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Studying effect of respiration on total cavopulmonary connection flows using real-time cardiac magnetic resonance


Accurate measurement of vessel flows in the Total Cavopulmonary Connection (TCPC) can lead to better estimation of hemodynamics, which has been related to clinical outcomes in single ventricle patients. CMR is usually acquired in breath held conditions; however, respiratory effects can be considerable since the blood is passively routed to the lungs in Fontan patients. Here, we assessed the effect of respiration on caval and aortic flows using real time CMR images.


Eight single ventricle patients with TCPC palliation underwent resting cardiac magnetic resonance imaging at both free breathing (FB) and breath held (BH) conditions. Real time, through-plane phase encoded velocity mapping (PC-MRI) was performed in superior (SVC), and inferior (IVC) vena cava, and ascending (AAO) and descending (DAO) aorta. FB and BH resting flow (Q) waveforms were then obtained at each vessel (Figure 1-a, b). Respiratory cycle, inspiration and expiration periods were determined by tracking chest wall motion from the PC-MRI magnitude images (Figure 1-c, d). Pulsatility Index was calculated as PI=(Q_max-Q_min)/(2×Q_mean)×100 for a Cardiac (PI_card) or Respiratory (PI_resp) cycle. Significance of the difference in cycle-averaged vessel flows and PI between FB and BH conditions were investigated using paired t-test (*p < 0.05).

Figure 1
figure 1

Positioning of the region of interest when mapping IVC flow rate (a, b); and sample chest wall motion tracking at the end of expiration (c), and the end of inspiration (d) showing the minimum and maximum areas of the thoracic cavity during respiration, respectively.


Mean flows in all the vessels trended toward an increase with respiration compared to the BH conditions; however, only the increase in SVC flow was significant (1.5 vs. 1.3 L/min, *p < 0.05). IVC and SVC flows were markedly phasic with the respiratory cycle (Figure 2), and their flow pulsatility increased with respiration (PI_resp/PI_card = 1.0 ± 0.1, 0.9 ± 0.2, *2.0 ± 0.7, and 1.5 ± 0.1 in DAO, AAO, IVC, and SVC, respectively). The IVC and SVC flows were significantly higher at inspiration compared to expiration (*p < 0.05). On the other hand, no significant effect of respiration was observed on the AAO and DAO flow waveforms (Q_insp/Q_exp at FB [BH] = 1.0 ± 0.0[1.0 ± 0.1], 1.1 ± 0.1[1.0 ± 0.1], *1.8 ± 0.5[1.0 ± 0.1], and *1.7 ± 0.3[1.0 ± 0.1] in DAO, AAO, IVC, and SVC, respectively).

Figure 2
figure 2

Sample resting flow waveforms of IVC (top-left) and SVC (top-right) at free breathing (dashed line) and breath held (solid line) conditions, along with the respiratory cycle determined by tracking the chest wall motion (bottom).


A novel technique of measuring flow and tracking respiration with the same slice plane was presented, obviating the need for respiratory bellows. Using this technique, we demonstrated that respiratory effects dominate the venous flow but have little effect on systemic arterial flow in Fontan patients. However, the effect of breath holding on mean flows is fairly small, supporting the routine use of breath holding in assessing flows in single ventricle patients.


This study was supported by the National Heart, Lung, and Blood Institute Grants HL67622, HL098252, and HL089647.

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Open Access This article is published under license to BioMed Central Ltd. This is an Open Access article is distributed under the terms of the Creative Commons Attribution License ( ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver ( ) applies to the data made available in this article, unless otherwise stated.

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Khiabani, R.H., Whitehead, K.K., Losse, J.D. et al. Studying effect of respiration on total cavopulmonary connection flows using real-time cardiac magnetic resonance. J Cardiovasc Magn Reson 16 (Suppl 1), P137 (2014).

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