Figure 7.
Lower trabecula work output and enthalpy but preserved mechanical efficiency. (A) Mechanical work output was quantified as the integral of stress with respect to length over a work-loop twitch, which denotes the area within the work-loop. The average relations of work and afterload (relative to peak total stress obtained at Lo) were fitted using cubic regression with both variables constrained at the origin. The regression lines are drawn to commence at relative passive stress. (B) Enthalpy is the sum of work and heat. The average relations of enthalpy and afterload (relative to peak total stress obtained at Lo) were fitted using quadratic regression. (C) Mechanical efficiency is the ratio of work to enthalpy. The average relations of mechanical efficiency and afterload (relative to peak total stress obtained at Lo) were fitted using cubic regression with both variables constrained at the origin. The regression lines are drawn to commence at relative passive stress. Control rat (solid lines), hypertrophic rat (broken lines), n = 12 trabeculae. SEM is superimposed at peak values for each dependent variable. The difference between regression lines was analyzed by the random coefficient model; *, P < 0.05. Insets in each panel show data from an exemplar trabecula.