Harvey V. Brown

Exercise Performance in Chronic Obstructive Pulmonary Diseases

Patients with chronic obstructive pulmonary diseases demonstrate exercise limitation as a consequence of both an increased ventilatory requirement and a decreased ventilatory capacity. The increased ventilatory requirement arises from the elevated wasted ventilation fraction of each breath (VD/VT) and hypoxemia secondary to ventilation-perfusion mismatching, both of which stimulate minute ventilation of increase. The reduced ventilatory capacity is primarily the result of airflow obstruction, which causes an increased work of breathing. Respiratory muscle fatigue may also play a role in reducing ventilatory capacity. The differentiation of heart failure from chronic obstructive pulmonary diseases as a cause of dyspnea can be accomplished using a variety of noninvasive and invasive techniques during exercise, including measurements of minute ventilation, the expiratory airflow pattern, ventilatory reserve (VEmax/MVV), ventilatory efficiency (VD/VT), arterial blood gases, the anaerobic threshold, heart rate, cardiac output, pulmonary hemodynamics and ventricular ejection fraction. Exercise training of patients with chronic obstructive pulmonary diseases improves exercise intolerance but appears to have little effect on pulmonary function tests, arterial blood gases and pulmonary hemodynamics. Supplemental oxygen during exercise training may be a useful adjunct for improving exercise tolerance in patients with chronic obstructive pulmonary diseases.

The effect of abnormal levels of hematocrit on the single breath diffusing capacity

In order to study the effect of different levels of hematocrit on the single breath diffusing capacity (DLCO), we studied 90 lifelong nonsmokers with either iron deficiency anemia, polycythemia vera or normal hematocrits, age range 9 to 81 years, with expiratory normal flow rates and lung volumes. The DLCO ranged from 10.6 to 41.3 ml/min/mmHg and hematocrit ranged from 28%–64%. We noted a significant relationship between the DLCO and age, height, and hematocrit. We recommend that DLCO measured in the conventional manner be corrected for anemia and polycythemia by incrementing or decrementing the measured value, if expressed as a percent of predicted, by 1.35% for each percent of measured hematocrit below or above the normal values of 44%.

Role of exercise testing in assessing functional respiratory impairment due to asbestos exposure.

To evaluate the complaint of exertional dyspnea in asbestos-exposed shipyard workers, pulmonary function tests were performed at rest and during exercise on 90 subjects with pleural plaques. We divided the subjects into four groups based on resting pulmonary function studies. Group I subjects (eight) had a restrictive defect; group II subjects (30) had an obstructive defect; group III subjects (six) had an isolated reduction in diffusing capacity; and group IV subjects (46) had a normal study. Subjects with a restrictive defect demonstrated minor physiologic abnormalities during exercise. Subjects with an obstructive defect demonstrated abnormalities consistent with their obstructive defect. Subjects in groups III and IV demonstrated an abnormally elevated wasted ventilation fraction, which may be an early indicator of interstitial disease due to asbestos exposure. We believe exercise testing was a useful tool in excluding the presence of significant functional exercise limitation due to asbestos exposure in the majority of subjects and also in disclosing some physiologic abnormalities in some of the subjects in our study.

Effect of Breathing Pattern on Dead Space Ventilation VD/VT during Exercise

In order to assess the effect of breathing pattern on measurements of dead space ventilation (VD/VT) during exercise, we studied 6 patients with the complaint of exertional dyspnea. They had essentially normal resting pulmonary function studies and the only abnormality noted during an initial exercise study was an elevated VD/VT associated with a rapid respiratory rate. A second exercise study was then performed during which they were coached to breathe at a slower rate and larger tidal volume. During the exercise study with coaching, the VD/VT response was normal. We conclude that breathing pattern during exercise influences VD/VT and that an increase in total minute ventilation which is accomplished by a preferential increase in respiratory rate may result in an abnormally high VD/VT.

Computerized body plethysmography: An algorithm for minimizing drift and hysteresis

The use of linear regression for on-line data processing of airway resistance measurements in the body plethysmograph may be difficult. When airflow (V) is plotted against plethysmographic pressure (Pbox), the resulting loop exhibits hysteresis and may drift along the PBox axis. Although the slope of the V-PBox loop can be estimated visually, computer calculations of the slope are difficult if baseline drift is present. Taking the derivatives of V and PBox eliminates the effect of drift and reduces the loops to a series of essentially parallel lines from which the slope can be readily calculated using linear regression. The identical technique can be employed when mouth pressure is plotted against plethysmographic pressure, enabling on-line calculation of thoracic gas volume.

Abnormal Wasted Ventilation Fraction and Normal Pulmonary Hemodynamics during Exercise in Patients with Exertional Dyspnea

We have previously reported a drop on wasted ventilation fraction (VD/VT) during exercise in patients with pulmonary vaso-occlusive diseases associated with collagen vascular disorders, despite an abnormally high mean pulmonary artery pressure and pulmonary vascular resistance at rest and during exercise. To further evaluate the diagnostic value of VD/VT measurements, we studied 8 subjects with normal spirometry, lung volumes and single-breath diffusing capacity who had previously demonstrated a high VD/VT at rest and during exercise. We found normal pulmonary hemodynamics in these subjects despite an abnormal rest and exercise VD/VT. Our findings effectively exclude hemodynamically significant pulmonary vascular obstruction, and do not support the use of VD/VT as a screening method for detecting diffuse pulmonary vaso-occlusive diseases.