Skeletal muscle oxygenation and regional blood volume during incremental limb loading in interstitial lung disease

IntroductionIndividuals with interstitial lung disease (ILD) exhibit reduced exercise capacity and exertional hypoxaemia. The role of peripheral (muscle) limitation to exercise tolerance in ILD is not well studied to date.MethodsA prospective cross-sectional study examined skeletal muscle oxygen saturation (SmO2) and regional blood volume of the knee extensors and elbow flexors during incremental limb loading in healthy people and people with varying severity of ILD. Isotonic concentric exercise was performed on an isokinetic dynamometer. SmO2 and regional blood volume were measured by near-infrared spectroscopy over the vastus lateralis and biceps.ResultsThirteen people who were dependent on oxygen, candidates for lung transplant and with severe ILD (forced vital capacity (FVC) 59±20% predicted), 10 people who were not oxygen dependent with mild ILD (FVC 81±17% predicted) and 13 healthy people (FVC 101±14% predicted) were included. Total haemoglobin, a marker of regional blood volume, was lower at task failure in the knee extensors in participants with severe ILD compared to healthy participants (p=0.05). At task failure for both knee-extensor loading and elbow-flexor loading, SmO2 was decreased to similar levels across all groups, but occurred at lower total workloads in the ILD groups (all p<0.01).ConclusionsOverall, people with severe ILD had lower levels of total work and experienced less increase in blood volume in the knee extensors after knee-extensor loading compared to healthy people. Peripheral muscle dysfunction in severe ILD may have contributed to muscle deoxygenation at lower workloads.

Mechanisms of sympathetic regulation in orthostatic intolerance

Sympathetic circulatory control is key to the rapid cardiovascular adjustments that occur within seconds of standing upright (orthostasis) and which are required for bipedal stance. Indeed, patients with ineffective sympathetic adrenergic vasoconstriction rapidly develop orthostatic hypotension, prohibiting effective upright activities. One speaks of orthostatic intolerance (OI) when signs, such as hypotension, and symptoms, such as lightheadedness, occur when upright and are relieved by recumbence. The experience of transient mild OI is part of daily life. However, many people experience episodic acute OI as postural faint or chronic OI in the form of orthostatic tachycardia and orthostatic hypotension that significantly reduce the quality of life. Potential mechanisms for OI are discussed including forms of sympathetic hypofunction, forms of sympathetic hyperfunction, and OI that results from regional blood volume redistribution attributable to regional adrenergic hypofunction.