Organism's resistance to acute severe hypoxia (3% O2) was studied after administration of GABA(A) receptor antagonist picrotoxin and adenosine receptor antagonist euphylline (aminophylline) and after neutralization of secondary hypocapnia by adding 7% CO2 to the hypoxic mixture. Administration of picrotoxin to anesthetized rats increased animal resistance to hypoxia. The resistance to hypoxia decreased after treatment with euphylline. Neutralization of secondary hypocapnia by adding 7% CO2 to the hypoxic mixture had no effect on animal lifespan.
We studied the effects of acute hypoxia on hemodynamics and respiration in cats. The animals were divided into high-, low-and medium-resistant to hypoxia by the time of respiratory arrest after breathing with 3% 02 gas mixture. In high-resistant animals, hemodynamic indices remained at a high level throughout the hypoxic episode, while in low-resistant cats they decreased shortly after the onset of hypoxia. It is suggested that the peculiarities of hemodynamic regulation play an important role in individual resistance to acute hypoxia. Key Words: acute hypoxia; hemodynamics; respiration; individual resistance to hypoxia, ultrasound techniquesRecent studies have confirmed the existence of individual, apart from species-specific sensitivity to hypoxia. Special normobaric and hypobaric tests make it possible to classify the animals as high-(HR), medium-(MR) and low-resistant (LR) to hypoxia [1][2][3]6,9]. Biochemical studies showed that animals with different resistance to hypoxia differ not only in parameters of energy, lipid, and carbohydrate metabolism [2,6], but also in the functional characteristics of hemodynamic regulation. However, complex analyses of cardiovascular resistance to different variants of hypoxia have not yet been performed.The aim of this study was to investigate the effect of acute hypoxic hypoxia on hemodynamics and respiration in HR, MR, and LR animals. MATERIALS AND METHODSAcute experiments were carried out on 35 male and female cats (1.8-4.4 kg) anesthetized with Nembutal with an ultrasound technique. Blood pressure in the femoral and pulmonary arteries (BP) was measured with an electric manometer [7]. Ultrasonic transducers were placed on the corresponding vessels during open thorax surgery under conditions of artificial ventilation (AV), then the tissues were sutured, and the animal was switched to natural ventilation. Respiratory movements were recorded with a strain transducer. The recorded indices were analyzed on line with a microcomputer to calculate total peripheral and pulmonary vascular resistance, heart rate (HR), stroke volume, and cardiac index. Changes in the cerebral blood supply were analyzed in 8 experiments. The linear and volume blood flow velocities in the common carotid and internal maxillary arteries were studied using miniature ultrasonic transducers with an inner diameter of 1.5 and 0.5 ram. In some experiments the arterial gasses were analyzed according to the method of Astroup--Ziggard--Andersen.Individual resistance to hypoxia was measured by the time from the onset of respiration with 3% O z in nitrogen to respiratory arrest (apnea). Then the gas flow was stopped for 2-3 rain. was discontinued and the recovery of respiration was awaited for the following 2-3 min. If spontaneous respiration did not recover, the animals were ventilated artificially until the appearance of spontaneous inspirations.0007 -4888/99/0009-0906522.00 ~ Kluwer Academic/Plenum Publishers
Peculiarities of application of two modes of ultrasonic measurements of blood flow in experimental research are considered, which are based on Doppler effect and on differential transit-time of upstream and downstream sound propagation. The efficiency of high-frequency ultrasound flowmeter equipped with 26.8 MHz transducers was demonstrated in measurements of blood flow in rat midbrain and coronary arteries. This approach can be used for evaluation of the dynamics of cardiac output with an intravascular catheter 0.6 mm in diameter working at 33 MHz. The probe and electronic scheme of the devise for measuring blood flow in microvessels are described. Blood flow rate measured in mesentery and m. cremaster arterioles under normal conditions was 2-12 mm/sec. One-element probe working at 38.5 MHz provided stable recording of blood microflows in 30-40-micro vessels.
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