RESUMEN
Low-flow continuous oxygen can lead to significant improvement in exercise capacity in selected patients with stable hypoxemic pulmonary disease. Although the mechanisms of improvement are incompletely understood, two tenable hypotheses are (1) the relief of hypoxic pulmonary vasoconstriction and (2) improved peripheral oxygen delivery. This prospective study was performed to examine these two hypotheses. Stable patients with hypoxemic lung disease performed symptom-limited ergometry with hemodynamic monitoring before and after greater than one month of long-term home oxygen therapy. There were 22 patients who increased exercise capacity by greater than 100 KPM/min and greater than 4 min duration and 11 patients who did not increase their exercise capacity greater than 2 min or in KPM/min. Neither the responders nor the nonresponders had significant changes in pulmonary pressures or resistances or effective arterial volume elastances at exercise after long-term O2 therapy. The responders had significant increases in oxygen delivery during exercise (148 +/- 33 ml/min vs 184 +/- 51 ml/min, p = 0.004), cardiac output (7.7 +/- 1.6 L/min vs 8.7 +/- 2.1 L/min, p = 0.003), and arterial oxygen content (18.6 +/- 2.6 ml/dl vs 20.2 +/- 2.8 ml/dl, p = 0.02). The nonresponders had no significant changes in these parameters during exercise. Increased exercise capacity in response to long-term O2 therapy is associated with increased O2 delivery not relief of hypoxic vasoconstriction (in terms of pressure or resistance or arterial elastance). Increased O2 delivery can accrue from both increased cardiac output and increased arterial O2 content. Increase in arterial O2 content is unique to O2 relative to all vasodilator drugs.
Asunto(s)
Ejercicio Físico/fisiología , Hipoxia/fisiopatología , Terapia por Inhalación de Oxígeno , Prueba de Esfuerzo/métodos , Prueba de Esfuerzo/estadística & datos numéricos , Hemodinámica/fisiología , Servicios de Atención de Salud a Domicilio , Humanos , Hipoxia/epidemiología , Hipoxia/terapia , Pulmón/fisiopatología , Enfermedades Pulmonares Obstructivas/epidemiología , Enfermedades Pulmonares Obstructivas/fisiopatología , Enfermedades Pulmonares Obstructivas/terapia , Consumo de Oxígeno/fisiología , Terapia por Inhalación de Oxígeno/estadística & datos numéricos , Estudios Prospectivos , Factores de Tiempo , Vasoconstricción/fisiologíaRESUMEN
This prospective study of symptom-limited supine ergometry was conducted to determine the contributions of right ventricular (RV) and left ventricular (LV) systolic function to the exercise capacity of a cohort of patients with coronary artery disease (CAD). Patients with unstable angina, angiographically proven CAD (n = 53) and stable symptoms after medical therapy or angioplasty were included. Documented myocardial infarction (greater than or equal to 2 weeks before exercise) was present in 43 of 53 patients. Angina was the limiting symptom in 11 of 53; the other 42 stopped exercise with dyspnea or fatigue, or both. Oxygen consumption was measured on-line during exercise with a metabolic cart. RV ejection fraction and LV ejection fraction were measured by validated methods from gated blood pool radionuclide ventriculography. There were weak but statistically significant correlations between exercise oxygen consumption and exercise RV ejection fraction (r = 0.30, p less than 0.05) and between exercise oxygen consumption and exercise LV ejection fraction (r = 0.38, p less than 0.01). Multivariate regression analysis, including exercise RV ejection fraction, exercise LV ejection fraction and exercise heart rate versus exercise oxygen consumption revealed a better relation (r = 0.48, p less than 0.005) than any variable in univariate regression. The values of RV and LV ejection fraction at rest did not correlate significantly (r = 0.2, difference not significant), but the exercise values did correlate weakly (r = 0.41, p less than 0.01). The reserve of LV ejection fraction, defined as exercise minus rest value, correlated weakly with exercise oxygen consumption (r = 0.32, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Enfermedad Coronaria/fisiopatología , Ejercicio Físico , Volumen Sistólico , Función Ventricular Izquierda , Función Ventricular Derecha , Enfermedad Coronaria/diagnóstico por imagen , Imagen de Acumulación Sanguínea de Compuerta , Frecuencia Cardíaca , Humanos , Consumo de Oxígeno , Estudios Prospectivos , Estadística como AsuntoRESUMEN
A noseclip and low resistance mouthpiece are often used to monitor exhaled gases during exercise. Because otolaryngologic studies suggest that 50% of airway resistance is in the nose and mouth, it was hypothesized that patients with advanced chronic obstructive pulmonary disease might be artifactually limited by exercise testing with a noseclip and mouthpiece. Accordingly, 12 patients with stable chronic obstructive pulmonary disease performed identical symptom-limited supine bicycle exercise tests with and without noseclip and mouthpiece. Right-sided cardiac hemodynamic measurements, radionuclide ventriculography and arterial and mixed venous gas sampling were performed during each exercise test. Exhaled gases were analyzed during the noseclip/mouthpiece exercise. The order of exercise tests was alternated. Comparing exercises with and without a noseclip, there were significant reductions in exercise duration (397 +/- 270 vs 300 +/- 230 seconds, p less than 0.01), exercise oxygen consumption (780 +/- 279 vs 638 +/- 200 ml/min, p less than 0.01) and exercise cardiac output (8.4 +/- 2.7 vs 7.3 +/- 2.0 liters/min, p less than 0.05), an increase in right ventricular ejection fraction (0.39 +/- 0.08 vs 0.43 +/- 0.08, p less than 0.01) and no change in exercise heart rate (106 +/- 14 vs 106 +/- 14), right-sided cardiac pressures or arterial and mixed venous blood gases. These data suggest that a noseclip/mouthpiece can limit exercise tolerance in advanced chronic obstructive pulmonary disease patients. This limitation may result from decreased right-sided cardiac preload (venous return).