title: Ultrasound-induced heart rate decrease: role of the vagus nerve.
abstract: The goal of this study is to investigate the role of the vagus nerve (VN) in the ultrasound (US)-induced negative chronotropic effect (deceased heart rate). One of the functions of the VN is to mediate lowering of the heart rate. A previous study showed a decrease of ~20% in the heart rate but the mechanism of the effect was not investigated. Sprague Dawley rats (n = 20) were exposed transthoracically to ultrasonic pulses at an approximate duty factor of 1% with sequentially 2.0, 2.5, and 3.0 MPa peak rarefactional pressure amplitudes (PRPAs). The ultrasonic exposure parameters herein were chosen to match those of the previous study to have confidence that an ultrasound-induced negative chronotropic effect would occur. For each of the three PRPA sequences, the pulse repetition frequency (PRF) started slightly greater than the rat's heart rate and then was decreased sequentially in 1-Hz steps every 10 s (i.e., 6, 5, and 4 Hz for a total duration of 30 s). The experiments were organized in a standard (2 × 2) factorial design with VN (cut versus intact) as one factor and US (on versus off) as another factor. VN (intact/cut) and US (on/off) groups were divided into four groups each consisting of 5 animals: 1) VN intact-US off, 2) VN intact-US on, 3) VN cut-US off, and 4) VN cut-US on. Two-way analysis of variance for repeated measures was used to compare heart rate, cardiac output, systolic volume, ejection fraction, end-diastolic volume, end-systolic volume, respiratory rate, and arterial pressure before and after ultrasound stimulation. In this study, the heart rate decreased ~4% for the non-vagotomy and vagotomy groups. The ultrasound effect was significant for heart rate (p = 0.02) and cardiac output (p = 0.005) at 3 min post US exposure; the vagotomy effect was not significant. For heart rate, the Bonferroni test showed no differences between the four groups. The vagotomy group showed similar ultrasound-induced cardiac effects compared with the non-vagotomy group, suggesting that the vagus nerve is not influenced by the ultrasound exposure procedures. The US application caused a negative chronotropic effect of the rat heart without affecting the hemodynamic conditions. The results at this point are suggestive for an alternative cardiac pacing capability.
authors: Olivia
authors: O
authors: Coiado
authors: Elaine
authors: E
authors: Buiochi
authors: William
authors: W
authors: O'Brien
mesh_terms: D000818:Animals; D005260:Female; D006339:Heart Rate / Q000528:radiation effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013016:Sound / Q000009:adverse effects; D014463:Ultrasonography; D014630:Vagus Nerve / Q000000981:diagnostic imaging* / Q000502:physiology* / Q000601:surgery
references: Resuscitation. 1981 Sep;9(3):233-42
references: 7291734
references: Ultrasound Med Biol. 1997;23(5):761-5
references: 9253824
references: Can J Physiol Pharmacol. 1980 Sep;58(9):1126-7
references: 7459704
references: J Acoust Soc Am. 2006 Nov;120(5 Pt 1):2958-64
references: 17139752
references: Ultrasound Med Biol. 1993;19(5):391-8
references: 8356783
references: Bull Exp Biol Med. 2002 Jan;133(1):9-11
references: 12170293
references: J Am Coll Cardiol. 1983 Jan;1(1):90-102
references: 6826948
references: Ultrasound Med Biol. 2011 Feb;37(2):177-83
references: 21257086
references: IEEE Trans Biomed Eng. 2006 Jul;53(7):1446-8
references: 16830952
references: Ann N Y Acad Sci. 1995 Mar 27;752:331-42
references: 7755278
references: Heart Rhythm. 2006 Oct;3(10):1202-6
references: 17018352
references: Cardiovasc Res. 1998 Jul;39(1):60-76
references: 9764190
references: J Pharmacol Methods. 1985 Jul;13(4):325-30
references: 4021499
references: Circ J. 2006 Oct;70(10):1356-61
references: 16998272
references: Circ Heart Fail. 2009 Mar;2(2):138-44
references: 19808329
references: Biull Eksp Biol Med. 1991 May;111(5):451-3
references: 1878551
references: Ann N Y Acad Sci. 2001 Jun;940:48-58
references: 11458703
references: J Ultrasound Med. 2009 Feb;28(2):139-50
references: 19168764
references: Br J Cancer Suppl. 1982 Mar;5:151-5
references: 6950751
references: Acta Physiol Scand. 1957 Nov 26;41(1):68-76
references: 13497759
references: J Biomed Biotechnol. 2011;2011:497841
references: 21403831
references: IEEE Trans Ultrason Ferroelectr Freq Control. 2012 Dec;59(12):2655-61
references: 23221214
references: J Acoust Soc Am. 2014 Sep;136(3):EL231
references: 25190426
references: Bull Exp Biol Med. 2000 Jul;130(7):620-3
references: 11140567
references: J Surg Res. 2008 Jan;144(1):124-6
references: 17560609
references: Pacing Clin Electrophysiol. 2010 Feb;33(2):209-16
references: 19889182
references: Pacing Clin Electrophysiol. 2006 Aug;29(8):917-20
references: 16923012
references: J Am Coll Cardiol. 2007 Aug 28;50(9):877-83
references: 17719475
references: J Cardiovasc Electrophysiol. 2009 Dec;20(12):1413-5
references: 19656249
references: Ultrasound Med Biol. 1993;19(5):385-90
references: 8356782