phosphocreatine and Hyperventilation

Topics: Adenosine Triphosphatases; Anesthesia; Blood Glucose; Brain; Brain Chemistry; Carbohydrate Metabolism; Carbon Dioxide; Cerebrovascular Circulation; Electroencephalography; Hemoglobins; Humans; Hyperventilation; Hypotension, Controlled; Hypoxia; Lactates; NAD; Oxygen Consumption; Phosphocreatine

Substantial controversy persists in the literature concerning the physiologic consequences hypocapnia, or low partial pressure of carbon dioxide (PaCO(2)). Invasive animal studies have demonstrated large pH increases (>0.25 U), phosphocreatine (PCr) decreases (>30%), and adenosine triphosphate (ATP) decreases (>10%) after hyperventilation (HV) (20 mm Hg PaCO(2)). However, using magnetic resonance spectroscopy, HV studies in awake humans have demonstrated only small pH changes ( approximately 0.05 U) and no changes in PCr or ATP. It remains important to ascertain whether this failure to detect PCr changes in human studies reflects a true absence of changes, or a limitation in data fidelity. The present study used a rapidly interleaved phosphorus-proton spectroscopy acquisition from large samples at high magnetic field (4 T), to measure pH, PCr, inorganic phosphate, beta-ATP, and lactate changes with high temporal and signal sensitivity. Five of six subjects had usable data. During 20 mins HV, PaCO(2) reached a minimum at 16 mins (17 mm Hg); however, the maximum pH change (+0.047) peaked earlier (14 mins). Maximal lactate increases were measured at 15 mins. By 10 mins, maximum changes were observed for PCr (-3.4%) and inorganic phosphate (+6.4%). No changes in beta-ATP were observed. The peak in pH, despite continued decreases in PaCO(2), suggests active buffering during HV. These data, and the small magnitude of early PCr and inorganic phosphate changes, do not support substantial energy compromise during HV. Other mitigating factors, such as anesthesia-induced deregulation of the cerebrovasculature, might have contributed to the exaggerated metabolic changes observed in previous animal investigations.

Topics: Adenosine Triphosphate; Adult; Brain; Female; Humans; Hydrogen-Ion Concentration; Hyperventilation; Hypocapnia; Lactic Acid; Magnetic Resonance Spectroscopy; Male; Phosphates; Phosphocreatine; Phosphorus; Protons

The effects of controlled voluntary hyperventilation (Hyp) on phosphocreatine (PCr) kinetics and muscle deoxygenation were examined during moderate-intensity plantar flexion exercise. Male subjects (n = 7) performed trials consisting of 20-min rest, 6-min exercise, and 10-min recovery in control [Con; end-tidal Pco(2) (Pet(CO(2))) approximately 33 mmHg] and Hyp (Pet(CO(2)) approximately 17 mmHg) conditions. Phosphorus-31 magnetic resonance and near-infrared spectroscopy were used simultaneously to monitor intramuscular acid-base status, high-energy phosphates, and muscle oxygenation. Resting intracellular hydrogen ion concentration ([H(+)](i)) was lower (P < 0.05) in Hyp [90 nM (SD 3)] than Con [96 nM (SD 4)]; however, at end exercise, [H(+)](i) was greater (P < 0.05) in Hyp [128 nM (SD 19)] than Con [120 nM (SD 17)]. At rest, [PCr] was not different between Con [36 mM (SD 2)] and Hyp [36 mM (SD 1)]. The time constant (tau) of PCr breakdown during transition from rest to exercise was greater (P < 0.05) in Hyp [39 s (SD 22)] than Con [32 s (SD 22)], and the PCr amplitude was greater (P < 0.05) in Hyp [26% (SD 4)] than Con [22% (SD 6)]. The deoxyhemoglobin and/or deoxymyoglobin (HHb) tau was similar between Hyp [13 s (SD 8)] and Con [10 s (SD 3)]; however, the amplitude was increased (P < 0.05) in Hyp [40 arbitrary units (au) (SD 23)] compared with Con [26 au (SD 17)]. In conclusion, our results indicate that Hyp-induced hypocapnia enhanced substrate-level phosphorylation during moderate-intensity exercise. In addition, the increased amplitude of the HHb response suggests a reduced local muscle perfusion in Hyp compared with Con.

Topics: Adult; Ankle Joint; Exercise Test; Humans; Hyperventilation; Kinetics; Male; Metabolic Clearance Rate; Muscle Contraction; Muscle, Skeletal; Oxidation-Reduction; Oxygen; Oxygen Consumption; Phosphocreatine; Physical Exertion

To clarify the changes that occur during marked hypocarbia in the neonate, we measured brain blood flow and metabolite levels after 90 minutes of hyperventilation in neonatal dogs. Brain blood flow decreased significantly in diencephalon, brainstem, and spinal cord but not in cerebral cortex or white matter. There was no substantial change in the electroencephalogram. Lactate concentrations, both in telencephalon and in superior sagittal sinus blood, increased significantly, although there was no alteration in levels of ATP or phosphocreatine. Marked hypocarbia in the neonatal dog produces an elevated brain lactate level that may be related to changes in glycolytic rate rather than to tissue ischemia or hypoxia.

Topics: Adenosine Triphosphate; Animals; Animals, Newborn; Blood Glucose; Brain; Brain Ischemia; Carbon Dioxide; Cerebrovascular Circulation; Dogs; Electroencephalography; Energy Metabolism; Female; Hydrogen-Ion Concentration; Hyperventilation; Lactates; Lactic Acid; Male; Phosphocreatine

The effect of a stepwise decrease in PaCO2 from 3.9-1.6 kPa on rCBF, rCMRO2, tissue PO2 and concentrations of glucose, lactate, pyruvate, ATP, ADP, AMP and phosphocreatine in the brain cortex was studied in cats lightly anaesthetized with sodium pentobarbital. 1. Moderate lowering of PaCO2 to 2.5 kPa induced in all animals a homogeneous decrease of rCBF in corresponding areas of the right and left hemisphere. Mean rCBF fell from 129.2 to 103.1 ml X 100 g-1 X min-1, while rCMRO2 remained unchanged (12.7-12.9 ml X 100 g-1 X min-1). The tissue PO2 frequency histograms showed a shift to lower values without indicating the presence of brain tissue hypoxia. 2. Severe arterial hypocapnia (PaCO2 = 1.6 kPa) caused an inhomogeneous blood flow reaction. Both further decreased as well as increased rCBF values were measured simultaneously in the brain cortex of individual animals (mean rCBF = 97.6 ml X 100 g-1 X min-1). At the same time tissue PO2 measurements and metabolite assays indicated the presence of pronounced brain tissue hypoxia. The tissue concentrations of lactate and pyruvate and the lactate/pyruvate ratio were significantly increased, while the phosphocreatine concentration was significantly reduced. In addition, rCMRO2 decreased to 11.3 ml X 100 g-1 X min-1. The results provide conclusive evidence that severe arterial hypocapnia leads to an insufficient O2 supply of the brain cortex, which in turn seems to counteract the influence of hypocapnia on cortical blood flow regulation.

Topics: Adenine Nucleotides; Animals; Carbon Dioxide; Cats; Cerebral Cortex; Cerebrovascular Circulation; Glucose; Hyperventilation; Lactates; Lactic Acid; Oxygen; Oxygen Consumption; Phosphocreatine; Pyruvates; Pyruvic Acid; Vascular Resistance

Hypocapnia of moderate and extreme degree (Paco2 21.1 and 13.5 torr, respectively)was induced by hyperventilation in rats subjected to the closed system of Lowry inorder to evaluate the effects on utilization rate of cerebral energy metabolites. The tissue levels of high-energy phosphates and calculated intracellular pH did not change, whereas glucose, pyruvate, and lactate increased significantly. The La/Pyratio and NADH/NAD-+ RATIO BOTH INCREASED IN PROPORTION TO THE DEGREE OF HYPOCAPNIA. Utilization rates of glucose, glycogen, and ATP were all significantly reduced by hypocapnia, whereas the utilization rate of phosphocreatine was increased. The rate oftotal high-energy phosphate use was also diminished in proportion to the degree of hypocapnia. The constant value of the energy charge (0.94 plus or minus 0.01) indicates that the energy production rate might also be reduced by hyperventilation; thus the intermediate metabolics and substrates increased. It is concluded that extreme hypocapnia reduces the rate of cerebral energy metabolism significantly.

Topics: Adenosine Triphosphate; Animals; Body Temperature; Brain; Carbon Dioxide; Energy Metabolism; Glucose; Hydrogen-Ion Concentration; Hyperventilation; Lactates; NAD; Partial Pressure; Phosphates; Phosphocreatine; Pyruvates; Rats

Topics: Adenine Nucleotides; Anesthesia, General; Animals; Brain; Carbon Dioxide; Citric Acid Cycle; Depression, Chemical; Glycolysis; Halothane; Hydrogen-Ion Concentration; Hypercapnia; Hyperventilation; Lactates; Male; Nitrous Oxide; Organophosphorus Compounds; Phenobarbital; Phosphocreatine; Pyruvates; Rats; Stimulation, Chemical

Topics: Acid-Base Equilibrium; Alkalosis, Respiratory; Ammonia; Animals; Bicarbonates; Blood; Brain; Carbon Dioxide; Energy Metabolism; Glucose; Hydrogen-Ion Concentration; Hyperventilation; Ketoglutaric Acids; Lactates; Malates; Partial Pressure; Phosphocreatine; Pyruvates; Rats; Ribonucleotides

Topics: Acid-Base Equilibrium; Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Blood; Blood Pressure; Body Water; Brain; Carbon Dioxide; Cerebrospinal Fluid; Cytoplasm; Energy Metabolism; Glucose; Hydrogen-Ion Concentration; Hyperventilation; Lactates; Male; Oxygen; Partial Pressure; Phosphocreatine; Pyruvates; Rats; Temperature; Time Factors

Topics: Adenine Nucleotides; Adenosine Triphosphate; Alkalosis; Animals; Bicarbonates; Brain Chemistry; Carbon Dioxide; Hydrogen-Ion Concentration; Hyperventilation; Lactates; Male; NAD; Nitrous Oxide; Oxygen; Partial Pressure; Phosphocreatine; Pyruvates; Rats; Sodium Chloride

Topics: Adenine Nucleotides; Animals; Brain; Brain Chemistry; Carbon Dioxide; Carbonates; Cerebrovascular Circulation; Halothane; Hydrogen-Ion Concentration; Hyperventilation; Hypotension; Lactates; Male; Oxygen; Phosphocreatine; Pyruvates; Rats; Regional Blood Flow

Topics: Acid-Base Equilibrium; Adenine Nucleotides; Animals; Brain Injuries; Humans; Hypercapnia; Hyperventilation; Hypoxia; Intracranial Pressure; Lactates; Phosphocreatine; Pyruvates; Rats; Time Factors

Topics: Animals; Blood Pressure; Brain; Carbon Dioxide; Hydrogen-Ion Concentration; Hyperventilation; Lactates; Male; Oxygen; Partial Pressure; Phosphocreatine; Pyruvates; Rats

Topics: Adenine Nucleotides; Adenosine Triphosphate; Animals; Bicarbonates; Brain; Brain Chemistry; Carbon Dioxide; Cats; Creatinine; Female; Hypercapnia; Hyperventilation; Hypoxia, Brain; Lactates; Male; Phosphocreatine; Pyruvates