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Is it possible to measure metabolic RQ during mechanical ventilation? A clinical and computer simulated study on carbon dioxide stores
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KINETICS OF l-METHYLHISTIDINE (IMH) AND 3-METHYLHISTIDINE (3MH) AFTER MEAT INTAKE J. Sjolin, L. Hambraeus, G. Friman (Departments of Infectious Diseases and Nutrition, University of Uppsala, Sweden). We have recently demonstrated that urinary excretion of IMH is increased after intake of beef and that the elimination curves of 1MH and 3MH followed first order kinetics with similar elimination rate constants. 1MH was present in all types of meat analyzed, the highest value, expressed as the lMH:3MH ratio, recorded in chicken: 8,40 and the lowest in pork: 0,6 (Clinical Research, April-85). The aim of the present investigation was (1) to study if urinary kinetics of IMH and 3MH are dose dependent and similar whether obtained from pork (low 1MH content) or chicken (high IMH content) and (2) to estimate the degree of absorption of 1MH.
5 healthy subjects were fed an ovolactovegetarian diet for two Y-day-periods. On day 5 of each period the diet was supplemented with different amounts of chicken, loo-287 g, and pork, 116-316 g. 24 h urine specimens were collected from day 3 and on for analysis of 1MH and 3MH in an amino acid analyzer. The increases in the urinary excretions of IMH and 3MH above the individual baseline values showed a strong linear relationship with the ingested amounts. Thus, the urinary increase per gram ingested meat was (mean + SD) for chicken; 1MH: 12,74 + 1,24 and 3MH: 1,04 + 0,13; for pork IMH: 0,89 + 0,17 and 3MH: 1,46 + 0,13 umoles. Individual baseline values were reached within 2 days after meat intake except for the two subjects eating the largest amounts of chicken (3 days). The mean elimination rate constants calculated from the latter two subjects were; KlMH chicken -0,060 and KlMH pork - 0,055 h-l compared to KlMH beef - 0,067 h-l. In conclusion our resultssuggest that 1MH shows similar dose independent kinetics as 3MH after meat intake regardless of source. The absorption is probably total as the contents of IMH and 3MH in chicken have earlier been shown to be 11,O and I,3 umoles/g. Thus, 1MH excretion may serve as an objective indicator of meat (3MH) intake, being the major bias when using 3MH excretion as a quantitative measure of myofibrillar protein catabolism.
0.124 IS IT POSSIBLE TO MEASURE METABOLIC RQ DURING MECHANICAL VENTILATION? A CLINICAL AND
D. SUderberg, T. Groth, COMPUTER SIMULATED STUDY ON CARBON DIOXIDE STORES .+s. S. Henneber H. StjernstrUm, L. Wiklund (Departments of Anaestheslo ogy and Biomedical Systems Analysis, University Hospital, Uppsala, Sweden)
The measurement of metabolic RQ in ventilator-treated patients involves methodological problems mainly because of the Cop-stores , which are in the order of 15-20 1 in normal man. Changes in C02-production and the time required to reach a steady state were studied in mechanically ventilated ICU-patients. Measurements were done using an Engstram ventilator (ECS 2000). Expired gases were led to a mixing chamber where gas analyses were made continuously with a masspectrometer (Perkin-Elmer). Signals from this and the volume signal from the ventilator were led to a computer where data storing and calculation of oxygen uptake and Cop-production were done. Changes in C02-stores were achieved by: 1) a 15 % change in ventilation, 2) reduction of body temperature, 3) different levels of sedation. In these situations 20-120 min were required to reach a new steady state, depending on the size of the patient and the circulatory response to the change. The electric analogue model of carbon dioxide stores suggested by Farhi and Rahn (1960) was transformed to a mathematical model and simulations of the clinical experiments gave similar results. Based on these experiments the following recommendations are given for the measurement of metabolic RQ in ventilated patients: a) no changes in body temperature and awareness 60 min before and during the gas sampling are allowed, b) adjustments of the ventilator are not allowed during the last 90 min before gas sampling, c) cardiac output and muscle blood flow should be without substantial changes for the last 2-3 h. Note that if muscle blood flow is low, the time required in a and b is prolonged. Conclusion: When metabolic calculations are made using RQ measurementsin ventilatortreated patients, great care should be taken regarding the steady state of C02-stores. For clinical purposes it is often best only to measure oxygen uptake. The equipment used will then be less complex and cheaper and the main purpose of indirect calorimetry, namely to determine energy requirements, is still achieved.
KINETICS OF l-METHYLHISTIDINE (IMH) AND 3-METHYLHISTIDINE (3MH) AFTER MEAT INTAKE J. Sjolin, L. Hambraeus, G. Friman (Departments of Infectious Diseases and Nutrition, University of Uppsala, Sweden). We have recently demonstrated that urinary excretion of IMH is increased after intake of beef and that the elimination curves of 1MH and 3MH followed first order kinetics with similar elimination rate constants. 1MH was present in all types of meat analyzed, the highest value, expressed as the lMH:3MH ratio, recorded in chicken: 8,40 and the lowest in pork: 0,6 (Clinical Research, April-85). The aim of the present investigation was (1) to study if urinary kinetics of IMH and 3MH are dose dependent and similar whether obtained from pork (low 1MH content) or chicken (high IMH content) and (2) to estimate the degree of absorption of 1MH.
5 healthy subjects were fed an ovolactovegetarian diet for two Y-day-periods. On day 5 of each period the diet was supplemented with different amounts of chicken, loo-287 g, and pork, 116-316 g. 24 h urine specimens were collected from day 3 and on for analysis of 1MH and 3MH in an amino acid analyzer. The increases in the urinary excretions of IMH and 3MH above the individual baseline values showed a strong linear relationship with the ingested amounts. Thus, the urinary increase per gram ingested meat was (mean + SD) for chicken; 1MH: 12,74 + 1,24 and 3MH: 1,04 + 0,13; for pork IMH: 0,89 + 0,17 and 3MH: 1,46 + 0,13 umoles. Individual baseline values were reached within 2 days after meat intake except for the two subjects eating the largest amounts of chicken (3 days). The mean elimination rate constants calculated from the latter two subjects were; KlMH chicken -0,060 and KlMH pork - 0,055 h-l compared to KlMH beef - 0,067 h-l. In conclusion our resultssuggest that 1MH shows similar dose independent kinetics as 3MH after meat intake regardless of source. The absorption is probably total as the contents of IMH and 3MH in chicken have earlier been shown to be 11,O and I,3 umoles/g. Thus, 1MH excretion may serve as an objective indicator of meat (3MH) intake, being the major bias when using 3MH excretion as a quantitative measure of myofibrillar protein catabolism.
0.124 IS IT POSSIBLE TO MEASURE METABOLIC RQ DURING MECHANICAL VENTILATION? A CLINICAL AND
D. SUderberg, T. Groth, COMPUTER SIMULATED STUDY ON CARBON DIOXIDE STORES .+s. S. Henneber H. StjernstrUm, L. Wiklund (Departments of Anaestheslo ogy and Biomedical Systems Analysis, University Hospital, Uppsala, Sweden)
The measurement of metabolic RQ in ventilator-treated patients involves methodological problems mainly because of the Cop-stores , which are in the order of 15-20 1 in normal man. Changes in C02-production and the time required to reach a steady state were studied in mechanically ventilated ICU-patients. Measurements were done using an Engstram ventilator (ECS 2000). Expired gases were led to a mixing chamber where gas analyses were made continuously with a masspectrometer (Perkin-Elmer). Signals from this and the volume signal from the ventilator were led to a computer where data storing and calculation of oxygen uptake and Cop-production were done. Changes in C02-stores were achieved by: 1) a 15 % change in ventilation, 2) reduction of body temperature, 3) different levels of sedation. In these situations 20-120 min were required to reach a new steady state, depending on the size of the patient and the circulatory response to the change. The electric analogue model of carbon dioxide stores suggested by Farhi and Rahn (1960) was transformed to a mathematical model and simulations of the clinical experiments gave similar results. Based on these experiments the following recommendations are given for the measurement of metabolic RQ in ventilated patients: a) no changes in body temperature and awareness 60 min before and during the gas sampling are allowed, b) adjustments of the ventilator are not allowed during the last 90 min before gas sampling, c) cardiac output and muscle blood flow should be without substantial changes for the last 2-3 h. Note that if muscle blood flow is low, the time required in a and b is prolonged. Conclusion: When metabolic calculations are made using RQ measurementsin ventilatortreated patients, great care should be taken regarding the steady state of C02-stores. For clinical purposes it is often best only to measure oxygen uptake. The equipment used will then be less complex and cheaper and the main purpose of indirect calorimetry, namely to determine energy requirements, is still achieved.