Abstract 114: Calf Muscle Oxygen Saturation During Standardized Treadmill Testing in Patients With Intermittent Claudication

Abstract

Objectives: Leg muscle hypoxia during walking is believed to be a key mechanism underlying the exercise intolerance of claudicating patients but detailed data on the changes exercise produces in the kinetics of leg muscle oxygenation are limited. Our objective was to record the calf muscle oxygen saturation (MO 2 S) at rest, during treadmill exercise and during recovery from exercise in patients with chronic claudication. Methods: We recruited 19 claudicating patients. The MO 2 S of the gastrocnemius was recorded with the Moxy near-infrared spectroscopy monitor (Hutchinson, MN). We measured resting MO 2 S for a period of three minutes and then performed a Gardner, standardized treadmill test. We recorded claudication onset time (COT) and peak walking time. We also measured the MO 2 S recovery for 30 minutes following the end of the TT or until muscle saturation reached a steady state. Results: Table I summarizes our results. Patients started experiencing a decrease in their MO 2 S 18.8 sec after initiation of TT; approximately 28 steps covering 16.8 meters. COT occurred when calf MO 2 S had dropped to 23.7%. Patients reached their minimum (14.1%) MO 2 S, 340.5 sec into the TT. During the post-TT recovery period, MO 2 S rebounded initially to 65.1% at 689.4 sec and 407.1 sec later it declined to a steady-state level of 56.3%, both above the pre-TT baseline reading. This relative hyperoxic state persisted for the duration of the post-exercise recording period (≥30 min). Conclusions: Our study objectively demonstrates considerable, walking-induced changes in MO 2 S in patients with claudication. During walking, MO 2 S drops quickly and the calf muscles experience substantial hypoxia while after the end of walking, MO 2 S rebounds above the baseline state and the leg muscles remain relatively hyperoxic beyond 30 min. This study provides much needed data concerning the kinetic patterns of muscle oxygenation claudicating patients experience in their everyday lives.