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Biomedical subjects

Alan R Hargens

Publications and source records attributed to Alan R Hargens.

At least 19 recordsLinked to original sources
PubMed2006

Ambulation in simulated fractional gravity using lower body positive pressure: cardiovascular safety and gait analyses.

The purpose of this study is to assess cardiovascular responses to lower body positive pressure (LBPP) and to examine the effects of LBPP unloading on gait mechanics during treadmill ambulation. We hypothesized that LBPP allows comfortable unloading of the body with minimal impact on the cardiovascular system and gait parameters. Fifteen healthy male and female subjects (22-55 yr) volunteered for the study. Nine underwent noninvasive cardiovascular studies while standing and ambulating upright in LBPP, and six completed a gait analysis protocol. During stance, heart rate decreased significantly from 83 +/- 3 beats/min in ambient pressure to 73 +/- 3 beats/min at 50 mmHg LBPP (P < 0.05). During ambulation in LBPP at 3 mph (1.34 m/s), heart rate decreased significantly from 99 +/- 4 beats/min in ambient pressure to 84 +/- 2 beats/min at 50 mmHg LBPP (P < 0.009). Blood pressure, brain oxygenation, blood flow velocity through the middle cerebral artery, and head skin microvascular blood flow did not change significantly with LBPP. As allowed by LBPP, ambulating at 60 and 20% body weight decreased ground reaction force (P < 0.05), whereas knee and ankle sagittal ranges of motion remained unaffected. In conclusion, ambulating in LBPP has no adverse impact on the systemic and head cardiovascular parameters while producing significant unweighting and minimal alterations in gait kinematics. Therefore, ambulating within LBPP is potentially a new and safe rehabilitation tool for patients to reduce loads on lower body musculoskeletal structures while preserving gait mechanics.

Adult↗
PubMed2006

Paraspinal muscle vasculature contributes to posterolateral spinal fusion.

STUDY DESIGN: Study of posterolateral fusions in a rabbit model. OBJECTIVES: To characterize the contribution of paraspinal musculature to the healing of posterolateral spinal fusions in a rabbit model. SUMMARY OF BACKGROUND DATA: Previous studies have demonstrated that successful spinal arthrodesis requires vascular ingrowth from adjacent decorticated bone. In other areas of the body, such as the tibia, vascular ingrowth from the surrounding musculature has also been shown to be important. The role of the surrounding paraspinal musculature in spinal fusions has yet to be assessed. METHODS: Twenty-five New Zealand white rabbits underwent posterolateral spinal fusion. One side of the animals was treated with autograft alone and served as the control group. On the contralateral side, the autograft was contained within porous or nonporous barrier sheets. Following euthanization, high-resolution radiographs, CT scans, and histologic analyses were performed to assess fusion and characterize vascular ingrowth. RESULTS: Using histologic evaluation, the fusion rate in the porous group was 90%, in the nonporous group 40%, and in the control group 55%. Vascular ingrowth was evident from the muscle through the porous sheet into the fusion mass. CONCLUSIONS: These results support our hypothesis that the paraspinal musculature provides important vascular ingrowth into the fusion site. Use of a porous barrier sheet appears to improve fusion by preventing muscle interposition while allowing vascular ingrowth from surrounding muscle.

Animals↗
PubMed2006

Noninvasive measurements of intramuscular pressure using pulsed phase-locked loop ultrasound for detecting compartment syndromes: a preliminary report.

OBJECTIVES: To develop a human model for compartment tamponade and test the efficacy of ultrasonic pulsed phase-locked loop (PPLL) fascial displacement waveform analysis for noninvasive measurement of intramuscular pressure (IMP). DESIGN: Human subject experiment. SETTING: University Level 1 trauma center. PARTICIPANTS: Nine male and 1 female volunteers (age 20 to 59),3 male acute compartment syndrome (ACS) patients (age 31 to 38). INTERVENTION: Thigh tourniquet was inflated in a stepwise fashion from 40 to 100 mm Hg to increase IMP transiently in volunteers. MAIN OUTCOME MEASUREMENTS: Invasive IMP by slit catheter and PPLL fascial displacement waveform in volunteers with model ACS and patients with ACS. RESULTS: In the model compartment tamponade group, thigh cuff occlusion increased IMP in the anterior compartment from a mean of 12.1 mm Hg (SE = 1.5) to a mean of 27.4 mm Hg (SE = 2.4, N = 8, P < 0.0001). By fast Fourier transform, the ratio of the amplitude of the fundamental frequency to the amplitude of the second harmonic frequency of the fascial displacement waveform as measured by PPLL increased from a resting mean of 1.12 (SE = 0.07) to a mean of 1.85 (SE = 0.18) under the same protocol (N = 6, P = 0.001). Combined data with compartment syndrome patients revealed linear correlation between IMP and PPLL with an R value of 0.8887. CONCLUSIONS: Subarterial thigh cuff pressure causes a significant and transient increase in IMP, serving as a model for anterior compartment tamponade. PPLL is able to detect fascial displacement waveforms corresponding to arterial pulsation and furthermore distinguishes between normal and elevated IMP. There is a linear correlation between PPLL measurements and invasive IMP. The PPLL shows potential utility as a device for noninvasive measurement of IMP for detecting compartment syndromes.

Adult↗
PubMed2005

A simple method for measuring interstitial fluid pressure in cancer tissues.

A novel procedure using a polyurethane transducer-tipped catheter (Millar) is described that allows reliable measurement of interstitial fluid pressure (IFP) in cancer tissues. Before and after each use, the transducer is calibrated at 37 degrees C by a water column. After calibration, the transducer is passed through the lumen of a surgical needle. The sensor is kept in the lumen of the needle during penetration into the tumor. The sensor tip is then introduced into the center core of the tumor as the needle sleeve is withdrawn from the tumor surface. Our new technique is simple and provides IFPs equal to those provided by the well-established, wick-in-needle technique. Using our new technique, we compared IFP in skin melanoma grafts in NG2 knockout and wild-type mice. Knocking out NG2 proteoglycan on vasculogenic and angiogenic pericytes reduced interstitial fluid pressure in melanoma from +4.9 cm H2O to -0.4 cm H2O (P=0.0054 Mann-Whitney U test).

Animals↗
PubMed2005

Exercise within lower body negative pressure partially counteracts lumbar spine deconditioning associated with 28-day bed rest.

Astronauts experience spine deconditioning during exposure to microgravity due to the lack of axial loads on the spine. Treadmill exercise in a lower body negative pressure (LBNP) chamber provides axial loads on the lumbar spine. We hypothesize that daily supine LBNP exercise helps counteract lumbar spine deconditioning during 28 days of microgravity simulated by bed rest. Twelve sets of healthy, identical twins underwent 6 degrees head-down-tilt bed rest for 28 days. One subject from each set of twins was randomly assigned to the exercise (Ex) group, whereas their sibling served as a nonexercise control (Con). The Ex group exercised in supine posture within a LBNP chamber for 45 min/day, 6 days/wk. All subjects underwent magnetic resonance imaging of their lumbar spine before and at the end of bed rest. Lumbar spinal length increased 3.7 +/- 0.5 mm in the Con group over 28-day bed rest, whereas, in the Ex group, lumbar spinal length increased significantly less (2.3 +/- 0.4 mm, P = 0.01). All lumbar intervertebral disk heights (L5-S1, L4-5, L3-4, L2-3, and L1-2) in the Con group increased significantly over the 28-day bed rest (P < 0.05). In the Ex group, there were no significant increases in L5-S1 and L4-5 disk heights. Lumbar lordosis decreased significantly by 3.3 +/- 1.2 degrees during bed rest in the Con group (P = 0.02), but it did not decrease significantly in the Ex group. Our results suggest that supine LBNP treadmill exercise partially counteracts lumbar spine lengthening and deconditioning associated with simulated microgravity.

Adaptation, Physiological↗
PubMed2005

Lower body positive-pressure exercise after knee surgery.

Lower body positive pressure allows unloading of the lower extremities during exercise in a pressurized treadmill chamber. This study assessed the preliminary feasibility of lower body positive pressure exercise as a rehabilitation technique by examining its effects on gait mechanics and pain, postoperatively. Fifteen patients who had arthroscopic meniscectomy or anterior cruciate ligament reconstruction participated in this study. Patients exercised for 5 minutes at 2.0 mph under three body weight conditions (normal body weight, 60% body weight, and 20% body weight) in random order. Bilateral ground reaction force, electromyographs, and dynamic knee range of motion were collected, and pain was assessed using a visual analog scale. Ground reaction forces for surgically treated and contralateral extremities were reduced 42% and 79% from normal body weight conditions when ambulating at 60% and 20% body weight, respectively. After meniscectomy, ambulatory knee range of motion decreased only at 20% body weight (37 degrees), compared with normal body weight conditions (49 degrees). Peak electromyographic activity of the biceps was maintained at all body weight conditions, whereas that of the vastus medialis was reduced at 20% body weight. Pain relief was significant with lower body positive pressure ambulation after anterior cruciate ligament reconstruction. This study showed that lower body positive pressure exercise is effective at reducing ground reaction forces, while safely facilitating gait postoperatively.

Adult↗
PubMed2005

Use of tissue ultrafiltration for treatment of compartment syndrome: a pilot study using porcine hindlimbs.

OBJECTIVES: To demonstrate the efficacy of compartment syndrome ultrafiltration for the treatment of acute compartment syndrome in an animal model. Our hypothesis is the removal of interstitial fluid will result in a reduction of intramuscular pressure compared with untreated controls in a model of bilateral induced compartment syndrome. DESIGN: Controlled experimental model. SETTING: Animal research facility. PATIENTS/PARTICIPANTS: Three pairs of porcine hindlimbs. INTERVENTION: Acute compartment syndrome was created in the pig hindlimb by infusion of saline to maintain the intramuscular pressure 30 mm Hg greater than the animal's mean arterial pressure for 8 hours. After a 2-hour reperfusion interval, ultrafiltration (removal of fluid through 1 mm diameter porous catheters, connected to -500 mm Hg suction) was commenced in 1 limb only and continued for 9.5 hours. MAIN OUTCOME MEASURES: Intramuscular pressure, ultrafiltrate volume, ultrafiltrate and serum levels of creatine kinase and lactate dehydrogenase, histologic measurement of extracellular and intracellular edema, as well as the degree of cellular necrosis. RESULTS: Intramuscular pressure tended to be lower on the treated side at the end of the treatment period [treated leg: 9.3 +/- 4.0 mm Hg (+/- SE), control leg: 19.3 +/- 1.4 mm Hg, P = 0.03]. Analysis of ultrafiltrate fluid showed that levels of creatine kinase and lactate dehydrogenase were elevated compared with serum levels. Creatine kinase levels in serum were measured at 4150 +/- 780 U/L, whereas ultrafiltrate levels of creatine kinase were 28,700 +/- 17,700 U/L (+/- SE) (P = 0.1). Lactate dehydrogenase was measured at 1950 +/- 180 U/L in serum, but markedly elevated in ultrafiltrate [160,000 +/- 88,900 U/L (+/- SE), P = 0.05]. Quantification of cellular and interstitial dimensions showed no difference in control and experimental limbs. Quantification of the degree of muscle necrosis revealed 6.1 +/- 2.7% necrosis in the treated limb compared to 11.3 +/- 1.6% necrosis in the control group (P = 0.02, df = 2, 1-tailed paired t test). CONCLUSION: This pilot study demonstrates the feasibility of tissue ultrafiltration for reduction of intramuscular pressure in this porcine model. Further studies are underway. Compartment syndrome ultrafiltration may be useful prophylactically in patients at risk for acute compartment syndrome. Sampling of interstitial fluid and frequent measurement of intramuscular pressure may allow earlier diagnosis and treatment of acute compartment syndrome, whereas the reduction of tissue pressure by compartment syndrome ultrafiltration may prevent acute compartment syndrome from occurring. Additionally, compartment syndrome ultrafiltration will not hinder the ability of clinicians to use the clinical examination and pressure monitoring as the gold standard.

Animals↗
PubMed2005

System for determination of ultrasonic wave speeds and their temperature dependence in liquids and in vitro tissues.

An interferometric technique capable of accurately measuring wave speed in liquids is reported. The hardware is adapted from a design to measure nonlinear responses of biological tissues to pressure changes (pressure derivatives) and temperature changes (temperature derivatives). It is used with the highly sensitive variable frequency pulsed phase-locked loop (VFPPLL) instrument. The system uses well-understood and well-characterized components and systems. The apparatus covers a temperature range from below 5 degrees C to above 45 degrees C. The system with the high-sensitivity VFPPLL is capable of measurement of wave speed to an uncertainty of less than 0.1%, and changes in wave speed to better than 0.001%. The transducer is an undamped temperature-characterized PZT-5A 500-kHz plate, whose output is corrected for off-resonance operation and for diffraction effects. To test the accuracy of the technique, measurement of ultrasonic compressional wave speed in water at temperatures from 10 degrees C to 45 degrees C are reported, with an estimated uncertainty of 0.07% and a temperature uncertainty of 0.15 degrees C. The agreement between mean values and literature values is better than 0.05%.

Acoustics↗
PubMed2005

Space exercise and Earth benefits.

The detrimental impact of long duration space flight on physiological systems necessitates the development of exercise countermeasures to protect work capabilities in gravity fields of Earth, Moon and Mars. The respective rates of physiological deconditioning for different organ systems during space flight has been described as a result of data collected during and after missions on the Space Shuttle, International Space Station, Mir, and bed rest studies on Earth. An integrated countermeasure that simulates the body's hydrostatic pressure gradient, provides mechanical stress to the bones and muscles, and stimulates the neurovestibular system may be critical for maintaining health and well being of crew during long-duration space travel, such as a mission to Mars. Here we review the results of our studies to date of an integrated exercise countermeasure for space flight, lower body negative pressure (LBNP) treadmill exercise, and potential benefits of its application to athletic training on Earth. Additionally, we review the benefits of Lower Body Positive Pressure (LBPP) exercise for rehabilitation of postoperative patients. Presented first are preliminary data from a 30-day bed rest study evaluating the efficacy of LBNP exercise as an integrated exercise countermeasure for the deconditioning effects of microgravity. Next, we review upright LBNP exercise as a training modality for athletes by evaluating effects on the cardiovascular system and gait mechanics. Finally, LBPP exercise as a rehabilitation device is examined with reference to gait mechanics and safety in two groups of postoperative patients.

Bed Rest↗
PubMed2005

Noninvasive assessment of intracranial pressure waveforms by using pulsed phase lock loop technology. Technical note.

Elevated intracranial pressure (ICP) is a major factor associated with incidences of morbidity and mortality in patients with neurological disorders. The use of conventional methods for ICP monitoring is currently limited to patients with severe neurological conditions because of the methods' invasive nature. The authors have developed an ultrasonic device capable of monitoring ICP waveforms noninvasively by using a pulsed phase lock loop (PPLL) technique. The PPLL device records skull movement (several meters) associated with ICP pulsations. The purpose of this study was to correlate PPLL waveforms with invasively measured ICP waveforms in patients at the University of California San Diego Medical Center (13 patients). A linear regression analysis revealed a high correlation between PPLL waveforms and invasively measured ICP waveforms during the same time domain (r2 = 0.88). A coherence function analysis, which provides the fractional portion of the mean square value at the output that is contributed by the input at a certain frequency, showed medium to high correlations (r2 = 0.50-0.90) between PPLL waveforms and invasively measured ICP waveforms at each harmonic wave components. Furthermore, there was a significant correlation (r2 = 0.680, p < 0.01) in the harmonic distortion ratio (an index representing how much a given waveform is distorted from a pure sine wave) between PPLL waveforms and invasively measured ICP waveforms. In conclusion, PPLL technology enables the noninvasive evaluation of ICP dynamics in clinical settings.

Adolescent↗
PubMed2005

Axial load-dependent cervical spinal alterations during simulated upright posture: a comparison of healthy controls and patients with cervical degenerative disease.

OBJECT: The objectives of this study were to simulate the upright loading condition in the cervical spine by applying a new compression device during supine posture and to assess intervertebral angles and cross-sectional areas of the spinal cord and dural tube before and during axial compression. METHODS: A magnetic resonance (MR) imaging-compatible device was developed to create axial compression with the patient in the supine position. Lateral radiographs were obtained in upright and supine positions with an axial load of 0% (supine) and by applying a cervical compression device at 7, 10, and 13% of body weight (BW) in 18 control individuals and seven symptomatic patients with cervical degenerative disc disease (DDD). Additionally, cervical MR images acquired in 17 controls and 12 patients were compared before and during an axial load of 8.4% BW in terms of anteroposterior diameter and cross-sectional area of the dural sac. The supine intervertebral angles with loads of 0, 7, 10, and 13% of the individuals' BW relative to upright posture were -8.1+/-1.3, -2.3+/-1.4, 1.3+/-1.9, and 2.8+/-2 degrees, respectively. Subsequent axial force was interpolated as 8.9% of BW to simulate upright cervical spine alignment. Under an axial loading similar to that created by the upright posture, the dural sac narrowed at the C5-6 interspace in asymptomatic individuals and at the C6-7 interspace in patients with cervical DDD. CONCLUSIONS: This cervical compression device may be a useful tool to simulate upright cervical spinal alignment. The results of this study help in understanding the pathophysiology of symptoms related to cervical degenerative disorders in upright posture.

Adult↗
PubMed2005

Intracranial pressure dynamics assessed by noninvasive ultrasound during 30 days of bed rest.

INTRODUCTION: Intracranial pressure (ICP) may be an important contributor to symptoms of space adaptation syndrome during the initial days of microgravity exposure. The temporary nature of these symptoms suggests that some physiologic adaptation or compensation occurs. Fluid shifts similar to those in microgravity can be simulated on Earth using head-down tilt (HDT) bed rest. This study was performed to calibrate a new noninvasive ICP instrument and to investigate ICP adaptation during 30 d of HDT bed rest. METHODS: A noninvasive ultrasound technique that measures small skull expansions with fluctuations in ICP was used to measure cranial oscillations before and near the end of 30-d HDT bed rest in eight healthy, male volunteers. Pulse phase-locked loop (PPLL) output voltage and arterial BP were continuously monitored and correlated. RESULTS: The amplitude of intracranial distance pulsation decreased during 30-d bed rest. Prior to bed rest, the PPLL amplitude was 25 +/- 9 mV and this amplitude was reduced by 60% to 9 +/- 4 mV (a value consistent with that of upright posture) at the end of HDT bed rest (p = 0.01). DISCUSSION: PPLL measurements of skull pulsations are acutely posture dependent, being significantly higher in supine and HDT as compared with upright posture. A cephalad fluid shift is probably the responsible mechanism. Our results indicate that there are adaptations to intracranial pooling of blood and tissue fluid during bed rest that reduce skull pulsation amplitudes to values similar to those obtained in normal upright posture. Detailed studies of the time course of cranial vessel and bone adaptations may provide insights into the potential adaptative mechanisms.

Aerospace Medicine↗
PubMed2005

Mechanical counter-pressure vs. gas-pressurized spacesuit gloves: grip and sensitivity.

INTRODUCTION: An elastic mechanical counter pressure (MCP) glove for spacesuits is under development. In this study we compared handgrip and pinch grip strength levels for the MCP glove and the current extravehicular mobility unit (EMU) gas-pressurized glove. METHODS: We employed handgrip and pinch grip dynamometers to assess strength levels and von Frey monofilaments to evaluate hand sensitivity. Tests were conducted with the gloved hand inserted in an evacuation chamber at 200 mmHg below atmospheric pressure to simulate conditions in space. RESULTS: Average bare hand strength was 463 N and decreased to 240 N for EMU and 250 N for MCP. Pinch grip and key grip testing showed no difference among conditions. However, there was a significant decrease in palmar grip strength from 111 N barehanded to 67 N in both gloves. Barehanded endurance time was 160 s and dropped to 63 and 69 s for EMU and MCP, respectively. Sensitivity was significantly better for MCP compared with the EMU. DISCUSSION: The MCP glove improved hand sensitivity when compared with the EMU glove and performed as well as the EMU glove in terms of overall handgrip strength, endurance at 25% of maximum handgrip strength, pinch grip, palmar grip, and key grip tests. Improvements in fabric composition and glove design may further improve ergonomic and other functional parameters of the MCP glove.

Adult↗
PubMed2005

The Bellagio Report: Cardiovascular risks of spaceflight: implications for the future of space travel.

BACKGROUND: Long-duration space missions, as well as emerging civilian tourist space travel activities, prompted review and assessment of data available to date focusing on cardiovascular risk and available risk mitigation strategies. The goal was the creation of tools for risk priority assessments taking into account the probability of the occurrence of an adverse cardiovascular event and available and published literature from spaceflight data as well as available risk mitigation strategies. METHODS: An international group of scientists convened in Bellagio, Italy, in 2004 under the auspices of the Aerospace Medical Association to review available literature for cardiac risks identified in the Bioastronautics Critical Path Roadmap (versions 2000, 2004). This effort led to the creation of a priority assessment framework to allow for an objective assessment of the hazard, probability of its occurrence, mission impact, and available risk mitigation measures. RESULTS/CONCLUSIONS: Spaceflight data are presented regarding evidence/ no evidence of cardiac dysrhythmias, cardiovascular disease, and cardiac function as well as orthostatic intolerance, exercise capacity, and peripheral resistance in presyncopal astronauts compared to non-presyncopal astronauts. Assessment of the priority of different countermeasures was achieved with a tabular framework with focus on probability of occurrence, mission impact, compliance, practicality, and effectiveness of countermeasures. Special operational settings and circumstances related to sensitive portions of any mission and the impact of environmental influences on mission effectiveness are addressed. The need for development of diagnostic tools, techniques, and countermeasure devices, food preparation, preservation technologies and medication, as well as an infrastructure to support these operations are stressed. Selected countermeasure options, including artificial gravity and pharmacological countermeasures need to be systematically evaluated and validated in flight, especially after long-duration exposures. Data need to be collected regarding the emerging field of suborbital and orbital civilian space travel, to allow for sound risk assessment.

Arrhythmias, Cardiac↗
PubMed2004

Human cutaneous vascular responses to whole-body tilting, Gz centrifugation, and LBNP.

We hypothesized that gravitational stimuli elicit cardiovascular responses in the following order with gravitational stress equalized at the level of the feet, from lowest to highest response: short-(SAC) and long-arm centrifugation (LAC), tilt, and lower body negative pressure (LBNP). Up to 15 healthy subjects underwent graded application of the four stimuli. Laser-Doppler flowmetry measured regional skin blood flow. At 0.6 G(z) (60 mmHg LBNP), tilt and LBNP similarly reduced leg skin blood flow to approximately 36% of supine baseline levels. Flow increased back toward baseline levels at 80-100 mmHg LBNP yet remained stable during 0.8-1.0 G(z) tilt. Centrifugation usually produced less leg vasoconstriction than tilt or LBNP. Surprisingly, SAC and LAC did not differ significantly. Thigh responses were less definitive than leg responses. No gravitational vasoconstriction occurred in the neck. All conditions except SAC increased heart rate, according to our hypothesized order. LBNP may be a more effective and practical means of simulating cardiovascular effects of gravity than centrifugation.

Adult↗
PubMed2004

Wavelet packet transform for R-R interval variability.

INTRODUCTION: Wavelet transform is used for time-frequency analysis. Recently, discrete wavelet transform (DWT) has been used to analyze R-R interval or heart rate variability. However, we hypothesized that wavelet packet transform (WPT) is a better way to analyze such variability. In the present study, we compared resolution of frequency band and amplitude, which are used for analysis of the variability, with DWT and WPT, followed by Hilbert transform. METHODS: A chirp signal which covers all frequency bands used for R-R interval variability was employed as a simulated signal. Levels 1-6 of DWT and level 3 of WPT were used for signal analysis. Amplitudes of the gained signal were evaluated with Hilbert transform. Differences in error of the gained amplitude from expected amplitude between CWT and DWT for low-frequency (LF) and high-frequency (HF) components were compared. To evaluate time-dependent changes in R-R interval variability, head-up tilt (HUT) was employed as an orthostatic challenge. RESULTS: Errors for both HF and LF, derived from the simulated signal with WPT, were significantly smaller than those of DWT. With HUT, time dependent changes in LF, HF, and LF/HF were observed. DISCUSSION: Although DWT is a valuable method for time-frequency analysis, WPT is a more appropriate method to utilize wavelet transform due to the equivalent resolution of the gained frequency band. WPT for time-frequency analysis improves analysis of time-dependent changes in R-R interval variability.

Adult↗
PubMed2004

Ischemic-preconditioning does not prevent neuromuscular dysfunction after ischemia-reperfusion injury.

The primary purpose of this study was to evaluate ischemic-preconditioning (IPC) as a means of improving tolerance to ischemia-reperfusion (IR) stress on neuromuscular function. A secondary objective was to isolate the area of injury within the neuromuscular unit responsible for contractile dysfunction after IR injury. Twenty-eight male rabbits were randomly assigned to four groups (sham, IPC only, sustained ischemia only, IPC and sustained ischemia). The IPC protocol consisted of three cycles of 10 min of tourniquet-induced ischemia (125 mmHg) followed by 10 min of reperfusion. Sustained ischemia was induced by 350 mmHg external compression for 2 h. Peak tetanic tension of the tibialis anterior (TA) muscle was evaluated 48 h after the tourniquet protocol by both peroneal nerve and direct muscle stimulation, with and without pharmacologic neuromuscular junction blockade. Animals subjected to combined IPC and sustained ischemia had an equivalent loss of contractile force to those undergoing sustained ischemia alone. Two hours of tourniquet-induced ischemia resulted in marked dysfunction of the TA neuromuscular unit when evaluated by peroneal nerve stimulation (p < 0.0001). Isolation of the TA muscle from the peroneal nerve with direct muscle stimulation and neuromuscular junction blockade preserved muscle function after 3 h of ischemia. In our model, these results clearly demonstrate that IPC provides no significant protective effect from IR injury to either nerve or muscle function in our model. In addition, nerve or neuromuscular junction injury, rather than muscle damage, is identified as primarily responsible for IR-related muscle dysfunction.

Algorithms↗