Dynamics of cardiac muscle: analysis of isotonic, isometric, and isochronal curves

1987 ◽  
Vol 253 (3) ◽  
pp. H645-H653
Author(s):  
O. N. Nwasokwa
Keyword(s):  
Muscle Force ◽  
Isometric Force ◽  
Impedance Matching ◽  
Time Intervals ◽  
Cross Sectional ◽  
Contraction Coupling ◽  
Force Development ◽  
Pentobarbital Sodium Anesthesia ◽  
Matching Transformer ◽  
Isotonic Shortening

Canine papillary muscle force-length-time relation (F-L-t) was investigated under pentobarbital sodium anesthesia. The time intervals taken from end diastole to any point (P) on the force-length plane was determined for isometric (t1) and isotonic (t2) systole and corrected for excitation contraction coupling duration. The ratio t1/t2, designated km, was approximately constant for widely scattered positions of P chosen systematically. The km in the 10 dogs ranged from 0.36 to 0.94 with means +/- SD of 0.66 +/- 0.16; km correlated negatively with muscle average cross-sectional area (r = -0.82; P less than 0.005). Assuming constancy of km, a general relationship was derived between (delta F/delta t)t1L, the rate of isometric force development at P; (delta L/delta t)t2F, the velocity of isotonic shortening at P; (delta F/delta L)(t1,t2)t, the stiffness; and (delta L/delta F)(t1,t2)t, the compliance of the myocardium (all taken at P) as follows (delta F/delta L)t1,t2t = -km(delta F/delta t)t1L/(delta L/delta t)t2F and (delta L/delta F)t1,t2t = -km-1(delta L/delta t)t2F/(delta F/delta t)t1t. The ratio of (delta F/delta t)t1L to (delta L/delta t)t2F defines functional proclivity and measures the differential propensity to force development relative to shortening. Thus myocardial stiffness or compliance determines functional proclivity by acting as an impedance-matching transformer that steps up or steps down force development of shortening as warranted by the loading conditions.

scholarly journals Advancements in the Protocol for Rate of Force Development/Relaxation Scaling Factor Evaluation

2021 ◽  
Vol 15 ◽  
Author(s):  
Darjan Smajla ◽  
Jure Žitnik ◽  
Nejc Šarabon
Keyword(s):  
Outcome Measure ◽  
Isometric Force ◽  
Cross Sectional Study ◽  
Scaling Factor ◽  
Rate Of Force Development ◽  
Knee Extensors ◽  
Cross Sectional ◽  
Force Development ◽  
Wide Range ◽  
Neuromuscular Assessment

Brief submaximal actions are important for wide range of functional movements. Until now, rate of force development and relaxation scaling factor (RFD-SF and RFR-SF) have been used for neuromuscular assessment using 100–120 isometric pulses which requires a high level of attention from the participant and may be influenced by physiological and/or psychological fatigue. All previous studies have been conducted on a smaller number of participants which calls into question the eligibility of some of the outcome measures reported to date. Our aims were: (1) to find the smallest number of rapid isometric force pulses at different force amplitudes is still valid and reliable for RFD-SF slope (kRFD–SF) and RFR-SF slope (kRFR–SF) calculation, (2) to introduce a new outcome measure – theoretical peak of rate of force development/relaxation (TPRFD and TPRFR) and (3) to investigate differences and associations between kRFD–SF and kRFR–SF. A cross-sectional study was conducted on a group of young healthy participants; 40 in the reliability study and 336 in the comparison/association study. We investigated the smallest number of rapid isometric pulses for knee extensors that still provides excellent reliability of the calculated kRFD–SF and kRFR–SF (ICC2,1 ≥ 0.95, CV < 5%). Our results showed excellent reliability of the reduced protocol when 36 pulses (nine for each of the four intensity ranges) were used for the calculations of kRFD–SF and kRFR–SF. We confirmed the negligibility of the y-intercepts and confirmed the reliability of the newly introduced TPRFD and TPRFR. Large negative associations were found between kRFD–SF and kRFR–SF (r = 0.502, p < 0.001), while comparison of the absolute values showed a significantly higher kRFD–SF (8.86 ± 1.0/s) compared to kRFR–SF (8.03 ± 1.3/s) (p < 0.001). The advantage of the reduced protocol (4 intensities × 9 pulses = 36 pulses) is the shorter assessment time and the reduction of possible influence of fatigue. In addition, the introduction of TPRFD and TPRFR as an outcome measure provides valuable information about the participant’s maximal theoretical RFD/RFR capacity. This can be useful for the assessment of maximal capacity in people with various impairments or pain problems.

Short-term memory in the in situ canine myocardium

1984 ◽  
Vol 247 (1) ◽  
pp. H8-H16
Author(s):  
O. Nwasokwa ◽  
K. Sagawa ◽  
H. Suga
Keyword(s):  
Short Term Memory ◽  
Isometric Force ◽  
Myocardial Performance ◽  
Short Term ◽  
Force Development ◽  
Length Relationship ◽  
History Of ◽  
Systolic Time ◽  
Length Changes ◽  
Isotonic Shortening

We studied the effect of intracycle (short-term) mechanical history on canine myocardial performance. Intracycle muscle force and/or length history was varied, and the resultant changes in end-systolic force-length relationship were analyzed. Antecedent isotonic shortening impaired, whereas isometric force development enhanced end-systolic myocardial performance. A history of shortening concurrent with force development produced an intermediate effect. We conclude that decreasing force or length impairs whereas increasing length or force enhances performance in the same cycle. Different combinations of antecedent force and length changes affect end-systolic performance by algebraic summation (superposition) of their disparate effects. Time measurements established that 1) total systolic time varied little with altered history, 2) isotonic shortening took longer than isometric contraction in reaching a point P in the force-length plane, and 3) less time was therefore available for contraction after P with antecedent isotonic shortening than with antecedent isometric force development. This history-dependent time differential accounts for the corresponding differential in performance.

A Numerical Method for Estimating Tendon Slack Length

2003 ◽  
Author(s):  
Kurt Manal ◽  
Thomas S. Buchanan
Keyword(s):  
Numerical Method ◽  
Fiber Length ◽  
Muscle Force ◽  
Isometric Force ◽  
Pennation Angle ◽  
Cross Sectional ◽  
Force Equation ◽  
Subject Specific ◽  
Maximum Isometric Force ◽  
Slack Length

Forces generated by muscle are transferred to bone via tendon. Since muscle force cannot be measured directly, computer modeling is a useful tool to enhance our understanding of normal and pathological movement. Hill-type muscle models have been used to estimate force based on information about a muscle’s architecture, activation and kinematics (Delp et al., 1995; Manal et al., 2002). Architectural parameters include optimal fiber length (lom), tendon slack length (lst), pennation angle (α), and maximum isometric force (Fmax). In addition, musculotendon length (lmt) and activation (a) are required inputs when estimating isometric muscle force (Equation I). Fm=f(lmt,lom,lst,Fmax,α,a)(1) Musculotendon length can be determined from MR images (Arnold et al., 2000), and activation recorded from EMGs (Manal, et al., 2002). Optimal fiber length and pennation angle can be measured experimentally (Murray, 2002), while Fmax can be estimated from the muscle’s physiologic cross-sectional area. Tendon slack length however cannot be measured readily, and therefore few estimates of lst can be found in the literature. In this paper we present a numerical method for estimating tendon slack from subject specific muscle parameters and musculotendon lengths. An advantage of this method is that it yields subject specific estimates of tendon slack length.

Contractile responses to ouabain and K+-free solution in aorta from hypertensive rats

1986 ◽  
Vol 250 (4) ◽  
pp. H612-H619 ◽  
Author(s):  
R. S. Moreland ◽  
T. C. Major ◽  
R. C. Webb
Keyword(s):  
Channel Blocker ◽  
Isometric Force ◽  
Maximal Response ◽  
Na Channel ◽  
Free Solution ◽  
Contractile Responses ◽  
Spontaneously Hypertensive ◽  
Force Development ◽  
Monensin A ◽  
Wistar Kyoto

This study characterizes isometric force development in response to ouabain and K+-free solution in isolated aortic strips from spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. SHR aortas were more sensitive to ouabain than those from WKY (threshold: SHR, 3.1 X 10(-5) M; WKY, 25.6 X 10(-5) M), and force development in response to 10(-3) M ouabain was greater in SHR (SHR, 586 +/- 51 mg; WKY, 245 +/- 24 mg). Monensin, a Na+ ionophore, potentiated contractile responses to ouabain, whereas amiloride, a Na+ channel blocker, and low Na+ solutions depressed contractile responses to ouabain. Contractile responses of SHR aortic strips to K+-free solution were faster than those of WKY aortic strips [time to half-maximal response (t1/2): SHR, 24 +/- 5 min; WKY, 47 +/- 4 min]. Maximal force development by aortic strips from SHR in response to K+-free solution was not different from that of WKY aortic strips (SHR, 808 +/- 34 mg; WKY, 750 +/- 37 mg). Monensin (10(-5) M) increased the rate of force development to K+-free solution to a greater extent in WKY aortic strips than in those from SHR (t1/2: SHR, 3 +/- 1 min; WKY, 4 +/- 2 min). Amiloride and low Na+ solution depressed contractile responses to K+-free solution in both SHR and WKY aortic strips. These observations demonstrate that SHR aortas are more responsive to ouabain and K+-free solution compared with WKY aortas. Contractile responses to ouabain and K+-free solution were sensitive to experimental interventions that alter transmembrane Na+ movements.(ABSTRACT TRUNCATED AT 250 WORDS)

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