Hypoxia-induced intrapulmonary arteriovenous shunting at rest in healthy humans

Abstract

Intrapulmonary arteriovenous (IPAV) shunting has been shown to occur at rest in some subjects breathing a hypoxic gas mixture [fraction of inspired oxygen (FI(O(2))) = 0.12] for brief periods of time. In the present study we set out to determine if IPAV shunting could be induced at rest in all subjects exposed to hypoxia for 30 min. Twelve subjects (6 women) breathed four levels of hypoxia (FI(O(2)) = 0.16, 0.14, 0.12, and 0.10) for 30 min each in either an ascending or descending order with a 15-min normoxic break between bouts. Saline contrast echocardiography was used to detect IPAV shunt and a shunt score (0-5) was assigned based on contrast in the left ventricle with a shunt score ≥ 2 considered significant. Pulmonary artery systolic pressure (PASP) was determined using Doppler ultrasound. The total number of subjects demonstrating shunt scores ≥ 2 for FI(O(2)) = 0.16, 0.14, 0.12, and 0.10 was 1/12, 7/12, 9/12, and 12/12, respectively. Shunt scores were variable between subjects but significantly greater than normoxia for FI(O(2)) = 0.12 and 0.10. Shunt scores correlated with peripheral measurements of arterial oxygen saturation (SpO(2)) (r(w) = -0.67) and PASP (r(w) = 0.44), despite an increased shunt score but no increase in PASP while breathing an FI(O(2)) = 0.12. It is unknown how hypoxia induces the opening of IPAV shunts, but these vessels may be controlled via similar mechanisms as systemic vessels that vasodilate in response to hypoxia. Despite intersubject variability our results indicate significant IPAV shunting occurs at rest in all subjects breathing an FI(O(2)) = 0.10 for 30 min.

Effects of Balloon Pulmonary Angioplasty on Oxygenation in Patients With Chronic Thromboembolic Pulmonary Hypertension – Importance of Intrapulmonary Shunt –

“…25 It has been reported that intrapulmonary shunt varies by the fraction of inspired O2 and that hypoxic conditions increase intrapulmonary shunt. 26 To minimize the influence of variation in SaO2 on intrapulmonary shunt, we used intrapulmonary shunt during O2 administration for the analyses. After administration of O2, we performed blood gas analyses again to obtain intrapulmonary shunt, which was calculated with the following formula: 25…”

Transient Intrapulmonary Shunting in a Patient Treated With β2-Adrenergic Agonists for Status Asthmaticus

“…We and others have documented the presence of transiently recruitable IPAVs in ∼90% of healthy humans. [2][3][4]8,9,[29][30] Although the size of IPAVs has never been directly determined in humans under physiologic conditions, data from isolated lung and intact animal studies suggest that these pathways are large (.200 mm) and are located early in the pulmonary vascular tree. 1,[31][32][33] Why Is This Case Relevant to the Clinician?…”

“…Laurie et al demonstrated that both the level of hypoxia and the duration of the exposure influence IPAVs such that a mild hypoxic stimulus can be effective if it is prolonged. 30 Similarly, exposure to adrenergic stimuli may overcome the effects of hyperoxia if the dosing is prolonged. It is possible that if they had prolonged the infusion of epinephrine, they would also have observed IPAV recruitment despite the 100% O 2 breathing.…”

Detection of Intracardiac and Intrapulmonary Shunts at Rest and During Exercise Using Saline Contrast Echocardiography

“…Typically, 0.5-1 ml of air and 4-10 ml of saline are used to manually agitate between two syringes connected by stopcocks for a total injection volume of 10 ml (Otto, 2004;Feigenbaum, 2005;Woods et al, 2010). In a research setting, equal success has been achieved in detecting right-to-left shunts via intrapulmonary arteriovenous anastomoses using 0.5-1 ml of air and 3-5 ml of saline, for a total injection volume of 5 ml (Stickland & Lovering, 2006;Laurie et al, 2010;Lovering et al, 2010;Elliott et al, 2011a). The agitated saline mix solution should be injected as a bolus, forcibly by hand.…”

“…There are numerous scoring methods used in both clinical and research settings for semiquantification of right-to-left shunt with saline contrast bubbles (Barzilai et al, 1991;Lovering et al, 2008b;La Gerche et al, 2010;Laurie et al, 2010). These scoring methods take into account the density and spatial distribution of saline contrast bubbles in the left heart.…”