Ventilatory effects of stimulation of phrenic afferents

The diaphragm, a ventilatory muscle, has abundant sensory innervation. The effects of phrenic afferent activation on ventilation have been varied. In this study the proximal end of the phrenic nerve was electrically stimulated, and the effects on ventilation were measured in supine dogs anesthetized with either alpha-chloralose or pentobarbital sodium. We found a maximum increase in ventilation of 45 +/- 4% in the alpha-chloralose group and an increase in mean arterial blood pressure of 18 +/- 4%. This response was obtained at high stimulus intensities (60 times twitch threshold). Stimulation of the proximal end of the gastrocnemius nerve produced a similar ventilatory response (61 +/- 10%) but at lower stimulus intensities. During pentobarbital sodium anesthesia both the hyperventilation and the pressor response were produced; however, ventilation was increased by an increase in respiratory frequency. The reflex was abolished by sectioning of the cervical dorsal roots (C4-C7). Proximal cold blockade of the nerve abolished the response at a perineural temperature of 1.35 +/- 0.64 degrees C. The main effect of activation of phrenic afferents was an increase in ventilation and blood pressure that was mediated by unmyelinated fibers and possibly thin myelinated fibers. This response is similar to skeletal muscle afferent activation and may play a role in ventilatory drive during such conditions as exercise and respiratory muscle fatigue.     

Ventilatory compensation for lactacidosis in ponies: role of carotid chemoreceptors and lung afferents

We investigated changes in arterial PCO2 (PaCO2) and pulmonary ventilation (VE) in normal, carotid chemoreceptor-denervated, and hilar nerve-denervated ponies during intravenous lactic acid infusion at rest and treadmill exercise at 1.8 mph-5% grade (mild) and 1.8 mph-15% grade (moderate). Lactic acid, (0.5 M) infusion of 0.10, 0.13, and 0.20 ml.min-1.kg-1 at rest and mild and moderate exercise increased arterial [H+] linearly throughout the 10 min of acid infusion. At 10 min of infusion, arterial [H+] had increased approximately 20 nmol/l (0.2 pH units) for each condition and group. Under most conditions, the temporal pattern of PaCO2 during acid infusion was biphasic. At rest and during mild exercise in all groups, and in carotid chemoreceptor-denervated ponies during moderate exercise, PaCO2 increased approximately 2 Torr (P less than 0.05) during the first 2 min of acid infusion. However, in normal ponies during moderate exercise, PaCO2 was not changed from control in the first 2 min of infusion. Between 2 and 10 min of infusion at rest and mild and moderate exercise in all groups, there was a 5-Torr significant decrease in PaCO2, which did not differ (P greater than 0.10) between groups. VE increased between 15-30 s and 2 min of infusion, but VE changed minimally between 2 and 10 min of infusion at rest and exercise in all groups of ponies. We conclude that lactacidosis does increase VE at rest and submaximal exercise in the pony.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation of respiratory responses to carotid sinus nerve stimulation by brain hypoxia.

This study examines the effect of progressive isocapnic CO hypoxemia on respiratory afterdischarge and the phrenic neurogram response to supramaximal carotid sinus nerve (CSN) stimulation. Twelve anesthetized, vagotomized, peripherally chemodenervated, ventilated cats with blood pressure controlled were studied. During isocapnic hypoxemia, the amplitude of the phrenic neurogram was progressively depressed. In contrast, the increase in peak phrenic amplitude produced by CSN stimulation was unchanged, suggesting that the central respiratory response to CSN stimulation is unaffected by progressive hypoxemia. The time constant of respiratory afterdischarge (tau) was calculated from best-fit plots of phrenic amplitude vs. time after cessation of CSN stimulation. Under control conditions the value of tau was 57.7 +/- 3 (SE) s (n = 12). During progressive isocapnic hypoxemia, tau decreased as a linear function of arterial O2 content (CaO2) such that a 40% reduction of CaO2 resulted in a 48% reduction in tau. This reduction of respiratory afterdischarge may contribute to the genesis of periodic breathing during hypoxia.     

Limb vasodilation provoked by stimulation of the carotid sinus. Importance of histaminergy in the dog

The vasodilator reflex induced by baroreceptor stimulation was studied on the hindlimbs of the dog. The reflex was induced by norepinephrine (1 microgram/kg) either by intravenous injection or by direct injection into the carotid sinus. In other experiences, the baroreceptor stimulation was obtained by distension of the sinus by rapid injection of 100 ml of physiological serum. The vascular response was studied by recording the hindlimbs blood flow. One of the limbs was previously pretreated by mepyramine and cimetidine (blockage of histaminergic H1 and H2 receptors). During the first minute after the baroreceptor stimulation, blood samples were collected from the venous blood of hindlimbs for histamine assay (fluorometric assay). Our results show: a much lower vasodilation on the limb pretreated by histamine antagonist, a significant increase during the reflex vasodilation of histamine blood levels measured in the efferent blood of hindlimbs. These results, obtained in experimental conditions as physiological as possible (blood perfusion of the limbs with "natural" hemodynamic parameters) permit to conclude that the vasodilation induced by baroreceptor reflex is at least partially histaminergic in the dog.     

Anatomical and functional characteristics of carotid sinus stimulation in humans

Transmission characteristics of pneumatic pressure to the carotid sinus were evaluated in 19 subjects at rest and during exercise. Either a percutaneous fluid-filled (n = 12) or balloon-tipped catheter (n = 7) was placed at the carotid bifurcation to record internal transmission of external neck pressure/neck suction (NP/NS). Sustained, 5-s pulses, and rapid ramping pulse protocols (+40 to -80 Torr) were recorded. Transmission of pressure stimuli was less with the fluid-filled catheter compared with that of the balloon-tipped catheter (65% vs. 82% negative pressure, 83% vs. 89% positive pressure; P < 0.05). Anatomical location of the carotid sinus averaged 3.2 cm (left) and 3.6 cm (right) from the gonion of the mandible with a range of 0-7.5 cm. Transmission was not altered by exercise or Valsalva maneuver, but did vary depending on the position of the carotid sinus locus beneath the sealed chamber. These data indicate that transmission of external NP/NS was higher than previously recorded in humans, and anatomical variation of carotid sinus location and equipment design can affect transmission results.     

Vasoconstriction of the isolated communicating cerebral artery induced by field electrical stimulation

The vasoconstrictor effect elicited by field electrical stimulation of the posterior communicating cerebral artery of the goat was analyzed before and after treatment with pharmacological agents to find out if the adrenergic system was involved in this response. For this purpose, trains of 300 square wave pulses (1-32 Hz, 0.5 msec.) at supramaximal voltage were applies to these arteries producing a frequency-dependent increase in tension. The vasoconstrictor response was significantly reduced by tetrodotoxin (3 x 10(-6) M), phentolamine (10(-6) M) and bretylium (5 x 10(-4) M), but it was not modified by cocaine (10(-6) M). The contraction produced by electrical stimulation of arterial segments from goats pretreated with reserpine (0.02 mg/kg/day for three days) and from goats on which a bilateral superior cervical gangliectomy had been performed 12 days previously, was significantly reduced as compared with controls. These results show that a large part of the vasoconstrictor response of the goat cerebral vessels to field electrical stimulation is mediated by an adrenergic mechanism.     

离体颈动脉窦压力感受器研究方法的改进——窦内压的自动控制

目的:创建一套离体颈动脉窦压力感受器研究中窦内压力的自动控制系统。方法:制备颈动脉窦-窦神经标本并对其进行灌流。在该系统中,引入一个重要的可接受电脑指令的压力控制装置(PRE-U,Hoerbiger,Deutschland),用以钳制窦内压。通过比较压力指令和相应产生的窦内压来鉴定本压力控制系统的可靠性。结果:利用该系统可以准确实现脉动式、斜坡式、阶跃式等多种窦内压力控制模式,并证实记录到压力依赖性窦神经放电活动。结论:应用这套颈动脉窦内压力控制系统可以实现多种压力模式的控制。该系统为深入研究压力感受器机电换能机制提供了有用且灵活的压力控制方法。     

The inhibition of efferent sympathetic activity by means of pressure stimulation of the carotid sinus pressoreceptors]

The influence of pressure stimulation of a barorecptor upon the activity of the sympathetic nerve branch terminating in the wall of the contralateral carotid bifurcation was studied on narcotized dogs. The potential activity of this branch is of efferent nature. On the average, 570 msec after the pressure load applied to the opposite carotid sinus preparation, a silent period occurred. The duration of this silent period and the activity of the sympathetic nerve branch depend on the internal pressure of the preparation. The influence of different structures (central and peripheral) on latency, total and partial inhibition of the sympathetic activity are discussed.