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A A Walker

Publications and source records attributed to A A Walker.

3 recordsLinked to original sources
PubMed1978

The effect of aging on ventricular contractile performance.

The effects of aging on mechanical performance of isolated canine right ventricular trabeculae were studied in two age groups. The first group was comprised of nine dogs, about 9 months of age. The second group was composed of seven dogs over 8 years of age. Aging had no significant effect on developed force. Extent of shortening tended to decrease. There was a significant decrease in both the rate of rise of tension and the velocity of shortening (20%). THis reduction was primarily due to an increased duration of contraction. Twitch duration increased by as much as 40% during aging but most of this prolongation was due to a profound slowing of relaxation. Aging caused a significant increase in passive stiffness since equivalent changes in muscle length brought about twice as much increase in resting tension in the aged muscle as in the young muscle. On the other hand, aging caused a significant shift of Lo to the right. Taken collectively, these results indicate that aging is associated with increased passive stiffness and decreased speed of contraction without changes in strength.

Aging↗
PubMed1975

Comparison of contractile performance of canine atrial and ventricular muscles.

This study compared the contractile performance of a canine right atrial trabecula with that of a macroscopically indistinguishable trabecula isolated from the right ventricular apex. The heart was removed from nine mongrel puppies weighing 6-8 kg and placed in Krebs-Ringer's bicarbonate solution. The bathing solution contained only 1.25 mmoles of Ca2+ and was bubbled with a 95% O2-5% CO2 gas mixture. Each atrial trabecula was specially selected from the right atrial appendage. Histologically, these trabeculae showed a remarkable longitudinal orientation of the fibers. At Lmax (the length of the muscle at which developed tension was maximum) under identical conditions of temperature, rate of stimulation, ionic milieu, pH, and O2 and CO2 supply, right atrial trabeculae achieved the same developed and total tensions but in a much shorter time than did ventricular trabeculae. In both muscle groups the maximum developed tension averaged about 2.5 g/mm2. Since Lo (expressed as a fraction of Lmax) was less in atrial muscle than it was in ventribular muscle, we concluded that atrial muscle can be stretched considerably more than can ventricular muscle before optimum length is reached. At any given initial muscle length, the maximum of tension rise for atrial trabeculae amounted to at least twice that for ventricular trabeculae. At any given load up to 1.5 g/mm2, the maximum velocity of shortening of an atrial trabecula was about three to four times that of a ventricular trabecula. These results collectively indicate that the contractile performance of the right atrial muscle is in many respects superior to that of the right ventricle, at least under the conditions of these experiments.

Animals↗