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Query: UMLS:C0085383 (hypocapnia)
 1,697 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We examined the bronchoconstriction produced by airway hypocapnia in normal subjects. Maximal expiratory flow at 25% vital capacity on partial expiratory flow-volume (PEFV) curves fell during hypocapnia both on air and on an 80% helium- 20% oxygen mixture. Density dependence also fell, suggesting predominantly small airway constriction. The changes seen on PEFV curves were not found on maximal expiratory flow-volume curves, indicating the inhalation to total lung capacity substantially reversed the constriction. Pretreatment with a beta-sympathomimetic agent blocked the response, whereas atropine pretreatment did not, suggesting that hypocapnia affects airway smooth muscle directly, not via cholinergic efferents.
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PMID:Pattern and mechanism of airway response to hypocapnia in normal subjects. 46 77

Extensive and severe bronchiectasis was found in 7 heroin-addicted individuals with pulmonary symptoms whose chest roentgenograms were not suggestive of severe airway disease. Abnormalities consisted of varicose and cylindrical alterations. Pulmonary function tests revealed airflow obstruction, decreased lung volumes, and diffusion capacity impairment. Arterial blood gas analysis demonstrated mild hypoxemia in all patients and chronic hypocapnia in 4. Serial pulmonary function tests in 2 patients revealed only modest improvement in the degree of airflow obstruction. The occurence of bronchiectasis appeared to be related to episodes of heroin-induced pulmonary edema and infection.
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PMID:Bronchiectasis: a cause of pulmonary symptoms in heroin addicts. 47 3

Ventilation, laryngeal resistance and electromyograms of the diaphragm, posterior cricoarytenoid (PCA) and thyroarytenoid (TA) muscles were recorded in anesthetized, spontaneously breathing cats during 100% O2 administration and during steady state inhalation of hypercapnic and hypoxic gas mixtures. As shown previously, hyperoxic hypercapnia lowered expiratory laryngeal resistance (RlarE). Isocapnic hypoxia also lowered RlarE, and hypercapnia superimposed on hypoxia decreased it further. Hypocapnia raised RlarE. Changes in inspiratory laryngeal resistance (RlarI) were similar to those in RlarE, but smaller. When ventilation was stimulated to the same extent by hypoxia and by hypercapnia, RlarE was lower under hypoxic than hypercapnic conditions in most animals. The electromyograms showed that the respiratory oscillations in laryngeal resistance and the laryngeal responses to hypercapnia and hypoxia were determined chiefly by the activity of the PCA muscle, the abductor of the vocal cords. The TA-a representative adductor muscle-was silent under all conditions studied. The results, considered with previous work, indicate that the larynx plays a part in determining the breathing pattern under resting conditions and during respiratory stimulation by hypercapnia and hypoxia.
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PMID:Effects of hypercapnia and hypoxia on laryngeal resistance to airflow. 49 50

Hypocapnia was induced in dogs lightly anaesthetized with nitrous oxide and fentanyl. Measurements were made of estimated renal plasma flow (ERPF), glomerular filtration rate, vascular resistance and urine production. During the (short) duration of the experiments hypocapnia was found to be associated with ERPF twice that during normocapnia. Glomerular filtration rate and urine output were increased by hypocapnia in an approximately similar proportion, whilst renal vascular resistance halved. Though some of the experimental animals had a degree of metabolic acidosis this was thought not to have greatly influenced the results.
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PMID:Effect of acute hypocapnia on some aspects of renal function in anaesthetized dogs. 49 69

The responses to hypocapnia and to hypercapnia of both the systemic and the coronary circulations have been studied in the dog during intermittent positive pressure ventilation under halothane anaesthesia. In the absence of significant variations of myocardial contractility, the reduction of cardiac output, because of hypocapnia, was determined by the increase of systemic vascular resistance, while the increase of cardiac output because of hypercapnia was determined by an increase of heart rate without change of stroke volume. The alterations of coronary blood flow (reduction following hypocapnia, augmentation following hypercapnia) were considerably larger than the changes of cardiac output and of myocardial oxygen consumption. Such disparity between oxygen supply and demand, together with the effect of pH and PCO2 on the oxyhaemoglobin dissociation curve led to a marked reduction of coronary sinus PO2 in response to hypocapnia and a marked increase of coronary sinus PO2 in response to hypercapnia. The data suggests that PCO2 (or respiratory alterations of pH) may have a direct effect on the regulation of coronary blood flow. The low coronary sinus PO2 observed at hypocapnia may suggest the risk of myocardial ischaemia.
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PMID:Effect of CO2 on the systemic and coronary circulations and on coronary sinus blood gas tensions. 49 91

The effect of various cardiovascular reflexes and reactions on the plethysmographically recorded penile volume in rabbit was investigated. Stimulation of the aortic nerve or direct stimulation of the carotid sinus produced increase in penile volume, while carotid occlusion produced decrease. Brief volume load or protoveratrine given into the right atrium produced increase in penile volume. Asphyxia, hypercapnia, hypoxia, cyanide and lobeline produced decrease in penile volume, while hypocapnia increased it. Moderate blood taps decreased penile volume, while hypocapnia increased it. Moderate blood taps decreased penile volume. With the exception of the response to asphyxia all these reactions required intact vasomotor nerves. Clonidine increased penile volume if vasomotor nerves were intact but decreased it if the penis was decentralized. Penile volume decreased in shivering animals but increased on warming. Carotid occlusion impaired erectile responses to hypogastric and pelvic nerve stimulation. In certain experiments this effect was more pronounced in the latter case. It is concluded that the medullary neuron pool responsible for penile vasomotor tone participates in general reflex cardiovascular homeostasis and that this may have implications for normal erectile responses.
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PMID:Changes in penile volume during some cardiovascular reflexes and reactions in rabbit. 50 67

Cerebral vasoconstrictive capacitance was measured during voluntary hyperventilation hypocapnia in 22 healthly normal volunteers aged 21--65 years by serial 133Xe inhalation estimates of rCBF by the initial slope index method of Risberg (ISI2) in the steady state followed by the hypocapnic state. End-tidal PCO2 was monitored by a capnograph. There was significant linear correlation between reduction of PECO2 and the ISI2 values. Significant reduction of cerebral vasoconstrictive response to hypocapnia was found with normal advancing age which is attributed to (1) minor atherosclerosis or loss of elasticity of cerebral vessels with advancing age, (2) the presence of an ischemic threshold during hyperventilation at which CBF tends to stabilize.
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PMID:Normal human aging and cerebral vasoconstrictive responses to hypocapnia. 51 93

A marked increase in the prostaglandin E (PGE) content in the cerebrospinal fluid (CSF) and the arterial blood of cats was observed under conditions of 3-minute hypocapnia. During 30-minute hypocapnia a restoration of the initial PGE level was seen. The PGE content in CSF increased while in the arterial blood it decreased comparatively to the control under conditions of 3-minute hypercapnia. In 30-minute hypercapnia the PGE amount in the CSF and the blood dropped in comparison with 3-minute hypercapnia being below the basal level in the blood. It is suggested that in hypocapnia PGE should limit its constrictive effect on the cerebral vessels while under conditions of hypercapnia they are to promote the realization of the cerebral vessel reaction to CO2.
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PMID:[Variations in prostaglandin E content in the arterial blood and cerebrospinal fluid under conditions of hypo- and hypercapnia]. 51 23

During sleep, of ventilated newborns and young infants, spontaneous respiratory movements may occur, unrelated to the ventilation impulsions. The respiratory pattern is then classified as "active". On the contrary, the respiratory pattern is classified as "passive", when all respiratory movements are related to the ventilation insufflation. The factors which influence the dependence on the ventilator are studied in a group of 20 newborn and young infants. Prematurity, some biological data such as hyperoxia, hypocapnia, seem to favor this dependence. A rapid rate of ventilation (superior to 30/minute) is rarely related to an active respiration; a slow rate of ventilation seems favor this respiratory pattern. It is clear that adaptation to artificial ventilation is better during quiet sleep than during active sleep. Some physiopathological considerations are developed.
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PMID:[Assisted ventilation of newborn infants during sleep. Study of factors modifying adaptation to ventilation]. 52 40

The reactivity of subpleural strips of lung parenchyma reflects primarily the tone of the smooth muscle in the peripheral airways. Lung strips taken from ten dogs relaxed when the oxygen level in the gas bubbling through the bath was reduced from 95% to 18%. Subsequent hypocapnia (carbon dioxide reduced from 5% to 0%) induced contraction of all strips. These changes were reversed when the oxygen or carbon dioxide tensions were restored to control levels. Addition of either indomethacin or meclofenamate, two chemically dissimilar inhibitors of prostaglandin synthetase, reduced the resting tone in each of six strips and prevented the hyperoxic constriction which was observed in paired, control strips (oxygen increased from 18% to 95%). Blockers of histamine and catecholamines had no effect. The reactivity of the distal airways to changes in gas tension provides a mechanism by which ventilation and perfusion can be matched. The action of indomethacin and meclofenamate indicates that a prostaglandin-like substance may be involved in the maintenance of distal airway tone and in the constriction produced by hyperoxia. The addition of prostaglandin F2 alpha or E1, after meclofenamate, in a further nine pairs of strips did not restore the hyperoxic constriction. This suggests that prostaglandins may mediate, rather than merely facilitate, the response.
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PMID:Distal airway responses to changes in oxygen and carbon dioxide tensions. 52 47


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