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Mild hypothermia induces incomplete left ventricular relaxation despite spontaneous bradycardia in pigs
Author(s) -
Schwarzl M.,
Alogna A.,
Zirngast B.,
Steendijk P.,
Verderber J.,
Zweiker D.,
Huber S.,
Maechler H.,
Pieske B. M.,
Post H.
Publication year - 2015
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/apha.12439
Subject(s) - medicine , cardiology , diastole , hypothermia , heart rate , bradycardia , diastolic function , anesthesia , blood pressure
Abstract 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 ( LVP ed), volume ( LVV ed) and pressure–volume relationships ( EDPVR s) were determined during stepwise right atrial pacing. LV capacitance (i.e. LVV ed at LVP ed of 10 mmHg, LV VP ed10) was derived from the EDPVR . Pacing‐induced changes of diastolic indices ( LVP ed, LVV ed and LV VP ed10) 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 ( τ L ) and monoexponential fit with zero asymptote ( τ Z ) and nonzero asymptote ( τ NZ ). Results Mild hypothermia decreased heart rate (85 ± 4 to 68 ± 3 bpm), increased τ L (22 ± 1 to 57 ± 4 ms), τ Z (26 ± 2 to 56 ± 5 ms) and τ NZ (41 ± 1 to 96 ± 5 ms), decreased t‐dia/ τ ratios, and shifted the EDPVR leftwards compared to NT (all P < 0.05). During NT , pacing at ≥140 bpm shifted the EDPVR progressively leftwards. During MH , relationships between diastolic indices and heart rate were shifted towards lower heart rates compared to NT . However, relationships between diastolic indices and t‐dia/ τ during NT and MH were superimposable. Conclusion We conclude that the loss of LV end‐diastolic capacitance during MH can be explained at least in part by slowed LV relaxation. MH thereby is an example of incomplete LV relaxation at a spontaneous low heart rate. Caution may be advised, when heart rate is increased in patients treated with MH .