Evidence for increased pulmonary vascular resistance during muscle metaboreflex activation

Isometric exercise and subsequent post exercise circulatory occlusion (PECO) are associated with muscle metaboreflex activation and reflex sympathoexcitation, but the effects of this reflex on the pulmonary circulation are unknown. This study examined pulmonary vascular responses in seven healthy, active subjects (5 men, 2 women; 22.86 ± 7.71 years; mean ± S.D.) during 5‐min rest, 2‐min isometric handgrip exercise at 50% of predetermined maximum voluntary contraction and a further 2‐min of PECO. Measurements of the maximum trans‐tricuspid pressure difference (ΔPmax), which has been shown to be a reliable index of pulmonary vascular resistance (PVR)1, and cardiac output (CO) were made using standard Doppler echocardiography techniques. Blood pressure (Portapres) and respiration frequency (R f ) were also monitored and recorded continuously. Mean blood pressure (MAP) and ΔPmax were significantly increased by 25.50% ± 2.57 (P≤0.0003) and 16.90% ± 4.67 (P≤0.006), respectively, during PECO, as compared to rest (mean ± S.E.M.). In contrast, CO remained relatively constant between rest and PECO (4.18 ± 0.31 vs. 4.32 ± 0.20 l/min, respectively; P≥0,48; means ± S.E.M.). R f did not change (P≥0.8). These results suggest that muscle chemoreflex mediated sympathoexcitation contributes to an increase in PVR.