Presence Of Carboxyhemoglobin Research Articles

Mechanisms of carbon monoxide toxicity

This review re-examines the possibility that some of the toxic effects of CO exposure in man could be due to CO binding within cells, as well as decreases in tissue pO 2 resulting from the presence of carboxyhemoglobin (HbCO). Data are reviewed from experiments designed to measure adverse effects of CO on isolated smooth muscle. These data show that CO tensions greater than 1,000 times those seen in intact tissues when HbCO is 5 to 10% saturation have only a small effect on oxygen uptake. Thus, it is unlikely that in vivo CO toxicity occurs in this tissue as a result of binding to cytochrome oxidase. I reviewed existing data which indicate that CO binding to myoglobin, in heart and skeletal muscle, is significant, even at low CO exposure giving HbCO less than 5% saturation. Whether myoglobin—CO binding is a significant cause of CO toxicity during exercise, or of the sensitivity of the myocardium to CO, is unknown.

Shunt effect of carboxyhemoglobin

Estimation of intrapulmonary blood shunt fraction requires accurate evaluation of pulmonary capillary, arterial, and mixed venous oxygen contents. The presence of carboxyhemoglobin, as well as methemoglobin and sulfhemoglobin, may lead to large errors in the calculated intrapulmonary blood shunt fraction. The errors are most pronounced at low values of carboxyhemoglobin and low values of true intrapulmonary shunt fraction.

Determining P50 in the presence of carboxyhemoglobin.

A method is proposed, using mathematical solutions to the Roughton-Darling analysis, that theoretically can correct the measurements used for P50 determinations, whenever HbCO is present in blood, either initially or after equilibration. The resulting P50 is calculated in a "CO-free" state, independent of the actual presence of HbCO. This can be converted to a term designated T50, which indicates the in vivo shift caused by the concentration of HbCO measured. The concept was tested by comparing the P50 measurements in subjects with normal hemoglobins who differed by smoking habits (smokers vs. nonsmokers). The results showed similar mean values for this definition of P50, despite an average 10-fold difference in initial concentrations of HbCO. The method is applicable both to the single point principle, wherein P50 is estimated directly from venous blood measurements, and to standard tonometry-mixing techniques, as long as instrumentation includes the measurement of CO saturation.

An EPR study of manganese(II) binding to 5′-ATP, hemoglobin, and hemocyanin

Several divalent metal ions affect the oxygen affinity of hemoglobin and hemocyanin. It is important, therefore, to understand the nature of metal-ion binding to these proteins. By comparing the EPR spectra of Mn(II), 0.001 M, in the absence and presence of carboxyhemoglobin or Limulus oxyhemocyanin (pH 7.3, Trizma buffer), the number of Mn binding sites, n, and the binding constant, K, can be determined. For carboxyhemoglobin, HbCO, we find 0.5 Mn binding sites per heme, K = 450 M −1. Each hemoglobin tetramer therefore binds two manganous ions suggesting that Mn(II), like Cu(II), may bind preferentially to one of the two types of subunits in hemoglobin. For hemocyanin, HcO 2, we find n = 5.8, K = 1.55 × 103 M −1. Each oxyhemocyanin therefore binds approximately six manganous ions, and the binding constant is three times larger than that for HbCO. We have also carried out similar experiments on 5′-ATP, and on solutions of HbCO and ATP containing MgCl 2 or ZnCl 2. Zn(II) effectively competes with Mn(II) in binding hemoglobin and ATP, whereas Mg(II) does not, in accord with expectations from data on oxygen affinity of hemoglobin.

Carboxyhemoglobin and the access to oxygen: an example of human counterevolution.

Carboxyhemoglobin (COHb) alters the oxyhemoglobin dissociation curve in such a manner that oxygen is released to the tissues with great difficulty and at a lower oxygen tension. The known effects on heart and brain of breathing .Sow concentrations of carbon monoxide are primarily related to this leftward shift and perhaps also to combination with myoglobin and certain iron-containing enzymes. Hemoglobin-oxygen equilibria in the presence of COHb resembles the equilibria of more primitive forms of hemoglobin and gives rise to the suggestion that this decrease in the access to oxygen is a form of counterevolution.

Elevated carbon monoxide levels from smoking in blood donors.

The greater affinity of hemoglobin for carbon monoxide than for oxygen can lead to increased carboxyhemoglobin in blood donors who smoke. The presence of carboxyhemoglobin has an adverse effect on the oxygen dissociation curve resulting in a decreased release of oxygen to the tissues. When this is present, along with the progressive decrease in oxygen‐carrying capacity resulting from storage, bank blood will have an even greater loss in ability to provide oxygen to the tissues of a recipient. Carbon monoxide can be displaced from hemoglobin by oxygen when there is room air exchange by donor respiration. The rate of this exchange can be accelerated by taking advantage of the natural gas laws and using a higher concentration of oxygen for respiration or by increasing ventilatory exchange. Volunteers in the present study raised their carboxyhemoglobin levels by heavy smoking and had the rate of decrease in carboxyhemoglobin tested either after breathing pure oxygen or after exercise‐induced hyperventilation. The decreases in carboxyhemoglobin levels were accelerated by either method. Donors who had not smoked showed low carboxyhemoglobin levels which did not decrease after exercise. Thus, blood banks could minimize carboxyhemoglobin levels in collected blood by restricting the smoking of donors, by not collecting blood for at least 2 to 4 hours after smoking, or by using oxygen breathing or exercise‐induced hyperventilation to accelerate the donors excretion of carbon monoxide.

Cytological demonstration of carboxyhaemoglobin in human erythrocytes.

ALTHOUGH oxyhaemoglobin is oxidized by nitrite to methaemoglobin, carboxyhaemoglobin is not. This difference can be used to demonstrate the presence of carboxyhaemoglobin in single erythrocytes of a blood smear, simply by extending the methaemoglobin- (cyanmethaemoglobin-) elution technique of Kleihauer and Betke1.

Spectrophotometric Determination of Oxygen Saturation of Hemoglobin in the Presence of Carboxyhemoglobin

Spectrophotometric Determination of Oxygen Saturation of Hemoglobin in the Presence of Carboxyhemoglobin

Spectrophotometric Determination of Oxygen Saturation of Hemoglobin in the Presence of Carboxyhemoglobin

Spectrophotometric Determination of Oxygen Saturation of Hemoglobin in the Presence of Carboxyhemoglobin