Long-term facilitation of ventilation and genioglossus muscle activity is evident in the presence of elevated levels of carbon dioxide in awake humans

We hypothesized that long-term facilitation (LTF) of minute ventilation and peak genioglossus muscle activity manifests itself in awake healthy humans when carbon dioxide is sustained at elevated levels. Eleven subjects completed two trials. During trial 1, baseline carbon dioxide levels were maintained during and after exposure to eight 4-min episodes of hypoxia. During trial 2, carbon dioxide was sustained 5 mmHg above baseline levels during exposure to episodic hypoxia. Seven subjects were exposed to sustained elevated levels of carbon dioxide in the absence of episodic hypoxia, which served as a control experiment. Minute ventilation was measured during trial 1, trial 2, and the control experiment. Peak genioglossus muscle activity was measured during trial 2. Minute ventilation during the recovery period of trial 1 was similar to baseline (9.3 +/- 0.5 vs. 9.2 +/- 0.7 l/min). Likewise, minute ventilation remained unchanged during the control experiment (beginning vs. end of control experiment, 14.4 +/- 1.7 vs. 14.7 +/- 1.4 l/min). In contrast, minute ventilation and peak genioglossus muscle activity during the recovery period of trial 2 was greater than baseline (minute ventilation: 28.4 +/- 1.7 vs. 19.6 +/- 1.0 l/min, P < 0.001; peak genioglossus activity: 1.6 +/- 0.3 vs. 1.0 fraction of baseline, P < 0.001). We conclude that exposure to episodic hypoxia is necessary to induce LTF of minute ventilation and peak genioglossus muscle activity and that LTF is only evident in awake humans in the presence of sustained elevated levels of carbon dioxide.     

Responses to chemical stimulation of upper airway muscles diaphragm in awake cats

The steady-state and transient effects of hyperoxic hypercapnia on the electromyographic activities of the genioglossus (GG), posterior cricoarytenoid (PCA), and diaphragm (D) were studied in conscious unsedated cats with chronically implanted electrodes. Hypercapnia (inhalation of 3.4 and 7.4% CO2 in O2) increased the phasic electrical activity occurring during inspiration in all three muscles and also increased tonic activity of the GG. The GG responded to steady-state CO2 inhalation alinearly and with larger increases in activity than the PCA and D. Phasic GG activity was present in only 4 of 10 cats breathing 100% O2, whereas phasic PCA and D activity could be observed in all animals studied. When gas mixtures containing CO2 were given, the GG reached its new steady-state level more slowly than the D or PCA, and when CO2 was rapidly removed from the inspired gas mixture, the GG attained its steady state sooner than either the PCA or D. These results suggest that in awake unsedated animals, chemical stimuli do not affect either transient or steady-state responses of the GG in the same way as the D. These differences seem to be explained mainly by different threshold characteristics of hypoglossal and phrenic neurons but also in part by dissimilarities in their steady-state responses.     

Effect of carbon dioxide on photorespiration

The isotopic CO₂ technique for measuring photorespiration was shown to be a valid technique for measuring the unidirectional inward and outward fluxes of CO₂ from a sunflower (Helianthus annuus L.) leaf in the light. The rate of photorespiration was decreased little as the CO₂ concentration was increased from 20 to 1,150 microliters per liter. This finding contradicts the widely held assumption that photorespiration is suppressed at high CO₂ concentrations. Some discussion regarding this apparent conflict is presented.     

Effect of carbon dioxide on nitrification rates

Lab-scale ideal mixed, aerated reactors were employed to test the influence of carbon dioxide (CO(2)) on the growth rate of a nitrifier community. The buffer medium used did not contain any carbon sources. Reactors were inoculated alternatively with sludge from a nitrifying membrane assisted bioreactor, reflecting autotrophic material, or with sludge from a plant having denitrification and nitrification steps, which reflects mixed heterotrophic and autotrophic material. CO(2) was added as a gas with the intake air supply. Nitrification rates were related to the CO(2) in the intake air as well as to the total inorganic carbon in the medium. The batch experiments show a relationship between CO(2) concentration and growth rate. The optimum growth rate occurred at 5 mg CO(2)/L, corresponding to 0.4% (V/V) CO(2) in the inlet air. Different CO(2) optima for autotrophic and mixed sludges were found. In the case of the autotrophic sludge, the observed optimum growth rate was about 0.47/d and the optimum for the mixed sludge was about 0.75/d. Higher CO(2) concentrations lead to a decreasing growth rate. The first part of the kinetic graph can be described by Monod kinetics. Overall, the resulting graph can be described by Haldane kinetics.     

Evidence for oxygen and carbon dioxide receptors in insect CNS influencing ventilation

We investigated heat activation and germination of Eurotium repens ascospores to follow high pressure inactivation. Activation energy and entropy values strengthen the idea of protein denaturation as the underlying mechanism of heat activation. Preceding activation, germination or a combination of both affected high pressure inactivation in different ways. Activation followed immediately by high pressure treatment led to the most efficient improvement in inactivation. However, a pause after activation caused a partial re-establishment of the spores' stability and less efficient high pressure inactivation. Germination stabilized the spores against high pressure. A combined treatment of activation and germination led to an initially fast inactivation, but compared to high pressure treatment of only activated spores the time course of inactivation was slowed down.     

Effect of carbon dioxide on yeast growth and fermentation

Inhibition of yeast function by ethanol and by high substrate concentrations is well recognized and, to a limited extent, quantified. The role of carbon dioxide in affecting yeast metabolism (particularly growth processes) is not clear although inhibition is generally found at moderate to high concentrations of the dissolved gas. A similar situation exists with other microorganisms and with other fermentation systems. An understanding of the role of carbon dioxide, and particularly of its inhibitory effects on enzyme action and membrane function, is required if the observed global inhibition of yeasts and other fermentation systems is to be partitioned to its appropriate causes.     

The neuropharmacology of upper airway motor control in the awake and asleep states: implications for obstructive sleep apnoea

Obstructive sleep apnoea is a common and serious breathing problem that is caused by effects of sleep on pharyngeal muscle tone in individuals with narrow upper airways. There has been increasing focus on delineating the brain mechanisms that modulate pharyngeal muscle activity in the awake and asleep states in order to understand the pathogenesis of obstructive apnoeas and to develop novel neurochemical treatments. Although initial clinical studies have met with only limited success, it is proposed that more rational and realistic approaches may be devised for neurochemical modulation of pharyngeal muscle tone as the relevant neurotransmitters and receptors that are involved in sleep-dependent modulation are identified following basic experiments.     

Improved method to detect trace amounts of gases in a carbon dioxide atmosphere

A method is described for concentrating and quantifying trace amounts of alkanes and alkenes, produced during phosphonate biodegradation, in a carbon dioxide atmosphere. The method is precise, repeatable, fast and cheap. Compared to direct headspace analysis, the variance in the quantification was reduced up to 50 times and the detection limit lowered 20 to 500 times. Quantification was independent of the pressure in the experimental tubes, the amount of dissolved gases in the medium, and the temperature.     

Measurement of airway resistance in awake cats

Airway resistance (Raw) measurement with continuous recording was studied in 10 awake cats. The method used was a transducer enabling to incorporate additive resistances by rotating blind. The signals were processed electronically. Part of the measuring device in a pneumotachographic transducer (measurement V') and VT is obtained by integrating V'. Values for mean Raw were read in both parts of the breathing cycle. The experiments have shown that the method could be used in awake cats. Values for mean Rawinsp. were 1.3 +/- 0.24 kPa.l-1.s, Rawexp. of 1.43 +/- 0.26 kPa.l-1.s, end-inspiratory Raw was 1.44 +/- 0.33 kPa.l-1.s and end-expiratory Raw of 1.49 +/- 0.31 kPa.l-1.s.     

Effect of carbon dioxide on the Oriental cockroach Blatta orientalis

Exposure to high concentrations of carbon dioxide (CO2) killed adult and nymphal stages of the oriental cockroach Blatta orientalis L. (Dictyoptera: Blattidae) with LT50 values of 11.5-16.2 h for 60% CO2 in air and 5.7-7.1 h for 100% CO2 at 20 degrees C; corresponding LT50s at 28 degrees C were 2.8-4.6 h for 60% CO2 in air and 2.3-3.6 h for 100% CO2. Complete kill of mobile stages was obtained within 24 h using 60% CO2 at 20 degrees C. Survivors of treatments with 100% CO2 at 28 degrees C remained completely paralysed for up to 3 days post-treatment and took up to 5 days to regain normal movement, but adult females then resumed production of oothecae with no significant loss in fecundity. Oothecae 5 or 30 days after deposition required 60-84 h exposure to 60% CO2 at 20 degrees C to prevent emergence of nymphs but less time using 100% CO2 at 28 degrees C. At 28 degrees C, when adult females were treated with 100% CO2 and 52% r.h. for 6 h (giving 100% mortality) loss of weight was significantly greater than that following treatment with air at 52% r.h. for 6 h (giving no mortality). However, significantly greater weight loss also occurred when they were treated with dried air (< 10% r.h.) for 6 h, also with no mortality. The toxicity of CO2 to mobile stages of the oriental cockroach appeared to result from irreversible effects on the nervous system, rather than from water loss during exposure.