Indirect Fick Method Research Articles

Arterialized capillary blood gases in exercise studies.

The PCO2, PO2 and pH of arterial blood and arterialized capillary blood from the ear lobe were compared in 13 patients at rest and during submaximal exercise. The mean capillary PCO2 was .6 mmHg lower than arterial PCO2 at rest and 1 mmHg lower in exercise. The variation in comparisons (S.D. 1.4 mmHg) at rest and exercise, was greater than between duplicate capillary samples (S.D. .7 mmHg). The mean capillary PO2 was 3.3 mmHg higher than arterial at rest, and 1.7 mmHg higher in exercise: the variation was also greater than for PCO2 (S.D. 5.2 MMHg at rest, 4.2 mmHg in exercise) and greater than in duplicate samples (S.D. 2.6 mmHg). A comparison was made of calculated cardiac output (indirect Fick method) and dead space: tidal volume ratio during exercise, using arterial PCO2 and capillary PCO2: cardiac output was systematically overestimated by 6% (S.D. 9.3%) and VD/VT ratio underestimated by 10% (S.D. 9-3%) when capillary PCO2 was used in the calculations. Capillary blood samples are an acceptable alternative to arterial blood, for measurement of blood gases and pH, as long as blood flow is brisk enough to fill a large (125 mgl) glass capillary tube within 30 seconds. The accuracy of the estimates is greatest for pH, and least for PO2. The PCO2 and PO2 measurements are sufficiently precise for their use in the calculation of cardiac output, VD/VT ratio, alveolar-arterial PO2 difference and venous admixture effect during exercise.

Reproducibility of indirect (CO 2 ) Fick method for calculation of cardiac output.

Reproducibility of indirect (CO 2 ) Fick method for calculation of cardiac output.

Cardiac output and arterial blood gases during exercise in pubertal boys.

Cardiac output and arterial blood gases during exercise in pubertal boys.

Exercise studies in children using the indirect (CO 2 ) Fick method.

Exercise studies in children using the indirect (CO 2 ) Fick method.

Cardio-respiratory response to treadmill exercise in normal children.

1. Studies have been made of the response to running on a treadmill in forty boys and girls aged 5–15 years. 2. Each child was studied at two consecutive levels of steady-state work representing about 50% and 80% of his physical working capacity. Cardiac output was measured by the Indirect (CO2) Fick method. 3. The cardiac and ventilatory responses to exercise were similar to those seen during cycling on an ergometer except that the heart rate and the respiratory exchange ratio were a little lower. Stroke volume was the same. 4. The responses of children to running and cycling are discussed and the similarity to the responses of adults is noted.

Cardio-respiratory response to exercise in normal children.

1. The results of studies during simple progressive exercise to exhaustion and steady-state submaximal exercise in 117 boys and girls aged 6–16 years are presented. 2. In the simple progressive exercise test, the highest work load achieved and the submaximal heart rate were related to size and sex. The maximum heart rate and submaximal ventilation were largely independent of size and sex. 3. Steady-state exercise was performed at one-third and two-thirds of the maximum work load achieved in the simple progressive test. The Indirect (CO2) Fick method was used to measure cardiac output. 4. At any given level of steady-state work, tidal volume, dead space, heart rate and stroke volume were closely related to size, with girls having higher heart rates and smaller stroke volumes than boys. Minute ventilation and cardiac output were virtually independent of size and sex. The cardiac output in children was the same as that in the adult for any given oxygen consumption. Blood lactate was related to size at any given work load, but was independent of size at any given fraction of the maximum working capacity.

Estimates of the CO 2 pressures in systemic arterial blood during rebreathing on exercise

Blood was sampled from the brachial arteries of 3 subjects on 120 occasions before or during the prolonged rebreathing of CO 2 in O 2 mixtures. Studies were made at rest and during 3 grades of exercise (300–900 kpm/min). The CO 2 tension in rebreathed gas was consistently higher than that measured in arterial blood and the difference increased with the level of exertion but at steady loads it did not change with time. The CO 2 contents of 45 samples were measured on the same occasions. Their tension-content coordinates fell on the in vitro dissociation curves of normal blood. Previous studies on the same subjects had shown a similar discrepancy between rebreathed gas and pulmonary arterial blood. In spite of these findings the indirect Fick method, based on rebreathing estimates of the mixed venous P CO 2 , and end-tidal estimates of the arterial P CO 2 , yields values for cardiac output which closely agree with those obtained in direct Fick and dye dilution studies published by others. The interpretation of oxygen based estimates of cardiac output is also discussed.

Aortopulmonary collateral flow in patients with pulmonary disease.

The aortopulmonary collateral in pulmonary disease has never been measured accurately despite many morphologic studies (1-7), which revealed numerous developments of the bronchial arteries and other systemic arteries connecting with the pulmonary vessels. To the writers' knowledge, four methods have been presented. The first (8, 9) is the detection of an increased pulmonary capillary by the indirect Fick method using carbon dioxide. The second (10) is the measurement of effective collateral flow by combined use of bronchospirometry and the Fick principle. The third ( 11-16) consists of simultaneous estimations of the right and left ventricular outputs by the indicator-dilution technique. The fourth (17, 18) is based on the concept that the early appearance of indicator in the left atrium following injection of indicator into the aortic root is carried by blood that has flowed through aortopulmonary shunts without traversing the systemic capillaries. The last method, which was proposed first by Cudkowicz and associates (17) in 1960, may be the most direct and it seems the most reliable. However, detailed information has not been available for either criticizing the method or evaluating the results. The purpose of this study was to measure the aortopulmonary collateral in various pulmonary diseases by using the direct dyedilution method and to discuss the significance of the collateral circulation.

Determination of Cardiac Output by Rebreathing Method ; with Special Reference to Its Reliability and Merit in Clinical Use

The PV^^co2, was determined graphically by the rate of rise in CO2 concentration while rebreathing pure oxygen. The reproducibility of consecutively determined PV^^co2 was fairly well and it correlated significantly with the PaCO2= directly measured from arterial blood. To make the procedure determining the cardiac output strictly non-bloody, PaCO2 was also determined indirectly by the end-tidal gas analysis. The CO2 output was measured conventionally. The PV^^co2 and PaCO2 were converted to their con-tent with CO2 dissociation curve for fully oxygenated blood, then the cardiac output was calculated applying these values to the Fick's formula. The range of the cardiac output determined consecutively during an hour was considered small enough to be included within the physiological fluctuation, and the cardiac output thus determined correlated significantly with that by direct Fick method. The cardiac output was significantly different between one another in three groups (healthy, ischemic heart disease and ischemic heart failure). The result agreed with that made by the dye dilution method and apexcardiogram. Having fairly good reproducibility and showing good accordance with the results by the other techniques, it was proved that this indirect Fick method is of great clinical use. Besides, the procedure does not give almost any mental or physical load to subjects.

EVALUATION OF MYOCARDIAL BLOOD PERFUSION IN MAN WITH RADIOACTIVE POTASSIUM OR RUBIDIUM AND PRECORDIAL COUNTING.

The myocardial clearance of potassium may be obtained by precordial counting after a single intravenous injection of K 42 Cl or Rb 86 Cl. The theoretical foundations of the method and the technic developed have been presented and discussed. The distribution of the values obtained in normal subjects and in subjects with coronary insufficiency is in agreement with the clinical expectancy, and changes of the observed MCK after nitroglycerin agree with the results obtained by other investigators who measured coronary blood flow by the indirect Fick method. In agreement with the observations of other investigators in rats and dogs, the amount of K 42 or Rb 86 in the myocardium was found to change very little for an appreciable time interval after the first circulation, despite the significant recirculation and the decreasing arterial concentration. This observation and the fact that MCK values in normal subjects closely agree with the accepted values for coronary blood flow confirm Sapirstein's findings in rats and dogs, and support the view that the organ uptake of Rb 86 or K 42 immediately after single intravenous injection reflects the fractional organ blood flow. As obtained with the present technic, and similarly with the indirect Fick method, MCK reflects the flow per gram of myocardium and not the total coronary blood flow. MCK, however, has the advantage that every unit volume of myocardium, no matter how well it is perfused or through which vessels it is drained, contributes to the precordial counting rate in variable proportions determined by the efficiency of the counting method.

New Indirect Fick Procedure for the Determination of Cardiac Output

THE indirect Fick method for determining cardiac output, which requires neither catheterization nor arterial puncture, would be the method of choice but for one serious drawback, namely, the difficulty of obtaining a reliable value for the carbon dioxide tension in (oxygenated) venous blood. It is now generally recognized that, when the breath is held, no equilibrium between alveolar and mixed venous Pco2 is attained in the 15–20 sec. before recirculation intervenes. It has been proposed to plot the increase in pressure of alveolar carbon dioxide, Pco2 while the breath is held, and to compute the mean value of venous Pco2 by means of extrapolation1. Since alveolar Pco2 cannot be measured while the breath is held, this method requires the determination of alveolar Pco2 at the end of a number of successive periods of holding the breath of different lengths. This results in considerable scatter of the experimental points and, thus, in an appreciable degree of uncertainty regarding the value for alveolar Pco2.