Parasympathetic cardiovascular control in human disease: a critical review of methods and results

Abstract

A variety of experimental approaches have been used to alter reflex parasympathetic cardiovascular control in normal human subjects and in patients with cardiovascular diseases. This review critically appraises several of these methods (the Valsalva maneuver, upright tilt, lower body negative pressure, pressor drug infusion, neck suction, and coronary arteriography) and summarizes the normal response patterns of healthy subjects and the abnormal response patterns of some patients with cardiovascular disease. Tests of parasympathetic function tend to be heterogeneous; they are not standardized, and, therefore, valid comparisons between results from different studies may be difficult to make. Moreover, although most of these tests are simple to perform, they may provoke surprisingly complex alterations of afferent and efferent autonomic activity. Notwithstanding these methodological difficulties, the research area of human parasympathetic cardiovascular control may have great importance, because parasympathetic reflex mechanisms are involved in diseases of major public health significance for which animal models may be imperfect or nonexistent.

Impaired autonomic control of heart interval changes to Valsalva manoeuvre in Chagas' disease without overt manifestation

“…The Valsalva manoeuvre is one of the most widely used and informative procedures for the study of the autonomic nervous system modulation on the sinus node activity (Ewing, 1978;Eckberg, 1980;Espi et al, 1986;Nishimura and Tajik, 1986). The heart rate responses to the Valsalva manoeuvre are the result of reflex mechanisms predominantly baroreceptor in origin, which involve the parasympathetic autonomic nervous system with doubtful Fig.…”

“…The chagasic and control groups were compared by the t-test or Mann -Whitney test according to the normality or not of the variables distribution. involvement of the sympathetic one (Ewing, 1978;Eckberg, 1980). It has been claimed that the bradycardia following the manoeuvre is entirely parasympathetic.…”

“…It has been claimed that the bradycardia following the manoeuvre is entirely parasympathetic. The mechanism of the tachycardia during the manoeuvre remains controversial, some workers suggesting exclusive enhancement of sympathetic activity and others suggesting depression of parasympathetic outflow; also, both parasympathetic withdrawal and increased sympathetic outflow have been suggested (Bennett et al, 1976;Eckberg, 1980). The quantification of heart interval variations during the Valsalva manoeuvre has been used as a sensitive and very simple method for characterizing cardiac parasympathetic activity in healthy subjects and in patients with diabetes (Bennett et al, 1976;Baldwa and Ewing, 1977;Ewing, 1978;Kruter et al, 1982;Ewing et al, 1985), coronary heart disease (Tristani et al, 1977), hypertension (Trimarco et al, 1983), and renal failure (Ewing and Winney, 1975) which showed reduced variations in the R -R interval as a result of cardiac autonomic dysfunction, as presently observed in chagasic subjects.…”

“…A critical concern is the comparability of the Valsalva manoeuvre procedure in different groups of individuals, since the R-R interval changes are not quantified in relation to the documented blood pressure alterations. According to Eckberg (1980), difficulties can arise in interpreting R -R interval or heart rate responses in the Valsalva manoeuvre when some elementary conditions of equality of the procedure are not met for comparison with control subjects. In this respect, we can state that the stimuli associated with the manoeuvres performed were comparable in both groups studied, that is, the depth of inspiration before straining, the intensity and duration of straining, and the magnitude of the intra-oral pressure were all well controlled.…”

“…Initially, each individual was instructed in the Valsalva manoeuvre and practiced it sometimes for training. In sequence, after sufficient time of resting, three to four spaced valid manoeuvres were done for each subject in the rest supine position by blowing with the closed glottis into the mouthpiece-tubing connected to an aneroid manometer in order to maintain a constant expiratory intra-oral pressure of 40 mm Hg for 20 s according to standardized previous protocol (Manc ßo et al, 1969;Eckberg, 1980;Junqueira, 1990;Marin-Neto et al, 1998). The Valsalva manoeuvre comprises four phases of baroreflex heart interval changes to arterial pressure modifications: (1) rapid inspiration and onset of the expiratory straining with a variably present evanescent bradycardia associated to a transient systolic arterial pressure rise (phase I); (2) maintenance of the straining with an incremental relative tachycardia secondary to a progressive arterial pressure decrease (phase II); (3) release of straining with progression of the tachycardia to the maximum following an additional sudden dip in arterial pressure (phase III); (4) post-straining cessation of the tachycardia in variable time and onset of the progressive relative bradycardia in response to the rapid arterial pressure overshooting, which lasts several seconds until the complete recovery to the basal level (phase IV).…”