Depression, mood state, and back pain during microgravity simulated by bed rest.

OBJECTIVE: The objective of this study was to develop a ground-based model for spinal adaptation to microgravity and to study the effects of spinal adaptation on depression, mood state, and pain intensity. METHODS: We investigated back pain, mood state, and depression in six subjects, all of whom were exposed to microgravity, simulated by two forms of bed rest, for 3 days. One form consisted of bed rest with 6 degrees of head-down tilt and balanced traction, and the other consisted of horizontal bed rest. Subjects had a 2-week period of recovery between the studies. The effects of bed rest on pain intensity in the lower back, depression, and mood state were investigated. RESULTS: Subjects experienced significantly more intense lower back pain, lower hemisphere abdominal pain, headache, and leg pain during head-down tilt bed rest. They had higher scores on the Beck Depression Inventory (ie, were more depressed) and significantly lower scores on the activity scale of the Bond-Lader questionnaire. CONCLUSIONS: Bed rest with 6 degrees of head-down tilt may be a better experimental model than horizontal bed rest for inducing the pain and psychosomatic reactions experienced in microgravity. Head-down tilt with balanced traction may be a useful method to induce low back pain, mood changes, and altered self-rated activity level in bed rest studies.

The predictive value of psychometric analysis in patients treated by extirpation of lumbar intervertebral disc herniation.

The authors studied the predictive value of a psychometric evaluation of 50 patients (14 women, 36 men) with a mean age of 40 years who were treated by extirpation of a lumbar disc herniation. Patient satisfaction was evaluated by an unbiased observer. The Beck Depression Inventory (BDI), the State-Trait Anxiety Inventory (STAI), and a Pain Visual Analogue Scale (PVAS) were used to assess pain and psychological distress before surgery and 3 and 12 months after surgery. Two years after surgery, 37 patients were contented with the surgical outcome and 10 patients were not. Three patients did not return the questionnaire. Before surgery, the patients who later became discontented were more depressed, more anxious, and experienced more pain. In a discriminant analysis, a combination of BDI, STAI, and PVAS scores correctly classified 78% of the discontented and 76% of the contented patients. The study shows psychometric analysis is a valuable tool for predicting the outcome of surgical treatment for lumbar disc herniation.

Hoffmann-reflex is delayed during 6 degree head-down tilt with balanced traction.

BACKGROUND: Increased spinal height due to the lack of of axial compression on spinal structures in microgravity may stretch the spinal cord, cauda equina, nerve roots, and paraspinal tissues. HYPOTHESIS: Exposure to simulated microgravity causes dysfunction of nerve roots so that the synaptic portion of the Achilles tendon reflex is delayed. METHODS: Six healthy male subjects were randomly divided into two groups with three in each group. The subjects in the first group underwent horizontal bed rest (HBR) for three days. After a two week interval they underwent bed rest in a position of head-down tilt with balanced traction (HDT). So that each subject could serve as his own control, the second group was treated identically but in opposite order. Bilateral F waves and H-reflexes were measured daily (18:30-20:30) on all subjects placed in a prone position. RESULTS: By means of ANOVA, differences between HDT and HBR were observed only in M-latency and F-ratio, not in F-latency, central latency, and H-latency. Differences during the course of the bed rest were observed in M-latency and H-latency only. Tibial H latency was significantly lengthened in HDT group on day 2 and 3, although no significant difference between HDT and HBR was observed. CONCLUSION: The monosynaptic reflex assessed by H-reflex was delayed during 6 degree HDT with traction. The exact mechanism of this delay and whether the change was due to lengthening of the lower part of the vertebrae remain to be clarified.

Intramuscular pressure in the leg and thigh related to tensile strap force during knee brace wear. An experimental study in man.

The effects of a functional knee brace on intramuscular pressure in the leg and thigh were measured in eight subjects with a mean age of 32 years. Pressures in the tibialis anterior and rectus femoris muscles were recorded without a knee brace and with a brace applied with strap tensile force of 25 N, 50 N, and a force preferred by the subject. External compression caused by the brace significantly increased intramuscular pressures at rest and muscle relaxation pressure during exercise in the leg and thigh muscles. Pressure in the tibialis anterior muscle increased 3 to 10 times, to mean values between 17.5 and 41 mm Hg, depending on the tensile force of the straps used at brace application. Corresponding mean pressure values in the rectus femoris muscle were between 17.5 and 32.5 mm Hg. Mean pressures in the standing subject varied between 37 and 62 mm Hg. Our study showed that intramuscular pressure at rest and muscle relaxation pressure during exercise in the tibialis anterior and the rectus femoris muscles increased significantly in the braced limb. Local blood perfusion pressure in the supine subject decreased significantly, by 16% to 42%, in the compressed muscles.

Effects of limb elevation on abnormally increased intramuscular pressure, blood perfusion pressure, and foot sensation: an experimental study in humans.

OBJECTIVES: To study the effects of limb elevation on abnormally increased intramuscular pressure (IMP) and blood perfusion pressure in the anterior compartment of the leg. DESIGN: An experimental cross-over design. The test leg was elevated and the control leg was kept at heart level. PARTICIPANTS: Eight healthy subjects with a mean age of twenty-nine years. INTERVENTION: IMP was measured in the anterior compartment of the leg, and blood pressures were taken in the left arm and both legs. Four variables were recorded (with or without venous stasis, with or without plaster cast). All measurements were made simultaneously in both legs. RESULTS: When the leg was obstructed by venous stasis and elevated to between thirty-three and thirty-five centimeters, IMP decreased from 16.5 to 9.8 millimeters of mercury. When venous stasis was simulated in a level casted leg, the IMP was thirty-eight (SD = 6.4) millimeters of mercury but showed only a slight decline to thirty-five (SD = 7.8) millimeters of mercury after the leg was elevated. Blood perfusion pressure fell significantly once the leg was elevated, decreasing 53 percent from forty-seven (SD = 7.8) to twenty-five (SD = 8.0) millimeters of mercury (p < 0.001). All subjects experienced loss of foot sensation in the elevated limb. CONCLUSION: In those cases in which venous stasis increased IMP levels in the anterior compartment of the leg, elevating the limb produced a 40 percent reduction in IMP. However, limb elevation did not significantly reduce increased IMP levels when the venous stasis occurred in a casted leg. Therefore, we believe casted legs in which abnormally increased IMP is attributable to venous stasis should not be elevated above heart level because elevation induces low perfusion pressure and sensory dysfunction.

The effects of external compression by three different retractors on pressure in the erector spine muscles during and after posterior lumbar spine surgery in humans.

STUDY DESIGN: An experimental study on patients undergoing posterior lumbar spine surgery. OBJECTIVES: To study the relation between external compression and muscle strain induced by spinal retractors and intramuscular pressure in the dorsolumbar compartment during posterior spinal surgery. SUMMARY OF BACKGROUND DATA: Pressures were studied as a function of the distance between the retractor blades during surgery. METHODS: Intramuscular pressure was measured bilaterally in the erector spinae muscle with intermittent microcapillary infusion technique in 12 patients undergoing posterior lumbar spine surgery during 271 (range 90-420) minutes. Three self-retaining retractors were tested; the McCulloch, the Viking, and the Richard retractors. RESULTS: Intramuscular pressure was 7.7 mm Hg before surgery. It varied between 35 mm Hg and 69 mm Hg during surgical exposure of the laminas and facet joints. Intramuscular pressure varied between 61 mm Hg and 158 mm Hg depending on which retractor was used and on the distance between the retractor blades. Intramuscular pressure never exceeded 30 mm Hg at rest after the operation. CONCLUSIONS: External compression and muscle strain from retractor blades during surgery increased intramuscular pressure in the paravertebral muscles to levels that, according to other studies, induce ischemia in the muscles.

Intramuscular deoxygenation during exercise in patients who have chronic anterior compartment syndrome of the leg.

Currently, the definitive diagnosis of chronic compartment syndrome is based on invasive measurements of intracompartmental pressure. We measured the intramuscular pressure and the relative oxygenation in the anterior compartment of the leg in eighteen patients who were suspected of having chronic compartment syndrome as well as in ten control subjects before, during, and after exercise. Chronic compartment syndrome was considered to be present if the intramuscular pressure was at least fifteen millimeters of mercury (2.00 kilopascals) before exercise, at least thirty millimeters of mercury (4.00 kilopascals) one minute after exercise, or at least twenty millimeters of mercury (2.67 kilopascals) five minutes after exercise. Changes in relative oxygenation were measured with use of the non-invasive method of near-infrared spectroscopy. In all patients and subjects, there was rapid relative deoxygenation after the initiation of exercise, the level of oxygenation remained relatively stable during continued exercise, and there was reoxygenation to a level that exceeded the pre-exercise resting level after the cessation of exercise. During exercise, maximum relative deoxygenation in the patients who had chronic compartment syndrome (mean relative deoxygenation [and standard error], -290 +/- 39 millivolts) was significantly greater than that in the patients who did not have chronic compartment syndrome (-190 +/- 10 millivolts) and that in the control subjects (-179 +/- 14 millivolts) (p < 0.05 for both comparisons). In addition, the interval between the cessation of exercise and the recovery of the pre-exercise resting level of oxygenation was significantly longer for the patients who had chronic compartment syndrome (184 +/- 54 seconds) than for the patients who did not have chronic compartment syndrome (39 +/- 19 seconds) and the control subjects (33 +/- 10 seconds) (p < 0.05 for both comparisons).

Height increase, neuromuscular function, and back pain during 6 degrees head-down tilt with traction.

BACKGROUND: Spinal lengthening and back pain are commonly experienced by astronauts exposed to microgravity. METHODS: To develop a ground-based simulation for spinal adaptation to microgravity, we investigated height increase, neuromuscular function and back pain in 6 subjects all of whom underwent two forms of bed rest for 3 d. One form consisted of 6 degrees of head-down tilt (HDT) with balanced traction, while the other was horizontal bed rest (HBR). Subjects had a 2-week recovery period in between the studies. RESULTS: Total body and spinal length increased significantly more and the subjects had significantly more back pain during HDT with balanced traction compared to HBR. The distance between the lower endplate of L4 and upper endplate of S1, as measured by ultrasonography, increased significantly in both treatments to the same degree. Intramuscular pressures in the erector spinae muscles and ankle torque measurements during plantarflexion and dorsiflexion did not change significantly during either treatment. CONCLUSION: Compared to HBR, HDT with balanced traction may be a better method to simulate changes of total body and spinal lengths, as well as back pain seen in microgravity.

Cutaneous microvascular flow in the foot during simulated variable gravities.

Our objective was to understand how weight bearing with varying gravitational fields affects blood perfusion in the sole of the foot. Human subjects underwent whole body tilting at four angles: upright [1 gravitational vector from head to foot (Gz)], 22 degrees (0.38 Gz), 10 degrees (0.17 Gz), and supine (0 Gz), simulating the gravitational fields of Earth, Mars, Moon, and microgravity, respectively. Cutaneous capillary blood flow was monitored on the plantar surface of the heel by laser Doppler flowmetry while weight-bearing load was measured. At each tilt angle, subjects increased weight bearing on one foot in graded load increments of 1 kg beginning with zero. The weight bearing at which null flow first occurred was determined as the closing load. Subsequently, the weight bearing was reduced in reverse steps until blood flow returned (opening load). Mean closing loads for simulated Earth gravity, Mars gravity, Moon gravity, and microgravity were 9.1, 4.6, 4.4, and 3.6 kg, respectively. Mean opening loads were 7.9, 4.1, 3.5, and 3.1 kg, respectively. Mean arterial pressures in the foot (MAP(foot)) calculated for each simulated gravitational field were 192, 127, 106, and 87 mmHg, respectively. Closing load and opening load were significantly correlated with MAP(foot) (r =0.70, 0.72, respectively) and were significantly different (P < 0.001) from each other. The data suggest that decreased local arterial pressure in the foot lowers tolerance to external compression. Consequently, the human foot sole may be more prone to cutaneous ischemia during load bearing in microgravity than on Earth.

Effects of a functional knee brace on leg muscle function.

The effects of a functional knee brace on local intramuscular pressures and on calculated blood perfusion pressure in the tibialis anterior muscle of the legs of six volunteers were determined. Torque generation during dorsiflexion of the ankle joint was measured with a Kinetic Computerized ergometer, and the time to elicit muscle fatigue during exercise was recorded. For each experimental subject studies compared right with left unbraced legs, then right braced with left unbraced legs, and finally right unbraced with left braced legs. In the braced leg, intramuscular pressure at rest and muscle relaxation pressure during exercise were significantly higher, and the time to elicit muscle fatigue was 35% shorter. The calculated local blood perfusion pressure was lower because of the increased muscle relaxation pressure. We conclude that the increased muscle relaxation pressure during exercise caused by a knee brace is a possible explanation for the premature development of muscle fatigue in the braced leg.

Intramuscular pressure varies with depth. The tibialis anterior muscle studied in 12 volunteers.

Pressures in the tibialis anterior muscle were recorded at rest and during exercise with transducer-tipped catheters in 12 volunteers while they were supine or standing. The recordings were repeated with venous stasis created by an inflated tourniquet cuff on the thigh. Catheters were placed at 3 different sites in the muscle: catheter I adjacent to the deep surface of the fascia over the anterior compartment; catheter II between the fascia and the central tendon; and catheter III deep in the muscle close to the interosseous membrane. In both the supine and standing positions the intramuscular pressure at rest and the muscle relaxation pressure during exercise, obtained by catheter II, were greater than the corresponding pressures measured by the superficially located catheter I in the normal as well as in the volume loaded limb. The same conditions for pressure measurement consistently revealed lower pressures recorded by catheter III compared to II, but the difference was not significant. Our results indicate that intramuscular pressure increases centripetally, as the centrally lying tendon is approached. We conclude that pressure measurements for diagnosis of acute and chronic compartment syndromes and in ergonomic studies should be based on recordings from a standard location of the catheter within the muscle and a standard posture of the subject.

Functional knee braces increase intramuscular pressures in the anterior compartment of the leg.

The effect of three different functional knee braces on intramuscular pressures in the anterior compartment of the leg was investigated in 8 healthy subjects. Pressures were recorded with the microcapillary infusion technique while the subjects were either supine, sitting, or standing. Pressures at rest in the anterior tibial muscle increased significantly following application of each of the three knee braces regardless of posture. Similarly, muscle relaxation pressure during exercise also increased significantly on brace application. A pressure of 40 mm Hg was exceeded in 9 of 18 intramuscular pressure measurements with the subject standing. The tested functional knee braces increased muscle pressures at rest and muscle relaxation pressure during exercise to levels that, according to other studies, might decrease muscle blood flow significantly. External compression from a knee brace on leg muscles might, therefore, induce premature muscle fatigue because of local insufficient perfusion of the working muscle.

Intramuscular pressures during exercise: an evaluation of a fiber optic transducer-tipped catheter system.

The efficacy of a modified fibre optic transducer-tipped catheter system for measuring intramuscular pressures during exercise was determined. A microcapillary infusion technique using a catheter was employed as the standard of comparison due to its established dynamic properties. Pressures were measured in the tibialis anterior muscle of six healthy adults at rest before exercise, during isometric and concentric exercise, and at rest after exercise. The fibre optic system measured contraction pressures equal to the microcapillary infusion technique during all phases of the exercise protocols but recorded a lower relaxation pressure during isometric exercise and a lower rest pressure following 20 min of concentric exercise. Negative relaxation pressures were recorded by the fibre optic system for two subjects during continuous concentric exercise. It is hypothesized that a piston effect, due to the sliding of muscle fibres at the catheter tip following a contraction, rendered falsely low pressures during relaxation and that this artefact was reflected in the subsequent rest pressure following exercise. The larger volume (157 mm3) and area (3.49 mm2) of the fibre optic catheter in the muscle made it more prone to this effect than the conventional catheter (39 mm3 and 0.87 mm2, respectively). The fibre optic system may be preferred when recording the muscle contraction pressures during complex limb movements but should not be used when assessing the relaxation pressures or the pressure at rest following exercise.

A new "transducer-tipped" fiber optic catheter for measuring intramuscular pressures.

Laboratory and clinical tests were used to determine the efficacy of a new fiber optic "transducer-tipped" catheter for measuring intramuscular pressures. When pressures ranging from 0 to 250 mm Hg were applied by a mercury manometer, the fiber optic system accurately recorded the pressures. In addition, the fiber optic system showed long-term stability by accurately recording the manometer pressure over a 3 day period. The Slit system showed a higher magnitude of hydrostatic pressure artifacts with catheter tip movement as compared to the fiber optic system. The two catheters showed no difference when measuring pressures in pig muscle at rest or when being compressed throughout a range of 0 to 250 mm Hg. In human volunteers, both catheters measured essentially equal pressures at rest, during venous stasis, and during a combination of venous stasis and compression. For long-term assessment, the Slit system required as many as three saline flushes, whereas the fiber optic system measured pressures continuously without manipulation. We conclude that the fiber optic system is as accurate as the Slit catheter for measuring tissue fluid pressures at rest. In addition, the fiber optic system offers distinct advantages over conventional fluid-filled systems for measuring intramuscular pressures due to a lack of hydrostatic pressure artifacts caused by limb position and to the lack of flushing for long-term measurements.

Intramuscular pressures during exercise. Comparison of measurements with and without infusion.

Our objective was to compare two techniques for measuring intramuscular pressures during dynamic exercise. In 20 volunteers muscle contraction and relaxation pressures were recorded with a noninfusion method (slit catheter) and with a microcapillary infusion method (Myopress catheter). Relaxation pressures measured by noninfusion were higher than those measured by infusion. The dynamic properties of the infusion method were higher as compared with the noninfusion method. The dynamic properties of the noninfusion method increased when microcapillary infusion was connected. This resulted in a lower recording of the muscle-relaxation pressure than without infusion. We concluded that the microcapillary infusion technique and the design of the tip of the Myopress catheter are better suited for pressure recordings during exercise.

Diagnosis of chronic anterior compartment syndrome in the lower leg.

Intramuscular pressure was recorded in 80 patients suspected of suffering from chronic anterior compartment syndrome in the lower leg; the diagnosis was verified in 22 of these patients. The history and clinical findings of the chronic compartment syndrome patients were compared with those of the 58 patients without the syndrome. Pain induced only by athletic activity and only in the anterior lower leg forcing the patient to interrupt running indicated chronic compartment syndrome. The history and clinical findings alone were found to be insufficient to establish the diagnosis. In relation to generally accepted pressure parameters at rest, the muscle relaxation pressure during exercise was found to be a reliable parameter for diagnosing chronic compartment syndrome, whereas mean muscle pressure and muscle contraction pressure were found to be unreliable.

Chronic anterior-compartment syndrome of the leg. Results of treatment by fasciotomy.

Thirty legs in nineteen patients, eleven with bilateral and eight with unilateral chronic anterior-compartment syndrome, were treated by fasciotomy. In addition, five of these patients (six legs) had compression of the superficial peroneal nerve: two before and three after fasciotomy. One patient also had lateral compartment syndrome in one leg. The patients who had compression of the superficial peroneal nerve were relieved by partial fasciectomy and fasciotomy of the lateral compartment. In one of these patients, with bilateral nerve compression, both superficial peroneal nerves were anomalous. The patient who had lateral compartment syndrome was relieved by fasciotomy of this compartment. Two patients required a second fasciotomy due to recurrence of the chronic compartment syndrome. At an average length of follow-up of twenty-five months after fasciotomy for anterior compartment syndrome, functional capacity was unlimited or increased in eighteen patients (twenty-eight legs) and was unchanged in one patient (two legs) who had had compression of the superficial peroneal nerve. The intramuscular pressures in the anterior compartment were normal at rest as well as during and after exercise eight months after the original fasciotomy in twenty-eight legs and eight months after the second fasciotomy in two legs.

Microcapillary infusion technique for measurement of intramuscular pressure during exercise.

The microcapillary infusion method (MCI) is described and compared to the pump infusion (PI) and the wick catheter methods for recording pressure in the anterior tibial muscle at rest and during exercise in 34 volunteers and in 11 patients with chronic compartment syndrome (CCS). The infusion techniques offered excellent dynamic properties in recording pressure during exercise with infusion rates exceeding 0.1 ml/hour. Infusion rates below 3.0 ml/hour in normal legs and below 1.5 ml/hour in CCS legs were found not to increase the pressure at rest during 30 minutes. The wick catheter method was found to be unsuitable in recording intramuscular pressure during exercise because of its slow response time. The MCI method had a lower compliance, a higher resonance frequency, and a shorter response time than the PI method. The muscle relaxation pressure (MRP) during exercise increased to 34.6 (SD = 5.6) mmHg in the CCS patients during exercise compared to 17.3 (SD = 4.6) mmHg in the control group. The MCI technique offers a practical tool for studying equilibrium pressures during muscle contraction and relaxation in routine clinical investigations and research.