Contractility
OVERVIEW
- Contractility = the change in force generated independent of preload
- Inotropy and contractility are essential synonymous — inotropes are agents that increase contractility.
- the slope of the end-systolic pressure volume relationship (ESPVR) curve indicates the maximum rate of force development by the ventricle.
DETERMINED BY
- substrate supply – glucose, fat, protein
- integrity of myofilaments
- co-ordinated depolarisation
- metabolic/electrolyte homeostasis
- functional muscle mass
- coronary blood flow (hypoxia)
- autonomic tone – sympathetic and parasympathetic
- hormones – thyroid, insulin/glucagon
Minor increases in contractility occur as an intrinsic response to:
- increased afterload (Anrep effect)
- increased heart rate (Bowditch effect, Bowditch phenomenon)
MANIPULATION IN ICU
- nutrition: substrate supply
- pacing: co-ordinated depolarisation
- electrolyte replacement
- treatment of negative inotropic conditions: acidosis, sepsis, heart failure, AMI
- avoidance of negative inotropic drugs: beta-blockers, Ca2+ channel blockers
- coronary blood flow + functional muscle mass: thrombolysis, PCI, bypass surgery; maintain DBP
- analgesia/sedation/paralysis: decrease autonomic tone, decrease O2 consumption
- inotropes: adrenaline, milrinone, noradrenaline, dobutamine, glucagon, insulin, levosemendin
- improve O2 delivery: increase FiO2, blood transfusion for severe anemia
- correct endocrine deficiencies: hydrocortisone, thyroxine replacement
References and links
- Cardiovascular Physiology Concepts — Cardiac inotropy (contractility)
- Noble MIM. An introduction to modern work on the Bowditch phenomenon. Cardiovascular Research 1988; 22(8): 586
- von Anrep G. On the part played by the suprarenals in the normal vascular reactions of the body. J Physiol. 1912 Dec 9;45(5):307-17. [PMC1512890]
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
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