Functional morphometry to estimate the alveolar surface area by using a premature baboon model

The main respiratory pathophysiological process following premature birth is the delayed or arrested alveolar development which translates to a smaller alveolar surface area (S­A). Histological morphometry is the gold standard method to measure the SA but requires invasive tissue sampling or the removal of the whole organ for analysis. Alternatively, the SA could be measured in living subjects by "functional morphometry" using Fick's first law of diffusion and non-invasive measurements of the ventilation perfusion ratio (VA/Q). We herein aim to describe a novel functional morphometric method to measure SA using a premature baboon model. We used both functional morphometry and post-mortem histological morphometry to measure SA in 11 premature baboons born at 135 days who received intensive care treatment for 14 days. For the calculation of the SA by functional morphology we measured the septal wall thickness using microscopy, the alveolar arterial oxygen gradient using concurrent measurements of arterial pressure of O2 and CO2 and pulmonary perfusion using echocardiography and integrated Doppler signals. The median (IQR) SA using functional morphometry was 3,100 (2,080-3,640) cm2 and using histological morphometry was 1,034 (634-1,210) cm2 (left lung only). The SA measured by functional morphometry was not related to the SA measured by histological morphometry. Following linear regression analysis, the VA/Q significantly predicted the histologically measured SA (R2=0.659,p=0.002). In conclusion, functional measurements of ventilation to perfusion ratio could be used to estimate the alveolar surface area in prematurely born baboons and the ventilation perfusion ratio was the main determinant of the alveolar surface area.

Effects of an open lung ventilatory strategy on lung gas exchange during laparoscopic surgery

In general anaesthesia, early collapse of poorly ventilated lung segments with low alveolar ventilation–perfusion ratios occurs and may lead to postoperative pulmonary complications after abdominal surgery. An ‘open lung’ ventilation strategy involves lung recruitment followed by ‘individualised’ positive end-expiratory pressure titrated to maintain recruitment of low alveolar ventilation–perfusion ratio lung segments. There are limited data in laparoscopic surgery on the effects of this on pulmonary gas exchange. Forty laparoscopic bowel surgery patients were randomly assigned to standard ventilation or an ‘open lung’ ventilation intervention, with end-tidal target sevoflurane of 1% supplemented by propofol infusion. After peritoneal insufflation, stepped lung recruitment was performed in the intervention group followed by maintenance positive end-expiratory pressure of 12–15 cmH2O adjusted to maintain dynamic lung compliance at post-recruitment levels. Baseline gas and blood samples were taken and repeated after a minimum of 30 minutes for oxygen and carbon dioxide and for sevoflurane partial pressures using headspace equilibration. The sevoflurane arterial/alveolar partial pressure ratio and alveolar deadspace fraction were unchanged from baseline and remained similar between groups (mean (standard deviation) control group = 0.754 (0.086) versus intervention group = 0.785 (0.099), P = 0.319), while the arterial oxygen partial pressure/fractional inspired oxygen concentration ratio was significantly higher in the intervention group at the second timepoint (control group median (interquartile range) 288 (234–372) versus 376 (297–470) mmHg in the intervention group, P = 0.011). There was no difference between groups in the sevoflurane consumption rate. The efficiency of sevoflurane uptake is not improved by open lung ventilation in laparoscopy, despite improved arterial oxygenation associated with effective and sustained recruitment of low alveolar ventilation–perfusion ratio lung segments.

Functional Pathophysiology of SARS-CoV-2 Induced Acute Lung Injury and Clinical Implications

The worldwide pandemic caused by the SARS-CoV-2 virus has resulted in over 84,407,000 cases with over 1,800,000 deaths when this paper was submitted, with comorbidities such as gender, race, age, body mass, diabetes, and hypertension greatly exacerbating mortality. This review will analyze the rapidly increasing knowledge of COVID-19 induced lung pathophysiology. Although controversial, the acute respiratory distress syndrome (ARDS) associated with COVID-19 (CARDS) seems to present as two distinct phenotypes: Type-L and Type-H. The 'L' refers to Low elastance, ventilation/perfusion ratio, lung weight, and recruitability, and the 'H' refers to High pulmonary elastance, shunt, edema, and recruitability. However, the LUNG SAFE and ESICM Trials Groups has shown that ~13% of the mechanically ventilated non-COVID-19 ARDS patients have the Type-L phenotype. However, other studies have shown that CARDS and ARDS respiratory mechanics overlap and that standard ventilation strategies apply to these patients. The mechanisms causing alterations in pulmonary perfusion could be caused by some combination of: 1) renin-angiotensin system (RAS) dysregulation, 2) thrombosis caused by loss of endothelial barrier, 3) endothelial dysfunction causing loss of hypoxic pulmonary vasoconstriction (HPV) perfusion control, and 4) hyper-perfusion of collapsed lung tissue that has been directly measured and supported by a computational model. A flow chart has been constructed highlighting the need for personalized and adaptive ventilation strategies, such as the time controlled adaptive ventilation (TCAV) method to set and adjust the airway pressure release ventilation (APRV) mode, which recently was shown effective at improving oxygenation and reducing FiO2, vasopressors, and sedation in COVID-19 patients.

EVALUATION OF VENTILATION-PERFUSION RATIO IN CHRONIC OBSTRUCTIVE PULMONARY DISEASE

To study ventilation-perfusion ratio (VPR) in patients with chronic obstructive pulmonary disease (COPD) using method of volumetric capnography.

Многокомпонентный анализ биомаркеров в выдыхаемом воздухе методами диодной лазерной спектроскопии-=SUP=-*-=/SUP=-

Methods of multicomponent spectral analysis of exhaled air based on application of tunable diode lases were proposed for biomedical diagnostics. Simmultaneous laser based spectral analysis of the gas pairs like CO and CO2, and CO and N2O in the 4.7 micron spectral region could be used for investigation of gas exchange in studies on breathing phisiology and cardiovascular diagnostics conducted with application of different loading tests, as well as for studies in anesteziology and for on-line monitoring of ventilation-perfusion ratio. Simmultaneous analysis of NO and CO2 in 5.4 micron region could be useful fot the control of breating maneuver in studies of inflammation processes in the distal part of the lungs. Simmultaneous detection of NH3, СO2 and C2H4 near 10.5 m could be promising in studies of basal metabolizm and metabolis cycles. Simmultaneous analisis of 13СO2 and 12С O2 near 2.05 m could be used for the detection of 13СO2/12СO2 izotope ratio for izotope breath tests. The results of promising spectral region analysis and of mutual location of absorption analytical lines in these regions are presented. A possibility of simmultaneous detection of several studied molecules in the provided spectral regions was experimetally demonstrated as well as experimental laser spectra of molecular absorption were obtained. A possibility of the proposed approach in applications to analysis of trace gases in exhaled air was demonstrated.