Ac. Nolan et al., RELATIVE MAGNITUDE AND ASYNCHRONY OF DIRECTIONAL COMPONENTS OF CONTRACTION IN SEDATED DOG LEFT-VENTRICLE, The American journal of physiology, 267(1), 1994, pp. 80000075-80000084
The purpose of this study was to quantitate the temporal relationships
and the extent and speed of shortening in segments of myocardium resp
onsive to contraction in circumferential, longitudinal, and oblique fi
ber groups. Measurements were made in five sedated dogs (morphine, dia
zepam) with and without alterations in preload and afterload (nitropru
sside, phenylephrine). The measurement interval was the phase of rapid
contraction, determined by differentiation of the segment length vs.
time. In the control state, percentage segment shortening was greater
in circumferential than in longitudinal [15.2 +/- 0.24 (SE) vs. 10.5 /- 0.80%; P = 0.0020] and in the subepicardial oblique than in the sub
endocardial oblique fiber directions (16.6 +/- 0.65 vs. 9.7 +/- 0.36%;
P = 0.0010). Shortening was proportional to both maximum speed and du
ration of shortening (r = 0.735 +/- 0.015 and 0.757 +/- 0.017, respect
ively). Duration of shortening was significantly longer in circumferen
tial than in longitudinal (mean difference 39.3 +/- 6.6 ms; P = 0.0039
) and in subepicardial oblique than in subendocardial oblique directio
ns (mean difference 27.7 +/- 5.5 ms; P = 0.0072). Velocities of up to
3.0 segment lengths/s were attained in response to nitroprusside. Thes
e data reveal the local anisotropy and asynchrony of contraction in th
e myocardium; however, they also support the concept of the myocardium
as a functional continuum. The dominance of circumferential over long
itudinal and subepicardial over subendocardial oblique contractile com
ponents indicates their relative contributions to the constriction of
the midmyocardial shell.