Microcirculation in the lungs: special features of construction and dynamics.

In this study we investigated microcirculation in the lungs in their in situ physiological location inside the thorax. The study was performed with the use of a system of contact optics. A 'window', 4 × 4 mm in size, was made in thorax tissues and pleura of an anaesthetized rat. The lung collapsed and then was filled with oxygen or hypoxic gas mixture under the pressure of 10-15 cm H(2)O through a tracheostomic canula. This almost excluded the respiratory movements of the lung. Then, the lung was brought in contact with a lens (1.7 mm aperture). We showed that there is a whole system of wide microvessels (20-30 µm in diameter) which run between the alveoli; the finding contradicting the hitherto notion that each alveolus is supplied with blood via the thinnest (5-10 µm in diameter) lung arterioles. The microvessels we visualized surround each alveolus almost from all sides. In this way, each alveolus receives a maximum amount of blood. Such a structure of lung circulation accounts for a substantial blood flow through the lungs (up to 6 l per min in humans) and for a rapid saturation of the blood with oxygen (about 100 ml per second). The alveoli saturate the blood with oxygen and subsequently the microvessels form the lung veins entering the left auricle. The photographs and video films of the alveoli at a high magnification were presented, demonstrate the special features of the structure and circulation in the alveoli. The plausible mechanisms of rapid saturation of the blood with oxygen are discussed.

Structure of microvascular networks in the lungs and peculiarities of blood circulation in them.

Microvessels and their relationship with alveoli in the lungs of albino rats under physiological condition in the thorax were studied by intravital microscopy. The structure of a network of large microvessels 20-30 µ in diameter surrounding each alveolus along the perimeter from all sides was demonstrated. Blood flow was investigated by video.

[Disturbance and restoration of the cortical brain microcirculation in the global ischemia].

In the global brain ischemia, the leucocytes are adhered in the venules and smallest veins thus impeding the capillary blood circulation. In a more severe ischemia, the leucocytes conglomerates are formed. This causes the occlusion of venous vessels, blocks the venous outflow and practically is a reason of animal' death from ischemia. We suggest a method for removing leucocytes and leucocytes conglomerates from vessels.

[About a correlation between calcium ion concentration (Ca2+) in the blood and the state of physiological functions in animals in deep cooling].

The changes in physiological functions of the organism (respiration, functions of the heart and vessels, thermoregulation) were studied. The concentration of Ca2+ ions in the blood of white rats was determined by the ion-selective electrodes at various stages of hypothermia. The aim of the study was to reveal changes in the blood concentration of ionized calcium in animals during their gradual cooling. In deep hypothermia (16 degrees C), calcium ion concentration in the blood increased by 30% against the norm which coincides with arrest of the cold shivering and lung ventilation. An increased content of Ca2+ in the blood is supposed to result in an increase in the content of these ions in the intercellular liquid and in the nervous cells, which is one of the reasons for the cold paralysis of the respiration and thermoregulation centers.

[Stimulation of physiological functions in cooled rats without rewarming after introducing ethylenediaminetetraacetate into lateral ventricles of the brain].

On cooling the animals to the rectum temperature from approximately 37 to 24-28 degrees C the decreases were shown to occur in the frequency and amplitude of respiration motions, in the intensity of muscle electrical activity (thermoregulation muscle tone and cold muscle shivering), in the frequency of heart contractions. In 3-8 min after introducing ethylenediaminetetraacetate into a lateral ventricle of the rat brain the frequency and the amplitude of respiration motions increased statistically reliable and so did the intensity of thermoregulation muscle tone and cold muscle shivering (judging from the total muscle electrical activity). The doses of EDTA, which caused this effect, were by a factor of 30 - 100 less than the doses, which caused a similar stimulation of the functions in cooled animals after introduction into the blood.

[Stimulation of thermoregulatory and respiratory functions with the help of EDTA and EGTA during deep hypothermia in rats]. / Stimuliatsiia termoreguliatornoi i dykhatel'noi funktsii s pomoshch'iu EDTA i EGTA glubokoi gipotermii u krys.

Influence of EDTA (C10H14N2Na2O8.2H2O) and EGTA (C14H24N2O10) on physiological functions homoiothermic organisms at deep hypothermia, was studied. White rats during cooling were in special sections without rigid fixing of head and limbs. In reply to intravenous introduction of EDTA and EGTA solutions, similar answers of the organisms were observed: raised breathing frequency and amplitude, intensity of electrical activity of muscles; these signs of activation of physiological functions lasted 8-10 minutes. Besides, of the 20th-30th minute after introduction of the second dose of preparations (at rectal temperature 17.1 +/- 0.5 degrees C), the secondary activation respiratory and thermoregulatory functions were registered. The termination of the cold shivering in experiments with introduction of EDTA and EGTA solutions occurred at lower temperatures in rectum and in a brain (16.7-17.3 degrees and 17.8-18.2 degrees C, resp.) than in control experiments (18.7 +/- 0.6 degrees C and 20.2 +/- 1.5 degrees C). The authors suppose that the activation of the thermoregulatory and respiratory functions is caused by a decrease in concentration of ions Ca2+ in the blood plasma.

[Development of deep hypothermia in rats with limited motor activity]. / Osobennosti razvitiia glubokoi gipotermii u krys pri razlichnoi stepeni ogranicheniia dvigatel'noi aktivnosti.

Changes of the main organism functions (breathing frequency, heart rate and shivering) were investigated under hypothermia in two groups of rats. Animals of the first group were fixed rigidly on the special platform with fixing of head and limbs, and those of the second one--the rats, were placed in a punched cylindrical chamber, inside which they could move freely forward and back. In 2.5-3.0 hours after anaesthesia the rats were placed in a refrigerator (-5 degrees C) until they stop breathing. Cessation of breathing of the first group rats occurred in 1.7 +/- 0.3 hours from the beginning of cooling at body temperature 17.3 +/- 0.6 degrees C and the brain temperature 15.7 +/- 0.5 degrees C. In the second group, a prolonged activation of the frequency of breathing, heart rate and intensity of electrical activity of muscles during 2.5-3.0 hours, was observed. Only in 4.5-5.0 hours, the breathing stopped at rectal temperature 12.3 +/- 1.1 degrees C and the brain temperature 12.9 +/- 0.9 degrees C. In these animals, the time of survival in the cold environment increased considerably and the temperature thresholds of the termination of breathing were lowered. Thus, the activation in the thermo-regulative muscle tone and in shivering muscles provides the most effective resistance against cooling of rats, reducing a surface of heat, dissipation and keeping the temperature of internal areas of body.

[The temperature-sensitive function of the skin mechanoreceptor endings]. / Temperaturno-chuvstvitel'naia funktsiia mekhanoretseptornykh okonchanii kozhi.

Impulse activity of the ischiatic nerves single fibres in response to focused ultrasound stimulation of the rat hind-foot receptive fields, was studied. The receptor units were divided into low-, average- and high-threshold groups by the value of their threshold responses. No impulse activity was revealed in response to direct action of cold or warm water on the foot in the afferent fibres. Warm stimulation evoked most obvious changes in the low-threshold units, whereas latency noticeably changed in the average-threshold, and potential activity--in the high-threshold units rather. The data suggests involvement of the average-threshold units in the temperature perception.

[Effect of extremely high-frequency electromagnetic radiation on the function of skin sensory endings]. / Vliianie élektromagnitnogo izlucheniia kraine vysokikh chastot na funktsiiu sensornykh okonchanii kozhi.

The specific features of skin receptor function on the sole of the hind limb of an albino rat were studied in an acute experiment. Impulse activity recorded from the solitary fibres of the tibial nerve showed that receptor units (RU) responded to mechanical stimulation of the skin. Irradiation of the skin surface by low-intensity millimeter band electromagnetic field (frequencies of 55.61 and 73 GHz) in the zone of the RU led to diminution of RU sensitivity to the mechanical stimulus. One half of the RU ceased to respond to the mechanical stimulation 25 minutes after irradiation. The other half continued responding to stimulation even after 35 minutes of irradiation, but the character of the RU response was significantly changed. A strict frequency-resonance dependence of the biological effects was revealed. It is concluded that electromagnetic radiation has a modulatory-inhibiting effect on the skin RU. The authors suggest a possible mechanism of realization of the effect of electromagnetic radiation of extremely high-frequencies and low power on the skin receptor function.

[The temperature dependence of receptor structures and temperature-related reception]. / Temperaturnaia zavisimost' retseptornykh struktur i temperaturnaia retseptsiia.

In acute experiments on rats, studies have been made on impulse activity of single fibres of n. ischiadicus evoked by stimulation of the receptive fields of the sole by focused ultrasound. Mechanical effects were produced by rectangular ultrasonic stimuli, thermal ones--by trapezoid ones. With respect to the magnitude of a threshold response to a rectangular stimuli, the receptor structures were divided into three groups, i.e. low, mean and high threshold ones. Low and mean threshold receptor units responded to local thermal stimulation. Mean threshold units exhibited an increase of the threshold to mechanical stimulation after local thermal one. In human subjects, the structures which are functionally similar to mean threshold units, evoke thermal sensations, and may be classified not only as temperature dependent, but also as temperature sensitive.

[Focused ultrasound in research on somatic reception]. / Fokusirovannyi ul'trazvuk v issledovanii somaticheskoi retseptsii.

Focused ultrasound has been used to induce the following skin sensations: tactile and temperature ones; specific and unspecific pain, underskin or deep sensations: tactile sensations and some varieties of pain (muscle, periosteum and so on). It has been established that: somatic reception is attributed to mechanoreception; the same receptive structures are cold and warm ones; ultrasound has the sensibilized action. Sensation differences of corporal and auricular acupuncture points and some accidental skin underskin spots have been investigated.

[Skin mechanoreceptor functioning in the white rat during transcranial electrostimulation]. / Funktsionirovanie mekhanoretseptorov kozhi beloi krysy pri transkranial'noi élektrostimuliatsii.

Functional properties of skin afferents were studied by the method of registration of spike activity from single nerve fibres, innervated non-hairy skin in white rats. It was found that mechanoreceptor units varied by the threshold intensity of applied stimulus. These units were divided to three functional groups: low-, medium- and high-threshold units. Transcranial electrical stimulation (TES) strongly affected on the functional characteristics of skin afferents. Full suppression of responses was observed in 18-20 min. irrespective of the category of units. A local intracutaneous injection of naloxon eliminated the effect of TES. It is supposed that endogenous opioid peptides regulate an afferent discharge on the level of sensory endings during TES.

[Changes in the excitability of the skin mechanoreceptors in the rat against a background of transcranial electrostimulation]. / Izmenenie vozbudimosti mekhanoretseptorov kozhi krysy na fone transkranial'noi élektrostimuliatsii.

Alterations in excitability of low-, medium- and high-threshold single mechanoreceptors (SMRs) of hairless hind paw skin elicited by transcranial electrical stimulation (TES) in analgesic regime were studied in anesthetized rats. Evoked impulsations of low- and medium-threshold SMRs were blocked by TES that lasted for about 1 and 5 min, respectively. TES for 18-20 min in duration abolished the reactions of high threshold SMRs activated only by nociceptive stimuli. Inhibitory effects of TES on all SMR types under study were eliminated by preliminary intraperitoneal or local intracutaneous (near SMRs location) injection of naloxone. Possible mechanisms of analgesic TES effects are discussed. An assumption is made that alterations of the SMR function are connected with an increase of the output of endogenous opioid peptides from the brain during TES.

[Functional characteristics of the skin receptor structures in animals and man]. / Funktsional'nye kharakteristiki retseptornykh struktur kozhi zhivotnykh i cheloveka.

Threshold electrical reactions of single fibers from the ischiadic nerve of rats to mechanical stimulation and rectangle impulses of focused ultrasound have been compared with respect to the parameters of stimulation to the effect of focused ultrasound on the skin of human fingers evoking different sensations. It was concluded that low-threshold fibers may be associated with tactile reception, mean-threshold ones--with tactile and thermal, whereas high-threshold fibers may be referred to reception of specific skin pain.

[Descending vasoconstrictor fibers in the thoracic region of the spinal cord]. / Niskhodiashchie vazokonstriktornye volokna v grudnom otdele spinnogo mozga.

Analysis of the arterial pressure responses to electric stimulation of the spinal cord structures at T1 to L3 showed two zones of the maximal pressure activity in the lateral and medial parts of the lateral funiculus. After destruction of the lateral part at T1-T2 level, a decrease in the systemic arterial pressure occurred after stimulation of the pressor zone of the vasomotor center and structures of the spinal cord at the levels of C5 and ischiatic nerve. These and previously obtained data suggest that the pressor responses to stimulation of the lateral part of the lateral funiculus of the spinal cord are of the reticulospinal origin. Participation of the propriospinal fibers in the pressor responses to stimulation of the medial zone of the lateral funiculus is discussed.