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Alterations in arterial oxygen and carbon dioxide influence cerebrovascular resistance and therefore cerebral blood flow (CBF), but the magnitude of these CBF responses have not been well defined in normal humans. Duplex scanning (B-mode imaging and pulsed Doppler shift analysis) was used to measure internal carotid blood flow (ICBF) as an indicator of CBF in 20 normal subjects during alterations of arterial O2 and CO2. End-tidal PCO2 (PETCO2) was measured by mass spectrometry, arterial oxygen saturation by pulse oximetry, and unilateral (right) ICBF by duplex scanning. A variety of gas mixtures were administered to achieve hypoxemia (FIO2 = 0.075-0.10) and hypercapnia (FICO2 = 0.05) or the subject was asked to hyperventilate to PETCO2 = 16-24 mm Hg. The ICBF was determined five times in each of six conditions: (1) normoxia/normocapnia; (2) normoxia/hypercapnia; (3) normoxia/hypocapnia; (4) hypoxia/normocapnia; (5) hypoxia/hypercapnia; and (6) hypoxia/hypocapnia. During normoxia and normocapnia, the mean ICBF was 330 +/- 19 (SEM) mL/min. Specific CO2 reactivity was 7.4 +/- 0.7 mL/min/mmHg, which is equivalent to 2.3% +/- 0.1% of normocapnic blood flow per mm Hg change in CO2. During normocapnia, ICBF increased by 2.9 +/- 0.9 mL/min for each percentage decrease in oxygen saturation. Using an ANOVA with repeated measures to fit the responses, the following statistically significant relationship was found: ICBF (mL/min) = 333 + 6.3.(PETCO2 - 40) + 2.7 DSO2 +/- 81 where DSO2 is arterial desaturation (100 - arterial saturation). An additional "between subject" variation had a mean of 0 and a standard deviation of 82 mL/min. There was no statistically significant evidence of an interaction between O2 and CO2 response. Our data suggest that hypoxia and carbon dioxide changes will alter CBF simultaneously and additively. Duplex scanning of the internal carotid artery, which can be performed at the bedside, is sufficiently sensitive to detect changes in ICBF and internal carotid artery oxygen delivery.
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PMID:Human cerebrovascular response to oxygen and carbon dioxide as determined by internal carotid artery duplex scanning. 158 51

Mouthguards are considered by most authorities to be an essential part of equipment for players participating in body-contact sports. Mouthguards provide excellent dental protection but not all players use them, complaining of breathing difficulties and problems with speaking. Although information exists concerning dental trauma and mouth protector use, there are no reported data that quantify the physiological effects of wearing mouthguards. The purpose of this study was to measure the ventilatory and gas exchange effects of wearing a mouthguard. Ten healthy men and seven women aged 20-36 years (mean(s.d.) 27.2(5.2) years) were used as subjects. Forced expiratory air volume at 1 s (FEV1) and peak expiratory flow rates (PEF) were measured on each subject while wearing either no mouthguard or one of three different over-the-counter mouthguards including one maxillary (mouthguard 1) and two different bimaxillary guards (mouthguards 2 and 3). To determine the effects of wearing each of the mouthguards during exercise, oxygen consumption (VO2) was measured while exercising on a cycle ergometer for 5 min at a light and heavy workload. An ANOVA of repeated measures was used to determine statistical differences. In each case, the wearing of a mouthguard significantly (P less than 0.05) reduced FEV1 and PEF in comparison with no mouthguard. FEV1 was reduced 8% with mouthguard 1, and 12% and 14% with mouthguards 2 and 3 respectively. PEF was reduced by 7, 15 and 15.8% with mouthguards 1, 2 and 3 respectively. The wearing of the different mouthguards did not significantly change VO2 while exercising at the lower work level whereas VO2 was significantly ( P < 0.05) reduced at the heavier workload. This surprising reduction in VO2 during heavy exercise may be due to a 'pursed-lip' type of breathing which has been shown to decrease CO2 tension, increase oxygenation and exercise tolerance. It can be concluded that although mouthguards may be perceptably uncomfortable and restrict forced expiratory air flow, they appear to be beneficial in prolonging exercise by improving ventilation and economy.
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PMID:Physiological effects of wearing mouthguards. 181 Jun 19

It has been shown that an epidural test dose with adrenaline does not always detect an intravascular injection in halothane-anaesthetized children. To ascertain whether test dosing with other agents might be more useful, we sought to determine if and at what dose levels three different intravenous drugs (adrenaline, isoprenaline and 1% lignocaine with 1/200,000 adrenaline) produced an increase in heart rate (HR) in halothane-anaesthetized lambs. Eight 2-week-old lambs were anaesthetized with 1% halothane in oxygen. The lambs were intubated and ventilated in order to maintain end-tidal and arterial CO2 within normal limits; HR and blood pressure before and 15-180 s after the injection of four increasing doses of each drug were recorded. The same set of measurements was repeated after the intravenous injection of atropine 10 micrograms kg-1. Adrenaline-containing doses produced a more sustained increase in HR (P less than 0.05, ANOVA) at lower doses of adrenaline when atropine was injected first. This increase did not occur in all lambs, and dysrhythmias were manifest in some. Isoprenaline always produced a significant increase in HR without dysrhythmias whether atropine was given or not. We conclude that in halothane-anaesthetized lambs, isoprenaline is a more reliable indicator of intravascular injection than adrenaline.
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PMID:Efficacy of adrenaline, lignocaine-adrenaline and isoprenaline as a test dose in halothane-anaesthetized lambs. 190 78

This study examined the relationship between expired non-metabolic CO2 (exCO2) and the accumulation of blood lactate. Particular emphasis was placed on the ventilatory (exCO2 and VE/VO2) and lactate threshold relationship. A total of 21 elite cyclists (15 males, 6 females) performed a progressive intensity bicycle ergometer test during which ventilatory parameters were monitored on-line at 15-s intervals, and blood lactate sampling occurred at each minute. Transition threshold values were determined for each of the three indices: excess CO2 (TexCO2), VE/VO2 (Tvent) and blood lactate (Tlac). The three threshold values (TexCO2, Tvent, Tlac) all correlated significantly (P less than 0.001) when each was expressed as an absolute VO2 (l min-1). A significant ANOVA (F = 8.41, P less than 0.001) and post-hoc correlated t-tests demonstrated significant differences between the TexCO2 and Tlac (P less than 0.001) and the TexCO2 and Tvent values (P less than 0.025). The Tlac occurred at an average blood lactate concentration of 3.35 mM, while the mean expired excess CO2 volume at the TexCO2 was 14.04 ml kg-1 min-1. Over an 11-min range across the threshold values (TexCO2 and Tlac), which were used as relative points of reference, the expired excess CO2 volume (ml kg-1 min-1) and blood lactate concentration (mM) correlated significantly (r = 0.69, P less than 0.001). Higher individual correlations over the same period of time (r = 0.82-0.96, P less than 0.001) stress the individual nature of this relationship. These results indicate a strong relationship between the three threshold values.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Relationship between blood lactate and excess CO2 in elite cyclists. 191 97

Previous investigations have revealed that propofol has a beneficial effect on intracranial dynamics in patients undergoing elective neurosurgery. In the present study we evaluated the impact of propofol in patients with normal or compromised intracranial compliance. METHODS. Epidural ICP probes were implanted in 14 patients with head injury. The heart rate, mean arterial pressure (MAP), intracranial pressure (ICP) and end-tidal CO2 were recorded continuously, and propofol was given in doses of 0.5, 1.0 and 2.0 mg/kg; there were 15 min between each application. The data were evaluated 1, 2, 5 and 10 min after each application. The patients were allocated to group I (ICP less than 20 mmHg) or group II (ICP greater than 20 mmHg) according to their ICP baseline level. A statistical analysis was performed by one-way ANOVA. A P value of less than 0.05 was regarded as significant. RESULTS. In group I decreases in MAP at all measuring points were detected with 1.0 and 2.0 mg/kg propofol; ICP with 1.0 and 2.0 mg/kg and CPP with 2.0 mg/kg fell significantly. In group II MAP decreased with all doses studied, as did ICP with 1.0 and 2.0 mg/kg; however, CPP was not particularly influenced. CONCLUSION. Propofol decreased ICP in patients with normal and compromised intracranial compliance, particularly with 2.0 mg/kg. As the responses to the hypotensive effects of propofol were mild and almost similar in both groups, no inadvertent CPP drops were observed with any of the doses studied. Thus, propofol as a bolus can be used safely for the sedation of ICU patients with head injury and normal or compromised intracranial compliance.
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PMID:[The effects of propofol bolus administration on the intracranial pressure in craniocerebral trauma]. 227 71

The CO2 laser can weld vessels together and vaporize plaque. This study evaluates its use as an intraluminal reparative tool. In 17 dogs, a 1-cm circumferential intimectomy with a 1-mm distal intimal flap was performed in both carotids. In each dog, one carotid (CON, control) underwent suture flap repair. On the contralateral side (LR, laser repair), the flap was tacked with 20 250-mW 1-sec pulses and the denuded medium was g-lased for 90 sec (250 mW continuous). Animals were randomized into five groups and sacrificed on the day of surgery (Group I, n = 3), at 3 days (Group II, n = 3), at 1 week (Group III, n = 4), at 2 weeks (Group IV, n = 4), or at 4 weeks (Group V, n = 3). Vessel patencies were 88.2 and 82.4% for CON and LR, respectively. Flap repair appeared similar. No aneurysms were noted. Histology revealed a relative absence of platelet adherence to the g-lased surfaces in Groups I and II when compared to that of mechanical methods (CON). The ratio of the thickness of the regenerated surface to the total wall thickness demonstrated hyperplasia in LR vessels (0.54 +/- 0.12) when compared to that in CON (0.30 +/- 0.15) at 2 and 4 weeks (ANOVA, P less than 0.001). Coverage with endothelial-like cells appeared complete at 4 weeks in both methods. The CO2 laser can effectively repair intimal flaps. However, our results demonstrate a significant increase in medial hyperplasia following g-lasing even in the face of minimal early platelet adherence. This may prove detrimental to the long-term patency of intraluminal CO2 laser-treated vessels.
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PMID:The CO2 laser as an intraluminal repair tool. 250 97

Estimates of substrate oxidation obtained from appearance of 13C or 14C from tracers in breath must be corrected for retention of labeled carbon in the body. We aimed to determine the effect of a defined experimental diet and metabolic status on recovery of infused Na [13C]bicarbonate in breath. Six healthy male subjects consumed an experimental diet for 7 days before receiving a continuous infusion of formula without tracer on day 8 and received either an intragastric (ig) or intravenous (iv) infusion of Na [13C]bicarbonate on day 9 or 11 during a 4-h postabsorptive (PA), 4-h continuously fed period. A trend toward increasing PA breath enrichment during the first 7 diet days approached statistical significance (P = 0.051), whereas breath enrichments measured 3 h postbreakfast were consistently higher than PA values throughout and did not change over the 7-day period. Breath enrichments during a 4-h continuous ig infusion of formula without tracer on day 8 rose 2.0 +/- 0.5 atom percent excess (APE).10(-3) above base line (P less than 0.001, ANOVA). In the tracer studies, breath enrichments were similar for the ig and iv routes of tracer infusion. For the ig infusion the fraction of infused Na [13C]bicarbonate recovered in breath as 13CO2 was 0.74 +/- 0.02 for the PA period and 0.79 +/- 0.02 for the fed period. For the iv infusion the fraction recovered was 0.70 +/- 0.04 for the PA period and 0.82 +/- 0.03 for the fed period. Fractional recoveries were not significantly different for ig and iv routes of administration but were different for PA and fed periods (P less than 0.0001, 2-way ANOVA). The fractional recoveries for the fed period obtained here were similar to the value 0.81 reported in a number of other studies. Recovery of tracer in breath increased linearly with O2 uptake and CO2 production, suggesting that factors affecting respiratory gas exchange may alter recovery. We conclude that the primary factor determining label recovery is the immediate and recent nutritional status of the host.
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PMID:Recovery of 13C in breath from NaH13CO3 infused by gut and vein: effect of feeding. 255 Nov 78

The Fay-Prince trap augmented with carbon dioxide (F-P/CO2) collected high numbers of male and female Aedes sierrensis (Ludlow). The F-P/CO2 trap collected 15-20 times more males, but statistically similar numbers of females as did a rabbit-baited CO2 trap (R/CO2). Carbon dioxide was essential to the successful operation of the F-P/CO2 trap for the collection of male and female Ae. sierrensis. A repeated measures ANOVA with polynomial contrasts found no significant differences in the population trends of female Ae. sierrensis measured by the two traps. Trap location also was a major source of variability, with one of the four locations accounting for 50% of all Ae. sierrensis collected. These results indicated that the F-P/CO2 trap was a simple but effective method for sampling Ae. sierrensis.
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PMID:Fay-Prince trap baited with CO2 for monitoring adult abundance of Aedes sierrensis (Diptera: Culicidae). 276 13

The purpose of this study was to determine cardiac output and related cardiovascular responses during postinversion by comparing preinversion (baseline data) to postinversion data in healthy, normal subjects. Each of 20 subjects (means = 22 years) was inverted for five minutes. Cardiac output was measured noninvasively with the Beckman MMC and CO2 rebreathing program. ANOVA with repeated measures was used to determine significance of change between preinversion and postinversion values. The alpha level was set at 0.05 for statistical significance. During postinversion stand, there were (a) significant decreases in oxygen uptake (p less than 0.0008), cardiac output (p less than 0.0005), and stroke volume (p less than 0.0018); (b) significant increases in arteriovenous oxygen difference (p less than 0.0281), peripheral vascular resistance (p less than 0.0001), and diastolic blood pressure (p less than 0.0087); and (c) nonsignificant changes in heart rate, systolic blood pressure, and double product from the preinversion baseline standing position. The results demonstrate little if any need for concern for a subject's return to the upright position.
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PMID:Postinversion responses to inversion in normal subjects. 338 90

We have studied the effect of alveolar hypoxia on fluid filtration characteristics of the pulmonary microcirculation in an in situ left upper lobe preparation with near static flow conditions (20 ml/min). In six dogs (group 1), rate of edema formation (delta W/delta t, where W is weight and t is time) was assessed over a wide range of vascular pressures under two inspired O2 fraction (FIO2) conditions (0.95 and 0.0 with 5% CO2-balance N2 in both cases). delta W/delta t was plotted against vascular pressure, and the best-fit linear regression was obtained. There was no significant difference (paired t test) in either threshold pressure for edema formation [18.3 +/- 1.8 and 17.1 +/- 1.2 (SE) mmHg, respectively] or the slopes (0.067 +/- 0.008 and 0.073 +/- 0.017 g.min-1. mmHg-1.100g-1, respectively). In another seven dogs (group 2), delta W/delta t was obtained at a constant vascular pressure of 40 mmHg under four FIO2 conditions (0.95, 0.21, 0.05, and 0.0, with 5% CO2-balance N2). Delta W/delta t for the four conditions averaged 0.60 +/- 0.11, 0.61 +/- 0.11, 0.61 +/- 0.10, and 0.61 +/- 0.10 (SE) g.min-1.mmHg-1.100g-1, respectively. No significant differences (ANOVA for repeated measures) were noted. We conclude that alveolar hypoxia does not alter the threshold for edema formation or delta W/delta t at a given microvascular pressure.
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PMID:Effect of alveolar hypoxia on pulmonary fluid filtration in in situ dog lungs. 340 89


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