.