Near-infrared monitoring of cerebral oxygen sufficiency. I. Spectra of cytochrome c oxidase

Near-infrared (NIR) difference spectra were obtained for oxidized cytochrome c oxidase of isolated mitochondria in vitro and of cerebral tissue in situ observed through scalp and skull. The broad peaks of maximal absorption observed in both were not inconsistent with the customary assignment of an 830 nm peak. However, the ratios of the intensity of the NIR band to that of the visible peak (605 nm), which we found to be identical for in-vitro and in-situ spectra, were consistently and significantly higher than those of the various purified enzyme preparations reported in the literature. In addition the half-band widths of our in-vitro and in-situ preparations were narrower. Haemoglobin spectra in the NIR obtained in clear and in highly light-scattering media showed almost total absence of band distortion in this spectral region, suggesting that the differences observed are not due to scattering effects. Anoxia and the specific oxidase inhibitors, cyanide and carbon monoxide, caused the expected disappearance of the band in both the mitochondria in vitro and the cerebrum in situ. The 830 nm band observed in intact, well-oxygenated animal preparations was therefore identified with the NIR absorption band of oxidized cytochrome c oxidase, notwithstanding the differences with the observations on purified preparations. This points to the possibility of developing instrumentation and techniques for the non-invasive monitoring of the redox state of cytochrome c oxidase as an index to cerebral oxygen sufficiency, i.e. adequate delivery and utilization of oxygen to and by brain tissue.

Skeletal muscle oxygen availability during respiratory acid-base disturbances in cats

Respiratory acid-base disorders elicit physiological responses that alter O2 delivery to various tissues. We have used a near infrared (NIR) optical technique to monitor cytochrome a,a3 oxidation state, tissue O2 store (relative hemoglobin plus myoglobin oxygenation), and regional blood volume in intact resting skeletal muscle during respiratory acid-base disturbances in anesthetized cats. Hypercapnic acidosis and hypocapnic alkalosis were produced in separate groups of animals by ventilation with increasing concentrations of CO2 (n = 13) or hyperventilation (n = 8). Respiratory acidosis decreased oxygen availability to hindlimb muscle while respiratory alkalosis did not change tissue oxygenation. Inspired CO2 progressively decreased muscle blood volume, cytochrome a,a3 oxidation level, and muscle oxygen store. These optical responses were greatly attenuated both by pre-treatment with bretylium and by hemorrhagic hypotension, suggesting mediation through sympathetic vasoconstriction. Metabolic acidosis, produced by intravenous HCl infusion (n = 8), did not reproduce the hindlimb optical responses mediated by CO2. These experiments demonstrate that hypercapnic acidosis significantly decreases oxygen supply to resting skeletal muscle in the anesthetized cat, probably via neuroregulatory responses to CO2 which do not depend on changes in arterial [H+] in the tested pH range.

Differences in brain cytochrome responses to carbon monoxide and cyanide in vivo

Cytochrome oxidation-reduction responses to two mitochondrial electron transport inhibitors, carbon monoxide (CO) and cyanide (CN), were studied in the intact brains of fluorocarbon-circulated rats. In vivo reflectance spectrophotometry indicated that cortical b-type cytochromes (564 nm) were highly resistant to reduction by CN in the presence of O2 but showed reduction responses to the administration of 1-5% CO in 90% O2. In contrast, cyanide-sensitive cytochromes aa3 (605 nm) and c + c1 (551 nm) did not increase their reduction levels during exposure to 5% CO in 90% O2. The in vivo CO-mediated b-cytochrome reduction responses did not occur after pretreatment with the cytochrome b inhibitor, antimycin A. Transmission spectrophotometry of superfused hemoglobin-free rat brain slices confirmed cortical b-type cytochromes to be CN-resistant in the presence of O2. Another cytochrome absorbing at 445 nm also was resistant to reduction by 1-mM cyanide in vitro, but it could be reduced anaerobically. The reduced 445-nm cytochrome bound CO in the presence of cyanide. We postulate that this CN-resistant CO binding component might account for in vivo cytochrome aa3-CO interactions and directly or indirectly modulate cytochrome b reduction responses to CO. In any event, the spectral data indicate different primary tissue target sites for CO and CN in living rat brain and also suggest different bioenergetic consequences of exposure to the two agents.

Asbestos bodies in bronchoalveolar lavage fluid. A study of 20 asbestos-exposed individuals and comparison to patients with other chronic interstitial lung diseases

We studied the asbestos body (AB) content of bronchoalveolar lavage fluid from 20 patients with a history of occupational asbestos exposure, 31 patients with sarcoidosis and 5 patients with idiopathic pulmonary fibrosis. The cellular lavage pellet was digested in sodium hypochlorite and filtered onto Nuclepore filters for AB quantification by light microscopy. ABs were found in 15 of 20 asbestos-exposed individuals, 9 of 31 sarcoidosis cases and 2 of 5 patients with idiopathic pulmonary fibrosis. There was a statistically significant difference in the number of ABs per million cells recovered or per milliliter of recovered lavage fluid in the asbestos-exposed group as compared to the other categories of chronic interstitial lung disease. The highest levels occurred in patients with asbestosis. Large numbers of asbestos bodies in the lavage fluid (greater than 1 AB/10(6) cells) were indicative of considerable occupational asbestos exposure, whereas occasional bodies were a nonspecific finding.

Near-infrared spectrophotometric monitoring of oxygen distribution to intact brain and skeletal muscle tissues

During continuous near-infrared optical monitoring of brain cortex and hindlimb skeletal muscles, anesthetized, ventilated cats were exposed either to progressive alveolar hypoxia, or to acute hemorrhage followed in some cases by resuscitation. Hypoxia decreased cytochrome a,a3 oxidation state in muscle more than in brain, while tissue blood volume increased in brain and decreased in muscle. At a PaO2 of 25 torr, cytochrome a,a3 oxidation level in the brain was sufficient to support EEG activity, but the cytochrome a,a,3 oxidation state in resting, innervated hindlimb muscle was near zero. Hemorrhagic hypotension invariably decreased cytochrome a,a3 oxidation state and tissue blood volume more in muscle than in brain, and muscle cytochrome a,a3 was completely reduced at about a 25-ml/kg blood loss. These observations, supported by noninvasively measured changes in near-infrared absorption in the tissues during serial intravascular injections of indocyanine green dye, indicate that different cytochrome responses to hypoxia and oligemia in muscle vs. brain tissue are attributable to different regional circulatory adjustments.

Regional cerebral blood flow in normal blood circulated and perfluorocarbon transfused rats

Perfluorocarbon blood substitutes have been shown to exert a protective effect in animal models of cerebral ischemia. The mechanisms by which PFCs improve cerebral hemodynamics are uncertain, however decreased viscosity, small particle size and high oxygen solubility relative to plasma are important factors. Extensive perfluorocarbon exchange transfusion (FC-43) in the rat to a hematocrit of 1%, produces a 100% increase in total cerebral blood flow (FIO2 = 1.0, CaO2 = 6 vol%). Similar increases were seen in normal blood circulated animals breathing 12% O2 (CaO2 = 12 vol%). Therefore, immediately following PFC exchange and the resulting decrease in CaO2, oxygen delivery to the brain is maintained by increasing total blood flow in a manner similar to hypoxic hypoxia.

Energy metabolism and in vivo cytochrome c oxidase redox relationships in hypoxic rat brain

Rats were subjected to graded arterial hypoxia while we measured changes in the oxidation level of cytochrome c oxidase (cytochrome aa3) in the brain by a non-invasive, optical technique. The experiments were terminated at different arterial oxygen tensions (hypoxic levels) and the in vivo observations were compared with in vitro measured changes in metabolites known to reflect limitations in cellular aerobic energy production, e.g. glucose, pyruvate, lactate, phosphocreatine, ATP and ADP. Using absorption changes at 605 nm, in vivo cytochrome aa3 was 46% reduced in normoxia as determined by the range between the maximal oxidation level attained with animals breathing 85% O2 + 15% CO2 and maximal reduction with anoxia (100% N2). Hypoxia reduced cytochrome aa3 to levels of 52, 67, 76, and 84% at mean PaO2 values of 53, 39, 35 and 28 mm Hg, respectively. These increases in reduced cytochrome correlated significantly (r = 0.94) with cortical phosphocreatine depletion, lactate production, and increases in the lactate/pyruvate ratio. However, there were no significant changes in ATP or ADP. Rats did not survive below an FIO2 of 7% because of a precipitous fall in arterial blood pressure. Hypoxically-induced cerebral isoelectricity was coincident with a 50% increase in the cytochrome reduction level (to 73% of the total range defined above). Our results indicate that in vivo monitoring of the reduction level of cytochrome aa3 provides an early, continuous, and direct measure of intracellular oxygen insufficiency at levels which adversely affect aerobic energy production.

Carbon monoxide-cytochrome interactions in the brain of the fluorocarbon-perfused rat

Reflectance spectrophotometry through the skull was used to investigate carbon monoxide (CO) binding by tissue hemoproteins in the brains of barbiturate-anesthetized Sprague-Dawley rats. After splenectomy and extensive perfluorotributylamine exchange transfusion, steady-state spectral scans were obtained in Soret and visible wave-length regions during O2 ventilation, during subsequent exposure to O2-enriched gases containing 1, 3, or 5% CO, and finally after N2 anoxia. These CO exposures were well-tolerated and electroencephalograph (EEG) activity continued to be present. Initial difference spectra were influenced by CO binding to residual hemoglobin, but spectral evidence of CO-mediated b-type cytochrome reduction was obtained in the visible region as CO concentration was increased to 3 or 5%. This was associated with Soret spectra compatible with formation of the reduced cytochrome a3-CO complex. Reduction of cytochrome a at 605 nm and cytochrome c + c1 at 550 nm was absent. These findings may indicate respiratory chain branching through b cytochromes, either to a separate a3-like oxidase independent of the classical cytochrome aa3 or to an unidentified alternative CO-sensitive oxidase.

Cerebral cytochrome a,a3 inhibition by cyanide in bloodless rats

Brain cytochrome a,a3 inhibition is presumed to be the site of lethal histotoxic hypoxia in cyanide poisoning perhaps because of the relative inability of the brain to metabolize cyanide. However, only limited data are available about cyanide toxic effects and possible antagonism in the in vivo brain. In this study, in situ, multiple wavelength, spectrophotometric monitoring of brain cytochrome a,a3 was used to observe oxidation-reduction (redox) responses of cerebral cytochrome a,a3 to intravenous potassium cyanide administration. Bloodless rats prepared by perfluorochemical emulsion (FC-43) exchange transfusion allowed monitoring of cyanide-cytochrome a,a3 interaction without spectral interference by hemoglobin. We found that cyanide-induced transient increases in cytochrome a,a3 reduction level and subsequent redox recovery kinetics were similar in bloodless and normal blood circulated rats. Electroencephalographic activity was maintained until a 50% increase in the reduction level of cytochrome a,a3 was induced with cyanide. Pre-treatment with the cyanide antagonist sodium thiosulfate also protected brain cytochrome a,a3 from cyanide-mediated redox state changes by approximately 4-fold both in normal blood circulated controls and during FC-43 circulation. These latter results indicate that sodium thiosulfate, presumably acting at tissue sites of rhodanese activity, can prevent cerebral cytochrome a,a3 reduction by cyanide even in the virtual absence of blood or circulating proteins.

Spectrophotometry of cerebral cytochrome a, a3 in bloodless rats

Bloodless, anesthetized Sprague-Dawley rats produced by perfluorochemical exchange transfusion and splenectomy were used to obtain cerebral mitochondrial difference spectra directly through the skull by both reflectance and transmission spectrophotometry. Reflectance peaks were about one-third in amplitude compared to transmission peaks, however percentage reduction levels of cytochrome a, a3 in animals breathing 100% oxygen were comparable. Cytochrome a, a3 was 13-14% reduced under these conditions as determined by the ratio of the optical density difference at 605 minus 620 nm to the optical density difference at the same wavelength pair with maximal cytochrome a, a3 oxidation during respiration on 95% oxygen + 5% carbon dioxide at 3 and 4 atm. absolute pressure.

Ga-67 uptake in the lung in sarcoidosis

Images were obtained with Ga-67 and bronchopulmonary lavage performed in 21 patients with sarcoidosis (31 studies). The Ga-67 index, a semiquantitative criterion, was compared to a quantitative computer index based on lung:liver activity ratios; accuracy in predicting active alveolitis (defined by lavage lymphocyte counts) was assessed and differences between 24- and 48-hour studies examined. Computer activity ratios correlated well with the Ga-67 index, which had a sensitivity of 64%, specificity of 71%, and accuracy of 68% compared to 71%, 82%, and 77%, respectively, for the computer scores. Scores at 24 and 48 hours were similar. These results suggest that (a) Ga-67 scanning is useful in staging activity in pulmonary sarcoidosis, (b) quantitative computer scores are accurate in predicting disease activity, and (c) scanning can be performed 24 or 48 hours after injection.

Cyanide-induced cytochrome a,a3 oxidation-reduction responses in rat brain in vivo

The sensitivity of the brain to cyanide-induced histotoxic hypoxia and the protective effects of known cyanide antagonists, have been assessed in vivo by reflectance spectrophotometry. Cyanide-related changes in cytochrome a,a3 (cytochrome c oxidase) oxidation-reduction (redox) state, tissue hemoglobin saturation, and local blood volume were continuously monitored in cerebral cortex of rats. Noncumulative, dose-dependent inhibition of the in situ mitochondrial respiratory chain was evaluated directly by measuring increases in reduction levels of the terminal oxidase. These transient cytochrome a,a3 reductions were accompanied by increases in regional cerebral hemoglobin saturation and blood volume. Cytochrome redox responses were not altered either in magnitude or kinetics by hyperoxia; however, the cyanide-cytochrome dose-response curve was greatly shifted to the right by pretreatment with sodium nitrite, and the recovery rate of cytochrome a,a3 from cyanide-induced reduction was enhanced fourfold by pretreatment with sodium thiosulfate.

Equations for predicting diver regional skin temperatures as a function of mean skin temperature

A series of linear algebraic equations have been derived from those of Kerslake (Flying Personnel Research Committee Memo 213, R.A.F. Institute of Aviation Medicine, 1964) for predicting the regional skin temperatures of a quasi-euthermic diver having pronounced vasoconstriction. The equations were developed by numerically analyzing twelve regional skin temperatures recorded from five resting subjects exposed to a hyperbaric chamber environment of 20 degrees C, 95% helium, and 5% oxygen pressurized to the equivalent of 200 msw (650 fsw). The independent variable of the basic correlation is an arbitrarily defined mean skin temperature; the empirical equations were developed for the purpose of assisting a designer in estimating regional supplementary heating requirements for a diver wearing a thermal protection garment of known composition. The developed equations were authenticated by comparing the predicted normalized regional temperature with the respective experimental normalized temperature obtained from several set of physiological data collected during the evaluation of the Naval Coastal System Center's diver thermal protecting garment (DTP). The results of these comparisons of nondimensionalized temperatures indicated that the derived correlations should accurately predict the skin temperature of the principal regions as a function of mean skin temperature with a normal error of no more than 15%.

Metabolic response to respiratory heat loss-induced core cooling

To study the phenomenon of isolated core cooling, four resting men breathed cooled helium-oxygen (T in = 14 +/- 2 degrees C, 40-60% relative humidity) in a warm hyperbaric chamber at pressures equivalent to 640, 1,000, and 1,400, and 1,800 ft seawater (fsw). Rectal temperature (T re) fell by 0.43 +/- 0.13 degrees C at 640 fsw to 0.98 +/- 0.15 degrees C at 1,800 fsw after 60 min. The rate at which T re fell was linearly related to the product of inspired gas density times specific heat. The metabolic response (VO2) to this isolated core cooling was more closely related to the rate of fall in T re than to the magnitude of this fall. A distinct threshold temperature, below which a rise in VO2 would occur, was not demonstrable. However, when the rate of fall of T re exceeded 0.70 degrees C . h-1, VO2 increased above base line, in spite of high skin temperatures that may have blunted the VO2 response. When VO2 did increase, its net benefit on thermal homeostasis was negated by the associated rise in pulmonary ventilation and its attendant increase in respiratory heat loss. Breathing cool helium-oxygen under hyperbaric conditions can rapidly lower deep body temperature, even in the presence of a warm body surface.

Calibration and characterization of heat flow transducers for use in hyperbaric helium

A calibration technique for heat flow transducers (HFT) verified to within 5% by the National Bureau of Standards was used to show significant errors in calibration constants supplied by the manufacturer of the transducers. The effects of variable ambient temperature and hyperbaric helium on HFT signal responses were defined. Application of accurate calibration constants and appropriate temperature correction factors when using HFTs in hyperbaric helium allowed measurement of convective heat flow to within l0%.

Thermal responses in humans exposed to cold hyperbaric helium-oxygen

The relationship of metabolic heat production to skin and core temperatures, cutaneous heat flow, and respiratory heat loss was measured in 10 male subjects cooled in hyperbaric helium at 20.7 ATA and 15 or 20 degrees C for 60-120 min. Under these conditions, metabolic heat production tended to compensate for the sum of convective and radiant heat losses from the skin but did not increase sufficiently to compensate for additional respiratory heat losses. There was a positive correlation between respiratory heat loss and fall in rectal temperature. Individual variability in ventilatory response to cold hyperbaric helium exposure as shown by a wide range of minute ventilation-to-oxygen consumption ratios (VE/VO2) was similar to that reported during cold water immersion. Subjects with high VE/VO2 had low mean physiological shell insulation values and lost more heat through the skin as well as through the respiratory tract than subjects with low VE/VO2.

Prolonged oxygen exposures in immersed exercising divers at 25 fsw (1.76 ATA)

Twenty-four oxygen exposures lasting 80 to 271 min were performed by six immersed exercising subjects at 25 fsw (1.76 ATA) in both warm and cold water. Two types of exercise were performed, moderate work (50 watts) for long periods of time, and graded exercise (25-150 watts) lasting 85 min. In 21 degrees C water, moderate exercise lasted 228 +/- 39 min, with a mean VO2 of 1.72 +/- 0.11 liter/min. In 4 degree C water, the duration was 163 +/- 22 min, with a mean VO2 of 1.83 +/- 0.16 liter/min. The differences in duration of oxygen exposure in warm and cold water reflect termination at an inspired PCO2 of 7.6 mmHg, a level reached earlier in cold water because of CO2 absorbent exhaustion. In 21 degrees C water, the VO2 for graded exercise ranged from 1.51 to 3.00 liter/min and in 4 degrees C water, from 2.00 to 3.16 liter/min. Central nervous system oxygen toxicity was not observed during these exposures, although two divers had clinical and spirometric evidence of early pulmonary oxygen toxicity. The absence of CNS oxygen toxicity is attributed to low resistance and minimization of dead space, which caused a low inspired PCO2, although the divers' experience with oxygen diving and their excellent physical condition may have contributed as well.

Breast carcinoma, thyroid carcinoma, and T3 thyrotoxicosis in a male cretin

A male patient with clinical and radiographic evidence of cretinism was found to have T3 thyrotoxicosis. The cause was thought to be a well-differentiated follicular carcinoma of the thyroid. Although the disease was not documented, the patient probably had long-standing hypothyroidism. Untreated primary thyroid failure accompanied by high serum thyroid stimulating hormone (TSH) may be carcinogenic to the thyroid. The association of thyroid abnormalities and male breast carcinoma is discussed.

Sequential activation of splenic nuclear RNA polymerases by erythropoietin

The spleen of the ex-hypoxic polycythemic mouse was employed to study the effect of erythropoietin on nuclear RNA polymerase activity. On the basis of ionic strength requirements and sensitivity to the fungal toxin alpha-amanitin, two major forms (I and II) of nuclear RNA polymerase were identified. Within 0.5 h after administration of erythropoietin, at a time when no morphologically identifiable erythroblasts were present in the spleen, there was an increase in the activity of polymerase II. By 2 h, polymerase II activity had declined to control levels. At 3 h, polymerase I activity began to increase, rising to a peak, 88% above control levels, by 12 h. During this period, early erythroblasts began to appear in the spleen. At 12 h, a second increase of similar magnitude occurred in polymerase II activity. Polymerase I activity fell to control levels by 18 h while polymerase II declined more slowly. These data indicate that stimulation of transcription is an early effect of erythropoietin. Multiple forms of RNA polymerase are involved and activation of these is sequential. Nuclear RNA polymerase activity is maximal during the period of early erythroblast proliferation and declines as these cells mature.