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Reduced mechanical efficiency in left-ventricular trabeculae of the spontaneously hypertensive rat.

Han JC, Tran K, Johnston CM, Nielsen PM, Barrett CJ, Taberner AJ, Loiselle DS - Physiol Rep (2014)

Bottom Line: Our results show that, whereas the performance of the SHR-F differed little from that of the SHR-NF, both SHR groups performed less stress-length work than that of Wistar trabeculae.Their lower work output arose from reduced ability to produce sufficient force and shortening.Consequently, mechanical efficiency (the ratio of work to change of enthalpy) of both SHR groups was lower than that of the Wistar trabeculae.

View Article: PubMed Central - PubMed

Affiliation: Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand.

No MeSH data available.


Related in: MedlinePlus

Isometric total and active stress‐length relations and heat‐length relation. (A) Records from a representative failing spontaneously hypertensive rat (SHR‐F) trabecula of steady‐state isometric twitches as functions of decreasing muscle length (a–g, where “a” represents the isometric developed stress at Lo). (B) Average total and passive stresses as functions of relative muscle length (L/Lo) obtained by fitting cubic regressions, respectively, to the peak stress and passive stress data; the inset plots stress development as a function of L/Lo of a representative trabecula. (C) Average active (total minus passive) stress‐length relations; the inset shows data from the same trabecula. (D) Record of rate of heat output from a representative trabecula subjected to variable muscle‐length isometric contractions. (E) Heat per twitch (rate of heat production divided by stimulus frequency) as function of L/Lo. The symbol “*” denotes significant effect of “Strain” (i.e., comparing the mean regression line of the Wistar group with the average of the regression lines of both the nonfailing SHR (SHR‐NF) and SHR‐F groups); “+” denotes significant effect of “Failing” (i.e., comparing the mean regression line of the SHR‐F group with that of the SHR‐NF group). Data (mean ± SE) at Lo were superimposed on appropriate panels to demonstrate the variability of each average regression line.
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fig01: Isometric total and active stress‐length relations and heat‐length relation. (A) Records from a representative failing spontaneously hypertensive rat (SHR‐F) trabecula of steady‐state isometric twitches as functions of decreasing muscle length (a–g, where “a” represents the isometric developed stress at Lo). (B) Average total and passive stresses as functions of relative muscle length (L/Lo) obtained by fitting cubic regressions, respectively, to the peak stress and passive stress data; the inset plots stress development as a function of L/Lo of a representative trabecula. (C) Average active (total minus passive) stress‐length relations; the inset shows data from the same trabecula. (D) Record of rate of heat output from a representative trabecula subjected to variable muscle‐length isometric contractions. (E) Heat per twitch (rate of heat production divided by stimulus frequency) as function of L/Lo. The symbol “*” denotes significant effect of “Strain” (i.e., comparing the mean regression line of the Wistar group with the average of the regression lines of both the nonfailing SHR (SHR‐NF) and SHR‐F groups); “+” denotes significant effect of “Failing” (i.e., comparing the mean regression line of the SHR‐F group with that of the SHR‐NF group). Data (mean ± SE) at Lo were superimposed on appropriate panels to demonstrate the variability of each average regression line.

Mentions: Both groups of SHR trabeculae produced lower stresses than that of Wistar trabeculae, as evidenced by their lower average total and average active stress‐length relations (Fig. 1). The average passive stress‐length relation of the SHR‐F was steeper than the SHR‐NF groups (Fig. 1B). The average heat‐length relations of both SHR groups were also lower than the Wistar group (Fig. 1E). Compared with the Wistar group, both SHR groups also demonstrated prolonged twitch duration (quantified at 5% and at 50% of peak stress), had lower maximal rates of rise and fall of twitch stress, and had smaller values of stress‐time integral (STI, the area under the twitch), as indicated by the respective relations shown in Figure 2. Given these mechanical differences, the heat production (plotted as functions of active stress and STI) of the SHR trabeculae was, surprisingly, not different from that of the Wistar trabeculae (Fig. 3). The average activation heat (predicted by the y‐intercept of the heat‐stress relation; Fig. 3A) was not different among the rat groups. The average values of activation heat were 2.35 kJ·m−3± 0.27 kJ·m−3, 2.30 kJ·m−3 ± 0.30 kJ·m−3, and 2.61 kJ·m−3 ± 0.43 kJ·m−3, respectively for the Wistar, SHR and SHR‐F groups. These values were not different from those predicted from the heat‐STI relation (Fig. 3B; respectively 2.49 kJ·m−3 ± 0.27 kJ·m−3, 2.31 kJ·m−3 ±0.31 kJ·m−3, and 2.54 kJ·m−3 ± 0.44 kJ·m−3).


Reduced mechanical efficiency in left-ventricular trabeculae of the spontaneously hypertensive rat.

Han JC, Tran K, Johnston CM, Nielsen PM, Barrett CJ, Taberner AJ, Loiselle DS - Physiol Rep (2014)

Isometric total and active stress‐length relations and heat‐length relation. (A) Records from a representative failing spontaneously hypertensive rat (SHR‐F) trabecula of steady‐state isometric twitches as functions of decreasing muscle length (a–g, where “a” represents the isometric developed stress at Lo). (B) Average total and passive stresses as functions of relative muscle length (L/Lo) obtained by fitting cubic regressions, respectively, to the peak stress and passive stress data; the inset plots stress development as a function of L/Lo of a representative trabecula. (C) Average active (total minus passive) stress‐length relations; the inset shows data from the same trabecula. (D) Record of rate of heat output from a representative trabecula subjected to variable muscle‐length isometric contractions. (E) Heat per twitch (rate of heat production divided by stimulus frequency) as function of L/Lo. The symbol “*” denotes significant effect of “Strain” (i.e., comparing the mean regression line of the Wistar group with the average of the regression lines of both the nonfailing SHR (SHR‐NF) and SHR‐F groups); “+” denotes significant effect of “Failing” (i.e., comparing the mean regression line of the SHR‐F group with that of the SHR‐NF group). Data (mean ± SE) at Lo were superimposed on appropriate panels to demonstrate the variability of each average regression line.
© Copyright Policy - open-access
Related In: Results  -  Collection

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fig01: Isometric total and active stress‐length relations and heat‐length relation. (A) Records from a representative failing spontaneously hypertensive rat (SHR‐F) trabecula of steady‐state isometric twitches as functions of decreasing muscle length (a–g, where “a” represents the isometric developed stress at Lo). (B) Average total and passive stresses as functions of relative muscle length (L/Lo) obtained by fitting cubic regressions, respectively, to the peak stress and passive stress data; the inset plots stress development as a function of L/Lo of a representative trabecula. (C) Average active (total minus passive) stress‐length relations; the inset shows data from the same trabecula. (D) Record of rate of heat output from a representative trabecula subjected to variable muscle‐length isometric contractions. (E) Heat per twitch (rate of heat production divided by stimulus frequency) as function of L/Lo. The symbol “*” denotes significant effect of “Strain” (i.e., comparing the mean regression line of the Wistar group with the average of the regression lines of both the nonfailing SHR (SHR‐NF) and SHR‐F groups); “+” denotes significant effect of “Failing” (i.e., comparing the mean regression line of the SHR‐F group with that of the SHR‐NF group). Data (mean ± SE) at Lo were superimposed on appropriate panels to demonstrate the variability of each average regression line.
Mentions: Both groups of SHR trabeculae produced lower stresses than that of Wistar trabeculae, as evidenced by their lower average total and average active stress‐length relations (Fig. 1). The average passive stress‐length relation of the SHR‐F was steeper than the SHR‐NF groups (Fig. 1B). The average heat‐length relations of both SHR groups were also lower than the Wistar group (Fig. 1E). Compared with the Wistar group, both SHR groups also demonstrated prolonged twitch duration (quantified at 5% and at 50% of peak stress), had lower maximal rates of rise and fall of twitch stress, and had smaller values of stress‐time integral (STI, the area under the twitch), as indicated by the respective relations shown in Figure 2. Given these mechanical differences, the heat production (plotted as functions of active stress and STI) of the SHR trabeculae was, surprisingly, not different from that of the Wistar trabeculae (Fig. 3). The average activation heat (predicted by the y‐intercept of the heat‐stress relation; Fig. 3A) was not different among the rat groups. The average values of activation heat were 2.35 kJ·m−3± 0.27 kJ·m−3, 2.30 kJ·m−3 ± 0.30 kJ·m−3, and 2.61 kJ·m−3 ± 0.43 kJ·m−3, respectively for the Wistar, SHR and SHR‐F groups. These values were not different from those predicted from the heat‐STI relation (Fig. 3B; respectively 2.49 kJ·m−3 ± 0.27 kJ·m−3, 2.31 kJ·m−3 ±0.31 kJ·m−3, and 2.54 kJ·m−3 ± 0.44 kJ·m−3).

Bottom Line: Our results show that, whereas the performance of the SHR-F differed little from that of the SHR-NF, both SHR groups performed less stress-length work than that of Wistar trabeculae.Their lower work output arose from reduced ability to produce sufficient force and shortening.Consequently, mechanical efficiency (the ratio of work to change of enthalpy) of both SHR groups was lower than that of the Wistar trabeculae.

View Article: PubMed Central - PubMed

Affiliation: Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand.

No MeSH data available.


Related in: MedlinePlus