Precisão da medida do limiar anaeróbio por meio do calorímetro portátil / Measurement precision of the anaerobic threshold by means of a portable calorimeter / Precisión de la medición del umbral anaerobio por medio del calorímetro portátil

FUNDAMENTO: Muitos métodos são empregados para determinar o Limiar Anaeróbio (LAn) por meio de ergoespirômetros sofisticados. OBJETIVO: Testar a variação no LAn, detectado por modelos matemáticos e de inspeção visual, quando empregado ergoespirômetro de baixo custo e destinado à aplicação clínica. MÉTODOS: Foram voluntários para esse estudo 79 indivíduos aparentemente saudáveis; desses, 57 homens. O VO2máx e o limiar ventilatório foram determinados por calorimetria indireta de circuito aberto. O método eletroenzimático foi empregado para análise da lactacidemia e determinação direta do limiar de lactato (LL). O LAn foi determinado por dois métodos matemáticos (MM SQR e MMslope), baseados nas trocas gasosas, e pelo método de inspeção visual do log-log, para determinação do LL. Dois pesquisadores independentes determinaram o LAn através da inspeção visual de três gráficos, considerando dois métodos (LAn-a= V-slope, EqV; e LAn-b = V-slope, EqV e ExCO2). Os dados foram analisados por meio da estatística paramétrica para determinação das diferenças entre LAn-a versus ExCO2, MM SQR e MMslope; LAn-b versus MM SQR e MMslope; e LL versus LAn-a, LAN-b, MM SQR e MMslope. RESULTADOS: O MMslope foi o único método que apresentou diferença significativa entre o LAn-a e LAn-b (p=0,001), com CV por cento >15. O LL versus MMslope não apresentou diferença significativa (p=0,274), contudo, observou-se um elevado CV (24 por cento). CONCLUSÃO: Conclui-se que com o equipamento de baixo custo os métodos MM SQR e LAn-a podem ser utilizados para a determinação do LAn. O método MMslope não apresentou precisão satisfatória para ser empregado com esses equipamentos.

BACKGROUND: Many methods are used for determining the Anaerobic Threshold (AT) by means of sophisticated ergospirometer. OBJECTIVE: To test the AT variation, detected by mathematical models and visual inspection, when low cost ergospirometer is used and intended for clinical application. METHODS: Seventy nine apparently healthy subjects were volunteers in this study; from these, 57 men. The VO2max and the ventilatory threshold were determined by indirect, open-circuit calorimetry. The electro-enzymatic method was used for analyzing the lactacidemia and direct determination of the Lactate Threshold (LT). The AT was determined by two mathematical methods (MM RSS and MMslope), based on the gases exchange, and by the log-log visual method, for determining the LT. Two independent investigators determined the AT through visual inspection of three graphs, considering two methods (AT-a= V-slope, EqV; and AT-b = V-slope, EqV and ExCO2). The data were analyzed by means of parametric statistics for determining the differences between AT-a versus ExCO2, MM RSS and MMslope; AT-b versus MM RSS and MMslope; and LT versus AT-a, AT-b, MM RSS and MMslope. RESULTS: The MMslope was the only method that presented a significant difference between the AT-a and AT-b (p=0.001), with CV percent >15. LT versus MMslope did not present significant difference (p=0.274), however, it was observed a high CV (24 percent). CONCLUSION: It was concluded that with the low cost equipment, the MM RSS and AT-a methods can be used for determining the TAn. The MMslope method did not present satisfactory precision to be employed with this equipment.

FUNDAMENTO: Muchos métodos se emplean para que se determine el Umbral Anaerobio (UAn) por medio de ergoespirómetros sofisticados. OBJETIVO: Probar la variación en el UAn, detectado por modelos matemáticos y de inspección visual, cuando empleado ergoespirómetro de bajo costo y destinado a la aplicación clínica. MÉTODOS: Fueron voluntarios para este estudio 79 individuos aparentemente sanos; de ellos, 57 varones. El VO2máx y el umbral ventilatorio se determinaron por calorimetría indirecta de circuito abierto. El método electroenzimático se empleó para análisis de lactacidemia y determinación directa del umbral de lactato (UL). El UAn fue determinado por dos métodos matemáticos (MM SQR y MMslope), basados en los cambios gaseosos, y por el método de inspección visual del log-log, para determinación del UL. Dos investigadores independientes determinaron el UAn a través de la inspección visual de tres gráficos, teniendo en cuenta dos métodos (UAn-a= V-slope, EqV; y UAn-b = V-slope, EqV y ExCO2). Los datos se analizaron por medio de la estadística paramétrica para determinación de las diferencias entre UAn-a versus ExCO2, MM SQR y MMslope; UAn-b versus MM SQR y MMslope; y UL versus UAn-a, UAN-b, MM SQR y MMslope. RESULTADOS: El MMslope fue el único método que presentó diferencia significativa entre el UAn-a y UAn-b (p=0,001), con CV por ciento >15. El UL versus MMslope no presentó diferencia significativa (p=0,274), con todo, se observó un elevado CV (24 por ciento). CONCLUSIÓN: Se concluyó que con el equipamiento de bajo costo los métodos MM SQR y UAn-a pueden utilizarse para la determinación del UAn. El método MMslope no presentó precisión satisfactoria para ser empleado con estos equipamientos.

Measurement precision of the anaerobic threshold by means of a portable calorimeter.

BACKGROUND: Many methods are used for determining the Anaerobic Threshold (AT) by means of sophisticated ergospirometer. OBJECTIVE: To test the AT variation, detected by mathematical models and visual inspection, when low cost ergospirometer is used and intended for clinical application. METHODS: Seventy nine apparently healthy subjects were volunteers in this study; from these, 57 men. The VO2(max) and the ventilatory threshold were determined by indirect, open-circuit calorimetry. The electro-enzymatic method was used for analyzing the lactacidemia and direct determination of the Lactate Threshold (LT). The AT was determined by two mathematical methods (MM(RSS) and MM(slope)), based on the gases exchange, and by the log-log visual method, for determining the LT. Two independent investigators determined the AT through visual inspection of three graphs, considering two methods (AT₋(a)= V-slope, EqV; and AT₋(b) = V-slope, EqV and ExCO2). The data were analyzed by means of parametric statistics for determining the differences between AT₋(a) versus ExCO2, MM(RSS) and MM(slope); AT-b versus MM(RSS) and MM(slope); and LT versus AT₋(a), AT₋(b), MM(RSS) and MM(slope). RESULTS: The MM(slope) was the only method that presented a significant difference between the AT₋(a) and AT₋(b) (p=0.001), with CV% >15. LT versus MM(slope) did not present significant difference (p=0.274), however, it was observed a high CV (24%). CONCLUSION: It was concluded that with the low cost equipment, the MM(RSS) and AT₋(a) methods can be used for determining the TAn. The MM(slope) method did not present satisfactory precision to be employed with this equipment.

Combined effect of body position, apparatus and distraction on children's resting metabolic rate.

OBJECTIVE: To verify the combined effect of body position, apparatus and distraction on children's resting metabolic rate (RMR). METHODS: Experiments were carried out on 14 children aged 8-12 (mean age = 10.1 years +/- 1.4). Each participant underwent two test sessions, one week apart under three different situations: a) using mouthpiece and nose-clip (MN) or facemask (FM); b) sitting (SEAT) or lying (LY); and c) TV viewing (TV) or no TV viewing. In the first session, following 20 min rest and watching TV, the protocol was: LY: 20 min stabilization; 10 min using MN and 10 min using FM. Body position was then changed to seated: 20 min stabilization; 10 min using FM; 10 min using MN. In the second session, FM and MN order was changed and participants did not watch TV. Data were analysed according to the eight combinations among the three studied parameters. RESULTS: Repeated measures ANOVA indicated statistically significant differences for VO2 (p =0.01) and RMR (p =0.02), with TVMNSEAT showing higher values than TVFMLY. Bland-Altman analysis showed a bias for VO2, VCO2, respiratory quotient (RQ) and RMR between TVFMLY and TVMNSEAT, respectively, of -17.8+/-14.5 (ml min), -8.8+/-14.5 (ml min), 0.03+/-0.05 and -115.2+/-101.9 (kcal/day). CONCLUSION: There were no differences in RMR measurements due to body position and apparatus when each variable was isolated. Analyses of distraction in three of four combinations indicated no difference between TV and no TV. Different parameter combinations can result in increased bias and variability, and thereby the reported differences among children's RMR measurement.

Validation of the VO2000 calorimeter for measuring resting metabolic rate.

BACKGROUND & AIMS: Metabolic carts used in laboratory settings for the measurement of resting metabolism are cumbersome limiting their use in the field. The validity of a newly developed portable calorimeter (Medical Graphics VO2000) under resting conditions was assessed in comparison to a well-established reference system, the DELTATRAC. METHODS: Gas exchange and energy expenditure were measured for 25 min consecutively using the two devices. Values of the last 20 min were averaged and used in the analysis. The order of device for the first subject was randomly chosen and the calorimeters were alternated thereafter. RESULTS: Among 33 subjects, acceptable measures of resting metabolism were obtained in 25 (11 men) aged 20-78 years because eight subjects (three men) either hyperventilated or did not adapt well enough to the facemask. VO(2), VCO(2), and RQ were not significantly different between devices. Small (2.8%) non-clinically relevant mean differences (-0.145+/-0.341 MJ day(-1)) were found. Results of the two devices were highly correlated (r=0.95) yielding a more accurate estimate than predictive equations. CONCLUSIONS: The VO2000 calorimeter is a valid system to measure resting metabolism but the facemask may not be suitable for some people.

Indirect calorimetry: methodology, instruments and clinical application.

PURPOSE OF REVIEW: This review aims to identify the basic methods for accurately measuring a patient's energy expenditure in clinical nutrition practice by indirect calorimetry, and the impact upon a disease state of applying the results obtained. RECENT FINDINGS: The open-circuit method is the most widely used in the majority of classical instruments for measuring energy consumption. Advances in gas exchange measurement have made this technique readily and precisely available at the bedside. Nevertheless, it is important to understand its intricate primary methodology for safe and correct application. The stress and activity factors should be carefully and specifically applied, and the respiratory quotient abandoned, for tailoring a patient's daily nutrition regimens. Caloric expenditure measured by indirect calorimetry coupled with the doubly labeled water technique introduced the concept of physical activity energy expenditure, which added to resting energy expenditure results in total daily energy expenditure. Compact modular and handheld devices have been introduced into the market, together with similar technology for evaluating exercise energy expenditure, making utilization easier, safer and precise. In the critically ill population, which is exposed to medical and surgical interventions, indirect calorimetry has greatly changed the practice of caloric administration, significantly reducing the total daily amount. SUMMARY: In conclusion, one has to be careful when choosing devices, and understanding and clinically applying the results obtained by indirect calorimetry, bearing in mind that measured resting energy expenditure should be the daily caloric goal in order to diminish clinical morbidity.