Mild hypothermia induces incomplete left ventricular relaxation despite spontaneous bradycardia in pigs
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Mild hypothermia induces incomplete left ventricular relaxation despite spontaneous bradycardia in pigs. / Schwarzl, M; Alogna, A; Zirngast, B; Steendijk, P; Verderber, J; Zweiker, D; Huber, S; Maechler, H; Pieske, B M; Post, H.
In: ACTA PHYSIOL, Vol. 213, No. 3, 03.2015, p. 653-663.Research output: SCORING: Contribution to journal › SCORING: Journal article › Research › peer-review
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TY - JOUR
T1 - Mild hypothermia induces incomplete left ventricular relaxation despite spontaneous bradycardia in pigs
AU - Schwarzl, M
AU - Alogna, A
AU - Zirngast, B
AU - Steendijk, P
AU - Verderber, J
AU - Zweiker, D
AU - Huber, S
AU - Maechler, H
AU - Pieske, B M
AU - Post, H
N1 - © 2014 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.
PY - 2015/3
Y1 - 2015/3
N2 - 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 < 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.
AB - 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 < 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.
KW - Animals
KW - Bradycardia/diagnosis
KW - Cardiac Pacing, Artificial
KW - Diastole
KW - Heart Rate
KW - Hypothermia, Induced/adverse effects
KW - Stroke Volume
KW - Swine
KW - Time Factors
KW - Ventricular Dysfunction, Left/diagnosis
KW - Ventricular Function, Left
KW - Ventricular Pressure
U2 - 10.1111/apha.12439
DO - 10.1111/apha.12439
M3 - SCORING: Journal article
C2 - 25515791
VL - 213
SP - 653
EP - 663
JO - ACTA PHYSIOL
JF - ACTA PHYSIOL
SN - 1748-1708
IS - 3
ER -
