Impact of Integrative Cardiopulmonary Exercise Testing (7)
If maximum Vo2 is reduced, other measurements are examined to determine whether the reduced 02 transport is a problem of the heart, lungs, peripheral circulation, or pulmonary circulation. As another example, the AT, the Vo2 at which Vco2 begins to increase at a faster rate than at lower work rates, is a marker of the increased lactic acid production by the exercising muscles, which increases in the tissues and blood. A low AT indicates impaired ability to perform sustained work and implies cardiovascular dysfunction. As shown in Table 3, other variables give important information about questions relating to pulmonary dysfunction, including ventilation-perfusion mismatching and dead space/tidal volume ratio. Arterial blood gas values, obtained most often from an arterial catheter, provide additional information about the effectiveness and efficiency of lung gas exchange. Oxygen saturation measurements obtained noninva-sively from a pulse oximeter are often substituted for arterial Po2, although a recent study has pointed out some instances during which pulse oximetry data may not be wholly satisfactory during exercise. ventolin 100 mcg
In our experience, the most expedient way to analyze the data from an integrative cardiopulmonary exercise test is to prepare the data in both table and graph form (Fig 2). We have also found that a systematic sequence of examining the data using flow charts is helpful for interpretation. Other sources give a more detailed discussion of exercise pathophysiology and interpretation of gas exchange data, and present and criticize predicted values for exercise gas exchange obtained from normal subjects.
Figure 2. Graph of gas exchange during exercise on a cycle ergometer in a normal subject during a progressive exercise test. The upper right panel shows the increase in metabolic rate (oxyen uptake, Vo*) during an exercise test in which work rate is increased by 20 W each minute (20, 40, 60, etc). The carbon dioxide output (Vco*) is also shown. The upper left panel shows the increase in heart rate (HR) and oxygen pulse (Vo/HR) during exercise. The lower left panel demonstrates the increase in minute ventilation (VE) during exercise. The lower right panel demonstrates the relationship between Vco2 and Vo2 during the progressive work rate increase period. Note that both variables increase throughout exercise, but that Vco2 increases disproportionally faster at the point shown by the arrow. This point represents the anaerobic threshold (see text).