Ventilation Perfusion Functional Difference Images in Lung Spect: A Quantitative Improvement on Ventilation Perfusion Ratio

Purpose: Ventilation (V) perfusion (Q) SPECT imaging is important in the diagnostics of lung diseases such as pulmonary embolism, chronic obstructive pulmonary disease and recently in COVID-19 lung disease. The combined assessment of ventilation and perfusion permits the identification of classical mismatched and reverse mismatched defects, especially when these two parameters are combined in one measure as the ventilation perfusion ratio. Unfortunately, the ratio is only linear for ventilation and the scale is not symmetrical regarding classical and reversed mismatches. Small perfusion values give rise to artifacts. The scaled ventilation perfusion difference is presented as an alternative. Material(s) and Method(s): VQ SPECT was performed on patients with and without defects. Kr-81m was used as a ventilation tracer and MAA labelled with Tc-99m as a perfusion tracer. Ratio is defined as V/kQ and difference as V-kQ, where k is a scaling factor. The iterative z-map method was applied for determining the scaling factor for ratio and difference images yielding a ratio of one and zero difference for matched ventilation and perfusion. Clinical thresholds for both the difference images are derived resulting in color maps of relevant mismatches with an absolute ratio larger than the arbitrary value of two. Result(s): The relative difference is in second order proportional to the logarithm of the ratio, and has a scale going from -1 to +1, where -1 is perfusion only and +1 is ventilation only. Still the diagnostic value is hampered by the fact that areas with both low perfusion and ventilation can have high ratios. Therefore, the scaled (functional) difference is presented. Ratio, relative difference and scaled difference have been investigated in ten patients and are shown for three patients (one without defects). Ratio and relative difference images suffer from a visual overexposure effect as is clearly visible for the respiratory tract. One patient with an area in a bottom lung with a very low perfusion and slightly decreased ventilation demonstrated overflow problems of the intensity in ratio images and an overestimation of the mismatched area in both the ratio and relative difference images. Conclusion(s): While the relative ventilation perfusion-difference is a promising improvement of the ventilation-perfusion ratio, because it has a symmetrical scale and is bound on a closed domain, a better diagnostic value and functionality might be obtained by utilizing the scaled functional difference. The latter one seems superior to both the relative difference and ratio.Copyright © 2023 Southern Society for Clinical Investigation.

Sildenafil for treating patients with COVID-19 and perfusion mismatch: a pilot randomized trial.

BACKGROUND: SARS-CoV-2 seems to affect the regulation of pulmonary perfusion. Hypoperfusion in areas of well-aerated lung parenchyma results in a ventilation-perfusion mismatch that can be characterized using subtraction computed tomography angiography (sCTA). This study aims to evaluate the efficacy of oral sildenafil in treating COVID-19 inpatients showing perfusion abnormalities in sCTA. METHODS: Triple-blinded, randomized, placebo-controlled trial was conducted in Chile in a tertiary-care hospital able to provide on-site sCTA scans and ventilatory support when needed between August 2020 and March 2021. In total, 82 eligible adults were admitted to the ED with RT-PCR-confirmed or highly probable SARS-COV-2 infection and sCTA performed within 24 h of admission showing perfusion abnormalities in areas of well-aerated lung parenchyma; 42 were excluded and 40 participants were enrolled and randomized (1:1 ratio) once hospitalized. The active intervention group received sildenafil (25 mg orally three times a day for seven days), and the control group received identical placebo capsules in the same way. Primary outcomes were differences in oxygenation parameters measured daily during follow-up (PaO2/FiO2 ratio and A-a gradient). Secondary outcomes included admission to the ICU, requirement of non-invasive ventilation, invasive mechanical ventilation (IMV), and mortality rates. Analysis was performed on an intention-to-treat basis. RESULTS: Totally, 40 participants were enrolled (20 in the placebo group and 20 in the sildenafil group); 33 [82.5%] were male; and median age was 57 [IQR 41-68] years. No significant differences in mean PaO2/FiO2 ratios and A-a gradients were found between groups (repeated-measures ANOVA p = 0.67 and p = 0.69). IMV was required in 4 patients who received placebo and none in the sildenafil arm (logrank p = 0.04). Patients in the sildenafil arm showed a significantly shorter median length of hospital stay than the placebo group (9 IQR 7-12 days vs. 12 IQR 9-21 days, p = 0.04). CONCLUSIONS: No statistically significant differences were found in the oxygenation parameters. Sildenafil treatment could have a potential therapeutic role regarding the need for IMV in COVID-19 patients with specific perfusion patterns in sCTA. A large-scale study is needed to confirm these results. TRIAL REGISTRATION: Sildenafil for treating patients with COVID-19 and perfusion mismatch: a pilot randomized trial, NCT04489446, Registered 28 July 2020, https://clinicaltrials.gov/ct2/show/NCT04489446 .

Real-time effects of PEEP and tidal volume on regional ventilation and perfusion in experimental lung injury.

BACKGROUND: Real-time bedside information on regional ventilation and perfusion during mechanical ventilation (MV) may help to elucidate the physiological and pathophysiological effects of MV settings in healthy and injured lungs. We aimed to study the effects of positive end-expiratory pressure (PEEP) and tidal volume (VT) on the distributions of regional ventilation and perfusion by electrical impedance tomography (EIT) in healthy and injured lungs. METHODS: One-hit acute lung injury model was established in 6 piglets by repeated lung lavages (injured group). Four ventilated piglets served as the control group. A randomized sequence of any possible combination of three VT (7, 10, and 15 ml/kg) and four levels of PEEP (5, 8, 10, and 12 cmH2O) was performed in all animals. Ventilation and perfusion distributions were computed by EIT within three regions-of-interest (ROIs): nondependent, middle, dependent. A mixed design with one between-subjects factor (group: intervention or control), and two within-subjects factors (PEEP and VT) was used, with a three-way mixed analysis of variance (ANOVA). RESULTS: Two-way interactions between PEEP and group, and VT and group, were observed for the dependent ROI (p = 0.035 and 0.012, respectively), indicating that the increase in the dependent ROI ventilation was greater at higher PEEP and VT in the injured group than in the control group. A two-way interaction between PEEP and VT was observed for perfusion distribution in each ROI: nondependent (p = 0.030), middle (p = 0.006), and dependent (p = 0.001); no interaction was observed between injured and control groups. CONCLUSIONS: Large PEEP and VT levels were associated with greater pulmonary ventilation of the dependent lung region in experimental lung injury, whereas they affected pulmonary perfusion of all lung regions both in the control and in the experimental lung injury groups.

Lung Function and Symptoms in Post-COVID-19 Patients: A Single-Center Experience.

OBJECTIVE: To address the lack of information about clinical sequelae of coronavirus disease 2019 (COVID-19). PATIENTS AND METHODS: Previously hospitalized COVID-19 patients who were attending the outpatient clinic for post-COVID-19 patients (ASST Ovest Milanese, Magenta, Italy) were included in this retrospective study. They underwent blood draw for complete blood count, C-reactive protein, ferritin, D-dimer, and arterial blood gas analysis and chest high-resolution computed tomography (HRCT) scan. The primary endpoint was the assessment of blood gas exchanges after 3 months. Other endpoints included the assessment of symptoms and chest HRCT scan abnormalities and changes in inflammatory biomarkers after 3 months from hospital admission. RESULTS: Eighty-eight patients (n = 65 men; 73.9%) were included. Admission arterial blood gas analysis showed hypoxia and hypocapnia and an arterial partial pressure of oxygen/fractional inspired oxygen ratio of 271.4 (interquartile range [IQR]: 238-304.7) mm Hg that greatly improved after 3 months (426.19 [IQR: 395.2-461.9] mm Hg, P<.001). Forty percent of patients were still hypocapnic after 3 months. Inflammatory biomarkers dramatically improved after 3 months from hospitalization. Fever, resting dyspnea, and cough were common at hospital admission and improved after 3 months, when dyspnea on exertion and arthralgias arose. On chest HRCT scan, more than half of individuals still presented with interstitial involvement after 3 months. Positive correlations between the interstitial pattern at 3 months and dyspnea on admission were found. C-reactive protein at admission was positively associated with the presence of interstitial involvement at follow-up. The persistence of cough was associated with presence of bronchiectasis and consolidation on follow-up chest HRCT scan. CONCLUSION: Whereas inflammatory biomarker levels normalized after 3 months, signs of lung damage persisted for a longer period. These findings support the need for implementing post-COVID-19 outpatient clinics to closely follow-up COVID-19 patients after hospitalization.

Pathophysiology of light phenotype SARS-CoV-2 interstitial pneumonia: from histopathological features to clinical presentations.

Little is known about the light phenotype of SARS-CoV-2 pneumonia, which behaves in an unusual way, unlike other known respiratory diseases. We believe that the histopathological features of early COVID-19 could be considered the pathophysiological hallmark of this disease. Lung cryobiopsies show almost pristine alveoli, enlarged/hyperplasic alveolar capillaries along with dilatation of the post capillary pulmonary venules. Hypoxemia could therefore be explained by a reduction of the normal V/Q ratio, due to blood overflow around well ventilated alveoli. This could clarify typical manifestations of type L COVID-19, such as happy hypoxemia, response to awake prone positioning, response to PEEP/CPAP and platypnea orthodeoxia.

COVID-19: What Iodine Maps From Perfusion CT can reveal-A Prospective Cohort Study.

BACKGROUND: Subtraction CT angiography (sCTA) is a technique used to evaluate pulmonary perfusion based on iodine distribution maps. The aim of this study is to assess lung perfusion changes with sCTA seen in patients with COVID-19 pneumonia and correlate them with clinical outcomes. MATERIAL AND METHODS: A prospective cohort study was carried out with 45 RT-PCR-confirmed COVID-19 patients that required hospitalization at three different hospitals, between April and May 2020. In all cases, a basic clinical and demographic profile was obtained. Lung perfusion was assessed using sCTA. Evaluated imaging features included: Pattern predominance of injured lung parenchyma in both lungs (ground-glass opacities, consolidation and mixed pattern) and anatomical extension; predominant type of perfusion abnormality (increased perfusion or hypoperfusion), perfusion abnormality distribution (focal or diffuse), extension of perfusion abnormalities (mild, moderate and severe involvement); presence of vascular dilatation and vascular tortuosity. All participants were followed-up until hospital discharge searching for the development of any of the study endpoints. These endpoints included intensive-care unit (ICU) admission, initiation of invasive mechanical ventilation (IMV) and death. RESULTS: Forty-one patients (55.2 ± 16.5 years, 22 men) with RT-PCR-confirmed SARS-CoV-2 infection and an interpretable iodine map were included. Patients with perfusion anomalies on sCTA in morphologically normal lung parenchyma showed lower Pa/Fi values (294 ± 111.3 vs. 397 ± 37.7, p = 0.035), and higher D-dimer levels (1156 ± 1018 vs. 378 ± 60.2, p < 0.01). The main common patterns seen in lung CT scans were ground-glass opacities, mixed pattern with predominant ground-glass opacities and mixed pattern with predominant consolidation in 56.1%, 24.4% and 19.5% respectively. Perfusion abnormalities were common (36 patients, 87.8%), mainly hypoperfusion in areas of apparently healthy lung. Patients with severe hypoperfusion in areas of apparently healthy lung parenchyma had an increased probability of being admitted to ICU and to initiate IMV (HR of 11.9 (95% CI 1.55-91.9) and HR 7.8 (95% CI 1.05-61.1), respectively). CONCLUSION: Perfusion abnormalities evidenced in iodine maps obtained by sCTA are associated with increased admission to ICU and initiation of IMV in COVID-19 patients.