Aortic-Radial Pulse Transit Time and ECG Q-Wave to Radial Pulse Wave Interval as Indices of Beat-By-Beat Blood Pressure Change

This study examined beat-by-beat relationships between blood pressure, the time interval from the ECG Q-wave to the radial pulse wave (QRPI), and its two components, the cardiac pre-ejection period (PEP) and aortic-radial arterial pulse transit time (AR-PTT). In 8 subjects, intra-arterial systolic (SBP) and diastolic (DBP) blood pressure, QRPI, PEP, and AR-PTT were measured during rest, mental arithmetic, cold pressor, and inhalation of amyl nitrite. Both PEP and AR-PTT varied widely during each experimental condition indicating that QRPI change reflected both PEP and AR-PTT change. AR-PTT varied inversely with SBP and DBP; PEP sometimes varied directly and sometimes inversely with both SBP and DBP. QRPI varied inversely with both SBP and DBP with the magnitude of the correlation in a particular instance depending on the relationships for that instance between blood pressure and both PEP and AR-PTT. Implications of the results for the use of either QRPI or AR-PTT as indices of blood pressure change are discussed.     

Effects of dynamic and static handgrip exercises on hand and wrist volume

It is not known how the mode of exercise, dynamic and static exercises, affects the limb volume. Therefore, the purpose of this study was to investigate hand and wrist volume (HWV) after dynamic and static handgrip exercise. Nine healthy subjects (age 31.8 ± 7.3 years; height 172.0 ± 5.7 cm; body mass 66.9 ± 8.1 kg, mean ± SD) volunteered for this study. HWV was measured with a hand and wrist volumeter before and immediately after dynamic and static exercises. Initially during rest, HWV was measured after the hand was passively hung for 5 min. Handgrip exercises with an ergonomic hand exerciser were performed at 20% of maximum voluntary contraction in right and left hands by static and dynamic exercises, respectively. Both dynamic and static handgrip exercises consisted of six sets of 30-s contractions with 10-s rest intervals between exercise bouts. The dynamic handgrip exercise was performed by repetitive contraction and relaxation of the hand at a maximum frequency. In order to determine intensity of handgrip exercises, maximum isometric handgrip strength of the right and left hand was measured with a handgrip dynamometer. Data are presented as mean ± SD. After dynamic and static handgrip exercises, HWV increased significantly, and these increases represent 2.2 ± 0.7% (P < 0.001) and 1.4 ± 0.8% (P < 0.001) of resting HWV, respectively. The elevation of HWV after dynamic exercise was significantly higher than that after static exercise (P < 0.05). These results suggest that the higher HWV after dynamic exercise may be caused by higher increased interstitial fluid volume, capillary volume and venous volume in hand and wrist tissues.     

Reduced arterial diameter during static exercise in humans

In eight subjects luminal diameter of the resting limb radial and dorsalis pedis arteries was determined by high-resolution ultrasound (20 MHz). This measurement was followed during rest and during 2 min of static handgrip or of one-leg knee extension at 30% of maximal voluntary contraction of another limb. Static exercise increased heart rate and mean arterial pressure, which were largest during one-leg knee extension. After exercise heart rate and mean arterial pressure returned to the resting level. No changes were recorded in arterial carbon dioxide tension, and the rate of perceived exertion was ? 15 units after both types of exercise. The dorsalis pedis arterial diameter was 1.50±0.20 mm (mean and SE) and the radial AD 2.45±0.12 mm. During both types of contractions the luminal diameters decreased ? 3.5% within the first 30 s (P< 0.05), and during one-leg knee extension they continued to decrease to a final exercise value 7.6±1.1% lower than at rest (P < 0.05). Thus, they became smaller than during the handgrip. After exercise resting values were reestablished. When the arterial diameter was expressed in relation to mean arterial pressure for the radial and dorsalis pedis artery was 22±3 and 28±3% lower during handgrip than the relation during rest, respectively. After one-leg knee extension both arteries reached 30±4% lower values. This study demonstrated arterial constriction in the resting limbs within the first 30 s of static exercise, and continued constriction during one-leg knee extension. These results support to the hypothesis that central command and/or muscle mechano- receptors influence arterial tone, and that the exercise pressor reflex becomes important with the involvement of a large muscle mass.     

Evaluation of a New Ambulatory Blood Pressure Monitor (Accutracker 102): Laboratory Comparisons With Direct Arterial Pressure, Stethoscopic Auscultatory Pressure, and Readings From a Similar Monitor (Spacelabs Model 5200)

Systolic (SBP) and diastolic (DBP) blood pressure levels generated by a new noninvasive ambulatory monitor, the Accutracker 102, were compared in the laboratory with intra-arterial pressure levels in 12 normotensive men, and with stethoscopic auscultatory determinations in 27 normotensive and hypertensive men and women over a wide range of within-subject pressure variations. In 11 subjects, its performance was also compared with another ambulatory monitor, the Spacelabs Model 5200. Highly positive correlations with both the intra-arterial (median r=+.90 for SBP, +.92 for DBP) and the stethoscopic standards (median r=+.93 for SBP, +.88 for DBP) were obtained using Accutracker's automatic readings (digital readout), while slightly higher correlations were obtained with hand-scoring of recorded data. The Spacelabs BP monitor also yielded readings that were highly correlated with stethoscopic readings (median r=+.83 for SBP, +.77 for DBP), although in 3 of the 11 subjects the Accutracker correlations were substantially higher than the Spacelabs correlations. Despite their generally good tracking of changes in pressure, both ambulatory monitors yielded absolute values in many subjects that differed by 5 mmHg or more from stethoscopic levels. The Accutracker's SBP levels were consistently too high and its DBP levels were occasionally too low, while Spacelabs' SBP and DBP values were too high and too low with equal frequency. However, mean deviation scores for each patient calculated from 5 concurrent ambulatory monitor and stethoscopic readings were shown to yield relatively stable correction factors for use when comparison with clinical standards is desired.     

Baroreflex control of sinus node during dynamic exercise in humans: effect of muscle mechanoreflex

Aim: This study evaluated the influence of muscle mechanical afferent stimulation on the integrated arterial baroreflex control of the sinus node during dynamic exercise. Methods: Systolic blood pressure (SBP) and pulse interval (PI) were measured continuously and non‐invasively in 15 subjects at rest and during passive cycling. The arterial baroreflex was evaluated with the cross‐correlation method (xBRS) for the computation of time‐domain baroreflex sensitivity on spontaneous blood pressure and PI variability. xBRS computes the greatest positive correlation between beat‐to‐beat SBP and PI, and when significant at P = 0.01, slope and delay are recorded as one xBRS value. Heart rate variability (HRV) was evaluated in the frequency domain. Results: Compared with rest, passive exercise resulted in a parallel increase in heart rate (67 ± 3.2 vs. 70 ± 3.6 beats min^?1; P < 0.05) and mean arterial pressure (87 ± 2 vs. 95 ± 2 mmHg; P < 0.05), and a significant decrease in xBRS (13.1 ± 1.8 vs. 10.5 ± 1.7 ms mmHg^?1; P < 0.01) with an apparent rightward shift in the regression line relating SBP to PI. Also low frequency power of HRV increased while high frequency power decreased (56.7 ± 3.5 vs. 62.7 ± 4.8 and 43.2 ± 3.4 vs. 36.9 ± 4.9 normalized units respectively; P < 0.05). Conclusion: These data suggest that the stimulation of mechanosensitive stretch receptors is capable of modifying the integrated baroreflex control of sinus node function by decreasing the cardiac vagal outflow during exercise.     

Muscle metaboreflex contribution to cardiovascular regulation during dynamic exercise in microgravity: insights from mission STS-107 of the space shuttle Columbia

One of the most important features of prolonged weightlessness is a progressive impairment of muscular function with a consequent decrease in exercise capacity. We tested the hypothesis that the impairment in musculo-skeletal function that occurs in microgravity results in a potentiation of the muscle metaboreflex mechanism and also affects baroreflex modulation of heart rate (HR) during exercise. Four astronauts participating in the 16 day Columbia shuttle mission (STS-107) were studied 72–71 days before launch and on days 12–13 in-flight. The protocol consisted of 6 min bicycle exercise at 50% of individual     followed by 4 min of postexercise leg circulatory occlusion (PECO). At rest, systolic (S) and diastolic (D) blood pressure (BP), R-R interval and baroreflex sensitivity (BRS) did not differ significantly between pre- and in-flight measurements. Both pre- and in-flight, SBP increased and R-R interval and BRS decreased during exercise, whereas DBP did not change. During PECO preflight, SBP and DBP were higher than at rest, whereas R-R interval and BRS recovered to resting levels. During PECO in-flight, SBP and DBP were significantly higher whereas R-R interval and BRS remained significantly lower than at rest. The part of the SBP response (Δ) that was maintained by PECO was significantly greater during spaceflight than before (34.5 ± 8.8 versus 13.8 ± 11.9 mmHg, P = 0.03). The tachycardic response to PECO was also significantly greater during spaceflight than preflight (−141.5 ± 25.2 versus −90.5 ± 33.3 ms, P = 0.02). This study suggests that the muscle metaboreflex is enhanced during dynamic exercise in space and that the potentiation of the muscle metaboreflex affects the vagally mediated arterial baroreflex contribution to HR control.     

Effect of interval training programme on pulse pressure in the management of hypertension: a randomized controlled trial

Background

Pulse pressure (PP), might be a stronger determinants of cardiovascular risk.

Objective

To investigate the effect of interval training program on PP in subjects with hypertension.

Methods

Two hundred and forty five male patients with mild to moderate (Systolic Blood Pressure [SBP] between 140–179 & Diastolic Blood Pressure [DBP] between 90–109 mmHg) essential hypertension were age-matched and grouped into exercise and control groups. The exercise (work: rest ratio of 1:1) groups involved in an 8-weeks interval training programs of between 45–60 minutes, at intensities of 60–79% of HR max (maximum heart rate), while the control group remained sedentary during this period. SBP, DBP, VO₂max and PP were assessed.

Results

Findings of the study revealed significant correlation between PP and blood pressure; correlation of PP with SBP was much stronger (95% variance). Also, there was significant effect of the exercise training program on SBP, DBP and PP. Changes in VO₂max also negatively correlated with changes in PP (r= −.285) at p<0.05.

Conclusion

Moderate intensity interval training programs is effective in the non-pharmacological management of hypertension and may prevent cardiovascular event through the down regulation of PP in hypertension.     

Pulse Transit Time and Blood Pressure: An Intensive Analysis

Relationships between pulse transit time (PTT) and intra-arterial systolic (SBP), diastolic (DBP), and mean arterial blood pressure (MAP) were examined in 4 subjects under three conditions: rest, paced respiration, and mental arithmetic. PTT was measured from the EKG R-wave to two peripheral pulses (brachial and radial) and from one pulse to the other. Three points on each pulse wave were used (peak, foot, slope) in the measurements, yielding nine different measures of PTT. The nine PTT measures were not consistently intercorrelated. PTTs initiated by the R-wave were moderately correlated with SBP, but not with DBP or MAP. Brachial to radial PTTs were not correlated with any measures of BP. Relationships between PTT and BP also varied from subject to subject. The limited magnitude of the correlations and their inconsistency suggest caution in the simple substitution of PTT for beat-to-beat measures of BP.     

Effects of rhythmic muscle compression on arterial blood pressure at rest and during dynamic exercise in humans

This study was designed to examine the hypothesis that a rhythmic mechanical compression of muscles would affect systemic blood pressure regulation at rest and during dynamic exercise in humans. We measured the changes in mean arterial pressure (MAP) occurring (a) at rest with pulsed (350 ms pulses at 50 pulses min^–1) or static compression (50 and 100 mmHg) of leg muscles with or without upper thigh occlusion, and (b) during 12‐min supine bicycle exercise (75 W, 50 r.p.m.) with or without pulsed compression (50, 100, 150 mmHg) of the legs in synchrony with the thigh extensor muscle contraction. At rest with thigh occlusion, MAP increased by 4–8 mmHg during static leg compression, and by 5–9 mmHg during pulsed leg compression. This suggests that at rest pulsed leg compression elicits a reflex pressor response of similar magnitude to that evoked by static compression. During dynamic exercise without leg compression, MAP (having risen initially) gradually declined, but imposition of graded pulsed leg compression prevented this decline, the MAP values being significantly higher than those recorded without pulsed leg compression by 7–10 mmHg. These results suggest that the rhythmic increase in intramuscular pressure that occurs during dynamic exercise evokes a pressor response in humans.     

Metabolic,body temperature and hormonal responses to repeated periods of prolonged cycle-ergometer exercise in men

Summary This study was designed to find out whether rest intervals and prevention of dehydration during prolonged exercise inhibit a drift in metabolic rate, body temperature and hormonal response typically occurring during continuous work. For this purpose in ten healthy men the heart rate (t _c), rectal temperature (T _re), oxygen uptake (VO₂), as well as blood metabolite and some hormone concentrations were measured during 2-h exercise at approximately 50% maximal oxygen uptake split into four equal parts by 30-min rest intervals during which body water losses were replaced. During each 30-min exercise period there was a rapid change in T _re and t _c superimposed on which, these values increased progressively in consecutive exercise periods (slow drift). The VO₂ showed similar changes but there were no significant differences in the respiratory exchange ratio, pulmonary ventilation, mechanical efficiency and plasma osmolality between successive periods of exercise. Blood glucose, insulin and C-peptide concentrations decreased in consecutive exercise periods, whereas plasma free fatty acid, glycerol, catecholamine, growth hormone and glucagon concentrations increased. Blood lactate concentrations did not show any regular drift and the plasma cortisol concentration decreased during the first two exercise periods and then increased. In conclusion, in spite of the relatively long rest intervals between the periods of prolonged exercise and the prevention of dehydration several physiological and hormonal variables showed a distinct drift with time. It is suggested that the slow drift in metabolic rate could have been attributable in the main to the increased concentrations of heat liberating hormones.     

Influence of age on blood pressure recovery after maximal effort ergometer exercise in non-athletic adult males

This study investigated whether age influences blood pressure recovery after maximal exercise in adult males. Forty healthy, non-athletic adult males (20 young, aged 22 ± 3.46 years and 20 older, aged 48 ± 6.91 years) participated in the study. Subjects performed a maximal-effort ergometer exercise test. Peak oxygen uptake (VO_2max) was measured during the exercise protocol; heart rate (HR) and blood pressure (BP) were measured before exercise, during exercise (at 2-min intervals), and at the first minute of post-exercise recovery and subsequently at 2-min intervals until the recovery of BP. Results indicated that young adults had lower systolic blood pressure (SBP) recovery ratio (P < 0.05), lower SBP recovery time (P < 0.001), higher SBP% decline in 1, and 3 min (P < 0.001), and higher DBP% decline in 1, and 3 min (P < 0.05, <0.001) than the older adults, thus indicating faster BP recovery in young than older adults. A bivariate correlation test, revealed significant associations (P < 0.001, <0.01) between age and BP recovery parameters: percentage SBP decline in 1 and 3 min (27 and 39%), percentage DBP decline in 1 and 3 min (14 and 26%), third minute SBP ratio (22%), and SBP recovery time (72%). After controlling for factors affecting BP recovery such as resting SBP, percentage HR decline, VO_2max and delta SBP, the observed correlations reduced in SBP recovery time (29%; P < 0.002) but disappeared (P > 0.01) in the other BP recovery parameters. These data indicate the need to take into account, factors affecting BP recovery when interpreting the effect of age on BP responses after exercise in future investigations.     

Stability of individual differences in cardiovascular reactivity: A thirteen month follow-up

This study concerns the stability of individual differences in cardiovascular reactivity among nineteen male subjects who had participated in a similar investigation thirteen months earlier. In the previous study (Year I), subjects were presented a frustrating task in concept formation to perform at each of two experimental sessions, scheduled one week apart, and recordings of heart rate (HR) and systolic and diastolic blood pressure (SBP, DBP) obtained during periods of rest and task performance on each occasion of testing. Under the current procedure (Year II), subjects were exposed to the same experimental stressor as on year I, as well as a second cognitive task involving a difficult problem in “mental arithmetic”; HR, SBP and DBP were again recorded both at rest and while subjects performed the instructed tasks. Measures of task-related cardiovascular arousal across the two years of observation revealed reproducible individual differences with respect to the magnitude of subjects' HR and SBP, but not DBP, reactivity. Although individual differences in HR and SBP responses correlated positively, neither HR nor SBP reactivity covaried reliably with DBP changes. It was suggested that concomitant response differences in HR and SBP, as observed under these experimental conditions, may reflect an underlying dimension of individual differences in beta-adrenergic reactivity.     

The influence of sexual maturation on blood pressure and body fatness in African‐American adolescent girls and boys

To examine the influence of sexual maturation (SM) on blood pressure (BP) and body fatness during puberty among African‐American children. Longitudinal data were collected from 283 African‐American children aged 9–15 years over a 1.5‐year period. Measured anthropometric measures included height, weight, skinfold thickness, waist circumference (WC), and systolic and diastolic BP (SBP/DBP) at baseline, 1‐year, and 1.5‐year follow‐up were used. SM was assessed using self‐reported Tanner stages (range 1–5) at baseline. Spearman correlation and regression analyses were conducted to test associations between study variables. Early maturing girls had higher BP and body mass index (BMI = weight (kg)/height (m)²) at follow‐up than nonearly maturing girls (SBP: 117.4 vs. 111.7; DBP: 66.3 vs. 60.7; BMI: 27.7 vs. 23.5; all P < 0.05, respectively). Baseline Tanner stage was positively associated with follow‐up SBP (r = 0.28), DBP (r = 0.37), BMI (r = 0.45), skinfold thickness (r = 0.37), and WC (r = 0.40) in girls, but not in boys. The influence of SM on BP independent of body size was tested via several different multiple linear regression models by adding measures of body size and their changes (height and BMI) between baseline and follow‐up. Early maturing girls had higher SBP and DBP (β = 4.30, P < 0.05; β = 3.28, P < 0.05; respectively) and BMI (β = 1.69, P < 0.05) at 1.5‐year follow‐up than their counterparts. In boys, a marginally significant reverse association (β = ?1.05 to ?1.19) between SM stages and DBP was detected. SM affects BP and body fatness in girls, and should be considered in assessment of BP and obesity in adolescents. Am. J. Hum. Biol., 2009. © 2008 Wiley‐Liss, Inc.     

Effect of low glycogen on glycogen synthase in human muscle during and after exercise

Subjects cycled at a work load calculated to elicit 75% of maximal oxygen uptake on two occasions: the first to fatigue (34.5 ± 5.3 min; mean ± SE), and the second at the same workload and for the same duration as the first. Biopsies were obtained from the quadriceps femoris muscle before and immediately after exercise, and 5 min post-exercise. Before the first experiment, muscle glycogen was lowered by a combination of exercise and diet, and before the second, experiment muscle glycogen was elevated. In the low glycogen condition (LG), muscle glycogen decreased from 169 ± 15 mmol glucosyl units kg^-1dry wt at to rest to 13 ± 6 after exercise. In the high glycogen condition (HG) glycogen decreased from 706 ± 52 at rest to 405 ± 68 after exercise. Glycogen synthase fractional activity (GSF) was always higher during the LG treatment. During exercise in the HG condition, those subjects who cycled for < 35 min (n= 3) had GSF values in muscle which were lower than at rest, whereas those subjects who cycled for > 35 min (n= 4) had values which were similar to or higher than at rest. Thus the change in GSF in muscle during HG was positively related to the exercise duration (r= 0.94; y = 254–17x + 0.3x²; P < 0.001) and negatively related to the glycogen content at the end of exercise (r=–0.82; y= 516–2x + 0.001x²; P < 0.05). During LG exercise GSF remained constant. GSF increased markedly after 5 min post-exercise in both HG and LG conditions. cAMP dependent protein kinase activity increased similarly during both LG and HG exercise and reverted to the preexercise values 5 min post-exercise. It is concluded that muscle contraction decreases GSF, but low glycogen levels can attenuate or abolish the decrease in GSF. The rapid increase of GSF during recovery from exercise does not require glycogen depletion during the exercise.     

Continuous percutaneous measurement by laser-Doppler flowmetry of skeletal muscle microcirculation at varying levels of contraction force determined electromyographically

Summary Laser-Doppler flowmetry (LDF) and electromyography (EMG) were used simultaneously for measuring skeletal muscle blood perfusion in relation to static load and fatigue. Percutaneous single-fibre LDF and bipolar surface EMG of the trapezius muscle were performed continuously during a 10-min series of alternating periods of static contractions and rest, each of 1-min duration. The muscle was exposed to static load expressed as shoulder torque, by keeping the arms straight and elevated at 30, 60, 90 and 135°. On-line computer processing of the LDF and EMG signals made possible the interpretation of the relationship between the perfusion and the activity of the muscle. The LDF and root mean square (rms)-EMG were normalized by using the average value of the serial examinations of each individual as a reference value. Spectrum analyses of EMG showed the lowest variability for median frequency (MDF) in the frequency range 10–1000 Hz and mean power frequency (MPF) at 2–1000 Hz. The LDF power spectrum density during low (muscle rest) and high (high-force muscle contraction) perfusion indicated that disturbances were small when measurements were performed during sustained static contraction with as little movement as possible. Vasomotion, i.e. rhythmic variations in the blood flow, were present and showed a frequency of 5–6 cycles · min^–1. Application of a tourniquet to the upper arm caused an arrest of the microcirculation in the distally situated brachioradial muscle which was followed by a postischaemic hyperaemia upon removal of the torniquet. In ten healthy men, regression analyses showed positive correlation between rms-EMG and shoulder torque (r=0.77), negative correlation between MPF and arm elevation angle (r= –0.89) indicating accumulated fatigue, and almost positive correlations between LDF and rms-EMG (r=0.65), and between LDF and shoulder angle (r=0.67) when the right trapezius muscle was examined.     

Residual effects of prior exercise and recovery on subsequent exercise-induced metabolic responses

Abstract Data on the metabolic responses to repeated endurance exercise sessions are limited. Thus, the aims of this study were to examine (1) the impact of prior exercise on metabolic responses to a subsequent exercise session and (2) the effect of different recovery periods between two daily exercise sessions on metabolic responses to the second bout of exercise. Nine male elite athletes participated in four 25-h trials: one bout of exercise (ONE), two bouts of exercise separated by 3 h of rest and one meal (SHORT), two bouts of exercise separated by 6 h of rest and two meals (LONG), and a trial with no exercise (REST). All exercise bouts consisted of 10 min cycling at 50% followed by 65 min at 75% of maximal O₂ uptake. Compared to no prior exercise (ONE), a previous bout of exercise (SHORT) was followed by higher mean O₂ uptake, heart rate (HR), rectal temperature (T_R), excess post-exercise oxygen consumption and lower respiratory exchange ratio (R) during and after a similar exercise session 3 h later. A longer rest interval between the two exercise bouts (6 h versus 3 h) and an additional meal resulted in a decrease in O₂ uptake, HR, T_R and an increase in R during the second bout of exercise, but no effects on post-exercise metabolism were found. Thus, augmented metabolic stress was observed when strenuous exercise was repeated after only 3 h of recovery, but this was attenuated when a longer recovery period including an additional meal was provided between the exercise sessions.     

Effects of blood-volume distribution on the characteristics of the carotid baroreflex in humans at rest and during exercise

Seven supine subjects were studied at rest and during mild to moderate dynamic leg exercise with and without unloading of the cardiopulmonary baroreceptors accomplished by exposing the lower portion of the body to a subatmospheric pressure of 20 mmHg (Lower Body Negative Pressure, LBNP). The function of the cardiac branch of the carotid baroreflex was studied over its full operational range by measuring R-R intervals during application of pulse synchronous graded pressures (40 to – 65 mmHg) in a neck-chamber device. Raising the carotid transmural pressure (systolic arterial pressure minus neck-chamber pressure) induced increasing R-R intervals in all conditions. In conformity with previous results from our laboratories it was found that the maximal rate of change in relative R-R intervals and the corresponding transmural pressure were higher during exercise than at rest, indicating that exercise increased the carotid baroreflex sensitivity and shifted its optimal buffering range to higher arterial pressures. LBNP did not affect the characteristics of the reflex at rest nor during exercise. It is concluded that reduced central venous pressure with consequent selective cardiopulmonary receptor disengagement exerts no influence on the carotid baroreflex control of heart rate (HR), as tested over the entire arterial pressure-effector response relation, either at rest or during mild-moderate exercise.     

Continuous blood pressure measurement by using the pulse transit time: comparison to a cuff-based method

Pulse transit time (PTT) and pulse wave velocity (PWV), respectively, were shown to have a correlation with systolic blood pressure (SBP) and have been reported to be suitable for indirect BP measurements. The aim of this study was to create a function between SBP and PWV, and to test its reliability for the determination of absolute SBP using a non-linear algorithm and a one-point calibration. 63 volunteers performed exercise to induce rises in BP. Arterial PTT was measured between the R-spike of the ECG and the plethysmographic curve of finger pulse-oximetry. The reference BP was measured using a cuff-based sphygmomanometric aneroid device. Data from 13 of the 63 volunteers served for the detection of the PWV–BP relationship. The created non-linear function was used to calculate BP values after individual correction for the BP offset in a group of 50 volunteers. Individual correlation coefficients for SBP measured by PTT (SBP_PTT) and by cuff (SBP_CUFF) varied between r = 0.69 and r = 0.99. Taking all data together, we found r = 0.83 (276 measurements in 50 volunteers). In the Bland–Altman plot, the limits of agreement were \textmean_{\textSBP\textPTT , \textSBP\textCUFF} {\text{mean}}_{{{\text{SBP}}_{\text{PTT}} , {\text{SBP}}_{\text{CUFF}} }} ± 19.8 mmHg. In conclusion, comparing SBP values using the PTT-based method and those measured by cuff resulted in a significant correlation. However, the Bland–Altman plot shows relevant differences between both methods, which are partly due to greater variability of the SBP_PTT measurement during intensified exercise. Results suggest that PTT can be used for measuring absolute SBP when performing an individual correction for the offset of the BP–PWV relation.     

Norepinephrine and epinephrine responses during orthostatic intolerance in healthy elderly men

In young individuals, orthostatic intolerance is associated with marked increases in plasma epinephrine (EPI) concentrations and attenuated rises in plasma norepinephrine (NE) concentrations. This study investigated the cardiovascular, EPI and NE responses of healthy elderly males during orthostatic stress. Twelve men (68 +/- 1 yr) with a recent history of orthostatic hypotension and who exhibited orthostatic intolerance (HYPO) during 90 degrees head-up tilt (HUT) were compared with 12 men (69 +/- 1 yr) without a history of orthostatic hypotension and who remained normotensive (NORMO) throughout 90 degrees HUT. Beat-by-beat recordings of heart rate (HR), mean (MAP), systolic (SBP), diastolic (DBP), and pulse (PP) pressures were made throughout 90 degrees HUT. Blood samples obtained during supine rest and 90 degrees HUT were analyzed for changes in EPI and NE concentrations, hematocrit, hemoglobin and plasma volume. Compared to supine rest, orthostatic intolerance was characterized by significant reductions (p < 0.0001) in MAP, SBP, DBP, and PP. The HR, MAP, SBP, DBP, and PP at the termination of 90 degrees HUT was significantly lower (p < 0.0001) for HYPO than NORMO. The 90 degrees HUT position resulted in significant increases (p < 0.01) in NE for both HYPO and NORMO, with the rise in NE significantly lower (p < 0.05) in HYPO. There were no differences between groups regarding EPI concentrations at the termination of 90 degrees HUT. These results suggest that the magnitude of arterial pressure (AP) reduction does not influence the EPI response during orthostasis in healthy elderly men. However, marked reductions in AP, leading to orthostatic intolerance, are associated with inadequate increases in NE in these individuals.     

Intracortical remodelling increases in highly loaded bone after exercise cessation

Resorption within cortices of long bones removes excess mass and damaged tissue and increases during periods of reduced mechanical loading. Returning to high-intensity exercise may place bones at risk of failure due to increased porosity caused by bone resorption. We used point-projection X-ray microscopy images of bone slices from highly loaded (metacarpal, tibia) and minimally loaded (rib) bones from 12 racehorses, 6 that died during a period of high-intensity exercise and 6 that had a period of intense exercise followed by at least 35 days of rest prior to death, and measured intracortical canal cross-sectional area (Ca.Ar) and number (N.Ca) to infer remodelling activity across sites and exercise groups. Large canals that are the consequence of bone resorption (Ca.Ar >0.04 mm²) were 1.4× to 18.7× greater in number and area in the third metacarpal bone from rested than exercised animals (p = 0.005–0.008), but were similar in number and area in ribs from rested and exercised animals (p = 0.575–0.688). An intermediate relationship was present in the tibia, and when large canals and smaller canals that result from partial bony infilling (Ca.Ar >0.002 mm²) were considered together. The mechanostat may override targeted remodelling during periods of high mechanical load by enhancing bone formation, reducing resorption and suppressing turnover. Both systems may work synergistically in rest periods to remove excess and damaged tissue.