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 147,016 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A wide range of respiratory, ventilatory, and cardiovascular parameters have been recorded under completely resting conditions in the starry flounder (Platichthys stellatus), a generally inactive benthic teleost. The results differ in a number of important respects from those of a previous study on the same species. The present data have also been compared with those reported for the active pelagic rainbow trout (Salmo gairdneri) and for other teleost species. Of particular note in the flounder, relative to the trout, are low arterial and venous PO2's, a low arterial-venous O2 content difference, a low transfer factor and high diffusion gradient for O2 across the gills, a high in vivo blood O2 affinity, a high cardiac output and stroke volume accompanied by a low peripheral vascular resistance, a low ventilation volume, a low ventilation-perfusion ratio, and a low capacity-rate ratio for O2 exchange at the gills. Parameters of CO2 transport and acid-base regulation appear conventional, though blood CO2 contents and lactate concentrations are low. The respiratory strategies of inactive versus active, and benthic versus pelagic teleosts are discussed.
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PMID:Respiratory gas exchange in the resting starry flounder, Platichthys stellatus: a comparison with other teleosts. 43 19

Three to twelve (7.1 +/- 3.2) months after myocardial infarction, subjects under 54 (45.0 +/- 4.7) yr were assigned randomly to high-intensity (HIE, n = 37) or low-intensity (LIE, n = 42) exercise programs. Cardiac outputs (Q) during graded bicycle ergometer exercise were measured by a CO2-rebreathing method on entry and after 6 and 12 mo of training. The initial exercise Q was low in relation to work load, due to a low stroke volume (SV). Over the year of training, the predicted maximal O2 intake of the HIE group increased significantly (from 26.0 to 30.3 ml.kg-1.min-1), while that of the LIE group showed no significant alteration. During the first 6 mo, the heart rate of the HIE group was significantly reduced at each work level. There was an associated widening of arteriovenous oxygen difference, but SV was unchanged. These findings were attributed to extracardiac factors, including a redistribution of blood flow, biochemical changes in the trained muscle, and a secondary reduction of sympathetic drive. Over the second 6 mo, the SV of the HIE group increased 10%; this may reflect an increase of intrinsic myocardial contractility that develops if high-intensity training is sustained. The LIE group showed no major changes of cardiovascular function over the year of observation.
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PMID:Effects of physical training on cardiovascular function following myocardial infarction. 53 40

Oxygen uptake (V32), heart rate (fH) and cardiac output (Q, CO2-rebreathing method) were measured in 8 paraplegics with complete low level (Th6-Th12) lesions and in 1 paraplegic with a Th2 lesion during graded exercise performed on an arm ergometer. The submaximal work rates taxed about 50, 70 and 90% of the estimated functional capacity of the subjects. A linear relationship between the work rate and VO2 were assessed in the three tests. The increase of Q with increasing VO2 was accomplished by a considerable increase in fH accompanied by a slight increase in stroke volume (SV, calculated). Markedly low values of Q were found in 6 of the 9 subjects. The resulting high arterial-mixed venous blood oxygen content differences (calculated) as well as the high blood lactate concentrations (3.5-4.5 mM/l at 20-30 W and 8-11 mM/l after maximal exertion) indicate that the blood flow in the arm muscles was not adequate.
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PMID:Oxygen uptake and cardiac output in graded arm exercise in paraplegics with low level spinal lesions. 59 87

Externally recorded systolic time intervals (STI's), indirect (CO2 re-breathing) cardiac output, and auscultatory blood pressures were measured during upright bicycle ergometer work in 20 healthy men, aged 24-56 yr. The subjects were studied on 2 separate days at steady-state work loads chosen to represent light (mean heart rate (HR) = 96 beats.min-1), moderate (HR = 118 beats.min-1) and heavy (HR = 147 beats.min-1) exercise. In addition to determinations of cardiac output, systolic time intervals, and blood pressure, the individual's mean systolic ejection rate (stroke volume/left ventricular ejection time) was calculated as a measure of left ventricular function. In general, heart-rate-corrected STI's were found to be reliable and reproducible. Reliability coefficients for total electromechanical systole and left ventricular ejection time ranged from 0.93 to 0.96 while those for the preejection period and its subcomponents were between 0.63 and 0.88. The reliability of cardiac output, stroke volume, mean systolic ejection rate, and systolic blood pressure was also considered to be acceptable but tended to be higher during moderate and heavy work (r = 0.85-0.95) compared to light exercise (r = 0.60-0.83).
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PMID:Reliability of noninvlasive methods for measuring cardiac function in exercise. 62 1

Cerebral cortical blood flow was measured in rabbits with the hydrogen clearance technique. The reactivity to CO2, tested by changing the end tidal CO2 (ETCO2) in steps from 2 to 6 volumes %, was highly dependent on the kind of anesthesia, being greatest under halothane and least under nitrous oxide. Reactivity to CO2 in halothane-anesthetized animals also depended on arterial blood pressure, being greatest when pressure was below 70 mm Hg. Intravenous atropine blocked the increase in reactivity in halothane-anesthetized animals at low blood pressures. Conversely, intravenous eserine (physostigmine) greatly increased the reactivity to CO2 in nitrous oxide-anesthetized animals. Precollicular decerebration considerably decreased CO2 reactivity of halothane-anesthetized rabbits, while partial brain stem lesions that spared midline structures had no effect on CO2 reactivity. It is concluded that a central neurogenic mechanism with a cholinergic link may be responsible, at least in part, for the cerebrovascular effect of CO2. Moreover, the cerebrovascular effects of halothane may result from stimulation of the same system.
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PMID:Cerebrovascular CO2 reactivity: role of a cholinergic mechanism modulated by anesthesia. 64 10

Pregnant Pygmy goats were trained to walk on a treadmill up a 10 degree grade at a rate of 1.5 mile/hr for 10 min. Hemodynamic measurements were made in duplicate during late pregnancy and postpartum, at rest and after 3 min of exercise. All kids were weighed within 12 hr of delivery to assess the effect of exercise on fetal growth. Pulse rate, cardiac output and oxygen consumption were higher during pregnancy than postpartum, at rest and also during exercise. Stroke volume increased significantly with exercise. Peripheral vascular resistance (pvr) at rest was lower during pregnancy than postpartum, and decreased significantly during exercise, especially in pregnancy. Exercise was associated with a fall in arterial P(CO2) during pregnancy and postpartum. In goats, as in humans, the increased oxygen demands of pregnancy, during exercise and at rest, are met by an increased cardiac output rather than by increased peripheral oxygen extraction. The individual birth weights of twins, triplets and quadruplets from Pygmy goats who were exercised during late pregnancy were smaller than birth weights of matched newborns from control animals.
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PMID:Responses to exercise in the pregnant pygmy goat. 66 45

Acute alterations in plasma bicarbonate concentration have minimal effects on intracerebral pH and cerebral blood flow, perhaps due to blood-brain barrier mechanisms. To test this hypothesis, the consequences of an acute rise in the plasma bicarbonate concentration were studied in anesthetized rats previously subjected to an acute pressure pulse in the carotid system with unilateral damage to the blood-brain barrier. In rats subjected to a "heavy" hypertensive insult, the hemisphere on the side of the lesion showed a lactic acidosis, edema, and a depression of cerebral blood flow. An increase in the plasma bicarbonate concentrations of 15--20 mEq/1 during 35 minutes provoked a marked rise in the total CO2 content of this hemisphere, and a further increase in the lactate concentration, but did not later the brain edema nor affect further the already very low cerebral blood flow. An increase in the lactate concentration and a decrease of cerebral blood flow in the "reference" hemisphere indicated that the lesion was not completely unilateral. In rats subjected to a "moderate" hypertensive insult the changes were less pronounced and statistically not significant for all the parameters. There results illustrate the importance of an intact blood-brain barrier for the maintenance of intracerebral pH in the face of acute alterations in plasma [HCO3]. The impaired cerebral blood flow after an acute hypertensive insult did not appear to be influenced by the intracerebral [HCO3].
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PMID:Effect of non-respiratory alkalosis on brain tissue and cerebral blood flow in rats with damaged blood-brain barrier. 67 46

Cerebrovascular autoregulation and CO2 reactivity were measured repeatedly in 3 patients with the multiple system atrophy type of autonomic insufficiency (Shy-Drager syndrome) by means of the 133Xe injection method. The degree of cerebral blood flow (CBF) dysautoregulation showed day-to-day variations in 2 of the 3 patients. The CO2 reactivity was normal or supernormal in the supine position in patients with impaired autoregulation. In the head-up position the response to CO2 was slightly suppressed in 2 of the patients, suggesting that chemical control may have tended to compensate for CBF dysautoregulation. It is concluded that the mechanism of chemical control of the cerebrovasculature is different from that which controls autoregulation and may have partially compensated for CBF dysautoregulation.
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PMID:Cerebral hemodynamics in Shy-Drager syndrome: variability of cerebral blood flow dysautoregulation and the compensatory role of chemical control in dysautoregulation. 70 33

CO2 rebreathing measurements of cardiac output have been made in 8 men and 7 women aged 60--76 years, before and immediately after participation in an 11-week endurance training programme. Initial values showed a lower heart rate than in younger subjects at a given percentage of maximum oxygen intake. Stroke volume decreased slightly over the range of 40--80% of maximum oxygen intake. Relative to younger subjects, metabolic needs were thus met to a larger extent by a widening of arterio-venous oxygen difference and redistribution of blood flow. Over the period of observation, training induced a decrease in heart rate and cardiac output at a given sub-maximum work load, with no change in stroke volume or arterio-venous oxygen difference.
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PMID:Training and oxygen conductance in the elderly. II. The cardiovascular system. 74 29

Platinum microelectrodes were used to measure H2 clearance in mouse brain, and the clearance curves were used to calculate regional cerebral blood flow (rCBF). The curves were usually biexponential, whether or not electrode placement was confined to the cortex. When calculated by the height over area method, rCBF in anesthetized mice averaged 37+/-14 and 49+/-15 ml/100 gm per minute in two successive groups where cortical placement had been made. After CO2 breathing, which raised PaCO2 to 77+/-18 torr, the mean rCBF of the latter group was elevated to 70+/-36 ml/100 gm per minute. Our basal rCBF values are lower than literature values for rats or mice, when compared with data obtained by other techniques. However, our data are comparable to rat rCBF data obtainted by others using H2 electrodes and are comparable also to data for whole brain CBF obtained by a variety of methods in larger anesthetized mammals. It is possible that H2 electrodes provide low values for supposedly "cortical" rCBF in the very small mouse brain, because is such brains the electrode is usually close enough to a slow clearing compartment for the electrode reading to be influenced by that compartment. At the same time one cannot rule out the possibility that other techniques when applied to small rodents may, on occasion, produce spuriously high values for CBF. Indeed, while some studies using the latter techniques do show unusually high values for cortical flow in these animals, other studies using similar methods do not.
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PMID:Regional cerebral blood flow in the anesthetized mouse as measured by local hydrogen clearance. 83 50


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