Noradrenaline suppression of the spinal efferent component of the pressor reflexes

Noradrenaline applied to the dorsal surface of spinal cord segments C6-T1 suppressed the pressor components of the blood pressure reflexes evoked by stimulation of radial nerve afferents in anesthetized cats. Noradrenaline applied to spinal cord segments L4-S1 suppressed pressor reflexes elicited by stimulation of tibial nerve afferents. The increase in noradrenaline concentration from 0.05 to 0.2% enhanced the duration and intensity of this effect.     

Nonsymmetrical double logistic analysis of ambulatory blood pressure recordings.

We developed an asymmetric double logistic curve-fitting procedure for circadian analysis that can determine the rate of change in variables during the day-to-night separately from the night-to-day transition for use in animal studies. We now have applied this procedure to 24-h systolic (SAP) and diastolic arterial pressure (DAP) and heart rate ambulatory recordings from 302 patients. In 292 cases, all parameters showed a pattern of higher day and lower night values. In men there was a similar rate of transition between day and night or from night to day for both SAP and DAP that lasted 3-4 h, indicating a symmetrical diurnal pattern. By contrast, women showed a faster rate of decrease in mean arterial pressure in the evening compared with men (P < 0.05) and therefore showed an asymmetric diurnal SAP pattern. For both men and women, there was a markedly greater rate of morning increase in heart rate compared with the rate of evening decrease (2.2- and 1.9-fold, respectively, P < 0.001). The logistic method provided a better fit than the square-wave or the cosinor method (P < 0.001) and more appropriately detected nondippers. We conclude that analysis of ambulatory recordings by a new logistic curve-fitting method reveals more rapid reductions in evening SAP in women than men but both have two- to threefold more rapid morning rates of tachycardia. The ability of the double logistic method to determine the diurnal blood pressure rates of change independently is key to determining new markers for cardiovascular risk.     

Comparative Evaluation of Heart Rate Variability Based on the Data of ECG and Blood Pressure Measurements

The development of new approaches to the assessment of heart rate variability (HRV) is an important problem, since HRV reflects the functioning of cardiovascular control and is affected by various diseases. The purpose of this study was to evaluate the informative value of statistical and spectral HRV parameters calculated from pulse interval (PI) data of blood pressure as compared with those calculated from RR-interval data of electrocardiograms (ECG). We recorded ECG in conscious rats using skin adhesive electrodes simultaneously with blood pressure signal obtained through a catheter in the femoral artery. It has been found that the PI sequence can be used to calculate the statistical HRV indices that describe the HRV at time intervals about 1 min or longer, but statistical indices of the PI and RR intervals may differ in the analysis of beat-tobeat variations. The power spectra of the RR intervals and PI coincide in the low-frequency region, including the band of baroreflex cardiac rhythm oscillation. However, they can differ in the high-frequency region (at respiration frequency and above).     

Spectral analysis of heart rate fluctuations: physiological basis and complicating factors

The main stages of investigation into the changes of the heart rate in human (HRH), are presented. A satisfactory coincidence of results of the HRH oscillation power estimation within two frequency ranges obtained with the aid of two techniques: by the Yamamoto algorithm and by search for sources of non-harmonic oscillations, was shown.     

Computer cardiokymography. On its way to long-term noninvasive monitoring of cardiac performance in daly life

A functioning heart generates low-frequency and low-amplitude movements (up to 40 (mrn) of soft tissues in the percardial area. Since the 1950-s of the XX-th century cardiologists have studied these movements to employ them in the diagnostics of ischemic heart disease (IHD). Indeed, changes of the movements have found their diagnostic application in this field. If blood supply to a certain area of ventricular myocardium is insufficient the contractions in this area diminish and even ceases. After systolic increase in ventricular pressure this area dilates and forces intercostal tissues out, causing a "bulge" wave on the record. For recording the patient must be in supine position and hold the breath. High frequency electromagnetic field generator was used in an attempt to examine the heart movements. It was found that such instrument measures the thickness of the air-gap that serves as a dielectric or a "capacitor" which forms between the skin and approaching it flat inductive coil. Nevertheless, such an instrument (cardiokymograph, CKG) can reveal changes in contractions of ischemic myocardium and markedly increases the sensitivity of the exercise ECG test. However, CKG can be recorded only after termination of the test. This principal disadvantage has been overcome by software that allowed the recording of CKG during the test. A low-frequency capacitance transducer developed recently by Chinese researchers has provided a simultaneous recording of several CKG. After modifying the transducer, we have established that 1) the shape of CKGs is the same as that CKGs recorded by all our predecessors, 2) CKGs are reproducible even within a 3-month interval, 3) the enormous mechanical interference caused by respiratory movements and, to a greater extent, by the vigorous movements of the legs and trunk during veloergometry can be eliminated by digital processing of the transducer signals, and 4) pathological changes appear in CKG of patients with IHD, which enables one to stop veloergometry at lower loads, thus increasing the safety of the test. Since for large medical insurance companies very simple and inexpensive cardiokymograph are quite unprofitable, their commercially production in USA and in Germany has been stopped. However, the goal of cardiokymography: a real-time, beat-to-beat, long-term monitoring of cardiac function in daily life, remains the major factor determining the future of the method.     

Reactions of arterial pressure to sciatic nerve A-fiber impulses in decerebrate and spinal frogs

Contrary to mammals, cutting of the spinal cord on the caudal part of the first segment in high-decerebrated nonanesthetized frogs does not evoke any statistically significant changes in blood pressure or lead to the depression of pressor responses to sciatic nerve A fibres stimulation. The intensity of the responses remains unchanged following cordotomy when stimulation frequency is low and increases when stimulation frequency is high. The results are believed to corroborate the conception on the predominant role of spinal shock in the depression of somato-sympathetic reflex reactions in cordotomized mammals.     

Conduction velocity and excitability of A and C fibers of cat mesenteric nerves

The conduction velocity and excitability of fibers running from the mesenteric into the splanchnic nerves were studied in experiments on cats. Among the A fibers of these nerves there were shown to be: 1) fibers with an excitation threshold of 0.06–0.10 V (stimulus duration 0.1 msec) and a maximal conduction velocity of 48–85 m/sec; 2) fibers with an excitation threshold of 0.3–0.7 V, impulses of which form up to five waves in the composition of the action potential, with maximal conduction velocities of between 8–10 and 33–39 m/sec; 3) fibers with an excitation threshold of over 1 V and a conduction velocity of between 1.8 and 7 m/sec. The excitation threshold of the group C fibers was 6–8 V. Impulses of these fibers form a low-amplitude wave in the composition of the action potential of the mesenteric and splanchnic nerves with a conduction velocity of 1.0–1.8 m/sec, several waves of higher amplitude with a conduction velocity of 0.5–1.2 m/sec, and several low-amplitude waves with a conduction velocity of 0.35–0.55 m/sec. The results of experiments with different combinations of arrangement of the stimulating and recording electrodes on the mesenteric and splanchnic nerves indicate that sympathetic postganglionic C fibers of the mesenteric nerves occur only in the second group, whereas afferent C fibers occur in all three of the groups distinguished.Institute of Normal and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 7, No. 3, pp. 272–278, May–June, 1975.     

Characteristics of the late A-response of vasoconstrictor neurons in cats decerebrated at different brain stem levels]

In cats decerebrated at the level of the rostral border of the midbrain (the mesencephalic animals) and in those decerebrated at different pontine levels, including the ponto-bulbar junction level, and the most rostral parts of the medulla oblongata (the "pontine" animals), or more caudal parts (the bulbar animals), single stimulus of the tibial nerve A-fibres elicited a late response in the renal nerve consisting of excitatory and inhibitory components. The excitatory component was relatively small or absent in 53% of the "pontine" animals, in 42% of the mesencephalic animals, and in 18% of the bulbar animals. The "pontine" animals had the most active and most excitable system of the inhibitory component generation. However, the signs of a comparatively more powerful inhibitory component of the A-afferent action of the vasoconstrictor neurones in the "pontine" animals were not as constant as to explain completely the transition of somatic A-afferent hypertensive reflexes into the hypotensive ones, occurring in separating the ponto-bulbar structure and the rostral parts of the medulla oblongata from the mesencephalon.     

Effect of tyramine on the spinal cord afferent link of pressor reflexes

In anesthetized cats, tyramine application on the dorsal surface of C6-TI spinal cord segments suppressed the pressor components of blood pressure reflexes evoked by radial nerve A sigma or A + C afferent stimulation. Tyramine application on L4-SI spinal cord segments suppressed pressor reflexes to tibial nerve stimulation. Both the degree and the rate of reflex suppression increased with the rise in tyramine concentration from I to 4%. Along with these local effects "distant" tyramine action was demonstrated: pressor reflexes to radial nerve stimulation increased when tyramine was applied on L4-SI segments, but after its application on C6-TI segments pressor reflexes to tibial nerve stimulation increased in some cats, decreased in the other ones, or remained practically unchanged.