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

The effects of hyper- and hypocapnia on oxidative metabolism were evaluated by near-infrared (NIR) multiwavelength spectroscopy in intact brain and skeletal muscle tissues of the anesthetized cat. A 3-wavelength NIR algorithm was used to monitor cytochrome a,a3 oxidation state, regional blood volume, and tissue oxyhemoglobin and O2 stores simultaneously in brain and muscle in ventilated animals. Incremental hypercapnia was produced in 10 cats by raising arterial pCO2 from 27.0 +/- 1.3 to 95.1 +/- 1.9 mmHg with inspired CO2. Hypercapnia produced progressive increases in cerebral HbO2, blood volume, and cytochrome a,a3 oxidation state (P less than 0.01). In contrast, CO2 simultaneously decreased all 3 NIR parameters in intact hindlimb muscles (P less than 0.01). Blood volume changes during hypercapnia correlated with changes in blood flow measured qualitatively by intravascular injections of indocyanine green dye. Hypocapnia produced by hyperventilation in 8 cats lowered paCO2 from 28.5 +/- 0.4 to 13.5 +/- 0.5 mmHg. Hypocapnia decreased cerebral HbO2, blood volume, and cytochrome a,a3 redox level (P less than 0.05), but NIR changes were not seen in skeletal muscle. These experiments demonstrate preferential distribution of oxygen to brain during hypercapnia and the ability of NIR spectroscopy to assess regional oxygenation in multiple tissues non-invasively.
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PMID:Near-infrared optical responses in feline brain and skeletal muscle tissues during respiratory acid-base imbalance. 211 21

Slow shifts in the human scalp-recorded EEG, including those related to changes in brain CO(2) levels, have been generally assumed to result from changes in the level of tonic excitation of apical dendrites of cortical pyramidal neurons. We readdressed this issue using DC-EEG shifts elicited in healthy adult subjects by hypo- or hypercapnia. A 3-min period of hyperventilation resulted in a prompt negative shift with a rate of up to 10 microV/s at the vertex (Cz) and an extremely steep dependence (up to 100 microV/mmHg) on the end-tidal Pco(2). This shift had a maximum of up to -2 mV at Cz versus the temporal derivations (T3/T4). Hyperventilation-like breathing of 5% CO(2)-95% O(2), which does not lead to a significant hypocapnia, resulted in a near-complete block of the negative DC shift at Cz. Hypoventilation, or breathing 5% CO(2) in air at normal respiratory rate, induced a positive shift. The high amplitude of the voltage gradients on the scalp induced by hyperventilation is not consistent with a neuronal origin. Instead, the present data suggest that they are generated by extracortical volume currents driven by a Pco(2)-dependent potential difference across epithelia separating the cerebrospinal fluid and blood. Since changes in respiratory patterns and, hence, in the level of brain Pco(2), are likely to occur under a number of experimental conditions in which slow EEG responses have been reported (e.g., attention shifts, preparatory states, epileptic seizures, and hypoxic episodes), the present results call for a thorough reexamination of the mechanisms underlying scalp-recorded DC-EEG responses.
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PMID:Millivolt-scale DC shifts in the human scalp EEG: evidence for a nonneuronal generator. 1261 37