RESUMO
RESUMEN El aumento del trabajo respiratorio (work of breathing, WOB) es uno de los problemas kinesiológicos frecuentes en el quehacer clínico. Un desafío profesional es contar con valores de variables fisiológicas que permitan objetivar el WOB facilitando así su interpretación entre los diferentes profesionales de la salud. El uso de dispositivos portátiles que registran la longitud de onda cercana al rango infrarrojo (680- 820 nm, Near Infrared Spectroscopy (NIRS)) en músculos superficiales permite obtener valores de hemoglobina total unida a oxígeno (tHb) y oxigenación muscular local (SmO2), variables relacionadas al trabajo muscular pues reportan el flujo sanguíneo en la microcirculación y consumo de oxígeno local, respectivamente. Estos dispositivos situados en musculatura intercostal nos informan el WOB asociado a la respiración. Para evaluar esto, se analizó el comportamiento de tHb y SmO2 en m. intercostal en 20 corredores de maratón durante la valoración de consumo de oxígeno máximo (VO2- max), instancia que implica aumento sostenido e incremental de la ventilación pulmonar (��E), y por tanto de la actividad muscular respiratoria. El aumento de V E en 128,4 L·min-1 ( ��E (máximo-reposo)) implicó una disminución en SmO2- m.intercostal del 34% ( SmO2 (reposo-máximo)), sin cambios en tHb (p=0,805). La tuvo una correlación inversa con SmO2-m.intercostal (rho=-0.565; p=0,001). Se concluye que la valoración de SmO2-m.intercostal es una forma novedosa de objetivar el WOB en sujetos sanos. Conocer la aplicabilidad clínica requiere de otros estudios que evalúen esta herramienta en pacientes con disfunciones cardiorrespiratorias, lo que permitiría incorporar su uso en nuestro desarrollo clínico profesional.
The work of breathing (WOB) increased is a commonkinesiological problems at the clinical practice. A professional challenge is to have values of physiological variables that allows to objective the WOB, thus facilitating its interpretation among different health professionals. The use of portable devices that measure by spectroscopy the near-infrared wavelength (680-820 nm) atsuperficial muscles allows to obtain values of total hemoglobin linked to oxygen (tHb) and local muscle oxygenation (SmO2), variables related to muscle work because give information of the blood flow at the microcirculation and local oxygen consumption, respectively. These devices located at the m.intercostal could give information about the WOB associated to breathing. To evaluate this, the tHb and SmO2 of the m.intercostal in 20 marathon runners were analyzed while they doing the maximum oxygen consumption test (VO2-max), an exercise that increase the pulmonary ventilation and the respiratory muscle activity. The increase of V E (128,4 L·min-1((max-rest)) implied a decrease in SmO2- m.intercostal (34% ( SmO2 (max-rest)), without changes in tHb (p=0.805). The showedan negative correlation to SmO2-m.intercostal (rho= -0.565; p=0.001). It is concluded that the assessment of SmO2-m.intercostal is a novel way to measure the WOB in healthy subjects. Their clinical applicability requires more studies that applied this tool in patients with cardiorespiratory dysfunctions, facilitating their incorporation in the professional clinical practice.
RESUMO
The purpose of this study was to confirm both the reproducibility of indices (NIRS slope, NT2, %NIRS fall) and the specificity obtained by analyzing the muscle oxygenation curve measured by near-infrared spectroscopy (NIRS) during ramp exercise. Ten healthy men participated in this study. The NIRS probe was placed on the vastus lateralis muscle. An increase in oxygenation was observed from rest to warm-up at 0 watts (Δ NIRS) . Oxygenation began to decrease lineally as the workload increased (NIRS slope) . In the latter phase of exercise, the oxygenation curve flattened out despite an increasing workload, and as a result, an inflection point was formed (NT2) . The minimum value of oxygenation during ramp exercise was indicated as“%NIRS fall.”<BR>Protocol 1. After a warm-up period of 3 min at 0 watts, a ramp exercise (20 watt/min) test was performed until volitional fatigue. The test was performed for each subject twice (test-1, test-2) with a 1-week interval. Protocol 2. A test was performed with three consecutive ramp exercises (lOwatt/min·20watt/min·30watt/min) up to120watt each with sufficient rest between the exercises.<BR>NT2 was observed in 7 of 10 subjects. Test-1 and test-2 mean values of ANIRS, NIRS slope, watts at NT2 (NT2) and %NIRS fall were not significantly different, and the correlations between test-1 and test-2 were highly significant (r=0.94, P<0.0001: ANIRS, r=0.99, P<0.0001: NIRS slope, r=0.91, P<0.002: NT2 and r=0.78, P<0.005 : %NIRS fall) . The regression lines obtained for correlations of results of test-1 and test-2 were y=-5.89+1.38X (Δ NIRS), y=0.02+ 1.03X (NIRS slope), y=31.52+0.83X (NT2), and y=19.91+0.61X (%NIRS fall) . No significant differences in both intercept and coefficient between the regression line and identity line were found in the NIRS slope and NT2. The rate of decrease in the oxygenation curve became steeper with an increase in work-load from 10 watts/min to 20 watts/min and to 30 watts/min. However, the mean values of the NIRS slope, modified by watts, were 0.29±0.06%/watt, 0.29±0.07%/watt and 0.29±0.07%/watt, respectively. There were no significant differences of the NIRS slopes among these exercises. The results indicate constancy of the rate of decrease in oxygenation per workload.<BR>In conclusion, these findings demonstrate the reproducibility of the NIRS slope and the appearance of NT2 during ramp exercise, and the specific way in which the decrease in muscle oxygenation reflects workload. They suggest that analysis of the muscle oxygenation curve can be used to estimate muscular metabolism and indices of training effects.
RESUMO
A study was conducted to establish a method for quantitative evaluation of both the rate and degree of muscle oxygenation during ramp exercise using Near Infrared Spectroscopy (NIRS), and to determine the relationship of the indices to body composition and physical fitness. The subjects were 13 healthy men. After a warm-up period of 3 min at 20-W, the ramp exercise test was conducted. The exercise consisted of an increasing work rate at a slope of 20 W/min on a cycle ergometer performed until volitional fatigue. The NIRS probe used in the cycling exercise was placed on the vastus lateralis muscle. After 30 min of exercise, calibration was performed by cuff occlusion for 10 min with a pressure of 260 mmHg for quantitative determination of the NIRS curve. The oxygenation curve measured by NIRS during the exercise initially exhibited a linear decrease as the work rate increased. This rate of decrease in oxygenation was indicated by the NIRS slope (%/W) obtained from the calibration curve. In later stages of the exercise, the NIRS curve became flattened with increased work rate. The breaking point between the sloping phase and the flat phase was named the “NIRS Threshold 2, NT 2”. In addition, the rate of decrease in oxygenation at the end of exercise per maximal NIRS decrease obtained from the calibration curve was indicated as the %NIRS fall. The mean NIRS slope and %NIRS fall were 0.3±0.1%/W (range, 0.13 to 0.50%/W) and 29.9±11.8% (range, 12.0 to 50.0%), respectively. NT 2 was observed in 8 of the 13 subjects. The subjects were divided into two groups (NT 2 (+) and NT 2 (-) ) based on the appearance of NT 2. Both the NIRS slope and %NIRS fall in the NT 2 (+) group were significantly higher than those in the NT 2 (-) group. The NIRS slope was significantly correlated with VO<SUB>2</SUB>/wt at VT (r=0.73, p<0.05) and wattage at VT (r=0.86, p<0.0001) . The %NIRS fall was significantly correlated with VO<SUB>2</SUB>/wt at peak (r=0.80, P<0.001) . The NIRS slope and %NIRS fall were not significantly correlated with body mass index, %fat or thigh circumference.<BR>These findings suggest that the NIRS slope indicates the efficiency of oxygen exchange in muscles activated during incremental exercise, and that the %NIRS fall indicates the ability to utilize Oxy-Hb+Mb against maximal oxygenation capacity in muscles. The NIRS slope and %NIRS fall can therefore be used as indices of muscular limitation during exercise, and as indices of muscular adaptation during exercise.