Significant Changes In Stroke Volume Research Articles

A Wireless Wearable Doppler Ultrasound Detects Changing Stroke Volume: Proof-of-Principle Comparison with Trans-Esophageal Echocardiography during Coronary Bypass Surgery.

Background: A novel, wireless, ultrasound biosensor that adheres to the neck and measures real-time Doppler of the carotid artery may be a useful functional hemodynamic monitor. A unique experimental set-up during elective coronary artery bypass surgery is described as a means to compare the wearable Doppler to trans-esophageal echocardiography (TEE). Methods: A total of two representative patients were studied at baseline and during Trendelenburg position. Carotid Doppler spectra from the wearable ultrasound and TEE were synchronously captured. Areas under the receiver operator curve (AUROC) were performed to assess the accuracy of changing common carotid artery velocity time integral (ccVTI∆) at detecting a clinically significant change in stroke volume (SV∆). Results: Synchronously measuring and comparing Doppler spectra from the wearable ultrasound and TEE is feasible during Trendelenburg positioning. In two representative cardiac surgical patients, the ccVTI∆ accurately detected a clinically significant SV∆ with AUROCs of 0.89, 0.91, and 0.95 when single-beat, 3-consecutive beat and 10-consecutive beat averages were assessed, respectively. Conclusion: In this proof-of-principle research communication, a wearable Doppler ultrasound system is successfully compared to TEE. Preliminary data suggests that the diagnostic accuracy of carotid Doppler ultrasonography at detecting clinically significant SV∆ is enhanced by averaging more cardiac cycles.

Cardiovascular changes during peanut-induced allergic reactions in human subjects

BackgroundFood allergy is the most common cause of anaphylaxis. Changes in posture during acute reactions can trigger fatal outcomes, but the impact of allergic reactions on the cardiovascular system in nonfatal reactions remains poorly understood.ObjectiveOur aim was to systematically evaluate changes in cardiovascular function during acute allergic reactions to peanut.MethodsParticipants underwent double-blind placebo-controlled food challenge to peanut as part of a clinical trial. Changes in hemodynamic parameters (heart rate, stroke volume, blood pressure, and peripheral blood flow) and electrocardiogram findings during food challenges were assessed using noninvasive continuous monitoring.ResultsA total of 57 adults (median age 24 years [interquartile range = 20-29]), 53% of whom were female, participated; 22 (39%) had anaphylaxis. Acute reactions were associated with significant changes in stroke volume (mean decrease of 4.2% [95% CI = 0.8-7.6; P = .03]), heart rate (mean increase 11.6% [95% CI = 8.4-14.8; P < .0001]), and peripheral blood flow (mean increase 19.7% [95% CI = 10.8-28.6; P < .0001]), irrespective of reaction severity. These changes were reproduced at a subsequent repeat peanut challenge in 26 participants, and could be reversed with administration of intravenous fluids which resulted in faster resolution of abdominal symptoms.ConclusionsIn this first detailed human study of cardiovascular changes during food-induced allergic reactions, we found evidence for significant fluid redistribution, independent of reaction severity. This provides a sound rationale for optimizing venous return during significant allergic reactions to food. Finally, these data provide a new paradigm for understanding severity in anaphylaxis, in which poor outcomes may occur as a result of a failure in compensatory mechanisms.

P4677Balloon pulmonary angioplasty improves pulmonary arterial compliance in patients with inoperable chronic thromboembolic pulmonary hypertension

Abstract Background Right ventricular (RV) pressure overload is directly related to the increase in mortality in pulmonary hypertension. Pulmonary arterial compliance (CPA; stroke volume/pulmonary pulse pressure) was reported to be an independent determinant of RV systolic afterload in patients with pulmonary arterial hypertension (PAH). Recently, balloon pulmonary angioplasty (BPA) has been reported to reduce mean pulmonary artery pressure (mPAP) and pulmonary vascular resistance (RPA) in patients with inoperable chronic thromboembolic pulmonary hypertension (CTEPH). However, the effects of BPA on CPA remain unclear. Purpose The aim of this study was to investigate the impact of BPA on CPA in patients with inoperable CTEPH. Methods We retrospectively analyzed 78 patients (388 BPA sessions) with inoperable CTEPH who underwent BPA in our hospital from September 2012 to June 2018. Total number of BPA sessions was 5.0±1.8 (range 1–10). The pressure values were obtained from right heart catheterization at baseline (n=78), just after the final BPA (n=78) and follow-up (n=19) periods. The intervals from baseline to the final BPA and the final BPA to follow-up were 593±498 days and 397±276 days, respectively. Results Mean age was 60.5±12.6 years old, and 64 (82%) were female. All patients were symptomatic (WHO functional class II/III/IV 16/55/7). Patients who had pulmonary vasodilators decreased from 70 (90%) at baseline to 23 (28%) at the final BPA and 2 (15%) at follow-up. BPA reduced mPAP and RPA significantly from baseline to the final BPA and follow-up periods. BPA also improved CPA with significant reduction of pulse pressure despite no significant changes in stroke volume between baseline and follow-up (Table). CPA between the final BPA and follow-up was equivalent (p=0.95). Conclusions BPA improved CPA just after the final BPA in inoperable CTEPH patients. In addition, CPA was preserved during the follow-up after the final BPA sessions. These data suggest that BPA consistently unloads RV systolic afterload in those patients.

Efficacy of Stroke Volume Variation, Cardiac Output and Cardiac Index as Predictors of Fluid Responsiveness using Minimally Invasive Vigileo Device in Intracranial Surgeries.

Introduction:Functional hemodynamic monitoring using dynamic parameters such as stroke volume variations (SVVs) based on pulse contour analysis is considered more accurate than central venous pressure and mean arterial pressure (MAP) in predicting fluid responsiveness. New device, i.e., Vigileo system, allows automatic and continuous monitoring of cardiac output (CO) based on pulse contour analysis and respiratory stroke volume.Aim:The study aims to test the above hypothesis using graded volume loading step (VLS) to assess the accuracy of SVV as a predictor of fluid responsiveness in patients undergoing intracranial surgery.Materials and Methods:After taking ethical committee approval and informed consent, 60 patients aged between 18 and 55 years belonging to the American Society of Anesthesiologists physical status Class I and II, of either sex, scheduled for brain surgery were included in the study. In this study, 5 min after intubation, with stable hemodynamics, patients received volume loading in successive steps (VLS) of 200 ml of lactated Ringer's solution until the stroke volume increased to <10%. Blood pressure (BP), heart rate (HR), stroke volume (SV), and SVV were measured before and after each VLS. Optimal preload augmentation required by each patient was measured by the number of VLS after which an increase in SV was <10%.Results:There was a significant decrease in the baseline BP and SV in responsive and nonresponsive groups for the first VLS, but there is no change in HR statistically. There was a significant change in SV after first VLS. Receiver operating characteristic analysis showed a larger area under the curve of 0.758 for SVV compared to other measured variables. The median number of VLS administered were 2 per patient equating to a mean ± SD requirement of 368 ± 176 ml of crystalloid per patient as the optimal preoperative infusion volume.Conclusion:SVV is a better predictor of preload responsiveness measured with third-generation Vigileo device when compared to BP and HR.

The effect of leptin treatment on in vivo cardiac parameters of streptozotocin induced diabetic rats

Aims Diabetes mellitus is a chronic metabolic disease, which results in serious cardiac complications. It has been shown that hemodynamic parameters are impaired in diabetic rat heart. Leptin is a hormon secreted from adipose tissue and have important effects on glucose metabolism. The effect of leptin treatment on cardiac hemodynamic parameters in streptozotocine (STZ) induced diabetic rat heart has not been studied yet. Thus, we aimed to investigate whether leptin treatment could ameliorate impaired basal cardiac hemodynamic parameters in STZ diabetic rat. Methods Male Sprague-Dawley rats were used for this study. The rats were divided into 3 groups; control (C), diabetic (D), leptin treated diabetic group (Lep). Diabetes was induced by single dose streptozotocin injection (40 mg/kg, i.v.). At the end of 10-week-diabetes period some of the diabetic rats were treated with leptin (150 μg/kg/day, via osmotic minipump) for 14 days. In vivo cardiac hemodynamic parameters were determined through pressure-volume (PV loop) relations. First pressure in carotid artery [systolic arterial pressure (SP), diastolic arterial pressure (DP), mean arterial pressure (MAP)] were measured, then PV loops were recorded under isofluoran anesthesia (%2). Cardiac hemodynamic parameters include heart rate (HR), end systolic pressure (ESP), end diastolic pressure (EDP), the rate of contraction and relaxation (dp/dtmax and dp/dtmin), end systolic volume (ESV), end diastolic volume (EDV), stroke volume (SV), cardiac output (CO), ejection fraction (EF), isovolumic relaxation constant (Tau, Weiss and glantz method), end systolic elastance (Ees), cardiac stiffness, preload recruitable stroke work (PRSW) and dp/dt-EDV relation. To assess preload recruitable cardiac parameters inferior vena cava occlusion was made. Results PV loop analysis showed that almost all cardiac hemodynamic parameters were altered in diabetic state as expected. Heart rate of rats were decreased in D group, leptin treatment did not improve it significantly. ESP values were decreased in D group. Leptin treatment increased it markedly, however it did not reach control levels. EDP values did not differ between the groups. Both dp/dtmax and dp/dtmin values were significantly attenuated in D group, leptin treatment ameliorated it markedly. EDV values were enhanced in D group, and decreased after leptin treatment. There were no significant changes in SV between the groups. CO was found to be attenuated in D group. EF values were not changed. Tau values were increased markedly in D group, and improved with leptin treatment, however it was still high compared to C group. Ees was decreased in D group. No significant change was seen after leptin treatment. The stiffness of the left ventricle was increased in D group and decresed after leptin treatment. PRSW was attenuated in D group and leptin treatment improved it markedly. dp/dt-EDV relation was also decreased in D group and ameliorated partly in Lep group. SP, DP and MAP were decreased in D group and ameliorated in Lep group. Conclusion In vivo cardiac experiments showed that heart function was impaired in diabetic rats. Leptin exerted beneficial effects on these parameters, however the values did not reach control levels. This may be related to chosen dose of leptin, which has been demonstrated effective in a previous study. To confirm the dose dependency of the effect, cardiac parameters should be evaluated in rats treated with a higher dose of leptin.

The Use of Epinephrine in Caudal Anesthesia Increases Stroke Volume and Cardiac Output in Children

Caudal anesthesia is a common and effective regional anesthesia technique in pediatric patients. The addition of epinephrine to local anesthetics in caudal anesthesia is a frequent practice; however, changes in hemodynamic and cardiac parameters produced by epinephrine in caudal anesthesia are not well studied. Using data collected with the ICON noninvasive cardiac output monitor, we examined the hemodynamic changes associated with the administration of epinephrine containing local anesthetics during caudal anesthesia in children. We performed a retrospective analysis of 40 patients who received caudal anesthesia among 402 patients from whom we prospectively collected continuous noninvasive cardiac output data using the ICON monitor, which estimates cardiac output by measuring changes in thoracic bioimpedance during the cardiac cycle. Twenty-three children received epinephrine with local anesthetic (ELA), and 17 children received only local anesthetic (OLA) in their caudal blocks. We compared heart rate (HR), stroke volume (SV), cardiac output (CO), and cardiac index (CI) changes from baseline before caudal injection to 1-minute intervals over 15 minutes after caudal injection for both ELA and OLA groups (Table, Supplemental Digital Content 1, http://links.lww.com/AAP/A179). We also performed subgroup analysis of the same parameters comparing both ELA and OLA groups in infants younger than 6 months and in children 6 months or older. Stroke volume, CO, and CI are significantly increased after caudal injection in the ELA group compared with baseline values at caudal injection time. Conversely, there were no statistically significant changes in SV, CO, and CI in the OLA group. There were no significant HR or blood pressure changes observed in either the ELA or OLA group within 15 minutes compared with baseline caudal injection time. In infants younger than 6 months, no significant differences were found in HR, SV, and CI in children in the ELA group compared with the OLA group. In children 6 months or older, SV and CI increased significantly in the ELA group compared with the OLA group. Epinephrine added to local anesthetic injected for caudal anesthesia produces significant increases in SV, CO, and CI in children. Stroke volume and CI changes from epinephrine added to local anesthetic for caudal anesthesia seem to take place only in children 6 months or older.

Effects of red blood cell transfusion on hemodynamic parameters: a prospective study in intensive care unit patients

BackgroundThe aim of the study was to investigate the effect of red blood cell (RBC) transfusion on hemodynamic parameters including transpulmonary thermodilution (TPTD)-derived variables.MethodsWe compared hemodynamic parameters obtained before and after RBC transfusion (2 RBC units) in 34 intensive care unit (ICU) patients.ResultsDirectly after RBC transfusion, we observed a significant increase in hematocrit (28 ± 3 vs. 22 ± 2%, p < 0.001), hemoglobin (9.4 ± 0.9 vs. 7.6 ± 0.8 g/dL, p < 0.001), arterial oxygen content (CaO2) (12.2 ± 1.2 vs. 9.9 ± 1.0 mL/dL, p < 0.001), and oxygen delivery (DO2) (1073 ± 369 vs. 934 ± 288 mL/min, p < 0.001) compared with baseline. Cardiac output (CO) (8.89 ± 3.06 vs. 9.42 ± 2.75 L/min, p = 0.020), cardiac index (CI) (4.53 ± 1.36 vs. 4.82 ± 1.21 L/min/m2, p = 0.016), and heart rate (91 ± 16 vs. 95 ± 14 bpm, p = 0.007) were significantly lower following RBC transfusion while no significant change in stroke volume (SV) was observed. Mean arterial pressure (MAP) (median 87 vs. 78 mmHg, p < 0.001) and systemic vascular resistance index (SVRI) (median 1212 vs. 1103 dyn*s*cm-5*m2, p = 0.001) significantly increased directly after RBC transfusion. Global end-diastolic volume index (GEDVI), extravascular lung water index (EVLWI), and pulmonary vascular permeability index (PVPI) did not significantly change.ConclusionsIn ICU patients, the transfusion of 2 RBC units induces a significant decrease in CO and CI because of a significant decrease in heart rate (while SV remains unchanged). Despite the decrease in CO, DO2 significantly increases because of a significant increase in CaO2. In addition, RBC transfusion results in a significant increase in MAP and SVRI. No significant changes in TPTD-parameters reflecting cardiac preload (GEDVI), pulmonary edema (EVLWI), and pulmonary vascular permeability (PVPI) are observed following RBC transfusion.

Measurement of systemic oxygen delivery and inotropy in healthy term neonates with the Ultrasonic Cardiac Output Monitor (USCOM)

IntroductionThe aim of this study was to assess the normal values for Smith–Madigan inotropy (SMI), Smith–Madigan inotropy index (SMII), oxygen delivery (DO2) and oxygen delivery index DO2I in healthy term neonates on the first day of life and during circulatory adaptation over the first three days of life. MethodsHemodynamics of the left heart were measured non-invasively in 71 normal full-term neonates over the first three days using the Ultrasonic Cardiac Output Monitor (USCOM). This was combined with hemoglobin concentration from umbilical cord blood and pulse oximetry to calculate DO2 and DO2I. Blood pressure was measured using automated oscillometry and combined with the hemodynamic measures and hemoglobin concentration using the Smith–Madigan method to calculate inotropy (SMI) and inotropy index (SMII). ResultsSMI and SMII showed no significant change during the study period, ranging from 154 to 168mW and 694 to 731mW/m2. Mean (SD) DO2 and DO2I showed a significant fall over three days from 131 (63) ml/min and 596 (278) ml/m2/min to 118 (46) ml/min and 517 (173) ml/m2/min (p<0.01 and <0.001 respectively) with a corresponding decrease in cardiac output from 758 (143) ml/min to 658 (131) ml/min, (p=0.002). There was no significant change in stroke volume, heart rate, SMI or SMII within the first day. DO2 and DO2I showed small but significant decreases within the first day from 153 (46) ml/min and 699 (174) ml/min/m2 to 129 (36) ml/min and 609 (141) ml/min/m2 (p=0.017 and 0.048 respectively). ConclusionsNormal inotropy of the left heart and systemic DO2 values in healthy full-term neonates over the first three days of life were assessed using the USCOM. Subjects showed stable myocardial contractility over the first three days with decreasing DO2 and DO2I in line with the decrease in cardiac output (CO). DO2 and DO2I showed small but significant reductions during the first 24h. USCOM proved to be a feasible and convenient non-invasive bedside tool to assess inotropy and oxygen delivery in neonates.

Impaired left ventricular function in the presence of preserved ejection in chronic hypertensive conscious pigs

Systolic function is often evaluated by measuring ejection fraction and its preservation is often assimilated with the lack of impairment of systolic left ventricular (LV) function. Considering the left ventricle as a muscular pump, we explored LV function during chronic hypertension independently of increased afterload conditions. Fourteen conscious and chronically instrumented pigs received continuous infusion of either angiotensin II (n = 8) or saline (n = 6) during 28 days. Hemodynamic recordings were regularly performed in the presence and 1 h after stopping angiotensin II infusion to evaluate intrinsic LV function. Throughout the protocol, the mean arterial pressure steadily increased by 55 ± 4 mmHg in angiotensin II-treated animals. There were no significant changes in stroke volume, LV fractional shortening or LV wall thickening, indicating the lack of alterations in LV ejection. In contrast, we observed maladaptive changes with (1) the lack of reduction in isovolumic contraction and relaxation durations with heart rate increases, (2) abnormally blunted isovolumic contraction and relaxation responses to dobutamine and (3) a linear correlation between isovolumic contraction and relaxation durations. None of these changes were observed in saline-infused animals. In conclusion, we provide evidence of impaired LV function with concomitant isovolumic contraction and relaxation abnormalities during chronic hypertension while ejection remains preserved and no sign of heart failure is present. The evaluation under unloaded conditions shows intrinsic LV abnormalities.

Effects on cardiopulmonary function and oxygen delivery of doses of romifidine and xylazine followed by constant rate infusions in standing horses

The objective of this study was to compare the cardiopulmonary effects of a xylazine or romifidine loading-dose, followed by a constant rate infusion (CRI) of the same α(2)-agonist. Nine research horses were treated in a randomized, blinded, crossover design with xylazine or romifidine. After instrumentation, a loading dose of intravenous xylazine (1mg/kg) or romifidine (80μg/kg) was administered, immediately followed by a CRI of xylazine (0.69mg/kg/h) or romifidine (30μg/kg/h) for a duration of 2h. Cardiopulmonary variables were recorded before bolus administration, during CRI, and for 1h after discontinuing drug administration. A significant decrease in haemoglobin concentration (tHb), arterial oxygen content (CaO(2)), oxygen delivery (D˙O(2)), mixed venous partial pressure of oxygen, heart rate, and cardiac output (Q˙t) followed the loading dose with both treatments. Carotid arterial blood pressure (ABP), systemic vascular resistance, and right atrial pressure (RAP) increased significantly. The increased ABP was followed by a significant decrease compared to baseline. Mean pulmonary arterial pressure increased significantly with romifidine only. No significant changes in stroke volume, arterial partial pressure of oxygen, and oxygen consumption were observed. Changes in Q˙t and RAP were more pronounced with romifidine. During CRI, tHb, and CaO(2) were significantly higher with romifidine, whereas D˙O(2) did not differ between treatments. Overall, cardiopulmonary effects were more pronounced and lasted longer with romifidine compared to xylazine. However, during CRI, there was no difference in D˙O(2) between drugs. With both α(2)-agonists, cardiovascular effects were most pronounced after loading dose administration and tended to stabilize during CRI.

Case Scenario

Case Scenario

Changes in Left Ventricular Preload, Afterload, and Cardiac Output in Response to a Single Dose of Mannitol in Neurosurgical Patients Undergoing Craniotomy

Mannitol increases intravascular volume by withdrawing water from the brain and causes significant changes in stroke volume, cardiac output (CO), systemic vascular resistance, central venous pressure (CVP), and blood pressure. No previous studies have demonstrated changes in left ventricular (LV) preload, afterload, and CO using transesophageal echocardiography (TEE). Fifteen adult patients undergoing elective supratentorial craniotomy received 20% mannitol 1.0 gm/kg over 15 minutes before dural opening. The following hemodynamic and TEE-derived parameters were recorded before and after the administration of mannitol: heart rate (HR), mean arterial pressure (MAP), CVP, LV end diastolic area (EDA), end systolic area, fractional area change, stroke volume, and CO. EDA and CVP significantly increased at 5 minutes (P=0.002 and <0.001) after mannitol infusion and remained insignificantly elevated till 15 minutes, thereafter returning to baseline values. CO also increased significantly at 5 and 15 minutes (P=0.001 and 0.013) and remained insignificantly elevated till 25 minutes, and thereafter returned to baseline values. A concomitant significant decline in systemic vascular resistance was observed at 5 and 15 minutes (P=0.002 and 0.008 at 5 and 15 min, respectively). Although EDA increased significantly at 5 minutes, there were no appreciable changes in MAP and HR throughout the study period. In conclusion, in patients undergoing craniotomy, TEE demonstrated that a single bolus dose of 20% mannitol (1.0 gm/kg) caused significant but short-duration alterations in LV preload, afterload, and CO without concomitant changes in hemodynamic variables (MAP/HR).

Clinically Significant Change in Stroke Volume in Pulmonary Hypertension

Stroke volume is probably the best hemodynamic parameter because it reflects therapeutic changes and contains prognostic information in pulmonary hypertension (PH). Stroke volume directly reflects right ventricular function in response to its load, without the correction of compensatory increased heart rate as is the case for cardiac output. For this reason, stroke volume, which can be measured noninvasively, is an important hemodynamic parameter to monitor during treatment. However, the extent of change in stroke volume that constitutes a clinically significant change is unknown. The aim of this study was to determine the minimal important difference (MID) in stroke volume in PH. One hundred eleven patients were evaluated at baseline and after 1 year of follow-up with a 6-min walk test (6MWT) and cardiac MRI. Using the anchor-based method with 6MWT as the anchor, and the distribution-based method, the MID of stroke volume change could be determined. After 1 year of treatment, there was, on average, a significant increase in stroke volume and 6MWT. The change in stroke volume was related to the change in 6MWT. Using the anchor-based method, an MID of 10 mL in stroke volume was calculated. The distribution-based method resulted in an MID of 8 to 12 mL. Both methods showed that a 10-mL change in stroke volume during follow-up should be considered as clinically relevant. This value can be used to interpret changes in stroke volume during clinical follow-up in PH.

Effects of oxygen inhalation on cardiac output, coronary blood flow and oxygen delivery in healthy individuals, assessed with MRI

Oxygen (O2) is a cornerstone in the treatment of critically ill patients, and the guidelines prescribe 10-15 l of O2/min even to those who are initially normoxic. Studies using indirect or invasive methods suggest, however, that supplemental O2 may have negative cardiovascular effects. The aim of this study was to test the hypothesis, using noninvasive cardiac magnetic resonance imaging, that inhaled supplemental O2 decreases cardiac output (CO) and coronary blood flow in healthy individuals. Sixteen healthy individuals inhaled O2 at 1, 8 and 15 l/min through a standard reservoir bag mask. A 1.5 T magnetic resonance imaging scanner was used to measure stroke volume, CO and coronary sinus blood flow. Left ventricular (LV) perfusion was calculated as coronary sinus blood flow/LV mass. The O2 response was dose-dependent. At 15 l of O2/min, blood partial pressure of O2 increased from an average 11.7 to 51.0 kPa with no significant changes in blood partial pressure of CO2 or arterial blood pressure. At the same dose, LV perfusion decreased by 23% (P=0.005) and CO decreased by 10% (P=0.003) owing to a decrease in heart rate (by 9%, P<0.002), with no significant changes in stroke volume or LV dimensions. Owing to the decreased CO and LV perfusion, systemic and coronary O2 delivery fell by 4 and 11% at 8 l of O2/min, despite the increased blood oxygen content. Our data indicate that O2 administration decreases CO, LV perfusion and systemic and coronary O2 delivery in healthy individuals. Further research should address the effects of O2 therapy in normoxic patients.

Do Acute Changes In Gross Body Weight Effect Running Economy And Cardiorespiratory Responses?

PURPOSE: To investigate the effects of acute gross bodyweight changes with added weight (3% and 4% of body weight) on running economy and cardiorespiratory responses. METHODS: Eight trained runners (44.3±4.2 years; 71.13±5.97kg; 174.3±6.9cm; 16.4±4.2% body fat) undertaken three randomized experimental trials with added weight to the torso of 3% (E3) and 4% (E4) body weight and without weight (E0) added to the torso. Each trial consisted of four different submaximal running velocities (65, 70, 75, 80% of VO2max; four minutes for each velocity) on the treadmill in thermoneutral conditions (20°C; 40%rh). Expired respiratory gas (VO2) samples were collected over the final 60 seconds at each velocity using the Douglas bag technique and cardiac output (CO) was measured using the CO2-rebreathing equilibrium technique (Collier plateau method) towards the end of each stage. Heart rate (HR) and Borg scale rating of perceived exercise (RPE) values were recorded for the final 15s of each stage of running. To ensure the subjects were well hydrated in all experimental trials, they were instructed to drink a prescribed volume (6 mL/kg BW/ 2.5 sessions per day) of water a day before and on the day of testing. Urine samples were collected for urine specific gravity (USG) measurement during pre-exercise. Two way ANOVA with repeated measures were used to compare the effects of added weights and running speeds. RESULTS: Subjects were well hydrated with the USG in E0 trial (1.005±0.004), E3 (1.005±0.002), and E4 (1.005±0.004) (p>0.05). VO2, HR and CO were increased significantly from 65% to 80% of VO2max in E0, E3 and E4 trials respectively (p<0.01), but no significant differences were seen between trials (p>0.05) (Figure 1). No significant changes in stroke volume were found at any of the four different submaximal running velocities of all experimental trials (p>0.05). For RPE, subjects reported ratings of 9.6±2.0 to 14.0±1.6 in E0 trial; and from 10.9±1.4, to 15.0±1.3 in E3 trial and from 10.3±1.1 to 15.0±1.4 in E4 trial. Significant differences were observed in RPE rating with increases in running velocity (p<0.001) but no difference was found between trials (p>0.05).CONCLUSION: Acute gross changes in body weight with added weight did not affect running economy and cardiorespiratory responses. We conclude that there is minimal sensitivity in the VO2 cost of running when additional weight (+3% and +4% of bodyweight) is added to the torso.Figure 1: Oxygen uptake (VO2) and cardioresporatory responses during four submximal speeds in three different conditions (E0: without weight; E3: added 3% of body weight; E4: added 4% of body weight).

Hemodynamic Changes After Administration of Mannitol Measured by a Noninvasive Cardiac Output Monitor

Mannitol is the most commonly used hyperosmotic agent in neurosurgery. Being an agent that increases intravascular volume by withdrawing water from the brain, it may cause significant changes in stroke volume (SV), cardiac output (CO), systemic vascular resistance and blood pressure. In this study, we monitored the hemodynamic changes in response to a single dose of mannitol by using a noninvasive CO monitor based on the thoracic electrical bioimpedance technique, in patients undergoing craniotomy. Eleven adult patients undergoing elective craniotomy received mannitol 1.0 g/kg 15 minutes before dural opening. The following hemodynamic variables were recorded: heart rate, systolic blood pressure, diastolic blood pressure, SV, CO, and cardiac index. The measurements were made before the administration of mannitol, at 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, and 45 minutes after the termination of the mannitol infusion. Urine output was measured at 10, 20, 30, 40, 50, 60, 90, and 120 minutes after termination of the mannitol infusion. Heart rate values from 25 to 45 minutes were significantly lower compared with the premannitol values (P<0.05). All the postmannitol systolic blood pressure values were significantly lower than the premannitol value (P<0.05). SV increased significantly for 15 minutes after administration of mannitol (P<0.05). SV at 45 minutes was significantly lower than that from 1 to 30 minutes (P<0.05). Cardiac index also showed a similar change with a significant increase at 1 to 10 minutes and a decrease at 40 to 45 minutes compared with 1 to 15 minutes.The rate of urine secretion was higher during the first 10 minutes (40+/-15 mL/kg/ h) than during the rest of the study period. The overall fluid balance at the end of 120 minutes was -370+/-987 mL. In this study using noninvasive measurement of CO by thoracic bioimpedance plethysmography during craniotomy, a single bolus dose of mannitol 1.0 g/kg caused a significant but short duration changes in the hemodynamic variables. The changes in SV, and CO, lasted for only 15 minutes after the infusion.

The oxygen delivery response to acute hypoxia during incremental knee extension exercise differs in active and trained males

BackgroundIt is well known that hypoxic exercise in healthy individuals increases limb blood flow, leg oxygen extraction and limb vascular conductance during knee extension exercise. However, the effect of hypoxia on cardiac output, and total vascular conductance is less clear. Furthermore, the oxygen delivery response to hypoxic exercise in well trained individuals is not well known. Therefore our aim was to determine the cardiac output (Doppler echocardiography), vascular conductance, limb blood flow (Doppler echocardiography) and muscle oxygenation response during hypoxic knee extension in normally active and endurance-trained males.MethodsTen normally active and nine endurance-trained males (VO2max = 46.1 and 65.5 mL/kg/min, respectively) performed 2 leg knee extension at 25, 50, 75 and 100% of their maximum intensity in both normoxic and hypoxic conditions (FIO2 = 15%; randomized order). Results were analyzed with a 2-way mixed model ANOVA (group × intensity).ResultsThe main finding was that in normally active individuals hypoxic sub-maximal exercise (25 – 75% of maximum intensity) brought about a 3 fold increase in limb blood flow but decreased stroke volume compared to normoxia. In the trained group there were no significant changes in stroke volume, cardiac output and limb blood flow at sub-maximal intensities (compared to normoxia). During maximal intensity hypoxic exercise limb blood flow increased approximately 300 mL/min compared to maximal intensity normoxic exercise.ConclusionCardiorespiratory fitness likely influences the oxygen delivery response to hypoxic exercise both at a systemic and limb level. The increase in limb blood flow during maximal exercise in hypoxia (both active and trained individuals) suggests a hypoxic stimulus that is not present in normoxic conditions.

Left Ventricular Response to Continuous Positive Airway Pressure: Role of Left Ventricular Geometry

Background: Continuous positive airway pressure (CPAP) may be a useful adjunct in patients with congestive heart failure. Objectives: To evaluate the relationship between left ventricular geometry and hemodynamic response to CPAP. Methods: Right heart catheter studies were performed in 26 patients before, during and after application of CPAP (8 cm H₂O) over 15 min. Response to therapy was defined as an increase in stroke volume using CPAP. Results: Cardiac output decreased from 6.9 ± 1.9 to 6.2 ± 1.4 liters/min (p = 0.01) with a slight increase after cessation of CPAP (not significant). There was no significant change in stroke volume (92 ± 34 vs. 90 ± 31 ml, p = 0.584) or pulmonary capillary wedge pressure (14.7 ± 7.0 vs. 14.2 ± 6.5 mm Hg, p = 0.26). There was a correlation between hemodynamic effects of CPAP therapy and left ventricular end-diastolic volume (r = 0.515, p = 0.01), mass-volume ratio (r = –0.41, p = 0.04) and pulmonary capillary wedge pressure (r = 0.654, p = 0.001) at baseline. Half the patients (n = 13) were categorized as responders with an average increase in stroke volume of 11.5 ± 2.1%. Responders showed significantly higher left ventricular end-diastolic volume, pulmonary capillary wedge pressure and lower mass-volume ratio. Conclusion: Patients with high pulmonary capillary wedge pressure, elevated end-diastolic volumes and a low left ventricular mass-volume ratio might profit from CPAP therapy.

Effect of eight weeks of endurance exercise training on right and left ventricular volume and mass in untrained obese subjects: a longitudinal MRI study

The aim of the present investigation was to examine how 8 weeks of intense endurance training influenced right and left ventricular volumes and mass in obese untrained subjects. Ten overweight subjects (19-47 years; body mass index of 34+/-5 kg/m(2)) underwent intensive endurance training (rowing) three times 30 min/week for 8 weeks at a relative intensity of 72+/-8% of their maximal heart rate response (mean+/-SD). Before and after 8 weeks of endurance training, the left and the right end-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), stroke volume (SV) and ventricular mass (VM) were measured by Magnetic resonance imaging (MRI). Submaximal heart rate decreased from 126+/-5 to 113+/-3 b.p.m. (10%; P<0.01), and from 155+/-5 to 141+/-4 b.p.m. (9%; P<0.001) at submaximal workloads of 70 and 140 W (110 W for women), respectively (mean+/-SEM). Resting ventricular parameters increased significantly: left ventricular SV, EDV and VM increased by 6%, 7% and 13%, respectively (P<0.01). The right side of the heart showed significant changes in SV, EDV and VM with increase of 4%, 4% and 12%, respectively (P<0.05). Eight weeks of endurance training significantly increased left ventricular SV and right ventricular SV, due to an increase in left ventricular EDV and right ventricular EDV. Furthermore, left VM and right VM increased. We conclude that using MRI and a longitudinal design it was possible to demonstrate similar and balanced changes in the right and left ventricle in response to training.

Integrated physiological responses to feeding in the blue crab Callinectes sapidus.

The passage of a barium meal (15 % by mass) was followed through the digestive system of the blue crab Callinectes sapidus by flash-freezing crabs at set intervals, followed by radiography of specimens. Food moved from the oesophagus into the stomach region within 15 min. After 1-2 h, food was visible in the midgut, at 6 h it had reached the hindgut, and material was still present in the stomach at this time. The stomach was emptied between 8 and 10 h after feeding, and the entire digestive system was cleared of material after 18 h. A pulsed-Doppler flowmeter was used to monitor cardiac variables and arterial haemolymph flows during a 4 h control and 24 h postprandial period. Heart rate increased immediately upon food detection and remained elevated for 16-18 h after food ingestion. There was no significant change in stroke volume of the heart, and total cardiac output increased significantly and remained elevated above pre-feeding levels for 24 h after feeding. There was no change in haemolymph flow through the anterior or posterior aorta, but flow increased in the sternal, anterolateral and hepatic arteries. These changes in haemolymph flow reflected the use of the chelae and mouthparts in feeding, contraction of the visceral muscle surrounding the gut system and mobilisation of enzymes from the hepatopancreas. There was also a postprandial increase in the rate of oxygen uptake (apparent specific dynamic action). The rate of oxygen consumption (M(dot)(O2)) reached maximal levels 4 h after feeding and decreased slowly thereafter, reflecting the increased use of oxygen in digestion and absorption.