Is there a competition for oxygen availability between respiratory and limb muscles?

If a competition between the oxygen demands of limb and respiratory muscles happens, hypoxia may favor redistribution of blood flow from peripheral to respiratory muscles during heavy exercise. This hypothesis was tested in eighteen lowlanders and 27 highlanders at 4350m altitude. During an incremental exercise, the regional tissue oxygen saturation (rSO2) and tissue hemoglobin concentration ([Hbt]) of the intercostal muscles and vastus medialis were monitored simultaneously by NIRS. The intercostal and vastus medialis rSO2 values were lower at altitude than at sea level (-10%, p<0.001) and decreased similarly during incremental exercise (p<0.001) while [Hbt] values increased. At maximal exercise, the intercostal rSO2 was lower than the vastus medialis rSO2 in lowlanders (-7%, p<0.001). In highlanders the time patterns were similar but intercostal rSO2 was less decreased at exercise (p<0.05). Maximal exercise performed in hypoxia did not alter the kinetics of rSO2 and [Hbt] in peripheral muscles. These findings do not favor the hypothesis of blood flow redistribution.

Effects of exercise training in patients with idiopathic pulmonary arterial hypertension.

We determined the physiological effects of exercise training on exercise capacity and quadriceps muscle function in patients with idiopathic pulmonary arterial hypertension (iPAH). In total, 19 clinically stable iPAH patients (New York Heart Association II-III) underwent a supervised exercise training programme for the duration of 12 weeks. Maximal capacity, endurance capacity and quadriceps function were assessed at baseline and after 12 weeks. In 12 patients, serial quadriceps muscle biopsies were obtained. 6-min walk distance and peak exercise capacity did not change after training. However, endurance capacity improved significantly after training, demonstrated by a shift of the anaerobic threshold to a higher workload (from 32+/-5 to 46+/-6 W; p = 0.003) together with an increase in exercise endurance time (p<0.001). Moreover, exercise training increased quadriceps strength by 13% (p = 0.005) and quadriceps endurance by 34% (p = 0.001). Training enhanced aerobic capacity of the quadriceps, by increasing capillarisation (1.36+/-0.10 to 1.78+/-0.13 capillaries per muscle fibre; p<0.001) and oxidative enzyme activity, especially of the type-I (slow) muscle fibres. No changes were found in cross-sectional area and fibre type distribution. Exercise training in iPAH improves exercise endurance and quadriceps muscle function, which is also reflected by structural changes of the quadriceps.

Cardiopulmonary exercise test characteristics in patients with chronic obstructive pulmonary disease and associated pulmonary hypertension.

BACKGROUND: Pulmonary hypertension (PH) is a well-known complication of chronic obstructive pulmonary disease (COPD). It remains unclear whether exercise parameters can be used to discriminate between COPD patients with associated PH (COPD-PH) and COPD patients without associated PH (COPD-nonPH). OBJECTIVE: To study whether the existence of pulmonary hypertension in COPD is related to characteristic findings in gas exchange and circulatory parameters during cardiopulmonary exercise testing (CPET). METHODS: We retrospectively analyzed CPET data in 25 COPD patients in whom right heart catheterization had been performed. Differences were assessed between COPD-PH and COPD-nonPH patients in peak oxygen uptake (VO(2) peak), ventilatory efficiency (VE/VCO(2)), oxygen pulse, maximal ventilation and pulse oximetry (S(p)O(2)). RESULTS: PH was found in 10 of 25 patients (mP(pa) = 33 +/- 7 mm Hg), in 15 patients mean pulmonary artery pressure (mP(pa)) was below 25 mm Hg (18 +/- 3 mm Hg). CPET in COPD-PH was characterized by a higher VE/VCO(2) at nadir, a higher VE/VCO(2) slope, and a lower S(p)O(2) at rest and during exercise, but values in both groups were overlapping considerably. In the whole group mP(pa) was associated with resting P(a)O(2) (r = -0.70, p < 0.001), VE/VCO(2) nadir (r = 0.43, p < 0.05), and inversely related to S(p)O(2) at rest and during exercise (r = -0.58 and r = -0.64, p < 0.01, respectively). CONCLUSION: Although CPET characteristics showed a large overlap in both groups, the existence of PH in COPD is associated with a significantly reduced ventilatory efficiency during CPET. However, a low S(p)O(2) at rest and a further decrease during exercise similarly suggest the presence of PH in COPD.