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Pulmonary gas exchange
Published in Andrew M. Luks, Philip N. Ainslie, Justin S. Lawley, Robert C. Roach, Tatum S. Simonson, Ward, Milledge and West's High Altitude Medicine and Physiology, 2021
Andrew M. Luks, Philip N. Ainslie, Justin S. Lawley, Robert C. Roach, Tatum S. Simonson
Another suggested source of right-to-left shunt is intrapulmonary arteriovenous anastomoses (Lovering et al. 2015). Following three weeks of acclimatization to 5050 m in volunteers without a PFO, it was reported that the bubble score, an index of blood flow through the intrapulmonary arteriovenous anastomoses assessed using transthoracic saline contrast echocardiography, was significantly reduced at maximal exercise when compared to sea level (Foster et al. 2014). These findings, in the absence of any changes in the (A-a)ΔO2, were confirmed upon measurement within a few hours of arrival to 5260 m; similar findings were also apparent in a chamber study in both normoxic and hypobaric hypoxia (Petrassi et al. 2018). The physiological significance of intrapulmonary arteriovenous anastomoses at altitude remain unclear but they do not seem important from the perspective of gas exchange efficiency.
Heart disease in pregnancy
Published in Clive Handler, Gerry Coghlan, Nick Brown, Management of Cardiac Problems in Primary Care, 2018
Clive Handler, Gerry Coghlan, Nick Brown
This is a right to left shunt, most commonly due to a large ventricular septal defect. Patients have pulmonary hypertension with equal pressures and resistances in the pulmonary and systemic circulations. At rest the shunt is bidirectional. Exertion decreases the systemic vascular resistance and this increases the right to left shunt, with arterial desaturation and fatigue. The pulmonary blood flow cannot increase with increased exercise and increased demands, so exercise results in increased arterial desaturation due to increased right to left shunting.
An aid to neuroimaging
Published in Christos Tziotzios, Jesse Dawson, Matthew Walters, Kennedy R Lees, Stroke in Practice, 2017
Christos Tziotzios, Jesse Dawson, Matthew Walters, Kennedy R Lees
Transoesophageal echocardiography is the gold standard investigation for detection of a cardiac right-to-left shunt. Sensitivity can be improved by use of contrast media, and although sensitivity is similar to TCD-based assessment, it is more specific as it allows direct visualisation of the atrial septum and distinction between PFO and other cardiac defects. In some cases, transthoracic echocardiography provides diagnostic clarity but its sensitivity is less. The disadvantages of transoesophageal echocardiography are that it is associated with a small but important risk and requires sedation and participants cannot perform Valsalva manoeuvres during the test.
Posture Dependent Hypoxia Following Lobectomy: The Achilles Tendon of the Lung Surgeon?
Published in Journal of Investigative Surgery, 2022
Athanassios Krassas, Aikaterini Tzifa, Stavroula Boulia, Kosmas Iliadis
POS is a rare and complex phenomenon that is not clearly understood. Various congenital cardiac malformations can be responsible for right to left shunting across an interatrial communication, but pulmonary and abdominal conditions may also be responsible for POS symptomatology (table 4)11. It is usually linked with a right to left shunt either intracardiac or intrapulmonary. The presence of an anatomical defect is not linked to the symptom’s manifestations. PFO is the most associated anatomical defect but also other malformations such as atrial septal defect or atrial septal aneurysms have been found. Usually, the isolated PFO do not produce a right-to-left shunt, because the PLa is 1-3 mmHg higher than the PRa leading to functional closure. This is the reason why PFO is found in 27% of adults but POS is rare. The main explanation of this discrepancy lies in the fact that for the manifestation of the syndrome two distinct conditions must co-exist: an anatomical and a functional factor. Pulmonary resection (pneumonectomy/lobectomy), as well as pericardial effusion, constrictive pericarditis, ascending aorta aneurysm and compression of the right heart chambers by liver lesions) are amongst the anatomical causes for the phenomenon. Functional factors include an elevated PRa or a condition that permits the redirection of blood stream through the shunt when the patient is moving from a recumbent to a sitting or standing position, thus producing positional hypoxia and dyspnea.
Patent foramen ovale closure for secondary prevention of cryptogenic stroke
Published in Expert Review of Cardiovascular Therapy, 2021
Dhaval Kolte, Igor F. Palacios
The PFO and atrial septal aneurysm (ASA) study group followed 581 ischemic stroke patients under the age of 55 years of age [10]. The patients were started on aspirin within 3 months of their neurological event and followed for a period of 4 years. The patients were divided into groups depending on the characteristics of the inter-atrial septum. Mas et al. [10] found that the presence of both atrial septal abnormalities was a significant predictor of increased risk of recurrent cerebrovascular events, whereas the presence of a PFO alone or an ASA alone was not. Moreover, their finding suggested that aspirin as secondary prevention for recurrent events may not be enough for this subgroup of patients. These findings are in agreement with the findings of other studies, especially in patients with right-to-left shunt at rest [11]. Stone et al. [12], followed prospectively a group of stroke patients found to have a PFO during TEE and divided them into ‘large’ degree shunt (≥20 microbubbles) and ‘small’ degree shunt (≥3 but <20 microbubbles). Patients with ‘large’ shunt had a 31% incidence of recurrent event versus none in the ‘small’ shunt group despite the use of antiplatelet therapy and/or anticoagulation. Therefore, patients with ‘large’ shunts should be considered at a significantly higher risk for subsequent adverse neurologic events.
Clinical outcomes for congenital heart disease patients presenting with infective endocarditis
Published in Expert Review of Cardiovascular Therapy, 2020
Imaging lesion(s) and cardiac location(s) is one of the major criteria for diagnosis of IE [37–40]. IEs of the right heart are more frequent in the population of patients with congenital heart disease, and mainly target left to right shunt (interventricular communication), or tricuspid and pulmonary valve disease, or prosthetic material (aortopulmonary anastomosis, ventriculopulmonary tube, pacemaker with endocavitary probe). In this case, the vegetations are located on the right side of the VSD and may also extend on the anterior wall of the right ventricle (LV to RV jet of the VSD), the tricuspid valve and/or the pulmonary valve. The left heart IE can spread to the right heart in case of a left to right shunt, the same as the right heart IE can reach the left heart in the presence of a right to left shunt (unrepaired tetralogy of Fallot in children for example, or complex CHD and univentricular heart in adults).