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PubMed1990

Effect of isometric exercise on mitral and aortic regurgitation as assessed by color Doppler flow imaging.

Isometric exercise produces well-defined hemodynamic changes in normal and diseased states. However, the effect of isometrics on the degree of valvular regurgitation recorded by color Doppler flow imaging (CDFI) has not been reported. CDFI was therefore used to evaluate changes in valvular regurgitation in 34 patients, mean age 53 +/- 16 years. Data were collected for 43 regurgitant lesions including 20 cases of aortic regurgitation and 23 cases of mitral regurgitation. Isometrics produced a significant increase in heart rate (71 to 83 beats/min) and blood pressure (132/64 to 153/70 mm Hg) in all patients (p less than 0.0001). Regurgitant jet area by CDFI increased significantly in both aortic regurgitation (4.5 to 6.2 cm2, p less than 0.0001) and mitral regurgitation (6.2 to 8.2 cm2, p less than 0.001). Patients taking concurrent vasodilator or angiotensin-converting enzyme inhibitor therapy had similar responses to those not receiving long-term therapy. Thus, CDFI detects an increase in aortic and mitral regurgitant jet area induced by isometric exertion. The change in CDFI jet area with handgrip demonstrates the influence of loading conditions on the size of a regurgitant jet area, and suggests that isometric exertion may increase the magnitude of mitral and aortic regurgitation.

Aortic Valve Insufficiency↗

PubMed1996

Spinal compression at peak isometric and isokinetic exertions in simulated lifting in symmetric and asymmetric planes.

OBJECTIVE: To determine if the spinal compression can be used as a criterion for the safety of the back. DESIGN: Various lifting strength activities were analysed using a 3-D biomechanical model to determine spinal compression forces. BACKGROUND: Despite many standards being set and the use of varied strategies, low-back injuries continue to be common in our society. Since the injuries occur to the tissues in the body, it may be more appropriate to investigate the effects of external loads on the tissues. Therefore it was decided to determine the spinal compression in standardized lifting tasks. METHODS: Twenty young adults (12 males and 8 females) performed maximal stoop and squat lifts in sagittal, 30 degrees lateral, and 60 degrees lateral planes at half, three-quarters, and full horizontal reach distances. The stoop lifts were performed in isokinetic and isometric modes; the isometric mode was performed with the hip at 60 degrees and 90 degrees. The squat lifts were also performed in isokinetic and isometric modes; the isometric mode consisted of postures with knee at 90 degrees and 135 degrees of flexion. In addition, the subjects also performed isometric lifts in stoop and squat postures at a self-selected optimum posture. During these activities the strength was measured using a static dynamic strength tester employing a load cell and force monitor. Three-dimensional postural recording was made using a 3-D Peak Performance Technologies imaging system. Using the postural and force data as input to a 3-D biomechanical model, the lumbosacral spinal compression was calculated. The values of strength and spinal compression were analysed and compared. RESULTS: The strength was significantly affected by the gender, the type of lift, plane of lift and reach of lift (P < 0.01); whereas the spinal compression was not affected by the reach at all. Two-way and three-way interactions were significant for strength (P < 0.02) but not for spinal compression. CONCLUSION: It was concluded that the spinal compression was the ultimate cost function in the safety of the back and as such preventative strategies should be based on this. RELEVANCE: The use of an appropriate cost function in a manner in which it can maximize the safety of the back will be of considerable value. Since injuries are biomechanical perturbation of the tissues, it is argued that the cost function be used in a manner where tissue load be considered as the primary factor.

Journal Article↗

PubMed1988

Regional left ventricular mechanical function during isometric exercise in patients with coronary artery disease: correlation with regional coronary blood flow changes.

The effects of isometric exercise on regional left ventricular mechanical function and regional coronary blood flow were evaluated in 17 patients with significant proximal stenosis of the left anterior descending coronary artery and 10 patients with normal coronary arteriograms. All patients had normal myocardial contractility in the basal condition. All performed isometric handgrip exercise at 50% of the maximal voluntary contraction for 3 min during two-dimensional echocardiographic monitoring and hemodynamic evaluation of great cardiac vein flow by thermodilution technique. During isometric exercise, 7 of the 17 patients with left anterior descending coronary stenosis developed asynergy in the anterior territory (anterior or septal segment, or both) (group I); the remaining 10 showed normal myocardial contraction during the test (group II). The 10 normal subjects manifested no regional asynergy during the test (control group). The increase in great cardiac vein flow at peak isometric exercise was significantly smaller (p less than 0.01) in group I (+15 +/- 8%) than that in group II (+98 +/- 48%) and the control group (+64 +/- 22%). Anterior coronary vascular resistance decreased in group II (-32 +/- 13%) and in the control group (-25 +/- 8%) but increased in group I (+6 +/- 8%, p less than 0.01 versus group II and control group). These data demonstrate that handgrip-induced myocardial asynergy is associated, in our study patients, with an abnormal response of the regional coronary circulation. The increase in coronary vascular resistance in group I patients with asynergy demonstrates that functional mechanisms play a dominant role in left ventricular mechanical dysfunction induced by isometric exercise.

Aged↗

PubMed2005

Assessment of skeletal muscle fatigue in men with coronary artery disease using surface electromyography during isometric contraction of quadriceps muscles.

OBJECTIVE: To evaluate whether using surface electromyography to assess skeletal muscle fatigue during an isometric exercise has the potential to be clinically useful in patients with coronary artery disease (CAD). DESIGN: Double sample comparative study. SETTING: Cardiac rehabilitation service in France. PARTICIPANTS: Sixteen men with documented CAD and 9 age-matched healthy men. INTERVENTIONS: Assessment of quadriceps skeletal muscle fatigue on an isokinetic apparatus with surface electromyography measurements and a symptom-limited exercise test in a laboratory. MAIN OUTCOME MEASURES: The maximal voluntary isometric force (MVIF) of the quadriceps was quantified as a measure of muscle strength and isometric endurance was defined as the time required to sustain a contraction at 50% of MVIF until exhaustion. Surface electromyography signals were recorded from the vastus lateralis, rectus femoris, and vastus medialis during isometric endurance. The root mean square (RMS) and the median frequency (MF) were directly calculated on a computer and then normalized (as a percentage of the initial value). RESULTS: Muscle strength did not differ significantly between the patients with CAD and the healthy subjects (229+/-21N/m vs 228+/-52N/m), but isometric endurance was reduced (64+/-17s vs 90+/-7s, P <.01). The RMS values showed a significantly higher increase in the healthy subjects versus the patients with CAD for the vastus lateralis and vastus medialis ( P <.001). The MF values were significantly lower for the vastus lateralis, rectus femoris ( P <.01), and vastus medialis ( P <.05) in patients with CAD compared with the healthy subjects. CONCLUSIONS: Skeletal muscle fatigue occurs sooner in men with CAD relative to matched healthy men, despite similar muscle strength. This finding may be the result of an abnormality of skeletal muscle function and may play an important role in measuring functional capacity. In addition, it may be a useful tool to assess the efficacy of cardiac rehabilitation interventions.

Coronary Artery Disease↗

PubMed2005

Graft length changes in the bi-socket anterior cruciate ligament reconstruction: comparison between isometric and anatomic femoral tunnel placement.

PURPOSE: To compare the length change of grafts in bi-socket anterior cruciate ligament (ACL) reconstruction between isometric and anatomic placement. TYPE OF STUDY: Case series. METHODS: The subjects were 110 knees of 110 patients with a mean age of 27 years. All knees were reconstructed using multistranded autogenous semitendinosus tendon and the bi-socket procedure. Of those, 43 knees were reconstructed in the isometric position, around the isometric point (group I) and the remaining 67 in the anatomic position, mimicking the anatomic footprint of ACL (group II). Grouping was performed based on the femoral socket position. Each femoral socket for the anterior medial graft (AMG) and the posterolateral graft (PLG) for the left knee was positioned at 1 o'clock and 2 o'clock to 2:30 in group I, or 2 o'clock and 3 o'clock in group II in the posterior border of the notch. Their positioning for the right knee was at 11 o'clock and 9:30 to 10 o'clock in group I, or 10 o'clock and 9 o'clock in group II. The length changes of grafts were intraoperatively measured while extending the knee from 120 degrees to full extension, using a commercially available isometric positioner. The Student t test was used for statistical analysis. RESULTS: All the grafts showed the pattern of elongation approaching extension. The length change of AMG and PLG was 1.3+/-0.6 mm and 2.2+/-1.0 mm in the group I, 1.4+/-0.7 mm and 2.5+/-0.9 mm in the group II, respectively. There was no statistically significant difference in the values of AMG (P = .51) and PLG (P = .074) between the 2 groups. CONCLUSIONS: The length change of ACL grafts placed in the anatomic position was not significantly different from that positioned in the isometric position. LEVEL OF EVIDENCE: Level IV, case series.

Adolescent↗

PubMed2006

A comparison between mechanomyographic condenser microphone and accelerometer measurements during submaximal isometric, concentric and eccentric contractions.

The aim of this study was to compare mechanomyogram (MMG) recorded by a condenser microphone (MIC) and an accelerometer (ACC) during submaximal isometric, concentric and eccentric contractions in 14 males. The maximal voluntary force (MVC) of the biceps brachii was measured. The subjects were asked to do short duration isometric, concentric and eccentric contraction at 10%, 30%, 50%, 70% MVC twice. For the concentric and eccentric contraction, the subject bent his arm for 3s (concentric) then held it for 3s and extended (eccentric) during 3s. The normalized root mean square (RMS) and mean power frequency (MPF) increased linearly with increased force for both transducers. There was a correlation between MIC MPF and ACC MPF at 10%, 30%, 50% MVC, and between MIC RMS and ACC RMS at 30% MVC during isometric contractions. There was significantly higher MPF for the ACC than for the MIC in concentric and eccentric modes, while the RMS did not differ among transducers in the three contraction modes. The RMS and MPF values coefficient of variations were significantly larger during anisometric contractions compared with isometric contractions and were lower for the accelerometer than for the microphone. The present results obtained during isometric, concentric and eccentric contractions of increased intensity showed that the information contained in microphone- and accelerometer-based MMG signals is different despite similar trends. It can be concluded that at low-moderate movement velocity, concentric contractions can be investigated by means of accelerometer and microphone.

Adult↗

PubMed2000

Measurement of the force produced by an intact bull sperm flagellum in isometric arrest and estimation of the dynein stall force.

The force generated by a detergent-extracted reactivated bull sperm flagellum during an isometric stall was measured with a force-calibrated glass microprobe. The average isometric stall force from 48 individual measurements was 2.5 +/- 0.7 x 10(-5) dyne (2.5 +/- 0.7 x 10(-10) N). The force measurements were obtained by positioning a calibrated microprobe in the beat path of sperm cells that were stuck by their heads to a glass microscope slide. The average position of the contact point of the flagellum with the probe was 15 microm from the head-tail junction. This average lever arm length multiplied by the measured force yields an estimate of the active bending moment (torque) of 3.9 x 10(-8) dyne x cm (3.9 x 10(-15) N x m). The force was sustained and was for the most part uniform, despite the fact that the flagellum beyond the point of contact with the probe usually continued beating. It appears that the dynein motors in the basal portion of the flagellum continue to pull in an isometric stall for as long as the motion of the flagellum is blocked. If dynein motors in the flagellum distal to the contact point with the probe were contributing force to the displacement of the probe, then the flagellar segment immediately past the point of contact would have to show a net curvature in the direction of the probe displacement. No such curvature bias was observed in the R-bend arrests, and only a small positive curvature bias was measured in the P-bend arrests. Our analysis of the data suggests that more than 90% of the sustained force component is generated by the part of the flagellum between the probe and the flagellar base. Based on this premise, the isometric stall force per dynein head is estimated to be 5.0 x 10(-7) dyne (5 pN). This equals approximately 1.0 x 10(-6) dyne (10 pN) per intact dynein arm. These values are close to the isometric stall force of isolated dynein. This suggests that all of the dynein heads between the base and the probe, on the active side of the axoneme, are contributing to the force exerted against the probe.

Adenosine Triphosphate↗

PubMed1998

Shortening versus isometric contractions in isolated human failing and non-failing left ventricular myocardium: dependency of external work and force on muscle length, heart rate and inotropic stimulation.

BACKGROUND: For reasons of simplicity, studies on isolated human myocardium have been conducted using exclusively isometric contractions, although positive inotropic interventions may differently influence force development, extent of shortening and myocardial work performance. We investigated human left ventricular failing and non-failing preparations comparing isometric versus isotonic, i.e., shortening contractions. RESULTS: (1) When muscle length is increased from 90% to 100% lMAX, peak developed force increases by 36% and 43% (p < 0.05) in non-failing and failing human left ventricular myocardium, respectively. Maximum performed work increases similarly in non-failing but decreases in failing myocardium. It can be shown that this discrepancy is due to significantly higher resting tension and does not present an insufficient intrinsic shortening capacity in failing myocardium. (2) When stimulation rate is increased from 0.5 to 2.0 Hz, isometric force increases significantly by 59% in non-failing and decreases by 27% in failing myocardium, whereas maximum performed work increases by 98% and decreases by 46%, respectively. (3) Pharmacological positive inotropic interventions by 7.2 mM calcium (n = 9), 3 x 10(-8) M isoproterenol (n = 7), 3 x 10(-8) M ouabain (n = 5), and 10(-5) M EMD 57033 (n = 3) equally increased force development and extent of shortening: When the fractional effect on shortening (y) was correlated to the fractional effect on force (x), the following linear regression equation was obtained: y = 0.91x + 0.26 (r = 0.86; p < 0.001). CONCLUSIONS: The data presented are of clinical and pharmacological importance: (1) The Frank-Starling mechanism is demonstrated to be existent in the failing human myocardium regarding both isometric force developed and maximum work performed. (2) Both force-frequency relations and--to a greater extent--work-frequency relations are reversed in failing human myocardium. (3) Independent of the pharmacological mode of action, positive inotropic compounds increase developed isometric force to the same extent as isotonic shortening and therefore potentiate maximum performed work.

Adolescent↗

PubMedDate not supplied

Doppler-derived aortic flow measurements during and after heavy isometric exercise in healthy men versus men with myocardial infarction.

Doppler echocardiography is a useful noninvasive determination of left ventricular function during dynamic exercise. Scarce data are available for the use of this technique during heavy isometric exercise. Therefore, Doppler-derived aortic flow indexes were assessed during and after 50% maximal upper-body isometric exercise in 25 healthy men (aged 47 +/- 6 years) and compared with those of 22 men (aged 48 +/- 9 years) who had suffered myocardial infarction. The heart rate increased (p = 0.01) in each of the groups from a mean of 68 +/- 12 at rest to 84 +/- 11 during isometric exercise. At rest, systolic blood pressure was higher (p = 0.05) in the patients with coronary artery disease. During exercise, the patients with cardiac disease, compared with the healthy volunteers, demonstrated a lesser reduction in flow velocity integral, stroke volume, and cardiac indexes (p = 0.001). Immediately on recovery, the patients with cardiac disease, compared with the healthy group, showed significantly greater (p = 0.001) increase in stroke volume and cardiac indexes. At 3 minute's recovery, the stroke volume index continued to increase in the patients with cardiac disease, while the healthy group showed a decrease to below its resting value. Although 50% of maximal upper-body isometric exercise caused similar heart rate and systolic blood pressure responses in healthy patients and patients with cardiac disease, there were significant group differences in Doppler-derived left ventricular systolic function indexes, which were greatest on immediate and 3 minute's recovery. The results suggest that this novel isometric test may be useful in clinical testing.

Aorta↗

PubMed1999

Maximal strength and power characteristics in isometric and dynamic actions of the upper and lower extremities in middle-aged and older men.

Muscle cross-sectional area of the quadriceps femoris (CSAQF), maximal isometric strength (handgrip test and unilateral knee extension/flexion), the shape of isometric force-time curves, and power-load curves during concentric and stretch-shortening cycle (SSC) actions with loads ranging from 15 to 70% of one repetition maximum half-squat (1RMHS) and bench-press (1RMBP) were examined in 26 middle-aged men in the 40-year-old (M40) (mean age 42, range 35-46) and 21 elderly men in the 65-year-old age group (M65) (mean age 65, range 60-74). Maximal bilateral concentric (1RMHS and 1RMBP), unilateral knee extension (isometric; MIFKE and concentric; 1RMKE) strength and muscle CSA in M65 were lower (P < 0.001) than in M40. The individual values of the CSAQF correlated with the individual values of maximal concentric 1RMHS, 1RMKE and MIFKE in M65, while the corresponding correlations were lower in M40. The maximal MIFKE value per CSA of 4.54 +/- 0.7 N m cm-2 in M40 was greater (P < 0. 05-0.01) than that of 4.02 +/- 0.7 N m cm-2 recorded in M65. The maximal rate of force development of the knee extensors and flexors in M65 was lower (P < 0.01-0.001) and the heights in squat and counter-movement jumps as much as 27-29% lower (P < 0.001) than those recorded in M40. M65 showed lower (P < 0.001) concentric power values for both upper and lower extremity performances than those recorded for M40. Maximal power output was maximized at the 30-45% loads for the upper extremity and at the 60-70% loads for the lower extremity extensors in both age groups. Muscle activation of the antagonists was significantly higher (P < 0.01-0.001) during the isometric and dynamic knee extension actions in M65 than in M40. The present results support a general concept that parallel declines in muscle mass and maximal strength take place with increasing age, although loss of strength may vary in both lower and upper extremity muscles in relation to the type of action and that ageing may also lead to a decrease in voluntary neural drive to the muscles. Explosive strength and power seem to decrease with increasing age even more than maximal isometric strength in both actions but power was maximized at the 30-45% loads for the upper and at the 60-70% loads for the lower extremity action in both age groups. High antagonist muscle activity may limit the full movement efficiency depending on the type of muscle action, testing conditions and the velocity and/or the time duration of the action, especially in the elderly.

Adult↗

PubMed2002

The effect of dynamic versus isometric resistance training on pain and functioning among adults with osteoarthritis of the knee.

OBJECTIVE: To compare 16 weeks of isometric versus dynamic resistance training versus a control on knee pain and functioning among patients with knee osteoarthritis (OA). DESIGN: Randomized clinical trial. SETTING: Outpatient setting. PARTICIPANTS: A total of 102 volunteer subjects with OA of the knee randomized to isometric (n=32) and dynamic (n=35) resistance training groups or a control (n=35). INTERVENTIONS: Strength exercises for the legs, 3 times weekly for 16 weeks. Dynamic group: exercises across a functional range of motion; isometric: exercises at discrete joint angles. MAIN OUTCOME MEASURES: The time to descend and ascend a flight of 27 stairs and to get down and up off of the floor. Knee pain was assessed immediately after each functional task. The Western Ontario and McMaster Universities Osteoarthritis Index was used to assess perceived pain, stiffness, and functional ability. RESULTS: In the isometric group, time to perform all 4 functional tasks decreased (P<.05) by 16% to 23%. In the dynamic group, time to descend and ascend stairs decreased by 13% to 17%. Both groups decreased knee pain while performing the functional tasks by 28% to 58%. Other measures of pain and functioning were significantly and favorably affected in the training groups. The improvements in the 2 training groups as a result of their respective therapies were not significantly different. The control group did not change over the duration of the study. CONCLUSION: Dynamic or isometric resistance training improves functional ability and reduces knee joint pain of patients with knee OA.

Analysis of Variance↗

PubMed1982

The relationship of forearm flexion isometric strength, endurance, and fiber composition; and the effect of heating.

Forearm flexion isometric strength and endurance and fiber composition of the biceps brachii were examined in ten college-age men. The isometric endurance exercise regimens were assessed at room temperature and in a heated water bath at 45 degrees C. On each session four baseline isometric strength trials (MVCs) were measured followed by three isometric endurance bouts with 11 min rest between bouts. Post-heating MVCs were assessed prior to the endurance bouts. Two types of isometric endurance times were measured: holding a weight amounting to (1) 50% of maximal strength (MVC) and (2) 80% MVC. The heat treatment significantly reduced both the baseline MVCs and the 50% and 80% MVC endurance times. Pre- and post-heating MVC measures did not correlate significantly with fiber type but did correlate with body weight and biceps girth. In the nonheated condition, endurance times were unrelated to fiber type or body size. However, in the heated condition, both 50% and 80% endurance times correlated negatively with percent fast-twitch fiber area, implying a selective influence of heat on muscle fiber types.

Adult↗

PubMed2001

Isometric back extension endurance tests: a review of the literature.

OBJECTIVE: To review the literature that describes and evaluates the use of isometric back extension endurance tests. DATA COLLECTION: Relevant articles in English were retrieved through a search of MEDLINE and the Index to Chiropractic Literature. Key search terms were back muscle endurance, isometric back endurance, trunk extensors, back muscle performance, and Sorensen test. DATA SYNTHESIS: The principal criterion for inclusion was as follows: any study that discussed or tested an isometric type of back endurance extension test. Studies that were excluded did not use an isometric testing protocol. Thirty-seven of the initial studies are included in this review. RESULTS: Six different types of isometric back extension endurance testing methods were found. Three of these procedures require special testing devices. Much of the research on this topic has centered on a procedure known as the Sorensen test. Normative databases have been established for the Sorensen test and 2 other test types. Validity and reliability have been assessed for some of the procedures. CONCLUSIONS: The influence of motivation and effort exerted by the subject are limiting factors in all of the tests reviewed. These psychologic factors warrant further research. On the basis of the literature reviewed, we determined that the Sorensen is probably the most clinically useful of these tests; it is easy to perform, requires no special equipment, and enjoys the most support from the literature.

Adult↗

PubMed2000

Age effects on the temporal evolution of isometric and swallowing pressure.

BACKGROUND: The tongue plays a key role in bolus propulsion through the oropharyngeal chamber. In this study, possible age effects on the magnitude and timing of lingual pressure generation were analyzed. METHODS: Oral pressure was measured during isometric and swallowing tasks for 10 elderly (mean age = 81 years) and 10 young (mean age = 51 years) subjects. Three trials each of the isometric task and swallows of three different boluses (3 ml semisolid, 3 ml liquid, and 10 ml liquid) were performed by each subject. The timing and magnitude of isometric and swallowing pressure generation along with the pattern of the swallowing pressure waveform were analyzed. RESULTS: Whereas maximum lingual isometric pressures decreased with age (p < .001). no significant age difference was found for swallowing pressure. Time taken to reach peak pressure also was reduced with age in both the isometric task and swallows of liquid boluses (p < .05), while no significant age effect was found for semisolid swallows. Finally, only elderly subjects showed a pattern of liquid swallowing pressure generation in which multiple lingual gestures were required to reach peak pressure (termed "pressure building"), a pattern demonstrated by both young and elderly groups for semisolids. CONCLUSIONS: Decreased lingual strength with age combined with unchanging swallowing pressure leads to a decreased "pressure reserve," perhaps leaving older individuals more at risk for dysphagia resulting from insults directly or indirectly to the swallowing system. Additionally, swallowing is generally "slowed" with age, apparently due to both central and peripheral factors, and this change may have an impact on bolus flow outcomes.

Aged↗

PubMed2002

Normative database of isometric cervical strength in a healthy population.

OBJECTIVES: This was a descriptive study involving maximal and average isometric strength measurements of the cervical musculature. The purpose of this study was 1) to determine the test-retest reliability of a computerized dynamometer for measuring muscular strength of the neck flexor and extensor muscles in a healthy population, and 2) to afford a normative database of the maximal and averaged isometric strength of the cervical flexors and extensors in a healthy population of 94 volunteers. The literature contains only a few descriptive studies pertaining to strength levels of the cervical musculature; none of these studies used a computerized dynamometer to determine cervical isometric strength. Only a few studies include cervical flexor and extensor isometric strength, evaluating its normal ratio as well as their correlation to body mass index. METHODS: Testing was carried out using a computerized dynamometer to measure isometric cervical strength at 0 degrees (neutral), 5 degrees, and 10 degrees of flexion and extension of the neck. RESULTS: Men show approximately 30 to 40% more strength than women both for flexion and extension at all angles and age groups. Neutral positioning showed the maximum strength values for both flexion and extension. CONCLUSION: There was a significant negative correlation between age and cervical strength and a significant positive correlation between weight and strength and between height and strength. However, the flexor/extensor ratio was maintained around 0.6 in all ages.

Adult↗

PubMed2004

Isometric tubular epithelial vacuolization in renal allograft biopsy specimens of patients receiving low-dose intravenous immunoglobulin for a positive crossmatch.

BACKGROUND: Perioperative treatment with plasmapheresis and intravenous immunoglobulin (IVIG), combined with a tacrolimus-based immunosuppressive regimen, has been used successfully to allow renal transplantations in cross-match-positive recipients. A common finding in biopsy specimens of these allografts is isometric vacuolization of proximal tubular epithelium. This finding presents a diagnostic dilemma because it may occur secondary to IVIG treatment or tacrolimus nephrotoxicity. METHODS: We compared the frequency and severity of isometric tubular vacuolization in renal allograft biopsy specimens obtained during the first 10 days after transplantation in 24 patients who received one or more postoperative treatments with IVIG (100 mg/kg; as part of a desensitization protocol also involving plasmapheresis) with specimens obtained in 91 patients who did not receive IVIG. All patients received tacrolimus. Isometric vacuolization was graded on a 0 to 4 scale based on the fraction of proximal tubules involved: 0, none; 1, less than 10%; 2, 10% to 25%; 3, 26% to 50%; 4, more than 50%. RESULTS: There was a higher frequency of isometric tubular vacuolization (71 % vs. 31%) and more widespread involvement in patients who received IVIG and tacrolimus versus tacrolimus alone, although mean tacrolimus levels were not significantly different between these groups. In control, but not IVIG, biopsy specimens, there was a significant association between vacuolization score and blood tacrolimus level on the day of biopsy. CONCLUSIONS: Isometric tubular vacuolization is a common finding in renal transplant biopsy specimens of patients who receive low-dose IVIG and in many cases is likely to be related, at least in part, to IVIG. In these patients, this finding should not necessarily be interpreted as indicative of tacrolimus (or cyclosporine) nephrotoxicity.

Biopsy↗

PubMed1975

Isometric and isotonic relaxation in venous smooth muscle.

The time course of relaxation under isometric and isotonic conditions was studied in preparations of rat portal vein which maintained regular phasic contractions in solutions with increased [K-+] and [Ca-2+]. It was found that the smooth muscle during isotonic lengthening was able to carry the afterload for a period of time which was longer than expected from the control isometric response. The difference was largest for afterloads corresponding to about half the isometric peak force. The terminal decline in force was identical in afterloaded and purely isometric responses. Inhibitory influences of isotonic shortening causing increased rates of relaxation, as reported for striated muscles, were not observed. The differences in the course of relaxation between isotonic and isometric responses of portal vein could not be attributed to variations in membrane excitation. It also appears that the differences are not due to changes in release or uptake of activator calcium, or to presence of viscous elements in the tissue. It is suggested that the ability of the smooth muscle to carry load over a relatively long period during isotonic relaxation may be attributed to the characteristics of the instantaneous force-velocity relations in the force range above Po.

Action Potentials↗

PubMed1969

The effects of length and stimulus rate on tension in the isometric cat soleus muscle.

1. By subdividing ventral roots and supplying stimulating pulses to different groups of motor units in rotation, smooth contractions of soleus could be obtained with low rates of stimulation.2. Isometric tension was recorded with different rates of stimulation, and at different muscle lengths.3. Longitudinal histological sections were cut from muscles fixed at different lengths, and sarcomeres were measured. Mean sarcomere lengths in soleus could then be related to the angle at the ankle.4. At high rates of stimulation the maximum active tension was obtained at a length corresponding to an angle of about 60 degrees at the ankle, and a mean sarcomere length of about 2.8 mu. The isometric tension fell only slightly on shortening the muscle to a length equivalent to 100 degrees , and a mean sarcomere length about 2.3 mu. Further shortening caused a marked fall in tension.5. There was a reciprocal relationship between stimulus rate and muscle length; when the muscle was long low rates of stimulation gave near maximal tension, whereas at short lengths the maximum tension was reached only when the stimulus rate was very high. It is suggested that stimulating pulses activate the contractile machinery of the muscle more effectively at long than at short muscle lengths.6. When at low rates of stimulation pulses were distributed among the motor units in rotation to give a smooth contraction, the tension rose higher than during the unfused tetanus that accompanied synchronous stimulation of the same motor units at the same rate. It is suggested that in an unfused tetanus internal movement of the muscle reduces the tension below that developed in a truly isometric state.7. The rate of rise of tension in an isometric tetanus varied with both muscle length and rate of stimulation. At each stimulus rate there was a range of lengths in which the isometric tension developed slowly, this was the same length range in which, at that stimulus rate, the length tension curve was steep.

Animals↗