Mild hypothermia induces incomplete left ventricular relaxation despite spontaneous bradycardia in pigs

Aim Mild hypothermia (MH) decreases left ventricular (LV) end-diastolic capacitance. We sought to clarify whether this results from incomplete relaxation. Methods Ten anaesthetized pigs were cooled from normothermia (NT, 38 °C) to MH (33 °C). LV end-diastolic pressure (LVPed), volume (LVVed) and pressure–volume relationships (EDPVRs) were determined during stepwise right atrial pacing. LV capacitance (i.e. LVVed at LVPed of 10 mmHg, LV VPed10) was derived from the EDPVR. Pacing-induced changes of diastolic indices (LVPed, LVVed and LV VPed10) were analysed as a function of (i) heart rate and (ii) the ratio between diastolic time interval (t-dia) and LV isovolumic relaxation constant τ, which was calculated using a logistic fit (τL) and monoexponential fit with zero asymptote (τZ) and nonzero asymptote (τNZ). Results Mild hypothermia decreased heart rate (85 ± 4 to 68 ± 3 bpm), increased τL (22 ± 1 to 57 ± 4 ms), τZ (26 ± 2 to 56 ± 5 ms) and τNZ (41 ± 1 to 96 ± 5 ms), decreased t-dia/τ ratios, and shifted the EDPVR leftwards compared to NT (all P