Repeated bout effect is not correlated with intraindividual variability during muscle-damaging exercise

The aim of this study was to test the hypothesis that the repeated bout effect depends on intraindividual variability during a second bout of eccentric exercise. Eleven healthy men performed 2 resistance training bouts consisting of maximal eccentric exercise (EE1 and EE2) using the knee extensor muscles. The interval between the exercise bouts was 2 weeks and consisted of 10 sets of 12 repetitions at 160° · s(-1). Maximal isokinetic concentric torque at 30° · s(-1) was measured before the bouts and 2 minutes and 24 hours thereafter. Muscle soreness score and creatine kinase activity were determined before and after exercise. Intraindividual variability in torque during each eccentric repetition was measured during exercise. Repeated bout effect manifested after EE2: Muscle soreness was less, the shift in optimal knee joint angle to a longer muscle length was less, and the decrease in isokinetic concentric torque 2 minutes after exercise was less for EE2 compared with that for EE1. During concentric (isokinetic) contraction, length-dependent changes in isokinetic torque (IT) occurred after both EE1 and EE2: The shorter the muscle length, the greater the change in IT. There was a significant relationship between the decrease in maximal isokinetic knee extension torque 24 hours after EE1 and intraindividual variability of EE1 (R2 = 0.71, p < 0.05), but this relationship was not significant for EE2 (R2 = 0.18). It seems that intraindividual variability during eccentric exercise protects against muscle fatigue and damage during the first exercise bout but not during a repeat bout. These findings may be useful to coaches who wish to improve muscle function in resistance training with less depression in muscle function and discomfort of their athletes, specifically, when muscle is most sensitive to muscle-damaging exercise.     

Comparison of three methods for beat-to-beat-interval extraction from continuous blood pressure and electrocardiogram with respect to heart rate variability analysis.

In recent years the analysis of heart rate variability (HRV) has become a suitable method for characterizing autonomous cardiovascular regulation. The aim of this study was to investigate the differences in HRV estimated from continuous blood pressure (BP) measurement by different methods in comparison to electrocardiogram (ECG) signals. The beat-to-beat intervals (BBI) were simultaneously extracted from the ECG and blood pressure of 9 cardiac patients (10 min, Colin system, 1000-Hz sampling frequency). For both data types, slope, peak, and correlation detection algorithms were applied. The short-term variability was calculated using concurrent 10-min BP and ECG segments. The root mean square errors in comparison to ECG slope detection were: 1.74 ms for ECG correlation detection; 5.42 ms for ECG peak detection; 5.45 ms for BP slope detection; 5.75 ms for BP correlation detection; and 11.96 ms for BP peak detection. Our results show that the variability obtained with ECG is the most reliable. Moreover, slope detection is superior to peak detection and slightly superior to correlation detection. In particular, for ECG signals with higher frequency characteristics, peak detection often exhibits more artificial variability. Besides measurement noise, respiratory modulation and pulse transit time play an important role in determining BBI. The slope detection method applied to ECG should be preferred, because it is more robust as regards morphological changes in the signals, as well as physiological properties. As the ECG is not recorded in most animal studies, distal pulse wave measurement in combination with correlation or slope detection may be considered an acceptable alternative.     

Middle cerebral artery flow velocity and pulse pressure during dynamic exercise in humans

Exercise challenges cerebral autoregulation (CA) by a large increase in pulse pressure (PP) that may make systolic pressure exceed what is normally considered the upper range of CA. This study examined the relationship between systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) and systolic (V(s)), diastolic (V(d)). and mean (V(m)) middle cerebral artery (MCA) blood flow velocity during mild, moderate, and heavy cycling exercise. Dynamic CA and steady-state changes in MCA V in relation to changes in arterial pressure were evaluated using transfer function analysis. PP increased by 37% and 57% during moderate and heavy exercise, respectively (P < 0.05), and the pulsatility of MCA V increased markedly. Thus exercise increased MCA V(m) and V(s) (P < 0.05) but tended to decrease MCA V(d) (P = 0.06). However, the normalized low-frequency transfer function gain between MAP and MCA V(m) and between SBP and MCA V(s) remained unchanged from rest to exercise, whereas that between DBP and MCA V(d) increased from rest to heavy exercise (P < 0.05). These findings suggest that during exercise, CA is challenged by a rapid decrease rather than by a rapid increase in blood pressure. However, dynamic CA remains able to modulate blood flow around the exercise-induced increase in MCA V(m), even during high-intensity exercise.     

Geographic distributions of within-population variability in blood pressure

Data on mean blood pressure with standard deviation were extracted from the medical and anthropologic literature for as many populations as possible. The populations were classified as traditional, transitional, or modern. Both mean and within-population variability were found to be higher in more modern populations, confirming the prediction that variability of a character of low heritability is higher in an adverse environment, where it is more difficult to maintain homeostasis. In addition, variability increases with age, indicating a breakdown in homeostasis with aging. On average, males had higher diastolic blood pressure than females, and on average, females had greater variability in systolic blood pressure than males. There was a highly significant negative relationship between latitude and within-population variability in blood pressure.     

Effect of heavy exercise on spectral baroreflex sensitivity, heart rate, and blood pressure variability in well-trained humans

The aim of the study was to assess the instantaneous spectral components of heart rate variability (HRV) and systolic blood pressure variability (SBPV) and determine the low-frequency (LF) and high-frequency baroreflex sensitivity (HF-BRS) during a graded maximal exercise test. The first hypothesis was that the hyperpnea elicited by heavy exercise could entail a significant increase in HF-SBPV by mechanical effect once the first and second ventilatory thresholds (VTs) were exceeded. It was secondly hypothesized that vagal tone progressively withdrawing with increasing load, HF-BRS could decrease during the exercise test. Fifteen well-trained subjects participated in this study. Electrocardiogram (ECG), blood pressure, and gas exchanges were recorded during a cycloergometer test. Ventilatory equivalents were computed from gas exchange parameters to assess VTs. Spectral analysis was applied on cardiovascular series to compute RR and systolic blood pressure power spectral densities, cross-spectral coherence, gain, and alpha index of BRS. Three exercise intensity stages were compared: below (A1), between (A2), and above (A3) VTs. From A1 to A3, both HF-SBPV (A1: 45 +/- 6, A2: 65 +/- 10, and A3: 120 +/- 23 mm2Hg, P < 0.001) and HF-HRV increased (A1: 20 +/- 5, A2: 23 +/- 8, and A3:40 +/- 11 ms2, P < 0.02), maintaining HF-BRS (gain, A1: 0.68 +/- 0.12, A2: 0.63 +/- 0.08, and A3: 0.57 +/- 0.09; alpha index, A1: 0.58 +/- 0.08, A2: 0.48 +/- 0.06, and A3: 0.50 +/- 0.09 ms/mmHg, not significant). However, LF-BRS decreased (gain, A1: 0.39 +/- 0.06, A2: 0.17 +/- 0.02, and A3: 0.11 +/- 0.01, P < 0.001; alpha index, A1: 0.46 +/- 0.07, A2: 0.20 +/- 0.02, and A3: 0.14 +/- 0.01 ms/mmHg, P < 0.001). As expected, once VTs were exceeded, hyperpnea induced a marked increase in both HF-HRV and HF-SBPV. However, this concomitant increase allowed the maintenance of HF-BRS, presumably by a mechanoelectric feedback mechanism.     

Cultural variations in the placebo effect: ulcers, anxiety, and blood pressure

An analysis of the control groups in double-blind trials of medicines demonstrates broad variation--from 0 to 100 percent--in placebo effectiveness rates for the same treatment for the same condition. In two cases considered here, drug healing rates covary with placebo healing rates; placebo healing is the ultimate and inescapable "complementary medicine." Several factors can account for the dramatic variation in placebo healing rates, including cultural ones. But because variation differs by illness, large placebo effects for one condition do not necessarily anticipate large placebo effects for other conditions as well. Deeper understanding of the intimate relationship between cultural and biological processes will require close ethnographic scrutiny of the meaningfulness of medical treatment in different societies.     

Physiological responses during interval training with different intensities and duration of exercise

The purpose of this study was to compare 4 interval training (IT) sessions with different intensities and durations of exercise to determine the effect on mean VO?, total VO?, and duration of exertion ≥95% maximum power output (MPO), and the effects on biomarkers of fatigue such as blood-lactate concentration (BLC) and rating of perceived exertion. The subjects were 12 recreationally competitive male (n = 7, mean ± SD age = 26.2 ± 3.9 years) and female (n = 5, mean ± SD age = 27.6 ± 4.3 years) triathletes. These subjects performed 4 IT sessions on a cycle ergometer varying in intensity (90 and 100% MPO) and duration of exercise (30 seconds and 3 minutes). This study revealed that IT using 30-second duration intervals (30-30 seconds) allows the athlete to perform a longer session, with a higher total and mean VO? HR and lower BLC than 3-minute durations. Similarly, submaximal exertion at 90% of MPO also allows performing longer sessions with a higher total VO? than 100% intensity. Thus, the results of the present study suggested that to increase the total time at high intensity of exercise and total VO? of a single exercise session performed by the athlete, IT protocols of short durations (i.e., 30 seconds) and submaximal intensities (i.e., 90% MPO) should be selected. Furthermore, performing short-duration intervals may allow the athlete to complete a longer IT session with greater metabolic demands (VO?) and lower BLC than longer (i.e., 3 minutes) intervals.     

Impact of chronic exercise training on the blood pressure response to orthostatic stimulation

Exercise training elicits morphological adaptations in the left ventricle (LV) and large-conduit arteries that are specific to the type of training performed (i.e., endurance vs. resistance exercise). We investigated whether the mode of chronic exercise training, and the associated cardiovascular adaptations, influence the blood pressure responses to orthostatic stimulation in 30 young healthy men (10 sedentary, 10 endurance trained, and 10 resistance trained). The endurance-trained group had a significantly larger LV end-diastolic volume normalized by body surface area (vs. sedentary and resistance-trained groups), whereas the resistance-trained group had a significantly higher LV wall thickness and aortic pulse wave velocity (PWV) compared with the endurance-trained group. In response to 60° head-up tilt (HUT), mean arterial pressure (MAP) rose in the resistance-trained group (+6.5 ± 1.6 mmHg, P < 0.05) but did not change significantly in sedentary and the endurance-trained groups. Systolic blood pressure (SBP) decreased in endurance-trained group (-8.3 ± 2.4 mmHg, P < 0.05) but did not significantly change in sedentary and resistance-trained groups. A forward stepwise multiple regression analysis revealed that LV wall thickness and aortic PWV were significantly and independently associated with the MAP response to HUT, explaining ～41% of its variability (R(2) =0.414, P < 0.001). Likewise, aortic PWV and the corresponding HUT-mediated change in stroke volume were significantly and independently associated with the SBP response to HUT, explaining ～52% of its variability (R(2) = 0.519, P < 0.0001). Furthermore, the change in stroke volume significantly correlated with LV wall thickness (r = 0.39, P < 0.01). These results indicate that chronic resistance and endurance exercise training differentially affect the BP response to HUT, and that this appears to be associated with training-induced morphological adaptations of the LV and large-conduit arteries.     

Circadian variations of catecholamines and blood pressure in patients with pseudohypoparathyroidism and hypertension

The relationship between 24-h recumbent blood pressure levels and secretory patterns of catecholamines was investigated in 4 patients with pseudohypoparathyroidism (PsHP) and hypertension and in 9 patients with essential hypertension. A clear circadian rhythm of blood pressure and catecholamines was documented in both groups with lowest levels of blood pressures and catecholamines occurring during sleep. During the 24-h period of recumbency mean arterial blood pressure (MAP) was correlated (r = 0.63, p less than or equal to 0.01) with plasma norepinephrine (N) in the patients with essential hypertension, but this correlation was weaker in patients with PsHP (r = 0.38, p less than or equal to 0.05). MAP was more closely related to plasma epinephrine (E) (r = 0.62, p less than or equal to 0.01) than to plasma NE in patients with PsHP. Plasma NE and E levels were considerably lower in patients with PsHP than in patients with essential hypertension throughout the 24-h recumbent period. The sleep-related decline in blood pressure and NE was less than in patients with essential hypertension. These results suggest that while the sympathetic nervous system may have a role in hour-to-hour maintenance of blood pressure in patients with PsHP and hypertension, it does not appear to be responsible for the elevated arterial pressure in these patients. Factors other than those investigated, such as obesity, alterations in sodium homeostasis of refractoriness of the vascular smooth muscle to the vasodilatory effect of PTH may be involved in the pathogenesis of hypertension in PsHP.     

Renal SNA as the primary mediator of slow oscillations in blood pressure during hemorrhage

Blood pressure contains a distinct low-frequency oscillation often termed the Mayer wave. This oscillation is caused by the action of the sympathetic nervous system on the vasculature and results from time delays in the baroreflex feedback loop for the control of sympathetic nerve activity (SNA) in response to changes in blood pressure. In this study, we used bilateral renal denervation to test the hypothesis that it is SNA to the kidney that contributes a large portion of the vascular resistance associated with changes in the strength of the slow oscillation in blood pressure. In conscious rabbits, SNA and blood pressure were measured during hemorrhage (blood withdrawal at 1.35 ml. min(-1). kg(-1) for 20 min). Spectral analysis identified a strong increase in power at 0.3 Hz in SNA and blood pressure in the initial compensatory phase of hemorrhage before blood pressure started to fall. However, in a separate group of renal denervated rabbits, although the power of the 0.3-Hz oscillation under control conditions in blood pressure was similar, it was not altered during hemorrhage. Wavelet analysis revealed the development of low-frequency oscillations at 0.1 Hz in both intact and denervated animals. In conclusion, we propose that changes in the strength of the oscillation at 0.3 Hz in arterial pressure during hemorrhage are primarily mediated by sympathetic activity directed to the kidney.     

Cerebral oxygenation is highly sensitive to blood pressure variability in sick preterm infants

Objectives

The significance of blood pressure variability (BPV) for cerebral oxygenation in extremely preterm infants has not been explored, though BPV may well be associated with end organ injury. We hypothesized that increased BPV in sick preterm infants, by exceeding the cerebral autoregulatory capacity, is associated with cerebral oxygenation changes which closely follow the blood pressure fluctuations. We assessed the autoregulatory capacity in the early postnatal period, by determining the correlation between BPV (mmHg²) and coherence of mean arterial blood pressure (MABP mmHg) and cerebral oxygenation (tissue oxygenation index, TOI %).

Study Design

Thirty-two preterm infants of mean gestational age of 26.3 (±1.5) weeks were studied on the first 3 postnatal days. Spectral analysis (Coherence and transfer-function gain analysis) was used to calculate coherence of MABP and TOI; BPV was quantified using power spectral density of MABP.

Results

Overall, maximum Coherence showed a trend for positive correlation with BPV (n = 32, p = 0.06). Infants identified as clinically unstable with documented brain injury (n = 7) had high Coherence values at low BPV. Separate analysis of stable infants (excluding the 7 critically ill infants) revealed a significant association between maximum Coherence and BPV (n = 25, p = 0.006).

Conclusions

Fluctuation in cerebral oxygenation is closely associated with increased BPV in preterm infants undergoing intensive care. Moreover, in the critically sick preterm infant, blood pressure-dependent variations in cerebral oxygenation occur even with relatively lower BPV, suggesting they have severely impaired autoregulation, and placing them at greater vulnerability to cerebral injury arising from blood pressure fluctuations.     

Evaluation of the effect of systolic blood pressure and pulse pressure on cognitive function: the Women's Health and Aging Study II

Background

Evidence suggests that elevated systolic blood pressure (SBP) and pulse pressure (PP) in midlife is associated with increased risk for cognitive impairment later in life. There is mixed evidence regarding the effects of late life elevated SBP or PP on cognitive function, and limited information on the role of female gender.

Methods/Principal Findings

Effects of SBPand PPon cognitive abilities at baseline and over a 9-year period were evaluated in 337 non-demented community-dwelling female participants over age 70 in the Women''s Health and Aging Study II using logistic and Cox proportional hazards regression analyses. Participants aged 76–80 years with SBP≥160 mmHg or PP≥84 mmHg showed increased incidence of impairment on Trail Making Test-Part B (TMT, Part B), a measure of executive function, over time when compared to the control group that included participants with normal and pre-hypertensive SBP (<120 and 120–139 mmHg) or participants with low PP (<68 mmHg) (HR = 5.05 [95%CI = 1.42, 18.04], [HR = 5.12 [95%CI = 1.11; 23.62], respectively). Participants aged 70–75 years with PP≥71 mmHg had at least a two-fold higher incidence of impairment on HVLT-I, a measure of verbal learning, over time when compared to participants with low PP (<68 mmHg) (HR = 2.44 [95%CI = 1.11, 5.39]).

Conclusions/Significance

Our data suggest that elevated SBP or PP in older non-demented women increases risk for late-life cognitive impairment and that PP could be used when assessing the risk for impairment in cognitive abilities. These results warrant further, larger studies to evaluate possible effects of elevated blood pressure in normal cognitive aging.