Abstract
Background: Pulmonary microcirculation abnormalities are the main determinants of pulmonary arterial hypertension (PAH) pathophysiology. We hypothesized that PAH patients have peripheral tissue microcirculation alterations that might benefit from hyperoxic breathing. The aim of this study was to evaluate peripheral muscle microcirculation before and after hyperoxic breathing by Near Infra-Red Spectroscopy (NIRS).
Methods: Eight PAH patients, eight healthy subjects (controls) matched for age, gender and BMI as well as 16 patients with chronic heart failure (CHF) matched for functional capacity with PAH patients underwent NIRS evaluation. Tissue O2 saturation (StO2,%), defined as the percentage of hemoglobin saturation in the microvasculature compartments, was measured on the thenar muscle. Subsequently, 3-min brachial artery occlusion technique was applied before, during, and after 15 min of 100% of O2-breathing. Main measurements included oxygen consumption rate (OCR,%/min), the reactive hyperemia time (RHT,min), the time needed for StO2 to reach its baseline values after the release of the occlusion.
Results: PAH patients had a significantly lower resting StO2 (65.8±14.9 versus 82.1±4.0,P=0.005), a trend to a decreased OCR (35.3±9.1 versus 43.4±19.7,P=0.6) and a significant higher RHT (3.0±0.6 versus 2.0±0.3,P<0.001) comparing to controls. PAH patients had also lower StO2 (P=0.08) and peripheral arterial oxygen saturation (P=0.01) values, and higher RHT (P=0.016) compared to CHF patients. After hyperoxic breathing in PAH, there was an increase in StO2 (65.8±14.9 to 71.4±14.5,P<0.05), while OCR was reduced (35.3±9.1 to 25.1±6.6,P<0.05) and RHT had a further increase (3.0±0.6 to 4.2±0.7,P<0.01).
Conclusions: PAH patients exhibit significant impairments of peripheral muscle microcirculation during evaluation with NIRS VOT. Specifically, PAH patients exhibit decreased StO2, possibly due to hypoxemia and slower RHT, possibly due to endothelium dysfunction and peripheral systemic vasoconstriction. Acute hyperoxic breathing improves resting StO2 as an expression of higher oxygen delivery, whilst it deteriorates OCR and RHT during reperfusion possibly due to increased oxidative stress and evoked vasoconstriction.
- endothelium
- microcirculation
- Near Infra-Red Spectroscopy
- oxygen breathing
- pulmonary arterial hypertension
Footnotes
- Corresponding Author: Stavros Dimopoulos MD, 1st Critical Care Medicine Department, Cardiopulmonary Exercise Testing and Rehabilitation Laboratory, “Evgenidio Hospital”, National & Kapodestrian University of Athens, Papadiamantopoulou str, 20, Athens, 11528, Greece, Tel: 0030-210-7236743, Fax: 0030-210-7242785, Email:a-icu{at}med.uoa.gr
The authors have no competing interests.
This work was supported by a grant from the special account for research grants of the National and Kapodistrian University of Athens, Athens, Greece.
- Copyright © 2013 by Daedalus Enterprises Inc.