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Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Changes in ventilation volume (Vg) of rainbow trout caused by hypercapnia, hypoxia and anaemia were measured directly by collection of expired water. 2. Exposure to hypercapnic water (PCO2 range 0.5-2 kPa) increased Vg (by up to four times) by augmenting ventilatory stroke volume; breathing frequency remained constant. O2 added to the inspired water in maintained hypercapnia reduced Vg at all but the highest level of PCO2. 3. Vg increased when blood oxygen content was decreased by exposure to normoxic hypercapnia, but addition of O2 to the water increased blood oxygen content and Vg decreased. 4. When blood oxygen-carrying capacity was depressed by hypoxia or anaemia, Vg increased as it did during normoxic hypercapnia. 5. We suggest that ventilatory responses to low levels of hypercapnia, to hyperoxic hypercapnia, to hypoxia, and to anaemia in trout are related to changes in levels of blood oxygen content under these conditions.
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PMID:The effect of changes in blood oxygen-carrying capacity on ventilation volume in the rainbow trout (Salmo gairdneri). 680 26

Cardiovascular responses to cessation of respiration and to progressive hypoxia and hypercapnia were investigated noninvasively in eight male volunteers. A total of five 90-s breath holds (BH) with face immersion were performed by each subject. A continuous BH (BH-1) eliminated the circulatory effects of respiratory movements, BH with air (BH-3) or with O2 (BH-5) with rebreathing at 15-s intervals through a CO2 scrubber reduced the effect of hypercapnia, and BH with air (BH-2) or with O2 (BH-4) with rebreathing at 15-s intervals bypassing the CO2 scrubber produced hypercapnia with or without concomitant hypoxia. Mean arterial blood pressure rose continuously in BH-1 and BH-2 and to a much lesser degree in other BHs. Vasoconstriction was evident within 30 s of BH. Determined by impedance cardiograph, stroke volume (SV) rose by 33%, which was balanced out by a 30% reduction in heart rate (HR) from the pre-BH values, at the end of a continuous BH. A transient depression of cardiac output (CO) was observed at 30 and 60 s of BH-1. CO values were maintained at pre-BH levels throughout the BHs where progressive hypercapnia occurred (BH-2 and BH-4) but were depressed to a similar degree as BH-1 when hypercapnia was prevented (BH-3 and BH-5). Alveolar CO2 levels were found to be correlated linearly and positively with SV, HR, and CO. No such relationship existed between alveolar O2 levels and these hemodynamic parameters. Thus rebreathing and hypercapnia during BH prevented CO from falling during BH. It is reasoned that hypercapnia and consequent acidosis, through enhanced sympathoadrenal release of catecholamines, was responsible for the compensatory SV response.
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PMID:Effects of hypercapnia, hypoxia, and rebreathing on circulatory response to apnea. 682 1

This investigation tests the hypothesis that the normal cerebral image obtained non-invasively during continuous inhalation of C15O2 is related to cerebral blood flow. Trace amounts of CO2 labeled with the positron-emitting radionuclide 15O were administered to 4 normal subjects at normo- and hypocapnia and to 2 of these subjects at hypercapnia. Hypocapnia typically caused a marked decrease in cerebral 15O activity, and hypercapnia a small increase in activity. The relative difference in the change in count rate in response to hypo- and hypercapnia is what one would expect if the activity represented bloow flow, according to a mathematical model which assumes the 15O label enters the brain as water of perfusion. The findings in this study suggest that the normal cerebral image obtained during continuous inhalation of C15O2 is related to cerebral blood flow, but in a non-linear fashion, and that the technique would be more sensitive to ischemic events than to hyperemic phenomena.
Stroke
PMID:Positron imaging of cerebral blood flow during continuous inhalation of C15O2. 696 50

Catecholamine cardiomyopathy (CM) was produced in rabbits by a 90-min infusion of norepinephrine (NE, 2 micrograms . kg-1 . min-1). Left ventricular (LV) contractility and pump function (VF) were examined 2 days later and compared with control animals. The effects of hypercapnia [CO2 tension (PCO2) greater than 70 mmHg] and inotropic responsiveness to NE were also determined. VF was assessed by means of left ventricular function curves obtained with constant aortic pressure and heart rate and quantified by determining stroke volume at left ventricular end-diastolic pressure of 10 cmH2O (SV10). Mean SV10 was 1.16 +/- 0.06 ml in controls but averaged only 0.93 +/- 0.05 in CM (P less than 0.02). Hypercapnia caused significantly greater depression of VF in CM than in controls. NE dose-response curves demonstrated increases in both LV dP/dtmax and SV10 in each group. The percent increase in LV dP/dtmax was markedly attenuated n CM, but the increments in SV10 did not differ. The mean histological score in the CM animals was 1.6 +/- 0.1, indicating extensive myofiber injury. No histological abnormalities were observed in the controls. Thus functional defects correlated with the presence of histopathological changes. In addition, a dissociation of velocity (dP/dtmax) and force (SV10) responsiveness to inotropic stimulation was identified in the CM group.
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PMID:Ventricular function in norepinephrine-induced cardiomyopathic rabbits. 706 51

From 1969 through 1973, 335 consecutive patients (mean age, 60 years) underwent 390 carotid endarterectomies using hypercarbic general anesthesia and no carotid shunting. Early neurologic complications were most common among patients with previous neurologic symptoms and among those with subtotal stenosis or occlusion of the contralateral internal carotid artery. The introduction of routine carotid shunting without hypercarbia during a subsequent series of 626 procedures from 1974 through 1978 has been associated with significantly fewer operative strokes in comparable groups of patients. Complete follow-up information during a mean interval of 8.6 years is available for 95% of 325 operative survivors. Late completed strokes have occurred in 17% of patients but have involved the cerebral hemisphere on the side of previous carotid endarterectomy in only 7%. Of 93 operative survivors who had subtotal stenosis of the contralateral internal carotid artery, 45 underwent contralateral endarterectomy as an elective procedure and 48 did not. The late contralateral stroke rates for these two groups of patients were 4% and 16%, respectively, although these differences did not attain statistical significance. Forty-nine (78%) of 63 patients with contralateral internal carotid occlusion have had no late neurologic symptoms following unilateral carotid endarterectomy.
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PMID:Postoperative stroke and late neurologic complications after carotid endarterectomy. 731 53

Superior sagittal sinus pressure, intracranial pressure and arterial pressure were recorded in an experimental series on 10 cats. During drug-induced, severe, acute arterial hypertension and parallel hypercapnia, venous pressure could exceed intracranial pressure in both the supra- and infratentorial compartment. From these data it is concluded that cerebral venous pressure during acute arterial hypertension may contribute to protein extravasation at the postcapillary-venular level.
Stroke
PMID:Cerebral venous pressure during actively induced hypertension and hypercapnia in cats. 736 47

The purpose of this study was to investigate the respiratory and heart rate (fH) responses to tethered controlled frequency breathing (CFB) swimming. Controlled frequency breathing swimming is an aquatic training technique in which ventilatory rate is voluntarily reduced in order to induce systemic hypoxia during training. Nine elite college swimmers experienced with CFB were studied. The tethered swimming tests were discontinuous, with 4 min work bouts interspersed with equal duration rest periods. The resisting forces during tethered swimming were 5.63, 6.82, and 7.95 kg. Each subject was tested breathing every two (control), three, four, and five arm strokes. Subjects performed all four breathing frequencies at a constant arm stroke rate of 30/min during freestyle swimming. As ventilatory volume decreased due to CFB, O2 extraction and estimated tidal volume significantly increased (P less than .05) to maintain a constant O2 consumption for a given workload. Carbon dioxide production, respiratory exchange ratio, and fH did not change significantly in response to CFB. Estimated alveolar partial pressure of O2 (PAO2) decreased and PACO2 increased significantly during CFB. However, estimated saturation of arterial blood with O2 (SAO2) was essentially undiminished during CFB. These responses do not indicate hypoxia, but rather hypercapnia during CFB.
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PMID:Respiratory and heart rate responses to tethered controlled frequency breathing swimming. 739 97

Circulatory and respiratory effects of alveolar concentrations of 1.31, 1.97, and 2.62 vol% of isoflurane in oxygen were studied in eight young, healthy horses during spontaneous and controlled ventilation. These isoflurane concentrations were equivalent, respectively, to 1.0, 1.5, and 2.0 times the minimal alveolar concentration of isoflurane, which prevents movement in horses in response to a standard pain stimulus. Results of the isoflurane studies were compared with similarly derived findings in these same horses during equipotent halothane in oxygen anesthesia. Isoflurane, similar to halothane, produced a dose-related depression of cardiovascular function which was less severe during spontaneous ventilation and associated hypercapnia. The two anesthetic agents produced similar circulatory effects during controlled ventilation and constant arterial carbon dioxide tension except for a significantly (P less than 0.05) less depressed cardiac output/kg of body weight and stroke volume that occurred with minimal alveolar concentration 1.5 and 2.0 isoflurane. Total peripheral resistance was greatest when these horses were anesthetized with halothane regardless of the alveolar dose. In horses, isoflurane was, in general, no more depressing than was halothane to circulatory and respiratory function.
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PMID:Comparison of circulatory and respiratory effects of isoflurane and halothane anesthesia in horses. 740 5

Controversy has been raised about the effects of systemic carbon dioxide accumulation versus the intra-abdominal pressure on hemodynamics during laparoscopy. We compared the acid-base and hemodynamic changes during pneumoperitoneum in a randomized cross-over study between CO2 and nitrogen gases to test the hypothesis that the CO2 absorbed during laparoscopy, rather than the 15 mmHg intra-abdominal pressure created, accounted for these changes. Eight adult pigs were anesthetized and ventilated with a fixed minute ventilation. Metabolic function was measured from analysis of expired flow by a metabolic measurement cart. After baseline periods, animals were randomized into two groups, for 2 hr of either CO2 or nitrogen pneumoperitoneum at 15 mmHg intra-abdominal pressure, followed by 1 hr of recovery. After at least a 48-hr recovery period, the experiment was repeated with the other gas. Metabolic data revealed that there was a significant absorption of CO2 gas across the peritoneal epithelium during CO2 pneumoperitoneum. Animals insufflated with CO2 gas experienced a 75% increase in pulmonary CO2 excretion, with significant acidemia and hypercapnia, whereas there were no acid-base disturbances in those with nitrogen insufflation. Oxygen consumption remained essentially unchanged in both groups, even during pneumoperitoneum. CO2 pneumoperitoneum was also associated with systemic and pulmonary arterial hypertension and a reduction in stroke volume of up to 15%. Pneumoperitoneum alone did not compromise hemodynamics. Pneumoperitoneum using CO2 gas during laparoscopy resulted in systemic CO2 absorption across the peritoneum. This led to acidemia, hypercapnea, and depressed hemodynamics. The intra-abdominal pressure routinely used during laparoscopic surgery did not affect metabolic function, acid-base balance, or hemodynamics in the experimental model.
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PMID:Effector of hemodynamics during laparoscopy: CO2 absorption or intra-abdominal pressure? 756 24

We measured cerebral vasomotor reactivity during normoventilation, hyperventilation (hypocapnia), and breathing of 6% CO2 (hypercapnia) in 20 normal subjects during the hours of 6 to 8 AM, 1 to 3 PM, and 7 to 9 PM. Cerebral vasomotor reactivity was calculated, using transcranial Doppler, as percent change in the mean blood flow velocity of the middle cerebral artery per mm Hg change in end-tidal CO2 during hypocapnia and hypercapnia. Vasomotor reactivity during hypercapnia was lower in the morning (1.72 +/- 0.66 %/mm Hg) than in the afternoon (2.34 +/- 0.74 %/mm Hg, p < 0.01) and evening (2.31 +/- 0.56 %/mm Hg, p < 0.001). Vasomotor reactivity during hypocapnia did not vary significantly during the three periods (2.34 +/- 0.59 %/mm Hg in the morning, 2.43 +/- 0.51 %/mm Hg in the afternoon, and 2.26 +/- 0.52 %/mm Hg in the evening). This reduced morning response to hypercapnia suggests diminished vasodilator reserve during this period, and may be related to the increased stroke risk during the morning hours.
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PMID:Morning reduction of cerebral vasomotor reactivity. 793 45


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