Biomedical subjects

E Bowes

Publications and source records attributed to E Bowes.

3 recordsLinked to original sources

PubMed1994

Increase in blood lactate during ramp exercise: comparison of continuous and threshold models.

Controversy persists regarding the mechanism underlying the lactate threshold. It has recently been argued that there is in fact no "threshold" and that blood lactate increases as a continuous function during exercise (Hughson J. Appl. Physiol. 62:1975-1981, 1987). In comparing continuous and threshold models, questions have been raised regarding the ramp rate, data sampling, and the mathematical models employed (Morton J. Appl. Physiol. 67:885-888, 1989). To address some of these concerns, we evaluated 61 subjects (mean age 45 +/- 15), who underwent maximal ramp treadmill tests with the ramp rate individualized such that test duration was approximately 10 min for each subject. The relationship between changes in blood lactate and oxygen uptake were evaluated using a modification of the log-log transformation model described by Beaver (J. Appl. Physiol. 59:1936-1940, 1985) and a continuous exponential plus constant model described by Hughson et al. (J. Appl. Physiol. 62:1975-1981, 1987). Model fitting, using mean squared error (MSE) and coefficient of determination (CD) for each method were as follows: [table: see text] The modified log-log model had a better fit as indicated by the lower MSE and higher CD, suggesting the change in lactate was better described by this model. However, the differences were so slight as to suggest: 1) a meaningful difference does not exist between the two; or 2) these methods may not be capable of detecting a difference, if one exists.

Adult↗

PubMed1992

Ventilatory mechanisms of exercise intolerance in chronic heart failure.

Mechanisms that have been suggested to underlie the abnormal ventilatory response to exercise in patients with chronic congestive heart failure (CHF) include high pulmonary pressures, ventilation-perfusion mismatching, early metabolic acidosis, and abnormal respiratory control. To evaluate the role that ventilation and gas exchange play in limiting exercise capacity in patients with CHF, data from 33 patients with CHF and 34 normal subjects of similar age who underwent maximal exercise testing were analyzed. Maximal oxygen uptake was higher among normal subjects (31.7 +/- 6 ml/kg/min) than among patients with CHF (17.7 +/- 4 ml/kg/min; p less than 0.001). The ventilatory equivalent for oxygen, expressed as a percentage of maximal oxygen uptake, was 25% to 35% higher among patients with CHF compared with normal subjects throughout exercise (p less than 0.01). A steeper component effect of ventilation on maximal oxygen uptake was observed among normal subjects compared with patients with CHF, which suggests that a significant portion of ventilation in CHF is wasted. Maximal oxygen uptake was inversely related to the ratio of maximal estimated ventilatory dead space to maximal tidal volume (VD/VT) in both groups (r = -0.73, p less than 0.001). Any given oxygen uptake at high levels of exercise among patients with CHF was accompanied by a higher VD/VT, lower tidal volume, and higher respiratory rate compared with normal subjects (p less than 0.01). Relative hyperventilation in patients with CHF started at the beginning of exercise and was observed both below and above the ventilatory threshold, which suggests that the excess ventilation was not directly related to earlier than normal metabolic acidosis. Thus abnormal ventilatory mechanisms contribute to exercise intolerance in CHF, and excess ventilation is associated with both a higher physiologic dead space and an abnormal breathing pattern. The high dead space is most likely due to ventilation-perfusion mismatching in the lungs, which is related to poor cardiac output, and the abnormal breathing pattern appears to be an effort to reduce the elevated work of breathing that is caused by high pulmonary pressures and poor lung compliance.

Adult↗

PubMed1992

Individualized ramp treadmill. Observations on a new protocol.

The many different approaches to exercise testing have hindered the consistent interpretation of hemodynamic, electrocardiographic, and ventilatory gas exchange responses. One of the most influential approaches is the choice of the exercise protocol. Recent data suggest that the protocol can have an important impact on test sensitivity, the reason for test termination, the ST/HR slope calculation, the interpretation of gas exchange responses, and the accuracy with which oxygen uptake is predicted from work rate. Recent recommendations for optimizing the test have focused on the test duration, reducing the increments in work rate, and individualizing the test relative to the purpose of the test and the subject tested. We describe a treadmill test which considers these recommendations for optimizing exercise testing.

Adult↗