Temporal age‐related changes in spectral,fractal and complexity characteristics of heart rate variability

Cross‐sectional studies have suggested that heart rate (HR) variability, analysed using traditional time and frequency domain methods, is related to ageing, but no longitudinal studies have estimated the age dependence of HR fluctuation. This study evaluated temporal age‐related changes in 12‐h measures of HR variability among 109 patients with coronary artery disease (CAD), who underwent repeat Holter recordings at 32‐month intervals. Time and frequency domain measures, along with fractal and complexity measures of HR variability, were determined at the baseline and after 32 months. Changes in HR dynamics were compared with various laboratory variables, exercise data and angiographic progression of CAD. Traditional time and frequency domain measures of HR variability did not change significantly during the follow‐up, but the power‐law scaling slope decreased from ?1·29 ± 0·20 to ?1·36 ± 0·23 (P<0·01) and the short‐term fractal exponent (α₁) of HR dynamics from 1·29 ± 0·14–1·22 ± 0·18 (P<0·001). The approximate entropy value also decreased from 1·00 ± 0·19 to 0·95 ± 0·18 (P<0·05). The changes in HR behaviour were not related to demographic data, laboratory values or angiographic progression of CAD. Only a weak correlation was observed between the change in the power‐law slope and the baseline glucose value (P<0·05). This longitudinal study shows that the fractal characteristics of HR dynamics and the complexity properties of R‐R intervals undergo rapid changes along with ageing, and that fractal and complexity analysis techniques are more sensitive than traditional analysis methods in documenting temporal age‐related changes in HR behaviour.     

Effects of pharmacological adrenergic and vagal modulation on fractal heart rate dynamics

Breakdown of short‐term fractal‐like behaviour of HR indicates an increased risk for adverse cardiovascular events and mortality, but the pathophysiological background for altered fractal HR dynamics is not known. Our aim was to study the effects of pharmacological modulation of autonomic function on fractal correlation properties of heart rate (HR) variability in healthy subjects. Short‐term fractal scaling exponent (α₁) along with spectral components of HR variability were analysed during the following pharmacological interventions in healthy subjects: (i) noradrenaline (NE) infusion (n=22), (ii) NE infusion after phentolamine (PHE) (n=8), (iii) combined NE + adrenaline (EPI) infusion (n=12), (iv) vagal blockade with high dose of atropine (n=10), (v) and vagal activation by low dose of atropine (n=10). Then α₁ decreased progressively during the incremental doses of NE (from 0·85 ± 0·250 to 0.55 ± 0·23, P<0·0001). NE also decreased the average HR (P<0·001) and increased the high frequency spectral power (P<0·001). Vagal blockade with atropine increased the α₁ value (from 0·82 ± 0·22 to 1·24 ± 0·41, P<0·05). Combined NE + EPI infusion and vagal activation with a low dose atropine did not result in any changes in α₁, and α‐adrenergic blockade by PHE did not completely reverse the effects of NE on α₁. Increased levels of circulating NE result in reduction of short‐term correlation properties of HR dynamics. The results suggest that coactivation of cardiac vagal outflow at the time of high levels of a circulating sympathetic transmitter explains the breakdown of fractal‐like behaviour of human HR dynamics.     

Changes in free radical generation and antioxidant capacity during ultramarathon foot race

Background Exhaustive exercise has been implicated in the generation of reactive oxygen species, resulting in oxidative stress. We studied the effect of a long‐distance, endurance exercise on oxidative stress parameters in athletes who participated in the ultramarathon race Spartathlon (246 km). Materials and methods This study included 18 runners (16 men and 2 women) aged 42·8 ± 1·4 years. Blood samples were obtained 24 h before (prerace), at the end (postrace) and 48 h after the end of the race (48 h postrace). We measured oxidative stress indices, including red cell glutathione, malonyldialdehyde and 8‐iso‐prostaglandin F_2a, as well as the total antioxidant capacity. Results 8‐Iso‐prostaglandin F_2a level increased significantly at the end of the race, compared to prerace levels (up to 914·7 ± 61·4 pg mL^?1 from 197·6 ± 8·4 pg mL^?1), and remained 2·5‐fold increased over the baseline 48 h after the race (532·0 ± 54·2 pg mL^?1, P < 0·000). The total antioxidant capacity of the athletes increased from a baseline of 289·6 ± 9·0 µmol L^?1 to 358·7 ± 11·0 µmol L^?1 immediately after the race and remained elevated 48 h later (350·6 ± 7·6 µmol L^?1) (P < 0·001). Conclusions Prolonged exercise induces a marked response of oxidative stress biomarkers, which in part is compensated by serum ability to scavenge free radicals. Whether these changes have long‐term negative effects in the organism needs further investigation.     

Heart rate variability and recurrence of atrial fibrillation after electrical cardioversion

BACKGROUND: Heart rate (HR) variability has been shown to predict spontaneous onset of atrial fibrillation (AF). This study was designed to test the hypothesis that HR variability after electrical cardioversion (CV) of persistent AF predicts the recurrence of AF. METHODS: Various time and frequency domain measures of HR variability, along with the non‐linear measures of HR dynamics, were analyzed from the 24‐hour ECG recordings in 78 patients with persistent AF after restoration of sinus rhythm with electrical CV. RESULTS: During the follow‐up of one month, 27 patients (35%) had recurrence of AF. The patients with AF recurrence had significantly higher standard deviation of all R‐R intervals (SDNN 117?±?34versus100?±?29P ?<?0.05), increased high‐frequency (lnHF 5.7?±?0.6versus5.3?±?0.7P ?<?0.05 ), low‐frequency (lnLF 6.2?±?0.8versus5.6?±?0.9P ?<?0.01) and very‐low‐frequency (InVLF 7.1?±?0.8versus6.5?±?0.8P ?<?0.01) power spectral components of HR variability than those who remained in sinus rhythm. Approximate entropy, a measure of complexity of HR dynamics, and the short‐term fractal scaling exponent did not differ between the groups, but the long‐term power‐law slope β was steeper among the patients who remained in sinus rhythm ( P ?<?0.05). During the first week after the CV, increased HF power (highest tertile) was the most powerful predictor of AF recurrence with odds ratio of 2.8 (95% confidence interval 1.0 to 8.0,P ?<?0.05). Increased VLF power spectral component at baseline predicted best the late recurrence of AF with odds ratio of 3.3 (95% confidence interval 1.6 to 7.2,P ?<?0.01). No clinical or echocardiographic variable predicted the recurrence of AF. CONCLUSIONS: Increased HR variability in all major power spectral bands is associated with late recurrence of AF after electrical CV. Enhanced cardiac vagal outflow, reflected as an increased HF power spectral component, seems to predict specifically the early recurrence of AF after the CV.     

Volumetric measurements of peripheral oedema in clinical conditions

Water‐displacement volumetry can be used for quantifying the volume of the leg. However, not much is known about its application in patients with peripheral oedema of cardiopulmonary origin. We measured the reproducibility of a water‐displacement apparatus with a solid object and in ten non‐oedematous clinical patients (group A). The day‐to‐day variability of the leg volume was assessed in the same group. The diurnal variability was assessed in ten patients with persisting peripheral oedema (group B). The effect of treatment on the severity of peripheral oedema was evaluated in another nine patients with peripheral oedema, who were in need of diuretic treatment (group C). Volumetric results were compared to the ankle circumference method and the body weight method. The coefficient of variation was 0·16% in the fixed object and 0·47% in group A. The day‐to‐day variability was 1·52% after 1 day and 1·76% after a mean interval of 4·8 days. In group B, leg volume and circumference increased during the day (5·9%, P<0·001, and 2·4%, P<0·01, respectively), while body weight remained unchanged. In group C, leg volume, circumference and body weight decreased significantly after treatment (13·1%, P<0·01, 7·1%, P<0·05, and 5·9%, P<0·05). The correlation between the changes in volume and body weight was poor (r=0·37, P=0·33). In conclusion, (1) water‐displacement volumetry is highly reproducible, (2) a diurnal variability of peripheral oedema was found, and (3) volumetry is a suitable tool for monitoring peripheral oedema, while the body weight method appears to be less accurate.     

Reproducibility of orthostatic changes in cerebral oxygenation in healthy subjects aged 70 years or older

In the elderly, standing can frequently be accompanied by blood pressure (BP) changes and cerebral symptoms such as dizziness, fall, or even syncope, but this may vary from day‐to‐day. Therefore, we aimed to investigate the reproducibility of orthostatic responses of cerebral cortical oxygenation and systemic haemodynamics in elderly subjects. In 27 healthy elderly subjects (age 70–84 years), changes in systolic BP (SBP), diastolic BP (DBP), heart rate (HR) and stroke volume (SV) were continuously monitored by Finapres (Finger Arterial Pressure), and changes in oxyhaemoglobin ([O₂Hb]) and deoxyhaemoglobin ([HHb]) concentrations were continuously measured over the right frontal cortex by near infrared spectroscopy (NIRS) during supine rest and 10 min of active standing on two separate occasions. SBP and DBP increased by 6·7 ± 15·4 mmHg (P<0·05, mean ± SD) and 8·2 ± 6·4 mmHg (P<0·01), respectively, whereas HR increased by 9·5 ± 5·0 bpm (P<0·01) and SV decreased by –8·3 ± 7·4 ml (P<0·01) during standing on the first occasion. [O₂Hb] decreased by –3·9 ± 2·9 μmol l^–1 (P<0·01), while [HHb] increased by 1·8 ± 2·2 μmol l^–1 (P<0·01). Group‐averaged orthostatic changes in cortical oxygenation and systemic haemodynamics were very similar on the two occasions, although an intraindividual variation was found. Cortical oxygenation changes were not accompanied by severe cerebral symptoms. Active standing induced reproducible group‐averaged frontal cortical oxygenation declines in healthy elderly subjects, although an intraindividual day‐to‐day variability was present, possibly related to the variability of orthostatic BP responses. These findings indicate that cerebral autoregulation fails to compensate completely for postural changes in elderly subjects, which might predispose elderly subjects to ischaemic cerebral symptoms.     

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.     

Effect of set configuration on hemodynamics and cardiac autonomic modulation after high‐intensity squat exercise

The aim of this study was to compare the effect of two different high‐intensity resistance exercise (RE) set configurations on the following: systolic blood pressure (SBP), rate pressure product (RPP), heart rate (HR) variability (HRV), and HR complexity (HRC). Ten well‐trained males performed three parallel squat sets until failure (traditional training; TT) with the four repetitions maximum load (4RM), and a rest of 3 min between sets. Thereafter, participants performed a cluster training session (CT) of equated load but with resting time distributed between each repetition. Dependent variables were recorded before, during, and after RE. Mean SBP (25·7 versus 10·9% percentage increase; P = 0·016) and RPP (112·5 versus 69·9%; P = 0·01) were significantly higher in TT. The decrease in HRV after exercise and the drop of HRC during exercise were similar in CT and TT. Change of standard deviation of normal RR intervals after TT correlated with change in SBP (r = 0·803; P = 0·009) while the change of Sample Entropy during exercise correlated with the increment of RPP during CT (ρ = ?0·667; P = 0·05). This study suggests that set configuration influences acute cardiovascular responses during RE. When intensity, volume and work‐to‐rest ratio are equated, CT is less demanding in terms of SBP and RPP. A greater hemodynamic response during exercise would be associated with a faster parasympathetic recovery.     

Changes in cardiovascular autonomic regulation among elderly subjects: Follow‐up of sixteen years

BACKGROUND. Previous cross‐sectional studies have suggested that cardiac autonomic regulation, measured as heart rate (HR) variability, is altered upon ageing, and that altered HR variability may predict mortality. However, there are no longitudinal follow‐up reports of the changes of HR dynamics in elderly subjects.

AIM & METHOD. This study was designed to examine the longitudinal changes in the spectral, fractal, and complexity measures of HR variability in a random sample of 41 elderly subjects (mean age 69±4 years), who underwent repeated 24‐hour Holter recordings at the baseline and after 16 years' follow‐up. Several cardiovascular risk factors were determined at the baseline.

RESULTS. A time‐domain index, standard deviation of N‐N intervals (SDNN) (142±34?msec versus 133±50?msec, not significant (NS)), and the high frequency spectral component of HR variability (219±222?msec² versus 268±287?msec², NS) did not change during the follow‐up. The low frequency power (LF) of HR variability decreased from 678±654?msec² to 436±651?msec² (P<0.01). Among the fractal HR variability indexes, the power‐law slope (β) (?1.31±0.20 versus ?1.47±0.21, P<0.001) and the short‐term fractal exponent α₁ (1.16±0.19 versus 1.06±0.18, P<0.01) decreased significantly. Approximate entropy remained unchanged.

CONCLUSIONS. The magnitude of total HR variability and the respiratory vagal modulation of HR do not change over time in the elderly. However, the spectral and fractal characteristics of HR behavior still undergo alterations upon ageing.     

Influence of exercise intensity on systemic oxidative stress and antioxidant capacity

The aim of the current study was to examine the influence of exercise intensity on systemic oxidative stress (OS) and endogenous antioxidant capacity. Non‐smoking, sedentary healthy adult males (n = 14) participated in two exercise sessions using an electronically braked cycle ergometer. The first session consisted of a graded exercise test to determine maximal power output and oxygen consumption (VO_2max). One week later, participants undertook 5‐min cycling bouts at 40%, 55%, 70%, 85% and 100% of VO_2max, with passive 12‐min rest between stages. Measures of systemic OS reactive oxygen metabolites (dROM), biological antioxidant potential (BAP), heart rate (HR), VO₂, blood lactate and rating of perceived exertion were assessed at rest and immediately following each exercise stage. Significant (P<0·05) differences between exercise bouts were examined via repeated measures ANOVA and post hoc pairwise comparisons with Bonferroni correction. Increasing exercise intensity significantly augmented HR (P<0·001), VO₂ (P<0·001), blood lactate (P<0·001) and perceived exertion (P<0·001) with no significant effect on dROM levels compared with resting values. In contrast, increasing exercise intensity resulted in significantly (P<0·01) greater BAP at 70% (2427 ± 106), 85% (2625 ± 121) and 100% (2651 ± 92) of VO_2max compared with resting levels (2105 ± 57 μmol Fe²⁺/L). The current results indicate that brief, moderate‐to‐high‐intensity exercise significantly elevates endogenous antioxidant defences, possibly to counteract increased levels of exercise‐induced reactive oxygen species. Regular moderate‐to‐high‐intensity exercise may protect against chronic OS associated diseases via activation, and subsequent upregulation of the endogenous antioxidant defence system.     

Does plasma L-arginine level play a role in regulation of blood pressure during exercise and autonomic nervous function?

Little is known of L -arginine's role in autonomic nervous regulation and physiological responses to dynamic exercise. We assessed heart rate and blood pressure during a maximal bicycle ergometer test and heart rate variability at rest in 15 healthy male volunteers, age 22–38 years. Venous blood samples for plasma L -arginine measurements were taken when subjects were sitting at rest before and at the end of exercise. The autonomic nervous function was assessed with time and frequency domain analysis of heart rate variability. Plasma L -arginine level decreased during maximal exercise from 71·4 μmol l^?1 to 51·0 μmol l^?1 (P < 0·0001) for all subjects studied. The systolic blood pressure during the maximal exercise test was inversely correlated with plasma L -arginine level at rest (r = ?0·70, P < 0·01). Normalized low frequency band of power spectral analysis of heart rate variability correlated with L -arginine level at rest (r = 0·66, P < 0·01). In conclusion, plasma L -arginine level decreased in physical exercise, and plasma L -arginine level at rest was positively associated with the sympathetic component of power spectral analysis of heart rate variability at rest, and inversely with systolic blood pressure during physical exercise.     

Assessment of the influence of age on the rate of heart rate decline after maximal exercise in non‐athletic adult males

This study investigated the influence of age on heart rate (HR) decline after exercise in non‐athletic adult males. One hundred and fourteen adult males (66 young, 25 ± 6·26 years; 48 old, 53 ± 8·54 years) participated in the study. Subjects performed maximum‐effort ergometer exercise in incremental stages. HR was measured at rest and continuously monitored during and after exercise. Maximum oxygen uptake (VO_2max) was measured during the exercise using respiratory gas analyser. Body mass index (BMI) was computed from weight and height measurements, while rating of perceived exertion (RPE) was obtained immediately after the exercise. Results indicated age differences in the rate of HR decline with the young presenting significantly higher %HR decline (P<0·001) than old adults at both levels of recovery. When linearly correlated with age, the rate of HR decline in 1 and 3 min indicated variances of (52%,56%) in young adults, and (54%,49%) in the old adults. After controlling for VO_2max, resting HR, BMI and RPE, the influence of age on rate of HR decline in the two phases of recovery disappeared in young. In the older adult group, it reduced greatly in the 1‐min recovery (r² = 25%; P = 0·001) and disappeared in the 3‐min recovery. Pattern of HR recovery did not differ between the two age groups while age threshold was observed in HR recovery in 1 min. In summary, the influence that age appeared to have on the rate of HR decline could not hold when factors affecting HR recovery were taken into account.     

Acute resistance exercise with blood flow restriction effects on heart rate,double product,oxygen saturation and perceived exertion

The aim of this study was to compare the acute effect of resistance exercise (RE) with and without blood flow restriction (BFR) on heart rate (HR), double product (DP), oxygen saturation (SpO₂) and rating of perceived exertion (RPE). Twenty‐four men (21·79 ± 3·21 years) performed three experimental protocols in a random order (crossover): (i) high‐intensity RE at 80% of 1RM (HI), (ii) low‐intensity RE at 20% of 1RM (LI) and (iii) low‐intensity RE at 20% of 1RM combined with partial blood flow restriction (LI+BFR). HR, blood pressure, SpO₂ and RPE were assessed. The data were analysed using repeated measures analysis of variance and the Wilcoxon test for RPE. The results indicated that all protocols significantly increased HR, both immediately postexercise and during the subsequent 60 min (P<0·05), and postexercise DP (P<0·05), but there were no differences between protocols. The protocols of LI and LI+BFR reduced postexercise SpO₂ (P = 0·033, P = 0·007), and the LI+BFR protocol presented a perception of greater exertion in the lower limbs compared with HI (P = 0·022). We conclude that RE performed at low intensity combined with BFR seems to reduce the SpO₂ after exercise and increase HR and DP while maintaining a perception of greater exertion on the lower limbs.     

Tissue oxygenation,strength and lactate response to different blood flow restrictive pressures

This study aimed to determine whether changes in initial restrictive pressures (IRP, tightness of the cuff before inflation with air) affect tissue oxygenation, lactate production and leg strength before, during and after knee extension exercises. The cuff was positioned on the right thigh, and the IRP of either 40–45 or 60–65 mmHg were applied randomly prior to inflating the cuff to the final restrictive pressure (the pressure reached after inflating the cuff with air). Subjects performed four sets (30, 15, 15 and 15 reps) of isotonic knee extensions with 1‐min rest between sets. Tissue oxygenation and blood lactate levels were assessed prior to, during and after exercise, and leg strength was assessed pre‐ and postexercise. There were significant condition by time interactions (P<0·01) and main effects for both condition (P<0·01) and time (P<0·01) for tissue oxygenation, deoxyhaemoglobin, total haemoglobin. Significant main effects were detected for both condition (P<0·01) and time (P<0·01) for leg strength values. There was only a significant time main effect for lactate concentrations. This study is the first to show that a higher IRP had a significant impact on percent tissue oxygenation, leg strength and deoxygenated haemoglobin accumulation during exercise.     

Exercise increases insulin clearance in healthy man and insulin-dependent diabetes mellitus patients

Exercise is known to decrease insulin secretion, but the effect on insulin clearance is unclear. We examined the effect of exercise on insulin clearance with euglycaemic insulin clamp in 28 healthy men either 12 h after a marathon run (n=14) or 44 h after a 2-h treadmill exercise (n=14), and in seven insulin-dependent diabetes mellitus (IDDM) patients 12 h after a marathon run, and after a resting, control day. During the post-exercise insulin infusion, steady-state plasma insulin concentration was reduced by 9% in healthy men after both types of exercise, and by 16% in the diabetic subjects compared with the control study (P<0·05 in all). In healthy men, C-peptide concentrations were more than one-third lower during insulin infusion, both after the marathon run (P<0·001) or treadmill exercise (P<0·02) compared with the control study. Insulin clearance was significantly increased by exercise both in healthy men (9%, P<0·05) and in IDDM subjects (15%, P<0·05). After exercise, endogenous insulin secretion in healthy men is reduced and insulin clearance is enhanced both in healthy men and in IDDM patients. Decreased insulin availability may allow enhanced muscle lipid utilization and spare glucose after long-term exercise.     

Chronotropic incompetence response to exercise in congestive heart failure,relationship with the cardiac autonomic status

In chronic congestive heart failure (CHF), attenuated heart rate response to exercise, a manifestation of chronotropic incompetence (CI), contributes to limiting exercise capacity. The present study was thus conducted to evaluate the respective role of chronic attenuation of cardiac vagal tone associated with depressed baroreflex sensitivity or affected cardiac sympathetic responsiveness in CHF patients with CI. Spontaneous cardiac baroreflex sensitivity (BRS) assessed by sequence method and spectral‐ and time‐domain analysis of heart rate variability (HRV) were analysed in 21 chronic CHF patients. All patients performed a symptom‐limited exercise test with measurement of gas exchange. Chronic incompetence which was defined as failure to achieve ≥80% of the heart rate reserve (%HRR) given by (HR_peak – HR_rest)/(predictive maximal heart rate – HR_rest) was observed in 14 (66%) patients. There was no significant difference in age, heart rate, peak oxygen uptake or left ventricular ejection fraction between the patients with and without CI. Although there was no significant difference in BRS, low frequency power of HRV in normalized units (LFnu) and SDNN were significantly lower in CI patients. Percentage of HRR correlated significantly with LFnu on 15 min (r=0·64, P<0·005) and, with LFnu on 24 h (r=0·52, P<0·01), SDNN (r=0·48, P=0·03) and SDANN (r=0·48, P=0·03), but not BRS (r=0·04, P=NS). Autonomic nervous system derangement is a complex process in CHF. The role of basal depressed cardiac sympathetic tone seems to contribute more closely than depressed baroreflex sensitivity to the impaired heart rate response to exercise frequently observed in CHF patients.     

Plasma oxidative stress is induced by single‐sprint anaerobic exercise in young cigarette smokers

Cigarette smoking increases oxidative stress, which is a risk factor for several diseases. Smoking has also been reported to enhance plasma oxidative stress during strenuous exercise. However, no prior study has examined the changes in plasma oxidative stress after single‐sprint anaerobic exercise in cigarette smokers. The purpose of this study was to investigate these changes in young cigarette smokers by measuring reactive oxygen species generation and total antioxidant content. Participants were 15 male smokers (mean age: 25·9 ± 2·9 years) and 18 male non‐smokers (mean age: 24·2 ± 4·3 years). Hydroperoxide concentration and biological antioxidant potential (BAP) in plasma were measured at baseline and after the Wingate anaerobic test. A significant interaction between group and time was observed for plasma hydroperoxide concentration (P = 0·037). Plasma hydroperoxide concentration was significantly increased after exercise in both smokers and non‐smokers (P = 0·001 and <0·001, respectively). However, no significant interaction was observed between groups by time on plasma BAP (P = 0·574), and a main effect of time was observed (P<0·001). Plasma BAP was significantly increased after exercise in both groups (both, P<0·001). These findings indicate that plasma oxidative stress is higher in cigarette smokers than in non‐smokers after single‐sprint anaerobic exercise, which may increase the risk of oxidative damage.     

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.     

Leg uptake of calcitonin gene‐related peptide during exercise in spinal cord injured humans

Exercise‐induced increases in cardiac output (CO) and oxygen uptake (VO₂) are tightly coupled, as also in absence of central motor activity and neural feedback from skeletal muscle. Neuromodulators of vascular tone and cardiac function – such as calcitonin gene related peptide (CGRP) – may be of importance. Spinal cord injured individuals (six tetraplegic and four paraplegic) performed electrically induced cycling (FES) with their paralyzed lower limbs for 29 ± 2 min to fatigue. Voluntary cycling performed both at VO₂ similar to FES and at maximal exercise in six healthy subjects served as control. In healthy subjects, CGRP in plasma increased only during maximal exercise (33·8 ± 3·1 pmol l^?1 (rest) to 39·5 ± 4·3 (14%, P<0·05)) with a mean extraction over the working leg of 10% (P<0·05). Spinal cord injured individuals had more pronounced increase in plasma CGRP (33·2 ± 3·8 to 46·9 ± 3·6 pmol l^?1, P<0·05), and paraplegic and tetraplegic individuals increased in average by 23% and 52%, respectively, with a 10% leg extraction in both groups (P<0·05). The exercise induced increase in leg blood flow was 10–12 fold in both spinal cord injured and controls at similar VO₂ (P<0·05), whereas CO increased more in the controls than in spinal man. Heart rate (HR) increased more in paraplegic subjects (67 ± 7 to 132 ± 15 bpm) compared with controls and tetraplegics (P<0·05). Mean arterial pressure (MAP) was unchanged during submaximal exercise and increased during maximal exercise in healthy subjects, but decreased during the last 15 min of exercise in the tetraplegics. It is concluded that plasma CGRP increases during exercise, and that it is taken up by contracting skeletal muscle. The study did not allow for a demonstration of the origin of the CGRP, but its release does not require activation of motor centres. Finally, the more marked increase in plasma CGRP and the decrease in blood pressure during exercise in tetraplegic humans may indicate a role of CGRP in regulation of vascular tone during exercise.     

Reduced cardiac sympathetic autonomic tone after long-term nasal continuous positive airway pressure in obstructive sleep apnoea syndrome

The increased sympathetic activation that occurs in obstructive sleep apnoea (OSA) may play an important role in associated morbidity. We investigated the effect of long-term (3 month) nasal continuous positive airway pressure (CPAP) on the autonomic nervous system assessed by heart rate variability (HRV). Fourteen patients (12 men), mean age 61·4 ± 8·1 years, with OSA underwent continuous synchronized electrocardiographic and polysomnographic monitoring. The apnoea/hypopnoea index (AHI) decreased from 50·6 ± 13·7 to 2·2 ± 2·5 events h^?1 after CPAP. HRV analysis showed significant decreases in low frequency (LF; from 7·12 ± 1·06 to 6·22 ± 1·18 ln ms² Hz^?1; P<0·001), high frequency (HF; from 5·91 ± 0·87 to 5·62 ± 0·92 ln ms² Hz^?1; P<0·05) and LF/HF (from 1·21 ± 0·12 to 1·11 ± 0·15 ln ms² Hz^?1; P<0·001) when the patients were asleep. The decrease in LF/HF was prolonged into the daytime (from 1·33 ± 0·22 to 1·24 ± 0·21 ln ms² Hz^?1; P<0·001). Treatment of OSA by CPAP significantly reduced the parameters of cardiac sympathetic tone, a favourable effect.