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Hypoxia, not pulmonary vascular pressure induces blood flow through intrapulmonary arteriovenous anastomoses

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Author
Tremblay, Joshua
Lovering, Andrew T.
Ainslie, Philip
Stembridge, Mike
Burgess, Keith R.
Bakker, Akke
Donnelly, Joseph
Lucas, Samuel J.E.
Lewis, Nia C. S.
Dominelli, Paolo B.
Henderson, William R.
Dominelli, Giulio S.
Sheel, A. William
Foster, Glen
Date
2014-12-23
Acceptance date
2014-11-10
Type
Article
Publisher
The Physiological Society
Metadata
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Abstract
Blood flow through intrapulmonary arteriovenous anastomoses (IPAVA) is increased with exposure to acute hypoxia and has been associated with pulmonary artery systolic pressure (PASP). We aimed to determine the direct relationship between blood flow through IPAVA and PASP in 10 participants with no detectable intracardiac shunt by comparing: (1) isocapnic hypoxia (control); (2) isocapnic hypoxia with oral administration of acetazolamide (AZ; 250 mg, three times-a-day for 48 h) to prevent increases in PASP, and (3) isocapnic hypoxia with AZ and 8.4% NaHCO3 infusion (AZ+HCO3-) to control for AZ-induced acidosis. Isocapnic hypoxia (20 min) was maintained by end-tidal forcing, blood flow through IPAVA was determined by agitated saline contrast echocardiography and PASP was estimated by Doppler ultrasound. Arterial blood samples were collected at rest before each isocapnic-hypoxia condition to determine pH, [HCO3-], and PaCO2. AZ decreased pH (-0.08 ± 0.01), [HCO3-] (-7.1 ± 0.7 mmol/l), and PaCO2 (-4.5 ± 1.4 mmHg; p<0.01), while intravenous NaHCO3 restored arterial blood gas parameters to control levels. Although PASP increased from baseline in all three hypoxic conditions (p<0.05), a main effect of condition expressed an 11 ± 2% reduction in PASP from control (p<0.001) following AZ administration while intravenous NaHCO3 partially restored the PASP response to isocapnic hypoxia. Blood flow through IPAVA increased during exposure to isocapnic hypoxia (p<0.01) and was unrelated to PASP, cardiac output and pulmonary vascular resistance for all conditions. In conclusion, isocapnic hypoxia induces blood flow through IPAVA independent of changes in PASP and the influence of AZ on the PASP response to isocapnic hypoxia is dependent upon the H+ concentration or PaCO2. Abbreviations list: AZ, acetazolamide; FEV1, forced expiratory volume in 1 second; FIO2, fraction of inspired oxygen; FVC, forced vital capacity; Hb, total haemoglobin; HPV, hypoxic pulmonary vasoconstriction; HR, heart rate; IPAVA, intrapulmonary arteriovenous anastomoses; MAP, mean arterial pressure; PASP, pulmonary artery systolic pressure; PETCO2, end-tidal partial pressure of carbon dioxide; PETO2, end-tidal partial pressure of oxygen; PFO, patent foramen ovale; PVR, pulmonary vascular resistance; Q̇c, cardiac output; RVOT, right ventricular outflow tract; SpO2, oxyhaemoglobin saturation; SV, stroke volume; TRV, tricuspid regurgitant velocity; V̇E, minute ventilation; VTI, velocity-time integral
Journal/conference proceeding
The Journal of Physiology;
Citation
Tremblay, J.C., Lovering, A.T., Ainslie, P.N., Stembridge, M., Burgess, K.R., Bakker, A., Donnelly, J., Lucas, S.J., Lewis, N., Dominelli, P.B. and Henderson, W.R. (2015) 'Hypoxia, not pulmonary vascular pressure, induces blood flow through intrapulmonary arteriovenous anastomoses', The Journal of Physiology, 593(3), pp.723-737.
URI
http://hdl.handle.net/10369/8184
DOI
http://dx.doi.org/10.1113/jphysiol.2014.282962
Description
This article was published in The Journal of Physiology on 23 December 2014 (online), available at http://dx.doi.org/10.1113/jphysiol.2014.282962
Rights
http://www.rioxx.net/licenses/all-rights-reserved
Sponsorship
Cardiff Metropolitan University (Grant ID: Cardiff Metropolian (Internal))
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