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At least 595 records · Page 33Linked to original sources
PubMed1988

Gravitational independence of single-breath washout tests in recumbent dogs.

To examine the mechanisms of lung filling and emptying, Ar-bolus and N2 single-breath washout tests were conducted in 10 anesthetized dogs (prone and supine) and in three of those dogs with body rotation. Transpulmonary pressure was measured simultaneously, allowing identification of the lung volume above residual volume at which there was an inflection point in the pressure-volume curve (VIP). Although phase IV for Ar was upward, phase IV for N2 was small and variable, especially in the prone position. No significant prone to supine differences in closing capacity for Ar were seen, indicating that airway closure was generated at the same lung volumes. The maximum deflections of phase IV for Ar and N2 from extrapolated phase III slopes were smaller in the prone position, suggesting more uniform tracer gas concentrations across the lungs. VIP was smaller than the closing volume for Ar, which is consistent with the effects of well-developed collateral ventilation in dogs. Body rotation tests in three dogs did not generally cause an inversion of phase III or IV. We conclude that in recumbent dogs regional distribution of ventilation is not primarily determined by the effect of gravity, but by lung, thorax, and mediastinum interactions and/or differences in regional mechanical properties of the lungs.

Animals↗
PubMed2002

Heterogeneous responses of human limbs to infused adrenergic agonists: a gravitational effect?

Unlike quadrupeds, the legs of humans are regularly exposed to elevated pressures relative to the arms. We hypothesized that this "dependent hypertension" would be associated with altered adrenergic responsiveness. Isoproterenol (0.75-24 ng x 100 ml limb volume-1 x min-1) and phenylephrine (0.025-0.8 microg x 100 ml limb volume-1 x min-1) were infused incrementally in the brachial and femoral arteries of 12 normal volunteers; changes in limb blood flow were quantified by using strain-gauge plethysmography. Compared with the forearm, baseline calf vascular resistance was greater (38.8 +/- 2.5 vs. 26.9 +/- 2.0 mmHg x 100 ml x min x ml-1; P < 0.001) and maximal conductance was lower (46.1 +/- 11.9 vs. 59.4 +/- 13.4 ml x ml-1 x min-1 x mmHg-1; P < 0.03). Vascular conductance did not differ between the two limbs during isoproterenol infusions, whereas decreases in vascular conductance were greater in the calf than the forearm during phenylephrine infusions (P < 0.001). With responses normalized to maximal conductance, the half-maximal response for phenylephrine was significantly less for the calf than the forearm (P < 0.001), whereas the half-maximal response for isoproterenol did not differ between limbs. We conclude that alpha1- but not beta-adrenergic-receptor responsiveness in human limbs is nonuniform. The relatively greater response to alpha1-adrenergic-receptor stimulation in the calf may represent an adaptive mechanism that limits blood pooling and capillary filtration in the legs during standing.

Adaptation, Physiological↗
PubMed1990

Influences of gravitational stress and total muscle mass on human cardiovascular adjustments during prolonged dynamic exercise.

To investigate cardiovascular adjustments to combined stress of gravity and exercise during dynamic exercise prolonged over 60 minutes in upright position, the three experiments were carried out. In Experiment I, as performing moderate upright bicycling (66% VO2 max) until exhaustion (average 86 minutes) in 4 trained men, changing manners of cardiovascular adjustments were shown in three phases, which were (1) regulating set-point body temperature, (2) making to maintain suitable blood pressure, and (3) failing to control the blood pressure. In Experiment II, as performing moderate supine cycling (55% VO2 max) for 50 minutes under several LBNP conditions in 5 sedentary women, there were correspondingly similar changing manners of the cardiovascular adjustments to each of the phases given in Experiment I. In Experiment III, as examining tolerance of orthostatic circulatory regulation, the tolerance was significantly correlated to VO2 max and lean body mass (LBM) (both p less than 0.05) in 8 sedentary women. When a moderate upright exercise is performed over 60 minutes in upright position, the performance should be influenced by total muscle mass indicated by LBM as well as by VO2 max, because the muscle mass could play a valuable role in the tolerance of orthostatic circulatory regulation vs. gravity.

Adult↗
PubMedDate not supplied

Eye movements induced by gravitational force and by angular acceleration: their relationship.

The relationship between putative 'canal' and 'otolith' function was studied by using both vertical axis and horizontal axis (barbecue spit) rotations. The vestibulo-ocular reflex (VOR) with eyes closed of 7 normal subjects during vertical axis rotation was characterized (0.02 to 1.67 Hz) using pseudorandom acceleration. Gain and phase points were calculated. The long time constant of the VOR was then estimated from the phase points using a simple linear systems model. The same subjects were also tested with eyes closed using earth horizontal axis rotations. Constant velocity rotation (60 degrees/sec) produced a periodic oscillation in the slope of the slow component of nystagmus known as the 'modulation component'. The amplitude of this component was averaged for clockwise and counterclockwise runs. For the 7 subjects, the amplitude of averaged modulation component correlated with the low-frequency phase values (r = 0.82 to 0.89) and VOR long time constant estimates (r = -0.95) obtained during vertical axis rotations. These data suggest a complementary relationship between responses to linear and to angular accelerations. Subjects having eye movement responses which are less sensitive to low-frequency angular acceleration also tend to have relatively greater responses to changing linear accelerations.

Eye Movements↗
PubMedDate not supplied

[The quantum gravitational therapy of myocarditis].

Complex therapy of myocarditis of rheumatic and non-rheumatic genesis using intravascular laser irradiation of blood, quercitrol, and enterosgel has an antiinflammatory, antioxidant action, improves myocardial contractility, is endowed with an antiaggregatory activity. The above therapeutic complex permits the reduction of the non-steroid antiinflammatory drugs intake as well as of the average time of hospital treatment by 2 to 3 days, it also makes for an earlier medical and social rehabilitation of patients.

Adult↗
PubMed1999

Effects of gravitational load on jaw movements in speech.

External loads arising as a result of the orientation of body segments relative to gravity can affect the achievement of movement goals. The degree to which subjects adjust control signals to compensate for these loads is a reflection of the extent to which forces affecting motion are represented neurally. In the present study we assessed whether subjects, when speaking, compensate for loads caused by the orientation of the head relative to gravity. We used a mathematical model of the jaw to predict the effects of control signals that are not adjusted for changes to head orientation. The simulations predicted a systematic change in sagittal plane jaw orientation and horizontal position resulting from changes to the orientation of the head. We conducted an empirical study in which subjects were tested under the same conditions. With one exception, empirical results were consistent with the simulations. In both simulation and empirical studies, the jaw was rotated closer to occlusion and translated in an anterior direction when the head was in the prone orientation. When the head was in the supine orientation, the jaw was rotated away from occlusion. The findings suggest that the nervous system does not completely compensate for changes in head orientation relative to gravity. A second study was conducted to assess possible changes in acoustical patterns attributable to changes in head orientation. The frequencies of the first (F1) and second (F2) formants associated with the steady-state portion of vowels were measured. As in the kinematic study, systematic differences in the values of F1 and F2 were observed with changes in head orientation. Thus the acoustical analysis further supports the conclusion that control signals are not completely adjusted to offset forces arising because of changes in orientation.

Biomechanical Phenomena↗
PubMedDate not supplied

[Gravitational cause of fluctuations of the rate of oxidation of unithiol by nitrite ion].

The rate of oxidation of unithiol (sodium dimercaptopropansulfonate) by nitrite ion was determined in the course of the annual experiment at the Antarctic station Mirny in 1996-1997. The rhythmic fluctuations in the oxidation rate were found. It is shown that these fluctuations correlate with changes in the velocity of the Earth's forward-rotational movement by the action of the Sun and Moon.

Gravitation↗