Supine Bicycle Research Articles

Exercise hemodynamics in Parkinson's disease and autonomic dysfunction

AimTo clarify the characteristics of hemodynamic responses to exercise and orthostasis in Parkinson's disease patients, especially those with autonomic failure. MethodsClinical audit of supine cycling exercise test data (with active standing tests pre- and post-exercise) of Parkinson's patients with autonomic dysfunction. 23 patients (71 ± 7 yr, 7 females) with a confirmed diagnosis of Parkinson's were identified. ResultsGroup mean systolic blood pressure (SBP) fell during pre-exercise standing (−39 ± 29 mmHg, P < 0.001, 17 patients had orthostatic hypotension (OH)), while heart rate (HR) increased (+13 ± 7 beats min−1, P < 0.001). SBP (P < 0.001) increased during exercise with a wide variation in responses. SBP increased in 13 patients (INC; +30 ± 14 mmHg) and either did not change or decreased in 10 patients (DEC −12 ± 11 mmHg, P < 0.001 vs INC). The increase in HR was not different between sub-groups (30 ± 12 vs 25 ± 10 beats min−1, INC vs. DEC, P = 0.29). The size of the pre-exercise stand SBP reduction was greater in DEC vs INC (−64 ± 23 (10 out of 10 had OH) vs −19 ± 16 mmHg (7 out of 13 had OH), respectively, P < 0.001). The HR elevation was not different between sub-groups (13 ± 8 vs 13 ± 4 beats min−1, DEC vs INC, P = 0.94). Post-exercise SBP/DBP were lower for both sub-groups compared to pre-exercise and the standing SBP reduction post-exercise was not greater relative to pre-exercise in either sub-group. ConclusionExercise-induced hypotension can occur in Parkinson's disease patients with autonomic failure with the magnitude of the exercise response being related to the severity of autonomic dysfunction. Exercise does not appear to worsen OH in this sample of Parkinson's patients.

Abstract 19010: Exercise but Not Pacing Affects Coronary-Cardiac Interaction via Reflected Waves From the Aorta

Background: Not only the interaction with cardiac mechanics, but also the systemic circulation determines coronary hemodynamic waveforms. Coronary wave intensity can distinguish between forward (FW) waves entering from the aorta and backward (BW) waves originating from the microcirculation. The aim of this study was to assess contributions of the systemic circulation to cardiac-coronary interaction by comparing exercise, having a profound influence on the systemic circulation, with right atrial pacing where the systemic circulation is minimally affected. Methods: During cardiac catheterization we recorded aortic pressure (Pa), distal coronary pressure (Pd) and flow velocity (U) in diseased coronary arteries. In 10 subjects heart rate (HR) was increased by right atrial pacing at 120 bpm. 11 other patients exercised using a supine cycle ergometer at increasing workload. Net wave intensity was computed as dI= (dPd/dt)(dU/dt) and the energy of the FW and BW waves was derived by the areas under the curve. Results: Resting values of systemic and coronary hemodynamic were similar in both groups, with HR = 73 ±4 bpm, Pa = 104 ±5 mmHg, Pd = 85 ±10 mmHg and U = 16.2 ±2.1 cm/s. Exercise increased HR to 108 ±7 bpm which did not differ from that during pacing. Pa and Pd increased with exercise by 20 mmHg and 8 mmHg, resp. (p&lt;0.05), whilst pacing raised Pa by only 5 mmHg (p&lt;0.05) at unchanged Pd. U similarly increased to 23.1±3.0 cm/s by pacing and exercise. Coronary wave energy at rest was the same for both groups. The BW compression wave more than doubled with both pacing and exercise, while the early FW compression wave was unchanged by exercise and much reduced by pacing from 1.9 ± 0.6 to 0.3±0.1 Jm -2 s -2 (p&lt;0.05). The FW expansion wave at the onset of relaxation increased from 1.6±0.5 to 3.5±1.0 Jm -2 s -2 (p&lt;0.05) with exercise but was not altered by pacing. The BW expansion wave that drives diastolic coronary flow more than doubled with exercise, but only increased by 63% with pacing. Conclusion: Exercise more profoundly affects cardiac-coronary interaction than pacing and improves the energy of FW and BW waves during cardiac relaxation. This is likely due to increased contractility, assisted by added reflection from the systemic circulation that enters the coronary arteries via the aorta.

Supine Cycling in Pediatric Exercise Testing: Disparity in Performance Measures

Supine cycling may be an important alternative modality for exercise testing. Subtle differences in supine and upright exercise physiology have been suggested but not fully explored in the pediatric population. The aim of this study was to compare peak and submaximal metabolic data in the upright and supine exercise positions. Healthy children (N = 100) performed cardiopulmonary exercise tests using supine and upright cycle ergometry. Recruitment was governed by grant funding and not based on sample size calculations. Subjects exercised to exhaustion. Paired Student's t-tests were used to compare upright and supine data; simple linear regression analyses examined correlations between the two modalities. Peak heart rate was similar in both testing positions. Although peak oxygen uptake (peak VO2), oxygen uptake at anaerobic threshold (VO2@AT), VO2 when the respiratory exchange ratio is consistently at or above 1.0 (VO2@RER1.0), and the oxygen uptake efficiency slope were significantly higher in the upright position, no difference was considered of practical significance when applying Cohen's effect size criteria. Therefore, it may be reasonable for pediatric exercise laboratories to use established normative data and predictions for upright cycling position and apply them to metabolic measures obtained in supine exercise testing. Supine cycling with submaximal parameters may allow objective assessment of exercise capacity in children who undergo exercise echocardiography or cannot perform upright exercise testing.

Dynamic cerebral autoregulation after bed rest: effects of volume loading and exercise countermeasures

This study assessed effects of head-down-tilt (HDT) bed rest on dynamic cerebral autoregulation (CA) in 21 healthy young adults with volume loading and exercise countermeasures. Of these, seven underwent an 18-day bed rest without exercise countermeasures (sedentary group). Volume loading with dextran infusion was performed after bed rest to restore reduced plasma volume to levels before bed rest. In the other 14 subjects, supine cycling during bed rest was performed to preserve cardiac work from before bed rest (exercise group). Volume loading was also performed in a subgroup of these subjects (Ex+Dex, n = 7). Dynamic CA was estimated by transfer function analysis of changes in arterial pressure and cerebral blood flow (CBF) velocity in the very low (VLF, 0.02-0.07 Hz), low (LF, 0.07-0.20 Hz), and high frequency ranges (HF, 0.20-0.35 Hz). After bed rest, transfer function gain was reduced in the sedentary group (VLF, 0.93 ± 0.23 to 0.61 ± 0.23 cm(-1)·s(-1)·mmHg; P = 0.007) and in the exercise group (LF, 1.22 ± 0.43 to 0.94 ± 0.26 cm(-1)·s(-1)·mmHg; P = 0.005, HF, 1.32 ± 0.55 to 1.00 ± 0.32 cm(-1)·s(-1)·mmHg; P = 0.010). After volume loading, transfer function gain increased in the sedentary group but not in the Ex+Dex group. Taken together, these findings suggest that dynamic CA was preserved or improved after HDT bed rest in both sedentary and exercise subjects. Furthermore, increases of transfer function gain with volume loading suggest that changes in plasma volume may play an important role in CBF regulation.

Exercise Central (Aortic) Blood Pressure Is Predominantly Driven by Forward Traveling Waves, Not Wave Reflection

Exercise hypertension independently predicts cardiovascular mortality, although little is known about exercise central hemodynamics. This study aimed to determine the contribution of arterial wave travel and aortic reservoir characteristics to central blood pressure (BP) during exercise. We hypothesized that exercise central BP would be principally related to forward wave travel and aortic reservoir function. After routine diagnostic coronary angiography, invasive pressure and flow velocity were recorded in the ascending aorta via sensor-tipped intra-arterial wires in 10 participants (age, 55±10 years; 70% men) free of coronary artery disease with normal left ventricular function. Measures were recorded at baseline and during supine cycle ergometry. Using wave intensity analysis, dominant wave types throughout the cardiac cycle were identified (forward and backward, compression, and decompression), and aortic reservoir and excess pressure were calculated. Central systolic BP increased significantly with exercise (Δ=19±12 mm Hg; P<0.001). This was associated with increases in systolic forward compression waves (Δ=12×10(6)±17×10(6) W·m(-2)·s(-1); P=0.045) and forward decompression waves in late systole (Δ=9×10(6)±6×10(6) W·m(-2)·s(-1); P<0.001). Despite significant augmentation in BP (Δ=9±6 mm Hg; P=0.002), reflected waves did not increase in magnitude (Δ=-1×10(6)±3×10(6) W·m(-2)·s(-1); P=0.2). Excess pressure rose significantly with exercise (Δ=16±9 mm Hg; P<0.001), and reservoir pressure integral fell (Δ=-5×10(5)±5×10(5) Pa·s; P=0.010). Change in reflection coefficient negatively correlated with change in central systolic BP (r=-0.68; P=0.03). We conclude that elevation of exercise central BP is principally because of increases in aortic forward traveling waves generated by left ventricular ejection. These findings have relevance to understanding central BP waveform morphology and pathophysiology of exercise hypertension.

Exercise-induced changes in left ventricular filling pressure after myocardial infarction assessed with simultaneous right heart catheterization and Doppler echocardiography

To assess whether changes in E/e´ (the ratio between peak early mitral inflow velocity (E) and peak early mitral annulus velocity (e´)) during exercise reflect changes in filling pressure in patients with a recent myocardial infarction (MI) and mild to moderate diastolic dysfunction at rest. A low E/e´ ratio is associated with low filling pressures while a high E/e´ ratio is associated with high filling pressures. In the intermediate range of E/e´ guidelines suggest additional measurements during exercise in order to determine filling pressures. Sixty-one patients with a recent MI and left ventricular ejection fraction (LVEF) ≥ 45%, left atrium (LA)>34 ml/m(2) and E/e´ between 8 and 15, underwent simultaneous right heart catheterization and Doppler echocardiography during a symptom limited semi supine cycle exercise test. E velocity increased from 75 ± 16 to 139 ± 27 cm/s and e´ increased from 7.1 ± 1.4 to 16.1 ± 3.6 cm/s with exercise. Thus, E/e´ decreased from 10.5 ± 1.7 to 9.3 ± 2.3 while pulmonary capillary wedge pressure (PCWP) increased from 13 ± 4 to 33 ± 8 mmHg. There was no correlation between LV filling pressure and E/e´ at rest, at 4 METS, at peak exercise or 5 min after termination of exercise. Neither was there any correlation between changes in PCWP and changes in E/e´. For post-MI patients with resting E/e´ in the intermediate range changes in E/e´ with physical exercise does not reflect changes in LV filling pressures.

Athlete's heart: adaptations in blood flow, oxygen utilization, and efficiency at rest and during exercise

We investigated here the characteristics of athlete's heart by applying [15O]‐labelled radiotracers and positron emission tomography. We measured myocardial blood flow (MBF), oxygen extraction fraction (OEF) and consumption (MVO2), and efficiency in 13 highly trained male endurance athletes (30 ± 5 yrs) and 13 untrained males (30 ± 5 yrs) at rest and during supine cycling exercise (100 watts). Echocardiography was also performed at rest and during exercise and the radial artery was cannulated for measurements of 2,3‐Diphosphoglycerate (DPG) and oxygen content. Many of the athletes had participated in Olympics and various world cups in running, XC‐skiing, cycling and walking, while untrained subjects did not exercise regularly. MBF was lower in athletes both at rest and during exercise. Arterial DPG was unchanged, but OEF increased in response to exercise in both groups, being higher in athletes both at rest (70 ± 21 vs. 63 ± 11 %) and during exercise (86 ± 13 vs. 73 ± 10 %). MVO2 per gram of myocardium trended (p=0.08) lower in athletes both at rest and during exercise. Myocardial efficiency was similar between the groups, although it trended higher in controls and lower in athletes in response to exercise. In conclusion, elite endurance athletes have lower than normal myocardial blood flow, higher oxygen extraction, and their cardiac oxygen consumption per gram of tissue trends lower both at rest and during exercise.

Safety and feasibility of femoral catheters during physical rehabilitation in the intensive care unit

ObjectiveFemoral catheters pose a potential barrier to early rehabilitation in the intensive care unit (ICU) due to concerns, such as catheter removal, local trauma, bleeding, and infection. We prospectively evaluated the feasibility and safety of physical therapy (PT) in ICU patients with femoral catheters. Design, Setting, and PatientsWe evaluated consecutive medical ICU patients who received PT with a femoral venous, arterial, or hemodialysis catheter(s) in situ. Measurements and Main ResultsOf 1074 consecutive patients, 239 (22%) received a femoral catheter (81% venous, 29% arterial, 6% hemodialysis; some patients had >1 catheter). Of those, 101 (42%) received PT interventions, while the catheter was in situ, for a total of 253 sessions over 210 medical ICU (MICU) days. On these 210 MICU days, the highest daily activity level achieved was 49 (23%) standing or walking, 57 (27%) sitting, 25 (12%) supine cycle ergometry, and 79 (38%) in-bed exercises. During 253 PT sessions, there were no catheter-related adverse events giving a 0% event rate (95% upper confidence limit of 2.1% for venous catheters). ConclusionsPhysical therapy interventions in MICU patients with in situ femoral catheters appear to be feasible and safe. The presence of a femoral catheter should not automatically restrict ICU patients to bed rest.

Sildenafil and Diastolic Dysfunction After Acute Myocardial Infarction Trial: Rationale and Design

Diastolic dysfunction following myocardial infarction is an important predictor of outcome, irrespective of left ventricular systolic function. Previous studies suggest that phosphordiesterase-5 inhibition has a favorable effect on the myocardium as well as on the pulmonary and systemic vasculature. Patients≥50 years old with recent myocardial infarction, preserved left ventricular ejection fraction (≥45%), and echocardiographic evidence of diastolic dysfunction (ratio between early [E] transmitral filling velocity and early diastolic tissue Doppler velocity [e']≥8 and left atrial volume≥34 mL/m2) will be double-blindly randomized 1:1 to receive 9 weeks of treatment with 40 mg sildenafil, 3 times per day, or comparable placebo. Before randomization and after 9 weeks of treatment, resting Doppler echocardiography, resting right heart catheterization, and symptom-limited supine cycle exercise testing with simultaneous echocardiography and right heart catheterization will be performed. The primary end point is filling pressure at rest and at peak exercise. With a power of 80% and a significance level of .05, a study group of 60 patients is needed to detect a 15% reduction at peak exercise, which is considered clinically relevant. To account for dropouts and noncompliance, 70 patients will be enrolled in the study. In addition to determining if sildenafil can reduce filling pressure at rest and at peak exercise, the Sildenafil and Diastolic Dysfunction After Acute Myocardial Infarction trial will provide additional hemodynamic information to help phenotypically classify this growing population of patients with diastolic dysfunction and preserved ejection fraction following myocardial infarction.

Quantification of thoracic aorta blood flow by magnetic resonance imaging during supine cycling exercise of increasing intensity

Background Cardiac magnetic resonance imaging (MRI) may be used for the diagnosis and follow-up of diseases affecting the thoracic aorta (TA). Typically, patients are imaged at rest. Quantifying TA blood flow distribution during activity may improve understanding of disease impact by assessing possible factors contributing to exercise intolerance. Blood flow quantification during exercise MRI, though, has heretofore been complicated by prolonged MRI scan times, motion artifact, and gradient field inhomogeneities. We developed a protocol for phase-contrast (PC) MRI flow quantification in the TA and head and neck arteries during three-tiered supine cycling submaximal exercise. Methods PC-MRI was acquired in the ascending aorta (AAo) and innominate (IA), left common carotid (LCCA), and left subclavian (LSA) arteries using a 1.5T Siemens MAGNETOM ® Symphony magnet. Six healthy volunteers (28±2 years) were imaged during rest and supine pedaling of an MRI-compatible cycle to reach 130%, 150%, and 170% of resting heart rate (HR130 ,H R150 ,H R170). Scan parameters balanced image quality with acquisition time, accounting for subject positioning in the magnet and motion from pedaling. Time-resolved volumetric blood flow was calculated from PC-MRI data and estimated in the descending aorta (dAo). Flow quantification included cardiac index from AAo flow, arterial normalized mean flow (NMF,L/min/m 2 ) and flow distribution (FD,% of AAo flow). Significance of flow quantification between HRs and rest was tested post-hoc with Student’s t-test. Results Cardiac index increased linearly (r 2 =0.99) from 3.1±0.3 to 5.2±0.3 L/min/m 2 from rest to HR170 (p<0.05). HR increased to 111±5.9 bpm and workload to 38±9 watts at HR170. In the dAo, NMF increased linearly with respect to HR (r 2 =0.99) by 46%, 72%, and 93% with significance at all levels (Table 1). The IA showed significant increase in NMF of 39% at HR170 compared to rest. Increases in NMF

Synergistic Adaptations to Exercise in the Systemic and Coronary Circulations That Underlie the Warm-Up Angina Phenomenon

The mechanisms of reduced angina on second exertion in patients with coronary arterial disease, also known as the warm-up angina phenomenon, are poorly understood. Adaptations within the coronary and systemic circulations have been suggested but never demonstrated in vivo. In this study we measured central and coronary hemodynamics during serial exercise. Sixteen patients (15 male, 61±4.3 years) with a positive exercise ECG and exertional angina completed the protocol. During cardiac catheterization via radial access, they performed 2 consecutive exertions (Ex1, Ex2) using a supine cycle ergometer. Throughout exertions, distal coronary pressure and flow velocity were recorded in the culprit vessel using a dual sensor wire while central aortic pressure was recorded using a second wire. Patients achieved a similar workload in Ex2 but with less ischemia than in Ex1 (P<0.01). A 33% decline in aortic pressure augmentation in Ex2 (P<0.0001) coincided with a reduction in tension time index, a major determinant of left ventricular afterload (P<0.001). Coronary stenosis resistance was unchanged. A sustained reduction in coronary microvascular resistance resulted in augmented coronary flow velocity on second exertion (both P<0.001). These changes were accompanied by a 21% increase in the energy of the early diastolic coronary backward-traveling expansion, or suction, wave on second exercise (P<0.05), indicating improved microvascular conductance and enhanced left ventricular relaxation. On repeat exercise in patients with effort angina, synergistic changes in the systemic and coronary circulations combine to improve vascular-ventricular coupling and enhance myocardial perfusion, thereby potentially contributing to the warm-up angina phenomenon.

Brachial Artery Flow-mediated Dilation Following Exercise with Augmented Oscillatory and Retrograde Shear Rate

BackgroundAcute doses of elevated retrograde shear rate (SR) appear to be detrimental to endothelial function in resting humans. However, retrograde shear increases during moderate intensity exercise which also enhances post-exercise endothelial function. Since SR patterns differ with the modality of exercise, it is important to determine if augmented retrograde SR during exercise influences post-exercise endothelial function. This study tested the hypothesis that (1) increased doses of retrograde SR in the brachial artery during lower body supine cycle ergometer exercise would attenuate post-exercise flow-mediated dilation (FMD) in a dose-dependent manner, and (2) antioxidant vitamin C supplementation would prevent the attenuated post-exercise FMD response.MethodsTwelve men participated in four randomized exercise sessions (90 W for 20 minutes) on separate days. During three of the sessions, one arm was subjected to increased oscillatory and retrograde SR using three different forearm cuff pressures (20, 40, 60 mmHg) (contralateral arm served as the control) and subjects ingested placebo capsules prior to exercise. A fourth session with 60 mmHg cuff pressure was performed with 1 g of vitamin C ingested prior to the session.ResultsPost-exercise FMD following the placebo conditions were lower in the cuffed arm versus the control arm (arm main effect: P < 0.05) and without differences between cuff pressures (20 mmHg: 5.7 ± 2.2%; 40 mmHg: 4.7 ± 1.3%; 60 mmHg: 5.4 ± 2.4%) (P > 0.05). Following vitamin C treatment, post-exercise FMD in the cuffed and control arm increased from baseline (P < 0.05) but were not different (control: 7.1 ± 3.5% vs. cuffed: 6.6 ± 3.3%) (P > 0.05).ConclusionsThese results indicate that augmented oscillatory and retrograde SR in non-working limbs during lower body exercise attenuates post-exercise FMD without an evident dose–response in the range of cuff pressures evaluated. Vitamin C supplementation prevented the attenuation of FMD following exercise with augmented oscillatory and retrograde SR suggesting that oxidative stress contributes to the adverse effects of oscillatory and retrograde shear during exercise on FMD.

Exercise Hemodynamics in Patients With and Without Diastolic Dysfunction and Preserved Ejection Fraction After Myocardial Infarction

Left ventricular diastolic dysfunction (DD) is common after myocardial infarction (MI) despite preservation of left ventricular ejection fraction, yet it remains unclear how or whether DD affects cardiac hemodynamics with stress. Invasive hemodynamic exercise testing was performed in 46 patients with a recent MI and left ventricular ejection fraction >45% and in 10 healthy volunteers. MI patients were enrolled prospectively and divided into those with DD (MI+DD; left atrial volume index >34 mL/m(2) and diastolic E/e' ratio>8; n=35) and those without DD (MI-DD; left atrial volume index <34 mL/m(2) and E/e' ratio<8; n=11). All underwent a supine cycle ergometer test with simultaneous right heart catheterization and echocardiography. At rest, 10 patients in MI+DD (29%) had pulmonary capillary wedge pressure >15 (14±4 mm Hg), whereas none of the MI-DD (10±2 mm Hg) or controls (9±2 mm Hg) displayed pulmonary capillary wedge pressure elevation (P=0.03). During exercise, an abnormal rise in pulmonary capillary wedge pressure (>25 mm Hg) was observed in 94% of MI+DD (36±6 mm Hg) compared with 36% of MI-DD (24±6 mm Hg) and none of the controls (16±6 mm Hg; P<0.0001). Exercise right atrial pressure was the highest in MI+DD followed by MI-DD and control (15±5 versus 9±4 versus 7±5 mm Hg; P<0.001), whereas no difference in cardiac index was found between groups. In post-MI patients with preserved ejection fraction and left ventricular DD, cardiac output with exercise is maintained at the expense of substantially increased filling pressure. DD and loss of diastolic reserve may promote progression from stage B to stage C heart failure after MI.

Supine Exercise Echocardiographic Measures of Systolic and Diastolic Function in Children

Echocardiography has been used to determine ventricular function, segmental wall motion abnormality, and pulmonary artery pressure before and after peak exercise. No prior study has investigated systolic and diastolic function using echocardiography at various phases of exercise in children. The aim of this study was to determine the fractional shortening (FS), systolic-to-diastolic (S/D) ratio, heart rate-corrected velocity of circumferential fiber shortening (VCFc), circumferential wall stress (WS), ratio of mitral passive inflow to active inflow (E/A), ratio of passive inflow by pulsed-wave to tissue Doppler (E/E'), and right ventricular-to-right atrial pressure gradient from tricuspid valve regurgitation jet velocity (RVP) and time duration at various phases of exercise in children. In an 8-month period (December 2007 to July 2008), 100 healthy children were evaluated, and 97 participants aged 8 to 17 years who performed complete cardiopulmonary exercise stress tests using supine cycle ergometry were prospectively enrolled. The participants consisted of 48 female and 49 male subjects with various body sizes, levels of exercise experience, and physical capacities. The cardiopulmonary exercise stress test consisted of baseline pulmonary function testing, continuous gas analysis and monitoring of blood pressure and heart rate responses, electrocardiographic recordings, and oxygen saturation measurement among participants who pedaled against a ramp protocol based on body weight. All participants exercised to exhaustion. Echocardiography was performed during exercise at baseline, at a heart rate of 130 beats/min, at a heart rate of 160 beats/min, at 5 min after exercise, and at 10 min after exercise. FS, S/D ratio, VCFc, WS, E/A, E', E/E', and RVP at these five phases were compared in all subjects. All echocardiographic parameters differed at baseline from 160 beats/min (P < .0001) except E/E', which remained at 5.4 to 5.8. Specifically, FS (from 37% to 46%), S/D ratio, VCFc (from 1.1 to 1.6), WS (from 200 to 258 g/cm(2)), E' (from 0.2 to 0.3), and RVP (from 18 to 35 mm Hg) increased from baseline to 160 beats/min and then subsequently decreased to at or near baseline, while tricuspid valve regurgitation duration decreased (from 370 to 178 msec). Normal values for systolic and diastolic echocardiographic measurements of function are now available. FS, VCFc, WS, and RVP increase with exercise and then return to near baseline levels. The E/E' ratio is unaltered with exercise in normal subjects.

ENOS and nNOS contribution to reflex cutaneous vasodilation during dynamic exercise in humans

Recent data suggests nNOS mediates NO‐component of reflex cutaneous vasodilation with passive heat stress. Our hypothesis was nNOS but not eNOS inhibition would attenuate reflex cutaneous vasodilation during dynamic exercise. Protocol 1: subjects performed a VO2 peak test on a supine cycle ergometer. Protocol 2: with experimental arm at heart level subjects cycled in supine posture at 60% VO2 peak to raise core temperature (Tc) 0.8–1.0°C (35–45 min). In protocol 2 subjects were equipped with 4 microdialysis fibers on the forearm and each randomly assigned as: 1) lactated Ringer's (control); 2) 5mM NPLA (nNOS inhibition); 3) 10mM L‐NIO (eNOS inhibition); and 4) 20mM L‐NAME (non‐selective NOS inhibition). At the end of protocol 2 all sites were locally heated to 43°C and infused with SNP to elicit maximal dilation. Mean arterial pressure (MAP), skin blood flow via laser‐Doppler flowmetry (LDF), and Tc via ingestible telemetric pill were measured; cutaneous vascular conductance (CVC) was calculated as LDF/MAP and normalized to maximum. In protocol 2 there was no significant difference between control (62±5 %CVCmax) and NPLA (61±6 %CVCmax). L‐NIO (38±4 %CVCmax) and L‐NAME (41±7 %CVCmax) significantly attenuated CVC compared to control and NPLA (p&lt;0.001 all conditions). There was no difference between L‐NIO and L‐NAME. We conclude eNOS, not nNOS, contribute to reflex cutaneous vasodilation during dynamic exercise.

The use of feature tracking to assess ventricular strain during exercise stress CMR

Background Exercise stress testing is the most physiological method of inducing myocardial stress, but its application to clinical and scientific CMR has been limited because of problems arising from cardiac and respiratory motion during stress. Under pharmacological stress, left ventricular strain measurement abnormalities by CMR have been demonstrated to be earlier and more sensitive markers of contractile dysfunction than global left ventricular ejection fraction or development of regional wall motion abnormalities alone. There are several validated methods of measuring myocardial strain. A recently proposed method is feature tracking (FT), which has advantages over other methods in having shorter acquisition and analysis times and not requiring additional scanning as the features are tracked from the clinically standard cine steady-state free precession (SSFP) sequences. This offers a potential method to assess myocardial strain during exercise stress. Methods Seven healthy volunteers without known cardiovascular disease gave informed consent and enrolled for supine cycle ergometry on the CMR scanner table (Lode, Groningen Netherlands). Subjects underwent a standardised incremental exercise protocol. Imaging included a standard short-axis stack of cine SSFP images from the cardiac base to apex, on a 3T Philips Achieva TX ® system using a 32-channel multi-transmit coil. Scan parameters included slice thickness of 10mm, repetition/echo time of 2.4/1.21ms, flip angle 40°, 9-11 slices, with 20 phases per slice. For this study, only the mid LV-slice was analysed. Diogenes CMR FT software (TomTec Imaging Systems, Munich, Germany) was used for strain analysis. This was based on contours manually drawn along the LV endocardial border of one frame, with the software automatically propagating the contour and following its features throughout the remainder of the imaged phases. Software-derived parameters include circumferential epicardial and endocardial, longitudinal, and radial tissue velocity, strain, strain rate and time to peak strain.

Early rehabilitation in critical care (eRiCC): functional electrical stimulation with cycling protocol for a randomised controlled trial

IntroductionIntensive care-acquired weakness is a common problem, leads to significant impairment in physical functioning and muscle strength, and is prevalent in individuals with sepsis. Early rehabilitation has been shown to...

Exercise plus volume loading prevents orthostatic intolerance but not reduction in cerebral blood flow velocity after bed rest

This study tested the hypothesis that reduction in cerebral blood flow (CBF) during orthostatic stress after bed rest can be ameliorated with volume loading, exercise, or both. Transcranial Doppler was used to measure changes in CBF velocity during lower body negative pressure (LBNP) before and after an 18-day bed rest in 33 healthy subjects. Subjects were assigned into four groups with similar age and sex: 1) supine cycling during bed rest (Exercise group; n = 7), 2) volume loading with Dextran infusion after bed rest to restore reduced left ventricular filling pressure (Dextran group; n = 7), 3) exercise combined with volume loading to prevent orthostatic intolerance (Ex-Dex group; n = 7), and 4) a control group (n = 12). LBNP tolerance was measured using a cumulative stress index (CSI). After bed rest, CBF velocity was reduced at a lower level of LBNP in the Control group, and the magnitude of reduction was greater in the Ex-Dex group. However, reduction in orthostatic tolerance was prevented in the Ex-Dex group. Notably, volume loading alone prevented greater reductions in CBF velocity after bed rest, but CSI was reduced still by 25%. Finally, decreases in CBF velocity during LBNP were correlated with reduction in cardiac output under all conditions (r(2) = 0.86; P = < 0.001). Taken together, these findings demonstrate that volume loading alone can ameliorate reductions in CBF during LBNP. However, the lack of associations between changes in CBF velocity and orthostatic tolerance suggests that reductions in CBF during LBNP under steady-state conditions by itself are unlikely to be a primary factor leading to orthostatic intolerance.

41 Reduced arterial wave reflection and enhanced LV relaxation contribute to warm-up angina

BackgroundThe mechanisms of the clinically observed phenomenon of reduced angina on second exertion, or warm-up angina, are poorly understood. This study compared changes in central haemodynamics, peripheral wave reflection and...

Left ventricular mechanical limitations to stroke volume in healthy humans during incremental exercise

During incremental exercise, stroke volume (SV) plateaus at 40-50% of maximal exercise capacity. In healthy individuals, left ventricular (LV) twist and untwisting ("LV twist mechanics") contribute to the generation of SV at rest, but whether the plateau in SV during incremental exercise is related to a blunting in LV twist mechanics remains unknown. To test this hypothesis, nine healthy young males performed continuous and discontinuous incremental supine cycling exercise up to 90% peak power in a randomized order. During both exercise protocols, end-diastolic volume (EDV), end-systolic volume (ESV), and SV reached a plateau at submaximal exercise intensities while heart rate increased continuously. Similar to LV volumes, two-dimensional speckle tracking-derived LV twist and untwisting velocity increased gradually from rest (all P < 0.001) and then leveled off at submaximal intensities. During continuous exercise, LV twist mechanics were linearly related to ESV, SV, heart rate, and cardiac output (all P < 0.01) while the relationship with EDV was exponential. In diastole, the increase in apical untwisting was significantly larger than that of basal untwisting (P < 0.01), emphasizing the importance of dynamic apical function. In conclusion, during incremental exercise, the plateau in LV twist mechanics and their close relationship with SV and cardiac output indicate a mechanical limitation in maximizing LV output during high exercise intensities. However, LV twist mechanics do not appear to be the sole factor limiting LV output, since EDV reaches its maximum before the plateau in LV twist mechanics, suggesting additional limitations in diastolic filling to the heart.