Gregory A. Breit

Near-Infrared Spectroscopy for Monitoring of Tissue Oxygenation of Exercising Skeletal Muscle in a Chronic Compartment Syndrome Model*

Variations in the levels of muscle hemoglobin and of myoglobin oxygen saturation can be detected non-invasively with near-infrared spectroscopy. This technique could be applied to the diagnosis of chronic compartment syndrome, in which invasive testing has shown increased intramuscular pressure associated with ischemia and pain during exercise. We simulated chronic compartment syndrome in ten healthy subjects (seven men and three women) by applying external compression, through a wide inflatable cuff, to increase the intramuscular pressure in the anterior compartment of the leg. The tissue oxygenation of the tibialis anterior muscle was measured with near-infrared spectroscopy during gradual inflation of the cuff to a pressure of forty millimeters of mercury (5.33 kilopascals) during fourteen minutes of cyclic isokinetic dorsiflexion and plantar flexion of the ankle. The subjects exercised with and without external compression. The data on tissue oxygenation for each subject then were normalized to a scale of 100 per cent (the baseline value, or the value at rest) to 0 per cent (the physiological minimum, or the level of oxygenation achieved by exercise to exhaustion during arterial occlusion of the lower extremity). With external compression, tissue oxygenation declined at a rate of 1.4 ± 0.3 per cent per minute (mean and standard error) during exercise. After an initial decrease at the onset, tissue oxygenation did not decline during exercise without compression. The recovery of tissue oxygenation after exercise was twice as slow with compression (2.5 ± 0.6 minutes) than it was without the use of compression (1.3 ± 0.2 minutes). CLINICAL RELEVANCE: The results of this study demonstrate that near-infrared spectroscopy can detect deoxygenation of skeletal muscle caused by elevated intramuscular pressure during exercise. Thus, this technique may prove to be a useful diagnostic tool for the non-invasive detection of chronic compartment syndrome.

Intramuscular Pressures Beneath Elastic and Inelastic Leggings

Leg compression devices have been used extensively by patients to combat chronic venous insufficiency and by astronauts to counteract orthostatic intolerance following spaceflight. However, the effects of elastic and inelastic leggings on the calf muscle pump have not been compared. The purpose of this study was to compare in normal subjects the effects of elastic and inelastic compression on leg intramuscular pressure (IMP), an objective index of calf muscle pump function. IMP in soleus and tibialis anterior muscles was measured with transducer-tipped catheters. Surface compression between each legging and the skin was recorded with an air bladder. Subjects were studied under three conditions: (1) control (no legging), (2) elastic legging, and (3) inelastic legging. Pressure data were recorded for each condition during recumbency, sitting, standing, walking, and running. Elastic leggings applied significantly greater surface compression during recumbency (20±1 mm Hg, mean±SE) than inelastic leggings (13±2 mm Hg). During recumbency, elastic leggings produced significantly higher soleus IMP of 25±1 mm Hg and tibialis anterior IMP of 28±1 mm Hg compared to 17±1 mm Hg and 20±2 mm Hg, respectively, generated by inelastic leggings and 8±1 mm Hg and 11±1 mm Hg, respectively, without leggings. During sitting, walking, and running, however, peak IMPs generated in the muscular compartments by elastic and inelastic leggings were similar. Our results suggest that elastic leg compression applied over a long period in the recumbent posture may impede microcirculation and jeopardize tissue viability. On the other hand, inelastic leggings do not compress leg tissues at levels above 20 mm Hg during recumbency. Therefore inelastic leggings may be more effective in improving venous circulation in the legs of patients with chronic venous insufficiency.