Sympathetically induced spontaneous fluctuations of the photoplethysmographic signal

The photoplethysmographic signal shows very low-frequency (VLF) spontaneous fluctuations that have been shown to be mediated by the sympathetic nervous system. In the current study, the photoplethysmographic signal was simultaneously measured in the two index fingers and the two second toes of 54 healthy male subjects. For each photoplethysmographic pulse, two parameters were derived: the pulse amplitude and its baseline, which are related to the arterial wall compliance and to the arterial blood volume, respectively. The baseline and the amplitude VLF fluctuations showed high right-left correlation both for hands (mean±SD 0.94±0.05 and 0.92±0.07, respectively) and for feet (0.90±0.08 and 0.89±0.07, respectively) that only slightly depended on the subject's age. Lower correlation was found between the hand and the foot (0.73±0.12 and 0.72±0.12 for the baseline and the amplitude, respectively). For each hand and foot the baseline and the amplitude VLF fluctuations were also correlated, with the baseline fluctuations lagging the amplitude fluctuations by 3–20 pulses. The amplitude-baseline correlation and the standard deviation of the amplitude or the baseline divided by its mean significantly decreased with age. The VLF fluctuations of the photoplethysmographic parameters and the correlation coefficients between them provide better understanding of the autonomic nervous regulation of the blood circulation.     

Neural network for photoplethysmographic respiratory rate monitoring

The reflection mode photoplethysmographic (PPG) signal was studied with the aim of determining respiratory rate. The PPG signal includes respiratory synchronous components, seen as frequency modulation of the heart rate (respiratory sinus arrhythmia), amplitude modulation of the cardiac pulse and respiratory-induced intensity variations (RIIVs) in the PPG baseline. PPG signals were recorded from the foreheads of 15 healthy subjects. From these signals, the systolic wavefrm diastolic waveform, respiratory sinus arrhythmia, pulse amplitude and RIIVs were extracted. Using basic algorithms, the rates of false positive and false negative detection of breaths were calculated separately for each of the five components. Furthermore, a neural network was assessed in a combined pattern recognition approach. The error rates (sum of false positive and false negative breath detections) for the basic algorithms ranged from 9.7% (pulse amplitude) to 14.5% (systolic waveform). The corresponding values for the neural network analysis were 9.5–9.6%. These results suggest the use of a combined PPG system for simultaneous monitoring of respiratory rate and arterial oxygen saturation (pulse oximetry).     

Intravascular pressure and spontaneous contraction of the lymphatics

Relations between spontaneous contractile activity and the level of the intravascular pressure were studied in isolated segments of lymphatics. Spontaneous contractions arise when the pressure is of the order of 0.5–1.5 cm water. With an increase in pressure up to 5 cm water the frequency and amplitude of the contractions increase, but when the pressure is 10 cm water they decrease. The indices of the spontaneous rhythm of the lymphatics change not only with absolute values of the intravascular pressure, but also with the rate of their change.Department of Normal Physiology and Section of Physiology, Central Scientific-Research Laboratory, Leningrad Public Health Medical Institute. (Presented by Academician V. N. Chernigovskii). Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 83, No. 4, pp. 392–394, April, 1977.     

Mathematical study of the role of non-linear venous compliance in the cranial volume-pressure test

The role of the cerebral venous bed in the cranial volume-pressure test was examined by means of a mathematical model. The cerebral vascular bed was represented by a single arterial compartment and two venous compartments in series. The lumped-parameter formulation for the vascular compartments was derived from a one-dimensional theory of flow in collapsible tubes. It was assumed in the model that the cranial volume is constant. The results show that most of the additional volume of cerebrospinal fluid (ΔV_CSF) was accommodated by collapse of the cerebral venous bed. This profoundly altered the venous haemodynamics and was reflected in the cranial pressure P_CSF. The cranial volume-pressure curve obtained from the model was consistent with experimental data; the curve was flat for 0<-ΔV_CSF<-20 ml and 35<-ΔV_CSF<-40 ml, and steep for 20<-ΔV_CSF<-35 ml and ΔV_CSF>-40 ml. For ΔV_CSF>25 ml and P_CSF>5.3 kPa (40 mmHg), cerebral blood flow dropped. When P_CSF was greater than the mean arterial pressure, all the veins collapsed. The conclusion of the study was that the shape of the cranial volume-pressure curve can be explained by changes in the venous bed caused by various degrees of collapse and/or distension.     

Changes of peripheral venous tone and central transmural venous pressure during immersion in a thermo-neutral bath

Summary Peripheral venous tone, central venous and oesophageal pressures were recorded while the upright sitting subjects were immersed to the neck in a thermoneutral water bath. The central venous pressure rose from 3.4 to 15.2 mm Hg and the oesophageal pressure from –0.4 to +3.4 mm Hg. The transmural pressure, which determines the enddiastolic volume of the heart, increased by 8.0 mm Hg. Plethysmographic determinations of peripheral venous tone revealed a relaxation of the peripheral veins: after a quick initial decrease of the volume elasticity coefficient (E₁₅) from 16.6 to 13.5 mm Hg/ml/100 g tissue there is a continuous decline to 11.8 mm Hg/ml/100 g tissue after 3 hrs immersion. This relaxation persists for at least 1 hr after termination of immersion.This work was supported by Contract No. F44620-71-C-0117 of the Air Force Office of Scientific Research (OAR), European Office of Aerospace Research.with the technical assistance of H. Dannenberg     

Effect of bombesin (6–14) on arterial pressure in health and in hypovolemic shock

Injection of active fragment of the neuropeptide bombesin (6–14) into cerebral ventricles of intact rabbits induces marked arterial hypertension accompanied by bradycardia and partial redistribution of blood to specialized heat-emitting organs (auricular conchae), which reduces body temperature. After a considerable blood loss, the peptide normalizes arterial pressure without affecting cardiac activity and body temperature. It is suggested that bombesins may be used for compensation of arterial hypotension during the early period of hypovolemic shock. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 122, No. 10, pp. 372–374, October, 1996     

Hydrocephalus shunts and waves of intracranial pressure

The majority of contemporary hydrocephalus valves are designed to introduce a low resistance to flow into the cerebrospinal fluid (CSF) drainage pathway, and an therefore intended to stabilise intracranial pressure (ICP) at a level close to the shunt's operating pressure. However, this goal cannot always be attained. Accelerated CSF drainage with vertical body posture in ventriculo-peritoneal shunts is one reason for the ICP decreasing below the shunt's operating pressure. Another possible factor has been studied: the impact of the pulsating pattern in the ICP on the operating pressure. Six popular constructions of medium-pressure valves were studied (Radionics Low-profile, Delta, Hakim Precision, Holter, Integra In-line and Hakim NMT). Valves were mounted in the testing rig in the UK. Shunt Evaluation Laboratory and perfused with de-ionised water at a rate of 0.3 ml min⁻¹, and proximal pulsating pressures of different amplitudes (from 2 to 30 mmHg peak-to-peak) and frequencies (70–10 cycles min⁻¹) were superimposed. Laboratory findings were compared with clinical material containing recordings of ICP made in patients to diagnose reasons for ventriculomegaly. The mean operating pressure decreased in all valves when the simulated amplitude of heart pulsations increased. The rate of this decrease was dependent on the type of valve (variable from 2.5 to 5 mm Hg per increase in peak-to-peak amplitude by 10 mm Hg). The decrease was not related to the frequency of the wave. The relationship between pulse amplitude and ICP in 35 patients with blocked shunts was strong (R=0.48; p<0.03; slope 0.14) and in 25 patients with properly functioning shunts was non-significant (R=0.057; p=0.765). Two examples of decrease in mean ICP in the presence of increased vasogenic ICP waves in shunted patients are presented. The shunt operating pressure, which ‘sets’ the ICP in shunted patients may be influenced by the dynamics of a patient's ICP waveform.     

Assessment of the human regional cerebral blood flow by venous occlusion rheoplethysmoencephalography

The possibility of using the method of venous occlusion rheoplethysmoencephalography (RPEG) for assessing the degree of change of the cerebral blood flow (CB) in the various zones of the cerebral hemispheres of the clinically healthy person during various functional loads was demonstrated. The change in CB is calculated as a percentage of its initial value. By means of venous occlusion RPEG evidence was obtained that CB is increased (by 114%) in the central-parietal region of the left hemisphere during movement of the right hand and reduced (by 45%) during acoustic stimulation. In the neighboring (temporal) zone the changes in CB were different in character.Laboratory of Clinical Physiology, Institute Work Hygiene and Occupational Diseases, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. M. Chernukh.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 82, No. 11, pp. 1402–1404, November, 1976.     

Comparative analysis of effects from prolonged peripheral and intracerebral administrations of angiotensin II in rats

Variations in arterial pressure and food and water consumption were studied in rats during and after their prolonged continuous exposure to angiotensin II using osmotic minipumps. Subcutaneously administered angiotensin-II (300 μg over 7 days) induced long-lasting hypertension followed by hypotension. Angiotensin-II administered into a lateral cerebral ventricle (3 μg over the same period) led to a significant fall in arterial pressure. The peripheral and intracerebral angiotensin-II administrations were both accompanied by increased water consumption. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 118, N^no 10, pp. 352–354, October, 1994 Presented by K. V. Sudakov, Member of the Russian Academy of Medical Sciences     

Automatic correction for drift in an integrator for phasic signals

An electronic integrator for phasic signals has been designed that does not undergo slow changes in output voltage (drift). Output is stabilised by means of negative feedback using an active 5-pole lowpass filter. Accurate integration of phasic signals with frequencies above 0·1 Hz is obtained. The integrator has been used for continuous determination of cyclincal volume changes, with a pneumotachograph as an input source, in the plotting of respiratory pressure-volume loops.     

Effect of pulsating local negative pressure with oxygen on bioelectrical activity of the uterus in pregnant albino rats with intrauterine streptococcal infection

Bloodborne intrauterine streptococcal infection of albino rats during pregnancy (implantation, placentation) leads to disturbances of uterine bioelectrical activity which are restored to normal by treatment with pulsating local negative pressure together with periodic administration of oxygen.Moscow Regional Research Institute of Obstetrics and Gynecology and Department of Normal Physiology, Patrice Lumumba Peoples' Friendship University, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR V. D. Timakov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 5, pp. 528–531, May, 1978.     

Relationship between the baroreceptor reflex and the variability of arterial pressure and of the heart beat period in rats with arterial hypertension

The relationship between depression of the cardiochronotropic component of the baroreceptor reflex and arterial pressure and heart beat variabilities was investigated in normotensive rats and rats with renal hypertension (one kidney — one clamp). In the hypertensive rats, the arterial pressure and heart rate were both increased and more variable, while the cardiochronotropic component of the baroreceptor reflex was depressed. No cause-effect relationship between baroreceptor reflex attenuation and increased variability of hemodynamic parameters was found in this rat model of arterial hypertension. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, No. 5, pp. 474–476, May, 1995 Presented by B. I. Tkachenko, Member of the Russian Academy of Medical Sciences     

Changes in inferior vena cava blood flow at increased negative intrathoracic pressure

An increase in the negative intrathoracic pressure had practically no effect on the mean blood flow in the posterior vena cava and femoral vein in cats and healthy volunteers, because instantaneous (phasic) values of the venous blood flow increased during inspiration, while during expiration they decreased to a lower extent than during natural respiration. These phasic changes in the venous blood flow were due to changes not only in intrathoracic, but also in transdiaphragmatic pressure. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 129, No. 3, pp. 248–251, March, 2000     

Magnesium deficiency in drinking water modulates blood pressure, Ca and Mg distribution in tissues, and compartmentalization of membrane-bound calcium in platelets of normotensive WKY rats

Magnesium deficiency in drinking water increases calcium-accumulating capacity of the aortic and myocardial walls in normotensive WKY rats, induces Ca resorption from bones, and impairs compartmentalization of membrane-bound Ca in platelets, resulting in accumulation of Ca in the external plasma membrane without changing blood pressure. Increased systolic blood pressure was characteristic of rats in Ca-deficient groups. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 127, No. 2, pp. 183–186, February, 1999     

Effect of early fasciotomy on intramuscular pressure and electrical excitability of muscles in experimental compartment syndrome

Experiments on rabbits with compartment syndrome of the leg showed that the main pathogenetic factors of muscle injury are postischemic contracture leading to extravascular microcirculatory disorders and tissue necrosis(early postcompression period) and progressive subfascial edema (18 h-4 days). Therapeutic effect of fasciotomy in the early period consists in restoration of bloodflow due to relaxation of contracted muscles and in the late period in decompression of edematous muscles and prevention of secondary ischemia. Fasciotomy through a small section does not lead to sufficient relaxation of rigid muscles and does not essentially increase the subfascial volume. Fasciotomy decreases subfascial pressure and muscle excitability threshold, however they remain considerably elevated during day 1. An electrodiagnostic test is proposed for early (before subfascial edema) detection of postischemic contracture. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 130, No. 9, pp. 284–288, September, 2000     

Effect of early fasciotomy on intramuscular pressure and electrical excitability of muscles in experimental compartment syndrome

Experiments on rabbits with compartment syndrome of the leg showed that the main pathogenetic factors of muscle injury are postischemic contracture leading to extravascular microcirculatory disorders and tissue necrosis(early postcompression period) and progressive subfascial edema (18 h-4 days). Therapeutic effect of fasciotomy in the early period consists in restoration of bloodflow due to relaxation of contracted muscles and in the late period in decompression of edematous muscles and prevention of secondary ischemia. Fasciotomy through a small section does not lead to sufficient relaxation of rigid muscles and does not essentially increase the subfascial volume. Fasciotomy decreases subfascial pressure and muscle excitability threshold, however they remain considerably elevated during day 1. An electrodiagnostic test is proposed for early (before subfascial edema) detection of postischemic contracture. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 130, No. 9, pp. 284–288, September, 2000