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First published online June 29, 2006
Journal of Experimental Biology 209, 2628-2636 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02278
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Evidence for a respiratory component, similar to mammalian respiratory sinus arrhythmia, in the heart rate variability signal from the rattlesnake, Crotalus durissus terrificus

Hamish A. Campbell1,2,*, Cleo A. C. Leite1,3, Tobias Wang1,4, Marianne Skals1,4, Augusto S. Abe1, Stuart Egginton2, F. Tadeu Rantin3, Charles M. Bishop5 and Edwin W. Taylor1,2

1 UNESP, Rio Claro, SP, Brazil
2 Department of Physiology, University of Birmingham, Birmingham, UK
3 Universidade Federal, Sao Carlos, SP, Brazil
4 Aarhus University, Denmark
5 University of Wales, Bangor, UK


Figure 1
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  		Fig. 1. Mean fH (black) calculated per minute from recordings of heart beat interval, from an unrestrained conscious C. durissus using an externally mounted miniature datalogging device. Recordings were made continually for 110 h. Environmental temperature (red) was recorded each minute by the same electronic device. Downward spikes on the fH trace indicate each hourly cycle of recording.

 

Figure 2
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  		Fig. 2. Power spectra generated from heart beat interval data obtained from four rattlesnakes fitted with external miniature dataloggers, recorded for 110 h. For power spectral analysis ten individual data sets consisting of 512 consecutive RR intervals were chosen from each animal within each of the fH categories. The resultant power spectra within 0.001 Hz frequency bins were pooled to produce the plots. The standard error for the pooled data is not shown on the graph as it would mask components, but is instead expressed as more meaningful total powers for either low or high frequency components (see Table 2).

 

Figure 3
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  		Fig. 3. Simultaneous recordings of instantaneous ECG (black) and ventilation, recorded as intra-peritoneal pressure (red; the upward spike indicates lung expiration). The interval tachogram (blue) describes the change in timing between heart beats (nominal scale), and shows that the heart beat is increased during lung inflation. The recordings were made from unrestrained, conscious animals, and unknown factors other than ventilation will also be affecting the timing of each heart beat. Confirmation that an oscillatory component exists in heart rate that is in phase with the ventilation cycle was made using power spectral analysis on a more extensive data set (512 heart beat intervals). The results are shown in Fig. 4.

 

Figure 4
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  		Fig. 4. Relative heart rate variability (HRV) parameters in a rattlesnake, carrying ECG electrodes and a peritoneal cannula (a short section of the raw data shown in Fig. 3), during rest (A), after treatment with propranalol (B) and atropine (C). Ai-Ci, heart beat interval tachogram; Aii-Cii, heart beat intervals as a probability distribution histogram; Aiiii-Ciii, power spectrum calculated by applying power spectral analysis to the heart beat tachogram in Ai-Ci.

 

Figure 5
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  		Fig. 5. Numbers of cell bodies of vagal preganglionic neurones (VPN) plotted against their rostrocaudal distribution around obex. The black area (VPNv) denotes the distribution of the major group of VPN located in the ventral area of the dorsal vagal motor nucleus (DVN), the green area (VPNd) denotes a smaller group of cells in the dorsal DVN and the red areas (VPNl) denote the scattered distribution of VPN ventrolaterally, outside the DVN (see Fig. 6).

 

Figure 6
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  		Fig. 6. (A) Transverse section (TS) of brainstem (40 µm) 0.12 mm caudal of obex to show fluorescing cell bodies of vagal preganglionic neurones (VPN) stained with True Blue. There are two cell groups separated by an area of clear of cells. (B) TS brainstem (40 µm) 1.08 mm caudal of obex showing fluorescing cell bodies in the medial dorsal vagal motor nucleus (DVN) and in a widely separated ventrolateral position. (D cells are cell bodies of VPN located in the DVN, D1 is the major ventral group, D2 is the smaller dorsal group; VL cells are VPN in scattered locations outside of the DVN; S is the surface of the brain; V is the fourth ventricle.)

 




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