Association between inspiratory muscle weakness and slowed oxygen uptake kinetics in patients with chronic obstructive pulmonary disease.

Patients with chronic obstructive pulmonary disease (COPD) may have poor inspiratory muscle function, which reduces minute and alveolar ventilation, leading to increased hypoxemia and slow pulmonary oxygen uptake kinetics. However, little is known about the effect of inspiratory muscle weakness (IMW) on oxygen uptake kinetics in patients with COPD. Thus, we tested the hypothesis that COPD patients with IMW have slowed oxygen uptake kinetics. An observational study was conducted that included COPD patients with moderate to severe airflow limitation and a history of intolerance to exercise. Participants were divided into 2 groups: (IMW+; n = 22) (IMW-; n = 23) of muscle weakness. The maximal inspiratory, expiratory, and sustained inspiratory strength as well as the maximal endurance of the inspiratory muscles were lower in IMW+ patients (36 ± 9.5 cm H2O; 52 ± 14 cm H2O; 20 ± 6.5 cm H2O; 94 ± 84 s, respectively) than in IMW- patients (88 ± 12 cm H2O; 97 ± 28 cm H2O; 82.5 ± 54 cm H2O; 559 ± 92 s, respectively; p < 0.05). Moreover, the 6-min walk test and peak oxygen uptake were reduced in the IMW+ patients. During the constant work test, oxygen uptake kinetics were slowed in the IMW+ compared with IMW- patients (88 ± 29 vs 61 ± 18 s, p < 0.05). Our findings demonstrate that inspiratory muscle weakness in COPD is associated with slowed oxygen uptake kinetics, and thus, reduced functional capacity.

Skeletal muscle metaboreflex in patients with chronic renal failure.

The sympathetic nervous system is affected in patients with chronic renal failure (CRF). This study tested the hypothesis that patients with CRF have an altered skeletal muscle metaboreflex. Twenty patients with CRF and 18 healthy subjects of similar age participated in the study. The muscle metaboreflex was determined based on heart rate (HR), mean arterial pressure, calf blood flow and calf vascular resistance (CVR) in response to handgrip exercise. The control of vascular resistance in the calf muscle mediated by the metaboreflex was estimated by subtracting the area under the curve with circulatory occlusion from that without occlusion. Arterial pressure and HR responses during exercise and recovery were similar in two groups of subjects. In the control group, CVR increased during exercise and remained elevated during circulatory occlusion, whereas no significant change was seen in the patients. Thus, the index of the metaboreflex was 7·82 ± 9·57 in the patients versus16·52 ± 14 units in the controls. The findings demonstrate that patients with CRF have a decreased vascular resistance response in the calf during the handgrip exercise, which suggests that CRF condition attenuates this reflex.