The heterogeneity of regional specific ventilation is unchanged following heavy exercise in athletes

Abstract

Heavy exercise increases ventilation-perfusion mismatch and decreases pulmonary gas exchange efficiency. Previous work using magnetic resonance imaging (MRI) arterial spin labeling in athletes has shown that, after 45 min of heavy exercise, the spatial heterogeneity of pulmonary blood flow was increased in recovery. We hypothesized that the heterogeneity of regional specific ventilation (SV, the local tidal volume over functional residual capacity ratio) would also be increased following sustained exercise, consistent with the previously documented changes in blood flow heterogeneity. Trained subjects (n = 6, maximal O2 consumption = 61 ± 7 ml·kg(-1)·min(-1)) cycled 45 min at their individually determined ventilatory threshold. Oxygen-enhanced MRI was used to quantify SV in a sagittal slice of the right lung in supine posture pre- (preexercise) and 15- and 60-min postexercise. Arterial spin labeling was used to measure pulmonary blood flow in the same slice bracketing the SV measures. Heterogeneity of SV and blood flow were quantified by relative dispersion (RD = SD/mean). The alveolar-arterial oxygen difference was increased during exercise, 23.3 ± 5.3 Torr, compared with rest, 6.3 ± 3.7 Torr, indicating a gas exchange impairment during exercise. No significant change in RD of SV was seen after exercise: preexercise 0.78 ± 0.15, 15 min postexercise 0.81 ± 0.13, 60 min postexercise 0.78 ± 0.08 (P = 0.5). The RD of blood flow increased significantly postexercise: preexercise 1.00 ± 0.12, 15 min postexercise 1.15 ± 0.10, 45 min postexercise 1.10 ± 0.10, 60 min postexercise 1.19 ± 0.11, 90 min postexercise 1.11 ± 0.12 (P < 0.005). The lack of a significant change in RD of SV postexercise, despite an increase in the RD of blood flow, suggests that airways may be less susceptible to the effects of exercise than blood vessels.

Keywords: lung imaging; magnetic resonance imaging; pulmonary gas exchange; ventilation-perfusion mismatch.

Figures

Fig. 1.

Procedure time line. During MRI, DEN is density, Asl is arterial spin labeling measured blood flow, and SVI is specific ventilation imaging measured specific ventilation. During pre- and postexercise measures, subjects lay supine in the scanner. During cycling exercise, subjects were in the upright posture. Arrows indicate timing of arterial blood-gas measurements.

Fig. 2.

Representative supine images of pulmonary blood flow preexercise (A) and 15 min postexercise (B) and specific ventilation preexercise (C) and 15 min postexercise (D) in subject 6. In all images, the apex of the lung is to the right, and base of the lung is to the left. Signal from the large conduit blood vessels is removed from the blood flow images in postprocessing.

Fig. 3.

Relative dispersion of pulmonary blood flow (ml·min·cm−3) and specific ventilation. *Relative dispersion of mean pulmonary blood flow postexercise is statistically different than rest, P = 0.0048. Post hoc analysis showed that pulmonary blood flow was different at 15 min (P < 0.001), 45 min (P = 0.001), 60 min (P = 0.001), and 90 min postexercise (P = 0.003), compared with rest. Relative dispersion of mean specific ventilation did not change after exercise (P = 0.50). a, Dotted line indicates baseline relative dispersion of pulmonary blood flow. b, Dotted line indicates baseline relative dispersion of specific ventilation.

Fig. 4.

Individual responses of relative dispersion of blood flow (ml·min·cm−3) and specific ventilation preexercise and 15 and 45 min postexercise.

Fig. 5.

Relative dispersion of specific ventilation per one-third of lung. Relative dispersion of specific ventilation was significantly different between lung regions at all time points (P < 0.001), but no interaction effect was seen with lung region by time postexercise (P = 0.46).