Physiologic Determinants of Near-Infrared Spectroscopy-Derived Cerebral and Tissue Oxygen Saturation Measurements in Critically Ill Patients

OBJECTIVES

Near-infrared spectroscopy (NIRS) is a potentially valuable modality to monitor the adequacy of oxygen delivery to the brain and other tissues in critically ill patients, but little is known about the physiologic determinants of NIRS-derived tissue oxygen saturations. The purpose of this study was to assess the contribution of routinely measured physiologic parameters to tissue oxygen saturation measured by NIRS.

DESIGN

An observational sub-study of patients enrolled in the Role of Active Deresuscitation After Resuscitation-2 (RADAR-2) randomized feasibility trial.

SETTING

Two ICUs in the United Kingdom.

PATIENTS

Patients were recruited for the RADAR-2 study, which compared a conservative approach to fluid therapy and deresuscitation with usual care. Those included in this sub-study underwent continuous NIRS monitoring of cerebral oxygen saturations (SctO2) and quadriceps muscle tissue saturations (SmtO2).

INTERVENTION

Synchronized and continuous mean arterial pressure (MAP), heart rate (HR), and pulse oximetry (oxygen saturation, Spo2) measurements were recorded alongside NIRS data. Arterial Paco2, Pao2, and hemoglobin concentration were recorded 12 hourly. Linear mixed effect models were used to investigate the association between these physiologic variables and cerebral and muscle tissue oxygen saturations.

MEASUREMENTS AND MAIN RESULTS

Sixty-six patients were included in the analysis. Linear mixed models demonstrated that Paco2, Spo2, MAP, and HR were weakly associated with SctO2 but only explained 7.1% of the total variation. Spo2 and MAP were associated with SmtO2, but together only explained 0.8% of its total variation. The remaining variability was predominantly accounted for by between-subject differences.

CONCLUSIONS

Our findings demonstrated that only a small proportion of variability in NIRS-derived cerebral and tissue oximetry measurements could be explained by routinely measured physiologic variables. We conclude that for NIRS to be a useful monitoring modality in critical care, considerable further research is required to understand physiologic determinants and prognostic significance.

A High Activity Level Is Required for Augmented Muscle Capillarization in Older Women

PURPOSE

This study aimed to evaluate the influence of lifelong regular physical activity on skeletal muscle capillarization in women.

METHODS

Postmenopausal women, 61±4 yr old, were divided according to self-reported physical activity level over the past 20 yrs: sedentary (SED; n = 14), moderately active (MOD; n = 12), and very active (VERY; n = 15). Leg blood flow (LBF) was determined by ultrasound Doppler, and blood samples were drawn from the femoral artery and vein for calculation of leg oxygen uptake (LVO2) at rest and during one-legged knee extensor exercise. A skeletal muscle biopsy was obtained from the vastus lateralis and analyzed for capillarization and vascular endothelial growth factor (VEGF) and mitochondrial OXPHOS proteins. Platelets were isolated from venous blood and analyzed for VEGF content and effect on endothelial cell proliferation.

RESULTS

The exercise-induced rise in LBF and LVO2 was faster (P = 0.008) in VERY compared with SED and MOD. Steady-state LBF and LVO2 were lower (P < 0.04) in MOD and VERY compared with SED. Capillary-fiber ratio and capillary density were greater (P < 0.03) in VERY (1.65 ± 0.48 and 409.3 ± 57.5) compared with MOD (1.30 ± 0.19 and 365.0 ± 40.2) and SED (1.30 ± 0.30 and 356.2 ± 66.3). Skeletal muscle VEGF and OXPHOS complexes I, II, and V were ~1.6-fold and ~1.25-fold (P < 0.01) higher, respectively, in VERY compared with SED. Platelets from all groups induced an approximately nine-fold (P < 0.001) increase in endothelial cell proliferation.

CONCLUSION

A very active lifestyle is associated with superior skeletal muscle exercise hemodynamics and greater potential for oxygen extraction concurrent with a higher skeletal muscle capillarization and mitochondrial capacity.

Blood Flow Restriction Combined with Electrical Stimulation Attenuates Thigh Muscle Disuse Atrophy

PURPOSE

This study aimed to investigate the effects of blood flow restriction (BFR) combined with electrical muscle stimulation (EMS) on skeletal muscle mass and strength during a period of limb disuse.

METHODS

Thirty healthy participants (22 ± 3 yr; 23 ± 3 kg·m-2) were randomly assigned to control (CON; n = 10), BFR alone (BFR; n = 10), or BFR combined with EMS (BFR + EMS; n = 10). All participants completed unloading of a single leg for 14 d, with no treatment (CON), or while treated with either BFR or BFR + EMS (twice daily, 5 d·wk-1). BFR treatment involved arterial three cycles of 5-min occlusion using suprasystolic pressure, each separated by 5 min of reperfusion. EMS (6 s on, 15 s off; 200 μs; 60 Hz; 15% maximal voluntary contraction [MVC]) was applied continuously throughout the three BFR cycles. Quadriceps muscle mass (whole-thigh lean mass via dual-energy x-ray absorptiometry and vastus lateralis [VL] muscle thickness via ultrasound) and strength (via knee extension MVC) were assessed before and after the 14-d unloading period.

RESULTS

After limb unloading, whole-thigh lean mass decreased in the control group (-4% ± 1%, P < 0.001) and BFR group (-3% ± 2%, P = 0.001), but not in the BFR + EMS group (-0.3% ± 3%, P = 0.8). VL muscle thickness decreased in the control group (-4% ± 4%, P = 0.005) and was trending toward a decrease in the BFR group (-8% ± 11%, P = 0.07) and increase in the BFR + EMS group (+5% ± 10%, P = 0.07). Knee extension MVC decreased over time (P < 0.005) in the control group (-18% ± 15%), BFR group (-10% ± 13%), and BFR + EMS group (-18% ± 15%), with no difference between groups (P > 0.5).

CONCLUSION

Unlike BFR performed in isolation, BFR + EMS represents an effective interventional strategy to attenuate the loss of muscle mass during limb disuse, but it does not demonstrate preservation of strength.

Effects of blood flow restriction on muscle size and gene expression in muscle during immobilization: A pilot study

PURPOSE

Muscle mass is known to rapidly decrease with muscle disuse. Previous reports suggest that repetitive blood flow restriction (BFR) mitigates the reduction of muscle mass with disuse. However, the effects of BFR on muscle atrophy and gene expression levels in muscle during cast immobilization have not been clarified.

METHODS

To investigate the effect of BFR on muscle atrophy and gene expression levels during cast immobilization in humans, we recruited 10 healthy males who were randomly divided into the control and BFR treatment groups. All subjects were immobilized with a cast for 14 days. BFR treatment was conducted only in the BFR group. We evaluated cross sectional area (CSA) of thigh muscles by magnetic resonance imaging before and 14 days after cast immobilization. A percutaneous biopsy of the vastus lateralis muscle (VL) was performed before and 1, 7, and 14 days after cast immobilization. Expression of genes related to muscle atrophy and synthesis were evaluated using real-time PCR.

RESULTS

The CSA of the VL and the thigh flexor muscles were significantly decreased in both groups; however, percent decrease in CSA was significantly smaller in the BFR group compared with the control group. In two-way repeated ANOVA analysis, the time × treatment interaction in gene expression of the muscle-specific ubiquitin ligases muscle ring finger 1 (MuRF1) was significant, and elevated MURF1 expression level by cast immobilization was seemed to be suppressed by the BFR treatment.

CONCLUSION

BFR treatment may prevent reduced VL and thigh flexor muscles and increased MuRF1 expression level during cast immobilization. Further study is required to confirm these results.

Extracorporeal shock wave-assisted adipose-derived fresh stromal vascular fraction restores the blood flow of critical limb ischemia in rat

We tested the hypothesis that extracorporeal-shock-wave (ECSW)-assisted adipose-derived stromal vascular fraction (SVF) therapy was better than either one for restoring the blood flow in critical limb ischemia (CLI). Adult male-SD rats were categorized into group 1 (sham-operated-control), group 2 (CLI), group 3 [CLI + ECSW (280 impulses/0.10 mJ/mm²) applied to left inguinal area at 3 h after CLI], group 4 [CLI + SVF (1.2 × 10⁶) implanted into CLI area at 3 h after CLI], group 5 (CLI + ECSW-SVF). In vitro studies showed that ECSW significantly enhanced angiogenesis in human umbilical-vein endothelial cells and carotid-artery ring, and SVF significantly suppressed inflammation (TNF-α/NF-Κb/IL-1ß/MMP-9) in smooth-muscle cells treated by LPS (all p < .001). By day 14 after CLI, the ratio of ischemic/normal blood flow (INBF) was highest in group 1, lowest in group 2, significantly higher in group 5 than in groups 3 and 4, but no difference was shown between the latter two groups (all p < .001). The fibrotic area in CLI region exhibited an opposite pattern of INBF ratio (all p < .0001). Protein (CD31/vWF/eNOS) and cellular (CD31/vWF) expressions and number of small vessels in CLI area exhibited an identical pattern, whilst protein expressions of apoptotic (caspase3/PARP/mitochondrial-Bax) fibrotic/DNA-damaged (Samd3/TFG-ß/γ-H2AX) biomarkers exhibited an opposite pattern to INBF among five groups (all p < .0001). The numbers of angiogenetic cells in CLI region (SDF-1α/VEGF/CXCR4) and endothelial-progenitor cells (C-kit/CD31+//Sca-1/CD31+//CD34/KDR+/VE-cadherin/CD34+) in circulation significantly and progressively increased from groups 2 to 5 (all p < .0001). In conclusion, ECSW-SVF therapy effectively enhanced angiogenesis and restoration of blood flow in CLI area.

Recurrent Diabetic Muscle Infarction Affecting Bilateral Thighs: Uncommon Presentation with Grave Prognosis

INTRODUCTION

Diabetic muscle infarction is a rare microangiopathic complication of poorly-controlled diabetes mellitus. Here we present the case of a female with a thirteen year history of poorly-controlled diabetes mellitus who presented with severe right leg pain and swelling and was eventually diagnosed with this condition.

CASE PRESENTATION

A 24-year-old female with a thirteen year history of poorly-controlled diabetes mellitus presented with intense right thigh pain and swelling. Initial labs revealed elevated hemoglobin A1c, CK, ESR, and CRP. White blood cell count was within normal limits and patient was afebrile with normal vitals at time of presentation. Magnetic resonance imaging of the right lower extremity demonstrated T1 isohypointensity in the vastus medialis and sartorius with diffuse fascial and subcutaneous edema. Bilateral lower extremity dopplers revealed no evidence of deep vein thrombosis and autoimmune workup was negative. The patient was diagnosed with diabetic muscle infarction given the combination of her clinical presentation and imaging findings. She was started on low-dose aspirin and glycemic control was achieved with a rigorous insulin regimen prior to discharge. She returned six weeks after discharge with persistent right thigh pain and swelling. MRI at this time revealed findings consistent with diabetic muscle infarction in left and right thighs.

DISCUSSION

Clinicians should include diabetic muscle infarction in the differential of any diabetic patient who presents with lower extremity pain and swelling and history of poor glycemic control. Maintaining a high index of suspicion can help confirm the diagnosis early and avoid unnecessary tests and interventions that can lengthen recovery time.

Improving Peripheral and Central Vascular Adjustments during Exercise through a Training Program in Adolescents with Obesity

OBJECTIVE

The effects of a training program (TP) on muscle microvascularization during exercise remained to be explored in adolescents with obesity. We hypothesized that a TP would lead to better microvascular adaptations to exercise in skeletal muscle.

METHODS

15 inactive adolescents followed a 12-week TP where both peripheral (muscular microvascularization) and central (cardiac) adaptations to exercise (40 min exercise set at 70% V̇O2peak) were assessed before and after intervention. Microvascular adaptations were evaluated in the Musculus vastus lateralis with near-infrared spectroscopy, by measurement of muscular blood volume (IR-BV) and tissue oxygen saturation (IR-SO2). Central adaptations were evaluated using thoracic impedance.

RESULTS

The TP favored lower BMI (p < 0.001), lower total and abdominal fat (p < 0.001), and a trend for the decrease in insulin resistance index (p = 0.07). V̇O2peak relative to weight (p = 0.008) and maximum power output increased (p = 0.0003). A smaller initial drop in IR-BV and IR-SO2 (p < 0.001), a prompter return of these parameters to their base values, and a higher IR-BV and IR-SO2 all times taken together (p < 0.001) were observed after completing the TP. Concerning central adaptation, cardiac output decreased (p < 0.001).

CONCLUSION

We demonstrate for the first time by noninvasive techniques that a training program induces peripheral and central vascular adaptations to exercise in adolescents with obesity.

The impact of delivery profile of essential amino acids upon skeletal muscle protein synthesis in older men: clinical efficacy of pulse vs. bolus supply

Essential amino acids (EAA) are responsible for skeletal muscle anabolic effects after nutrient intake. The pattern of appearance of EAA in blood, e.g., after intake of "slow" or "fast" protein sources or in response to grazing vs. bolus feeding patterns, may impact anabolism. However, the influence of this on muscle anabolism is poorly understood, particularly in older individuals. We determined the effects of divergent feeding profiles of EAA on blood flow, anabolic signaling, and muscle protein synthesis (MPS) in older men. Sixteen men (∼70 yr) consumed EAA either as a single dose (bolus, 15 g; n = 8) or as small repeated fractions (pulse, 4 × 3.75 g every 45 min; n = 8) during (13)C6 phenylalanine infusion. Repeated blood samples and muscle biopsies permitted measurement of fasting and postprandial plasma EAA, insulin, anabolic signaling, and MPS. Muscle blood flow was assessed by contrast-enhanced ultrasound (Sonovue). Bolus achieved rapid insulinemia (12.7 μiU/ml 25-min postfeed), essential aminoacidemia (∼3,000 μM, 45-65 min postfeed), and mTORC1 activity; pulse achieved attenuated insulin responses, gradual low-amplitude aminoacidemia (∼1,800 μM 80-195 min after feeding), and undetectable mTORC1 signaling. Despite this, equivalent anabolic responses were observed: fasting FSRs of 0.051 and 0.047%/h (bolus and pulse, respectively) increased to 0.084 and 0.073%/h, respectively. Moreover, pulse led to sustainment of MPS beyond 180 min, when bolus MPS had returned to basal rates. We detected no benefit of rapid aminoacidemia in this older population despite enhanced anabolic signaling and greater overall EAA exposure. Rather, apparent delayed onset of the "muscle-full" effect permitted identical MPS following low-amplitude-sustained EAA exposure.

Diabetic Muscle Infarction (Myonecrosis): Underdiagnosed or Underreported?

Diabetic muscle infarction is a rare complication of diabetes. It is seen more in Type 1 DM than Type 2 DM, but in both it is associated with longer duration of diabetes, poor glycemic control with or without microvascular complications. We present a case report of a 47 year diabetic male, who presented with sudden onset of painful swelling of the left thigh muscles (vastus group). The patient had microvascular complications of diabetes. Apart for mild elevation of CPK and LDH other investigations were normal. MRI findings of left thigh showed T2 hyperintensities in the involved muscles which established the diagnosis. Muscle biopsy revealed necrosis of the muscle fibres, presence of inflammatory cell infiltrates and hyalinization of the blood vessels with luminal narrowing which is characteristic of diabetic muscle infarction. The patient was treated with immobilization, analgesics and adequate blood sugar control. This case highlights the rarity of finding vascular changes as well as the poor prognosis and the occurrence of fatal complications in near future.

Blood flow restriction rehabilitation for extremity weakness: a case series

BACKGROUND

Blood flow restricted (BFR) training, the brief and partial restriction of venous outflow of an extremity during low load resistance exercises, is a safe and effective method of improving strength in healthy, active individuals. A relatively unexplored potential of this adjunctive modality lies in treating patients with severe musculoskeletal trauma, persistent chronic quadriceps and hamstring weakness despite traditional therapy, and low improvement during early postoperative strengthening.

METHODS

This case series describes patients with chronic quadriceps and hamstring weakness who received an intervention of BFR at low loads, 20% of 1 repetition max (1RM), to restore strength. A case series was conducted of seven patients, all located at one hospital and all with traumatic lower extremity injuries. The seven patients were treated at the same medical center and with the same BFR protocol. All seven patients had isokinetic dynamometer testing that showed persistent thigh muscle weakness despite previous rehabilitation with traditional therapy and 35% to 75% peak torque deficit in either knee extension or flexion compared with the contralateral lower extremity. Patients underwent 2 weeks of BFR training therapy using a pneumatic tourniquet set at 110mmHg while performing leg extensions, leg presses, and reverse leg presses. All affected extremities were retested after 2 weeks (six treatment sessions). Dynamometer measurements were done with flexion and extension at two speeds: 90° and 300°/sec. The data recorded included peak torque normalized for body weight, average power, and total work.

RESULTS

All seven patients demonstrated improvements in peak torque, average power, and total work for both knee flexion and extension, with power being the most improved overall. Peak torque improved an average of 13% to 37%, depending on contraction direction and speed. Average power improved an average of 42% to 81%, and total work improved an average of 35% to 55%.

CONCLUSION

BFR therapy at low loads can affect improvement in muscle strength in patients who are unable to perform high-resistance exercise or patients who have persistent extremity weakness despite traditional therapy.

Central and peripheral adjustments during high-intensity exercise following cold water immersion

PURPOSE

We investigated the acute effects of cold water immersion (CWI) or passive recovery (PAS) on physiological responses during high-intensity interval training (HIIT).

METHODS

In a crossover design, 14 cyclists completed 2 HIIT sessions (HIIT1 and HIIT2) separated by 30 min. Between HIIT sessions, they stood in cold water (10 °C) up to their umbilicus, or at room temperature (27 °C) for 5 min. The natural logarithm of square-root of mean squared differences of successive R-R intervals (ln rMSSD) was assessed pre- and post-HIIT1 and HIIT2. Stroke volume (SV), cardiac output (Q), O2 uptake (VO2), total muscle hemoglobin (t Hb) and oxygenation of the vastus lateralis were recorded (using near infrared spectroscopy); heart rate, Q, and VO2 on-kinetics (i.e., mean response time, MRT), muscle de-oxygenation rate, and anaerobic contribution to exercise were calculated for HIIT1 and HIIT2.

RESULTS

ln rMSSD was likely higher [between-trial difference (90% confidence interval) [+13.2% (3.3; 24.0)] after CWI compared with PAS. CWI also likely increased SV [+5.9% (-0.1; 12.1)], possibly increased Q [+4.4% (-1.0; 10.3)], possibly slowed Q MRT [+18.3% (-4.1; 46.0)], very likely slowed VO2 MRT [+16.5% (5.8; 28.4)], and likely increased the anaerobic contribution to exercise [+9.7% (-1.7; 22.5)].

CONCLUSION

CWI between HIIT slowed VO2 on-kinetics, leading to increased anaerobic contribution during HIIT2. This detrimental effect of CWI was likely related to peripheral adjustments, because the slowing of VO2 on-kinetics was twofold greater than that of central delivery of O2 (i.e., Q). CWI has detrimental effects on high-intensity aerobic exercise performance that persist for ≥ 45 min.

Sex differences in blood flow restricted isotonic knee extensions to fatigue

AIM

It has been shown that females have greater muscular endurance than males and that this advantage is eliminated when blood flow is restricted. It is unknown if sex differences in dynamic endurance exist during low-load blood flow restricted (BFR) resistance exercise. The purpose of this study was to investigate sex differences in quadriceps femoris fatigability during isotonic knee extension exercise coupled with a blood flow restriction.

METHODS

Ten males and ten females completed three sets of low-load isotonic knee extension exercises (20% of peak torque) to volitional failure under two conditions: blood flow restricted (BFR) and non-restricted free flow (FF). The number of repetitions, exercise volume, post-exercise strength loss and surface electromyography (EMG) were measured.

RESULTS

Females performed more repetitions than males in the FF (252±37 vs. 112±17 repetitions; P<0.01) and BFR conditions (165±29 vs. 79±8 repetitions; P<0.01). Both sexes performed ~30% fewer repetitions during the BFR condition. MVC torque decreased approximately 37% following both conditions (P<0.01) and EMG activity increased (P<0.05) during the exercise bouts.

CONCLUSION

Similar fatigue characteristics were evident in FF and BFR conditions for both sexes, and females demonstrated greater endurance, as determined by the number of repetitions completed, in both conditions. It may be beneficial to increase the relative exercise load for females in order to decrease the time under BFR.

Myogenic and proteolytic mRNA expression following blood flow restricted exercise

AIM

Resistance exercise performed at low loads (20-30% of maximal strength) with blood flow restriction (BFR) acutely increases protein synthesis and induces hypertrophy when performed chronically. We investigated myogenic and proteolytic mRNA expression 8 h following an acute bout of knee extension exercise.

METHODS

Fifteen subjects (22.8 ± 3.7 years, eight men and seven women) were randomized to two exercise conditions: BFR or control exercise. All participants performed four sets of exercise (30, 15, 15 and 15 repetitions) at 20% of maximal strength. Persons in the BFR group had a cuff placed on the upper thigh inflated to 1.5 times brachial systolic blood pressure (cuff pressure range: 135-186 mmHg). Muscle biopsies from the vastus lateralis were excised 24 h before and 8 h following the exercise.

RESULTS

  RT-PCR analysis demonstrated no change in myogenic gene expression (insulin-like growth factor-1, MyoD, myogenin, myostatin - a negative regulator) with either exercise condition (P > 0.123). However, BFR exercise downregulated mRNA expression in transcripts associated with proteolytic pathways (FOXO3A, Atrogin-1 and MuRF-1) with no change in the control exercise condition. Specifically, median mRNA expression of FOXO3A decreased by 1.92-fold (P = 0.01), Atrogin-1 by 2.10-fold (P = 0.01) and MuRF-1 by 2.44-fold (P = 0.01).

CONCLUSION

  These data are consistent with the downregulation of proteolytic transcripts observed following high-load resistance exercise. In summary, myogenic genes are unchanged and proteolytic genes associated with muscle remodelling are reduced 8 h following low-load BFR exercise.

Delayed-onset muscle soreness induced by low-load blood flow-restricted exercise

We performed two experiments to describe the magnitude of delayed-onset muscle soreness (DOMS) associated with blood flow restriction (BFR) exercise and to determine the contribution of the concentric (CON) versus eccentric (ECC) actions of BFR exercise on DOMS. In experiment 1, nine subjects performed three sets of unilateral knee extension BFR exercise at 35% of maximal voluntary contraction (MVC) to failure with a thigh cuff inflated 30% above brachial systolic pressure. Subjects repeated the protocol with the contralateral limb without flow restriction. Resting soreness (0-10 scale) and algometry (pain-pressure threshold; PPT) were assessed before and 24, 48 and 96 h post-exercise. Additionally, MVC and vastus lateralis cross-sectional area (CSA) were measured as indices of exercise-induced muscle damage. At 24-h post-exercise, BFR exercise resulted in more soreness than exercise without BFR (2.8 +/- 0.3 vs 1.7 +/- 0.5) and greater reductions in PPT (15.2 +/- 1.7 vs. 20 +/- 2.3 N) and MVC (14.1 +/- 2.5% decrease vs. 1.5 +/- 4.5% decrease) (p <or= 0.05). In experiment 2, 15 different subjects performed three sets of unilateral BFR exercise at 35% MVC with one limb performing only the CON action and the contralateral performing the ECC action. The aforementioned indices of DOMS were assessed before exercise and 24, 48 and 96 h post-exercise. At 24 h post-exercise, CON BFR exercise resulted in more resting soreness than ECC BFR exercise (3.0 +/- 0.5 vs. 1.6 +/- 0.4), and a greater decrease in MVC (9.8 +/- 2.7% decrease vs. 3.4 +/- 2.5% decrease) (p <or= 0.05). These data suggest that knee extension BFR exercise induces mild DOMS and that BFR exercise elicits muscle damage under atypical conditions with low-tension concentric contractions.

Knee extensor fatigability after bedrest for 8 weeks with and without countermeasure

We analyzed the effects of gravitational unloading on muscular fatigability and the effectiveness of resistive vibration exercise to counteract these changes. Changes in knee extensor fatigability as a consequence of 8 weeks of horizontal bedrest with or without daily resistive vibration exercise were evaluated in 17 healthy male volunteers. Bedrest increased fatigability (% decrease in maximal voluntary isometric torque per minute exercise) from -7.2 +/- 0.5 to -10.2 +/- 1.0%/min (P < 0.05), which was accompanied by a decline (of 52.0 +/- 3.7%, P < 0.05) in muscle blood flow. Daily resistive vibration exercise training during bedrest prevented increases in fatigability (from -10.8 +/- 1.8 to -8.4 +/- 1.6%/min, P < 0.05), and mitigated the reduction in blood flow (decline of 26.1 +/- 5.1%, P < 0.05). Daily resistive exercise may thus be suggested as an effective countermeasure during spaceflight and illness-related prolonged bedrest to combat the detrimental changes in muscle endurance that result from gravitational unloading.

Effects of exercise load and blood-flow restriction on skeletal muscle function

Resistance training at low loads with blood flow restriction (BFR) (also known as Kaatsu) has been shown to stimulate increases in muscle size and strength. It is unclear how occlusion pressure, exercise intensity, and occlusion duration interact, or which combination of these factors results in the most potent muscle stimulus.

PURPOSE

To determine the effect of eight BFR protocols on muscle fatigue (decrement in maximal voluntary contraction (MVC) after the performance of exercise), and to compare the decrement in MVC with the currently recommended resistance exercise intensity (~80% MVC).

METHODS

During five test sessions, 21 subjects (14 males and 7 females, 27.7 +/- 4.9 yr) completed nine protocols, each consisting of three sets of knee extensions (KE) to failure. One protocol was high-load (HL) exercise (80% MVC) with no BFR, and the other eight were BFR at varying levels of contraction intensity (20 or 40% MVC), occlusion pressure (partial (~160 mm Hg) or complete (~300 mm Hg)), and occlusion duration (off during the rest between sets or continuously applied). To evaluate each protocol, MVC were performed before and after exercise, and the decrement in force was calculated.

RESULTS

Three sets of KE at 20% MVC with continuous partial occlusion (20%(ConPar)) resulted in a greater decrement in MVC compared with HL (31 vs 19%, P = 0.001). None of the other BFR protocols were different from the HL protocol, nor were they different from 20%(ConPar) (P > 0.05).

CONCLUSION

All BFR protocols elicited at least as much fatigue as HL, even though lower loads were used. The 20%(ConPar) protocol was the only one that elicited significantly more fatigue than HL. Future research should evaluate protocol training effectiveness and overall safety of BFR exercise.

Role of adenosine in regulating the heterogeneity of skeletal muscle blood flow during exercise in humans

Evidence from both animal and human studies suggests that adenosine plays a role in the regulation of exercise hyperemia in skeletal muscle. We tested whether adenosine also plays a role in the regulation of blood flow (BF) distribution and heterogeneity among and within quadriceps femoris (QF) muscles during exercise, measured using positron emission tomography. In six healthy young women, BF was measured at rest and then during three incremental low and moderate intermittent isometric one-legged knee-extension exercise intensities without and with theophylline-induced nonselective adenosine receptor blockade. BF heterogeneity within muscles was calculated from 16-mm3voxels in BF images and heterogeneity among the muscles from the mean values of the four QF compartments. Mean BF in the whole QF and its four parts increased, and heterogeneity decreased with workload both without and with theophylline ( P < 0.001). Adenosine receptor blockade did not have any effect on mean bulk BF or BF heterogeneity among the QF muscles, yet blockade increased within-muscle BF heterogeneity in all four QF muscles ( P = 0.03). Taken together, these results show that BF becomes less heterogeneous with increasing exercise intensity in the QF muscle group. Adenosine seems to play a role in muscle BF heterogeneity even in the absence of changes in bulk BF at low and moderate one-leg intermittent isometric exercise intensities.

Sex differences in leg vasodilation during graded knee extensor exercise in young adults

Limb vascular conductance responses to pharmacological and nonexercise vasodilator stimuli are generally augmented in women compared with men. In the present investigation, we tested the hypothesis that exercise-induced vasodilator responses are also greater in women than men. Sixteen women and 15 men (20–30 yr) with similar fitness and activity levels performed graded quadriceps exercise (supine, single-leg knee extensions, 40 contractions/min) to maximal exertion. Active limb hemodynamics (left common femoral artery diameter and volumetric blood flow), heart rate (ECG), and beat-to-beat mean arterial blood pressure (MAP; radial artery tonometry) were measured during each 3-min workload (4.8 and 8 W/stage for women and men, respectively). The hyperemic response to exercise (slope of femoral blood flow vs. workload) was greater ( P < 0.01) in women as was femoral blood flow at workloads >15 W. The leg vasodilatory response to exercise (slope of calculated femoral vascular conductance vs. absolute workload) was also greater in women than in men ( P < 0.01) because of the sex difference in hyperemia and the women's lower MAP (∼10–15 mmHg) at all workloads ( P < 0.05). The femoral artery dilated to a significantly greater extent in the women (∼0.5 mm) than in the men (∼0.1 mm) across all submaximal workloads. At maximal exertion, femoral vascular conductance was lower in the men (men, 18.0 ± 0.6 ml·min−1·mmHg−1; women, 22.6 ± 1.4 ml·min−1·mmHg−1; P < 0.01). Collectively, these findings suggest that the vasodilatory response to dynamic leg exercise is greater in young women vs. men.

Spatial heterogeneity of quadriceps muscle deoxygenation kinetics during cycle exercise

To test the hypothesis that, during exercise, substantial heterogeneity of muscle hemoglobin and myoglobin deoxygenation [deoxy(Hb + Mb)] dynamics exists and to determine whether such heterogeneity is associated with the speed of pulmonary O(2) uptake (pVo(2)) kinetics, we adapted multi-optical fibers near-infrared spectroscopy (NIRS) to characterize the spatial distribution of muscle deoxygenation kinetics at exercise onset. Seven subjects performed cycle exercise transitions from unloaded to moderate [<gas exchange threshold (GET)] and heavy (>GET) work rates and the relative changes in deoxy(Hb + Mb), at 10 sites in the quadriceps, were sampled by NIRS. At exercise onset, the time delays in muscle deoxy(Hb + Mb) were spatially inhomogeneous [intersite coefficient of variation (CV), 3~56% for <GET, 2~21% for >GET]. The primary component kinetics (time constant) of muscle deoxy(Hb + Mb) reflecting increased O(2) extraction were also spatially inhomogeneous (intersite CV, 6~48% for <GET, 7~47% for >GET) and faster (P < 0.05) than those of phase 2 pVo(2). However, the degree of dynamic intersite heterogeneity in muscle deoxygenation did not correlate significantly with phase 2 pVo(2) kinetics. In conclusion, the dynamics of quadriceps microvascular oxygenation demonstrates substantial spatial heterogeneity that must arise from disparities in the relative kinetics of Vo(2) and O(2) delivery increase across the regions sampled.

Effects of acute hypoxia on cerebral and muscle oxygenation during incremental exercise

To determine if fatigue at maximal aerobic power output was associated with a critical decrease in cerebral oxygenation, 13 male cyclists performed incremental maximal exercise tests (25 W/min ramp) under normoxic (Norm: 21% FiO2) and acute hypoxic (Hypox: 12% FiO2) conditions. Near-infrared spectroscopy (NIRS) was used to monitor concentration (μM) changes of oxy- and deoxyhemoglobin (Δ[O2Hb], Δ[HHb]) in the left vastus lateralis muscle and frontal cerebral cortex. Changes in total Hb were calculated (Δ[THb] = Δ[O2Hb] + Δ[HHb]) and used as an index of change in regional blood volume. Repeated-measures ANOVA were performed across treatments and work rates (α = 0.05). During Norm, cerebral oxygenation rose between 25 and 75% peak power output {Powerpeak; increased (inc) Δ[O2Hb], inc. Δ[HHb], inc. Δ[THb]}, but fell from 75 to 100% Powerpeak {decreased (dec) Δ[O2Hb], inc. Δ[HHb], no change Δ[THb]}. In contrast, during Hypox, cerebral oxygenation dropped progressively across all work rates (dec. Δ[O2Hb], inc. Δ[HHb]), whereas Δ[THb] again rose up to 75% Powerpeak and remained constant thereafter. Changes in cerebral oxygenation during Hypox were larger than Norm. In muscle, oxygenation decreased progressively throughout exercise in both Norm and Hypox (dec. Δ[O2Hb], inc. Δ [HHb], inc. Δ[THb]), although Δ[O2Hb] was unchanged between 75 and 100% Powerpeak. Changes in muscle oxygenation were also greater in Hypox compared with Norm. On the basis of these findings, it is unlikely that changes in cerebral oxygenation limit incremental exercise performance in normoxia, yet it is possible that such changes play a more pivotal role in hypoxia.

Vastus Lateralis Motor Nerve Can Adversely Affect Anterolateral Thigh Flap Harvest

BACKGROUND

The vascular anatomy of the anterolateral thigh flap has been well studied, but no study has evaluated the effect of the vastus lateralis motor nerve anatomy on anterolateral thigh flap harvest.

METHODS

A retrospective review was performed of all anterolateral thigh flaps from January of 2003 through December of 2004. Information regarding the motor nerve to the vastus lateralis muscle was recorded, along with its influence on anterolateral thigh flap harvest.

RESULTS

Forty-three anterolateral thigh flap procedures were performed over a 2-year period. In three cases (7 percent), the course of the motor nerve to the vastus lateralis resulted in a significant modification in anterolateral thigh flap harvest. In one case, the motor nerve passed between the venae comitantes of the descending branch of the lateral femoral circumflex artery just proximal to the midperforator origin. In two cases, large skin islands were raised with two perforators included in each flap. The motor nerve passed between the two perforators in these cases.

CONCLUSIONS

Two patterns of vastus lateralis motor nerve anatomy can adversely influence anterolateral thigh flap elevation. One involves the motor nerve passing through the main vascular pedicle. The other occurs when multiple perforators are required to support large flaps with the motor nerve passing between these perforators. In some cases, the course of the nerve may require transection of the nerve, with a subsequent deficit in vastus lateralis function. In similar cases, if the nerve is preserved, the vascular pedicle may require significant modification, which may possibly compromise flap perfusion.

Diabetic muscle infarction: a rare complication of advanced diabetes mellitus

Diabetic muscle infarction is a rare complication of diabetes mellitus first described in 1965. It typically arises in patients with long-standing diabetes mellitus who have complications of the disease, including nephropathy, retinopathy, and neuropathy. It typically presents with acute onset of thigh pain with an associated palpable tender mass. Recurrent episodes in the same or opposite limb are common. Laboratory evaluation does not generally show any consistent abnormality except for poor glucose control. Histologic features of diabetic muscle infarction consist of large areas of muscle necrosis and edema. Magnetic resonance imaging (MRI) findings in patients without clinical evidence of infection may be typical enough to make tissue biopsy unnecessary. In the appropriate clinical setting, MRI may obviate invasive testing and is the preferred imaging modality. Treatment is supportive with analgesics, rest, and immobilization.

Prevention of pressure-induced deep tissue injury using intermittent electrical stimulation

Pressure ulcers develop due to morphological and biochemical changes triggered by the combined effects of mechanical deformation, ischemia, and reperfusion that occur during extended periods of immobility. The goal of this study was to test the effectiveness of a novel electrical stimulation technique in the prevention of deep tissue injury (DTI). We propose that contractions elicited by intermittent electrical stimulation (IES) in muscles subjected to constant pressure would induce periodic relief in internal pressure; additionally, each contraction would also restore blood flow to the tissue. The application of constant pressure to the quadriceps muscles of rats generated a DTI that affected 60 ± 15% of the compressed muscle as assessed by magnetic resonance imaging. In contrast, in the groups of rats that received IES at 10- and 5-min intervals, DTI of the muscle was limited to 16 ± 16 and 25 ± 13%, respectively. Injury to the muscle was corroborated by histology. In an experiment with a human volunteer, compression of the buttocks reduced the oxygenation level of the muscles by ∼4%; after IES, oxygenation levels increased by ∼6% beyond baseline. Concurrently, the surface pressure profiles of the loaded muscles were redistributed and the high-pressure points were reduced during each IES-induced contraction. The results of this study indicate that IES significantly reduces the amount of DTI by increasing the oxygen available to the tissue and by modifying the pressure profiles of the loaded muscles. This presents a promising technique for the prevention of pressure ulcers in immobilized and/or insensate individuals.

Noninvasive in vivo assessment of the skeletal muscle and small intestine serous surface microcirculation in rat: sidestream dark-field (SDF) imaging

The pathophysiology of microcirculation is intensively investigated to understand disease development at the microscopic level. Orthogonal polarization spectral (OPS) imaging and its successor sidestream dark-field (SDF) imaging are relatively new noninvasive optical techniques allowing direct visualization of microcirculation in both clinical and experimental studies. The goal of this experimental study was to describe basic microcirculatory parameters of skeletal muscle and ileal serous surface microcirculation in the rat using SDF imaging and to standardize the technical aspects of the protocol. Interindividual variability in functional capillary density (FCD) and small vessels (<25 microm in diameter) proportion was determined in anesthetized rats on the surface of quadriceps femoris (m. rectus femoris and m. vastus medialis) and serous surface of ileum. Special custom made flexible arm was used to fix the SDF probe minimizing the pressure movement artifacts. Clear high contrast images were analyzed off-line. The mean FCD obtained from the surface of skeletal muscle and ileal serous surface was 219 (213-225 cm/cm(2)) and 290 (282-298 cm/cm(2)) respectively. There was no statistically significant difference between rats in mean values of FCD obtained from the muscle (P = 0.273) in contrast to ileal serous surface, where such difference was statistically significant (P = 0.036). No statistically significant differences in small vessels percentage was detected on either the muscle surface (P = 0.739) or on ileal serous surface (P = 0.659). Our study has shown that interindividual variability of basic microcirculatory parameters in rat skeletal muscle and ileum is acceptable when using SDF imaging technique according to a highly standardized protocol and with appropriate fixation device. SDF imaging represents promising technology for experimental and clinical studies.

Muscle metabolism during graded quadriceps exercise in man

The aim of the study was to examine local muscle metabolism in response to graded exercise when the involved muscle mass is too small to elicit marked hormonal changes and local blood flow restriction. Nine healthy overnight fasted male subjects performed knee extension exercise with both thighs kicking at 25% of maximal power (Wmax) for 45 min (23+/-1% of pulmonary) followed by 35 min of kicking with one thigh at 65% and the other at 85% W(max) (40+/-1% ). Primed constant infusion of [U-13C] palmitate and [2H5]glycerol was carried out. Blood was sampled from a femoral artery and both femoral veins, and thigh blood flow was determined by thermodilution. Muscle biopsies were obtained from m. vastus lateralis of both thighs. From rest through exercise at 25, 65 and 85% Wmax the thigh blood flow (0.3+/-0.1, 2.5+/-0.2, 3.5+/-0.2, 4.1+/-0.3 l min(-1)) and oxygen uptake (0.02+/-0.01, 0.27+/-0.03, 0.48+/-0.04, 0.55+/-0.05 l min(-1)) increased (P<0.05). The plasma fatty acids oxidized in the thigh (5+/-1, 114+/-15, 162+/-30, 180+/-31 micromol min(-1)) increased (P<0.05) with exercise intensity, whereas the total thigh fat oxidation (19+/-6, 312+/-64, 356+/-93, 323+/-120 micromol min(-1)) increased (P<0.05) from rest, but remained unchanged through exercise. The thigh glycerol uptake (1+/-1, 16+/-4, 24+/-10, 39+/-8 micromol min(-1)) increased significantly from rest through exercise at 25-65 and 85% Wmax, respectively. Glucose uptake and glycogen breakdown always increased with exercise intensity. In conclusion, in the presence of a high blood flow and oxygen supply and only small hormonal changes, total fat oxidation in muscle increases from rest to light exercise, but then remains constant with exercise intensity up to heavy exercise. However, with increasing exercise intensity, oxidation of plasma free fatty acids increases and accordingly oxidation of other fat sources decreases. These findings are in contrast to whole body measurements performed during graded exercise involving a large muscle mass during which fat oxidation peaks at around 60% of .

Characterization of pre- and post-treatment pathology after enzyme replacement therapy for Pompe disease

In Pompe disease, a genetic deficiency of lysosomal acid alpha-glucosidase, glycogen accumulates abnormally in the lysosomes of skeletal, cardiac and smooth muscle, and contributes to clinically progressive and debilitating muscle weakness. The present study involved 8 infantile-onset Pompe patients, treated weekly with 10 mg/kg of recombinant human acid alpha-glucosidase (rhGAA). Muscle biopsies were obtained at baseline, 12 and 52 weeks post-treatment to establish an indicator of efficacy. Several histologic strategies were employed to characterize changes in pre- and post-treatment samples, including high-resolution light microscopy and digital histomorphometry, electron microscopy, capillary density and fiber type analysis, and confocal microscopy for satellite cell activation analysis. Histomorphometric analysis was performed on muscle samples to assess glycogen depletion in response to enzyme replacement therapy (ERT). The extent of glycogen clearance varied widely among these patient samples, and correlated well with clinical outcome. Low glycogen levels, mild ultrastructural damage, a high proportion of type I fibers, and young age at baseline were all features associated with good histologic response. There was no correlation between capillary density and glycogen clearance, and activated satellite cell levels were shown to be higher in post-treatment biopsies with poor histologic responses. This histopathologic study of infantile Pompe disease provides detailed insight into the cellular progression of the disease and its response to therapy while highlighting a number of methodologies which may be employed to assess regression or progression of the associated pathology. As enzyme replacement therapy becomes more prevalent for the treatment of lysosomal storage diseases, such evaluation of post-treatment pathology will likely become a more common occurrence in the daily practice of pathologists.

Effects of vascular occlusion on maximal force, exercise-induced T2 changes, and EMG activities of quadriceps femoris muscles

The purpose of our study was to determine the effect of vascular occlusion on neuromuscular activation and/or the energy metabolic characteristics of the quadriceps femoris (QF) muscles during muscle contractions. Seven men participated in the study. An occlusion cuff was attached to the proximal end of the right thigh, so that blood flow in the anterior medial malleolar artery was reduced to approximately 88 % of the non-occluded flow. Muscle functional magnetic resonance imaging and maximal voluntary contraction (MVC) were carried out before and immediately after 5 sets of 10 repetitions of knee extension exercises at 50 % of the 10 repetitions maximum, from which transverse relaxation times (T2) and maximal force were measured, respectively. Integrated electromyography (iEMG) activity was recorded from the belly of the rectus femoris, vastus lateralis, and vastus medialis muscles during MVC and repetitive exercises. The percentage change in T2 was significantly increased for individual QF muscles, and there was a significant increase in iEMG activity over the 5 sets of repetitive exercises under conditions of vascular occlusion, but there was no significant effect on isometric force and iEMG activity during MVC. These results are consistent with the idea that there is greater osmolite accumulation during exercise with occlusion, although increased neural activation cannot be ruled out.

Relationship between local perfusion and FFA uptake in human skeletal muscle—no effect of increased physical activity and aerobic fitness

We investigated heredity-independent effects of increased physical activity and aerobic fitness on skeletal muscle free fatty acid (FFA) uptake, perfusion, and their heterogeneity at rest and during exercise. Also, the relationship between local skeletal muscle FFA uptake and perfusion was studied. Nine young adult male monozygotic twin pairs with significant difference in physical activity [229 min (SD 156) average time spent for conditioning exercise per week in more and 98 min (SD 71) in less active twins, P = 0.013] and aerobic fitness [18% (SD 10) difference in maximum O2 uptake] between brothers were studied using positron emission tomography. Submaximal knee-extension exercise increased perfusion, FFA uptake, and oxygen uptake in quadriceps femoris muscles 6–10 times compared with resting values ( P < 0.001). More active twins tended to utilize more oxygen, while no differences were found in muscle perfusion or FFA uptake between groups. Mean perfusion and FFA uptake correlated strongly at a whole muscle level, both at rest ( r = 0.97, P = 0.03 in more and r = 0.98, P = 0.02 in less active twins) and during exercise ( r = 0.99, P = 0.01 and r = 0.94, P = 0.06), but at the voxel level (87 mm3) correlation was only moderate during exercise [ r = 0.73 (SD 0.08) vs. r = 0.74 (SD 0.10), P = 0.92] and weak at rest [ r = 0.28 (SD 0.13) vs. r = 0.33 (SD 0.21), P = 0.58]. Exercise decreased both perfusion and FFA uptake heterogeneity within the muscles ( P < 0.001) similarly in both groups. In conclusion, long-term history of moderately increased physical activity tends to enhance muscle oxidative metabolism, but it does not have any significant influence on the FFA uptake or perfusion rates or their heterogeneity in skeletal muscle. Submaximal knee-extension exercise decreases heterogeneity of muscle FFA uptake and perfusion and improves matching between local muscle perfusion and FFA uptake. Thus it seems that the genetic influence is more important to determine the heterogeneity of perfusion and FFA uptake in skeletal muscle than exercise training.

Exercise restores skeletal muscle glucose delivery but not insulin-mediated glucose transport and phosphorylation in obese subjects

CONTEXT/OBJECTIVE

Insulin resistance in obese subjects results in the impaired disposal of glucose by skeletal muscle. The current study examined the effects of insulin and/or exercise on glucose transport and phosphorylation in skeletal muscle and the influence of obesity on these processes.

SUBJECTS/METHODS

Seven obese and 12 lean men underwent positron emission tomography with 2-deoxy-2-[(18)F]fluoro-d-glucose in resting and isometrically exercising skeletal muscle during normoglycemic hyperinsulinemia. Data were analyzed by two-tissue compartmental modeling. Perfusion and oxidative capacity were measured during insulin stimulation by [15O]H2O and [15O]O2.

RESULTS

Exercise increased glucose fractional uptake (K), inward transport rate (K(1)), and the k(3) parameter, combining transport and intracellular phosphorylation, in lean and obese subjects. In each group, there was no statistically significant difference between plasma flow and K(1). At rest, a significant defect in K(1) (P = 0.0016), k(3) (P = 0.016), and K (P = 0.022) was found in obese subjects. Exercise restored K(1), improved but did not normalize K (P = 0.03 vs. lean), and did not ameliorate the more than 60% relative impairment in k(3) in obese individuals (P = 0.002 vs. lean). The glucose oxidative potential tended to be reduced by obesity.

CONCLUSIONS/INTERPRETATION

The study indicates that exercise restores the impairment in insulin-mediated skeletal muscle perfusion and glucose delivery associated with obesity but does not normalize the defect involving the proximal steps regulating glucose disposal in obese individuals. Our data support the use of 2-deoxy-2-[18F]fluoro-d-glucose-positron emission tomography in the dissection between substrate supply and intrinsic tissue metabolism.

The anterolateral thigh as a universal donor site for soft tissue reconstruction in maxillofacial surgery

OBJECTIVE

The experience with 191 flaps from the anterolateral thigh is described with special regard to variations of vascular anatomy and possible flap designs.

PATIENTS

Since 1992, 191 flaps from the anterolateral thigh donor site were used in 187 patients. The size of the defects varied from 3 x 5 cm to 21 x 10 cm, being located in nearly all areas of the head and neck region including the skull base.

METHODS

The functional and aesthetic outcome was routinely evaluated during follow-up of the patients. All complications and secondary procedures were documented during the whole follow-up period ranging from 4 weeks to 11.2 years.

RESULTS

Six different patterns of variations were observed concerning the flap pedicle, but none of these resulted in failure of flap raising except for two patients, in whom no perforators could be found. Poor functional results were observed in 17 patients, and debulking procedures or scar revisions were carried out in 58 of the 187 patients. Nine flap types reaching from voluminous and large myocutaneous flaps to ultra-thin cutaneous perforator flaps were used, enabling closure of virtually any type of soft tissue defect. Twelve flaps were lost, resulting in a success rate of 93.7%.

CONCLUSION

Due to the combined advantages of minimal donor site morbidity, the option of simultaneous flaps and the satisfying results, the anterolateral thigh can be considered a universal donor site which is ideally suited for soft tissue reconstruction in cranio-maxillofacial surgery.

The association between muscle EMG and perfusion in knee extensor muscles

The relationships between electromyographic (EMG) activity and force as well as muscle blood flow and work have been well established. However, the association between muscle blood flow and EMG activity remains unsolved. Thus, to test the hypothesis that muscle EMG activity relates to muscle perfusion in different compartments of the quadriceps femoris (QF) muscle, 12 healthy male subjects were studied. During two very submaximal exercise bouts, at different exercise intensities, oxygen labelled radiowater and positron emission tomography were used to measure muscle perfusion. In addition, produced force of knee extensors and muscle EMG activity in the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles were recorded during both exercise bouts. Although the exercise intensity and average force production was higher during the second exercise bout (38 +/- 15 versus 51 +/- 17 N; P = 0.007), the mean EMG activity was lower (RF; P<0.001) or unchanged (VL; P = 0.722 and VM; P = 0.640). During the second exercise period, perfusion also remained unchanged in the entire QF muscle (P = 0.223) and in its separate muscles (VL, P = 0.703; VM, P = 0.141; RF, P = 0.113) in a group level. However, the individual changes in muscle perfusion were tightly related to changes in muscle EMG activity in VL (r = 0.84; P = 0.002) and VM (r = 0.68; P = 0.015) but poorly in the RF muscle (r = 0.40; P = 0.257). In conclusion, the different associations between muscle perfusion and EMG activity in different QF muscles suggests specific functional role of the vasti muscles and the RF muscle.

A model for determining baseline morphometrics of the capillary bed in skeletal muscle

Changes in capillary diameter (CD) have been used to detect the effect of pharmacological interventions, physical treatments and ischaemic reperfusion injury in skin and muscle. For comparison, CDs within similar structures in the untreated limb of the same subject have been used as the control, with the assumption that CDs are the same in both limbs. This study employs light microscopic morphometry (LMM) to explore this premise, investigates the repeatability of LMM and determines the number of CDs that should be measured to produce a reliable result. Muscle biopsies were obtained from the left (L) and right (R) vastus lateralis of four rabbits and the left and right tibialis anterior of three vervet monkeys. Thin (1-micro m) resin sections were prepared for LMM examination and CDs were measured using computerised image analysis. To determine the repeatability of measurement, two specimens were re-measured on five occasions at monthly intervals. The mean CD of each biopsy from L and R limbs were compared and the number of measurements necessary to produce a result with less than a 3% difference was determined. A minimum of 58 and a maximum of 175 CDs were measured from each specimen. Repeated measurement of the same biopsies showed a non-significant mean difference of less than 2% in CD means between the first measurement and each of the four subsequent measurements. There was a non-significant difference of 3.7% in CD means between R and L limbs in one animal, in which less than 70 CDs were measured on each side. When 100 CDs or more were measured, the difference was always less than 2.3%. When grouped, the difference in CD means between L and R limbs was 0.5% in rabbits and 2.0% in vervet monkeys. The results confirm that firstly, CD data derived from a muscle in an untreated limb can be used as a control for experiment-mediated changes of CD in the other; secondly, LMM appears to be a reliable means of measuring CD; and thirdly, while fewer measurements may suffice, ideally 75-100 CDs are needed to provide a dependable result.

Hemodynamic and metabolic responses to interstitial angiotensin II in normal weight and obese men

OBJECTIVE

The expression of the AT1 receptor in adipose tissue is not decreased or even increased in obese subjects despite systemic activation of the renin-angiotensin system. Therefore, we hypothesized that peripheral tissues of obese subjects are hypersensitive to angiotensin (Ang) II.

METHODS

We characterized the effect of locally applied Ang II in skeletal muscle and subcutaneous adipose tissue of healthy non-obese (n = 12) and obese (n = 11) men using the microdialysis technique. Tissues were perfused with Ringer's solution + ethanol and incremental doses of Ang II (0.01, 0.1 and 1 micromol/l). Dialysate ethanol, glycerol, glucose, lactate, and pyruvate concentrations were measured to assess changes in blood flow (ethanol dilution technique), lipolysis and glycolysis, respectively.

RESULTS

In adipose tissue, basal ethanol ratio was significantly higher and dialysate metabolite concentrations were significantly lower in obese versus non-obese men. In muscle, basal dialysate glycerol was significantly higher in obese versus non-obese men. Ang II elicited small increases in ethanol ratio and decreases in dialysate glucose in adipose tissue and skeletal muscle in both non-obese and obese men. Dialysate lactate increased significantly in both tissues of obese, but not non-obese men. Dialysate glycerol increased in adipose tissue of non-obese (+ 40%) but not of obese and remained almost unchanged in muscle of both groups.

CONCLUSIONS

Interstitially applied Ang II elicits subtle changes in tissue perfusion and metabolism. However, we did not find a major increase in interstitial Ang II responsiveness in obese men.

Effect of inspiratory muscle work on peripheral fatigue of locomotor muscles in healthy humans

The work of breathing required during maximal exercise compromises blood flow to limb locomotor muscles and reduces exercise performance. We asked if force output of the inspiratory muscles affected exercise-induced peripheral fatigue of locomotor muscles. Eight male cyclists exercised at > or = 90% peak O2 uptake to exhaustion (CTRL). On a separate occasion, subjects exercised for the same duration and power output as CTRL (13.2 +/- 0.9 min, 292 W), but force output of the inspiratory muscles was reduced (-56% versus CTRL) using a proportional assist ventilator (PAV). Subjects also exercised to exhaustion (7.9 +/- 0.6 min, 292 W) while force output of the inspiratory muscles was increased (+80%versus CTRL) via inspiratory resistive loads (IRLs), and again for the same duration and power output with breathing unimpeded (IRL-CTRL). Quadriceps twitch force (Q(tw)), in response to supramaximal paired magnetic stimuli of the femoral nerve (1-100 Hz), was assessed pre- and at 2.5 through to 70 min postexercise. Immediately after CTRL exercise, Q(tw) was reduced -28 +/- 5% below pre-exercise baseline and this reduction was attenuated following PAV exercise (-20 +/- 5%; P < 0.05). Conversely, increasing the force output of the inspiratory muscles (IRL) exacerbated exercise-induced quadriceps muscle fatigue (Q(tw) = -12 +/- 8% IRL-CTRL versus-20 +/- 7% IRL; P < 0.05). Repeat studies between days showed that the effects of exercise per se, and of superimposed inspiratory muscle loading on quadriceps fatigue were highly reproducible. In conclusion, peripheral fatigue of locomotor muscles resulting from high-intensity sustained exercise is, in part, due to the accompanying high levels of respiratory muscle work.

Effect of arm cranking on oxygenation of vastus lateralis and lateral gastrocnemius muscles during leg cycling

AIM

The purpose of this study was to compare the changes in oxygenation in exercising vastus lateralis muscle (VL) and lateral gastrocnemius muscle (LG) when arm cranking is added to on-going leg cycling.

METHODS

Change in oxygenation (difference between concentrations of oxygenated hemoglobin and deoxygenated hemoglobin, HbD) was determined using near-infrared spectrometry. Before the combined exercise, each subject (n=8) rested for 5 min and then performed 10-min constant-work-rate leg cycling. The intensities of leg cycling were 20% and 40% of peak oxygen uptake (VO2peak) during incremental leg cycling (LC20 and LC40). Arm cranking at an intensity of 60% of VO2peak recorded during incremental arm cranking (AC60) was added to the on-going leg cycling (both AC60LC20 and AC60LC40 in two separate sessions) for 6 min.

RESULTS

During AC60LC20, HbD in both the VL and LG showed significant decreases compared to the control value (1 min before combined exercise: LC20). During AC60LC40, a significant decrease in HbD compared to the control value (1 min before combined exercise: LC40) was observed only in the LG. In the VL, the integrated electromyogram (iEMG) during AC60LC40 was significantly larger than that during AC60LC20, whereas in the LG, no significant difference was found between the iEMG during AC60LC40 and that during AC60LC20. These results suggest that the decrease in HbD in the exercising leg muscles is related to the level of its muscle activity after the addition of arm cranking.

CONCLUSION

The results suggest that HbD shows different changes in exercising leg muscles due to the difference in its activity level when arm cranking is added to on-going leg cycling.

Muscle and plasma coenzyme Q10 concentration, aerobic power and exercise economy of healthy men in response to four weeks of supplementation

AIM

To investigate whether 4 weeks of oral supplementation with coenzyme Q10 (CoQ10) would increase its concentration in skeletal muscle, and affect aerobic power (VO2max) and oxygen consumption during submaximal exercise in healthy, physically active men.

METHODS

Six volunteers with an average (+/-SD) age of 29.7+/-7.2 years and VO2max of 39.4+/-8.5 mL.kg-1.min-1, participated in a single-blind trial. The experiment consisted of 4 2-week phases, in the order of placebo run-in, CoQ10 supplementation (150 mg daily), CoQ10 (150 mg) plus vitamin E (1,000 IU daily), and placebo wash-out. A three-stage cycle economy test (4 minutes at each of 50, 100, and 150 watts), followed by a VO2max test (25 watts increment every minute till exhaustion), were performed prior to the supplementation and at the end of each phase. Blood samples were taken pre and post each VO2max test, and biopsy samples were obtained from the vastus lateralis muscle pre and post the 4 weeks of CoQ10 supplementation.

RESULTS

The plasma CoQ10 concentration was significantly elevated by the supplementation (P<0.05), however, it did not vary significantly pre and post each exercise test (P>0.05). The muscle CoQ10 concentration, VO2max ventilatory threshold, exercise economy and oxygen deficit showed no significant changes in response to the supplementation.

CONCLUSION

It was speculated that the non-significant effects of supplementation in healthy, non CoQ10-deficient men could be due to either that the mitochondrial membrane is normally saturated with CoQ10, or that the selected exercise testing protocol and variables were not sensitive enough to detect the effects.

Effects of the Compact Mutant Myostatin Allele Mstn Cmpt-dl1Abc Introgressed into a High Growth Mouse Line on Skeletal Muscle Cellularity

The murine myostatin mutation Mstn(Cmpt-dl1Abc) (Compact; C) was introduced into an inbred mouse line with extreme growth (DUHi) by marker-assisted introgression. To study the allelic effects on muscle fibre hyperplasia and hypertrophy, myonuclear proliferation, protein accretion, capillary density, and muscle fibre metabolism, samples from M. rectus femoris (RF) and M. longissimus dorsi (LD) muscles of animals wild-type (+/+), heterozygous (C/+), and homozygous (C/C) for the Mstn(Cmpt-dl1Abc) allele were examined by histological and biochemical analyses. Homozygous C/C mice exhibited lower body (-12%) but higher muscle weights (+38%) than ++ mice. Total muscle fibre number was increased (+24%), whereas fibre size was not significantly affected. Protein and DNA concentrations and DNA:protein ratios as well as specific CK activity remained unchanged for higher mass muscle implying increases in the total contents of DNA and muscle specific protein. Fibre type distribution was markedly shifted to the white glycolytic muscle fibres (+16-17% units) at the expense of red oxidative fibres. Capillary density was substantially lower in C/C than in ++ mice as seen by lower number of capillaries per fibre (-35%) and larger fibre area per capillary (+77%). However, the Mstn(Cmpt-dl1Abc) allele was partially recessive in heterozygous C/+ mice for both fibre type frequencies and capillary density. The results show that hypermuscularity caused by mutations in the myostatin gene results from muscle fibre hyperplasia rather than hypertrophy, and from balanced increases in myonuclear proliferation and protein accretion. However, capillary supply is adversely affected and muscle metabolism shifted towards glycolysis, which could have negative consequences for physical fitness.

[Transferring neurovascular rectus femoris muscle segment for treatment of facial paralysis]

OBJECTIVE

To investigate a new technique for functional treatment of chronic facial paralysis.

METHODS

Based on anatomy of intramuscular neurovascular structure in the rectus femoris muscle, 7 consecutive patients with facial paralysis were treated by using a technique of microsurgically free-transferring neurovascular rectus femoris muscle segment to the face in one-stage. Follow-ups were 10 to 24 months.

RESULTS

All of the 7 patients showed significantly improvement in the appearance of the oral commissure and oral competence. No complications occurred in the donor site.

CONCLUSIONS

The above mentioned technique may have the advantages of preventing the intramuscular nerve and vessel from the surgical injury during splitting the muscle. It could also maintain the transferred muscular segment in a proper tension in the recipient site.

[The neurovascular anatomy and its clinical implication of the rectus femoris muscle]

OBJECTIVE

The objective of this anatomic study was to investigate the intramuscular neurovascular configuration and to evaluate whether the muscle could be split into two functional units in transplantation.

METHODS

Ten fresh cadavers and ten preserved cadavers were used in the study. A mixture of lead oxide, gelatin and water was injected to the femoral artery of the fresh cadaver. The rectus femoris muscle with its neurovascular pedicles was dissected and radiographed.

RESULTS

Three vascular patterns of the rectus femoris muscle were found in the 40 cadaver legs. The muscle received its blood supply through a single vascular pedicle (12.5%), or a dominant pedicle with 1-2 ramified (80%), or two dominant vascular pedicles (7.5%).

CONCLUSIONS

The study provided a detailed description on the intramuscular neurovascular territories of the rectus femoris muscle. Based on the neurovascular supply of the muscle, it is possible to subdivide the muscle into two functional units for segmental muscle transfer.