ATS Pulmonary Function Laboratory Manual

ATS Pulmonary Function Laboratory Management & Procedure Manual | 3rd Edition

6. Anaerobic threshold (AT), ventilatory threshold (VT), and gas exchange threshold (GET), are alternative names for the same measurement and are determined from graphical analysis of data (53). 6.1. The conventional method (51) for determining AT uses ventilatory equivalents plotted against ˙ V o 2 . Usually, data are smoothed or averaged to reduce breath-by-breath variability, facilitating location of the AT. The AT coincides with the minimum of ˙ V o 2 . The ˙ V e/ ˙ V co 2 should either be constant or declining in the region around the AT. An increasing ˙ V e/ ˙ V co 2 suggests the increase in both param- eters is due simply to hyperventilation rather than to a change caused by lactic acidosis. 6.2. AT can also be located using V-slope analysis (54, 55), where the ˙ V co 2 (vertical axis) is plotted ver- sus the ˙ V o 2 (horizontal axis). The AT is the point where the slope of ˙ V co 2 versus ˙ V o 2 increases; this can be located either manually or by using computerized analytic routines. If computerized analysis routines are used, the AT should always be verified by visual inspection of the data. 6.3. Another approach is to plot the lactate concentration values in arterial blood against ˙ V o 2 (using either manual or computerized data analysis routines). The AT is the point where the rate of rise in lactate increases or the total lactate concentration exceeds a threshold value (usually about 2 mEq/L). Presenting the log(lactate) versus log( ˙ V o 2 ) amplifies the change in slope, allowing easier identifica- tion of the threshold (56). Reporting Results 1. Typically data from several representative work rates are reported in tabular format. In some laboratories, data from all work rates are reported. 1.1. The patient’s response, the physician interpreting the results, or the laboratory practice may influ- ence which variables are chosen for the report. 1.2. At a minimum, data should be reported from: ( 1 ) rest; ( 2 ) near or at AT, if identifiable; and ( 3 ) maxi- mal power output. 2. Report ˙ V o 2 max and ˙ V co 2 at STPD conditions in L/min 2.1. ˙ V o 2 max may also be normalized for body weight (ml/min/kg). However, this may be misleading in obese individuals (57). 2.2. Report ˙ V o 2 max using one of several approaches to process the individual data points. 1. All the breaths within a specific interval of time 2. Middle 5 of 7 breaths 3. Median of 7 breaths 4. Average of 8 breaths 2.3 The automated systems allow several options for averaging the individual data points. Because of the noise observed in the breath-by-breath measurements and the fact that the units of the cardiopul- monary variables are L/min, it is recommended that the data be reported in 0.5-minute intervals. The minimum acceptable would be 20-second intervals. 7. The normal alveolar–arterial O 2 years of age, the mean P(a-a)O 2 of age, the mean P(a-a)O 2 gradient [P(a-a)O 2 ] increases with age and during exercise. At 20 to 39 is 8 mm Hg at rest, and 15 mm Hg at maximal exercise. At 40 to 69 years is 13 mm Hg at rest, and 19 mm Hg at maximal exercise. In this older group, at maximum exercise the upper limit of normal (i.e., 95% confidence interval) is 28 mm Hg (3). A general guideline for the upper limit of adults is a P(a-a)O 2 <35 mm Hg (8).

˙ V e is reported at BTPS conditions in L/min.

3. 4. 5.

Pa O 2 Sp O 2

, Pa CO 2

(if obtained), Pet O 2

, and Pet CO 2

are reported in mm Hg.

and Sa O 2

(from CO-oximetry) are reported as percent.

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