The Response of Cardiac and Pulmonary Disease to Exercise Testing

Breathing reserve at the lactate threshold to differentiate a pulmonary mechanical from cardiovascular limit to exercise

STUDY OBJECTIVES

Criteria used to define the respective roles of pulmonary mechanics and cardiovascular disease in limiting exercise performance are usually obtained at peak exercise, but are dependent on maximal patient effort. To differentiate heart from lung disease during a less effort-dependent domain of exercise, the predictive value of the breathing reserve index (BRI=minute ventilation [VE]/maximal voluntary ventilation [MVV]) at the lactate threshold (LT) was evaluated.

DESIGN

Thirty-two patients with COPD and a pulmonary mechanical limit (PML) to exercise defined by classic criteria at maximum oxygen uptake (VO2max) were compared with 29 patients with a cardiovascular limit (CVL) and 12 normal control subjects. Expired gases and VE were measured breath by breath using a commercially available metabolic cart (Model 2001; MedGraphics Corp; St. Paul, Minn). Arterial blood gases, pH, and lactate were sampled each minute during exercise, and cardiac output (Q) was measured by first-pass radionuclide ventriculography (System 77; Baird Corp; Bedford, Mass) at rest and peak exercise.

RESULTS

For all patients, the BRI at lactate threshold (BRILT) correlated with the BRI at VO2max (BRIMAX) (r=0.85, p<0.0001). The BRILT was higher for PML (0.73+/-0.03, mean+/-SEM) vs CVL (0.27+/-0.02, p<0.0001), and vs control subjects (0.24+/-0.03, p<0.0001). A BRILT > or = 0.42 predicted a PML at maximum exercise, with a sensitivity of 96.9%, a specificity of 95.1%, a positive predictive value of 93.9%, and a negative predictive value of 97.5%.

CONCLUSIONS

The BRILT, a variable measured during the submaximal realm of exercise, can distinguish a PML from CVL.

Preoperative cardiopulmonary exercise testing: determining the limit to exercise and predicting outcome after thoracotomy

Over the past 15 years evaluation of the patient with exertional complaints has changed from a simple qualitative estimate of overall fitness to a detailed assessment of cardiovascular and pulmonary pathophysiology. By quantifying exercise impairment and identifying the physiological limit to exercise, CPEx can help direct and evaluate the efficacy of medical and surgical interventions. Although no clear consensus has emerged, an objective determination of the etiology of exercise intolerance may also help identify the patient at increased risk for postthoracotomy complications.

Quantifying ventilatory reserve to predict respiratory failure in exacerbations of COPD

We developed a concept of VR in patients with acute exacerbation of advanced COPD and tested the hypothesis that it is predictable and clinically useful in the ER. Our concept of VR was based on the idea that a threshold VF and a MSV capacity are measurable; ie, VR = MSV - VF. We measured resting minute ventilation, the 15-s MVV, FEV1 and ABG values in 13 patients with exacerbation of COPD in the ER and 11 stable subjects with similar degrees of COPD. We tested if measures of VR could distinguish between ER patients progressing to respiratory failure, ER patients who avoided progression to respiratory failure and stable patients. There were significant differences in measures of the mean VR between various groups of patients. We conclude that in this COPD population, VR can be accurately predicted in the ER and that it may be a clinically valid predictor of patient outcomes.

Graded exercise testing and postthoracotomy complications

A controversy exists over whether or not preoperative exercise testing can predict postthoracotomy complications. This study was designed to evaluate the usefulness of a presurgical exercise protocol in patients with lung disease, but no evidence of cardiac disease. Seventy patients underwent baseline pulmonary function testing and split function perfusion studies, when indicated, to calculate predicted postoperative pulmonary function. Noninvasive data were incrementally collected from 17 patients by using a treadmill exercise tolerance test that was designed to elicit maximal performance. Inhaled and exhaled gas flow and volume, the partial pressure of O2 and CO2, maximal O2 consumption (VO2max), and maximal minute ventilation (VE max) were measured. The breathing and heart rate reserves were calculated by standard formulae in an attempt to separate cardiac from pulmonary exercise limitation. Two patients had postoperative cardiopulmonary complications after thoracotomy and lung resection, and six patients had noncardiopulmonary complications. There was no significant prognostic relationship among VO2max, VE max, maximum O2 pulse, and the incidence of postoperative cardiopulmonary complications. The percentages of predicted VE max and predicted maximum heart rate were related to the occurrence of total complications, but not specifically to cardiopulmonary complications. The results emphasize the difficulty in attempting to exercise thoracotomy candidates with chronic lung disease to maximal performance. Excluding patients from further surgical consideration because of exercise limitation is not feasible based on these data.

Long-term follow-up of symptoms, pulmonary function, respiratory muscle strength, and exercise performance after botulism

Respiratory muscle weakness occurs commonly at presentation in patients with botulism. Although clinical improvement occurs over several months, symptoms such as fatigue and dyspnea persist in many patients in the long term. To determine whether continued respiratory muscle weakness might contribute to these symptoms, we compared lung function tests, respiratory muscle strength, and exercise performance in 13 patients 2 years after type B botulism. We found that residual symptoms including dyspnea and fatigue were common in botulism patients at 2 years postintoxication. Lung function tests had returned to normal in all patients. Maximal inspiratory and expiratory pressures were similar between botulism patients and control subjects. Evaluation of individual results showed evidence of inspiratory muscle weakness in four of 13 patients with botulism (Plmax less than 65% predicted). Maximal oxygen consumption and maximal workload during exercise were reduced in botulism patients in comparison to control subjects. During exercise, botulism patients had a more rapid and shallow breathing pattern and a higher dyspnea score at a given minute ventilation in comparison to control subjects. Reasons for premature exercise termination in botulism patients were multifactorial. Although respiratory muscle weakness may have been contributory in some patients, most appeared to be limited by reduced cardiovascular fitness, leg fatigue, or reduced motivation.

Cardiopulmonary stress testing. A review of noninvasive approaches

With readily available techniques, cardiopulmonary exercise testing permits noninvasive measurement of such parameters as heart rate, cardiac output, oxygen saturation, ventilation, and gas exchange to bring out abnormalities which are either underestimated or not detectable at rest. These parameters may be used to characterize a patient's primary limitation of exercise tolerance as either cardiac or pulmonary in origin. They can also provide precise data to assess response to treatment. Pulmonary gas exchange is evaluated primarily by measurement of oxygen consumption, carbon dioxide production, and ventilation over time. The relationship of these parameters to one another changes throughout the course of incremental exercise testing. By appreciating these basic relationships, the more complex abnormalities found in disease states can be understood.

Endurance Exercise: Normal Physiology and Limitations Imposed by Pathological Processes (Part 1)

In brief: Endurance exercise induces significant and rapid changes in many physiological functions. To maintain homeostasis, adaptations in the oxygen transport and delivery chain are necessary. Increases in minute ventilation and diffusion across the alveolar-capillary membrane enhance oxygenation of blood in the lungs. Parallel changes in cardiac output, muscle blood flow, and arteriovenous oxygen difference increase oxygen transport and delivery. Pulmonary and cardiovascular diseases can limit oxygen transport and/or delivery, while muscle diseases can impair oxygen delivery.