Maximal Exercise Level Research Articles

Cardiovascular and respiratory adjustments in normal volunteers during modified exercise tests in comparison to standard exercise tests.

Sixteen normal, non-smoking first year medical students underwent four standard exercise tests, while cardiovascular (heart rate and blood pressure) and pulmonary (respiratory rate, tidal volume and oxygen consumption) adjustments were being monitored. Maximal exercise level for all tests were defined following the Jones scale. No variation was noted in respiratory rate among the four exercise tests. The cycle ergometry (CE), hand ergometry (HE), and treadmill (TM) exercise tests produced progressive increases of the various parameters as expected, although target maximal heart rates were not reached in most cases secondary to muscle fatigue. The step test (ST) approximated the physiological parameter changes noted in these three tests during the early stages of exercise, but levelled off after 3 minutes, probably due to lack of incremental load. The ST took the longest time to reach maximal level of exercise parameters, and recorded the lowest tidal volume increase. The same subjects underwent a modified step test (MST1) by adding 1 kg sandbags every 3 min to backpacks worn by the subjects, to provide incremental load. This modification provided a slight increase in the parameters measured, but still plateaued after 3 min. Another set of 18 normal, non-smoking medical students underwent bicycle ergometry and two other modified exercise tests. The modified step test two (MST2) was similar to our initial MST1, except that the sandbags added every 3 min were not fixed at 1 kg but were also incremental (1, 2, 3 and 4 kg). The other test (Ramp test or RT) required the subjects to walk up and down a ramp, which entailed not only the addition of incremental weights of sandbags every 3 min, but also increasing the elevation of the ramp at each stage. Data analysis showed that these two tests showed almost similar changes in cardiovascular and respiratory adjustments in the subjects, compared to the standard bicycle ergometry. These pilot studies showed that low-cost modified step tests may be utilized to approximate the expensive standard treadmill and bicycle exercise tests. More studies on larger populations have to be done to validate these results.

Influence of Maximal Ergometric Exercise on Endothelin Concentrations in Relation to Molecular Markers of the Hemostatic System

The effects of moderate 30 min cycle ergometer exercise (aerobic metabolism; 0.85-3.71 mmol.1(-1) lactate) followed by short-term exercise at maximal capacity (anaerobic metabolism; 5.09 to 17.75 mmol.1(-1) lactate) on endothelin (ET) and hemostatic variables (tissue plasminogen activator [t-PA] antigen, prothrombin fragments [F1,2], thrombin-antithrombin III complex [TAT], prothrombin time and partial thromboplastin time) were investigated in 15 male healthy subjects of varying fitness levels. Endothelin was measured twice before and immediately after maximal cycle exercise. The results show an increase in endothelin concentration [10.0 pg.ml-1 (baseline) + 6.1 pg.ml-1 (increase post exercise)]. ET did not increase under control conditions. Moderate 30 min exercise caused an increase in t-PA antigen concentration (3.66 + 3.15 ng.ml-1) and short-term maximal exercise produced a markedly higher elevation in this variable (+10.6 ng.ml-1). F1,2 increased (810 + 40 pmol.l-1) under moderate and by 150 pmol.l-1 under anaerobic exercise. TAT increased only at maximal exercise levels (1.01 + 0.32 ng.l-1). No changes were found in any of these variables under control conditions. No correlation of endothelin and the hemostatic variables was found. It is concluded that endothelin and hemostatic markers increase independently during moderate and maximal exercise.

Effect of an abdominal binder during wheelchair exercise

The purpose of this study was to determine whether use of an abdominal binder would affect oxygen uptake, trunk range of motion, and duration of the stroke phase during wheelchair propulsion. The subjects were six paraplegic wheelchair athletes with T1-T6 injuries and no abdominal muscle function. Each subject performed two trials, one while wearing the binder and one without the binder. Each trial consisted of submaximal and maximal exercise tests conducted on wheelchair rollers. Oxygen uptake was determined by open circuit spirometry while heart rate was determined by telemetry. Max VO2 values averaged 2.51 l.min-1 while average maximum heart rate values were 190 b.min-1. A 3-D video-based motion analysis system was used to obtain kinematic parameters of wheelchair propulsion. In general, 30% of the cycle time was comprised of the stroke phase, while 70% was comprised of the recovery phase across speeds. There were no statistically significant effects of the abdominal binder on any of the cardiovascular or kinematic variables at submaximal or maximal levels of exercise. Under the conditions of this laboratory investigation, it appears that an abdominal binder does not alter physiological or selected biomechanical measures in highly trained athletes.

Patterns of neuroendocrine activation at rest and during exercise following acute myocardial infarction.

Previous studies of neurohumoral activation following myocardial infarction have concentrated on the within-hospital phase and have only made measurements at rest. The objectives of this study were to measure neuroendocrine activity in the early convalescent phase of myocardial infarction at rest and during symptom-limited maximal exercise and to study the effects of early drug therapy. We studied 75 patients, mean age 57 (range 37-74) without evidence of overt heart failure, following Q-wave myocardial infarction. Patients were studied a mean of 17 days following myocardial infarction and compared with 11 age-matched control subjects. Plasma noradrenaline, adrenaline, atrial natriuretic peptide and plasma renin activity were measured at rest, at submaximal and symptom-limited maximal treadmill exercise. At the time of study 40 patients were taking beta-blockers, 19 diuretics and 16 no treatment. Atrial natriuretic peptide levels were higher at rest (P = 0.0001) and at symptom-limited exercise (P = 0.002) in the patient group than in the control subjects. Although there were no significant resting differences between the patient subgroups, at symptom-limited exercise plasma atrial natriuretic peptide levels were significantly higher in the patients taking beta-blockers than in the other patient groups (P = 0.001). Plasma renin activity was no different between the patients and the control subjects at rest or during exercise. Those patients taking diuretics had higher values at rest (P = 0.001) and during exercise (P = 0.005) compared with the remaining patients. There were no significant differences in resting or maximal exercise levels of plasma noradrenaline and adrenaline between the patients and the control subjects (all P > 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)

Exertional Hypotension in Spinal Cord Injury

To assess blood pressure (BP) response to continuous maximal arm ergometry in patients with spinal cord injury (SCI). Cross-sectional analysis of data collected for a prospective study of functional electrical stimulation in patients with SCI. Short-term rehabilitation hospital. Twenty individuals with SCI; 4 cervical (C6 to C8), 10 high thoracic (T1 to T6), and 6 low thoracic (T7 to T12). Each subject performed continuous maximal arm ergometry with expired gas analysis. Blood pressure was measured using a technician-assisted protocol. The BP at maximal exercise was compared with the highest submaximal BP reached during the test (delta BP = final BP minus highest submaximal BP). All 20 subjects had a negative delta BP (mean +/- SD; -22.8 +/- 12.1 mm Hg) for mean BP and 19 of 20 had a negative delta BP (-25.8 +/- 14.4 mm Hg) for systolic BP. The delta BP was not significantly related to maximum exercise parameters, resting BP, or level of lesion. Four able-bodied subjects and six wheelchair-bound individuals without SCI showed no exertional hypotension. Repeated testing on the four able-bodied subjects showed excellent reproducibility for mean BP (coefficient of variation [CV] = 3.6 percent; r = 0.98; p < 0.01) and systolic BP (CV = 2.2 percent; r = 0.99; p < 0.01) using this protocol. These data describe, for the first time to our knowledge, that exertional hypotension is present in all individuals with SCI during continuous arm ergometry. Further studies are needed to clarify the mechanisms responsible for this phenomenon and to evaluate the long-term consequences for individuals with SCI.

Doppler echocardiographic assessment of the hemodynamic benefits of rate adaptive AV delay during exercise in paced patients with complete heart block.

To determine if rate adaptation of the atrioventricular (AV) delay (i.e., linearly decreasing the AV interval for increasing sinus rate) improves exercise left ventricular systolic hemodynamics, we performed paired maximal semi-upright bicycle exercise tests (EXTs) on 14 chronotropically competent patients with dual chamber pacemakers. Nine patients with complete AV block (CAVB) and total ventricular pacing dependence during exercise comprised the experimental group. Pacemakers in these patients were programmed randomly to rate adaptive AV delay (AVDR) for one EXT and fixed AV delay (AVDF) for the other EXT. AVDF was 156 msec; AVDR decreased linearly from 156-63 msec from rates of 78-142 beats/min. The other five patients had intact AV conduction and comprised the control group who were exercised in identical fashion while their pacemakers were inhibited throughout exercise to assure reproducibility of hemodynamic measurements between EXTs. Cardiac hemodynamics were calculated using measured Doppler echocardiographic systolic aortic valve flows recorded suprasternally with an independent 2-MHz Doppler transducer during a graded ramp exercise protocol. For analysis, exercise was divided into four phases to compare Doppler measurements at submaximal and maximal levels of exercise: rest, early exercise (1st stage), late exercise (stage preceding peak), and peak. Patients achieved statistically similar heart rates between EXTs at each phase of exercise. Although at lower levels of exercise cardiac hemodynamics did not differ, experimental patients (with CAVB) showed a statistically significant benefit to cardiac output at peak exercise with heart rates of 129 +/- 13 beats/min (AVDR: 9.4 +/- 2.8 L/min; AVDF: 8.2 +/- 2.6 L/min, P = 0.002), stroke volume (AVDR: 74.1 +/- 25.6 mL; AVDF: 64.3 +/- 24.4 mL, P = 0.0003), and aortic ejection time (AVDR: 253.3 +/- 35.7 msec; AVDF: 226.7 +/- 35.0 msec, P = 0.002). Duration of exercise, peak rate pressure product, peak aortic flow velocities, and acceleration times did not differ. In contrast, control group patients (intact AV conduction throughout exercise) showed no statistical differences between any hemodynamic parameters measured at any phase of exercise from the first to second exercise test. These data demonstrate that systolic cardiac hemodynamics measured echocardiographically at the high heart rates achieved with peak exercise are improved with AVDR compared to AVDF in chronotropically competent patients with complete AV block. This is due primarily to improved stroke volume and a longer systolic ejection time with AV delay rate adaptation.

The relationship between the transfer factor obtained at rest, and arterial oxygen tension during exercise, in patients with miscellaneous pulmonary diseases.

Forty-one consecutive patients with the symptom 'exertional dyspnoea' were referred to the Department of Clinical Physiology for evaluation. Pulmonary fibrosis and chronic obstructive pulmonary disease were the most common diagnoses but other diagnoses were also represented. Some patients had no clinical diagnosis or radiological signs. All patients underwent exercise testing with sampling of arterial blood for blood gas analysis and pulmonary function testing including measurement of the transfer factor (carbon monoxide diffusing capacity) at rest. Independent of spirometric findings and diagnosis a significant correlation (r = 0.80, P < 0.001) was shown to exist between the transfer factor measured at rest and the arterial oxygen tension at maximal exercise level. We recommend measurement of the transfer factor as a screening test for exertional hypoxaemia and suggest that exercise blood gas analysis only seems necessary in patients with a transfer factor between 55% and 80% of the predicted value.

Reversible protective effect of propafenone or flecainide during atrial fibrillation in patients with an accessory atrioventricular connection

In 34 patients with a symptomatic accessory atrioventricular connection the reversible protective effect of orally administered flecainide (300 mg/day) and of propafenone (900 mg/day) in control of ventricular response during atrial fibrillation by exercise was assessed. The study consisted of three sections of 1 week each: an initial treatment phase during which propafenone or flecainide was administered, a drug-free phase, and a period of crossover to treatment with the other drug. At the end of each phase, transesophageal stimulation was performed during physical exercise to induce atrial fibrillation episodes: the goal was to control the persistence of drug effectiveness. At rest, the mean and shortest R-R interval during the period of induced atrial fibrillation in patients who were treated with flecainide or propafenone increased significantly as compared with the drug-free period. On the other hand, at maximum exercise levels no difference in both shortest and mean R-R intervals during atrial fibrillation was observed between patients who were treated with flecainide and those who were treated with propafenone, as well as between flecainide treatment and the drug-free period, whereas a slightly significant difference persisted with propafenone treatment ( p < 0.05). In addition, at maximum exercise levels no significant difference in the number of preexcited QRS complexes among the three treatments was noted. The data from this study suggests that a reversible protective effect against rapid ventricular rate as the result of an episode of atrial fibrillation exists during exercise in patients with a symptomatic accessory atrioventricular connection who are treated with flecainide or propafenone.

Running on land and in water

The effect of water immersion on cardiorespiratory and blood lactate responses during running was investigated. Wearing a buoyant vest, 10 trained runners (mean age 26 yr) ran in water at four different and specified submaximal loads (target heart rates 115, 130, 145, and 155-160 beats.min-1) and at maximal exercise intensity. Oxygen uptakes (VO2), heart rates, perceived exertion, and blood lactate concentrations were measured. Values were compared with levels obtained during treadmill running. For a given VO2, heart rate was 8-11 beats.min-1 lower during water running than during treadmill running, irrespective of exercise intensity. Both the maximal oxygen uptake (4.03 vs 4.60 1 x min-1) and heart rate (172 vs 188 beats.min-1) were lower during water running. Perceived exertion (legs and breathing) and the respiratory exchange ratio (RER) were higher during submaximal water running than during treadmill running, while ventilation (1 x min-1) was similar. The blood lactate concentrations were consistently higher in water than on the treadmill, both when related to VO2 and to %VO2max. Partly in conformity with earlier cycle ergometer studies, these data suggest that immersion induces acute cardiac adjustments that extend up to the maximal exercise level. Furthermore, both the external hydrostatic load and an altered running technique may add to an increased anaerobic metabolism during supported water running.

Effect of timolol on cardiopulmonary exercise performance in men after myocardial infarction

The effect of the nonselective β blocker timolol on maximal cardiopulmonary exercise performance was evaluated in 28 men with previous myocardial infarction without effort angina (mean age 63 ± 8 years). Patients were randomized to placebo or timolol (10 mg twice daily) for 4 weeks and then crossed over to the alternative therapy in a double-blind manner. At the completion of each treatment period, patients underwent symptom-limited maximal cardiopulmonary exercise on a cycle ergometer. Exercise time, heart rate, oxygen consumption (VO 2), oxygen (O 2) pulse and respiratory exchange ratio were measured at peak exercise and at a submaximal exercise level defined at a respiratory exchange ratio of 1.00. Timolol treatment reduced peak heart rate from 153 ± 11 to 102 ± 14 beats/min (−33%, p <0.001). Exercise time decreased from 680 ± 91 to 633 ± 78 seconds (−7%, p <0.001). Peak VO 2 decreased from 25.3 ± 4.7 to 21.4 ± 3.5 ml/min/kg (−15%, p <0.001). O 2 pulse increased from 12.9 ± 1.9 to 16.7 ± 2.3 ml/beat (+29%, p <0.001). Peak respiratory exchange ratio did not change significantly, indicating comparable effort. At submaximal exercise, defined at a respiratory exchange ratio of 1.00, there was no difference in exercise time between placebo and timolol. Heart rate decreased with timolol compared with placebo, from 126 ± 16 beats/min by 31% (p <0.001), VO 2 decreased from 18.5 ± 4.3 ml/min/kg by 10% (p <0.001), O 2 pulse increased from 11.5 ± 2.0 ml/beat by 30% (p <0.001). The results indicate that timolol significantly reduced peak VO 2, heart rate and exercise time at peak exercise. The increased O 2 pulse at maximal level of exercise only partially compensated for the reduction in heart rate. At submaximal exercise, VO 2 and heart rate were reduced during timolol treatment, and the increase in O 2 pulse more completely compensated for the reduced heart rate. The remits indicate that the use of β blockade for secondary prophylaxis substantially compromises functional capacity at peak and maximal exercise.

Volumetric response of right ventricle during progressive supine exercise in men

Right ventricular (RV) adaptation to supine exercise has been studied in 10 young male volunteers by 81mKr electrocardiogram (ECG)-gated radionuclide ventriculography. During progressive supine exercise, the ejection fraction gradually increased from a mean value of 46% at rest up to 60% at a maximal exercise level. End-diastolic volume however remained unchanged at a low exercise level and even slightly decreased at a higher exercise level. Little or no change in end-diastolic volume and an increase in ejection fraction produced a significant decrease in end-systolic volume and a net increase in stroke volume. These results indicate that the Frank-Starling mechanism does not contribute to the increase in right ventricular stroke volume during progressive supine exercise, but the increase in right ventricular stroke volume rather seems related to an increased contractility, presumably mediated by an increased sympathetic activity.

Latissimus Dorsi Cardiomyoplasty in Severe Congestive Heart Failure: The Lyon Experience

Eleven male patients, New York Heart Association (NYHA) Class III, have undergone cardiomyoplasty (Chachques and Carpentier technique). There were no deaths. Two patients suffered from low cardiac output, one patient suffered a massive aortic bifurcation embolism, and one patient had a Legionella pneumonia. All patients recovered well. The follow-up was 6.9 +/- 2.3 months. One patient had a Cardiomyostimulator Pulse Train Generator failure and had it replaced. The first seven patients were evaluated 6 months after surgery. They all improved (Class II) except for one, who was transplanted. The maximal level of exercise was improved (92 +/- 18 W vs 60 +/- 24 W), as was the heart rate-systolic blood pressure product (30,262 +/- 3,119 vs 19,908 +/- 4,190), mainly due to an increase in systolic blood pressure (200.0 +/- 25.5 vs 141.5 +/- 20.3 mmHg). Echographic parameters, maximal oxygen consumption, left ventricular ejection fraction (LVEF), cardiac index, oxygen arteriovenous difference, and cardiac filling pressures did not change. The left ventricular (LV) angiography always showed good contraction of the latissimus dorsi. A problem needing investigation is the principle of cardiomyoplasty (CMP) itself, as the muscle acts more as a lift than as pincers. Our patients, and patients from other series, improved functionally, and they exercised more. Improvement in survival can be studied only by a randomized clinical trial.

Submaximal oxygen consumption in liver cirrhosis: Evidence of severe functional aerobic impairment

We studied maximal aerobic work capacity in 24 cirrhotic patients whose clinical condition was well compensated. Nineteen of our patients had no heart or lung disease, and five had mild mechanical ventilatory impairment. The patients performed incremental exercise on a treadmill until subjective exhaustion. The maximal exercise levels reached by all were relatively low and led to a lower observed maximal oxygen uptake ( VO 2 max), than predicted uptake (19.6 ± 0.5 vs. 37.9 ± 0.6 ml/kg; p < 0.001). Observed VO 2 max values correlated strongly with the Pugh score, which reflects the degree of liver failure ( r = −0.571; p < 0.01). Since there were no clear cardiac or pulmonary causes to explain the decrease in work capacity, these observations suggest that liver cirrhosis might induce or be accompanied by muscular impairment. VO 2 max, which seems to decline with the functional severity of the disease, may be a useful index for evaluating the capacity of patients for physical rehabilitation.

Behavior of a Respiratory Driven Pacemaker and Direct Respiratory Measurements

In 10 patients with a mean age of 76 +/- 8 years, a rate responsive pacemaker (Meta-MV, Telectronics) was implanted in the left pectoral site. An exercise test was performed in SSI ("adaptive") mode, allowing the device to measure the changes in thoracic impedance. The "slope number" at maximal exercise was chosen to program the pacemaker for a second exercise test in rate responsive mode. Direct measurements of respiratory rate and minute volume were correlated with the pacing rate. After 1 minute of exercise, pacing rate increased by 6% and it decreased smoothly after maximal exercise. The programmed maximal rate was reached at the maximum exercise level in six patients. During 24-hour Holter recording, the mean maximal pacing rate was 103 +/- 18 beats/min. For individual patients, a good correlation of pacing rate with respiratory rate (r = 0.757), oxygen consumption (r = 0.731), and minute volume (r = 0.800) was observed. The data from the entire group showed a highly significant correlation of changes in pacing rate and in respiratory parameters for different levels of exercise and recovery. In a subgroup of five patients, the slope numbers at maximal exercise were reproducible after 10 months. It was concluded that minute volume and its changes were recognized in a reliable way by the Meta-MV pacemaker.

Blood pressure and cardiac output during exercise: A longitudinal study of children undergoing repair of coarctation

Data were examined from 21 children who underwent graded exercise studies prior to and within 5 years after repair of coarctation. A control group of 10 normal children was also studied longitudinally on two occasions. The exercise was performed on an upright bicycle ergometer using a continuous graded exercise protocol. Parameters measured were heart rate, systolic and diastolic blood pressure at rest, and these pressures at the maximal voluntary exercise level. In addition, a subset of patients and controls had measurement of cardiac output by a modified acetylene rebreathing technique. Results indicate that coarctation patients had significant elevation of systolic and diastolic blood pressures at rest ( p < 0.001 for both) and with exercise ( p < 0.02 for both) prior to surgery. The group mean values for systolic and diastolic blood pressure did not differ from control values after surgery; however, some individuals continued to have hypertension at rest when compared to population-based norms. Heart rate, cardiac index, and stroke volume index did not differ from those of control subjects either at rest or during exercise before or after surgery. In conclusion, a group of coarctation patients studied longitudinally demonstrated marked improvement in both systolic and diastolic hypertension after surgery. The findings of normal cardiac output and stroke volume indices may have implications for the etiology of postoperative hypertension.

Effects of Pressure-Demand Respirator Wear on Physiological and Perceptual Variables during Progressive Exercise to Maximal Levels

Current regulations governing the certification of respiratory protective devices are based on data published in the early 1950s. The limited data base of this early work and documented increases in the average height of the population underscore the need for additional information concerning the parameters of certification. In the present study, a protocol using an inclined treadmill (0.5% grade every 12 sec) was used to test a heterogeneous population (n=38). Through submaximal up to and including maximal exercise levels with and without respirator wear, maximal oxygen uptake (V˙O2max) was significantly greater (p<0.01) with the respirator (44.11±1.3 mL/kg·min) than without the respirator (42.18±1.4 mL/kg·min) while maximal ventilation volumes (V˙Emax) were not significantly different (with=118.7±4 L/min; without 119.6±5 L/min). While peak inspired flows (PFI) with the respirator (268±7 L/min) were less than without the respirator (281±9 L/min), p>0.05, the lower peak expired flow (PFE) with the respirator (289±12 L/min) than without the respirator (324±13 L/min), p<0.01, indicated a significant blunting effect of the respiratory flows by the expired resistance during exercise to maximal levels. Peak inspired pressures (PPi) with and without the respirator were not significantly different (p>0.05). The negative values obtained within the facepiece of the respirator (−7.65±0.8 cmH2O), however, indicate that the positive pressure within the facepiece was lost, and respiratory protection may be compromised. Peak expired pressure with the respirator (13.05±0.7 cmH2O) was significantly greater than without the respirator (10.7±0.5 cmH2O) indicating that, despite a lower PFE, greater force was required to overcome the resistances of the respirator on expiration. The dyspnea index, an index of physiological effort; suggests that the subjects were working at a higher percentage of their respiratory reserve with the respirator (p<0.05) than without. Perceptually, subjects also felt that breathing with the respirator was more difficult (p<0.05). The maximum heart rate and the ratings of perceived exertion were not significantly different between the two tests at maximal exercise levels. Maximum oxygen uptake was considered reached when subjects attained a respiratory exchange ratio of at least 1.15, when a heart rate response at or greater than age-predicted maximum was achieved, when ratings of perceived exertion indicated exhaustion, and/or when the measure of V˙O2 had plateaued during the final minute of exercise. The significance of these data lies not within the average values but the extreme ranges that represent the general population needing respiratory protection. Current respirator designs provide respiratory protection for 50% of the population up to exercise intensities of 50% V˙O2max. It is recommended that pressure demand respiratory devices be redesigned to provide adequate protection for up to 99% of the general population up to maximal exercise levels. These new designs should provide respiratory protection for V˙ES up to 199 L/min, PFis to 400 L/min, PFEs to 496 L/min, and pressure swings of 30 cmH2.

Effects of pressure-demand respirator wear on physiological and perceptual variables during progressive exercise to maximal levels.

Current regulations governing the certification of respiratory protective devices are based on data published in the early 1950s. The limited data base of this early work and documented increases in the average height of the population underscore the need for additional information concerning the parameters of certification. In the present study, a protocol using an inclined treadmill (0.5% grade every 12 sec) was used to test a heterogeneous population (n = 38). Through submaximal up to and including maximal exercise levels with and without respirator wear, maximal oxygen uptake (VO2max) was significantly greater (p less than 0.01) with the respirator (44.11 +/- 1.3 mL/kg.min) than without the respirator (42.18 +/- 1.4 mL/kg.min) while maximal ventilation volumes (VEmax) were not significantly different (with = 118.7 +/- 4 L/min; without 119.6 +/- 5 L/min). While peak inspired flows (PFI) with the respirator (268 +/- 7 L/min) were less than without the respirator (281 +/- 9 L/min), p greater than 0.05, the lower peak expired flow (PFE) with the respirator (289 +/- 12 L/min) than without the respirator (324 +/- 13 L/min), p less than 0.01, indicated a significant blunting effect of the respiratory flows by the expired resistance during exercise to maximal levels. Peak inspired pressures (PPi) with and without the respirator were not significantly different (p greater than 0.05). The negative values obtained within the facepiece of the respirator (-7.65 +/- 0.8 cmH2O), however, indicate that the positive pressure within the facepiece was lost, and respiratory protection may be compromised. Peak expired pressure with the respirator (13.05 +/- 0.7 cmH2O) was significantly greater than without the respirator (10.7 +/- 0.5 cmH2O) indicating that, despite a lower PFE, greater force was required to overcome the resistances of the respirator on expiration. The dyspnea index, an index of physiological effort; suggests that the subjects were working at a higher percentage of their respiratory reserve with the respirator (p less than 0.05) than without. Perceptually, subjects also felt that breathing with the respirator was more difficult (p less than 0.05). The maximum heart rate and the ratings of perceived exertion were not significantly different between the two tests at maximal exercise levels. Maximum oxygen uptake was considered reached when subjects attained a respiratory exchange ratio of at least 1.15, when a heart rate response at or greater than age-predicted maximum was achieved, when ratings of perceived exertion indicated exhaustion, and/or when the measure of VO2 had plateaued during the final minute of exercise.(ABSTRACT TRUNCATED AT 400 WORDS)

Left ventricular response to submaximal and maximal exercise in asymptomatic aortic regurgitation

In patients with chronic aortic regurgitation the quantitative changes in loading conditions and left ventricular performance from rest to submaximal exercise have not been related to the magnitude of change observed from rest to maximal exercise. Changes in end-diastolic volume index, as a measure of preload, and measures of contractile performance (ejection fraction and the systolic blood pressure/end-systolic volume index ratio) were assessed at rest, submaximal and maximal supine bicycle exercise using radionuclide angiography in 74 patients with chronic moderate to severe aortic regurgitation. With exercise, end-diastolic volume index decreased in a stepwise manner from 166 ± 47 to 152 ± 41 to 143 ± 41 ml/m 2 at rest, submaximal and maximal exercise, respectively. For the entire group, these changes were not associated with a significant change in ejection fraction but were associated with stepwise increases in systolic blood pressure to end-systolic volume index ratio. However, when patients were divided into 3 subgroups based on an increase (group I), minimal change (group II) or a decrease (group III) in ejection fraction from rest to maximal exercise, stepwise increases in systolic blood pressure to endsystolic volume index were again observed in groups I and II but not in group III. These changes were significantly greater in group I than in group II at submaximal and maximal exercise levels. Differences in ejection fraction response and end-diastolic and end-systolic volumes with exercise in the 3 groups were evident at the submaximal exercise level. These data suggest that the stepwise changes in left ventricular volumes and performance that occur during submaximal exertion are smaller but directionally similar to changes at maximal exertion. Conversely, the findings at maximal exertion may be used to infer the response of the left ventricle at submaximal exertion during activities of daily living.

Comparison of the cardiac output and stroke volume response to upright exercise in children with valvular and subvalvular aortic stenosis

Cardiac output and stroke volume were evaluated in 17 children (mean age 11.5 ± 3 years) with discrete, membranous subvalvular (Group I, n = 7) and valvular (Group II, n = 10) aortic stenosis during submaximal and maximal (>75% predicted maximal oxygen consumption) upright cycle ergometry. Patients with valvular aortic stenosis were further subdivided on the basis of their aortic valve gradient at rest determined by cardiac catheterization (Group IIA, gradient <40 mm Hg; Group IIB, gradient ≥ 40 mm Hg). These patients were matched with 17 control subjects on the basis of age, sex, height and intensity of exercise during maximal exertion. Cardiac and stroke indexes were determined by the acetylene rebreathing method at each exercise level.Stroke volume index in Group I was significantly greater at rest when compared with that in control subjects (69 ± 13 versus 53 ± 11 ml/m2, α = 0.01, p < 0.05) and that in patients in Group II (69 ± 13 versus 47 ± 12 ml/m2, α = 0.01, p < 0.05). Patients with subvalvular aortic stenosis were unable to increase their stroke volume index from rest to submaximal exercise and also decreased their stroke volume index at maximal exercise levels. In contrast, patients with mild valvular aortic stenosis (Group IIA) displayed a normal exercise response. Patients with severe valvular aortic stenosis (Group IIB) had a blunted stroke volume response at rest and at each level of exercise, as well as signs of myocardial ischemia (ST segment depression) during maximal exercise.Cardiac output measurements during exercise testing permitted analysis of stroke volume patterns that differ by anatomic type and severity of left ventricular outflow tract obstruction. These findings have implications regarding the timing of treatment and exercise prescription for children with aortic stenosis.

Effect of Alprazolam on Exercise and Dyspnea in Patients with Chronic Obstructive Pulmonary Disease

To evaluate the efficacy of a mild anxiolytic, alprazolam, in relieving dyspnea, we conducted a randomized, placebo-controlled double-blind study on patients with chronic obstructive lung disease. Twenty-four patients had alprazolam (0.5 mg bid) or placebo administered for one week, followed by placebo for one week, then either placebo or alprazolam for the third week. Assessment tests were performed at the outset, end of the first and second weeks, and finally end of the third week. The parameters measured were: pulmonary function, exercise testing on a bicycle ergometer, and the distance covered in a 12 minute walk. Subjective sensations of dyspnea at rest and during guarded exercise, as well as subjective feelings of calmness or anxiety were also recorded. There was no difference in mechanical lung function, but the PO2 tended to decrease and PCO2 to increase after alprazolam administration. The maximum exercise level attained and the distance covered in the 12 minute walk was unchanged. The subjective perception of dyspnea was the same before and after alprazolam, at rest and during exercise. We conclude that alprazolam is not effective in relieving exercise dyspnea in patients with obstructive lung disease.