Should Patients With Haemorrhage Be Kept Warm?
ARMY INST OF SURGICAL RESEARCH FORT SAM HOUSTON TX
Pagination or Media Count:
It has been more than 95 years since Ernest Starling provided experimental evidence to support the concept that energy of contraction is proportional to the initial length of the cardiac muscle fibre Patterson Starling, 1914. This concept, known as Starling s law of the heart, defined the fundamental relationship between cardiac preload end-diastolic volume or filling pressure and stroke volume cardiac performance. Subsequent investigations have revealed that this mechanism can be represented by an operational point that shifts across a family of hyperbolic curves depending on varying physiological conditions. An operational point that functions on the flat portion of the curve is viewed as protective of cardiac performance since a given drop in filling volume or pressure has little impact on stroke volume while function on the steep portion of the curve can lead to drastic reductions in cardiac output with only small decreases in venous return. The latter condition can lead to marked hypotension with subsequent failure to adequately perfuse vital organs. A reduction in central blood volume central hypovolaemia such as that caused by an orthostatic challenge or haemorrhage is one condition that elicits a left and upward shift of the Starling relationship by way of a compensatory sympathetic excitation Braunwald et al. 1967. The resultant increase in myocardial contractility maintains stroke volume in the face of lowered cardiac filling, but the setting of the operational point on a steeper curve places the cardiovascular system at risk for collapse with any further reduction in filling pressure. The latter condition forms the basis for the development of fainting or haemorrhagic shock.
- Anatomy and Physiology
- Medicine and Medical Research