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Cardiac resistance to flow; pressure-flow relationships in quiescent and beating turtle heart

, : Cardiac resistance to flow; pressure-flow relationships in quiescent and beating turtle heart. American Journal of Physiology 169(2): 412-422

"Cardiac resistance" to flow was studied by perfusing the quiescent turtle heart with isotonic solns. Pressure-flow curves were detd. for a) the flaccid state resembling diastole (perfusion with NaCl) and b) the contracted state, resembling systole (perfusion with KC1, CaCl2 and BaCl2). Resistance was lowest in the flaccid, relaxed heart. The pressure-flow relationship was almost linear and avg. P/Q was 0.9 mm. saline/ml./min. With con-tracture (perfusion with CaCl2 and BaCl2) a yield pressure appeared and plasticity of the cardiac muscle modified the pressure-flow curves. Reversible quiescence of the heart, produced by adding barbiturate to the perfusion fluid, demonstrated the degree to which the muscular activity of the beating heart concealed the heart's internal resistance to flow. The work required to overcome the internal resistance of the turtle heart has been compared to the external pressure-volume work. The former ranged from 2-18% of the latter depending upon cardiac output and arterial pressure. A similar comparison with "useful work" yielded percentages of 3-47.


PMID: 14933608

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