Total External Work Research Articles

Effect of Distractive Auditory Stimuli on Exercise Tolerance in Patients With COPD

We tested the hypothesis that a distractive stimulus, such as music, introduced during exercise can reduce perception of respiratory effort at any given level of exercise, whereas sensory deprivation increases effort perception. Thirty-six patients with moderate COPD participated in four sessions of symptom-limited exercise. The first session familiarized the subject with the protocol. The other sessions were performed under partial visual isolation while listening to music (M), or to grey noise (GN), or in silence (SIL), presented in randomized order. Subjects graded their respiratory effort using the Borg rating of perceived exertion (RPE) scale. Total exercise time (EXT) and external work (WT) were objective indices of exercise tolerance. EXT was 22% longer with M than with either GN or SIL (p < 0.001), and WT was 44% and 53% greater with M than with GN or SIL, respectively (p < 0.001). These increases occurred at a heart rate that was only a few beats higher than during GN or SIL (104 +/- 3 bpm for M and 101 +/- 3 bpm for GN and SIL), a minimal difference that was statistically significant (p < 0.001). At every level of exercise, perceived exertion with M was lower than for either GN or SIL (p < 0.001). Although the respective RPE was higher for SIL than for GN (p < 0.01) at every level of exercise, WT and EXT were no different. These data indicate that perceived effort can be significantly influenced by external factors. This in turn suggests that the use of distractive stimuli during exercise training programs with patients with COPD may significantly decrease perceived symptoms of respiratory discomfort, thus allowing the patient to exercise to a higher intensity, and potentially achieving more effective exercise reconditioning training.

Effect of Time of Day on the Relationship between Mood State, Anaerobic Power, and Capacity

Mood state was estimated in six men using the Profile of Mood States questionnaire, with a "right now" directional set prior to performance of a modified Wingate power test, once at 03.00 hr., 09.00 hr., 15.00 hr., and 21.00 hr., on different days. Anaerobic power was measured as peak power output in 5 sec., and anaerobic capacity was measured as total external work performed during the 30-sec. test. Intraindividual difference scores were calculated as a subject's score minus his mean over the four tests. Multiple regression analyses showed that time of day and the Profile of Mood States fatigue score accounted for 51% of the variance in peak power and 62% of the variance in anaerobic capacity. However, the relationships between fatigue and subsequent anaerobic power and capacity reached statistical significance only at 21.00 hr. These results suggest that intraindividual differences in the mood state are related to subsequent performance. Greater than usual levels of fatigue are associated with reduced performance capacity. However, this relationship is dynamic and is dependent upon the time of day.

Aortic impedance and hydraulic power in the chick embryo from stages 18 to 29.

Little is known about the hemodynamic properties of the rapidly expanding arterial bed during embryonic development. Using a servo-null pressure system and 20-MHz pulsed Doppler velocity meter, we recorded simultaneous dorsal aortic pressure and velocity waveforms. The waveforms were digitized at 3-msec intervals and subjected to Fourier analysis. We calculated hydraulic energy and the impedance spectrum to 10 Hz. From stages 18 to 29, heart rate (148 +/- 3 to 193 +/- 9 beats/min), systolic pressure (1.14 +/- 0.12 to 3.04 +/- 0.10 mm Hg), and mean dorsal aortic blood flow (21 +/- 2 to 214 +/- 19 mm3/min) increased. Peripheral vascular resistance (Z0: 30.4 +/- 4.8 to 6.4 +/- 0.7 dyne x sec/mm5), and the impedance moduli (Z1: 6.5 +/- 1.0 to 1.7 +/- 0.2 dyne x sec/mm5; Z2: 6.1 +/- 1.2 to 1.7 +/- 0.1 dyne x sec/mm5; Z3: 7.3 +/- 1.1 to 1.7 +/- 0.2 dyne x sec/mm5) decreased. Total hydraulic power increased from 48 +/- 7 to 2,606 +/- 96 nW, while the proportion of oscillatory energy increased from 29 +/- 2% to 65 +/- 4%. With development hydraulic load decreases, total external work increases and the dorsal aorta and embryonic vascular bed becomes more compliant. A greater proportion of total energy is expanded in pulsatile blood flow, suggesting that ventricular-arterial coupling is less efficient later in development.

Dual potentials and extremum work principles in single crystal plasticity

T his paper is concerned with modelling the rigid plastic deformation of a rate insensitive single crystal by crystallographic slip when subjected to mixed boundary conditions. By introducing a flow polyhedron as the dual surface of the classical yield polyhedron, new extremum work principles are derived, which enable the unknown stress and strain rate components to be evaluated. In particular, it is shown that by using a suitable mixture of the yield and flow polyhedra as a function of the boundary conditions, the total internal plastic work rate per unit volume is a minimum for the actual solution. Alternatively the total external plastic work is maximal.

Beta 2-mediated changes in central haemodynamics, coronary circulation and myocardial metabolism in canine.

The combined effect of terbutaline on systemic and coronary circulation was investigated in dogs to clarify its influence on myocardial oxygen supply and lactate balance. The dogs were anaesthetized and the chest opened. Coronary sinus blood flow and cardiac output were monitored by thermodilution, aortic pressure was measured by tip-transducer and heart rate by RR-interval on ECG, coronary sinus blood were analyzed for lactate, oxygen and carbon dioxide. Terbutaline caused a substantial systemic vasodilation and an increased heart rate, the total external cardiac work increased to a minor degree. Terbutaline increased arterial lactate concentration. Coronary vascular resistance was reduced after terbutaline. Even if myocardial perfusion pressure was reduced and an increased external cardiac work was present, no signs of myocardial distress was observed in lactate metabolism or coronary sinus oxygen content. In fact a tendency to increased myocardial aerobic metabolism was observed, as myocardial lactate consumption increased after terbutaline. Terbutaline seems to be a coronary vasodilator in dogs. However, the demand for oxygen secondary to both an increase in cardiac work and aerobic metabolism can be hazardous to the potentially ischaemic myocardium.

Plasma lactate dehydrogenase and creatine kinase after anaerobic exercise.

Eight untrained men performed 15-s and 60-s high-intensity exercise on a bicycle ergometer. Activities of the creatine kinase (CK) and lactate dehydrogenase (LDH) were measured in blood 3 min and 2, 6, and 24 h after cessation of exercise. The results indicate that anaerobic exercise induces a transient increase in plasma LDH activity and a more prolonged elevation in plasma CK activity. A negative correlation was found between CK activity measured before and 3 min after exercise and mean power, and total external work performed in both test types. A similar correlation was ascertained between pre- and post-exercise CK activity and maximal power output measured in the 60-s test. After the 15-s exercise test, only post-exercise plasma CK activity was negatively correlated with the maximal power output.

Treadmill exercise training in chronic obstructive pulmonary disease.

Eight men and six women with severe chronic obstructive pulmonary disease (COPD) performed a pulmonary function test and a treadmill exercise stress test before and after an individualized training program, which nominally consisted of three 20-minute sessions of treadmill exercise per week for five consecutive weeks. Training sessions were terminated before 20 minutes if there were subjective complaints, or if the subject's heart rate reached 80% of the maximum heart rate observed during the pretraining stress test. This program failed to improve any of the pulmonary function test parameters (lung volumes, airflows, maximum voluntary ventilation, and resting levels of blood gases) and failed to improve most exercise stress test parameters (maximum oxygen consumption and carbon dioxide production, respiratory exchange ratio, and heart rate at termination of exercise). This program, however, did increase the group's average stress test time from 9.0-13.7 minutes (p less than 0.001) and increased the total external work (calculated from the sum of its vertical and horizontal components) from 3.5-6.8kcal (p less than 0.01). Eight of the 11 subjects who initially received 2L/min of 100% oxygen, via a nasal cannula, to alleviate dyspnea and to promote endurance were completely weaned from supplemental oxygen by the end of the training program. These findings demonstrate that a treadmill exercise program based on stress test data can increase the efficiency (external work per unit of oxygen consumed) and thus, the exercise tolerance, of persons with severe COPD.

Accuracy of Pulmonary Function Tests in Predicting Exercise Tolerance in Chronic Obstructive Pulmonary Disease

The ability of pulmonary function tests (PFTs) to predict exercise capacity was investigated by using linear regression analysis to quantify the relationships between: (1) maximum oxygen consumption during treadmill exercise and PFT parameters; and (2) total external work performed during treadmill exercise and PFT parameters. In a group containing 11 healthy subjects, nine with mild/moderate chronic obstructive pulmonary disease (COPD) and ten with severe COPD, both maximum oxygen consumption (measured directly) and total external work (calculated indirectly from the sum of its horizontal and vertical components) correlated most strongly with indices of expiratory airflow (FEV1, FEF25-75%), less strongly with indices of ventilatory output (MVV) and resting levels of oxygen (PO2, SaO2), and weakly with indices of hyperinflation (FRC) and carbon dioxide retention (PCO2). Thus, FEV1, accounting for 56 percent and 60 percent of the observed variation in oxygen consumption and external work, respectively, can predict exercise tolerance from PFT measurements with some accuracy. If a more accurate evaluation is required, exercise testing should be prescribed.

Growth hormone responses during intermittent weight lifting exercise in men.

Five normal male volunteers performed two intermittent weight lifting exercises of equal total external work output and duration (20 min) with identical work-rest intervals but different load and frequency of movements. Exercise I consisted of seven sets of seven vertical leg lifts at 85% of the subject's Seven Repetition Maximum (SRM) and, 5 days later, seven sets of 21 vertical leg lifts with one-third of the previously used load (Exercise II). Blood was sampled throughout the exercise and recovery periods for growth hormone, lactate, and glucose analysis. Growth hormone increased after 20 min of Exercise I to a peak during the recovery period. Significantly elevated growth hormone (GH) levels were found 5, 10, and 15 min (P less than 0.025, P less than 0.05, P less than 0.025 respectively) of recovery after Exercise I. No significant elevations of GH occurred in Exercise II. Significant linear correlations (r = 0.99, P less than 0.01) with a time lag of 16 min were found between lactate and GH levels in Exercise I (lactate increases preceded those of GH). No significant differences in plasma glucose concentrations were detected. The results suggests that in intermittent weight lifting exercises of equal total external work output and duration as well as identical work-rest intervals, the load and/or frequency of an exercise are determinant factors in the regulation of plasma GH levels.

Propranolol in angina pectoris: Duration of improved exercise tolerance and circulatory effects after acute oral administration

The duration of the effects of single oral doses of 80 and 160 mg of propranolol was studied in 11 patients with stable, exercise-induced angina pectoris. After administration of both doses, plasma propranolol levels peaked at 2 hours in 8 of the 11 patients and thereafter declined exponentially with an average plasma half-life of 3.98 hours (range 1.4 to 4.3) after the 80 mg dose and 4.28 hours (range 1.9 to 5.4) after the 160 mg dose. There was wide interindividual variation in plasma propranolol concentration at any given time after each dose. Treadmill walking time to the onset of angina, the total duration of exercise and the total external work performed were significantly greater by 1 hour after each dose of propranolol than after placebo. This improvement in exercise tolerance persisted unchanged for 8 hours ( P < 0.001) and was still significant although less marked at 12 hours ( P < 0.05). Improvement in exercise tolerance after propranolol was associated with a significant reduction in S-T segment depression during exercise. Both at rest and during exercise, heart rate, systolic blood pressure and rate-pressure product decreased after propranolol, and these circulatory effects persisted for 12 hours. Changes in walking time, heart rate and systolic blood pressure were similar after 80 and 160 mg of propranolol. Despite the increase in exercise duration and in total work performed after propranolol, the rate-pressure product at the onset of angina was lower after propranolol. In view of the prolonged effects of single oral doses of 80 and 160 mg of propranolol, it is suggested that administration of propranolol twice daily should be adequate in treating patients with stable angina pectoris. These studies also demonstrate that routine measurement of plasma propranolol levels is of little practical value in the management of patients with angina pectoris.

Differentiation of the roles of histamine H1- and H2-receptors in the mediation of the effects of histamine in the isolated working heart of the guinea-pig.

1 Differentiation of the roles of histamine H1- and H2-receptors in the mediation of the effects of histamine on the isolated working heart of the guinea-pig was achieved through the use of histamine and selective histamine receptor agonists and antagonists. 2 Histamine over the dose range 10(-9) mol to 10(-6) mol produced dose-related increases in sinus rate, left intraventricular pressure (LVP)max, LVdP/dtmax, coronary flow, aortic flow, total cardiac output and external pressure-volume work. 3 Dimaprit, a selective histamine H2-receptor agonist, produced very similar responses to histamine. 4 2-Pyridylethylamine, a selective histamine H1-receptor agonist, had little effect on cardiac function unless large doses were administered. Such doses produced increases in all measured parameters. 5 Cimetidine, a selective histamine H2-receptor antagonist, antagonized the effects of histamine and dimaprit and some but not all effects of 2-pyridylethylamine. In the presence of cimetidine a decrease in all parameters with the exception of sinus rate was observed with both histamine and 2-pyridylethylamine. 6 The selective histamine H1-receptor antagonist, mepyramine, had little effect on responses to all three agonists. However, the depressant effects observed with histamine and 2-pyridylethylamine in the presence of cimetidine were antagonized by mepyramine. 7 The results indicate the important role of the histamine H2-receptor in the mediation of the gross cardiac effects of histamine and also indicate that histamine H1-receptors can mediate cardiac depression.

Steady and pulsatile energy losses in the systemic circulation under normal conditions and in simulated arterial disease.

External left ventricular work was calculated from records of pressure and flow in the ascending aorta of 1 unanaesthetized and 21 anaesthetized dogs. Work was divided into pulsatile and steady components, the former representing energy lost in vascular pulsations and the latter, energy lost in maintaining steady flow. The ratio of pulsatile to total (steady + pulsatile) external work averaged 10% under control conditions but increased markedly when heart rate slowed, when cardiac output rose, or when arterial distensibility was impaired.

External work in walking

From records obtained from a triple accelerometer applied to the trunk of a subject the displacements of the trunk in vertical, forward, and lateral directions have been calculated. With motion pictures taken simultaneously, displacements of the center of gravity within the body were measured. From these data the external mechanical work of walking was calculated. The sum of work for vertical and for forward displacements of the center of gravity of the body gives the total external work; energy for the lateral displacements was negligible. Total external work appears to be lower than that calculated from the vertical displacements alone, because work done in lifting is partly sustained by the inertial force of the forward-moving body. Total external work reaches a highest value (0.1 kcal/km kg) at the most economical speed of walking, 4 km/hr, which corresponds to an energy consumption of 0.48 kcal/km kg. At this speed the internal work appears negligible; it amounts to appreciable entities at very low speeds because of the static contractions of the muscles, and at high speeds because of considerable stiffening of the limbs and movements not involving a displacement of the center of gravity. Submitted on May 25, 1962

Societies and Academies

Societies and Academies