A fractal approach for evaluation of pulmonary circulation in man at rest and during exercise

Changes in pulmonary circulation caused by muscular exercise and body position are usual in daily life. By using first-pass radiocardiography and fractal analysis, pulmonary circulation in man was evaluated at rest and during muscular exercise. At rest, pulmonary circulation was heterogeneous as described by the relative dispersion (which is the coefficient of variation, i.e. the standard deviation of the pulmonary transit times divided by the mean transit time; RD = 0·51 ± 0·06) and fractal in nature. During exercise, pulmonary circulation became more homogeneous (RD = 0·35 ± 0·04; P<0·001). The calculated fractal dimension decreases from 1·09 at rest to 1·06 during exercise. The model identifies a cubic-law response for circulation heterogeneity and a quarter-power law for resistance during muscular exercise.     

Ventilatory responses to inhaled carbon dioxide at rest and during exercise in man

1. Rapid steady-state CO2 responses were determined in six normal subjects at rest and five subjects at four different work loads up to 125 W, by injecting pure CO2 at constant flow into a small mixing chamber in the inspiratory limb of a breathing circuit. 2. The time course of the response of ventilation (V) and mean alveolar PCO2 (PACO2) was checked in separate experiments, where the flow rate of injected CO2 was changed abruptly and the effects were followed for 10 min. 3. V and PACO2 were measured every breath, and the results ensemble-averaged for each subject (two or three runs per subject) and then for the groups as a whole, in 30 s or 60 s time bins. 4. PACO2 during exercise was estimated by graphical reconstruction from the sloping alveolar plateau, and separately by the empirical equation of Jones, Robertson & Kane [1]. At rest, PACO2 was assumed equal to end-tidal PCO2 (PetCO2). 5. With the constant inflow technique, 4 min was required to reach steady-state V and PACO2 during exercise, and 6 min at rest. 6. At rest, with 4 min steps (doubtful steady state) the averaged CO2 response was concave up. With 6 min steps the response was almost linear. In neither case was the deviation from linearity statistically significant. 7. During exercise, the averaged CO2 responses were essentially isocapnic at work loads greater than 75 W with either method of deriving PACO2.     

Quantitative radiocardiographic evaluation of cardiac dynamics in man at rest and during exercise

113Inm radiocardiography in conjunction with a gamma camera and a digital computer is applied to measurements of cardiac output, stroke volume, ejection fraction, end-diastolic volume, pulmonary blood volume, pulmonary transfer time and dispersion both at rest and during muscular exercise. A modified gamma function is used in calculations of radiocardiographic curves. In twelve supine male subjects the maximal increase of cardiac output was 220%, stroke volume 30%, ejection fraction 15%, and pulmonary blood volume 30%. The present method provides a non-invasive tool for cardiovascular examinations during exercise.     

Non-invasive determination of the distribution of cardiac output in man at rest and during exercise

Summary. The distribution of cardiac output, as expressed by the regional uptake of thallium-201 following injection, has been studied by whole body scanning with a gamma-camera in six healthy persons and eight patients with aortic valvular disease. In the patients, cardiac output at rest and during exercise was also measured by the dye dilution technique. Combining the values of cardiac output and regional thallium uptake enabled the calculation of organ blood flow. The myocardial uptake of thallium at rest was 3·2 ± 0·32% in the control group, which is significantly lower than 8·3 ± 1·52%, found in the patients. The corresponding values measured in the kidneys were 12·5 ±1·91% in the healthy subjects and 7·1 ± 0·50% in the patient material. Myocardial uptake increased and kidney uptake decreased in both groups following injection at peak exercise. Thallium uptake in the legs increased from about 13% at rest to about 39% at exercise in both groups. Distribution of thallium after injection at peak exercise did not, however, vary significantly between the two groups in the kidneys, abdominal area or the legs. Further methodological work is required before it can be ascertained to what extent the regional thallium uptake reflects the distribution of cardiac output. We nevertheless propose that the technique should be explored further, since it appears to be a simple non-invasive means of visualizing the distribution of the cardiac output in man under certain conditions.     

Timing of deep breaths during rest and light exercise in man

1. We used digital filtering techniques and segmental analysis to dissect a series of respiratory variables into three components: (a) outlying values, including deep breaths or sighs; (b) random variation; (c) non-stationary baseline variation. 2. Records of about 30 min breathing were obtained from normal adults at rest and at 50 W exercise. 3. Deep breaths were defined as having a tidal volume greater than 2.5 sd above the mean. 4. We related these deep breaths to preceding trends in tidal volume and end-tidal partial pressure of CO2. 5. At rest, there was no relation between deep breaths and tidal volume, but the deep breaths were significantly clustered around the troughs in end-tidal partial pressure of CO2. 6. At 50 W exercise, there was no relation between deep breaths and end-tidal partial pressure of CO2, but the deep breaths were significantly clustered around tidal volume troughs. 7. Results obtained by pneumography were concordant with those obtained by using a mouthpiece to measure ventilation.     

The renin-angiotensin-aldosterone system in normal 85-year-old people

Active and total plasma renin concentration, as well as plasma angiotensin II, aldosterone and renin substrate concentrations were measured in venous blood samples from 17 normal 85-year-old people at rest. No discernible sex-related differences were seen. Active plasma renin and plasma aldosterone concentrations were significantly lower in the old people compared to a group of normal 40-year-old people. Plasma angiotensin II concentration showed no decrease with increasing age. Active plasma renin concentration constituted approximately 20% of total plasma renin concentration, with a significant correlation between the two renin moieties. The values for plasma renin substrate concentration are similar to those reported for younger age groups. The lack of standardization of methods severely hampers inter-laboratory comparisons of both active plasma renin and total plasma renin concentrations.     

Pulmonary vascular reactivity and hemorheology in patients with chronic cor pulmonale: Responses to pentoxifylline at rest and during exercise

Summary This study was carried out in order to evaluate changes in pulmonary vascular reactivity and in hemorheology induced by pentoxifylline infusion (100 mg) at rest and during standardized exercise in patients with chronic cor pulmonale secondary to chronic obstructive pulmonary disease. The administration of pentoxifylline at rest was associated with reduction in mean pulmonary artery pressure (p<0.01), pulmonary vascular resistance (p<0.01) and right ventricular stroke work index (p<0.02). Standard exercise performed after pentoxifylline infusion was also associated with significant reduction in mean pulmonary artery pressure and pulmonary vascular resistance. Rheologic tests showed less evident changes. Our data suggest that pentoxifylline significantly improves pulmonary hemodynamics at rest and partly reverses its changes, after exercise, in patients with chronic obstructive pulmonary disease.     

Forearm and splanchnic blood flow at rest and during exercise in relation to the systemic arteriovenous oxygen difference in cardiac patients.

In eleven patients with chronic heart failure forearm blood flow (FBF) was measured by plethysmography with a mercury-in-silastic strain gauge and splanchnic blood flow (SBF) with indocyanine green (ICG) infusion clearance at rest during right heart catheterization. The measurements were repeated during 8 min supine exercise on a bicycle ergometer, SBF during exercise being calculated from the changes of the brachial artery to hepatic vein oxygen differences and the ICG values at rest. Close correlations were found between cardiac output and FBF, and cardiac output and SBF at rest. During exercise forearm and splanchnic vascular resistances were both closely correlated with the brachial to pulmonary artery oxygen difference. It is concluded that in patients with heart failure vasoconstriction occurs during exercise in resting limbs and visceral organs, both closely related to the circulatory strain.     

Atrial natriuretic factor: comparability of venous and arterial plasma measurements in man at rest and during exercise

1. Simultaneously obtained arterial and venous plasma atrial natriuretic factor (ANF) concentrations were compared at supine rest and during graded dynamic leg exercise in 10 healthy male subjects (aged 33-51 years). 2. Arterial ANF concentrations ranged between 12 and 179 pg/ml and venous concentrations between 9 and 177 pg/ml. 3. A positive correlation between arterial and venous concentrations was found (r = 0.984). 4. Arterial ANF concentrations were higher than venous concentrations in all pairs of samples (n = 31), but the difference was small and changed little with exercise: the mean difference was 5 pg/ml at rest, 12 pg/ml during submaximal exercise and 6 pg/ml during maximal exercise. 5. The extraction ratios for ANF varied greatly, but were in general lower (P less than 0.05) during maximal exercise (median 0.07, range 0.01-0.32) than at rest (median 0.22, range 0.05-0.33). 6. It was concluded that the plasma ANF concentration in a peripheral arm vein is a good indicator of the systemic peptide concentration at rest as well as during dynamic leg exercise.     

Regional pulmonary clearance of inhaled C15O and C15O2 in man at rest and during exercise

Summary. The regional clearance of radioactive carbon monoxide (C¹⁵O₂) and carbon dioxide (C¹⁵O₂), after a single maximal inspiration, was investigated in six normal subjects seated on a bicycle, at rest and during exercise at 50 W. The clearances were measured sequentially during breath-holding by four pairs of scintillation counters vertically aligned over the right lung. The clearance rate (k) for C¹⁵O and C¹⁵O₂ increased from apex to base and from rest to exercise. On exercise, the apex base gradient (calculated over 11 cm vertical distance) for C¹⁵O decreased by 52% because of a larger increase in the upper zones but the C¹⁵O₂ gradient did not change. Thus the increase in blood flow (=kC¹⁵O₂) on exercise was accompanied by recruitment and/or distension of pulmonary capillary blood volume (=kC¹⁵O₂), most marked in the upper regions. The ratio of the clearance (C¹⁵O/C¹⁵O₂) decreased in the lower zones on exercise by 25% without significant change in the upper zone. This ratio reflects the product of capillary mean transit times and peripheral vascular and extravascular volumes. Since the latter increase on exercise, capillary transit times must have shortened considerably at a moderate level of exercise at all levels in the lung.     

Mucociliary clearance in healthy men at rest and during exercise

Summary. We measured mucociliary clearance at rest and during exercise in 11 healthy non-smoking men. The subjects inhaled an aerosol containing [⁹⁹Tc^m]albumin millimicrospheres with deep inhalations. Four sets of scintigraphic images were obtained with 15-min intervals. Lung retention of radioactivity was quantified using a gamma camera and the clearance of particles from the lungs calculated for each 15-min period. The first image was obtained directly after inhalation, the second after a period of 15-min rest, the third after a period of exercise on a bicycle ergometer (workload approximately 80% of predicted maximum capacity) and the final fourth image after another period of rest. We found small differences in clearance rate at rest and during exercise indicating that there is no substantial change in the clearance rate during exercise in normal subjects.     

Abnormal vascular reactivity at rest and exercise in obese boys

Background Obese children exhibit vascular disorders at rest depending on their pubertal status, degree of obesity, and level of insulin resistance. However, data regarding their vascular function during exercise remain scarce. The aims of the present study were to evaluate vascular morphology and function at rest, and lower limb blood flow during exercise, in prepubertal boys with mild‐to‐moderate obesity and in lean controls. Materials and methods Twelve moderately obese prepubertal boys [Body Mass Index (BMI: 23·9 ± 2·6 kg m^?2)] and thirteen controls (BMI:17·4 ± 1·8 kg m^?2), matched for age (mean age: 11·6 ± 0·6 years) were recruited. We measured carotid intima‐media thickness (IMT) and wall compliance and incremental elastic modulus, resting brachial flow‐mediated dilation (FMD) and nitrate‐dependent dilation (NDD), lower limb blood flow during local knee‐extensor incremental and maximal exercise, body fat content (DEXA), blood pressure, blood lipids, insulin and glucose. Results Compared to lean controls, obese boys had greater IMT (0·47 ± 0·06 vs. 0·42 ± 0·03 mm, P < 0·05) but lower FMD (4·6 ± 2·8 vs. 8·8 ± 3·2%, P < 0·01) in spite of similar maximal shear rate, without NDD differences. Lower limb blood flow (mL min^?1·100 g^?1) increased significantly from rest to maximal exercise in both groups, although obese children reached lower values than lean counterparts whatever the exercise intensity. Conclusions Mild‐to‐moderate obesity in prepubertal boys without insulin resistance is associated with impaired endothelial function and blunted muscle perfusion response to local dynamic exercise without alteration of vascular smooth muscle reactivity.