Development of Exercise Protocol to Improve Hypoxic Tolerance

INTRODUCTION

Advanced transport technology gives people opportunity to visit high altitude within short time. Therefore, not enough time is available for them to acclimatize to the hypoxic environment and this is typically associated with decreased arterial oxygen saturation and increased pulmonary artery pressures, both of which contribute to the impaired exercise performance experienced there. Significant portion of this impairment is attributed to hypoxic pulmonary vasoconstriction (HPV). This response leads to increased pulmonary arterial pressure resulting in increased right ventricular afterload and decreased cardiac output. The complex underlying mechanisms responsible for HPV are suggested to be largely mediated through vasoactive and inflammatory pathways. Though pharmacological and non-pharmacological interventions to attenuate HPV at simulated and high altitude environments improve arterial oxygen saturation (SpO2), still, inconstant results have been observed in exercise performance. These outcomes in healthy subjects have important implications in clinical practice, for example, common high morbidity conditions such as sleep apnea syndromes, chronic obstructive pulmonary disease, interstitial lung diseases, congestive heart failure and critically ill patients requiring respiratory support are often complicated by HPV.

Exercise training is being increasingly used in the management of patients with acute and chronic cardio-respiratory diseases where it has been clearly demonstrated to reduce dyspnea, increase exercise performance and improve health-related quality of life (HRQL). Meta-analyses and systemic reviews have shown that beneficial effects of exercise training are mediated by reduction in inflammatory and oxidative stress markers, improvement of endothelial function, increased oxidative capacity & skeletal muscle mass, enhanced vagal and lower sympathetic tone in chronic heart and respiratory patients.

Recently, ischemic preconditioning (IPC), a procedure which is performed by repetitive occlusion of arterial blood flow to an organ or extremity (e.g., 5 minutes occlusion, followed by 5 minutes of restored blood flow, repeated several times) has been shown to induce systemic effects that protect the myocardium and other organs from subsequent ischemic injury. In acute coronary syndrome, ischemic conditioning has been shown to reduce infarct size and incidence of arrhythmias while recovery of contractile and vascular function is taking place. These effects have also been observed in pulmonary vasculature, where it has been demonstrated that the hypoxic increase in pulmonary artery systolic pressure during acute simulated altitude conditions is significantly attenuated by IPC. The protective effects of IPC on local and remote tissues are largely attributed to effects on vasoactive and inflammatory pathways.

Since IPC and HPV have similar mechanistic pathways i.e. hypoxia, but confer opposing effects, it is hypothesized that IPC exposure would attenuate HPV and improve hypoxic tolerance. Further, in view of the fact that exercise training is known to improve exercise capacity in chronic respiratory disease patients, this study will also examine whether addition of IPC before exercise training imparts greater increase in exercise endurance.

LACUNAE IN LITERATURE

There are studies that show relationship between ischemic pre-conditioning (IPC) and attenuation in hypoxic pulmonary vasoconstriction (HPV) in exercising, healthy subjects.  However, the impact of IPC on hypoxia response and exercise training in chronic respiratory patients is yet to be evaluated.

AIMS

Aim of this study is to develop a protocol in which ‘ischemic pre-conditioning’ will be added to the routine activity or an exercise program that will lead to increase in tolerance to hypoxia.

HYPOTHESIS

It is hypothesized that ischemic pre-conditioning along with structured exercise training will provide tolerance to acute hypoxia exposure and prevent hypoxic pulmonary vasoconstriction.Secondarily, it will also improve functional exercise capacity.