LAUSR

Myocardial contractility (MC) is commonly defined in a vague matter as the intrinsic contractile property of cardiac muscle, or its ability to generate force and shorten. This understanding is insufficient. In this abstract, we propose that MC should be comprehensively conceptualized through multiple dimensions, (i.e., it is not merely intrinsic and it is more than an ability) through logical analysis as follows. First, when conceptualizing MC in medical physiology, it is no doubt that force (F) and velocity (V) of muscle shortening are two aspects of the muscle’s ability. Both F and V are dependent on afterload, an extrinsic factor. This extrinsic factor-dependency indicates the following: 1) muscle contraction exhibits adaptability, i.e., muscles are intelligent when interacting with extrinsic factors and only produce F and/or V appropriate to the given extrinsic factor(s); and 2) what is intrinsic is not ability (F and/or V), but capacity (including FC and VC) which is truly independent of extrinsic factors. An ability is always a fraction of capacity and a result of adaptability; capacity (FC and VC, although not quantifiable so far, but theoretically present) is the ultimate source of ability (F and V) which can be experimentally quantified. Second, it is well known that F is determined by at least two aspects: a component (F_FS) governed by the Frank-Starling Law (i.e., the force-length relationship) and a component (F_Ca) by the level of intracellular Ca2+ transient during cross bridge cycles that determines the actual number of cross-bridges binding to thin filaments. A gap in current medical physiology education is that when introducing muscle physiology, the Frank-Starling law that determines F_FS is always introduced, but when presenting MC specifically, quite often, the contribution of F_FS to F is ignored and only F_Ca (i.e., inotropism) is included. Finally, V can also be at least subdivided into the rate of Ca2+ releasing into the cytoplasm (V_Ca) from the sarcoplasmic reticulum as well as the rate of ATP hydrolysis catalyzed by the myosin heads (V_ATP). In conclusion, MC is a complex concept, which needs to be described through multiple dimensions including but not limited to its capacity, adaptability, and ability. The capacity can be further differentiated into Fc and Vc, and ability into F and V, both of which having at least two subdimensions, respectively: F_FS and F_Ca; V_Ca, and V_ATP. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.