Submitted on January 9, 2004
Accepted on March 9, 2004
Blood Flow Conditions in the Proximal Pulmonary Arteries and Vena Cavae in Healthy Children During Upright Seated Rest and Cycling Exercise, Quantified with MRI
Christopher P. Cheng1*, Robert J. Herfkens2, Amy L. Lightner1, Charles A. Taylor3, and Jeffrey A. Feinstein4
1 Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
2 Department of Radiology, Stanford University, Stanford, CA, USA
3 Department of Mechanical Engineering, Stanford University, Stanford, CA, USA; Department of Surgery, Stanford University, Stanford, CA, USA
4 Department of Pediatrics, Stanford University, Stanford, CA, USA
* To whom correspondence should be addressed. E-mail: cpc{at}stanford.edu.
Diagnostic testing in patients with congenital heart disease is usually performed supine and at rest - conditions not representative of their typical hemodynamics. Upright exercise measurements of blood flow may prove valuable in the assessment of these patients
but data in normal subjects is first required. Using a 0.5T open-magnet, a magnetic resonance-compatible exercise cycle and cine phase-contrast techniques, time-dependent
blood flow velocities were measured in the right (RPA), left (LPA), and main (MPA) pulmonary arteries and superior (SVC) and inferior (IVC) vena cavae of ten healthy 10-14
year-olds. Measurements were made at seated rest and during upright cycling exercise (150% resting heart rate). Mean blood flow (L/min) and reverse flow index were computed
from the velocity data. With exercise, RPA and LPA mean flow increased: 2.0+/-0.5 to 3.7+/-0.7 (p<0.05) and 1.6+/-0.4 to 2.9+/-0.8 (p<0.05), respectively. Pulmonary reverse flow index (rest vs. exercise) decreased with exercise: MPA: 0.014+/-0.012 vs. 0.006+/-0.006 (p=NS), RPA: 0.005+/-0.004 vs. 0.000+/-0.000 (p<0.05), and LPA: 0.041+/-0.019 vs.
0.014+/-0.016 (p<0.05). SVC and IVC flow increased from 1.5+/-0.2 to 1.9+/-0.6 (p=NS) and 1.6+/-0.4 to 4.9+/-1.3 (p<0.05), respectively. A 56%/44% RPA/LPA flow distribution at both rest and during exercise suggests blood flow distribution is dominated by distal pulmonary resistance. Reverse flow in the MPA appears to originate solely from the LPA while the RPA is in relative isolation. During seated rest, the SVC/IVC venous return ratio is 50%/50%. With light/moderate cycling exercise, IVC flow increases by 3-fold while SVC remains essentially constant.
