Interbeat interval variability in isolated working rat hearts at various dynamic conditions and temperatures

Abstract

This study quantifies the effect of afterload and preload changes and of temperature on interbeat interval variability of the intact isolated heart. Ventricular pressure pulse records were obtained from isolated working rat hearts. The variability of interbeat intervals (BIs) was quantified by C90, the central 90% range of the BIs during 10 min periods; predominant frequencies were searched for by power spectral analysis. At 37 degrees C the BI lengths oscillated pseudo-randomly with BI variability C90< or =4 ms. Alternating signs of consecutive BI differences were predominant, and no peaks. were seen in the power spectra. Changes in end-diastolic and aortic pressure had little effect. From 37 degrees C down to 27 degrees C the variability increased about sevenfold, run phase length became randomly distributed, and individual, time-variant peaks occurred in the power spectra. BI variability vanished during atrial pacing. We conclude that: (1) effective mutual synchronization with minimal fluctuation happens within the sino-atrial node of intact rat hearts at body temperature, and synchronization is not affected even by extreme changes in pre- and afterload, (2) the sino-atrial node is the sole source of BI variability in the intact isolated rat heart, (3) low temperature hampers this functional organization which can be reestablished by sinus node accelerating agents (isoprenaline, theophylline), (4) decreasing frequency by N6-Cyclopentyladenosine at normothermia also increases BI variability but less pronouncedly than hypothermia does.

Cold-impaired cardiac performance in rats is only partially overcome by cold acclimation

“…in hibernators. In vivo HRV in the rat is low and preserved despite cooling to a new set point (T b 25°C), with similar observations for isolated perfused hearts (T b 27°C) (Langer et al, 1999), suggesting this may be an intrinsic characteristic of the sinoatrial node rather than a physiological response to cooling. Supporting this contention, HRV following Langendorff perfusion was entirely derived from the sinoatrial node and extremes of preload or afterload were without effect on HRV for the perfused heart (data not shown), demonstrating that periodicity of sinoatrial node discharge was maintained at low temperatures.…”

Autocorrelation Patterns in the Left-Ventricular Pressure Course of Isolated Working Hearts at Sinus Rhythm

“…The similar distribution of microrhythmic patterns in the LVP of different species (with the particulars discussed about the guinea pig sample), and its long term persistence, argue for that fixed condition as enabling the specimens to express different types of microrhythms individually. Inspecting power spectra of individual peak r curves (and their derivatives) from the present material does not reveal consistent rhythms with periods above two BI lengths, according to previous negative findings in the spectra of BI length itself [17].…”

“…Variability of BI in LVP is not higher than in electrical RR intervals but even smaller if analysed at 10 kHz [17] (compare LVP with ECG in Fig. 1).…”

“…1). Spontaneous pulse generation in the sino-atrial node, and its further propagation, yield BI differing from each other by less than 1 ms (theoretically: Weibull distributed) at constant normothermia, whereas random oscillation (normal distribution in Poincaré plots [4,7] occurs at hypothermia [17]. Increasing resistance of the electrical intercell coupling [18] may explain for this effect, because BI variability of pacemaker cell clusters decreases as the number of (electrically) interconnected cells rises [2,3].…”

Autonome Funktionen beim Gesunden Autonome Steuerung von Herzkreislauf- und Lungenfunktion und deren Koordination

“…intrinsische kardiale regulatorische Mechanismen, wie an zentralnervös denervierten Herzen beobachtet, ist bei der Ratte [18] und an anderen Spezies nachgewiesen [17]. Die Mechanismen sind im Detail unbekannt, die neuroendokrine Eigenregulation des Herzens aber dafür am wahrscheinlichsten.…”