Vestibulo-sympathetic reflex in patients with bilateral vestibular loss

This study assessed cardiovascular control during head-down neck flexion (HDNF) in a group of patients suffering from total bilateral idiopathic vestibular loss (BVL) for 7 ± 2 yr. Nine adult patients (age 54 ± 6 yr) with BVL were recruited. Calf blood flow (CBF), mean arterial pressure (MAP), and heart rate (HR) were measured with subjects’ eyes closed in two lying body positions: ventral prone (VP) and lateral (LP) on the left side. Vascular resistance (CVR) was calculated as MAP/CBF. The HDNF protocol consisted in passively changing the head position: head up (HU)–head down (HD)–HU. Measurements were taken twice at each head position. In VP CBF significantly decreased in HD (3.65 ± 0.65 mL·min−1·100 mL−1) vs. HU (4.64 ± 0.71 mL·min−1·100 mL−1) ( P < 0.002), whereas CVR in VP significantly rose in HD (31.87 ± 6.93 arbitrary units) vs. HU (25.61 ± 6.36 arbitrary units) ( P < 0.01). In LP no change in CBF or CVR was found between the two head positions. MAP and HR presented no difference between HU and HD in both body positions. Age of patients did not significantly affect the results. The decrease in CBF of the BVL patients was similar to the decrease observed with the same HDNF protocol in normal subjects. This suggests a sensory compensation for the lost vestibular inputs that could originate from the integration of inputs from trunk graviceptors and proprioceptive and cutaneous receptors. Another possibility is that the HDNF vascular effect is evoked mostly by nonlabyrinthine sensors. NEW & NOTEWORTHY The so-called vestibulo-sympathetic reflex, as demonstrated by the head-down neck flexion (HDNF) protocol, is present in patients with total bilateral vestibular idiopathic loss, equally in young and old subjects. The origin of the sympathetic effect of HDNF is questioned. Moreover, the physiological significance of the vestibulo-sympathetic reflex remains obscure, because it acts in opposition to the orthostatic baroreflex. It may serve to inhibit the excessively powerful baroreflex.

The role of vegetovascular malfunction in primary dysmenorrhea pathogenesis

Peculiarities of vegetovascular malfunction at functional dysmenorrhea has been investigated. 107 women with dysmenorrhea and 10 healthy women have been examined. Methods of pelvis minor organ rheography, rheoencephalography and cardiointervalography have been used. It has been revealed that at women with dysmenohhrea a disorganization of pelvis minor regional circulation developed during the first phase of menstrual cycle. It was evident in simultaneous decrease of cerebral vessel blood filling and increase of venous drainage, development of microcirculation disturbances. Simultaneously the enhancement of sympathetic effect and decrease of the effect degree of parasympathetic nervous system have been observed. On the contrary, at healthy women it is observed the enhancement of parasympathetic effect and the hemodynamic factors remain fixed.The obtained results are evidence that at women with dysmenorrhea the marked vegetovascular disturbances connected with sympathetic tone prevalence and being evident mainly at cerebral hemodymanics level take place in the first days of menstrual cycle. The nature of revealed disturbances is connected with the peculiarities of disease clinics.

Interaction of brief sympathetic stimuli and heart period on atrial contractile force

We studied the dynamic interaction between the independent effects of sympathetic stimuli and heart period on atrial contractile force with three experiments: 1) we measured the inotropic response to brief sympathetic stimuli when the heart was paced; this represented the pure sympathetic effect on contractile force. 2) We measured the responses to identical stimuli when the heart was not paced; this represented the effect of the combined influences. 3) We measured the contractile responses to the identical sequences of changing cycle lengths that were recorded (expt 2) but in the absence of sympathetic activity; this represented the pure effect of changing cardiac cycle length on contractile force. We subtracted the paced from the unpaced responses. This difference represented the linear elimination of the pure sympathetic effect from the combined responses. We then compared this difference with the responses to changing cycle lengths that were measured in the absence of sympathetic activity (expt 3). The values were not equal from 2.5 through 22.5 s after the stimulus of experiment 1 of the protocol above. We performed a similar comparison after expressing the results in the frequency domain. The values were significantly different for most of the frequency spectrum where the greatest power was concentrated. We therefore conclude that there is a significant interaction between the effects of sympathetic activity and changing heart periods, and this interaction determines the resultant inotropic state on any specific beat.

The effect of isoproterenol on isolated muskrat and guinea pig hearts

Isoproterenol, a β-adrenergic agonist, was given by bolus injection to Langendorff-perfused muskrat and guinea pig hearts. Bolus content ranged from 18 to 29 200 pmol. The hearts responded by increasing left ventricular pressure, heart rate, and release of lactate. The drug threshold was similar for the hearts of the two species but the magnitude of the response differed both at threshold and at saturation doses. The increase in left ventricular pressure and heart rate was greater in guinea pig hearts compared with muskrat hearts. Lactate release was stimulated earlier and increased more in muskrat hearts compared with guinea pig hearts. The weak β-adrenergic stimulation of heart rate and left ventricular pressure in the muskrat may be of benefit when the animal dives to escape a potential predator. Under these conditions of fear, exercise, hypoxia, and diving there would be opposing effects of sympathetic versus vagal stimulation of the myocardium. The sympathetic effect would be to increase myocardial oxygen consumption while the vagal effect would be to reduce it. In the diving mammal the vagal effect predominates and this may be augmented by a blunted rate and pressure response to β-stimulation.

Autonomic modulation of refractoriness in canine specialized His-Purkinje system

The effects of autonomic efferent stimulation on refractoriness of the specialized His-Purkinje system were examined in open-chest dogs anesthetized with 1.0% halothane. In eight animals submaximal bilateral stimulation of the ventral ansae subclavia decreased (P less than or equal to 0.01) the average functional refractory period for the propagation of His bundle extrastimuli to five ventricular recording sites (HP-FRP) by 10.9 +/- 0.6 ms. Submaximal stimulation of the decentralized vagal nerves that produced first degree atrioventricular block did not affect ventricular refractoriness. Combined vagosympathetic stimulation produced a smaller (P less than or equal to 0.01) decrease of the average HP-FRP (7.2 +/- 1.1 ms) than that produced by sympathetic stimulation alone. Administration of atropine abolished (P less than or equal to 0.05) vagal antagonism of the shortening effect of isoproterenol on the average HP-FRP. Treatment with propranolol reversed (P less than or equal to 0.01) the sympathetic effect on the average HP-FRP and nonuniformly increased refractoriness in the His-Purkinje system. The latter changes were abolished (P less than or equal to 0.05) by infusion of phentolamine. The autonomic nervous system modulates His-Purkinje refractoriness by actions mediated by cholinergic and both alpha- and beta-adrenergic receptors.