Maximal Stroke Volume Research Articles

Heavy cycling exercise at fixed heart rate prevent the decline of stroke volume and delay time to exhaustion in trained adolescents

Summary Previous studies showed an interaction between the response over time of oxygen uptake ( V ˙ O 2 ), the drift of heart rate (HR) and the drop of stroke volume (SV) during constant workload exercise. Objective To compare the responses of oxygen uptake ( V ˙ O 2 ) and stroke volume (SV) in exhaustive exercises performed at a constant workload or at heart rate steady state. Methods Nine well-trained adolescents (14.6 ± 1.1 years, 1.7 ± 0.1 m and 59.7 ± 14.8 kg) performed an incremental exercise test on a cycle ergometer to determine the maximal power associated with V ˙ O 2 max ( p V ˙ O 2 max ) and the power inducing SVmax (pSVmax). Two days later, they performed two continuous exercises at pSVmax (tlimpSVmax: 10 min 10 s ± 6 min 41 s) and at a heart rate steady state associated with SVmax (tlimHR@SVmax: 21 min 04 s ± 13 min 20 s, P V ˙ O 2 , HR and SV values were continuously measured by impedance. Results Maximal values of blood lactate and V ˙ O 2 were not different between the three exercises, but maximal cardiac output and SV values were higher in tlimHR@SVmax (21.3 ± 8.6 L·min−1 and 112 ± 46 mL·beat−1) compared to tlimpSVmax (19.8 ± 7.6 L·min−1 and 102 ± 40 mL·beat−1, P V ˙ O 2 values significantly fell before both exercise exhaustions (P Conclusion According to the exercise modalities, the interactive effects of increased HR or SV are responsible of the V ˙ O 2 max attainment during exhaustive exercise.

Usefulness of stroke volume monitoring during upright ramp incremental cycle exercise in young patients with Fontan circulation

BackgroundAerobic capacity (VO2 max) of patients with Fontan circulation (FC) is lowest within patients with congenital heart disease. The reasons have not been completely elucidated. MethodsTwenty five young patients with non-failing FC underwent a cardiopulmonary test during an upright ramp cycling. By using a signal morphology impedance cardiography device (physioflow®), stroke volume (SV) was evaluated along with effort. The results were compared with paired healthy controls. ResultsFC patients had lower VO2 max (24 vs 32ml/Kg/min) and maximal cardiac index (CI) (6.4 vs 9.9l/min/m2) than controls, due to impaired maximal SV (42 vs 54ml/m2) and maximal Heart Rate (HR) (154 vs 184/min) (p<0.001). No correlation between SV and HR at peak was found. At ventilatory threshold, SV continued to rise in a part of FC patients. Other FC patients showed an almost a “plateau” as in controls. The more maximal CI was impaired, the more was maximal arterio-venous difference (r=−0.6, p=0.001). Compared to controls, stroke work was lower in FC patients (p<0.01) even though maximal vascular resistance was higher in them (p<0.001). ConclusionImpaired SV and chronotropic incompetence are both independently responsible for impaired CI at peak. The increase in arteriovenous difference appeared to be an adaptive response. As the stroke work was low among FC patients, high systemic vascular resistance does not appear to be the cause of SV impairment but rather a consequence. SV monitoring at effort evidences heterogeneous SV profiles among FC patients that could be considered for the management of patients.

Comparison of esophageal Doppler and plethysmographic variability index to guide intraoperative fluid therapy for low-risk patients undergoing colorectal surgery

Study objectiveThis study aims to investigate if there is equivalence in volumes of fluid administered when intravenous fluid therapy is guided by Pleth Variability Index (PVI) compared to the established technology of esophageal Doppler in low-risk patients undergoing major colorectal surgery. DesignRandomized controlled trial. SettingOperating room. PatientsForty low-risk patients undergoing elective colorectal surgery. InterventionPatients were monitored by esophageal Doppler and PVI probes and were randomized to have fluid therapy directed by using one of these technologies, with 250 mL boluses of colloid to maintain a maximal stroke volume, or a PVI of less than 14%. MeasurementsAbsolute volumes of fluid volumes given intraoperatively were measured as were 24 hours fluid volumes. Perioperative measurements of lactate and base excess were recorded as were postoperative complications. Main resultThere was no significant difference between PVI and esophageal Doppler groups in mean total fluid administered (1286 vs 1520 mL, P=.300) or mean intraoperative fluid balance (+839 v+1145 mL, P=.150). ConclusionsPVI offers an entirely non-invasive alternative for goal-directed fluid therapy in this group of patients.

Increased cardiac output and maximal oxygen uptake in response to ten sessions of high intensity interval training.

Increases in maximal oxygen uptake (VO2max) are widely reported in response to completion of high intensity interval training (HIIT), yet the mechanism explaining this result is poorly understood. This study examined changes in VO2max and cardiac output (CO) in response to 10 sessions of low-volume HIIT. Participants included 30 active men and women (mean age and VO2max=22.9±5.4 years and 39.6±5.6 mL/kg/min) who performed HIIT and 30 men and women (age and VO2max=25.7±4.5 years and 40.7±5.2 mL/kg/min) who served as non-exercising controls (CON). High intensity interval training consisted of 6-10 s bouts of cycling per session at 90-110 percent peak power output (PPO) interspersed with 75 s recovery. Before and after training, progressive cycling to exhaustion was completed during which CO, stroke volume (SV), and heart rate (HR) were estimated using thoracic impedance. To confirm VO2max attainment, a verification test was completed after progressive cycling at a work rate equal to 110%PPO. Data demonstrated significant improvements in VO2max (2.71±0.63 L/min to 2.86±0.63 L/min, P<0.001) and COmax (20.0±3.1 L/min to 21.7±3.2 L/min, P=0.04) via HIIT that were not exhibited in CON. Maximal SV was increased in HIIT (P=0.04) although there was no change in maximal HR (P=0.57). The increase in VO2max seen in response to ten sessions of HIIT is due to improvements in oxygen delivery.

Concomitant application of sprint and high-intensity interval training on maximal oxygen uptake and work output in well-trained cyclists.

In this study, we compared the effects of two different training modalities on maximal oxygen uptake and work output. Participants included 26 well-trained mountain bike cyclists were divided into two groups. The first group trained using a conventional endurance protocol at steady-state (moderate) intensity and variable-intensity (high-moderate-low) free of maximal efforts. The second group combined endurance training with a sprint and high-intensity interval training protocol, which, respectively, were based on 30s maximal repetitions and 4min high intensity repetitions. Training duration was 8weeks. A graded exercise test was administered pre- and post-training. Work output, oxygen uptake, minute pulmonary ventilation, heart rate and stroke volume were determined during the test. While work output significantly increased post-training in both groups (P<0.05), the interval training group showed a greater magnitude of change (from 284.4±91.9 to 314.2±95.1kJ) than the endurance training group (from 271.8±73.3 to 283.4±72.3kJ). Significant increases in maximal oxygen uptake (from 57.9±6.8 to 66.6±5.3mlkg(-1)min(-1)), maximal pulmonary ventilation and stroke volume were observed only in the interval training group. An exercise protocol involving endurance and sprint and high-intensity interval training was found to induce positive effects on maximal oxygen uptake in a group of well-trained cyclists with several years athletic experience.

Modeling and Analysis of Single Hydraulic Props in Coal Mines

This research is focused on dynamic performance of water hydraulic single hydraulic prop, the mathematical and AMESim model of single hydraulic prop are established. And the drop hammer is introduced to simulate the impact load of the surrounding rock acting on the prop. The performance parameters of prop retract displacement and cavity pressure are used as the research objects. The working process of single hydraulic prop is reproduced by the simulation. And the influence of safety valve parameters on the support system is analyzed. The results show that: increasing maximal valve core stroke and dead volume or reducing valve damping hole diameter can improve the support performance of the single hydraulic prop. But the influence of equivalent damping has two sides. For support system, decrease damping can improve the support performance, but for the safety valve, reduce the damping make the valve core stability decline. In addition, the pressure overshoot of the optimized system is 18.3%, adjusting time is 0.5s and the retract displacement is 10mm. The dynamic performances meet the technology requirements of the coal mine safety production of China.

Effects of the High Intensity Interval Training on Myocardial Mitochondria Function in Patients with Type 2 Diabetes

PURPOSE: Although impaired myocardial function is commonly observed in patients with type 2 diabetes (T2DM), it remains unclear whether this impairment can be improved. We hypothesized that high-intensity interval training (HIIT) has a favorable effect on myocardial function in patients with T2DM. METHODS: Twelve patients with T2DM (men/women, 6/6; mean age, 54.2 years; mean hemoglobin A1c, 6.8%) were randomized into a either conventional moderate-intensity walking program (CWP: n = 7) or into a HIIT program (n = 5; twice weekly for 12 weeks). The oxygen consumption over heart rate (VO2/HR), which is an exercise-related index of stroke volume, was assessed using cardiopulmonary exercise testing at baseline and after training. Additionally, myocardial mitochondrial function was assessed using technetium-99m sestamibi (MIBI) imaging. RESULTS: After training, the peak VO2/HR tend to be greater extent in the HIIT group than in the CWP group (10.8 vs. 0.8%: p=0.097). Furthermore, the peak VO2/HR was associated with MIBI counts (r = 0.60, p=0.06). CONCLUSIONS: In patients with T2DM, HIIT training was more beneficial than CWP for increasing the maximal stroke volume. This may be linked to superior effects on myocardial mitochondria function.

Long-term hypoxia exposure alters the cardiorespiratory physiology of steelhead trout (Oncorhynchus mykiss), but does not affect their upper thermal tolerance

It has been suggested that exposure to high temperature or hypoxia may confer tolerance to the other oxygen-limited stressor (i.e., ‘cross-tolerance’). Thus, we investigated if chronic hypoxia-acclimation (>3 months at 40% air saturation) improved the steelhead trout's critical thermal maximum (CTMax), or affected key physiological variables that could impact upper thermal tolerance. Neither CTMax (24.7 vs. 25.3°C) itself, nor oxygen consumption (ṀO2), haematocrit, blood haemoglobin concentration, or heart rate differed between hypoxia- and normoxia-acclimated trout when acutely warmed. However, the cardiac output (Q̇) of hypoxia-acclimated fish plateaued earlier compared to normoxia-acclimated fish due to an inability to maintain stroke volume (SV), and this resulted in a ~50% lower maximum Q̇. Despite this reduced maximum cardiac function, hypoxia-acclimated trout were able to consume more O2 per volume of blood pumped as evidenced by the equivalent ṀO2. These results provide additional evidence that long-term hypoxia improves tissue oxygen utilization, and that this compensates for diminished cardiac pumping capacity. The limited SV in hypoxia-acclimated trout in vivo was not associated with changes in cardiac morphology or in vitro maximum SV, but the affinity and density of myocardial ß-adrenoreceptors were lower and higher, respectively, than in normoxia-acclimated fish. These data suggest that alterations in ventricular filling dynamics or myocardial contractility constrain cardiac function in hypoxia-acclimated fish at high temperatures. Our results do not support (1) ‘cross-tolerance’ between high temperature and hypoxia when hypoxia is chronic, or (2) that cardiac function is always the determinant of temperature-induced changes in fish ṀO2, and thus thermal tolerance, as suggested by the oxygen- and capacity-limited thermal tolerance (OCLTT) theory.

Unexplained exertional dyspnea caused by low ventricular filling pressures: results from clinical invasive cardiopulmonary exercise testing.

To determine whether low ventricular filling pressures are a clinically relevant etiology of unexplained dyspnea on exertion, a database of 619 consecutive, clinically indicated invasive cardiopulmonary exercise tests (iCPETs) was reviewed to identify patients with low maximum aerobic capacity (V̇o2max) due to inadequate peak cardiac output (Qtmax) with normal biventricular ejection fractions and without pulmonary hypertension (impaired: n = 49, V̇o2max = 53% predicted [interquartile range (IQR): 47%-64%], Qtmax = 72% predicted [62%-76%]). These were compared to patients with a normal exercise response (normal: n = 28, V̇o2max = 86% predicted [84%-97%], Qtmax = 108% predicted [97%-115%]). Before exercise, all patients received up to 2 L of intravenous normal saline to target an upright pulmonary capillary wedge pressure (PCWP) of ≥5 mmHg. Despite this treatment, biventricular filling pressures at peak exercise were lower in the impaired group than in the normal group (right atrial pressure [RAP]: 6 [IQR: 5-8] vs. 9 [7-10] mmHg, P = 0.004; PCWP: 12 [10-16] vs. 17 [14-19] mmHg, P < 0.001), associated with decreased stroke volume (SV) augmentation with exercise (+13 ± 10 [standard deviation (SD)] vs. +18 ± 10 mL/m(2), P = 0.014). A review of hemodynamic data from 23 patients with low RAP on an initial iCPET who underwent a second iCPET after saline infusion (2.0 ± 0.5 L) demonstrated that 16 of 23 patients responded with increases in Qtmax ([+24% predicted [IQR: 14%-34%]), V̇o2max (+10% predicted [7%-12%]), and maximum SV (+26% ± 17% [SD]). These data suggest that inadequate ventricular filling related to low venous pressure is a clinically relevant cause of exercise intolerance.

Multiaxial Deformation Apparatus for Testing of Microtubes Under Combined Axial-Force and Internal-Pressure

An apparatus for multiaxial loading of microtubes with an outside diameter of less than a few millimeters is described. The apparatus is capable of applying axial-force and internal-pressure in a fully-coupled way, so that biaxial principal stresses along either proportional or non-proportional loading paths can be applied to the microtubes. The requirements of the apparatus for this fully-coupled loading and the resulting functional layout are described first. The hardware that was selected is then detailed. The maximum force and pressure capacities are 2000 N and 1034 bar, while the maximum available stroke and pressurized fluid volume are 50 mm and 68 ml, respectively. Since the apparatus is required to perform dynamic loading as well, with the stresses varying on the order of 1 Hz, the dynamic behavior of the pump used in the apparatus is established experimentally. It was determined that the dynamic response depends not only on the amplitude and frequency of the desired loading, but also, partially because of the minute dimensions of the apparatus, on the volume of fluid in the system and the compressibility of the fluid used for the inflation. The capabilities of the apparatus are demonstrated by proportional and non-proportional biaxial experiments on 304L stainless steel microtubes of 2.38 mm outside diameter and 0.15 mm nominal thickness. Two different strategies for performing these experiments, i.e., force- & volume-control and displacement- & pressure-control were implemented and are compared to each other. The former leads to a more stable system and thus is the preferred mode of operation of the apparatus, while the latter can allow better tracking of the microtube response past the observed limit-load instability. In the proportional loading experiments, the nominal stress paths are shown to be exactly linear, as desired. Although not pursued here, such experiments can be used to establish the plastic anisotropy of the microtube material. Two types of non-proportional experiments are performed: in both cases the microtube is loaded uniaxially (axial or hoop direction); then, by keeping that stress constant, the other principal stress (i.e., hoop or axial) is increased until failure. Digital Image Correlation is used to measure the full strain fields during the testing, establishing the strains at the limit of uniform deformation. Furthermore, comparison of the strain paths induced during the proportional and non-proportional experiments established the path-dependency of the failure strains. These successful experiments demonstrate that any complex loading path inside (or adjacent to) the first quadrant of the plane-stress space can be implemented with this apparatus.

Use of Oxygen Pulse in Predicting Doppler-Derived Maximal Stroke Volume in Adolescents.

Clinical exercise physiologists and physicians administering stress tests in the young have used oxygen pulse as a surrogate measure of stroke volume. It is important to recognize 1) the accuracy of O₂ pulse in predicting maximal stroke volume during exercise, and 2) the normal pattern of O₂ pulse during a progressive exercise test. This study examined both of these issues in a cohort of 44 healthy adolescent males and females (ages 14-16 years) who performed routine progressive cycle exercise to exhaustion. Gas exchange variables were measured by standard open circuit techniques. Stroke volume at rest and during exercise was assessed by the Doppler ultrasound method. At peak exercise O₂ pulse correlated closely with stroke volume (r = .73) with a SEE of 12.6 ml·beat⁻¹. Values of maximal O₂ pulse in nonathletic boys and girls were 13.3 ± 2.5 and 11.0 ± 1.7 ml·beat⁻¹, respectively. After the initial workload, a steady rise was observed in O₂ pulse, entirely reflecting an increasing arterial venous oxygen difference, with a slope of approximately 4 ml/beat per 100 watts work load. The findings support the use of O₂ pulse as a valid predictor of stroke volume during exercise in youth with a moderately high level of accuracy.

Progressive, High Intensity Endurance Exercise Training Significantly Increases Submaximal and Maximal Stroke Volume In Middle Aged, Previously Sedentary Adults

High intensity, endurance exercise increases maximal stroke volume (SV) in young, healthy adults. It is less clear whether such gains are realized among sedentary adults who begin such a program during middle-age. PURPOSE: To determine whether a progressive, high-intensity endurance exercise program will increase SV in healthy, middle-aged adults. METHODS: We studied 42 middle-aged adults (18 males; 52.1 ± 5.0yrs). 21 were randomized to a non-aerobic exercise group (Control). The remaining 21 (10 males) were assigned to an endurance training group (Exercise), all whom completed the 9-month progression phase of a 24 month exercise prescription. This progressive regimen was gradually expanded from 3*30min moderate intensity sess./wk to 1-2*30 min and 1*60 min moderate intensity (55-70% of VO2max) sess./wk + 2 high intensity interval (≥95%peakHR) sess./wk; and 1 low intensity recovery sess./wk. Endurance training sessions were recorded by each participant via both Polar heart rate monitoring and manual data logs. VO2max was measured using the Douglas Bag method via an incremental treadmill protocol. Cardiac output (Qc) was measured by a non-invasive acetylene rebreathing method. VO2 and Qc were measured at rest, two submaximal (SS1 and SS2, 30 and 60% of peak VO2, respectively) and maximal workloads. SV was calculated from the Qc and HR measured via ECG. RESULTS: Exercise participants increased their SV at the submaximal (10.2 and 11.6%, respectively; both p<0.01) and maximal (9.7%, p=0.02) workloads (reference Table 1). SV of the Control group decreased slightly at all workloads. CONCLUSION: Healthy, previously sedentary middle-aged adults who completed a progressive endurance exercise program realized a significant increase in SV during both submaximal and maximal exercise.Table 1: Stroke Volume Increases with Progressive Endurance Training

Surgical implantation of the CardioWest Total Artificial Heart.

The CardioWest Total Artificial Heart (CW-TAH) is a pneumatically driven pump that completely replaces the patient’s native ventricles orthotopically. The device weighs 160 g and consists of two artificial ventricles, four Medtronic Hall tilting disk valves, two membranes, and two drivelines tunneled through the skin, which connect the ventricles to an external console generating pulsatile flow (1). At maximum stroke volume (close to 70 mL), it delivers a cardiac output between seven and nine litres per minute. Variations in cardiac output are determined by variations in venous return and peripheral resistance linked to the patient’s position and level of physical activity (2). The CW-TAH is indicated for use in patients with refractory cardiac failure as a bridge to transplantation, and when used for this indication, improves survival to transplant (3). Portable drivers have been approved in both Europe and the United States to allow stable patients to be discharged home while awaiting their transplant (4).

Cardiac remodeling in response to 1 year of intensive endurance training.

It is unclear whether, and to what extent, the striking cardiac morphological manifestations of endurance athletes are a result of exercise training or a genetically determined characteristic of talented athletes. We hypothesized that prolonged and intensive endurance training in previously sedentary healthy young individuals could induce cardiac remodeling similar to that observed cross-sectionally in elite endurance athletes. Twelve previously sedentary subjects (aged 29±6 years; 7 men and 5 women) trained progressively and intensively for 12 months such that they could compete in a marathon. Magnetic resonance images for assessment of right and left ventricular mass and volumes were obtained at baseline and after 3, 6, 9, and 12 months of training. Maximum oxygen uptake ( max) and cardiac output at rest and during exercise (C2H2 rebreathing) were measured at the same time periods. Pulmonary artery catheterization was performed before and after 1 year of training, and pressure-volume and Starling curves were constructed during decreases (lower body negative pressure) and increases (saline infusion) in cardiac volume. Mean max rose from 40.3±1.6 to 48.7±2.5 mL/kg per minute after 1 year (P<0.00001), associated with an increase in both maximal cardiac output and stroke volume. Left and right ventricular mass increased progressively with training duration and intensity and reached levels similar to those observed in elite endurance athletes. In contrast, left ventricular volume did not change significantly until 6 months of training, although right ventricular volume increased progressively from the outset; Starling and pressure-volume curves approached but did not match those of elite athletes. One year of prolonged and intensive endurance training leads to cardiac morphological adaptations in previously sedentary young subjects similar to those observed in elite endurance athletes; however, it is not sufficient to achieve similar levels of cardiac compliance and performance. Contrary to conventional thinking, the left ventricle responds to exercise with initial concentric but not eccentric remodeling during the first 6 to 9 months after commencement of endurance training depending on the duration and intensity of exercise. Thereafter, the left ventricle dilates and restores the baseline mass-to-volume ratio. In contrast, the right ventricle responds to endurance training with eccentric remodeling at all levels of training.

Nitric oxide improves the hemodynamic performance of the hypoxic goldfish (Carassius auratus) heart

Goldfish tolerate prolonged and severe hypoxia, thus representing a well-suited model to study the maintenance of cardiac function when O2 availability represents a limiting factor.Using a working heart preparation, we explored the role of the intracardiac nitric oxide synthase (NOS)-derived nitric oxide (NO) under normoxic and hypoxic conditions. Cardiac performance was examined both under basal (constant preload and afterload) and loading conditions, i.e. preload-induced increases in stroke volume (SV) and hence cardiac output at constant afterload (the Frank–Starling response).Hypoxic hearts showed an increased basal mechanical performance compared to the normoxic counterpart. Under basal conditions, in both normoxic and hypoxic hearts, NOS and soluble guanylyl cyclase (sGC) inhibition increased SV, while exogenous NO supply decreased it.The normoxic heart was very sensitive to filling pressure increases; the maximum SV = 1.08 ± 0.09 mL/kg body mass was obtained at 0.4 kPa. Acute hypoxia increased this sensitivity, SV reaching the maximum value (1.45 ± 0.12 mL/kg body mass) at 0.25 kPa. NOS inhibition by L-NMMA reduced the Frank–Starling response under normoxia, but was ineffective under acute hypoxia, where NO may come from nitrite reduction. In both conditions, sGC inhibition induced a reduction of the cardiac response to preload. Moreover, under acute hypoxia, NO scavenging significantly reduced the Frank–Starling response. The hypoxia-induced hemodynamic patterns were complemented by Western blotting analysis which revealed increased expressions of NOS and hypoxia inducible factor α(HIF-1α). In conclusion, we demonstrated that intracardiac NO/NOS enhances goldfish heart performance, remarkably expanding its hypoxic tolerance.

Phase-contrast MRI for Detection of Mild Systemic Hemodynamic Response after Segmental Allergen Challenge in Asthmatic Patients

Detection of a systemic hemodynamic response in patients suffering from allergic asthma after segmental endobronchial allergen challenge using phase-contrast magnetic resonance imaging (MRI). Nine asthma patients and four healthy volunteers were examined using MRI (1.5T) before (0 hour), 6 hours, and 24 hours after segmental allergen challenge. Two-dimensional phase-contrast MRI measurements were performed in the aorta (AO) and in the pulmonary artery (PA). In addition, short-axis balanced steady state free precession cardiac cine MRI was performed. Maximum systolic flow, maximum flow acceleration, acceleration volume, acceleration time, distensibility, ejection fraction, stroke volume, end-systolic/diastolic volume, cardiac mass, heart rate (HR), and cardiac output (CO) were determined. Spirometry and bronchoalveolar lavage were also performed. In patients with asthma, maximal systolic flow and maximal flow acceleration increased 6 hours after provocation in the AO (112.3% and 118.9%, respectively) and PA (113.9% and 116.0%, respectively) compared to baseline (100%, P<.05). HR and CO increased significantly at 6 hours (115% and 118%, respectively) compared to baseline (100%, P=.003). In healthy subjects, almost all MRI-derived hemodynamic parameters did not significantly change at 6 hours and were significantly lower than baseline values at 24 hours (P<.02). Twenty-four hours after allergen challenge, all MRI-derived flow parameters were significantly lower in the control group compared to the asthma group (P<.05). HR, CO, and cardiac function parameters measured at 24 hours showed no significant difference comparing the two groups (P>.05). In asthmatic patients, MRI-derived hemodynamic parameters using phase-contrast MRI are slightly altered after segmental allergen provocation compared to normal controls indicating a mild systemic reaction to local allergen challenge.

Goal-directed therapy after cardiac surgery and the incidence of acute kidney injury

ObjectiveThe purpose of this study was to assess the effect of goal-directed therapy (GDT), after cardiac surgery, on the incidence of acute kidney injury (AKI). DesignThis is a prospective observational study designed to achieve and maintain maximum stroke volume for 8 hours, in patients after cardiac surgery. SettingThis is a single-center study in a 15-bedded cardiothoracic intensive care unit (ICU). ParticipantsParticipants are patients after coronary artery bypass grafting and/or aortic valve surgery. InterventionsPatients in the GDT group received cardiac output monitoring and fluid challenges targeting an increase in stroke volume by at least 10%. Stroke volume maximization was maintained for a period of 8 hours from admission to the ICU. All other aspects of care were dictated by the clinical team. Patients in the standard therapy (ST) group had intravenous fluids in accordance with the routine practice of the unit. Patients were divided into the GDT and ST group dependant on availability of cardiac output monitors and allocation of nursing staff with training in GDT. Patients’ data were collected prospectively in both groups. Measurements and main resultsOne hundred twenty-three patients received GDT compared with 141 patients in the ST group. Both groups received similar volumes of fluid (GDT, 2905 [1367] mL vs 2704 [1393] mL; P = .09). Incidence of AKI was reduced in the GDT group (n = 8 [6.5%] vs n = 28 [19.9%]; P = .002). The median duration of hospital stay was 6 (4) days in the GDT group vs 7 (8) days in the ST, P = .004. ConclusionPostoperative GDT in patients after cardiac surgery was associated with reduction in the incidence of AKI and a reduction in ICU and hospital duration of stay.

Effects of Different Exercise Intensities During Detraining on Aerobic Capacity in Thoroughbred Horses

IntroductionThoroughbred racehorses often experience periods of detraining due to locomotor disorders and subsequent rehabilitation. We hypothesised that regularly exercising horses at different intensities during a period of detraining would differentially maintain their cardiopulmonary and O2 transport capacities.MethodsTwenty‐seven Thoroughbred horses trained for 18 weeks then underwent 12 weeks of detraining according to one of three protocols: 1) cantering at 70% maximal rate of O2 consumption (VO2max) for 3 min/d for 5 d/wk (C group), 2) walking for 1 h/d for 5 d/wk (W group) and 3) stall rest (S group). Standardised treadmill exercise tests were performed before and after detraining during which cardiopulmonary and O2 transport variables were measured. Data were analysed with two‐way ANOVA and pairwise comparisons made with Tukey's test. Significance was defined as P≤0.05.ResultsMass‐specific VO2max, maximal cardiac output and maximal stroke volume of all groups decreased after detraining with no differences between groups. The run time to exhaustion, speed eliciting VO2max, speed eliciting maximal heart rate and speed at which plasma lactate concentration reached 4 mmol/l of the C group did not change but those of the W and S groups decreased after detraining. Arterial‐(mixed‐venous) O2 concentration difference did not change after detraining in any group, and maximal heart rate decreased in the W and S groups.ConclusionsThese results suggest it may be possible to identify a minimum threshold exercise intensity or protocol during detraining in horses that maintains significant elements of performance‐related variables and minimises reductions in O2 transport capacity.Ethical Animal ResearchProtocols for the study were approved by the Animal Welfare and Ethics Committee of the Japan Racing Association (JRA) Equine Research Institute. Sources of funding: Japan Racing Association. Competing interests: none.

Pushing the limits: exercise stress in the healthy human heart.

Pushing the limits: exercise stress in the healthy human heart.

The effect of lifelong exercise dose on cardiovascular function during exercise

An increased "dose" of endurance exercise training is associated with a greater maximal oxygen uptake (Vo2max), a larger left ventricular (LV) mass, and improved heart rate and blood pressure control. However, the effect of lifelong exercise dose on metabolic and hemodynamic response during exercise has not been previously examined. We performed a cross-sectional study on 101 (69 men) seniors (60 yr and older) focusing on lifelong exercise frequency as an index of exercise dose. These included 27 who had performed ≤ 2 exercise sessions/wk (sedentary), 25 who performed 2-3 sessions/wk (casual), 24 who performed 4-5 sessions/wk (committed) and 25 who performed ≥ 6 sessions/wk plus regular competitions (Masters athletes) over at least the last 25 yr. Oxygen uptake and hemodynamics [cardiac output, stroke volume (SV)] were collected at rest, two levels of steady-state submaximal exercise, and maximal exercise. Doppler ultrasound measures of LV diastolic filling were assessed at rest and during LV loading (saline infusion) to simulate increased LV filling. Body composition, total blood volume, and heart rate recovery after maximal exercise were also examined. Vo2max increased in a dose-dependent manner (P < 0.05). At maximal exercise, cardiac output and SV were largest in committed exercisers and Masters athletes (P < 0.05), while arteriovenous oxygen difference was greater in all trained groups (P < 0.05). At maximal exercise, effective arterial elastance, an index of ventricular-arterial coupling, was lower in committed exercisers and Masters athletes (P < 0.05). Doppler measures of LV filling were not enhanced at any condition, irrespective of lifelong exercise frequency. These data suggest that performing four or more weekly endurance exercise sessions over a lifetime results in significant gains in Vo2max, SV, and heart rate regulation during exercise; however, improved SV regulation during exercise is not coupled with favorable effects on LV filling, even when the heart is fully loaded.