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

Rats maintained in a hypoxic environment during the 1st wk after birth decrease body growth and O2 consumption (VO2) and increase minute ventilation (VE). At the same time the lungs undergo changes in structure, which suggests a protection of the gas exchange area (Mortola et al. J. Appl. Physiol. 61: 1329-1336, 1986). In this study we asked to what extent these adaptive changes would persist after return to normoxia. Newborn rats were kept in 10% O2 during the 1st wk of life, then returned to normoxic breathing, and measurements were performed weekly. Body weight (BW) increased very little during the week of hypoxia, but after return to normoxia body growth was more than in control rats, and eventually BW reached the control value at 2 mo of age. Both VO2/BW (measured manometrically) and VE/BW (measured by flow plethysmography or by the barometric method) were above control in the 1st wk after hypoxia, probably reflecting the higher O2 demands of the rapidly growing animals. However, VE remained elevated even at 7-8 wk of age (i.e., postpuberty), at a time when both BW and VO2 were as in controls. Measurements of blood gases at this age indicated that the persistent hyperventilation was not due to hypoxemia and was accompanied by hypocapnia and alkalosis. Hematocrit and heart mass-to-BW ratio, elevated in hypoxia, returned to control values within 1 wk, whereas dry lung weight-to-BW ratio remained above the control values as much as during the hypoxic exposure. These results suggest that early postnatal hypoxia in the rat could have long-term effects on the regulation of breathing.
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PMID:Long-term respiratory effects of neonatal hypoxia in the rat. 336 50

The relationships between pHi (intracellular pH) and phosphate compounds were evaluated by nuclear magnetic resonance (NMR) in normo-, hypo-, and hypercapnia, obtained by changing fractional inspired concentration of CO2 in dogs anesthetized with 0.75% isoflurane and 66% N2O. Phosphocreatine (PCr) fell by 2.02 mM and Pi (inorganic phosphate) rose by 1.92 mM due to pHi shift from 7.10 to 6.83 during hypercapnia. The stoichiometric coefficient was 1.05 (r2 = 0.78) on log PCr/Cr against pHi, showing minimum change of ADP/ATP and equilibrium of creatine kinase in the pH range of 6.7 to 7.25. [ADP] varied from 21.6 +/- 4.1 microM in control (pHi = 7.10) to 26.8 +/- 6.3 microM in hypercapnia (pHi = 6.83) and 24.0 +/- 6.8 microM in hypocapnia (pHi = 7.17). ATP/ADP X Pi decreased from 66.4 +/- 17.1 mM-1 during normocapnia to 25.8 +/- 6.3 mM-1 in hypercapnia. The ADP values are near the in vitro Km; thus ADP is the main controller. The velocity of oxidative metabolism (V) in relation to its maximum (Vmax) as calculated by a steady-state Michaelis-Menten formulation is approximately 50% in normocapnia. In acidosis (pH 6.7) and alkalosis (pH 7.25), V/Vmax is 10% higher than the normocapnic brain. This increase of V/Vmax is required to maintain cellular homeostasis of energy metabolism in the face of either inhibition at extremes of pH or higher ATPase activity.
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PMID:Relationship between intracellular pH and energy metabolism in dog brain as measured by 31P-NMR. 359 78

To assess the role of intrapulmonary receptors on the ventilatory responses to exercise we studied six beagle dogs before and after chronic pulmonary denervation and five dogs before and after sham thoracotomies. Each exercise challenge consisted of 6 min of treadmill exercise with measurements taken during the third minute at 3.2 km/h, 0% grade, and during the third minute at 5.0 km/h, 0% grade. Inspiratory and expiratory airflows were monitored with a low-dead-space latex mask and pneumotachographs coupled to differential pressure transducers. Both pre- and postsurgery, all dogs exhibited a significant arterial hypocapnia and alkalosis during exercise. Denervation of the lungs had no significant effect on minute ventilation at rest or during exercise, although there was a lower frequency and higher tidal volume in the lung-denervated dogs at all measurement periods. Breathing frequency increased significantly during exercise in lung-denervated dogs but to a lesser magnitude than in the control dogs. The changes that occurred in breathing frequency in all animals were due predominantly to the shortening of expiratory time. Inspiratory time did not shorten significantly during exercise following lung denervation. We conclude from these data that intrapulmonary receptors which are deafferented by sectioning the vagi at the hilum are not responsible for setting the level of ventilation during rest or exercise but are involved in determining the pattern of breathing.
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PMID:Effect of chronic pulmonary denervation on ventilatory responses to exercise. 374 50

Infants born to opiate-dependent women frequently have low birth weights and low 1- and 5-min Apgar scores. Significant postnatal problems, excluding neonatal withdrawal, can include jaundice, infection, aspiration pneumonia, transient tachypnea, and hyaline membrane disease. Neonatal abstinence may be severe and persist for as long as 3 months. Abstinence symptoms can include central nervous system hyperirritability, gastrointestinal dysfunction, respiratory distress, tremors, fever, high-pitched cry, increased muscle tone, uncoordinated sucking and swallowing reflexes, dehydration, and possible electrolyte imbalance. During the first week of life, increased respirations associated with hypocapnia and alkalosis may occur. The Brazelton Neonatal Behavioral Assessment Scale has been used to quantify the neurobehavioral effects on neonates of narcotics administered prenatally. A marked decline in mortality rates of infants born to opiate-dependent mothers is evident. In Philadelphia, infant morbidity has been related not only to the type of maternal narcotic dependence, but also to the amount of prenatal care. Infants whose mothers received prenatal care have been found to have higher birth weights similar to infants of control mothers. Although the newborn with intrauterine exposure to narcotic agents may appear normal at birth, the effects of the pharmacologic agent may not become apparent until later in development. To obtain a more favorable outcome for the high-risk mother and child involved in the problems of perinatal addiction, several recommendations are proposed.
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PMID:Effects of maternal opiate abuse on the newborn. 388 86

Studies of acutely induced hyperammonemia and chronic hyperammonemia associated with liver dysfunction suggest that cerebral blood flow (CBF) and O2 consumption (CMRO2) become uncoupled and that CMRo2 may depend on arterial CO2 tension (PaCO2). We examined CBF (radiolabeled microspheres) and CMRO2 during hypercapnia (PaCO2 congruent to 74 Torr) and hypocapnia (PaCO2 congruent to 21 Torr) both before and during intravenous ammonium acetate infusion in pentobarbital-anesthetized dogs. Continuous infusion over 120 min produced stable increases of arterial ammonia levels (1,400 mumol/l) by 30 min, whereas CBF, CMRO2, and O2 extraction (measured at sagittal sinus) remained unchanged when PaCO2 was held constant (congruent to 35 Torr). Acute hyperammonemia attenuated the increase in CBF during hypercapnia by 44% and abolished the decrease in CBF during hypercapnia. Regional blood flow to pons and midbrain increased under normocapnic conditions, and midbrain blood flow increased further during hypocapnia. Sodium acetate infusion did not affect CBF responses to CO2. Thus we failed to observe an uncoupling of global CBF and CMRO2 during normocapnic hyperammonemia, or an interaction of CO2 and ammonia on CMRO2, although the increased pons and midbrain blood flow may reflect regional effects of ammonia on reticular activating system metabolism. On the basis of the literature, we suggest that the attenuated hypercapnic CBF response may arise from impaired glial regulation of extracellular potassium and bicarbonate concentrations and that lactic acid production, enhanced by combined alkalosis and hyperammonemia, may contribute to the abolition of hypocapnic vasoconstriction.
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PMID:Interaction of CO2 and ammonia on cerebral blood flow and O2 consumption in dogs. 392 Sep 20

The authors of this article studied the influence of hypoxia, on thirteen groups of male rats, at altitudes of 2 200 m; 5 000 m; and 8 000 m assimilated in a barochamber by chronic or acute exposure (from 2 hours to 21 days) upon the parameters of acid-base equilibrium. The data obtained demonstrated the development of gaseous alkalosis, which is directly proportional to the altitude and time of exposure, hypocapnia, a decrease in excess base and actual bicarbonate, as well as decreased in oxygen pressure. Adrenalin and noradrenalin administered intraperitoneally produced an acidotic effect. Adrenalectomized animals exposed to hypoxia developed mixed alkalosis-respiratory and metabolic reaction.
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PMID:A study of acid-base equilibrium in altitudinal hypoxia. 392 88

Central sleep apnea is a disorder characterized by apneic episodes during sleep with no associated ventilatory effort. More commonly than not these apneas are seen in patients who also have obstructive and mixed events. Although patients with this disorder frequently complain of insomnia and depression, frank hypersomnolence is rarely encountered. As these complaints are common ones seen in numerous clinical situations, and since sleep studies are rarely conducted to investigate their etiology, the true incidence of central sleep apnea has not been determined. The etiology of central apnea remains unknown, although the association between these breathing events and a number of other disease processes has increased our understanding of the disorder. Central apneas during sleep commonly occur after hyperventilation with the associated hypocapnic alkalosis. This occurs at high altitude when hyperventilation is induced by hypoxia and at sea level when spontaneous nocturnal hyperventilation occurs. This suggests that PCO2 is the primary stimulus to ventilation during sleep and that loss of this drive, as occurs with hypocapnia, may produce dysrhythmic breathing. Patients with complete absence of ventilatory chemosensitivity such as occurs with Ondine's curse (central alveolar hypoventilation) or the obesity-hypoventilation syndrome may also have central apneas. For reasons that remain unexplained, central sleep apnea is commonly seen in patients with congestive heart failure, nasal obstruction, and certain neurologic disorders. However, in most patients with central sleep apnea no obvious cause or association can be found. The treatment of this disorder is not entirely satisfactory. If it is severe, mechanical ventilation during sleep can be provided by any one of a number of techniques. However, for the patient who simply complains of insomnia and is found to have a moderate number of central apneas, the treatment choices are limited. Acetazolamide has been shown to decrease central apneas during short-term use, but results have been variable with prolonged administration. Other ventilatory stimulants seem to have little efficacy. Interestingly, oxygen administration has been shown to reduce central apneas considerably in a number of studies, although the explanation for its success is unknown. Central sleep apnea therefore remains a relatively rare disorder whose etiology is not fully understood and whose treatment is not completely satisfactory.
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PMID:Central sleep apnea. 393 82

Hypophosphatemia occurs in a variety of clinical conditions. It develops in parallel with phosphate depletion from body losses or more commonly as a sequel to the redistribution of phosphate from the extracellular to the intracellular compartment. Hypophosphatemia is a multisystem disturbance capable of involving the neurological, immunological, and muscular systems, among others. In this report, we describe five patients with severe head injury who developed marked hypophosphatemia (less than 1 mg/dl) within 24 hours of hospitalization. This fall in serum phosphate coincided with the induction of respiratory alkalosis consequent to mechanical ventilation. In four of the five patients, as acid-base parameters returned to normal, serum phosphate values rose, in all instances reaching values greater than 2.5 mg/dl. Urinary phosphorus excretion, ordinarily negligible after hypophosphatemia induced by hypocapnia, was still present in Cases 1 and 4 (greater than 600 mg/24 hours). This is unexplained by any of the known hormonal or fluid alterations that accompany head injury. These five patients developed severe, yet transient, hypophosphatemia that resolved upon correction of hyperventilation-induced acid-base abnormalities. We discuss the pathophysiology of this entity and the implications for the head trauma patient.
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PMID:Severe hypophosphatemia after head injury. 402 85

Altogether 228 patients with hereditary microspherocytic anemia (HMA), autoimmune hemolytic anemia (AIHA) and hypoplastic anemia (HA) were examined over time for the acid-base state of the arterial blood with the use of the pCO2-buffer bases coordinate system (BE/pCO2 and pCO2/BE diagrams). Prior to surgery the respiratory alkalosis was diagnosed in 60% of HMA patients (of these, 41.7% of patients had a decompensated alkalosis), in 61.7% of AIHA patients (73%), and in 69.7% of HA patients (82.1%). It is shown that the development in the patients of chronic respiratory alkalosis should be regarded as a compensatory mechanisms associated with hemic hypoxia complicated by arterial hypoxemia. During splenectomy, there was an increase in the incidence of decompensated respiratory alkalosis. Mixed respiratory and metabolic alkalosis occurred in 8.3% of AIHA patients and in 19.6% of HA patients because of artificial ventilation of the lungs. Two hours after operation compensated metabolic acytosis was identified in 72% of HMA patients, in 33.3% of AIHA patients, and in 33.9% of HA patients. Twenty-four hours following operation the patients of all the groups had arterial hypoxemia and hypocapnia. In view of this fact the blood acid-base state was determined by the presence of respiratory alkalosis: in 47.5% of patients with HMA, in 60% of patients with AIHA, and in 54% of patients with HA. Analysis of the BE/pCO2 diagram demonstrated that in 2/3 of the patients with HMA and AIHA and in all the patients with HA, respiratory alkalosis was decompensated. It was established that electrolyte imbalance detected in the patients interfered with metabolic compensation for chronic respiratory alkalosis.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Mechanisms of compensation of disorders of acid-base status of the blood in patients with chronic anemia]. 404 71

1. Birds lose water in evaporation from the respiratory tract and, in many species, through the skin. Anatomical arrangements in the nasal passages to conservation of water and hear from the expired air in the absence of heat loads. However, most species still expend more water in evaporation than they produce in metabolism when either quiescent or vigorously active. Certain small birds, several of them associated with arid environments, represent exceptions to this and their more favorable situation appears in part to reflect as an ability to curtail cutaneous water loss. 2. Birds typically resort to panting in dealing with substantial heat loads developing in hot environments or accumulated over bouts of activity. In a number of species this form of evaporative cooling is supplemented by gular fluttering. 3. The ubiquitousness of active heat defense appears to reflect more the importance for birds of dealing with heat loads existing following flight or sustained running than any universal affinity for hot climates. Panting can be sustained for hours, despite progressive dehydration and, in some instances, hypocapnia and respiratory alkalosis. The prominent involvement of thermoreceptors in the spinal cord in its initiation is of considerable interest.
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PMID:Evaporative losses of water by birds. 612 38


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