Cardiac repolarization properties during standardized exercise test as studied by QT,QT peak and terminated T-wave intervals

Summary. Changes in QT, QT peak (QT_p) and terminal T-wave, T_p–T_e (QT–QT_p) were studied in 11 apparently healthy subjects during and after a standardized exercise test. ECG was recorded at scalar lead positions. Averaged complexes were later analysed by computer for the different time intervals. QT and QT_p decreased in parallel with increasing heart rate with a ratio QT_p/QT of 0·80 ± 0.02 at rest and 0·74 ± 0·02 at maximal heart rate around 170. After exercise QT and QT_p prolonged disproportionately slower than heart rate, reaching the relation observed during exercise only 9·5 min post exercise. T_p–T_e was 75 ± 10 ms at rest and 65 ± 8 ms at maximal heart rate. The decrease was significant (P<0·001). The main part of the rate-associated shortening of the QT interval occurred in the QT_p interval where it was about six to seven times larger than in the T_p–T_e interval. In conclusion, QT and QT_p decreased similarly with heart rate during exercise. Post exercise there was an initial slower return of these intervals to the resting state than for heart rate. T_p–T_e changes were minimal.     

Differential Response of QTU Interval to Exercise, Isoproterenol, and Atrial Pacing in Patients with Congenital Long QT Syndrome

Sympathetic stimulation is well known to contribute to the genesis of QTU prolongation and ventricular lachyarrhythmias in patients with congenital long QT syndrome. In this study, we performed exercise treadmill testing, isoproterenol infusion (1–2 μg/min), and right atrial pacing (cycle length 500 msec) in 11 patients with congenital long QT (LQT) syndrome (LQT group) and in 12 age- and sex-matched controls (control group). The responses of the corrected QT (QT_c; Bazett's method) interval and the TU wave complex tvere evaluated. The QT_c interval was prolonged from 482 ± 63 msec^1/2 to 548 ± 28 msec^1/2 by exercise in the LQT group (n = 11; P < 0.005), and this was associated with fusion of the T waves with enlarged U waves, whereas the QT_c interval did not increase with exercise in the control group (n = 12; 402 ± 19 msec^1/2 vs 409 ± 22 msec^1/2). The QT_c interval was also prolonged from 466 ± 50 msec^1/2 to 556 ± 33 msec^1/2 by isoproterenol in the LQT group (n = 7; P < 0.005) in association with morphological changes of the TU wave complex like those seen with exercise, whereas it was only slightly increased from 399 ± 10 msec^1/2 to 436 ± 13 msec^1/2 by isoproterenol in the control group (n = 77; P < 0.001). However, the QT_c interval did not increase with atrial pacing in the LQT group (n = 8; 476 ± 57 msec^1/2 vs 486 ± 59 msec^1/2), whereas it was slightly increased from 400 ± 21 msec^1/2 to 426 ± 18 msec^1/2 by atrial paring in (he control group (n = 8; P < 0.005). These results suggest that sympathetic stimulation plays an important role in the QTU prolongation and marked TU wave complex abnormalities in patients with congenital long QT syndrome.     

Ambulatory Assessment of the QT Interval in Patients with Hypertrophic Cardiomyopathy: Risk Stratification and Effect of Low Dose Amiodarone

This study aims to assess the dynamics of the QT interval in patients with hypertrophic cardiomyopathy (HCM). Three consecutive QT intervals and the preceding RR intervals were measured on 24-hour ambulatory electrocardiograms at 30-minute intervals in ten high risk patients with HCM (sudden cardiac death [SCD] and/or documented ventricular fibrillation), aged 29 ± 17 years, compared with ten age and sex matched low risk patients with HCM (no syncope, no adverse family history, and no ventricular tachycardia on Holter monitoring), and ten normal subjects. Another ten patients who were on amiodarone therapy (200-mg daily) were also studied. Patients witb intraventricular conduction defects were excluded. There were 4,424 pairs of QT intervals and their preceding RR intervals were measured in this study. A nonsignificant prolongation in the QT interval and a significant prolongation in QT_c values (Bazett's and Fridericia's formulas) were demonstrated in patients with HCM compared with normals. There were no significant differences in the QT and QT_c between high and low risk patients. The slope of regression line for the QT against RR interval was significantly different between normals and HCM (0.1583 ± 0.040 vs 0.2017 ± 0.043. P < 0.05), but not between high and low risk patients. Amiodarone significantly prolonged the QT and QT_c without significantly altering the slope of the regression line (0.2017 ± 0.043 vs 0.2099 ± 0.037, NS). Our findings support the observations that there is a prolonged QT interval in patients with HCM and that there is no significant use dependent effect of amiodarone on ventricular repolarization. In conclusion, ambulatory assessment of the QT interval provides an alternative method for the assessment of ventricular repolarization and for the assessment of use dependent effects of anti arrhythmic drugs on ventricular repolarization during normal daily activities. However, this method does not help in the identification of patients at high risk of SCD in HCM.     

Autonomic nervous function at rest in aerobically trained and untrained oldermen

Therelationship between aerobictraining, vagal influence on the heart and ageing was examined by assessing aerobic fitness andresting heart rate variability in trained and untrained older men. Subjects were 11 trained cyclistsand runners (mean age=6±61·6 years) and 11 untrained, age-matchedmen (mean age=66±1·2 years). Heart rate variability testing involvedsubjects lying supine for 25 min during which subjects’ breathing was paced andmonitored (7·5 breaths min^?1). Heart rate variability was assessedthrough time series analysis (HRV_ts) of the interbeat interval. Results indicated thattrained older men (3·55±0·21 l min^?1) hadsignificantly (P<0·05) greater VO _2maxthan that of control subjects (2·35±0·15 l min^?1).Also, trained older men (52±1·8 beats min^?1) hadsignificantly (P<0·05) lower supine resting heart rate than that of controlsubjects (65±4·2 beats min^?1). HRV_ts at highfrequencies was greater for trained men (5·98±0·22) than for untrainedmen (5·23±0·32). These data suggest that regular aerobic exercise inolder men is associated with greater levels of HRV_ts at rest.     

Standardized submaximal exercise testing in never smokers: a normative study

In a population survey on the south‐western coast of Norway, 373 never smokers aged 18–73 years (230 women) without respiratory symptoms performed a standardized, progressive, incremental submaximal bicycle exercise test. All individuals were able to do an exercise involving oxygen uptake of 1·0 l min^–1, 80% of the subjects reached 1·5 l min^–1 and 50% of the subjects reached 2·0 l min^–1. The respiratory frequency (RF), ventilation (VE) and heart rate (HR) for a given oxygen uptake were all higher in women than in men. Significant predictors of failure to reach oxygen uptake of 1·5 and 2·0 l min^–1 were sex, age, body height and weight. Prediction equations are given for respiratory frequency, heart rate and ventilation for an oxygen uptake of 1·0 l min^–1 in women and 1·5 l min^–1 in men; and body height is a strong predictor for all dependent variables. A multiple linear regression analysis in women showed that age was a significant predictor of respiratory frequency (P<0·05), ventilation (P<0·001) and heart rate (P<0·001), while in men age was a significant predictor only of ventilation (P<0·001) during the bicycle exercise protocol.     

The influence of a fast ramp rate on peak cardiopulmonary parameters during arm crank ergometry

The influence of a very fast ramp rate on cardiopulmonary variables at ventilatory threshold and peak exercise during a maximal arm crank exercise test has not been extensively studied. Considering that short arm crank tests could be sufficient to achieve maximal oxygen consumption (VO₂), it would be of practical interest to explore this possibility. Thus, this study aimed to analyse the influence of a fast ramp rate (20 W min^?1) on the cardiopulmonary responses of healthy individuals during a maximal arm crank ergometry test. Seventeen healthy individuals performed maximal cardiopulmonary exercise tests (Ultima CardiO2; Medical Graphics Corporation, St Louis, USA) in arm ergometer (Angio, LODE, Groningen, The Netherlands) following two protocols in random order: fast protocol (increment: 2 w/6 s) and slow protocol (increment: 1 w/6 s). The fast protocol was repeated 60–90 days after the 1st test to evaluate protocol reproducibility. Both protocols elicited the same peak VO₂ (fast: 23·51 ± 6·00 versus slow: 23·28 ± 7·77 ml kg^?1 min^?1; P = 0·12) but peak power load in the fast ramp protocol was higher than the one in the slow ramp protocol (119 ± 43 versus. 102 ± 39 W, P < 0·001). There was no other difference in ventilatory threshold and peak exercise variables when 1st and 2nd fast protocols were compared. Fast protocol seems to be useful when healthy young individuals perform arm cardiopulmonary exercise test. The usefulness of this protocol in other populations remains to be evaluated.     

Measurement of cardiac output with non-invasive Aesculon impedance versus thermodilution

Background: This study compared the non‐invasive thoracic electrical bioimpedance Aesculon^® technique (TEB_Aesculon) with thermodilution (TD) to evaluate whether TEB_Aesculon may offer a reliable means for estimating cardiac output (CO) in humans. Material and method: Cardiac output was measured with TD and TEB_Aesculon in 33 patients, with a mean age ± SEM of 59 ± 2·7 years, that underwent right heart catheterization for clinical investigation of pulmonary hypertension or severe heart failure. Four to five CO measurements were performed with each technique simultaneously in 33 patients at rest, 11 during exercise and seven during NO inhalation. Result: Cardiac output correlated poorly between TEB_Aesculon and TD at rest (r = 0·46, P<0·001), during exercise (r = 0·35, P<0·013) and NO inhalation (r = 0·41, P<0·017). CO was higher for TEB_Aesculon than TD with 0·86 ± 0·14 l min^?1 at rest (P<0·001) and 2·95 ± 0·69 l min^?1 during exercise (P<0·003), but similar during NO inhalation, with a tendency (P<0·079) to be 0·44 ± 0·19 l min^?1 higher for TEB_Aesculon than TD. CO increased from rest to exercise for TEB_Aesculon and TD with 6·11 ± 0·6 l min^?1 (P<0·001) and 3·91 ± 0·36 l min^?1 (P<0·001), respectively; an increase that was higher (P<0·002) for TEB_Aesculon than TD. During NO inhalation, compared to rest, CO decreased for TEB_Aesculon with 0·62 ± 0·11 l min^?1 (P<0·002), but not significantly for TD with 0·21 ± 0·12 l min^?1 (P<0·11). Bland–Altman analysis showed a poor agreement between TEB_Aesculon and TD. Conclusion: TEB_Aesculon overestimated CO compared to TD with ～17% at rest and ～34% during exercise, but the techniques showed similar results during NO inhalation. CO, furthermore, correlated poorly between TEB_Aesculon and TD. TEB_Aesculon may at present not replace TD for reliable CO measurements in humans.     

Intensity of Nordic Walking in young females with different peak O2 consumption

The purpose of this cross‐sectional study was to determine the physiological reaction to the different intensity Nordic Walking exercise in young females with different aerobic capacity values. Twenty‐eight 19–24‐year‐old female university students participated in the study. Their peak O₂ consumption (VO₂ peak kg^?1) and individual ventilatory threshold (IVT) were measured using a continuous incremental protocol until volitional exhaustion on treadmill. The subjects were analysed as a whole group (n = 28) and were also divided into three groups based on the measured VO₂ peak kg^?1 (Difference between groups is 1 SD) as follows: 1. >46 ml min^?1 kg^?1 (n = 8), 2. 41–46 ml min^?1 kg^?1 (n = 12) and 3. <41 ml min^?1 kg^?1 (n = 8). The second test consisted of four times 1 km Nordic Walking with increasing speed on the 200 m indoor track, performed as a continuous study (Step 1 – slow walking, Step 2 – usual speed walking, Step 3 – faster speed walking and Step 4 – maximal speed walking). During the walking test expired gas was sampled breath‐by‐breath and heart rate (HR) was recorded continuously. Ratings of perceived exertion (RPE) were asked using the Borg RPE scale separately for every 1 km of the walking test. No significant differences emerged between groups in HR of IVT (172·4 ± 10·3–176·4 ± 4·9 beats min^?1) or maximal HR (190·1 ± 7·3–191·6 ± 7·8 beats min^?1) during the treadmill test. During maximal speed walking the speed (7·4 ± 0·4–7·5 ± 0·6 km h^?1) and O₂ consumption (30·4 ± 3·9–34·0 ± 4·5 ml min^?1 kg^?1) were relatively similar between groups (P > 0·05). However, during maximal speed walking, the O₂ consumption in the second and third groups was similar with the IVT (94·9 ± 17·5% and 99·4 ± 15·5%, respectively) but in the first group it was only 75·5 ± 8·0% from IVT. Mean HR during the maximal speed walking was in the first group 151·6 ± 12·5 beats min^?1, in the second (169·7 ± 10·3 beats min^?1) and the third (173·1 ± 15·8 beats min^?1) groups it was comparable with the calculated IVT level. The Borg RPE was very low in every group (11·9 ± 2·0–14·4 ± 2·3) and the relationship with VO₂and HR was not significant during maximal speed Nordic Walking. In summary, the present study indicated that walking is an acceptable exercise for young females independent of their initial VO₂ peak level. However, females with low initial VO₂ peak can be recommended to exercise with the subjective ‘faster speed walking’. In contrast, females with high initial VO₂ peak should exercise with maximal speed.     

Q‐T interval (QTC) in patients with cirrhosis: relation to vasoactive peptides and heart rate

Objective. Prolonged Q‐T interval (QT) has been reported in patients with cirrhosis who also exhibit profound abnormalities in vasoactive peptides and often present with elevated heart rate (HR). The aim of this study was to relate QT to the circulating level of endothelins (ET‐1 and ET‐3) and calcitonin gene‐related peptide (CGRP) in patients with cirrhosis. In addition, we studied problems with HR correction of QT. Material and methods. Forty‐eight patients with cirrhosis and portal hypertension were studied during a haemodynamic investigation. Circulating levels of ETs and CGRP were determined by radioimmunoassays. Correction of QT for HR above 60 beats per min was performed using the methods described by Bazett (QT_C) and Fridericia (QT_F). Results. Prolonged QT_C (above 440?ms), found in 56?% of the patients, was related to the presence of significant portal hypertension and liver dysfunction (p<0.05 to 0.001), but not to elevated ET‐1, ET‐3 or CGRP. When corrected according to Bazett, QT_C showed no significant relation to differences in HR between patients (r = 0.07, ns). QT_F showed some undercorrection of HR (r = ?0.36; p<0.02). During HR variation in the individual patient, QT_C revealed a small but significant overcorrection (2.6?ms per heartbeat per min; p<0.001). This value was significantly (p<0.02) smaller with QT_F (1.2?ms per heartbeat per min). Conclusions. The prolonged QT_C in cirrhosis is related to liver dysfunction and the presence of portal hypertension, but not to the elevated powerful vasoconstrictor (ET‐1) or vasodilator (CGRP, ET‐3) peptides. The problems with correction of the QT for elevated HR in cirrhosis are complex, and the lowest HR should be applied for determination of the QT.     

Endurance training,overtraining and baroreflex sensitivity in female athletes

We examined heavy training-induced changes in baroreflex sensitivity, plasma volume and resting heart rate and blood pressure variability in female endurance athletes. Nine athletes (experimental training group, ETG) increased intense training (70–90% VO _2max) volume by 130% and low-intensity training (<70% VO _2max) volume by 100% during 6–9 weeks, whereas the corresponding increases in six control athletes (CG) were 5% and 10% respectively. Maximal oxygen uptake (VO _2max) in the ETG and CG did not change, but in five ETG athletes VO _2max decreased from 53·0 ± 2·2 (mean ± SEM) (CI 46·8–59·2) ml kg^–1 min^–1 to 50·2 ± 2·3 (43·8–56·6) ml kg^–1 min^–1 (P<0·01), indicating overtraining. Baroreflex sensitivity (BRS) measured using the phenylephrine technique and blood pressure variability (BPV) did not change, but the low-frequency power of the R–R interval variability increased in the ETG (P<0·05). The relative change in plasma volume was 7% in the ETG and 3% in the CG. The changes in BRS did not correlate with the changes in plasma volume, heart rate variability and BPV. We conclude that heavy endurance training and overtraining did not change baroreflex sensitivity or BPV but significantly increased the low-frequency power of the R–R interval variability during supine rest in female athletes as a marker of increased cardiac sympathetic modulation.     

Ventilatory response and arterial potassium concentration during incremental exercise in patients with chronic airways obstruction

Summary. The relationship of ventilation response (V?_E) to arterial potassium concentration (K⁺) during ramp incremental exercise was assessed in nine patients with chronic obstructive pulmonary disease (COPD), and in 10 healthy subjects. For COPD patients the maximum oxygen uptake (VO_max) was 19.6±3.8 ml kg^-1 min^-1 (± SD), and percentage of forced expired volume at 1 s (% FEV₁) was 47.8 ± 10.4%. In healthy subjects, Vo₂max was 44.4±7.0 ml kg^-1 min^-1 and FEV₁, was 89.7 ± 7.4%. Breath-by-breath determinations for V?_E, oxygen uptake (V?o₂) and carbon dioxide output (V?co₂), as well as determinations for K⁺, partial pressure of oxygen (Po₂), partial pressure of carbon dioxide (Pco₂), pH and lactate in arterial blood were performed during a workout on an exercise bicycle at a ramp function work rate of 20 W min^-1, preceded by a 40 min warm-up period. The major findings in the present study are: (1) that there is a linear relation between ventilation and arterial K⁺ concentration during ramp exercise in both healthy subjects and COPD patients; (2) that the slope of the V?_E-K⁺ relationship is significantly lower in COPD patients (16.2 ± 7.31 min^-1 mM^-1) than in normal subjects (37.4 ± 6.91 min^-1 mM^-1, P<0.01); and, (3) that the slope of the V?_E-K⁺ relationship is significantly related to the ability to ventilate during maximal exercise in both healthy subjects and COPD patients (P<0.05). It is thought that the significantly reduced slope of the V?_E-K⁺ relationship in the COPD patients could be interpreted as a reduced sensitivity to the stimulus and/or as a mechanical impairment of the ventilation.     

Heart Rate‐Dependence of QTc Intervals Assessed by Different Correction Methods in Patients with Normal or Prolonged Repolarization

Background: There is a continuing debate about the optimal method for QT interval adjustment to heart rate changes. We evaluated the heart rate dependence of QTc intervals derived from five different QT correction methods. Methods: Study patients (n = 123, age 68 ± 11 years) were dual‐chamber device recipients with baseline normal or prolonged QT interval who had preserved intrinsic ventricular activation with narrow QRS complexes. Patients were classified to either Normal‐QT (n = 69) or Prolonged‐QT (n = 54) groups. Serial QT intervals were recorded at baseline (52 ± 3 beats per minute) and following atrial pacing stages at 60, 80, and 100 beats per minute. The QTc formulae of Bazett, Fridericia, Sagie‐Framingham, Hodges, and Karjalainen‐Nomogram were applied to assess the effect of heart rate on the derived QTc values by using linear mixed‐effects models. Results: Heart rate had a significant effect on QTc regardless of the formula used (P < 0.05 for all formulae). The Bazett's formula demonstrated the highest QTc variability across heart rate stages (highest F values) in both patient groups (in the total cohort, F = 175.9). In the following rank order, the formulae Hodges, Karjalainen‐Nomogram, Sagie‐Framingham, and Fridericia showed similar QTc heart rate dependence at both slower and faster heart rates in both patient groups (F = 21.8, 25.6, 28.8, 36.9, in the total cohort, respectively). Conclusions: Of the studied QTc formulae, the Bazett appeared the most heart rate dependent. Our results suggest the use of Hodges and the Karjalainen‐Nomogram secondly to ensure least heart rate dependence of QTc intervals in patients with either normal or prolonged repolarization. (PACE 2010; 553–560)     

Influence of Early Coronary Reperfusion on QT Interval Dispersion After Acute Myocardial Infarction

We studied the influence of early coronary reperfusion on QT interval dispersion in patients with acute myocardial infarction (MI). Tbere were 54 males and 18 females witb a mean age of 60 ± 10 years. Of the 51 patients with recanalization of the infarct related vessel in the recovery phase, 28 (group A) had early coronary reperfusion (5.5 ± 2.7 bours), 23 other patients (group B) were not confirmed with early coronary reperfusion. Twenty-one patients (group C) did not undergo recanalization of the infarct related vessel in the recovery phase. Corrected QT (QT_c) maximum, QT_c minimum, and QT_C dispersion calculated as tbe difference between the maximum and minimum QT_c intervals, were compared among these three groups at both acute and recovery phase. At the acute phase after MI, there were no significant differences in the QT_c maximum, QT_c minimum, QT dispersion, and QT_c dispersion among these three groups. At the recovery phase after MI, there were also no significant differences in the QTc maximum and QTc minimum. However, there were significant differences in the QT dispersion (0.035 ± 0.010 in group A, 0.049 ± 0.015 in group B, and 0.061 ± 0.031 s in group C, respectively; P = 0.0001), and QT_c dispersion (0.038 ± 0.012 in group A, 0.050 ± 0.015 in group B, and 0.063 ± 0.032 s in group C, respectively; P = 0.0003) among the three groups. Comparison of QT_c dispersion between acute and recovery phase revealed significant reduction from acute to recovery phase in group A. The number of premature ventricular contraction was lower in groups A and B than group C. In summary, early coronary reperfusion may reduce electrophysiological instability by reducing QT dispersion in the recovery phase after acute MI.     

Biochemical changes in relation to a maximal exercise test in patients with fibromyalgia

Summary. Patients with fibromyalgia often complain of fatigue and pain during exercise and of worsening of pain days after exercise. The aim of the study described here was to determine if abnormal changes in potassium or lactate could be observed during an exercise test in fibromyalgia. Whether an abnormal incline in plasma creatine kinase or myoglobin could be observed days after the test was studied also. Fifteen female fibromyalgia patients and 15 age- and sex-matched controls performed a stepwise incremental maximal bicycle-ergometer test. Blood samples were collected from a catheter in a cubital vein. The changes in heart rate, potassium levels, and haematocrit during the exercise test were similar in the two groups. The maximal obtained lactate concentration was 4-2 mmol 1^-1 (3–5-5-6) in the patients as compared to 4–9 mmol l^-1 (3–9-5-9) in the controls (NS). The estimated anaerobic threshold of 2 mmol 1^-1 was reached at a heart rate of 124 min^-1 in the patients with fibromyalgia as compared to 140 min^-1 in the controls (P= 0–02). In relation to workload, the patients scored higher on a Borg scale for perceived exertion during exercise, but if the Borg score was related to lactate no significant difference was found. The patients reported 86% and 79% of maximal pain in the thighs on the visual analogue scale 1 and 2 days after the test, but the creatine kinase and myoglobin concentrations were not increased.,     

The exercise heart rate profile in master athletes compared to healthy controls

Endurance exercise protects the heart via effects on autonomic control of heart rate (HR); however, its effects on HR indices in healthy middle‐aged men are unclear. This study compared HR profiles, including resting HR, increase in HR during exercise and HR recovery after exercise, in middle‐aged athletes and controls. Fifty endurance‐trained athletes and 50 controls (all male; mean age, 48·7 ± 5·8 years) performed an incremental symptom‐limited exercise treadmill test. The electrocardiographic findings and HR profiles were evaluated. Maximal O₂ uptake (52·6 ± 7·0 versus 34·8 ± 4·5 ml kg^?1 min^?1; P<0·001) and the metabolic equivalent of task (15·4 ± 1·6 versus 12·2 ± 1·5; P<0·001) were significantly higher in athletes than in controls. Resting HR was significantly lower in athletes than in controls (62·8 ± 6·7 versus 74·0 ± 10·4 beats per minute (bpm), respectively; P<0·001). Athletes showed a greater increase in HR during exercise than controls (110·1 ± 11·0 versus 88·1 ± 15·4 bpm; P<0·001); however, there was no significant between‐group difference in HR recovery at 1 min after cessation of exercise (22·9 ± 5·6 versus 21·3 ± 6·7 bpm; P = 0·20). Additionally, athletes showed a lower incidence of premature ventricular contractions (PVCs) during exercise (0·0% versus 24·0%; P<0·001). Healthy middle‐aged men participating in regular endurance exercise showed more favourable exercise HR profiles and a lower incidence of PVCs during exercise than sedentary men. These results reflect the beneficial effect of endurance training on autonomic control of the heart.     

Non-invasive cardiac output assessment during moderate exercise: pulse contour compared with CO2 rebreathing

The arterial pulse contour method called Modelflow 2·1 calculates stroke volume continuously, beat to beat, from the non-invasive blood pressure signal measured by Finapres or Portapres. Portapres is the portable version of Finapres. The purpose of this study was to compare cardiac output (CO) calculated using Modelflow 2·1 (CO_mf) with CO obtained by the CO₂ rebreathing method (CO_re) during steady state at moderate exercise levels. Twelve subjects visited the laboratory twice and performed submaximal exercise on a bicycle ergometer at 20%, 40% and 60% of their individual peak power output (PO_peak). The averaged correlation between CO_mf and CO_re gives an r-value of 0·69, whereas the slope and intercept of the regression line were 1·06 and 1·65 respectively. The averaged difference between CO_mf and CO_re was 2·27 ± 3·9 l min^–1 (mean ± standard deviation). However, the test–retest difference between CO_mf and CO_re was 2·5 ± 3·1 and 0·5 ± 1·3 l min^–1 respectively. These results suggest that Modelflow 2·1 is not an accurate method for estimating CO from non-invasive blood pressure data collected by Portapres during exercise at up to 60% of the individual PO_peak corresponding with daily life activity.     

Relationship Between Perceived Exertion and Physiologic Markers During Arm Exercise With Able-Bodied Participants and Participants With Poliomyelitis

Al-Rahamneh HQ, Faulkner JA, Byrne C, Eston RG. Relationship between perceived exertion and physiologic markers during arm exercise with able-bodied participants and participants with poliomyelitis.

Objective

To investigate the strength of the relationship between ratings of perceived exertion (RPE) and oxygen uptake (V?o₂), heart rate, ventilation (V?e) and power output (PO) during an arm-crank ramped exercise test to volitional exhaustion in men and women who differed in physical status.

Design

Each participant completed an arm-crank ramp exercise test to volitional exhaustion. PO was increased by 15W·min⁻¹ and 6W·min⁻¹ for men and women able-bodied participants, respectively; for the poliomyelitis participants, 9W·min⁻¹ and 6W·min⁻¹ increments were used for men and women, respectively.

Setting

Laboratory facilities at a university.

Participants

Able-bodied participants (n=16; 9 men, 7 women) and participants with poliomyelitis (n=15, 8 men, 7 women) volunteered for the study.

Main Outcome Measures

Strength of the relationship (R² values) between RPE and V?o₂, heart rate, V?e and PO.

Results

There were significantly higher values for maximum V?o₂ and maximum PO for able-bodied men compared with their counterparts with poliomyelitis (P<.05). However, when the data were controlled for age, there were no significant differences in these values (P>.05). Similar results were observed for the women who were able-bodied as well as for the women who had poliomyelitis (P>.05). The relationships between heart rate and RPE and V?e and RPE for able-bodied patients and patients with poliomyelitis were similar (R²>.87). The relationship between V?o₂ and RPE was stronger in the able-bodied participants compared wih the participants with poliomyelitis, regardless of sex (P<.05). However, when the data were controlled for age, there was no significant difference in the strength of this relationship between able-bodied participants and those with poliomyelitis, regardless of sex (P>.05).

Conclusions

RPE is strongly related to physiologic markers of exercise intensity during arm exercise, irrespective of sex or participant's poliomyelitis status.     

Middle cerebral artery blood velocity during exercise in patients with atrial fibrillation

Atrial fibrillation limits the ability to increase cardiac output during exercise and may, in turn, affect the exercise-associated elevation in cerebral perfusion. In nine patients with atrial fibrillation (AF) and in five age-matched healthy subjects, middle cerebral artery blood velocity (MCA V_mean) was measured during incremental exercise using the transcranial Doppler. The AF patient group exhibited a lower aerobic capacity than the control group [peak work rate: 106 W (71–153 W; median and range) vs. 129 W (118–159 W) and maximal oxygen uptake: 1·4 l min^–1 (1·0–1·9 l min^–1) vs. 1·7 l min^–1 (1·4–2·2 l min^–1); P = 0·05]. At rest, MCA V_mean was not significantly different between the two groups [43 cm s^–1 (39–56 cm s^–1) vs. 52 cm s^–1 (40–68 cm s^–1)]. During intense cycling, the increase in MCA V_mean was to 51 cm s^–1 (40–78 cm s^–1) (9%) in the AF group and lower than in the healthy subjects [to 62 cm s^–1 (50–81 cm s^–1) 23%; P<0·05], which corresponded with the smaller than expected increase in cardiac output [156% (130–169%) vs. 180%]. Thus, there was a correlation between the increase in MCA V_mean and the ability to increase cardiac output (r² = 0·55, P<0·01). We suggest that, during exercise with a large muscle mass, atrial fibrillation affects the ability to elevate cerebral perfusion, and this results from an impaired ability to increase cardiac output.     

Reproducibility of peak oxygen consumption and the impact of test variability on classification of individual training responses in young recreationally active adults

This study investigated whether VO₂peak is reproducible across repeated tests before (PRE) and after (POST) training, and whether variability across tests impacts how individual responses are classified following 3 weeks of aerobic exercise training (cycle ergometry). Data from 45 young healthy adults (age: 20·1 ± 0·9 years; VO₂peak, 42·0 ± 6·7 ml·min^?1) from two previously published studies were utilized in the current analysis. Non‐responders were classified as individuals who failed to demonstrate an increase or decrease in VO₂peak that was greater than 2·0 times the typical error of measurement (107 ml·min^?1) away from zero, while responders and adverse responders were above and below this cut‐off, respectively. VO₂peak tests at PRE (three total) and POST (three total) were highly reproducible (PRE and POST average and single measures ICCs: range 0·938–0·992), with low coefficients of variation (PRE:4·9 ± 3·1%, POST: 4·8 ± 2·7%). However, a potential learning effect was observed in the VO₂peak tests prior to training, as the initial pretraining test was significantly lower than the third (p = 0·010, PRE 1: 2 946 ± 924 ml·min^?1, PRE 3: 3 042 ± 919 ml·min^?1). This resulted in fewer individuals classified as adverse responders for Test 3 compared to any combination of tests that included Test 1, suggesting that a single ramp test at baseline may not be sufficient to accurately classify the VO₂peak response in young recreationally active individuals. Thus, it is our recommendation that the initial VO₂peak test be used as a familiarization visit and not included for analysis.     

Effects of chronic dobutamine administration on the response to acute exercise in dogs

Summary. The effects of chronic dobutamine administration on haemodynamic and metabolic responses to submaximal and maximal exercise were studied in dogs. Dobutamine was infused at a rate of 40 μg/kg min^-1, 2 h day^-1, 5 days week^-1 for a period of 6 weeks. Acute infusion of dobutamine for 1 h increased heart rate by 73 ± 30 beats min^-1 and cardiac output by 143 ± 141 ml/min kg^-1, reduced mean arterial blood pressure by 12 ± 10 mmHg and arterial-venous O₂ difference by 1.5 ± 1 vol%. Maximal oxygen consumption, heart rate, stroke volume, cardiac output and arterial-venous O₂ difference were unchanged after 6 weeks of treatment. Reductions in heart rate at rest and during submaximal exercise following chronic dobutamine treatment were small and significant only at the lowest exercise level studied. Mixed venous lactate concentrations measured at rest, during submaximal and maximal exercise and at 2 min of recovery were not different after dobutamine treatment. Chronic dobutamine infusion did not change the citrate synthase activity in the lateral gastrocnemius muscle. These results suggest that chronic dobutamine therapy in healthy dogs does not produce aerobic training responses.