Sympatho Vagal

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PowerSpectralAnalysisofHeartRateand

ArterialPressureVariabilitiesasaMarkerof

Sympatho-VagalInteractioninManandConsciousDog

n57normalsubjects(age20-60years),weanalyzedthespontaneousbeat-to-beatoscillationinR-R
intervalduringcontrolrecumbentposition,90°uprighttilt,controlledrespiration(n=16)andacute
(n=10)andchronic(n=12)/3-adrenergicreceptorblockade.Automaticcomputeranalysispro-
videdtheautoregressivepowerspectraldensity,aswellasthenumberandrelativepowerofthe
individualcomponents.ThepowerspectraldensityofR-Rintervalvariabilitycontainedtwomajor
componentsinpower,ahighfrequencyat-0.25Hzandalowfrequencyat~0.1Hz,witha
normalizedlowfrequency:highfrequencyratioof3.6±0.7.Withtilt,thelow-frequencycomponent
becamelargelypredominant(90±1%)withalowfrequency:highfrequencyratioof21±4.Acute/3-
adrenergicreceptorblockade(0.2mg/kgIVpropranolol)increasedvarianceatrestandmarkedly
bluntedtheincreaseinlowfrequencyandlowfrequency:highfrequencyratioinducedbytilt.
Chronic/3-adrenergicreceptorblockade(0.6mg/kgp.o.propranolol,t.i.d.),inaddition,reducedlow
frequencyandincreasedhighfrequencyatrest,whilelimitingthelowfrequency:highfrequencyratio
increaseproducedbytilt.Controlledrespirationproducedatrestamarkedincreaseinthehigh-
frequencycomponent,withareductionofthelow-frequencycomponentandofthelowfrequency:
highfrequencyratio(0.7±0.1);duringtilt,theincreaseinthelowfrequency:highfrequencyratio
(8.3±1.6)wassignificantlysmaller.Insevenadditionalsubjectsinwhomdirecthigh-fidelityarterial
pressurewasrecorded,simultaneousR-Rintervalandarterialpressurevariabilitieswereexamined
atrestandduringtilt.Also,thepowerspectraldensityofarterialpressurevariabilitycontainedtwo
majorcomponents,witharelativelowfrequency:highfrequencyratioatrestof2.8±0.7,which
became17±5withtilt.Thesepowerspectraldensitycomponentswerenumericallysimilartothose
observedinR-Rvariability.Thus,invasiveandnoninvasivestudiesprovidedsimilarresults.More
directinformationontheroleofcardiacsympatheticnervesonR-Randarterialpressurevariabilities
wasderivedfromagroupofexperimentsinconsciousdogsbeforeandafterbilateralstellectomy.
Undercontrolconditions,highfrequencywaspredominantandlowfrequencywasverysmallor
absent,owingtoapredominantvagaltone.Duringa9%decreaseinarterialpressureobtainedwith
IVnitroglycerin,therewasamarkedincreaseinlowfrequency,asaresultofreflexsympathetic
activation.Bilateralstellectomypreventedthislow-frequencyincreaseinR-Rbutnotinarterial
pressureautospectra,indicatingthatsympatheticnervestotheheartareinstrumentalinthegenesisof
low-frequencyoscillationsinR-Rinterval.

T
hasprovedthatrhythmscanoftenbemarkers
ofnormalfunctionalstatessuchaswakeful-
nessorsleep,orofabnormalstatessuchasepilepsy.In
thepresentcontext,thegeneralhypothesisisthat
rhythmicalbeat-to-beatoscillationsofonecardiovas-
cularcontrolledvariablemightprovidesomecriteriato
interpretthecomplexinterplayamongtheneuralregu-
latoryoutflows.Ontheotherhand,theexistence,un-
derstableconditions,ofrhythmicfluctuationsincar-
FromtheIstitutoRicercheCardiovascolari,CNR;PatologiaMe-
dica.Centre"Fidia,"Ospedale"L.Sacco,"UniversityMilano;
CentraTeoriaSistemi.CNR,DipartimentoElettronica,Politecnico
Milano,Italy.
Addressforreprints:Dr.AlbertoMalliani,IstitutoRicercheCar-
diovascolari,ViaBonfadini214,20138Milano,Italy.
ReceivedAugust8.1985;acceptedApril7,1986.
pressurehasbeenrecognizedforalongtime.1"7In
recentyears,thepossibilityofquantifyingtheseoscil-
lationsbyusingcomputertechniques,particularlyon
thevariabilityofelectrocardiographicR-Rinterval,
hasarousedagrowinginterest.8"13
Indeed,asinstantaneousheartratedependsonthe
interactionbetweensympatheticandparasympathetic
efferentactivitiesandpacemakerproperties,ithas
beensuggestedthatthisanalysiscouldleadtoanonin-
vasiveassessmentofthe"tonic"autonomicregulation
ofheartfrequency.12Thenonrandomcomponentsof
R-Rvariabilityusuallyareassessedwithspectraltech-
niquesbasedonthefastFouriertransform,inspiteof
theconsiderationthattheheartratevariabilitysignalis
notstrictlyperiodical,asrequestedbythedeterminis-
ticnatureofthealgorithm.16