Scintigraphic diagnosis of a right to left shunt in end-stage lung disease

Hypoxemia in COVID-19 patients: An hypothesis

The current SARS-Cov-2 virus pandemic challenges critical care physicians and other caregivers to find effective treatment for desperately ill patients - especially those with sudden and extreme hypoxemia. Unlike patients with other forms of Acute Respiratory Distress Syndrome, these patients do not exhibit increased lung stiffness or dramatic dyspnea., even in the presence of arterial blood oxygen levels lower than that seen normally in mixed venous blood. Urgent intubation and mechanical ventilation with high inflation pressures and raised inhaled oxygen concentration have proved unhelpful or worse, but why? Our Hypothesis is that sudden opening of a previously undetected probe-patent foramen ovale (PPFO) may explain this mystery. As hypoxemia without acidosis is a rather weak stimulus of dyspnea or increased ventilation, and opening of such an intracardiac shunt would not worsen lung mechanical properties, the absence of dramatic symptom changes would not be surprising. We point out the high frequency of PFO both in life and at autopsy, and the physiological evidence of large shunt fractions found in Covid-19 patients. Published evidence of hypercoagulability and abundant evidence of pulmonary emboli found at autopsy are in accord with our hypothesis, as they would contribute to raised pressure in the pulmonary arteries and right heart chambers, potentially causing a shunt to open. We review the interaction between viral corona spike protein and ACE-2 receptors present on the surface of alveolar lining cells, and contribution to hypercoagulabilty caused by the spike protein. Search for an open PFO after a large drop in arterial oxygen saturation can be performed at the bedside with a variety of well-established techniques including bedside echocardiography, nitrogen washout test, and imaging studies. Potential treatments might include balloon or patch closure of the shunt, and various drug treatments to lower pulmonary vascular resistance.

Physiology of the lung in idiopathic pulmonary fibrosis

The clinical expression of idiopathic pulmonary fibrosis (IPF) is directly related to multiple alterations in lung function. These alterations derive from a complex disease process affecting all compartments of the lower respiratory system, from the conducting airways to the lung vasculature. In this article we review the profound alterations in lung mechanics (reduced lung compliance and lung volumes), pulmonary gas exchange (reduced diffusing capacity, increased dead space ventilation, chronic arterial hypoxaemia) and airway physiology (increased cough reflex and increased airway volume), as well as pulmonary haemodynamics related to IPF. The relative contribution of these alterations to exertional limitation and dyspnoea in IPF is discussed.

Physiological impairment in IPF is complex and involves all compartments of the respiratory systemhttp://ow.ly/gyao30hdHUb

Ventilation/perfusion lung scintigraphy: what is still needed? A review considering technetium-99m-labeled macro-aggregates of albumin

Lung perfusion scintigraphy (LPS) with technetium-99m-labeled macro-aggregates of albumin (Tc-99m-MAA) is well established in the diagnostic of pulmonary embolism (PE). In the last decade, it was shown that single-photon emission computer tomography (SPECT) acquisition of LPS overcame static scintigraphy. Furthermore, there are rare indications for LPS, such as preoperative quantification of regional lung function prior to lung resection or transplantation, optimization of lung cancer radiation therapy, quantification of right-left shunt, planning of intra-arterial chemotherapy, and several rare indications in pediatrics. Moreover, LPS with Tc-99m-MAA is a safe method with low radiation exposure. PE can also be diagnosed by spiral computer tomography (CT), ultrasound, magnetic resonance angiography, or pulmonary angiography (PA, former gold standard). The present review considers all these methods, especially spiral CT, and compares them with LPS with respect to sensitivity and specificity and gives an overview of established and newer publications. It shows that LPS with Tc-99m-MAA represents a diagnostic method of continuing value for PE. In comparison with spiral CT and/or PA, LPS is not to be defeated as mentioned also by the most actual Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) II reports. This applies in particular to chronic or recurring embolisms, whereas currently spiral CT may be of greater value for major or life-threatening embolisms. At present, LPS cannot be replaced by other methods in some applications, such as pediatrics or in the quantification of regional pulmonary function in a preoperative context or prior to radiation therapy. LPS still has a place in the diagnostics of PE and is irreplaceable in several rare indications as described earlier.

Renal Uptake on Lung Perfusion Scintigraphy in a Patient With Primary Pulmonary Hypertension

An 18-year-old woman presented with primary pulmonary hypertension (PPH) and was hospitalized because of hemoptysis and was referred to our department for a differential diagnosis pulmonary thromboembolism. Doppler ultrasonography of the lower extremities was normal. Echocardiography and cardiac catheterization showed right ventricular dilatation and increased pulmonary artery pressure without anatomic (intracardiac) shunt. The mean pulmonary arterial pressure was 110 mm Hg. Tc-99m MAA lung perfusion scans showed nonsegmental patchy defects. Extrapulmonary renal uptake and increased systemic deposition of radiotracer were seen in the MAA scintigraphy. It could be related to a functional intrapulmonary shunt resulting in increasing pressure in the pulmonary artery in PPH.

Interatrial Right-to-Left Shunt after Lung Surgery: Diagnostic Value of Perfusion Lung Scanning

A 61-year-old woman presented with platypnea and orthodeoxia after right pneumonectomy for lung cancer. A perfusion lung scan taken after tracer injection in the sitting position showed an extrapulmonary uptake of radioactivity consistent with a right-to-left shunt. Such extrapulmonary uptake was no longer evident when tracer was injected in supine posture. The authors emphasize the value of perfusion lung scanning in the assessment of patients with unexplained dyspnea after thoracic surgery.