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Variability in interbeat duration influences myocardial contractility in rat cardiac trabeculae.

Torres CA, Varian KD, Janssen PM - Open Cardiovasc Med J (2008)

Bottom Line: Fixed rate response was measured before and after each variable period and average force was calculated.We observed no significant change in force at 4 Hz (n=17), and 6 Hz (n=6) between fixed and variable pacing but observed a significant, 10% increase in contractile strength at 8 Hz (from 15.1 to 16.5 mN/mm(2), p<0.05, n=6).Our results show that under certain conditions, by simply introducing variation in the beat-to-beat duration without affecting the number of beats per minute, a positive inotropic effect with corresponding changes in the calcium transients can be generated.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Cell Biology, and Department of Emergency Medicine, 304 Hamilton Hall, 1645 Neil Avenue, The Ohio State University, Columbus, OH, USA.

ABSTRACT
There is an intense search for positive inotropic strategies. It is well known that the interbeat duration is a critical determinant of cardiac contractility. Generally, when frequency increases, so does contractile strength. We hypothesize that the beat-to-beat variability at a given heart rate also modulates cardiac contractility. To test this hypothesis, thin, uniform rat cardiac trabeculae were isolated from the right ventricle and stimulated to isometrically contract, alternating between fixed steady state versus variable inter-beat intervals (same total number of beats in each period). Trabeculae were stimulated at 4 Hz with interbeat variation between 20 and 120% (n=17). In a second series of experiments trabeculae were stimulated at 3 different physiologic frequencies with a 40% interbeat variation. Fixed rate response was measured before and after each variable period and average force was calculated. In order to investigate the mechanism underlying the changes in contractility we used iontophoretically loaded bis-fura-2 salt to monitor intracellular calcium transients. We observed no significant change in force at 4 Hz (n=17), and 6 Hz (n=6) between fixed and variable pacing but observed a significant, 10% increase in contractile strength at 8 Hz (from 15.1 to 16.5 mN/mm(2), p<0.05, n=6). Our results show that under certain conditions, by simply introducing variation in the beat-to-beat duration without affecting the number of beats per minute, a positive inotropic effect with corresponding changes in the calcium transients can be generated.

No MeSH data available.


At a base cycle time of 250 ms (4 Hz), between 10 and 120% variability (reflecting cycle times from 237.5-262.5 ms and 125-375 ms resp.), the small increases in average Fdev were not significant, but on the other hand did not impair contractility either (n = 17).
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Figure 2: At a base cycle time of 250 ms (4 Hz), between 10 and 120% variability (reflecting cycle times from 237.5-262.5 ms and 125-375 ms resp.), the small increases in average Fdev were not significant, but on the other hand did not impair contractility either (n = 17).

Mentions: For each stimulation period, we averaged the mean twitch force. By comparing the developed force at 4 Hz between fixed and variable pacing we noticed small, increases in force due to variable pacing with a trend towards increasing force with increasing varibility (with the notable exception of 100% variability). The highest increase was noted at 120% variability (+1.3%, SEM 1.0 n = 17, Fig. 2) although this did not achieve statistical significance.


Variability in interbeat duration influences myocardial contractility in rat cardiac trabeculae.

Torres CA, Varian KD, Janssen PM - Open Cardiovasc Med J (2008)

At a base cycle time of 250 ms (4 Hz), between 10 and 120% variability (reflecting cycle times from 237.5-262.5 ms and 125-375 ms resp.), the small increases in average Fdev were not significant, but on the other hand did not impair contractility either (n = 17).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2627530&req=5

Figure 2: At a base cycle time of 250 ms (4 Hz), between 10 and 120% variability (reflecting cycle times from 237.5-262.5 ms and 125-375 ms resp.), the small increases in average Fdev were not significant, but on the other hand did not impair contractility either (n = 17).
Mentions: For each stimulation period, we averaged the mean twitch force. By comparing the developed force at 4 Hz between fixed and variable pacing we noticed small, increases in force due to variable pacing with a trend towards increasing force with increasing varibility (with the notable exception of 100% variability). The highest increase was noted at 120% variability (+1.3%, SEM 1.0 n = 17, Fig. 2) although this did not achieve statistical significance.

Bottom Line: Fixed rate response was measured before and after each variable period and average force was calculated.We observed no significant change in force at 4 Hz (n=17), and 6 Hz (n=6) between fixed and variable pacing but observed a significant, 10% increase in contractile strength at 8 Hz (from 15.1 to 16.5 mN/mm(2), p<0.05, n=6).Our results show that under certain conditions, by simply introducing variation in the beat-to-beat duration without affecting the number of beats per minute, a positive inotropic effect with corresponding changes in the calcium transients can be generated.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Cell Biology, and Department of Emergency Medicine, 304 Hamilton Hall, 1645 Neil Avenue, The Ohio State University, Columbus, OH, USA.

ABSTRACT
There is an intense search for positive inotropic strategies. It is well known that the interbeat duration is a critical determinant of cardiac contractility. Generally, when frequency increases, so does contractile strength. We hypothesize that the beat-to-beat variability at a given heart rate also modulates cardiac contractility. To test this hypothesis, thin, uniform rat cardiac trabeculae were isolated from the right ventricle and stimulated to isometrically contract, alternating between fixed steady state versus variable inter-beat intervals (same total number of beats in each period). Trabeculae were stimulated at 4 Hz with interbeat variation between 20 and 120% (n=17). In a second series of experiments trabeculae were stimulated at 3 different physiologic frequencies with a 40% interbeat variation. Fixed rate response was measured before and after each variable period and average force was calculated. In order to investigate the mechanism underlying the changes in contractility we used iontophoretically loaded bis-fura-2 salt to monitor intracellular calcium transients. We observed no significant change in force at 4 Hz (n=17), and 6 Hz (n=6) between fixed and variable pacing but observed a significant, 10% increase in contractile strength at 8 Hz (from 15.1 to 16.5 mN/mm(2), p<0.05, n=6). Our results show that under certain conditions, by simply introducing variation in the beat-to-beat duration without affecting the number of beats per minute, a positive inotropic effect with corresponding changes in the calcium transients can be generated.

No MeSH data available.