Force-time integral decreases with ejection despite constant oxygen consumption and pressure-volume area in dog left ventricle.

We tested the hypothesis that economy and efficiency are independent of length in intact cardiac muscle over its normal working range. We measured force, force-time integral, force-length area, and myocardial oxygen consumption in eight isometrically contracting rabbit right ventricular papillary muscles. 2,3-Butanedione monoxime was used to partition nonbasal oxygen consumption into tension-independent and tension-dependent components. Developed force, force-time integral, and force-length area increased by factors of 2.4, 2.7, and 4.8, respectively, as muscle length was increased from 90% to 100% maximal length, whereas tension-dependent oxygen consumption increased only 1.6-fold. Economy (the ratio of force-time integral to tension-dependent oxygen consumption) increased significantly with muscle length, as did contractile efficiency, the ratio of force-length area to tension-dependent oxygen consumption. The average force-length area-nonbasal oxygen consumption intercept was more than the twice tension-independent oxygen consumption. We conclude that economy and efficiency increase with length in rabbit myocardium. This conclusion is consistent with published data in isolated rabbit and dog hearts but at odds with studies in skinned myocardium.

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Energy expenditure of longitudinal smooth muscle of rabbit urinary bladder

AJP Cell Physiology ◽

10.1152/ajpcell.1987.252.1.c88 ◽

1987 ◽

Vol 252 (1) ◽

pp. C88-C96 ◽

Cited By ~ 17

Author(s):

I. R. Wendt ◽

C. L. Gibbs

Keyword(s):

Oxygen Consumption ◽

Energy Expenditure ◽

Total Energy ◽

Heat Production ◽

Lactate Production ◽

Time Integral ◽

Force Maintenance ◽

Force Time ◽

Rabbit Urinary Bladder ◽

Force Time Integral

Heat production, oxygen consumption, and lactate production of longitudinal smooth muscle from rabbit urinary bladder has been measured at 27 degrees C. In isometric contractions (initiated by 1-Hz electrical stimulation) ranging in duration from 2 to 300 s, total energy expenditure correlated linearly with the force-time integral. For any given force-time integral oxygen consumption could account for only approximately 60% of the total energy measured as heat production. A substantial contribution of aerobic lactate production to the total energy flux was observed. This lactate production was also linearly correlated with force-time integral and was of sufficient magnitude to account for the discrepancy between total energy expenditure determined as heat production and oxygen consumption. The suprabasal rate of energy expenditure during the maintenance of force was approximately 2.6 mW/g and remained constant throughout contractions of up to 5-min duration, suggesting that in this muscle there is no change in the energetic cost of force maintenance with increasing duration of contraction. The rate of energy expenditure during the initial period of force development was, however, about twofold greater than that during subsequent force maintenance, indicating that there is an extra energy cost associated with the activation of contraction and development of force above that required for force maintenance.

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Force-time integral does not improve predictability of cardiac O2 consumption from pressure-volume area (PVA) in dog left ventricle

Heart and Vessels ◽

10.1007/bf02059910 ◽

1990 ◽

Vol 5 (3) ◽

pp. 152-158 ◽

Cited By ~ 3

Author(s):

Hiroyuki Suga ◽

Takashi Nozawa ◽

Yoshio Yasumura ◽

Shiho Futaki ◽

Yuichi Ohgoshi ◽

...

Keyword(s):

Left Ventricle ◽

O2 Consumption ◽

Time Integral ◽

Force Time ◽

Force Time Integral

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The Effect of Muscle Lentgh on Force-Time Integral in Relation to Energy-Rich Phosphate Consumption

Biomechanics: Current Interdisciplinary Research ◽

10.1007/978-94-011-7432-9_90 ◽

1985 ◽

pp. 605-610 ◽

Cited By ~ 1

Author(s):

A. De Haan ◽

J. E. Van Doorn ◽

P. A. Huijing ◽

R. D. Woittiez ◽

H. G. Westra

Keyword(s):

Time Integral ◽

Force Time ◽

Force Time Integral

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Regulation of energy consumption in cardiac muscle: analysis of isometric contractions

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1999.276.3.h998 ◽

1999 ◽

Vol 276 (3) ◽

pp. H998-H1011 ◽

Cited By ~ 10

Author(s):

Amir Landesberg ◽

Samuel Sideman

Keyword(s):

Energy Consumption ◽

Cardiac Muscle ◽

Feedback Mechanism ◽

Isometric Contractions ◽

Cross Bridge ◽

Time Integral ◽

Length Relationship ◽

Cross Bridges ◽

Force Time ◽

Force Time Integral

The well-known linear relationship between oxygen consumption and force-length area or the force-time integral is analyzed here for isometric contractions. The analysis, which is based on a biochemical model that couples calcium kinetics with cross-bridge cycling, indicates that the change in the number of force-generating cross bridges with the change in the sarcomere length depends on the force generated by the cross bridges. This positive-feedback phenomenon is consistent with our reported cooperativity mechanism, whereby the affinity of the troponin for calcium and, hence, cross-bridge recruitment depends on the number of force-generating cross bridges. Moreover, it is demonstrated that a model that does not include a feedback mechanism cannot describe the dependence of energy consumption on the loading conditions. The cooperativity mechanism, which has been shown to determine the force-length relationship and the related Frank-Starling law, is shown here to provide the basis for the regulation of energy consumption in the cardiac muscle.

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Preload does not influence nonmechanical O2 consumption in isolated rabbit heart

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1994.266.3.h1047 ◽

1994 ◽

Vol 266 (3) ◽

pp. H1047-H1054 ◽

Cited By ~ 4

Author(s):

A. Higashiyama ◽

M. W. Watkins ◽

Z. Chen ◽

M. M. LeWinter

Keyword(s):

Energy Consumption ◽

Diastolic Pressure ◽

Rabbit Heart ◽

Left Ventricular ◽

Energetic Cost ◽

O2 Consumption ◽

Time Integral ◽

Force Time ◽

Whole Heart ◽

Force Time Integral

Myocardial energy consumption for nonmechanical activity (excitation-contraction coupling) has been shown to be length dependent in isolated muscle studies but no more than minimally affected by preload in the whole heart. However, unloaded O2 consumption (VO2, which is used to estimate nonmechanical VO2 in whole heart) may not be accurate for quantifying nonmechanical energy consumption, because it contains VO2 for residual cross-bridge cycling. To more accurately determine the influence of left ventricular (LV) diastolic volume on nonmechanical VO2 in whole heart, we employed a new method for quantifying nonmechanical VO2, using the drug 2,3-butanedione monoxime (BDM). We measured VO2 and force-time integral during infusion of BDM (< or = 5 mM) at high (VH) and low LV volumes (VL) in 16 excised isovolumically contracting red blood cell-perfused rabbit ventricles. LV end-diastolic pressure was 9.7 +/- 4.6 and 3.8 +/- 2.8 (SD) mmHg at VH and VL, respectively. Nonmechanical VO2, estimated as the VO2-axis intercept of the linear VO2-force-time integral relation obtained during BDM infusion, did not differ significantly between VH and VL (0.0137 +/- 0.0083 and 0.0132 +/- 0.0090 ml O2.beat-1 x 100 gLV-1, P = 0.702). A multiple linear regression analysis for the pooled data confirmed this finding (P = 0.361). We conclude that, in the rabbit heart, LV diastolic volume does not importantly affect nonmechanical energy consumption over a physiological range of LV end-diastolic pressure. This indicates that length-dependent activation does not have an energetic cost in whole rabbit heart and suggests that its predominant mechanism is increased Ca2+ affinity for the contractile proteins.

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1160Early experience with ablation index-guided pulmonary vein isolation compared with force-time integral-guided ablation using surround flow catheter tip irrigation for ablation of atrial fibrillation

EP Europace ◽

10.1093/ehjci/eux152.008 ◽

2017 ◽

Vol 19 (suppl_3) ◽

pp. iii246-iii246

Author(s):

V. Weberndoerfer ◽

S. Toggweiler ◽

T. Schefer ◽

I. Russi ◽

M. Brinkert ◽

...

Keyword(s):

Atrial Fibrillation ◽

Pulmonary Vein ◽

Pulmonary Vein Isolation ◽

Time Integral ◽

Ablation Index ◽

Catheter Tip ◽

Force Time ◽

Force Time Integral

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Stimulation Pattern That Maximizes Force in Paralyzed and Control Whole Thenar Muscles

Journal of Neurophysiology ◽

10.1152/jn.2002.87.5.2271 ◽

2002 ◽

Vol 87 (5) ◽

pp. 2271-2278 ◽

Cited By ~ 25

Author(s):

Lisa Griffin ◽

Sharlene Godfrey ◽

Christine K. Thomas

Keyword(s):

Short Interval ◽

Motor Units ◽

Muscle Stiffness ◽

Peak Force ◽

Single Motor Units ◽

Time Integral ◽

Cord Injury ◽

Force Time ◽

And Control ◽

Force Time Integral

The pattern of seven pulses that elicited maximal thenar force was determined for control muscles and those that have been paralyzed chronically by spinal cord injury. For each subject group ( n = 6), the peak force evoked by two pulses occurred at a short interval (5–15 ms; a “doublet”), but higher mean relative forces were achieved in paralyzed versus control muscles (41.4 ± 3.9% vs. 22.7 ± 2.0% maximal). Thereafter, longer intervals evoked peak force in each type of muscle (mean: 35 ± 1 ms, 36 ± 2 ms, respectively). With seven pulses, paralyzed and control muscles reached 76.4 ± 5.6% and 57.0 ± 2.6% maximal force, respectively. These force differences resulted from significantly greater doublet/twitch and doublet/tetanic force ratios in paralyzed (2.73 ± 0.08, 0.35 ± 0.03) compared with control muscles (2.07 ± 0.07, 0.25 ± 0.01). The greater force enhancement produced in paralyzed muscles with two closely spaced pulses may relate to changes in muscle stiffness and calcium metabolism. Peak force-time integrals were also achieved with an initial short interpulse interval, followed by longer intervals. The postdoublet intervals that produced peak force-time integrals in paralyzed and control muscles were longer than those for peak force, however (77 ± 3 ms, 95 ± 4 ms, respectively). These data show that the pulse patterns that maximize force and force-time integral in paralyzed muscles are similar to those that maximize these parameters in single motor units and various whole muscles across species. Thus the changes in neuromuscular properties that occur with chronic paralysis do not strongly influence the pulse pattern that optimizes muscle force or force-time integral.

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Effect of rearfoot posts in reducing forefoot forces. A single-subject design

Journal of the American Podiatric Medical Association ◽

10.7547/87507315-82-7-371 ◽

1992 ◽

Vol 82 (7) ◽

pp. 371-374 ◽

Cited By ~ 9

Author(s):

MW Cornwall ◽

TG McPoil

Keyword(s):

Varus Deformity ◽

Single Subject ◽

Foot Orthoses ◽

Single Subject Design ◽

Time Integral ◽

Subject Design ◽

Force Time ◽

Foot Orthosis ◽

Force Time Integral

The purpose of this study was to assess the effectiveness of a semirigid foot orthosis with a varus wedge on forefoot vertical forces in a 24-year-old female with a compensated rearfoot varus deformity. The results of this study indicate that the use of total contact semirigid foot orthoses reduces the forefoot force-time integral during walking, whether a rearfoot varus wedge was or was not used. The authors recommend that total contact construction of the foot orthoses be considered when a reduction of the forces acting on the forefoot is the goal of treatment.

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