Cent Oxygen Research Articles

Control of the Microcirculation of the Inner Ear

In general, many similarities are seen between cerebral blood flow and cochlear blood flow in response to vasodilating drugs. Cochlear vessels appear to be weakly controlled by the adrenergic nervous system. Cholinergic agents dilate cochlear vessels, although the vasodilation in the cochlea does not necessarily cause an increase in cochlear blood flow because of the associated hypotension. The effect on the systemic circulation is too profound to make these agents clinically useful. Papaverine, dipyridamole, amyl nitrite, and the plasma kinins produce transient increases in cochlear blood flow. Ten per cent carbon dioxide and 90 per cent oxygen product progressive vasodilation as long as the mixture is inhaled. Hydralazine produces too profound an effect on systemic blood pressure. Histamine and betahistine increase cochlear blood flow but only in doses that produce bronchiospasm in the guinea pig. Nicotinic acid and nicotinyl tartrate have no effect on cochlear blood flow. If one considers safety and efficacy as well as patient tolerance, papaverine appears to be the drug of choice for increasing cochlear blood flow clinically. Histamine and betahistine appear to be acceptable alternatives. Betahistine is no longer available for clinical use because of the failure to demonstrate clinical efficacy of therapy.

Recognition and treatment of adult respiratory distress syndrome secondary to viral interstitial pneumonia

Four cases of adult respiratory distress syndrome secondary to viral interstitial pneumonia were treated successfully. The illnesses started with a prodrome of upper respiratory symptoms. The development of dyspnea was a key symptom from which point respiratory failure developed within 24 to 48 hours. Chest roentgenograms showed alveolar infiltrative patterns which later became coalescent. The clinical course consisted of fever, dyspnea, hypoxia and acidosis. There was no response to therapy with antibiotics, 100 per cent oxygen by mask and intermittent positive pressure breathing (IPPB) over the first 24 hours. Supportive therapy then initiated included endotracheal intubation, the administration of humidified oxygen by volume cycled respirator with positive end expiratory pressures of 10 to 15 cm H 2O and corticosteroids. It is concluded that early recognition of the syndrome, coupled with prompt institution of aggressive supportive respiratory management may be lifesaving in patients with severe interstitial pneumonia.

Weaning from controlled ventilation and supplemental oxygen.

Weaning from Intermittent Positive-Pressure VentilationCriteriaTHE criteria for the discontinuation of controlled ventilation are the converse of those for the institution of controlled ventilation. The patient should have an alveolar arterial oxygen tension difference measured breathing 100 per cent oxygen (Aa DO2 1.0) of less than 300 to 350 mm Hg.1 A minimum vital capacity of 10 to 15 ml per kilogram of body weight is necessary. The maximum inspiratory force should be numerically greater than -20 cm of water.2 The ratio of dead space to tidal volume (VD/VT) is an accurate measure of whether a patient will . . .

The action of carbon dioxide on the collateral pathways of pulmonary ventilation

The major collateral ventilatory pathways between the segments of the lobes of the dog are lined with smooth muscle and course from bronchiole to alveolus and from bronchiole to bronchiole. In previous studies, we showed that the channels constricted with metacholine and dilated with epinephrine. Carbon dioxide elevations in the inspired air, as noted in this study, greatly increased the collateral flow, whereas 100 per cent oxygen did not affect it. The greatest dilatation occurred when the inspired carbon dioxide increased from 2.5 to 6 per cent, with little if any further change when increased to 15 per cent. When perfusion of the in situ lung was blocked, or when the lung was excised, carbon dioxide still had a marked bronchodilating effect. This indicates its direct action on smooth muscle. The fact that carbon dioxide acts as a dilator of the collateral channels, independent of neural and humoral influences, confirms its important role in ensuring maximal pulmonary ventilation.

MATERNAL ARTERIAL OXYGEN TENSION DURING INTERMITTENT INHALATION ANALGESIA

In mothers nursed in a semi-recumbent position, arterial oxygen tension was measured at the beginning and END OF AN an intermittent period of inhalation, Lasting for six contractions, during the first stage of labour. Ten mothers had methoxyflurane 0.35 per cent and air, followed by methoxyflurane 0.35 per cent with approximately 50 per cent oxygen. Another 10 mothers had 50 per cent nitrous oxide and 50 per cent oxygen (Entonox). The mean values of PaO2 at the beginning of periods of inhalation in those who received methoxyflurane in air, methoxyflurane in 50 per cent oxygen, and nitrous oxide in oxygen were 109, 120 and 106 mm Hg respectively. The mean increases in PaO2 by the ends of periods of inhalation were 18, 43 and 63 mm Hg respectively. On average, increasing the inspired concentration of oxygen to 50 per cent significantly and substantially increased maternal PsO2 with both agents by the emd pf inhalation. There would therefore be some increase in available oxygen during the phase of higher blood flow following a uterine contraction. However, the lowest maternal PaO2 measured was 72 mm Hg; therefore additional oxygen is unlikely to offer much advantage except in patients with respiratory or cardiac deficiencies. In the intervals between inhalations of the analgesic mixture the PaO2 decreased to about the level found during air breathing. Consequently it would be necessary to breather additional oxygen continuously, between as well as during contractions, to ensure an increased maternal PaO2 throughout labour.

The influence of environmental agents on prostaglandin biosynthesis and metabolism in the lung. Inhibition of lung 15-hydroxyprostaglandin dehydrogenase by exposure of guinea pigs to 100 per cent oxygen at atmospheric pressure

Enzymes in the 100 000g supernatant fraction of guinea-pig lungs, in the presence of NAD-+, converted PGF-2 alpha (prostaglanding F-2 alpha) into a less-polar compound. The u.v. spectrum of this metabolite showed a strong absorption band at 230 nm, which is characteristic of a carbonyl group in conjugation with a double bond. Reduction of this metabolite with NaBH4 resulted in a compound that behaved like PGF2 ALPHA on t.l.c. and g.l.c. From this evidence we concluded that PGF2alpha is metabolized in vitro to 15-oxo-PGF2 alpha by the NAD-+-dependent prostaglandin dehydrogenase system of guinea-pig lung. The effect of exposure of the animal to SO-2 and O2 on the rate of prostaglanding biosynthesis and catabolism by lung fractions in vitro was studied. Exposure of guinea pigs to 500 p.m. of SO2 for 5h or to 50p.p.m for 9 days (6h/day) did not alter the production or degradation of prostaglandings by lung fractions in vitro. In contrast, exposure of guinea pigs to 100% O2 for 48 h inhibited the rate of prostaglanding metabolism in vitro by 60-70% without significantly altering the rate of biosynthesis by lung fractions. Inhibition of prostaglandin dehydrogenase activity in vitro by lung fractions after exposure of the animal to O2 was dependent on the duration of exposure. Gluthathione S-aryltransferase and catechol O-methyltransferase activites of guinea-pig lung 100 000g supernatant were unaltered by exposure of the animal to O2. Thus it appears that inhibition of pulmonary prostaglandin dehydrogenase by exposure of the animal to O2 is not the result of a general toxic response. It was postulated that the inhibition of prostaglanding dehydrogenase may occur after exposure of the animal to other oxidant gases.

PERINATAL FACTORS INFLUENCING THE ARTERIAL OXYGEN TENSION IN PRETERM INFANTS WITH RDS WHILE BREATHING 100 PER CENT OXYGEN

The relationship of surfactant deficiency, immaturity, and intrapartum complications to the arterial oxygen tension (Pa O 2 ) while breathing 100 per cent oxygen (hyperoxia test) was studied in 88 preterm infants, who were the products of 80 highrisk pregnancies. The hyperoxia test was performed from one to six hours of life. The Pa O 2 was significantly related to the foam stability test (FST) if there was no RDS and the 5 minute Apgar score was ≥6. A low Pa O 2 was significantly related to a history of intrapartum complications and a 5 minute Apgar score ≤5, but not to the FST. A hyperoxia test value greater than 200 mm. Hg was not associated with any deaths from RDS nor with the need of mechanically assisted ventilation. All of the 21 deaths were associated with history of intrapartum complications. A Pa O 2 ≤200 mm. Hg defines the high-risk group for RDS. The highest predictability of deaths from RDS (85 per cent) was further defined by the combination of factors: Pa O 2 ≤200 mm. Hg, intrapartum complications, 5 minute Apgar score ≤5, and arterial pH≤7.20.

Anesthetic Effects on Ventilation in Patients with Chronic Obstructive Pulmonary Disease

The effects of 1.0 per cent end-tidal halothane-oxygen anesthesia on spontaneous ventilation, ventilatory deadspace, functional residual capacity (FRC), and alveolar-arterial oxygen difference (A-aD-O-2) were measured in patients with chronic obstructive pulmonary disease and in normal patients of similar age. results obtained were compared with values obtained preoperatively from the same patients. The following were measured: 1) ventilation and ventilatory deadspace, breathing room air and breathing 100 per cent oxygen; 2) functional residual capacity (FRC) and alveolar-arterial oxygen tension difference (A-aD-O-2); 3) forced expiratory volume in 1 second (FEV1.0); 4) ventilatory response to exogenous carbon dioxide. Findings indicated that ventilation is depressed more during halothane anesthesia in patients with emphysema than in normal patients and that the extent of depression is best related to a preoperative measurement of FEV1.0 (P less than 0.001, r = 0.86). The depression in alveolar ventilation results primarily from a reduction in tidal volume. A-aD-O-2 and ventilatory deadspace-to-tidal volume ratio are increaded and FRC decreased with anesthesia in patients with COPD, but the changes are no greater than those found in normal patients.

Relationship of air trapping to increased lung recoil pressure induced by chest cage restriction.

Chest cage restriction was produced in 13 normal male subjects. We could not detect trapped air during restriction by comparing lung volumes determined by nitrogen washout with those determined by plethysmography. However, 3 subjects did have definite evidence of trapping because they released small amounts of air (mean, 61 ml) when the restriction was removed. Two subjects had suggestive evidence of trapping. Yet there was no correlation between trapping and the degree of increase in static lung recoil associated with restriction. Seven subjects had chest restriction produced while they were breathing air and again while they were breathing 100 per cent oxygen, in an attempt to reveal the presence of airway closure. In only one subject was oxygen breathing clearly associated with a greater then expected increase in lung recoil after restriction; suggestive changes were seen in 2 other subjects. However, there was no definite correlation between unusual increases in lung recoil induced by restriction while breathing oxygen and the presence of air trapping. We conclude that trapping, hence airway closure, is not required for the increase in static lung recoil that occurs with chest cage restriction.

Cardiovascular responses to hypoxemia and acidemia in fetal lambs

Circulatory responses to hypoxemia and acidemia were studied in 10 fetal lambs in utero with gestational ages of 122 to 142 days. Vinyl catheters were placed in fetal and maternal vessels, and the fetuses were studied 2 to 5 days postoperatively. Fetal heart rate, arterial pressure,Po2,Pco2, and pH were measured during a control period and while the standing ewe breathed 6 per cent oxygen and 3 per cent carbon dioxide through a plastic bag over its head. Fetal cardiac output and distribution and absolute organ blood flows were calculated from injections of 15μ nuclide-labeled microspheres, during the control and hypoxemic states. One group of 5 fetuses only became hypoxemic (meanPo2 12 and mean pH 7.36), but the other 5 fetuses also developed acidemia (meanPo2 12 and mean pH 7.28). Fetal arterialPco2 values were normal throughout. During hypoxemia, fetal arterial pressure increased, and fetal heart rate decreased. Although cardiac output fell in all but one fetus, the decrease was significant only in the acidemic group. Blood flow to the fetal body decreased in all, but the change was significantly greater in the acidemic group. Umbilical blood flow was maintained in all fetuses during hypoxemia. The per cent distribution of cardiac output to the placenta rose from 41 to 48 per cent and from 41 to 57 per cent in the hypoxemic and acidemic groups, respectively. Blood flow to the brain, heart, and adrenals increased two- to three-fold in all fetuses during hypoxemia while pulmonary, renal, splenic, gut, and carcass flows decreased. The changes were of greater magnitude in fetuses with combined hypoxemia and acidemia. These studies quantitate the fetal circulatory changes that occur in unanesthetized fetal lambs in utero during maternal hypoxemia.

Acute cyanide poisoning.

Cyanide poisoning results in cytotoxic hypoxia due to the inactivation of mitochondrial cytochrome oxidase. The pathophysiology of this intoxication is discussed and antidotal therapies are examined and contrasted. Two case reports of patients with acute poisoning are presented. The importance of general supportive measures, the administration of 100 per cent oxygen and reversal of metabolic acidosis are stressed.

Air bolus method compared to single breath method for determination of closing volume.

A method of measuring closing volume by using a bolus of room air is described. In 9 of 12 normal subjects, this method produced tracings that were superior to the single breath nitrogen washout method because of a steeper rise of the nitrogen slope in Phase IV. Closing volume was not affected by breathing 100 per cent oxygen. This method is suggested as an inexpensive modification of the single breath method in subjects with poorly discernible Phase IV.

Hypoxic vascular response of the lung: effect of aminophylline and epinephrine.

Regional alveolar hypoxia produces regional pulmonary vasoconstriction. Experiments were conducted to assess the influence of epinephrine and aminophylline infusion on the hypoxic vasoconstrictor r...

Perinatal factors influencing the arterial oxygen tension in preterm infants with RDS while breathing 100 per cent oxygen

The relationship of surfactant deficiency, immaturity, and intrapartum complications to the arterial oxygen tension (Pa O 2 ) while breathing 100 per cent oxygen (hyperoxia test) was studied in 88 preterm infants, who were the products of 80 highrisk pregnancies. The hyperoxia test was performed from one to six hours of life. The Pa O 2 was significantly related to the foam stability test (FST) if there was no RDS and the 5 minute Apgar score was ≥6. A low Pa O 2 was significantly related to a history of intrapartum complications and a 5 minute Apgar score ≤5, but not to the FST. A hyperoxia test value greater than 200 mm. Hg was not associated with any deaths from RDS nor with the need of mechanically assisted ventilation. All of the 21 deaths were associated with history of intrapartum complications. A Pa O 2 ≤200 mm. Hg defines the high-risk group for RDS. The highest predictability of deaths from RDS (85 per cent) was further defined by the combination of factors: Pa O 2 ≤200 mm. Hg, intrapartum complications, 5 minute Apgar score ≤5, and arterial pH≤7.20.

Changes in the rates of apparent photosynthesis in 21% and 1% oxygen and of dark respiration following a single exposure of three-year-old Pinus strobus L. Plants to gamma radiation

Rates of apparent photosynthesis (in 21 per cent and 1 per cent oxygen) and dark respiration were measured 1–21 days following a single exposure of young white pines to doses of gamma radiation ranging from approximately 230–7500 rad. At all dose levels, the rates of apparent photosynthesis were reduced. The per cent change in the rates at both O 2 concentrations following irradiation were similar suggesting that the initial response was at the photosystem level. In contrast to photorespiration which was probably reduced by the radiation, the rate of dark respiration, though unchanged one day after radiation, increased thereafter. The data reaffirm the sensitivity of the photosynthetic capacity of white pines to ionizing radiation and the differential response of the chloroplast and mitochondrion organelles.

Ideas and anomalies in the evolution of modern oxygen therapy.

Ideas and anomalies in the evolution of modern oxygen therapy.

Role of the carotid bodies in breath-holding.

Abstract To determine the role of the carotid bodies in the sensation of breathlessness during breath-holding, studies were performed in six normal subjects and in five patients with asymptomatic asthma who had had both carotid bodies resected. Breath-holding followed single inspirations of 100, 50, 21 and 12 per cent oxygen and after breathing of 12 per cent oxygen for one minute. In the normal subjects, breath-holding time and alveolar carbon dioxide tension at the breaking point progressively decreased as alveolar oxygen tension decreased. In contrast, there was no change in alveolar carbon dioxide tension or breath-holding time until alveolar oxygen tension was reduced below 50 mm Hg in this patient group. Breath-holding time was twice that for the normal subjects at 50 mm Hg. These studies indicate that the carotid bodies are active chemoreceptors for oxygen through levels greater than 200 mm Hg, that interaction of carbon dioxide and oxygen on respiratory control occurs at the level of the carotid b...

6 - Non-hormonal Methods of Antenatal Monitoring

A stringent but precise method of predicting whether a baby is likely to be depressed at birth or not is discussed. This should be an important objective in obstetric practice if fetal quality is to be ensured. Long-term follow-up studies are urgently needed to confirm the value of the various tests in current use. Non-endocrine tests of fetoplacental function are discussed. Increased utilisation of newer methods of monitoring are foreseen with emphasis upon stressing of the fetus under steady-state conditions. Considerable precision has been achieved utilising a stress of 12 per cent oxygen although further developments are to be expected in this field.

Studies on circulatory response to hypoxia in the denervated transplanted human heart

The relative importance of centrally mediated reflex responses versus the release of circulating humoral substances in the heart's response to acute hypoxia was studied in the transplanted human heart with its residual innervated recipient atrium and denervated donor atrium. The sinus node rates of both the donor and recipient atria were compared by monitoring P wave activity on the standard electrocardiogram in six patients during control and hypoxic conditions. Breathing 13 per cent oxygen for 10 minutes resulted in an average oxygen saturation of 75 per cent and an oxygen tension (pO 2) of 40 mm Hg, and was associated with a 16 per cent (p 0̌.05) increase in the recipient sinus node rate, but with no change in the donor sinus node rate. Pretreatment with atropine abolishes this increase in the innervated recipient sinus node. Breathing 10 per cent oxygen resulted in an oxygen saturation of 55 per cent and a pO 2 of 25 mm Hg, with an associated 10 per cent increase in both donor and recipient sinus node rate. These studies indicate that changes in heart rate during mild degrees of hypoxemia are mediated by a central reflex mechanism which leads to the release of normal vagal parasympathetic tone. The increase in heart rate that occurs in both the innervated and denervated sinus node rates during more severe degrees of hypoxia is probably due to the release of circulating humoral substances, since reinnervation has not been documented in the human cardiac allograft.

Uterine vascular bed: Effects of acute hyperoxia

The acute effects of inspiration of 100 per cent oxygen on the uterine vascular beds of castrated and pregnant ewes were evaluated in chronic conscious preparations. In castrated ewes, vascular conductance decreased to 90.8 ± 17.9 (standard deviation) per cent of control levels. During pregnancy, no significant changes in conductance occurred. The results suggest that acute maternal hyperoxia causes no significant change in placental blood flow.