A mathematical model for breath gas analysis of volatile organic compounds with special emphasis on acetone

Recommended standardized procedures for determining exhaled lower respiratory nitric oxide and nasal nitric oxide have been developed by task forces of the European Respiratory Society and the American Thoracic Society. These recommendations have paved the way for the measurement of nitric oxide to become a diagnostic tool for specific clinical applications. It would be desirable to develop similar guidelines for the sampling of other trace gases in exhaled breath, especially volatile organic compounds (VOCs) which reflect ongoing metabolism. The concentrations of water-soluble, blood-borne substances in exhaled breath are influenced by: (i) breathing patterns affecting gas exchange in the conducting airways; (ii) the concentrations in the tracheo-bronchial lining fluid; (iii) the alveolar and systemic concentrations of the compound. The classical Farhi equation takes only the alveolar concentrations into account. Real-time measurements of acetone in end-tidal breath under an ergometer challenge show characteristics which cannot be explained within the Farhi setting. Here we develop a compartment model that reliably captures these profiles and is capable of relating breath to the systemic concentrations of acetone. By comparison with experimental data it is inferred that the major part of variability in breath acetone concentrations (e.g., in response to moderate exercise or altered breathing patterns) can be attributed to airway gas exchange, with minimal changes of the underlying blood and tissue concentrations. Moreover, it is deduced that measured end-tidal breath concentrations of acetone determined during resting conditions and free breathing will be rather poor indicators for endogenous levels. Particularly, the current formulation includes the classical Farhi and the Scheid series inhomogeneity model as special limiting cases.Comment: 38 page

Minimal Holocene retreat of large tidewater glaciers in Køge Bugt, southeast Greenland

Abstract Køge Bugt, in southeast Greenland, hosts three of the largest glaciers of the Greenland Ice Sheet; these have been major contributors to ice loss in the last two decades. Despite its importance, the Holocene history of this area has not been investigated. We present a 9100 year sediment core record of glaciological and oceanographic changes from analysis of foraminiferal assemblages, the abundance of ice-rafted debris, and sortable silt grain size data. Results show that ice-rafted debris accumulated constantly throughout the core; this demonstrates that glaciers in Køge Bugt remained in tidewater settings throughout the last 9100 years. This observation constrains maximum Holocene glacier retreat here to less than 6 km from present-day positions. Retreat was minimal despite oceanic and climatic conditions during the early-Holocene that were at least as warm as the present-day. The limited Holocene retreat of glaciers in Køge Bugt was controlled by the subglacial topography of the area; the steeply sloping bed allowed glaciers here to stabilise during retreat. These findings underscore the need to account for individual glacier geometry when predicting future behaviour. We anticipate that glaciers in Køge Bugt will remain in stable configurations in the near-future, despite the predicted continuation of atmospheric and oceanic warming

The hepatopulmonary syndrome: NO way out (multiple letters) [2]

SCOPUS: le.jinfo:eu-repo/semantics/publishe

Speed of response and accuracy of two transcutaneous carbon dioxide monitors

Two instruments (Radiometer and Hewlett-Packard) for measuring transcutaneous carbon dioxide levels have been compared. Their warm-up times, speed of response and accuracy in predicting arterial PCO 2 have been assessed in six normal subjects and ten patients with respiratory problems. They both performed well with similar accuracy in predicting PaCO 2 [95% confidence limits ± 0.9 kPa (6.7 mmHg)]. The warm-up time following application depended on actual PaCO 2 but was approximately 10 min for normal subjects and 15 min in patients. Their response to step changes in PaCO 2 was complete in approximately 6 min. Prior skin abrasion (essential for the Hewlett-Packard) increased the speed of response of the Radiometer considerably and this is the faster instrument. The Hewlett-Packard proved easier to use. These instruments are a significant advance in non-invasive monitoring

Long-term outcomes of patients with pulmonary arteriovenous malformations considered for lung transplantation, compared with similarly hypoxaemic cohorts

INTRODUCTION: Pulmonary arteriovenous malformations (PAVMs) may not be amenable to treatment by embolization or surgical resection, and many patients are left with significant hypoxemia. Lung transplantation has been undertaken . T here is no guidance on selection criteria. METHODS : To guide transplantation listing assessments , the outcomes of the six patients who had been considered for transplantation were compared to a similarly hypoxemic patient group recruited prospectively between 2005 - 2016 at the same UK institution. RESULTS : Six patients had been formally considered for lung transplantation purely for PAVMs . One underwent a single lung transplantation for diffuse PAVMs and died within 4 weeks of surgery. The other five were not transplanted, in four c ases at the patients’ request . Their current survival ranges from 16 - 27 (median 21) years post transplant assessment. Of 444 consecutive patients with PAVMs recruited between 2005 - 2016, 42 were similarly hypoxemic to the “ transplant - considered ” coho rt ( SaO 2 <86.5%). H ypoxemic cohorts maintained arterial oxygen content through secondary erythrocytosis and higher haemoglobin. Th e “transplant - considered” cohort had similar CaO 2 to the hypoxemic comparator group, but higher MRC dyspnea scores (p= 0.023 ) , higher rates of cerebral abscesses (p=0.0043) and higher rates of venous thromboemboli (p=0.0009) that were evident before and after the decision to list for transplantation. CONCLUSIONS : The non - transplanted patients demonstrated marked longevity . Symp toms and co - morbidities were better predictors of health than oxygen measurements. While a case - by - case decision, weighing survival estimates and quality of life will help patients in their decision making, the data suggest a very strong case must be made before lung transplantation is considered