Dataset Information

Pulmonary ventilation-perfusion mismatch: a novel hypothesis for how diving vertebrates may avoid the bends.

ABSTRACT: Hydrostatic lung compression in diving marine mammals, with collapsing alveoli blocking gas exchange at depth, has been the main theoretical basis for limiting N2 uptake and avoiding gas emboli (GE) as they ascend. However, studies of beached and bycaught cetaceans and sea turtles imply that air-breathing marine vertebrates may, under unusual circumstances, develop GE that result in decompression sickness (DCS) symptoms. Theoretical modelling of tissue and blood gas dynamics of breath-hold divers suggests that changes in perfusion and blood flow distribution may also play a significant role. The results from the modelling work suggest that our current understanding of diving physiology in many species is poor, as the models predict blood and tissue N2 levels that would result in severe DCS symptoms (chokes, paralysis and death) in a large fraction of natural dive profiles. In this review, we combine published results from marine mammals and turtles to propose alternative mechanisms for how marine vertebrates control gas exchange in the lung, through management of the pulmonary distribution of alveolar ventilation ([Formula: see text]) and cardiac output/lung perfusion ([Formula: see text]), varying the level of [Formula: see text] in different regions of the lung. Man-made disturbances, causing stress, could alter the [Formula: see text] mismatch level in the lung, resulting in an abnormally elevated uptake of N2, increasing the risk for GE. Our hypothesis provides avenues for new areas of research, offers an explanation for how sonar exposure may alter physiology causing GE and provides a new mechanism for how air-breathing marine vertebrates usually avoid the diving-related problems observed in human divers.

SUBMITTER: Garcia Parraga D

PROVIDER: S-EPMC5936736 | biostudies-literature | 2018 Apr

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Pulmonary ventilation-perfusion mismatch: a novel hypothesis for how diving vertebrates may avoid the bends.

Garcia Párraga Daniel D Moore Michael M Fahlman Andreas A

Proceedings. Biological sciences 20180401 1877

Hydrostatic lung compression in diving marine mammals, with collapsing alveoli blocking gas exchange at depth, has been the main theoretical basis for limiting N<sub>2</sub> uptake and avoiding gas emboli (GE) as they ascend. However, studies of beached and bycaught cetaceans and sea turtles imply that air-breathing marine vertebrates may, under unusual circumstances, develop GE that result in decompression sickness (DCS) symptoms. Theoretical modelling of tissue and blood gas dynamics of breath ...[more]

PMID: 29695441

Similar Datasets

Project description:Pulmonary hypertension (PH) in adults with sickle cell disease (SCD) is associated with early mortality. Chronic thromboembolic PH (CTEPH) is an important complication and contributor to PH in SCD but is likely underappreciated. Guidelines recommend ventilation-perfusion (V/Q) scintigraphy as the imaging modality of choice to exclude CTEPH. Data on V/Q scanning are limited in SCD. Our objective was to compare the performance of V/Q scanning with that of CT pulmonary angiography (CTPA) and to report clinical outcomes associated with abnormal V/Q findings. Methods: Laboratory data, echocardiography, 6-min-walk testing, V/Q scanning, CTPA, and right heart catheterization (RHC) were prospectively obtained. High-probability and intermediate-probability V/Q findings were considered to be abnormal. Included for analysis were 142 SCD adults (aged 40.1 ± 13.7 y, 83 women, 87% hemoglobin SS) in a stable state enrolled consecutively between March 13, 2002, and June 8, 2017. Results: V/Q results were abnormal in 65 of 142 patients (45.8%). CTPA was positive for pulmonary embolism in 16 of 60 (26.7%). RHC confirmed PH (mean pulmonary artery pressure ≥ 25 mmHg) in 46 of 64 (71.9%), of whom 34 (73.9%) had abnormal V/Q findings. Among those without PH by RHC (n = 18), 2 of 18 patients had abnormal V/Q findings. Thirty-three patients had a complete dataset (V/Q scanning, CTPA, and RHC); 29 of 33 had abnormal RHC findings, of whom 26 had abnormal V/Q findings, compared with 11 who had abnormal CTPA findings. There was greater concordance between V/Q findings and RHC (κ-value = 0.53; P < 0.001) than between CTPA and RHC (κ-value = 0.13; P = 0.065). The sensitivity and specificity for V/Q scanning was 89.7% and 75.0%, respectively, whereas CTPA had sensitivity of 37.3% and specificity of 100%. Abnormal V/Q finding swere associated with hemodynamic severity (mean pulmonary artery pressure, 35.2 ± 9.6 vs. 26.9 ± 10.5 mm Hg, P = 0.002; transpulmonary gradient, 21.5 ± 9.7 vs. 12.16 ± 11 mmHg, P = 0.005; and pulmonary vascular resistance, 226.5 ± 135 vs. 140.7 ± 123.7 dynes⋅s⋅cm-5, P = 0.013) and exercise capacity (6-min-walk distance, 382.8 ± 122.3 vs. 442.3 ± 110.6 m, P < 0.010). Thirty-four deaths were observed over 15 y. All-cause mortality was higher in the abnormal-V/Q group (21 [61.8%]) than in the normal-V/Q group (13 [38.2%]) (log-rank test, P = 0.006; hazard ratio, 2.54). Conclusion: V/Q scanning is superior to CTPA in detecting thrombotic events in SCD. Abnormal V/Q findings are associated with PH, worse hemodynamics, lower functional capacity, and higher mortality. Despite high sensitivity in detecting CTEPH, V/Q scanning is underutilized. We recommend the use of V/Q scanning in the evaluation of dyspnea in adult SCD patients given the important implications toward management.

Project description:BackgroundSeveral studies have found only a weak to moderate correlation between oxygenation and lung aeration in response to changes in PEEP. This study aimed to investigate the association between changes in shunt, low and high ventilation/perfusion (V/Q) mismatch, and computed tomography-measured lung aeration following an increase in PEEP in patients with ARDS.MethodsIn this preliminary study, 12 ARDS patients were subjected to recruitment maneuvers followed by setting PEEP at 5 and then either 15 or 20 cmH2O. Lung aeration was measured by computed tomography. Values of pulmonary shunt and low and high V/Q mismatch were calculated by a model-based method from measurements of oxygenation, ventilation, and metabolism taken at different inspired oxygen levels and an arterial blood gas sample.ResultsIncreasing PEEP resulted in reduced values of pulmonary shunt and the percentage of non-aerated tissue, and an increased percentage of normally aerated tissue (p < 0.05). Changes in shunt and normally aerated tissue were significantly correlated (r = - 0.665, p = 0.018). Three distinct responses to increase in PEEP were observed in values of shunt and V/Q mismatch: a beneficial response in seven patients, where shunt decreased without increasing high V/Q; a detrimental response in four patients where both shunt and high V/Q increased; and a detrimental response in a patient with reduced shunt but increased high V/Q mismatch. Non-aerated tissue decreased with increased PEEP in all patients, and hyperinflated tissue increased only in patients with a detrimental response in shunt and V/Q mismatch.ConclusionsThe results show that improved lung aeration following an increase in PEEP is not always consistent with reduced shunt and V/Q mismatch. Poorly matched redistribution of ventilation and perfusion, between dependent and non-dependent regions of the lung, may explain why patients showed detrimental changes in shunt and V/Q mismatch on increase in PEEP, despite improved aeration.Trial registrationClinicalTrails.gov, NCT04067154. Retrospectively registered on August 26, 2019.

Project description:BackgroundThe aim of this study was to validate whether regional ventilation and perfusion data measured by electrical impedance tomography (EIT) with saline bolus could discriminate three broad acute respiratory failure (ARF) etiologies.MethodsPerfusion image was generated from EIT-based impedance-time curves caused by 10 ml 10% NaCl injection during a respiratory hold. Ventilation image was captured before the breath holding period under regular mechanical ventilation. DeadSpace%, Shunt% and VQMatch% were calculated based on lung perfusion and ventilation images. Ventilation and perfusion maps were divided into four cross-quadrants (lower left and right, upper left and right). Regional distribution defects of each quadrant were scored as 0 (distribution% ≥ 15%), 1 (15% > distribution% ≥ 10%) and 2 (distribution% < 10%). Data percentile distributions in the control group and clinical simplicity were taken into consideration when defining the scores. Overall defect scores (DefectV, DefectQ and DefectV+Q) were the sum of four cross-quadrants of the corresponding images.ResultsA total of 108 ICU patients were prospectively included: 93 with ARF and 15 without as a control. PaO2/FiO2 was significantly correlated with VQMatch% (r = 0.324, P = 0.001). Three broad etiologies of ARF were identified based on clinical judgment: pulmonary embolism-related disease (PED, n = 14); diffuse lung involvement disease (DLD, n = 21) and focal lung involvement disease (FLD, n = 58). The PED group had a significantly higher DeadSpace% [40(24)% vs. 14(15)%, PED group vs. the rest of the subjects; median(interquartile range); P < 0.0001] and DefectQ score than the other groups [1(1) vs. 0(1), PED vs. the rest; P < 0.0001]. The DLD group had a significantly lower DefectV+Q score than the PED and FLD groups [0(1) vs. 2.5(2) vs. 3(3), DLD vs. PED vs. FLD; P < 0.0001]. The FLD group had a significantly higher DefectV score than the other groups [2(2) vs. 0(1), FLD vs. the rest; P < 0.0001]. The area under the receiver operating characteristic (AUC) for using DeadSpace% to identify PED was 0.894 in all ARF patients. The AUC for using the DefectV+Q score to identify DLD was 0.893. The AUC for using the DefectV score to identify FLD was 0.832.ConclusionsOur study showed that it was feasible to characterize three broad etiologies of ARF with EIT-based regional ventilation and perfusion. Further study is required to validate clinical applicability of this method. Trial registration clinicaltrials, NCT04081142. Registered 9 September 2019-retrospectively registered, https://clinicaltrials.gov/show/NCT04081142 .

Dataset Information

Pulmonary ventilation-perfusion mismatch: a novel hypothesis for how diving vertebrates may avoid the bends.

Publications

Pulmonary ventilation-perfusion mismatch: a novel hypothesis for how diving vertebrates may avoid the bends.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets