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Negin Nadvar ACF Abstract FY10

Compared to In Vivo, Isolated Hearts Respond Differently to Acetylcholine after Reperfusion Injury

Conference Name: Biomedical Engineering Society 2009 (BMES)

We examined changes in power spectral density (PSD) of atrial (AA) and ventricular (VV) tachograms (interbeat interval vs. beat number) in guinea pig isolated hearts to quantify the myogenic component of heart rate variability (HRV) unrelated to autonomic tone. Three groups (n=6 each) of guinea pig hearts were perfused at a constant pressure of 55 mmHg with 37oC Kreb’s-Ringers (KR) solution. After baseline (BL) stabilization, hearts were perfused continuously either with KR (CON), KR+ 1 μM atropine (ATR; cholinergic blocker), or KR + 5 μM esmolol (ESM; adrenergic blocker) for 30 min followed by 30 min global ischemia and 120 min reperfusion (REP). Bipolar electrograms were recorded from the right atrium and ventricle for 4 min at BL, 20 min after KR, ATR, or ESM perfusion, and after 0 min (REP00), 60 min (REP60), and 120 min (REP120) of reperfusion. From the resulting AA and VV tachograms, we computed a) total power (TP, 0.04-0.4 Hz), b) power in low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-0.4 Hz) bands normalized to TP (pLF and pHF in ms2/Hz), and c) pLF/pHF. Results showed: i) AA and VV TP increased at REP00 in all groups and stayed elevated at REP60 and REP120 in ATR, ii) VV pLF increased and pHF decreased at REP00, REP60 in all groups , iii) VV pLF/pHF ratio increased at all REP in all groups. Hence, results from CON and ATR, but not ESM, agree with in vivo results suggesting that after ischemia i) denervated hearts exhibit attenuated parasympathetic vs. sympathetic response to residual neurotransmitters and ii) the changes in PSD may be myogenic.

Negin Nadvar1, David F Stowe2, Amadou KS Camara2, James Heisner2, Samhita Rhodes1,2 

1School of Engineering, Grand Valley State University, Grand Rapids, MI 

2Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI