Joshua R. Rodman

Consequences of exercise-induced respiratory muscle work

We briefly review the evidence for a hypothesis, which links the ventilatory response to heavy intensity, sustained exercise-to-exercise performance limitation in health. A key step in this linkage is a respiratory muscle fatigue-induced metaboreflex, which increases sympathetic vasoconstrictor outflow, causing reduced blood flow to locomotor muscles and locomotor muscle fatigue. In turn, the limb fatigue comprises an important dual contribution to both peripheral and central fatigue mechanisms, which contribute to limiting exercise performance. Clinical implications for respiratory limitations to exercise in patients with chronic obstructive lung disease (COPD) and chronic heart failure (CHF) are discussed and key unresolved problems are outlined.

Diaphragm plasticity following intrinsic laryngeal muscle denervation in rats.

PURPOSE During inspiration, recruitment of the intrinsic laryngeal muscles (ILM) reduces the inspiratory load on the ventilatory pump muscles. The purpose of our study was to determine 1) whether the diaphragm adapts to denervation of the ILM, and 2) whether the additional stimulus of exercise training affects the degree to which the diaphragm adapts to ILM denervation. METHODS Thirty-six male Sprague-Dawley rats (2 months) were randomly divided into sedentary control (SC), sedentary-denervated (SD), and exercise-denervated (ED) groups. Control animals underwent sham operations, whereas ILM-denervated animals underwent bilateral transection of the recurrent laryngeal nerves. Three weeks after surgery, animals in the ED group performed a treadmill training protocol for a period of 6 wk. RESULTS Denervation (SD and ED animals) of the ILM significantly increased diaphragm citrate synthase activity (20%), in vitro endurance, and time to peak twitch tension (15%), and reduced (13%) peak tetanic tension (Po, N x cm(-2)). No independent training effect over and above the effects attributed to denervation of ILM were noted in ED animals. CONCLUSION The results highlight the role of vocal cord dilator function during both eupnea and exercise-induced hyperpnea.