Validation of a computerized technique for detection of the gas exchange anaerobic threshold in cardiac disease

Development of deep-learning models for real-time anaerobic threshold and peak VO2 prediction during cardiopulmonary exercise testing

AIMS

Exercise intolerance is a clinical feature of patients with heart failure (HF). Cardiopulmonary exercise testing (CPET) is the first-line examination for assessing exercise capacity in patients with HF. However, the need for extensive experience in assessing anaerobic threshold (AT) and the potential risk associated with the excessive exercise load when measuring peak oxygen uptake (peak VO2) limit the utility of CPET. This study aimed to use deep-learning approaches to identify AT in real time during testing (defined as real-time AT) and to predict peak VO2 at real-time AT.

METHODS AND RESULTS

This study included the time-series data of CPET recorded at the Department of Cardiovascular Medicine, Kyushu University Hospital. Two deep neural network models were developed to: (i) estimate the AT probability using breath-by-breath data and (ii) predict peak VO2 using the data at the real-time AT. The eligible CPET contained 1472 records of 1053 participants aged 18-90 years and 20% were used for model evaluation. The developed model identified real-time AT with 0.82 for correlation coefficient (Corr) and 1.20 mL/kg/min for mean absolute error (MAE), and the corresponding AT time with 0.86 for Corr and 0.66 min for MAE. The peak VO2 prediction model achieved 0.87 for Corr and 2.25 mL/kg/min for MAE.

CONCLUSION

Deep-learning models for real-time CPET analysis can accurately identify AT and predict peak VO2. The developed models can be a competent assistant system to assess a patient's condition in real time, expanding CPET utility.

Cardiopulmonary Exercise Testing Distinguishes between Post-COVID-19 as a Dysfunctional Syndrome and Organ Pathologies

(1) Background: Dyspnea is one of the most frequent symptoms among post-COVID-19 patients. Cardiopulmonary exercise testing (CPET) is key to a differential diagnosis of dyspnea. This study aimed to describe and classify patterns of cardiopulmonary dysfunction in post-COVID-19 patients, using CPET. (2) Methods: A total of 143 symptomatic post-COVID-19 patients were included in the study. All patients underwent CPET, including oxygen consumption, slope of minute ventilation to CO₂ production, and capillary blood gas testing, and were evaluated for signs of limitation by two experienced examiners. In total, 120 patients reached a satisfactory level of exertion and were included in further analyses. (3) Results: Using CPET, cardiovascular diseases such as venous thromboembolism or ischemic and nonischemic heart disease were identified as either cardiac (4.2%) or pulmonary vascular (5.8%) limitations. Some patients also exhibited dysfunctional states, such as deconditioning (15.8%) or pulmonary mechanical limitation (9.2%), mostly resulting from dysfunctional breathing patterns. Most (65%) patients showed no signs of limitation. (4) Conclusions: CPET can identify patients with distinct limitation patterns, and potentially guide further therapy and rehabilitation. Dysfunctional breathing and deconditioning are crucial factors for the evaluation of post-COVID-19 patients, as they can differentiate these dysfunctional syndromes from organic diseases. This highlights the importance of dynamic (as opposed to static) investigations in the post-COVID-19 context.

Novel Computerized Method for Automated Determination of Ventilatory Threshold and Respiratory Compensation Point

Introduction: The ventilatory threshold (named as VT₁) and the respiratory compensation point (named as VT₂) describe prominent changes of metabolic demand and exercise intensity domains during an incremental exercise test.

Methods: A novel computerized method based on the optimization method was developed for automatically determining VT₁ and VT₂ from expired air during a progressive maximal exercise test. A total of 109 peak cycle tests were performed by members of the US astronaut corps (74 males and 35 females). We compared the automatically determined VT₁ and VT₂ values against the visual subjective and independent analyses of three trained evaluators. We also characterized VT₁ and VT₂ and the respective absolute and relative work rates and distinguished differences between sexes.

Results: The automated compared to the visual subjective values were analyzed for differences with t test, for agreement with Bland–Altman plots, and for equivalence with a two one-sided test approach. The results showed that the automated and visual subjective methods were statistically equivalent, and the proposed approach reliably determined VT₁ and VT₂ values. Females had lower absolute O₂ uptake, work rate, and ventilation, and relative O₂ uptake at VT₁ and VT₂ compared to men (p ≤ 0.04). VT₁ and VT₂ occurred at a greater relative percentage of their peak VO₂ for females (67 and 88%) compared to males (55 and 74%; main effect for sex: p < 0.001). Overall, VT₁ occurred at 58% of peak VO_2, and VT₂ occurred at 79% of peak VO₂ (p < 0.0001).

Conclusion: Improvements in determining of VT₁ and VT₂ by automated analysis are time efficient, valid, and comparable to subjective visual analysis and may provide valuable information in research and clinical practice as well as identifying exercise intensity domains of crewmembers in space.

New method for the mathematical derivation of the ventilatory anaerobic threshold: a retrospective study

Background

Ventilatory anaerobic threshold (VAT) is a useful submaximal measure of exercise tolerance; however, it must be visually determined. We developed a new mathematical method to objectively determine VAT.

Methods

We employed two retrospective population data sets (A/B). Data A (from 128 healthy subjects, patients with cardiovascular risk factors, and cardiac subjects at institution A, who underwent symptom-limited cardiopulmonary exercise testing) were used to develop the method. Data B (from 163 cardiac patients at institution B, who underwent pre−/post-rehabilitation submaximal exercise testing) were used to apply the developed method. VAT (by V-slope) was visually determined (vVAT), assuming that the pre-VAT segment is parallel to the respiratory exchange ratio (R) = 1 line.

Results

First, from data A, exponential fitting of ramp V-slope data yielded the equation y = ba^x, where a is the slope of the exponential function: a smaller value signified a less steep curve, representing less VCO₂ against VO₂. Next, a tangential line parallel to R = 1 was drawn. The x-axis value of the contact point was the derived VAT, termed the expVAT (VCO₂) (calculated as LN (1/[b*LN(a)]/LN(a). This point represents an instantaneous ΔVCO₂/ΔVO₂ of 1.0. Second, in a similar way, the relation of VO2 vs. VE (minute ventilation) was fitted exponentially. The tangent line that crosses zero was drawn and the x-axis value was termed expVAT (VE) (calculated as 1/LN(a). For data A, the correlation coefficients (r) of vVAT versus VAT (CO₂), and VAT (VE) were 0.924 and 0.903, respectively (p < 0.001), with no significant difference between mean values with the limits of agreement (1.96*SD of the pair difference) being ±276 and ± 278 mL/min, respectively. expVAT (VCO₂) and expVAT (VE) significantly correlated with VO₂peak (r = 0.971, r = 0.935, p < 0.001). For data B, after cardiac rehabilitation, expVAT (CO₂) and exp. (VE) (mL/min) increased from 641 ± 185 to 685 ± 201 and from 696 ± 182 to 727 ± 209, respectively (p < 0.001, p < 0.008), while vVAT increased from 673 ± 191 to 734 ± 226 (p < 0.001). During submaximal testing, expVAT (VCO₂) underestimated VAT, whereas expVAT (VE) did not.

Conclusions

Two new mathematically-derived estimates to determine VAT are promising because they yielded an objective VAT that significantly correlated with VO₂peak, and detected training effect as well as visual VAT did.

Electronic supplementary material

The online version of this article (10.1186/s13102-019-0122-z) contains supplementary material, which is available to authorized users.

The relationship between ventilatory threshold and repeated-sprint ability in competitive male ice hockey players

Background/objective

The relationship between ventilatory threshold (VT1, VT2) and repeated-sprint ability (RSA) in competitive male ice hockey players was investigated.

Methods

Forty-three male ice hockey players aged 18-23 years competing in NCAA Division I, NCAA Division III, and Junior A level participated. Participants performed an incremental graded exercise test on a skate treadmill to determine V ˙ O_2peak, VT1, and VT2 using MedGraphics Breezesuit™ software (v-slope). Participants performed an on-ice repeated shift (RSA) test consisting of 8-maximal skating bouts, lasting approximately 25 s and interspersed with 90 s of passive recovery, to determine first gate, second gate, and total sprint decrement (%_dec). Pearson product-moment correlations and multiple regressions were used to assess relationships between ventilatory threshold variables (VT1, VT2, Stage at VT1, and Stage at VT2) and RSA (first gate, second gate, and total course decrement).

Results

Stage at VT2 was the only variable substantially correlated with first gate (r = -0.35; P < 0.05), second gate (r = -0.58; P < 0.001) and total course decrement (r = -0.42; P < 0.05).

Conclusion

The results of this study demonstrated that VT is substantially associated with RSA, and VT2 is more strongly correlated with RSA than V ˙ O_2peak. This study suggests that longer duration high-intensity interval training at intensities that increase workrate at VT2 may lead to possible improvements in RSA.

Phase I safety study of ranolazine in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) causes right ventricular ischemia, dysfunction, and failure. PAH patients may benefit from antianginal agents based on a shared pathophysiology with left ventricular ischemia. A single-center, randomized, placebo-controlled trial (1∶1) to assess the acute vasoreactivity and safety of ranolazine in PAH was conducted. Plasma samples for pharmacokinetic (PK) studies were drawn during hemodynamic measurements at 0, 60, 90, 120, 240, and 360 minutes from a Swan-Ganz catheter. All patients received 500-mg doses, uptitrated to 1,000 mg at week 4, monthly evaluations, and a complete objective assessment after 12 weeks, followed by an open-label extension. Thirteen patients were randomized and 12 enrolled (6 ranolazine, 6 placebo). All patients completed the acute phase; 10 completed the 12-week study. There were no acute changes in invasive hemodynamics. At 12 weeks ranolazine was well tolerated. Only 1 of the 5 patients on ranolazine had a serum concentration considered to be in the therapeutic range. Two serious adverse events required early withdrawal (both in the ranolazine group); gastrointestinal complaints were the most common adverse event. Efficacy measures did not demonstrate any differences between treatment groups. During the open-label trial, 2 additional patients reached a therapeutic concentration. Ranolazine in PAH appears safe, without acute hemodynamic effects after a 500-mg dose. Ranolazine administrated to PAH patients receiving background PAH therapies did not consistently reach therapeutic levels. Future studies should first perform PK analysis in PAH patients receiving PAH therapies and explore the safety and tolerability of the higher doses perhaps necessary to achieve therapeutic levels in PAH patients. (

TRIAL REGISTRATION

Clinicaltrials.gov identifier NCT01757808.).

Endurance exercise intensity determination in the rehabilitation of coronary artery disease patients: a critical re-appraisal of current evidence

In the care of coronary artery disease (CAD) patients, the benefits of exercise therapy are generally established. Even though the selected endurance exercise intensity might affect medical safety, therapy adherence and effectiveness in the rehabilitation of CAD patients in how to determine endurance exercise intensity properly remains difficult. The aim of this review is to describe the available methods for endurance exercise intensity determination in the rehabilitation of CAD patients, accompanied with their (dis)advantages, validity and reproducibility. In general, endurance exercise intensity can objectively be determined in CAD patients by calculating a fraction of maximal exercise tolerance and/or determining ventilatory threshold after execution of a cardiopulmonary exercise test with ergospirometry. This can be translated to a corresponding training heart rate (HR) or workload. In the absence of ergospirometry equipment, target exercise HR can be calculated directly by different ways (fraction of maximal HR and/or Karvonen formula), and/or anaerobic threshold can be determined. However, the use of HR for determining exercise intensity during training sessions seems complicated, because many factors/conditions affect the HR. In this regard, proper standardization of the exercise sessions, as well as exercise testing, might be required to improve the accuracy of exercise intensity determination. Alternatively, subjective methods for the determination of endurance exercise intensity in CAD patients, such as the Borg ratings of perceived exertion and the talk test, have been developed. However, these methods lack proper validity and reliability to determine endurance exercise intensity in CAD patients. In conclusion, a practical and systematic approach for the determination of endurance exercise intensity in CAD patients is presented in this article.

Do regression-based computer algorithms for determining the ventilatory threshold agree?

The determination of the ventilatory threshold has been a persistent problem in research and clinical practice. Several computerized methods have been developed to overcome the subjectivity of visual methods but it remains unclear whether different computerized methods yield similar results. The purpose of this study was to compare nine regression-based computerized methods for the determination of the ventilatory threshold. Two samples of young and healthy volunteers (n = 30 each) participated in incremental treadmill protocols to volitional fatigue. The ventilatory data were averaged in 20-s segments and analysed with a computer program. Significant variance among methods was found in both samples (Sample 1: F = 11.50; Sample 2: F = 11.70, P < 0.001 for both). The estimates of the ventilatory threshold ranged from 2.47 litres.min(-1) (71% VO2max) to 3.13 litres.min(-1) (90% VO2max) in Sample 1 and from 2.37 litres.min(-1) (67% VO2max) to 3.03 litres.min(-1) (83% VO2max) in Sample 2. The substantial differences between methods challenge the practice of relying on any single computerized method. A standardized protocol, likely based on a combination of methods, might be necessary to increase the methodological consistency in both research and clinical practice.

Low agreement of ventilatory threshold between training modes in cardiac patients

In cardiac rehabilitation, different endurance exercises such as walking and cycling are often performed. The training intensity for these modes is determined from a single treadmill or bicycle test by ventilatory threshold (VT). In this study, differences of VT between walking and cycling and agreement of VT between training modes were assessed in cardiac patients. A total of 46 cardiac rehabilitation patients (mean age 59.5+/-8.4 years, 45 males) (31 untrained and 15 trained) completed a maximal exercise test on bicycle and treadmill, with breath-by-breath analysis of oxygen uptake (VO2), carbon dioxide production and expiratory volume. VT was determined by V-slope method. Correlations of VT and VO2peak were calculated between exercise modes. Bland-Altman plots were made for determining VT agreement between modes. VT was significantly different between walking and cycling in trained patients (P<0.05), but not in untrained patients (P>0.05). When untrained and trained patients were compared, VT correlation was lower (r=0.50) in the former group, as compared to the latter group (r=0.78). Also, Bland-Altman plots showed smaller limits of agreement for VT in trained (2 SD -1.6 to 7.8 ml/min/kg), as compared to untrained patients (2 SD -7.0 to 9.6 ml/min/kg). In trained patients, VT correlates well between training methods, but is highly exercise mode specific. In untrained patients, VT is not exercise mode specific, but the VT has a low correlation between training modes. This study shows that VT should be assessed by the appropriate exercise model for determining exercise intensity in cardiac rehabilitation.

What intensity of physical activity do previously sedentary middle-aged women select? Evidence of a coherent pattern from physiological, perceptual, and affective markers

BACKGROUND

The intensity of physical activity has been found to be inversely related to adherence, thus contributing to the problem of physical inactivity. Although most physical activity is unsupervised and participants, therefore, self-select the intensity, very little is known about the level of intensity that they select. We hypothesized that participants would select, on average, an intensity proximal to the level of transition from aerobic to anaerobic metabolism.

METHODS

Twenty-three middle-aged, formerly sedentary women participated in (a) an incremental treadmill test to determine their maximal aerobic capacity and gas exchange ventilatory threshold, an index of the aerobic-anaerobic transition, and (b) a 20-min bout of treadmill exercise during which they were allowed to select the speed.

RESULTS

On average, but with considerable interindividual variability, the women selected an intensity that, in terms of treadmill speed, heart rate, oxygen uptake, and perceived exertion was no different from the intensity corresponding to their gas exchange ventilatory threshold. Moreover, affective valence remained positive and stable.

CONCLUSIONS

On average, middle-aged, formerly sedentary women selected an intensity that is considered physiologically effective and reported that it did not feel hard or unpleasant. Future research should examine the sources of interindividual variability and the consequences of exercising at an intensity that exceeds one's preferred level.

Reproducibility of Cardiopulmonary Exercise Measurements in Patients With Pulmonary Arterial Hypertension

BACKGROUND AND OBJECTIVES

As part of a recent study, cardiopulmonary exercise tests (CPETs) were used to evaluate and follow up patients with pulmonary arterial hypertension (PAH). These patients were more impaired than those in other published series evaluating CPET reproducibility. We used these patient tests to assess patient performance variability and evaluate reading variability. To achieve this end, six independent evaluators graded key CPET measurements in patients with PAH who underwent duplicate CPETs within 3 days of each other.

SETTING AND PATIENTS

Over a 15-month period at two tertiary-care teaching hospitals, 42 patients with PAH underwent repeated, paired CPETs using cycle ergometry.

INTERVENTIONS AND MEASUREMENTS

Each patient underwent one to six pairs of cycle ergometry tests to maximal tolerance. Each pair of tests was separated by 3 months, with each test in the pair separated by 1 to 3 days. Specific guidelines were given to the independent evaluators for the key measurements assessed from each CPET study: peak O(2) uptake (Vo(2)), peak heart rate, peak O(2) pulse, anaerobic threshold (AT), and end-tidal Po(2), end-tidal Pco(2), and the ventilatory equivalent for CO(2) at the AT (Ve/Vco(2)@AT).

RESULTS

There were no fatalities or complications occurring among the 242 tests performed on 42 patients. The mean peak Vo(2) was 722 mL/min or 41% of predicted; 34 patients were Weber class C or D. Using the specific guidelines to measure the variability of measurements made by the six independent evaluators, the coefficients of variation were < 2.2% for peak Vo(2), peak heart rate, peak O(2) pulse, end-tidal values at the AT, and Ve/Vco(2)@AT, while for the AT, it was 8.5%. There were no significant differences in these measurements between the first and second tests of any pair or between the earlier and later sets of pairs.

CONCLUSIONS

Using specific guidelines, key CPET measurements can be safely, reliably, and reproducibly assessed even in patients with severe exercise intolerance.

A refined technique for determining the respiratory gas exchange responses to anaerobic metabolism during progressive exercise - repeatability in a group of healthy men

The respiratory gas exchange and ventilation during an incremental cycle exercise test were analysed in a group of 19 healthy, moderately fit men. Different computer algorithms were used to estimate the VO2 values where: (i) the rate of VCO(2) increase just exceeds the rate of VO(2) increase (DX, derivative crossing), (ii) VCO(2)/VO(2) = 1.00 (PX, point of crossing) and (iii) ventilation (VE) increases disproportionately in relation to VCO(2) (PQ, point of VCO(2) equivalent rise). The DX and PQ measurements were analysed using a new approach employing polynomial regression and the value of PX was determined following low-pass filtration of raw data. The repeatability of the measurements was evaluated with a 5-6 week interval between the tests. The correlations between tests were 0.75 at DX, 0.85 at PX and 0.62 at PQ. The mean differences between the repeated tests were not statistically significant. The repeatability of VO2, in absolute values expressed as +/-2 SD of the differences between the tests, had values of 5.0, 6.1 and 9.5 ml min(-1) kg(-1) for DX, PX and PQ, respectively. The mean value of VO(2) for each measurement point expressed as a percentage of VO(2 max) was 54% at DX, 68% at PX and 70% at PQ. The most common sequence of the measured values was DX < PX < PQ, but the sequence DX < PQ < PX was also observed. It is concluded that the gas exchange responses to developing anaerobic metabolism during progressive exercise can be characterized by a series of thresholds. However, the considerable variation in absolute values in the two testing occasions requires further attention.

Relations among heart failure severity, left ventricular loading conditions, and repolarization length in advanced heart failure secondary to ischemic or idiopathic dilated cardiomyopathy

In patients with heart failure (HF), low peak oxygen consumption (VO(2)) and prolonged QT interval or enhanced QT variability are associated with poor prognosis. Whether HF severity or left ventricular (LV) loading conditions can influence repolarization length is unknown. Survival, QTc interval, peak VO(2), clinical, laboratory, echocardiographic, and invasive hemodynamic data were analyzed in 154 transplant candidates; mortality was examined after a mean follow-up of 4.3 +/- 1.8 years. The relation between the QTc interval and other variables was examined using multivariate analysis and multiple correlation coefficients. Patients were stratified by peak VO(2) to study its relation with peak VO(2), mortality, loading conditions, and QTc intervals. Mean ejection fraction was 10 +/- 9%; mean cardiac index was 2.06 +/- 0.7 L/min/m(2). Seventy-one patients (47%) were dead at the end of study. Mortality and nonfatal ventricular arrythmias were higher (p <0.01) in patients with lower peak VO(2) and longer QTc intervals (p <0.001). An inverse correlation was found between QTc interval length and peak VO(2) (r = -0.790, p <0.0001). No correlation was found between QTc interval and LV loading conditions or the other analyzed variables. Thus, repolarization length measured by the QTc interval is inversely correlated with HF severity measured by peak VO(2) and is independent of LV loading conditions in patients with severe HF.

Use of the gas exchange threshold to noninvasively determine the lactate threshold in patients with cystic fibrosis

OBJECTIVE

The anaerobic threshold (AT) is a submaximal index related to endurance exercise performance, which is usually determined by the measurement of blood lactate concentration during an incremental exercise test (lactate threshold [LT]). The LT, and thus the AT, can also be detected noninvasively in normal subjects by means of the gas exchange threshold (GET). This study was undertaken to validate the use of GET in patients with cystic fibrosis (CF) with a wide range of disease severity, and to assess the reproducibility of this index.

METHODS

In patients with CF (FEV(1) range, 23 to 118% of predicted) and control subjects, gas exchange was measured breath by breath during the incremental exercise tests to allow determination of the GET. Arterialized-venous blood was sampled for determination of the LT. The GET and LT were determined in a blinded manner.

RESULTS

The mean differences (GET - LT) for control subjects (n = 18) and patients with CF (n = 23) were - 40 mL/min and + 10 mL/min, respectively, neither being significantly different from zero. The limits of agreement were +/- 550 mL/min and +/- 410 mL/min, respectively. The mean test-retest differences in GET for control subjects (n = 14) and patients with CF (n = 12) were - 50 mL/min and 0 mL/min, respectively, neither being significantly different from zero; the respective limits of reproducibility were +/- 450 mL/min and +/- 350 mL/min.

CONCLUSIONS

This study demonstrates that in patients with CF, the GET can be used to obtain an unbiased estimate of the LT, and that the GET is reproducible.

Insulin resistance, exercise capacity and body composition in subjects with two hypertensive parents

OBJECTIVE

To study insulin resistance in subjects with strong genetic predisposition to essential hypertension, compared with non-disposed subjects.

SUBJECTS

Thirty normotensive subjects aged 18-35 years whose parents both had essential hypertension, and 30 age- and sex matched subjects whose parents were both normotensive, were studied. Subjects or parents with diabetes and morbid obesity were excluded.

METHODS

The study comprised (1) a frequent sampling oral glucose tolerance test; (2) an isoglycemic hyperinsulinemic clamp study; (3) an analysis of body composition by dual-energy X-ray absorptiometry; (4) an exercise test with gas exchange analysis; and (5) investigation of composition of usual diet by diet registration for 5 days.

RESULTS

The 24-h diastolic blood pressure was higher in subjects predisposed to hypertension compared with the controls: 78.1 versus 74.0 mmHg (confidence interval for the difference between the means; -0.5; -7.9), but the insulin sensitivity index was similar: 312 versus 362 I(2) min(-1) pmol(-1) kg(-1) (28; -129). The two groups were similar in terms of body composition, exercise capacity and composition of usual diet. Resting and 24-h diastolic blood pressures were correlated to abdominal fat mass but not to insulin sensitivity.

CONCLUSION

Subjects with a strong genetic predisposition to essential hypertension had increased diastolic blood pressure compared with subjects with normotensive parents, but they were not insulin resistant. This may be due to the subjects being highly selected as to confounding factors. The increased blood pressure in the hypertension prone subjects could not be attributed to differences in body composition, exercise capacity or dietary habits.

Dangerous curves. A perspective on exercise, lactate, and the anaerobic threshold

A number of general observations can be made from these recent studies. Lactate is a ubiquitous substance that is produced and removed from the body at all times, even at rest, both with and without the availability of oxygen. It is now recognized that lactate accumulates in the blood for several reasons, not just the fact that oxygen supply to the muscle is inadequate. Lactate production and removal is a continuous process; it is a change in the rate of one or the other that determines the blood lactate level. Rather than a specific threshold, there is most likely a period of time during which lactate production begins to exceed the body's capacity to remove it (through buffering or oxidation in other fibers). It may be appropriate to replace the term "anaerobic threshold" to a more functional description, since the muscles are never entirely anaerobic nor is there always a distinct threshold ("oxygen independent glycolysis" among others has been suggested) Lactate plays a major role as a metabolic substrate during exercise, is the preferred fuel for slow-twitch muscle fibers, and is a precursor for liver gluconeogenesis. The point at which lactate begins to accumulate in the blood, causing an increase in ventilation, is important to document clinically. Irrespective of the underlying mechanism or specific model that describes the process, the physiologic changes associated with lactate accumulation have significant import for cardiopulmonary performance. These include metabolic acidosis, impaired muscle contraction, hyperventilation, and altered oxygen kinetics, all of which contribute to an impaired capacity to perform work. Thus, any delay in the accumulation of blood lactate which can be attributed to an intervention (drug, exercise training, surgical, etc) may add important information concerning the efficacy of the intervention. A substantial body of evidence is available demonstrating that lactate accumulation occurs later (shifting to a higher percentage of Vo2max) after a period of endurance training. In athletes, the level of work that can be sustained prior to lactate accumulation, visually determined, is an accurate predictor of endurance performance. Presumably, these concepts have implications related to vocation/disability among patients with cardiovascular and pulmonary disease, but few such applied studies have been performed outside the laboratory. Blood lactate during exercise and its associated ventilatory changes maintain useful and interesting applications in both the clinical exercise laboratory and the sport sciences. However, the mechanism, interpretation, and application of these changes continue to rely more on tradition and convenience than science.

Ammonia response to exercise in patients with congestive heart failure

OBJECTIVE

To assess energy depletion in skeletal muscle in patients with congestive heart failure by measuring blood purine metabolites during exercise and, at the same time, determine the implications of the ammonia response to exercise in these patients.

SETTING

Tottori University Hospital, Yonago, Japan.

PATIENTS

49 heart failure patients (New York Heart Association (NYHA) grades I-III) and 16 normal subjects.

MAIN OUTCOME MEASURES

Blood lactate, ammonia, and hypoxanthine levels were measured during exercise with expired gas analysis.

RESULTS

In normal exercising subjects as well as in each heart failure subgroup, the ammonia threshold was significantly higher than both the lactate threshold [control: 21.8 (SD 5.3) v 17.4 (3.3) ml/kg/min; NYHA class I: 18.9 (3.8) v 15.5 (2.6); class II: 14.8 (2.5) v 12.7 (2.4); class III: 13.5 (2.6) v 11.8 (2.5)] and the ventilatory threshold (P < 0.01). The difference between the ammonia and lactate thresholds was noted in all normal subjects and in all heart failure patients. The ammonia threshold, however, was significantly lower in heart failure patients than in normal subjects and it decreased with increasing NYHA class (P < 0.01). Maximum ammonia levels were lower in the heart failure group and decreased further with higher NYHA classifications [control: 198 (52) mg/dl; NYHA class I: 170 (74); class II: 134 (58); class III: 72 (15); P < 0.01]. There were significant correlations between maximum ammonia values and maximum lactate, oxygen consumption, and hypoxanthine levels (r = 0.74, 0.48, and 0.87, respectively; P < 0.001).

CONCLUSIONS

The ammonia threshold may reflect the onset of ATP depletion in exercising skeletal muscles, as opposed to the onset of anaerobic respiration. It seems therefore that energy depletion in skeletal muscles during exercise occurs after attaining the anaerobic threshold. Both aerobic and anaerobic capacities of skeletal muscle are reduced in patients with congestive heart failure.

The effect of beta-blockade therapy on the response to exercise training in postmyocardial infarction patients

Cardiac rehabilitation after a myocardial infarction has been shown to improve exercise capacity. Beta blockade has been shown to be effective in treating angina and reducing mortality, but studies are controversial as to whether beta-blockade therapy attenuates the effects of training. We attempted to study the effects of beta blockade (metoprolol) on the response to training in patients enrolled in a cardiac rehabilitation program after an uncomplicated myocardial infarction. We studied 27 patients with a recent uncomplicated myocardial infarction who were subdivided in two groups: Group 1 (13 patients) not taking a beta blocker, and Group 2 (14 patients) taking metoprolol (mean 142 +/- 57 mg daily). All patients underwent a maximal cardiopulmonary exercise test before and after a 3-month training program. The training intensity was designed to approximate the ventilatory threshold. Results showed an increase in peak VO2 in both Group 1 (27%, p < 0.01) and Group 2 (33%, p < 0.001), and an increase in VO2 at the ventilatory threshold (39% in Group 1 and 28% in Group 2, p < 0.01). The mean changes in exercise capacity were not different between groups. It was concluded that metoprolol did not influence the beneficial effects of a cardiac rehabilitation program in postmyocardial infarction patients.

Oxygen uptake kinetics are determined by cardiac function at onset of exercise rather than peak exercise in patients with prior myocardial infarction

BACKGROUND

Resting cardiac function does not necessarily affect exercise capacity. However, to determine whether it affects early dynamics of oxygen uptake (VO2) during exercise, we measured VO2 during a constant work rate and during incremental exercise testing in patients with a history of myocardial infarction. VO2 kinetics and exercise capacity were compared between patients with relatively high left ventricular ejection fractions (LVEF > or = 35%, group 1) and those with lower ejection fractions (LVEF < 35%, group 2).

METHODS AND RESULTS

Forty patients with a history of prior myocardial infarction (age, 57 +/- 10 years) were monitored during 6 minutes of moderate constant work rate testing (40 +/- 8 W) and during symptom-limited incremental exercise testing with a cycle ergometer. VO2 was calculated from respired gas analysis on a breath-by-breath basis. Cardiac output determinations were made with a computerized cadmium telluride detector every 10 seconds during exercise. The VO2 time constant during constant work rate exercise was slower in group 2 (58.0 +/- 7.6 seconds) compared with group 1 (45.8 +/- 10.5 seconds, P = .0002), indicating slower kinetics in group 2. The time constant for the rise in cardiac output during exercise was also slower in patients with lower EFs (63.0 +/- 12.8 versus 50.0 +/- 12.2 seconds). However, there were no differences in exercise capacity parameters, such as the VO2 or cardiac output at peak exercise, obtained during incremental exercise testing among the two groups.

CONCLUSIONS

The prolonged time constant of VO2, which is primarily determined during early parts of exercise, reflects delayed cardiac output response in patients with severely impaired LV function. The time constant of VO2 during submaximal constant work rate exercise can be used as a sensitive and discriminant measure of impaired cardiac reserve in these patients.

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

The effect of the nonselective beta 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 (VO2), oxygen (O2) 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 less than 0.001). Exercise time decreased from 680 +/- 91 to 633 +/- 78 seconds (-7%, p less than 0.001). Peak VO2 decreased from 25.3 +/- 4.7 to 21.4 +/- 3.5 ml/min/kg (-15%, p less than 0.001). O2 pulse increased from 12.9 +/- 1.9 to 16.7 +/- 2.3 ml/beat (+29%, p less than 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 less than 0.001), VO2 decreased from 18.5 +/- 4.3 ml/min/kg by 10% (p less than 0.001), O2 pulse increased from 11.5 +/- 2.0 ml/beat by 30% (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of long-term enalapril therapy on cardiopulmonary exercise performance in men with mild heart failure and previous myocardial infarction

Forty-one men with documented myocardial infarction greater than 6 months previously were randomized to long-term (48 weeks) therapy with placebo or enalapril on a double-blind basis. All patients were receiving concurrent therapy with digitalis and a diuretic drug for symptomatic heart failure (functional class II or III). The mean age was 64 +/- 7.3 years and no patient suffered from exertional chest pain. Patients underwent maximal cardiopulmonary exertional chest pain. Patients underwent maximal cardiopulmonary exercise testing to exhaustion on an ergometer cycle nine times over the course of 48 weeks. Gas exchange data were collected on a breath by breath basis with use of a continuous ramp protocol. In the placebo group (n = 21), the mean (+/- SD) peak oxygen consumption (VO2) at baseline was 18.8 +/- 5.2 versus 18.5 +/- 5.5 ml/kg per min at 48 weeks (-1.4%, p = NS). In the enalapril group (n = 20), the corresponding values were 18.1 +/- 3.1 versus 18.3 +/- 2.6 ml/kg per min (+2.8%, p = NS). The mean VO2 at the anaerobic threshold for the placebo group at baseline study was 13.1 +/- 3.5 versus 12.8 +/- 2.1 ml/kg per min at 48 weeks (-2.2%, p = NS). The corresponding values for the enalapril group were 11.8 +/- 2.3 versus 11.8 +/- 2.4 ml/kg per min (+1.4%, p = NS). The mean total exercise duration in the placebo group at baseline study was 589 +/- 153 versus 620 +/- 181 s at 48 weeks (+5.4%, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of long-term enalapril therapy on cardiopulmonary exercise performance after myocardial infarction

BACKGROUND

The Enalapril Postinfarction Exercise (EPIE) trial was designed to study the effect of enalapril treatment on peak and submaximal cardiopulmonary exercise performance over the course of 1 year in men after myocardial infarction with mild exercise intolerance.

METHODS AND RESULTS

One hundred sixty men with a peak VO2 less than 25 ml/kg/min and without effort angina were randomized to receive enalapril 20 mg qd or placebo on a double-blind basis. The mean age was 60.3 +/- 7.6 years. All patients received concurrent beta-blocker therapy for secondary prophylaxis. Treatment began at 21 days (group 1, n = 100) or more than 6 months after infarction (group 2, n = 60). Patients underwent exercise with real-time gas-exchange analysis nine times over the course of 48 weeks. In group 1, improvement in exercise performance occurred during the course of the trial in both groups of patients receiving placebo or enalapril. The mean peak VO2 for the placebo-treated patients in group 1 increased from 18.3 +/- 3.4 ml/kg/min by 4.9% at 48 weeks (p less than 0.05). The corresponding values for enalapril-treated patients were 18.9 +/- 3.8 ml/kg/min with a 3.7% increase (p = 0.07). Total exercise time increased in the placebo-treated patients from 645 +/- 96 seconds by 7.3% (p less than 0.01). Corresponding values for enalapril-treated patients were 674 +/- 103 seconds with a 5.4% increase (p less than 0.01). In group 2, the mean peak VO2 at baseline for the placebo-treated patients of 20.3 +/- 3.8 ml/kg/min increased by 4.4% at 48 weeks (p = NS). The corresponding values for enalapril-treated patients were 19.2 +/- 3.6 ml/kg/min with a 2.6% increase (p = NS). Total exercise time increased in the placebo-treated patients from 677 +/- 114 seconds by 0.7% (p = NS). Corresponding values for enalapril-treated patients were 659 +/- 99 seconds with a 1.1% increase (p = NS). There were no significant differences between the placebo and enalapril subgroups at any time with regard to peak VO2, exercise duration, or the VO2 at the anaerobic threshold.

CONCLUSIONS

This trial demonstrates that long-term converting enzyme inhibition with enalapril had no significant effect on the peak or submaximal cardiopulmonary exercise performance over the course of 1 year in men after myocardial infarction with only mildly reduced exercise capacity.