Vol. 86, Issue 2, 694-700, February 1999
Beat-to-beat modulation of heart rate is coupled to coronary
perfusion pressure in the isolated heart
David P.
Slovut1,3,
John C.
Wenstrom,
Richard B.
Moeckel2,
Christopher T.
Salerno3,
Soon J.
Park3, and
John W.
Osborn1
Departments of 1 Physiology and
2 Mathematics and
3 Division of Cardiovascular
and Thoracic Surgery, University of Minnesota, Minneapolis, Minnesota
55455
A goal of
clinicians caring for heart transplant recipients has been to use heart
rate variability as a noninvasive means of diagnosing graft
rejection. The determinants of beat-to-beat variability in
the surgically denervated heart have yet to be elucidated. We used an
isolated, blood buffer-perfused porcine heart preparation to
quantitatively assess the relationship between coronary perfusion and
sinus node automaticity. Hearts
(n = 9) were suspended in a
Langendorff preparation, and heart rate (HR) fluctuations were
quantified while perfusion pressure was modulated between 70/50, 80/60,
90/70, and 100/80 mmHg at 0.067 Hz. In 32 of 32 recordings, the cross
spectrum of perfusion pressure vs. HR showed the largest peak centered
at 0.067 Hz. In eight of nine experiments during nonpulsatile
perfusion, HR accelerated as perfusion pressure was increased from 40 to 110 mmHg (mean increase 24.2 ± 3.0 beats/min). HR increased 0.34 beats/min per mmHg increase in perfusion pressure (least squares linear
regression y = 
25.8 mmHg + 0.34x;
r = 0.88, P < 0.0001). Administration of low-
and high-dose nitroglycerin (Ntg) resulted in a modest increase in flow
but produced a significant decrease in HR and blunted the response of
HR to changes in perfusion pressure (HR increase 0.26 beats · min
1 · mmHg1,
r = 0.87, P < 0.0001 after low-dose Ntg; 0.25 beats · min1 · mmHg1,
r = 0.78, P < 0.0001 after high-dose Ntg).
These experiments suggest that sinus node discharge in the isolated
perfused heart is mechanically coupled to perfusion pressure on a
beat-to-beat basis.
heart rate variability; heart transplantation
