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Acta Physiol (Oxf). 2012 Jul;205(3):341-8. doi: 10.1111/j.1748-1716.2012.02419.x. Epub 2012 Feb 18.

Respiratory variations in pulmonary and systemic blood flow in healthy humans.

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Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.



Cardiovascular oscillations are tightly coupled to respiration. Respiratory sinus arrhythmia (RSA) is an important part of heart rate variability with unknown function. Stroke volumes from the right (r-SV) and left (l-SV) side of the heart are assumed to vary differently with respiration, but have not previously been recorded non-invasively and simultaneously in humans. The present study introduces an improved technique for capturing respiratory variations in r-SV.


Six young volunteers were investigated during spontaneous and metronome-paced breathing in the left lateral decubitus position. Heart rate (HR, from ECG), l-SV (from finger blood arterial pressure curve) and r-SV (pulsed ultrasound Doppler) were recorded. Left and right cardiac outputs (l-CO and r-CO) were calculated beat by beat from HR, l-SV and r-SV. Respiratory variations in cardiovascular variables and phase angles were estimated by spectral analysis at respiratory frequency (0.15-0.40 Hz).


The amplitude of respiratory variations in l-CO was 17% of r-CO (94% CI (6%, 35%), P=0.03). The amplitude of the respiratory variations in l-SV was not different from r-SV (74%, 94% CI (50%, 127%) non-significant). Increases in HR and r-SV were in phase with inspiration, while l-SV decreased during inspiration.


The amplitude of respiratory variations in l-CO is significantly smaller than in r-CO. Respiratory variations in HR and in l-SV are in inverse phase; thus, RSA buffers respiratory variations in l-SV. RSA plays an important role in reducing oscillations in systemic blood flow resulting from respiratory changes in venous return.

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