Comparison of the Clearance of ^99mTechnetium‐DTPA From the Lung and Lung Function Indices Derived From the Single Breath Diagram for Carbon Dioxide in Horses with Chronic Obstructive Pulmonary Disease

Abstract

The elimination of carbon dioxide from the lung can be used to monitor ventilation and perfusion, and 99mtechnetium-diethylenetriaminepentaacetate (99mTc-DTPA) clearance is a highly sensitive index of alveolar epithelial integrity, which is a presupposition for effective gas exchange. The aim of this study was to determine whether a correlation exists between indices of lung function derived from the single breath diagram for CO2, and 99mTc-DTPA clearance in horses with chronic obstructive pulmonary disease. The rate of 99mTc-DTPA elimination was negatively and substantially correlated with the dead space according to Bohr's formula, and the physiological and alveolar dead space. Strong and significant correlations existed between the three dead space indices and the alveolar fraction of CO2, and the ratio A1/A2 as an index of alveolar efficiency. The associations found were dependent on the clinical status of health and the mode of calculation of 99mTc-DTPA alveolar clearance.

Use of volumetric capnography to identify pulmonary dysfunction in horses with and without clinically apparent recurrent airway obstruction

“…Measuring procedures were performed as described elsewhere. 6,7,9 Briefly, the protocol consisted of 3 or 4 measurement sessions for each horse with a mean of 22 breath cycles recorded during each session. At least 60 breath cycles of each horse were selected (end-tidal CO 2 , ≥ 3%; deviation of inspiratory and expiratory volume, < 10%) and analyzed.…”

“…Values for the measured expired VCO 2 (A 1 ) and the VCO 2 that would have been expired in an ideal lung (A 2 ) were determined (Fig 1). 9,10 Values for A 2 were calculated by use of the following equation:…”

“…Therefore, more sensitive pulmonary function tests have been developed, including forced oscillation combined with histamine bronchoprovocation, 5 forced expiration, 3 and volumetric capnography. 6,7 A graph of expired CO 2 concentration versus expired volume is termed the volumetric capnogram or single-breath diagram for CO 2 (SBD-CO 2 ). Volumetric capnography provides indices of the existence of nonuniformities in the distribution of pulmonary blood flow relative to ventilation (ie, alveolar ventilation/perfusion [V…”

“…] mismatching). 8 As an effort-independent method of pulmonary function testing, volumetric capnograms may be recorded in awake, 6,7,9,10 anesthetized, or mechanically ventilated horses. a A number of pulmonary function indices can be obtained from the volumetric capnogram in a noninvasive manner (eg, anatomic dead-space fraction or dead-space fraction determined by use of the Bohr equation).…”

“…Calculation of physiologic and alveolar dead-space fractions necessitates collection of arterial blood samples. Volumetric capnography indices have high repeatability 6,7 and correlate with the severity of clinical signs in horses with varying degrees of bronchiolar or alveolar disease. 9 We hypothesized that pulmonary function testing based on volumetric capnography indices would allow detection of differences in V • A /Q • mismatching between healthy control horses without evidence of airway disease, horses with RAO that were in remission, horses with mild RAO, and horses with RAO that was exacerbated.…”