RESUMO
BACKGROUND: Assessment of regional ventilation/perfusion (V'/Q) mismatch using electrical impedance tomography (EIT) represents a promising advancement for personalized management of the acute respiratory distress syndrome (ARDS). However, accuracy is still hindered by the need for invasive monitoring to calibrate ventilation and perfusion. Here, we propose a non-invasive correction that uses only EIT data and characterized patients with more pronounced compensation of V'/Q mismatch. METHODS: We enrolled twenty-one ARDS patients on controlled mechanical ventilation. Cardiac output was measured invasively, and ventilation and perfusion were assessed by EIT. Relative V'/Q maps by EIT were calibrated to absolute values using the minute ventilation to invasive cardiac output (MV/CO) ratio (V'/Q-ABS), left unadjusted (V'/Q-REL), or corrected by MV/CO ratio derived from EIT data (V'/Q-CORR). The ratio between ventilation to dependent regions and perfusion reaching shunted units ( V D ' /QSHUNT) was calculated as an index of more effective hypoxic pulmonary vasoconstriction. The ratio between perfusion to non-dependent regions and ventilation to dead space units (QND/ V DS ' ) was calculated as an index of hypocapnic pneumoconstriction. RESULTS: Our calibration factor correlated with invasive MV/CO (r = 0.65, p < 0.001), showed good accuracy and no apparent bias. Compared to V'/Q-ABS, V'/Q-REL maps overestimated ventilation (p = 0.013) and perfusion (p = 0.002) to low V'/Q units and underestimated ventilation (p = 0.011) and perfusion (p = 0.008) to high V'/Q units. The heterogeneity of ventilation and perfusion reaching different V'/Q compartments was underestimated. V'/Q-CORR maps eliminated all these differences with V'/Q-ABS (p > 0.05). Higher V D ' / Q SHUNT correlated with higher PaO2/FiO2 (r = 0.49, p = 0.025) and lower shunt fraction (ρ = - 0.59, p = 0.005). Higher Q ND / V DS ' correlated with lower PEEP (ρ = - 0.62, p = 0.003) and plateau pressure (ρ = - 0.59, p = 0.005). Lower values of both indexes were associated with less ventilator-free days (p = 0.05 and p = 0.03, respectively). CONCLUSIONS: Regional V'/Q maps calibrated with a non-invasive EIT-only method closely approximate the ones obtained with invasive monitoring. Higher efficiency of shunt compensation improves oxygenation while compensation of dead space is less needed at lower airway pressure. Patients with more effective compensation mechanisms could have better outcomes.
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Impedância Elétrica , Síndrome do Desconforto Respiratório , Tomografia , Relação Ventilação-Perfusão , Humanos , Feminino , Masculino , Pessoa de Meia-Idade , Síndrome do Desconforto Respiratório/fisiopatologia , Síndrome do Desconforto Respiratório/terapia , Impedância Elétrica/uso terapêutico , Idoso , Relação Ventilação-Perfusão/fisiologia , Tomografia/métodos , Espaço Morto Respiratório/fisiologia , Respiração Artificial/métodos , Adulto , Monitorização Fisiológica/métodos , Débito Cardíaco/fisiologiaRESUMO
INTRODUCTION: Pulmonary embolism (PE) is a challenge to diagnose and when missed, exposes patients to potentially fatal recurrent events. Beyond CT pulmonary angiography (CTPA) and planar ventilation/perfusion (V/Q) scan, single photon emission CT (SPECT) V/Q emerged a new diagnostic modality of scintigraphic acquisition that has been reported to improve diagnostic performances. To date, no management outcome study or randomised trial evaluated an algorithm based on SPECT V/Q for PE diagnosis. We present the design of a randomised multicentre, international management study comparing SPECT V/Q with validated strategies. MATERIAL AND METHODS: We will include a total of 3672 patients with suspected PE requiring chest imaging, randomised into three different groups, each using a different diagnostic strategy based on SPECT V/Q, CTPA and planar V/Q scan. Randomisation will be unbalanced (2:1:1), with twice as many patients in SPECT V/Q arm (n=1836) as in CTPA and planar V/Q arms (n=918 in each). Our primary objective will be to determine whether a diagnostic strategy based on SPECT V/Q is non-inferior to previously validated strategies in terms of diagnostic exclusion safety as assessed by the 3-month risk of thromboembolism in patients with a negative diagnostic workup. Secondary outcomes will be the proportion of patients diagnosed with PE in each arm, patients requiring additional tests, the incidence of major and clinically relevant non-major bleeding and the incidence and cause of death in each arm. ETHICS AND DISSEMINATION: This trial is funded by a grant from Brest University Hospital and by INVENT. The study protocol was approved by Biomedical Research Ethics Committee. The investigator or delegate will obtain signed informed consent from all patients prior to inclusion in the trial. Our results will inform future clinical practice guidelines and solve the current discrepancy between nuclear medicine guidelines and clinical scientific society guidelines. TRIAL REGISTRATION NUMBER: NCT02983760.
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Angiografia por Tomografia Computadorizada , Embolia Pulmonar , Tomografia Computadorizada de Emissão de Fóton Único , Cintilografia de Ventilação/Perfusão , Feminino , Humanos , Masculino , Angiografia por Tomografia Computadorizada/métodos , Embolia Pulmonar/diagnóstico por imagem , Ensaios Clínicos Controlados Aleatórios como Assunto , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Relação Ventilação-Perfusão , Cintilografia de Ventilação/Perfusão/métodosRESUMO
PURPOSE: Ventilation Perfusion SPECT is important in the diagnostics of e.g. pulmonary embolism and chronic obstructive pulmonary disease. Classical and reverse mismatched defects can be identified by utilizing the ventilation-perfusion ratio. Unfortunately, this ratio is only linear in the ventilation, the scale is not symmetrical regarding classical and reversed mismatches and small perfusion values give rise to artifacts. The ventilation-perfusion (VQ) difference is developed as an alternative. METHODS: For both VQ-ratio and VQ-difference a scaling factor for the perfusion is computed, so that voxels with matched ventilation and perfusion (on average) yield zero signal. The relative VQ-difference is calculated by scaling with the summed VQ-signal in each voxel. The scaled VQ-difference is calculated by scaling with the global maximum of this sum. RESULTS: The relative and scaled differences have a scale from -1 (perfusion only) to + 1 (ventilation only). Image quality of relative VQ-difference and VQ-ratio images is hampered by artifacts from areas with both low perfusion and low ventilation. Ratio and differences have been investigated in ten patients and are shown for three patients (one without defects). Clinical thresholds for the difference images are derived resulting in color maps of relevant (reversed) mismatches with a (reciprocal) ratio larger than two. CONCLUSIONS: The relative ventilation-perfusion difference is a methodological improvement on the ventilation-perfusion ratio, because it has a symmetrical scale and is bound on a closed domain. A better diagnostic value is expected by utilizing the scaled difference, which represents functional difference instead of relative difference.
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Pulmão , Embolia Pulmonar , Humanos , Relação Ventilação-Perfusão , Pulmão/diagnóstico por imagem , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Embolia Pulmonar/diagnóstico por imagem , PerfusãoRESUMO
BACKGROUND: Ventilation-perfusion (V/Q) scan coupled with single photon emission computed tomography (SPECT) is commonly used for the diagnosis of pulmonary embolism (PE). An abnormal chest x-ray (CXR) is deemed to hinder the interpretation of V/Q scan and therefore a normal CXR is recommended prior to V/Q scan. AIMS: To determine if an abnormal CXR impacted on V/Q scan interpretation and subsequent management. METHODS: A retrospective cohort analysis of all patients who underwent a V/Q scan for diagnosis of suspected acute PE between March 2016 and 2022 was performed. CXR reports were reviewed and classified as normal or abnormal. Low-dose computerised tomography was routinely performed in patients above the age of 70. Data regarding V/Q scan results and subsequent management including initiation of anticoagulation for PE or further diagnostic investigations were collected. RESULTS: A total of 340 cases were evaluated. Of the positive V/Q scans (92/340), 98.3% of the normal CXR were anticoagulated compared to 100% of the abnormal CXR group. Of the negative V/Q scans (239/340), no cases were started on anticoagulation and no further investigations were performed across both normal and abnormal CXR groups. Indeterminate results occurred in only 9 cases with no significant difference in management between normal and abnormal CXR groups. CONCLUSION: An abnormal CXR does not affect the reliability of V/Q scan interpretation in the diagnosis of PE when coupled with SPECT. Unless clinically indicated, the mandate by clinical society guidelines for a normal CXR prior to V/Q should be revisited.
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Embolia Pulmonar , Cintilografia de Ventilação/Perfusão , Humanos , Raios X , Estudos Retrospectivos , Reprodutibilidade dos Testes , Relação Ventilação-Perfusão , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Pulmão , AnticoagulantesRESUMO
BACKGROUND: Despite the fervent scientific effort, a state-of-the art assessment of the different causes of hypoxemia (shunt, ventilation-perfusion mismatch, and diffusion limitation) in COVID-19 acute respiratory distress syndrome (ARDS) is currently lacking. In this study, the authors hypothesized a multifactorial genesis of hypoxemia and aimed to measure the relative contribution of each of the different mechanism and their relationship with the distribution of tissue and blood within the lung. METHODS: In this cross-sectional study, the authors prospectively enrolled 10 patients with COVID-19 ARDS who had been intubated for less than 7 days. The multiple inert gas elimination technique (MIGET) and a dual-energy computed tomography (DECT) were performed and quantitatively analyzed for both tissue and blood volume. Variables related to the respiratory mechanics and invasive hemodynamics (PiCCO [Getinge, Sweden]) were also recorded. RESULTS: The sample (51 ± 15 yr; Pao2/Fio2, 172 ± 86 mmHg) had a mortality of 50%. The MIGET showed a shunt of 25 ± 16% and a dead space of 53 ± 11%. Ventilation and perfusion were mismatched (LogSD, Q, 0.86 ± 0.33). Unexpectedly, evidence of diffusion limitation or postpulmonary shunting was also found. In the well aerated regions, the blood volume was in excess compared to the tissue, while the opposite happened in the atelectasis. Shunt was proportional to the blood volume of the atelectasis (R2 = 0.70, P = 0.003). VËA/QËT mismatch was correlated with the blood volume of the poorly aerated tissue (R2 = 0.54, P = 0.016). The overperfusion coefficient was related to Pao2/Fio2 (R2 = 0.66, P = 0.002), excess tissue mass (R2 = 0.84, P < 0.001), and Etco2/Paco2 (R2 = 0.63, P = 0.004). CONCLUSIONS: These data support the hypothesis of a highly multifactorial genesis of hypoxemia. Moreover, recent evidence from post-mortem studies (i.e., opening of intrapulmonary bronchopulmonary anastomosis) may explain the findings regarding the postpulmonary shunting. The hyperperfusion might be related to the disease severity.
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COVID-19 , Atelectasia Pulmonar , Síndrome do Desconforto Respiratório , Humanos , Relação Ventilação-Perfusão , Estudos Transversais , COVID-19/complicações , Síndrome do Desconforto Respiratório/diagnóstico por imagem , Hipóxia/diagnóstico por imagem , Hipóxia/etiologia , Tomografia , Troca Gasosa PulmonarRESUMO
We have investigated the elimination of inert gases in the lung during the elimination of nitrous oxide (N2 O) using a two-step mathematical model that allows the contribution from net gas volume expansion, which occurs in Step 2, to be separated from other factors. When a second inert gas is used in addition to N2 O, the effect on that gas appears as an extra volume of the gas eliminated in association with the dilution produced by N2 O washout in Step 2. We first considered the effect of elimination in a single gas-exchanging unit under steady-state conditions and then extended our analysis to a lung having a log-normal distribution of ventilation and perfusion. A further increase in inert gas elimination was demonstrated with gases of low solubility in the presence of the increased ventilation-perfusion mismatch that is known to occur during anesthesia. These effects are transient because N2 O elimination depletes the input of that gas from mixed venous blood to the lung, thereby rapidly reducing the magnitude of the diluting action.
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Gases , Troca Gasosa Pulmonar , Relação Ventilação-Perfusão , Pulmão , Gases Nobres , Modelos BiológicosAssuntos
COVID-19 , Embolia Pulmonar , Humanos , Pulmão/diagnóstico por imagem , Perfusão , Relação Ventilação-PerfusãoRESUMO
We investigated whether machine learning (ML) analysis of ICU monitoring data incorporating volumetric capnography measurements of mean alveolar PCO2 can partition venous admixture (VenAd) into its shunt and low V/Q components without manipulating the inspired oxygen fraction (FiO2). From a 21-compartment ventilation / perfusion (V/Q) model of pulmonary blood flow we generated blood gas and mean alveolar PCO2 data in simulated scenarios with shunt values from 7.3% to 36.5% and a range of FiO2 settings, indirect calorimetry and cardiac output measurements and acid- base and hemoglobin oxygen affinity conditions. A 'deep learning' ML application, trained and validated solely on single FiO2 bedside monitoring data from 14,736 scenarios, then recovered shunt values in 500 test scenarios with true shunt values 'held back'. ML shunt estimates versus true values (n = 500) produced a linear regression model with slope = 0.987, intercept = -0.001 and R2 = 0.999. Kernel density estimate and error plots confirmed close agreement. With corresponding VenAd values calculated from the same bedside data, low V/Q flow can be reported as VenAd-shunt. ML analysis of blood gas, indirect calorimetry, volumetric capnography and cardiac output measurements can quantify pulmonary oxygenation deficits as percentage shunt flow (V/Q = 0) versus percentage low V/Q flow (V/Q > 0). High fidelity reports are possible from analysis of data collected solely at the operating FiO2.
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Capnografia , Pulmão , Humanos , Relação Ventilação-Perfusão/fisiologia , Simulação por Computador , Oxigênio , Troca Gasosa Pulmonar/fisiologiaRESUMO
OBJECTIVE: To investigate the outcomes of ventilation/perfusion scintigraphy on the diagnosis of pulmonary embolism in coronavirus disease 2019 (COVID-19) patients, we performed a systematic review of the available literature. MATERIALS AND METHODS: PubMed and Scopus were systematically searched up to 4 June 2022, for relevant studies. We included studies on patients with COVID-19 who have performed ventilation/perfusion scintigraphy for diagnosis of pulmonary embolism to describe any diagnosis outcome. Irrelevant and non-English articles were excluded. RESULTS: Overall, 27 articles were included in our review. The database search yielded studies from PubMed, Scopus, and studies identified through reviewing the reference list of included studies. Extracted information from the included studies could be categorized into several aspects: Diagnosis of pulmonary embolism with Q single-photon emission computed tomography (SPECT) CT, Tracheobronchial uptake, Diagnostic value of V/Q rather than Q at diagnosis pulmonary embolism, Different characteristics (morphological alterations) of COVID-19 in ventilation orperfusion scan, the prevalence of pulmonary embolism with Q or V/Q criteria, and Design of radiotherapy planning in lung cancer patients with COVID-19. CONCLUSION: Different perfusion patterns in COVID-19 are challenging but can be alleviated by adding SPECT/computed tomography (CT) to lung perfusion scans. Although perfusion only SPECT/CT can rule out or rule in others in considerable number of patients, ventilation scan is still needed in certain patients.
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COVID-19 , Embolia Pulmonar , Humanos , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Pulmão , Perfusão , Relação Ventilação-Perfusão , Teste para COVID-19RESUMO
Ventilation and perfusion (V/Q) lung scintigraphy has been used in the assessment of patients with suspected pulmonary embolism for more than 50 y. Advances in imaging technology make SPECT and SPECT/CT feasible. This article will examine the application and technical considerations associated with performing 3-dimensional V/Q SPECT and the contribution of a coacquired CT scan. The literature tends to be mixed and contradictory in terms of appropriate investigation algorithms for pulmonary embolism. V/Q SPECT and SPECT/CT offer significant advantages over planar V/Q, with or without the advantages of Technegas ventilation, and if available should be the preferred option in the evaluation of patients with suspected pulmonary embolism.
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Embolia Pulmonar , Tomografia Computadorizada de Emissão de Fóton Único , Humanos , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Tomografia Computadorizada por Raios X/métodos , Pulmão , Tomografia Computadorizada com Tomografia Computadorizada de Emissão de Fóton Único , Relação Ventilação-PerfusãoRESUMO
ABSTRACT: Although COVID-19 infection is associated with the increased risk of pulmonary thromboembolism (PTE), COVID-19 pulmonary lesions cause ventilation-perfusion (V/Q) patterns other than PTE. Although extensive research has been done to address different anatomical patterns of COVID-19, there is a knowledge gap in terms of V/Q lung scintigraphy in these patients. The purpose of this study is to demonstrate these patterns and to show how important it is to use SPECT/CT in addition to planar images to differentiate between these patterns from PTE. In the current collection, we presented various patterns of V/Q SPECT/CT abnormalities in COVID-19 patients.
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COVID-19 , Embolia Pulmonar , Humanos , Cintilografia de Ventilação/Perfusão , Tomografia Computadorizada de Emissão de Fóton Único/métodos , COVID-19/diagnóstico por imagem , Pulmão/diagnóstico por imagem , Embolia Pulmonar/diagnóstico por imagem , Relação Ventilação-Perfusão , PerfusãoRESUMO
Using computer simulation we investigated whether machine learning (ML) analysis of selected ICU monitoring data can quantify pulmonary gas exchange in multi-compartment format. A 21 compartment ventilation/perfusion (V/Q) model of pulmonary blood flow processed 34,551 combinations of cardiac output, hemoglobin concentration, standard P50, base excess, VO2 and VCO2 plus three model-defining parameters: shunt, log SD and mean V/Q. From these inputs the model produced paired arterial blood gases, first with the inspired O2 fraction (FiO2) adjusted to arterial saturation (SaO2) = 0.90, and second with FiO2 increased by 0.1. 'Stacked regressor' ML ensembles were trained/validated on 90% of this dataset. The remainder with shunt, log SD, and mean 'held back' formed the test-set. 'Two-Point' ML estimates of shunt, log SD and mean utilized data from both FiO2 settings. 'Single-Point' estimates used only data from SaO2 = 0.90. From 3454 test gas exchange scenarios, two-point shunt, log SD and mean estimates produced linear regression models versus true values with slopes ~ 1.00, intercepts ~ 0.00 and R2 ~ 1.00. Kernel density and Bland-Altman plots confirmed close agreement. Single-point estimates were less accurate: R2 = 0.77-0.89, slope = 0.991-0.993, intercept = 0.009-0.334. ML applications using blood gas, indirect calorimetry, and cardiac output data can quantify pulmonary gas exchange in terms describing a 20 compartment V/Q model of pulmonary blood flow. High fidelity reports require data from two FiO2 settings.
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Pulmão , Troca Gasosa Pulmonar , Humanos , Troca Gasosa Pulmonar/fisiologia , Simulação por Computador , Pulmão/fisiologia , Circulação Pulmonar , Respiração , Relação Ventilação-Perfusão/fisiologiaRESUMO
ABSTRACT: A 67-year-old woman presented with shortness of breath and a ventilation/perfusion scan was performed. Initial images demonstrated mismatched bilateral apical defects that would be classified as high probability for pulmonary emboli. However, it was unusual that the defects were only in the bilateral apices. Investigation discovered that 99m Tc-MAA was administered while the patient was in a seated position. Repeat scan the following day with the patient in the correct, supine, position during 99m Tc-MAA administration demonstrated no defects. In this case, incorrect patient positioning could have resulted in an incorrect diagnosis of pulmonary emboli and inappropriate treatment of the patient.
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Embolia Pulmonar , Tomografia Computadorizada por Raios X , Feminino , Humanos , Idoso , Embolia Pulmonar/diagnóstico por imagem , Cintilografia de Ventilação/Perfusão , Perfusão , Posicionamento do Paciente , Agregado de Albumina Marcado com Tecnécio Tc 99m , Relação Ventilação-Perfusão , PulmãoRESUMO
ABSTRACT: Invented and first approved for clinical use in Australia 36 years ago, Technegas is the technology that enabled ventilation scintigraphy with 99m Tc-labeled carbon nanoparticles ( 99m Tc-CNP). The US Food and Drug Administration (FDA) has considered this technology for more than 30 years but only now is getting close to approving it. Meanwhile, more than 4.4 million patients benefited from this technology in 64 countries worldwide. The primary application of 99m Tc-CNP ventilation imaging is the diagnostic evaluation for suspicion of pulmonary embolism using ventilation-perfusion quotient (V/Q) imaging. Because of 99m Tc-CNP's long pulmonary residence, tomographic imaging emerged as the preferred V/Q methodology. The FDA-approved ventilation imaging agents are primarily suitable for planar imaging, which is less sensitive. After the FDA approval of Technegas, the US practice will likely shift to tomographic V/Q. The 99m Tc-CNP use is of particular interest in the COVID-19 pandemic because it offers an option of a dry radioaerosol that takes approximately only 3 to 5 tidal breaths, allowing the shortest exposure to and contact with possibly infected patients. Indeed, countries where 99m Tc-CNP was approved for clinical use continued using it throughout the COVID-19 pandemic without known negative viral transmission consequences. Conversely, the ventilation imaging was halted in most US facilities from the beginning of the pandemic. This review is intended to familiarize the US clinical nuclear medicine community with the basic science of 99m Tc-CNP ventilation imaging and its clinical applications, including common artifacts and interpretation criteria for tomographic V/Q imaging for pulmonary embolism.
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COVID-19 , Embolia Pulmonar , Humanos , Carbono , COVID-19/diagnóstico por imagem , Pulmão , Pandemias , Embolia Pulmonar/diagnóstico por imagem , Ventilação Pulmonar , Cintilografia , Aerossóis e Gotículas Respiratórios , Tecnécio , Relação Ventilação-Perfusão , NanoestruturasRESUMO
INTRODUCTION: Computed tomography angiography (CTA) and ventilation/perfusion (V/Q) single photon emission computed tomography/CT (SPECT/CT) images have been widely used to detect PE, but few studies have performed a direct comparison between them. We aimed to evaluate the performance of these tests in the same group of patients, selected from the routine practice of a general hospital. METHODS: Patients with suspected acute PE were prospectively submitted to CTA and V/Q SPECT/CT. General radiologists and nuclear physicians, respectively, interpreted the images. Data regarding age, sex, time between examinations, symptoms, and Wells score were also recorded. The final diagnosis was decided through a consensus among the clinicians, taking into account clinical, laboratory, follow-up, and all imaging procedures data. RESULTS: Twenty-eight patients (15 male, 13 female, and median age of 51.5 years) were studied. Median duration of the onset of symptoms was 4 (1-14) days, and the median Wells score was 3.5 (1.5-6). Sensitivity, specificity, positive and negative predictive values, and accuracy were 84.6%, 80.0%, 78.6%, 85.7%, and 82.1% for V/Q SPECT/CT, and 46.1%, 100%, 100%, 68.2%, and 75.0% for CTA. The overall agreement between the methods was 57.1%. Of the 22 patients with negative CTA, 10 (45.4%) had positives V/Q SPECT/CT and seven of them classified as true positives. CONCLUSIONS: Our results suggest that V/Q SPECT/CT is more sensitive and accurate than CTA when interpreted by general radiologists and nuclear medicine physicians.
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Tomografia Computadorizada Multidetectores , Embolia Pulmonar , Humanos , Masculino , Feminino , Pessoa de Meia-Idade , Relação Ventilação-Perfusão , Embolia Pulmonar/diagnóstico por imagem , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Angiografia , Doença Aguda , PerfusãoRESUMO
BACKGROUND Chronic thromboembolic pulmonary disease (CTEPD) is the persistent occlusion of pulmonary arteries resulting from 1 or more thrombo-emboli. Its presentation is often non-specific, with exertional dyspnea and fatigue, yet if left undiagnosed risks of chronic thromboembolic pulmonary hypertension and right-sided cardiac failure can ensue. Computed tomography pulmonary angiography (CTPA) and ventilation/perfusion (V/Q) imaging are most commonly utilized for investigating CTEPD. This report is of a 60-year-old woman with a 6-week history of breathlessness and intermittent chest pain due to CTEPD, undetected by CTPA and diagnosed by V/Q imaging. CASE REPORT A 60-year-old woman presented with a 6-week history of breathlessness, intermittent chest pain, and reduced mobility. Her past medical history included chronic obstructive pulmonary disease, pulmonary sarcoidosis, and obesity. Screening tests for infective and ischemic cardiac etiologies were unremarkable. A calculated Wells score was 6, making CTEPD the main differential diagnosis, and she was commenced on therapeutic dose anticoagulation. A CTPA performed on day 2 of admission showed no evidence of acute thromboembolic pulmonary disease or CTEPD. Instead, V/Q scintigraphy on day 6 revealed a perfusion mismatch in the right lung apex, consistent with CTEPD. The patient improved clinically and was discharged on long-term apixaban. CONCLUSIONS A negative CTPA does not necessarily exclude CTEPD. The sensitivity of CTPA for CTEPD is lower than that of V/Q imaging, and can hence lead to false-negative results, as this case highlights. When there is a high clinical suspicion for CTEPD but a negative CTPA study, V/Q imaging should always be undertaken.
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Embolia Pulmonar , Tromboembolia , Feminino , Humanos , Pessoa de Meia-Idade , Angiografia/métodos , Dor no Peito/etiologia , Dispneia/etiologia , Pulmão , Perfusão , Imagem de Perfusão , Embolia Pulmonar/diagnóstico por imagem , Cintilografia , Tomografia Computadorizada por Raios X , Relação Ventilação-PerfusãoRESUMO
BACKGROUND: The pathophysiology of COVID-19 remains poorly understood. We aimed to estimate the contribution of intrapulmonary shunting and ventilation-to-perfusion (VA/Q) mismatch using a mathematical model to construct oxygen-haemoglobin dissociation curves (ODCs). METHODS: ODCs were constructed using transcutaneous pulse oximetry at two different fractions of inspired oxygen (FiO2). 199 patients were included from two large district general hospitals in the South East of England from 1st to 14th January 2021. The study was supported by the National Institute of Health Research (NIHR) Clinical Research Network. RESULTS: Overall mortality was 29%. Mean age was 68.2 years (SEM 1·2) with 46% female. Median shunt on admission was 17% (IQR 8-24.5); VA/Q was 0.61 (IQR 0.52-0.73). Shunt was 37.5% higher in deaths (median 22%, IQR 9-29) compared to survivors (16%, 8-21; p = 0.0088) and was a predictor of mortality (OR 1.04; 95% CI 1.01-1.07). Admission oxygen saturations were more strongly predictive of mortality (OR 0.91, 95% CI 0.87-0.96). There was no difference in VA/Q mismatch between deaths (0.60; IQR 0.50-0.73) and survivors (0.61; IQR 0.52-0.73; p = 0.63) and it was not predictive of mortality (OR 0.68; 95% CI 0.18-2.52; p = 0.55). Shunt negatively correlated with admission oxygen saturation (R -0.533; p<0.0001) whereas VA/Q was not (R 0.1137; p = 0.12). INTERPRETATION: Shunt, not VA/Q mismatch, was associated with worsening hypoxia, though calculating shunt was not of prognostic value. This study adds to our understanding of the pathophysiology of hypoxaemia in COVID-19. Our inexpensive and reliable technique may provide further insights into the pathophysiology of hypoxia in other respiratory diseases.
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COVID-19 , Pneumopatias , Humanos , Feminino , Idoso , Masculino , Relação Ventilação-Perfusão/fisiologia , Hipóxia , Oximetria/métodos , Oxigênio/fisiologiaRESUMO
This study seeks to understand the value of ventilation imaging in pregnant patients imaged for suspected pulmonary embolism (PE). Ventilation-perfusion (VQ) scans in this high-risk population were compared to ventilation-only scans. We hypothesize that in this relatively healthy population, the exclusion of ventilation scans will not impact the rate of scans interpreted as positive. This retrospective blinded comparative reader study on collated VQ scans performed on pregnant patients in the course of routine clinical care in aâ >â 5 year period (03/2012 to 07/2017). Each set of VQ and perfusion only (Q) studies were reviewed by 8 readers (4 nuclear radiology fellows and 4 nuclear medicine faculty) in random order; the Q scans simply omitted the ventilation images. Readers recorded each study as PE, no PE, or non-diagnostic (prospective investigative study of acute PE diagnosis classifications). Logistic mixed effects models were used to test the association between scan type (VQ vs Q). 203 pairs of studies in 197 patients were included (6 patients had 2 scans). Subjects ranged from 14 to 45 years of age, with a median 28 years. A significant association between scan type and positive/negative classification. Q-scans received more positive classifications than VQ-scans (median of 7.6% vs 6.7%). No association was seen between scan type and positive/indeterminate classification, nor between scan type and negative/indeterminate classification. The exclusion of ventilation images in VQ-scans was associated with a higher rate of positive studies, but this difference was small (<1%). Given the overwhelmingly normal percentage of Q-exams (>90% in our study), and the benefits of omitting ventilation imaging, perfusion-only imaging should be considered a reasonable option for imaging the pregnant patient to exclude PE.
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Gestantes , Embolia Pulmonar , Adulto , Feminino , Humanos , Perfusão , Gravidez , Estudos Prospectivos , Embolia Pulmonar/diagnóstico por imagem , Estudos Retrospectivos , Relação Ventilação-PerfusãoRESUMO
Busana et al. (doi.org/10.1152/japplphysiol.00871.2020) published 5 patients with COVID-19 in whom the fraction of non-aerated lung tissue had been quantified by computed tomography. They assumed that shunt flow fraction was proportional to the non-aerated lung fraction, and, by randomly generating 106 different bimodal distributions for the ventilation-perfusion ([Formula: see text]) ratios in the lung, specified as sets of paired values {[Formula: see text]}, sought to identify as solutions those that generated the observed arterial partial pressures of CO2 and O2 (PaCO2 and PaO2). Our study sought to develop a direct method of calculation to replace the approach of randomly generating different distributions, and so provide more accurate solutions that were within the measurement error of the blood-gas data. For the one patient in whom Busana et al. did not find solutions, we demonstrated that the assumed shunt flow fraction led to a non-shunt blood flow that was too low to support the required gas exchange. For the other four patients, we found precise solutions (prediction error < 1x10-3 mmHg for both PaCO2 and PaO2), with distributions qualitatively similar to those of Busana et al. These distributions were extremely wide and unlikely to be physically realisable, because they predict the maintenance of very large concentration gradients in regions of the lung where convection is slow. We consider that these wide distributions arise because the assumed value for shunt flow is too low in these patients, and we discuss possible reasons why the assumption relating to shunt flow fraction may break down in COVID-19 pneumonia.