Changes In Systemic Vascular Resistance Research Articles

Mechanism of Increased Spinal Cord Blood Flow due to Noradrenaline Administration Using Vascular Resistance: An Experimental Study Using a Canine Model

During thoracoabdominal aortic surgery, the spinal cord is placed under ischemic conditions. Elevation of systemic blood pressure is thus recommended as a method of increasing the blood supply from collateral networks. This study examined the mechanisms by which noradrenaline administration increases spinal cord blood flow (SCBF) by elevating systemic blood pressure. In beagles (n = 7), the thoracoabdominal aorta and L2-L7 spinal cord segmental arteries (SAs) were exposed and a distal perfusion bypass was created to simulate clinical practice. SCBF was measured by laser flowmetry at the L5 dura mater and spinal cord perfusion pressure (SCPP) was measured inside the clamped aorta. The six pairs of SAs from L2 to L7 were clamped, and mean systemic blood pressure (mSBP), SCBF, and SCPP were measured before and after clamping and after starting continuous infusion of noradrenaline at 0.5 µg/kg/min. Rates of change in systemic vascular resistance (SVR) and spinal cord vascular resistance (SCVR) were calculated from the measured values. With no SA clamping (control), the rate of increase in SCVR was 0.74 times the rate of increase in SVR (y = 0.2 + 0.74x, r = 0.889, r2 = 0.789; P < 0.01). When all six pairs of SAs were clamped, a weak correlation was evident between rate of change in SCVR and rate of change in SVR, and the rate of increase in SCVR was lower than the rate of increase in SVR (y = 0.39 + 0.07x, r = 0.209, r2 = 0.039; P < 0.01). When all six pairs of SAs were clamped in the absence of distal perfusion, a weak correlation was also evident between rate of change in SCVR and rate of change in SVR, and the rate of increase in SCVR was lower than the rate of increase in SVR (y = 0.19 + 0.08x, r = 0.379, r2 = 0.144; P < 0.01). The rate of increase in SCVR induced by noradrenaline administration was lower than the rate of increase in SVR in the control group with no spinal cord SA clamping and in both experimental groups with clamped SAs (with and without distal perfusion), creating an environment conducive to spinal cord flow distribution.

Does Intra-Aortic Balloon pump (IABP) improve hemodynamics in Asian Indian patients with Acute Coronary Syndrome with cardiogenic Shock? (DIASTASIS study)

Introduction: Intra-aortic balloon pump (IABP) is widely used as a mechanical support device. Current evidence after the IABP-SHOCK II trial is ambiguous. We evaluated the impact of IABP on hemodynamic parameters (Cardiac Output (CO), Cardiac Power Output (CPO) and Systemic Vascular Resistance (SVR)) measured at 6 and 24 hours in patients presenting with cardiogenic shock (CS) with Acute Coronary Syndrome (ACS) amongst Asian Indians. Methods: The efficacy of IABP was evaluated in patients presenting with CS in open-label, prospective, randomized (for randomization every alternate patient presented to an emergency was given IABP support), consecutive 60 patients in ACS with CS with group A (N=30) comprising of those with IABP and Group B without IABP (n=30). Results: Both the groups were matched for baseline characteristics. The revascularization rate was 85% and only the culprit vessel was addressed during the study. Total 9 (15%) patients were managed medically and did not undergo revascularization. The mean changes in Systemic vascular resistance (SVR), cardiac output (CO) and cardiac power output (CPO) after 24 hours in patients with and without IABP showed no statistical difference except for the lower mean dose use of dobutamine in Group A (with IABP) vs Group B (without IABP) (4.08 (1.41) vs. 7.92 (2.52) mcg/kg/min, p&amp;lt;0.0001). Conclusion: The use of IABP in Asian Indians with CS in ACS did not provide any improvement in hemodynamic parameters.

Posture-Related Differences in Cardiovascular Function Between Young Men and Women: Study of Noninvasive Hemodynamics in Rural Malawi.

BackgroundCardiovascular risk is higher in men than in women, but little information exists about sex‐related differences in cardiovascular function from low‐income countries. We compared hemodynamics between sexes in rural Malawi in a cohort followed up since their birth.Methods and ResultsSupine, seated, and standing hemodynamics were recorded from 251 women and 168 men (mean age, 21 years; body mass index, 21 kg/m2) using oscillometric brachial waveform analyses (Mobil‐O‐Graph). The results were adjusted for estimated glomerular filtration rate, and plasma potassium, lipids, and glucose. Men had higher brachial and aortic systolic blood pressure and stroke index regardless of posture (P<0.001), and higher upright but similar supine diastolic blood pressure than women. Regardless of posture, heart rate was lower in men (P<0.001), whereas cardiac index did not differ between sexes. Women presented with lower supine and standing systemic vascular resistance index (P<0.001), whereas supine‐to‐standing increase in vascular resistance (P=0.012) and decrease in cardiac index (P=0.010) were higher in women. Supine left cardiac work index was similar in both sexes, whereas standing and seated left cardiac work index was higher in men than in women (P<0.001).ConclusionsIn young Malawian adults, men had higher systolic blood pressure, systemic vascular resistance, and upright cardiac workload, whereas women presented with higher posture‐related changes in systemic vascular resistance and cardiac output. These findings show systematic sex‐related differences in cardiovascular function in a cohort from a low‐income country with high exposure to prenatal and postnatal malnutrition and infectious diseases.

Exercise Training Combined with Calanus Oil Supplementation Improves the Central Cardiodynamic Function in Older Women.

The aim of this study was to investigate the possible beneficial effects of exercise training (ET) with omega-3/Calanus oil supplementation on cardiorespiratory and adiposity parameters in elderly women. Fifty-five women (BMI: 19–37 kg/m2, 62–80 years old) were recruited and randomly assigned to the 4 month intervention with ET and omega-3 supplementation (Calanus oil, ET-Calanus) or ET and the placebo (sunflower oil; ET-Placebo). The body composition was determined by dual-energy X-ray absorptiometry (DXA), and cardiorespiratory parameters were measured using spiroergometry and PhysioFlow hemodynamic testing. Both interventions resulted in an increased lean mass whereas the fat mass was reduced in the leg and trunk as well as the android and gynoid regions. The content of trunk fat (in percent of the total fat) was lower and the content of the leg fat was higher in the ET-Calanus group compared with the ET-Placebo. Although both interventions resulted in similar improvements in cardiorespiratory fitness (VO2max), it was explained by an increased peripheral oxygen extraction (a-vO2diff) alone in the ET-Placebo group whereas increased values of both a-vO2diff and maximal cardiac output (COmax) were observed in the ET-Calanus group. Changes in COmax were associated with changes in systemic vascular resistance, circulating free fatty acids, and the omega-3 index. In conclusion, Calanus oil supplementation during a 4 month ET intervention in elderly women improved the cardiorespiratory function, which was due to combined central and peripheral cardiodynamic mechanisms.

Relationship Between Left Ventricular Ejection Fraction Variation and Systemic Vascular Resistance: A Prospective Cardiovascular Magnetic Resonance Study.

Introduction: This cardiovascular magnetic resonance (CMR) study aims to determine whether changes in systemic vascular resistance (SVR), obtained from CMR flow sequences, might explain the significant long-term changes in left ventricular (LV) ejection fraction (EF) observed in subjects with no cardiac disease history.Methods: Cohort subjects without any known cardiac disease but with high rates of hypertension and obesity, underwent CMR with phase-contrast sequences both at baseline and at a median follow-up of 5.2 years. Longitudinal changes in EF were analyzed for any concomitant changes in blood pressure and vascular function, notably the indexed SVR given by the formula: mean brachial blood pressure / cardiac output x body surface area.Results: A total of 118 subjects (53 ± 12 years, 52% women) were included, 26% had hypertension, and 52% were obese. Eighteen (15%) had significant EF variations between baseline and follow-up (7 increased EF and 11 decreased EF). Longitudinal changes in EF were inversely related to concomitant changes in mean and diastolic blood pressures (p = 0.030 and p = 0.027, respectively) and much more significantly to SVR (p < 0.001). On average, these SVR changes were −8.08 ± 9.21 and +8.14 ± 8.28 mmHg.min.m2.L−1, respectively, in subjects with significant increases and decreases in EF, and 3.32 ± 7.53 mmHg.min.m2.L−1 in subjects with a stable EF (overall p < 0.001).Conclusions: Significant EF variations are not uncommon during the long-term CMR follow-up of populations with no evident health issues except for uncomplicated hypertension and obesity. However, most of these variations are linked to SVR changes and may therefore be unrelated to any intrinsic change in LV contractility. This underscores the benefits of specifically assessing LV afterload when EF is monitored in populations at risk of vascular dysfunction.Clinical Trial Registration: ClinicalTrials.gov, identifier: NCT01716819 and NCT02430805.

Individual changes of central blood pressure in response to upright posture: different hemodynamic phenotypes.

Most studies about upright regulation of blood pressure have focused on orthostatic hypotension despite the diverse hemodynamic changes induced by orthostatic challenge. We investigated the effect of passive head-up tilt on aortic blood pressure. Noninvasive peripheral and central hemodynamics in 613 volunteers without cardiovascular morbidities or medications were examined using pulse wave analysis, whole-body impedance cardiography and heart rate variability analysis. In all participants, mean aortic SBP decreased by -4 (-5 to -3) mmHg [mean (95% confidence intervals)] and DBP increased by 6 (5--6) mmHg in response to upright posture. When divided into tertiles according to the supine-to-upright change in aortic SBP, two tertiles presented with a decrease [-15 (-14 to -16) and -4 (-3 to -4) mmHg, respectively] whereas one tertile presented with an increase [+7 (7-- 8) mmHg] in aortic SBP. There were no major differences in demographic characteristics between the tertiles. In regression analysis, the strongest explanatory factors for upright changes in aortic SBP were the supine values of, and upright changes in systemic vascular resistance and cardiac output, and supine aortic SBP. In participants without cardiovascular disease, the changes in central SBP during orthostatic challenge are not uniform. One-third presented with higher upright than supine aortic SBP with underlying differences in the regulation of systemic vascular resistance and cardiac output. These findings emphasize that resting blood pressure measurements give only limited information about the blood pressure status.

Abstract 15823: Diminished Vasoresponsiveness in Patients With Heart Failure

Introduction: Vasoplegia is a severe complication after cardiac surgery and is associated with impaired clinical outcome. Pre-operative heart failure (HF) is considered an independent predictor of post-operative vasoplegia. We hypothesize that HF patients are more susceptible to vasoplegia due to altered vascular responsiveness. In this study, vasoresponsiveness in patients undergoing cardiac surgery for HF is investigated. Methods: A prospective, observational study was conducted at Leiden University Medical Center. We included patients with HF (N=18) and without HF (N=18) who underwent cardiac surgery on cardiopulmonary bypass. Vasoresponsiveness was assessed at 4 different timepoints: 1) before induction, 2) after induction, 3) after cessation of cardiopulmonary bypass and 4) on the first postoperative day. The vascular response was recorded as change in systemic vascular resistance (SVR) after the administration of phenylephrine (bolus 2 μg/kg). Results: Thirty-six patients were included [67 (61-71) years, 78% male]. Vascular responsiveness was significantly attenuated in patients with HF compared to controls. The response to phenylephrine was already diminished at baseline in HF patients and was almost abolished after cessation of cardiopulmonary bypass (Figure). Roughly the same pattern of vasoresponsiveness was found when excluding patients that received norepinephrine. Moreover, HF patients required a significantly higher amount of noradrenaline [169.80 (IQR 14.77-318.97) ug/kg] compared to controls [3.61 (IQR 0-41.60) ug/kg] to maintain similar SVR during the first 24h postoperatively. Conclusions: The vascular responsiveness is altered in patients with HF and this might explain the higher prevalence of vasoplegia in this patient population.

A Novel Control Method for Rotary Blood Pumps as Left Ventricular Assist Device Utilizing Aortic Valve State Detection.

A novel control method for rotary blood pumps is proposed relying on two different objectives: regulation of pump flow in accordance with desired value and the maintenance of partial support with an open aortic valve by the variation of pump speed. The estimation of pump flow and detection of aortic valve state was performed with mathematical models describing the first- and second generation of Sputnik rotary blood pumps. The control method was validated using a cardiovascular system model. The state of the aortic valve was detected with a mean accuracy of 91% for Sputnik 1 and 96.2% for Sputnik 2 when contractility, heart rate, and systemic vascular resistance was changed. In silico results for both pumps showed that the proposed control method can achieve the desired pump flow level and maintain the open state of the aortic valve by periodically switching between two objectives under contractility, heart rate, and systemic vascular resistance changes. The proposed method showed its potential for safe operation without adverse events and for the improvement of chances for myocardial recovery.

Maternal functional hemodynamics in uncomplicated twin pregnancies: A longitudinal study using impedance cardiography.

Longitudinal studies of maternal hemodynamics in twin pregnancy are scarce and preload reserve in twin pregnancies has not been studied. Thus, we aimed to investigate serial changes in maternal systemic hemodynamics from the first to third trimester, and cardiovascular response to passive leg raising to evaluate preload reserve using impedance cardiography in a cohort of uncomplicated twin pregnancies. This was a prospective longitudinal study of 50 twin pregnancies. Maternal hemodynamics was assessed at baseline and 120seconds after passive leg raising using impedance cardiography, at five time points during gestation. Women were excluded from the analysis if there were pregnancy complications or fewer than three of five planned assessments were available. Data from 37 uncomplicated twin pregnancies were available for analysis. Mean arterial pressure slightly decreased until 17weeks' gestation, then increased. Systemic vascular resistance was constant in the first half of pregnancy before rising steadily thereafter, whereas the cardiac output increased from the first trimester, peaked by the end of the second trimester and then decreased in the third trimester. The change in stroke volume and cardiac output following passive leg raising during pregnancy ranged from -2.2% to 1.6% and from -3.7% to 3.2%, respectively. Although passive leg raising caused no significant changes in systemic vascular resistance, cardiac output or heart rate, mean arterial pressure decreased in the first and second trimesters. In uncomplicated twin pregnancies, maternal cardiovascular adaptation is evident from the first trimester. Twin pregnancies show a reduced preload reserve in the second half of gestation.

Maternal cardiac output response to colloid preload and vasopressor therapy during spinal anaesthesia for caesarean section in patients with severe pre‐eclampsia: a randomised, controlled trial

We examined the haemodynamic effects of colloid preload, and phenylephrine and ephedrine administered for spinal hypotension, during caesarean section in 42 women with severe early onset pre-eclampsia. Twenty patients with pre-delivery spinal hypotension were randomly allocated to receive an initial dose of either 50 μg phenylephrine or 7.5 mg ephedrine; the primary outcome was percentage change in cardiac index. After a 300-ml colloid preload, mean (SD) cardiac index increased from 4.9 (1.1) to 5.6 (1.2) l.min-1 .m-2 (p < 0.01), resulting from an increase in both heart rate, from 81.3 (17.2) to 86.3 (16.5) beats.min-1 (p = 0.2), and stroke volume, from 111.8 (19.0) to 119.8 (17.9) ml (p = 0.049). Fourteen (33%) and 23 (54.8%) patients exhibited a stroke volume response > 10% and > 5%, respectively; a significant negative correlation was found between heart rate and stroke volume changes. Spinal hypotension in 20 patients was associated with an increase from baseline in cardiac index of 0.6 l.min-1 .m-2 (mean difference 11.5%; p < 0.0001). After a median [range] dose of 50 [50-150] μg phenylephrine or 15 [7.5-37.5] mg ephedrine, the percentage change in cardiac index during the measurement period of 150 s was greater, and negative, in patients receiving phenylephrine vs. ephedrine, at -12.0 (7.3)% vs. 2.6 (6.0)%, respectively (p = 0.0001). The percentage change in heart rate after vasopressor was higher in patients receiving phenylephrine, at -9.1 (3.4)% vs. 5.3 (12.6)% (p = 0.0027), as was the change in systemic vascular resistance, at 22.3 (7.5) vs. -1.9 (10.5)% (p < 0.0001). Phenylephrine effectively reverses spinal anaesthesia-induced haemodynamic changes in severe pre-eclampsia, if left ventricular systolic function is preserved.

The association of air temperature with cardiac arrhythmias.

The body response to meteorological influences may activate pathophysiological mechanisms facilitating the occurrence of cardiac arrhythmias in susceptible patients. Putative underlying mechanisms include changes in systemic vascular resistance and blood pressure, as well as a network of proinflammatory and procoagulant processes. Such a chain reaction probably occurs within the time window of several hours, so use of daily average values of meteorological elements do not seem appropriate for investigation in this area. In addition, overall synoptic situation, and season-specific combinations of meteorological elements and air pollutant levels probably cause the overall effect rather than a single atmospheric element. Particularly strong interrelations have been described among wind speed, air pressure and temperature, relative air humidity, and suspended particulate matter. This may be the main reason why studies examining the association between temperature and ventricular arrhythmias have found linear positive, negative, J-shaped or no association. Further understanding of the pathophysiological adaptation to atmospheric environment may help in providing recommendations for protective measures during "bad" weather conditions in patients with cardiac arrhythmias.

Haemodynamic changes with paracetamol in critically-ill children

PurposeParacetamol has been associated with a reduction in blood pressure, especially in febrile, critically-ill adults. We hypothesised that blood pressure would fall following administration of paracetamol in critically-ill children and this effect would be greater during fever and among children with a high body surface area to weight ratio. MethodsA 12-month prospective observational study of children (0–16years) admitted to paediatric intensive care, who underwent pulse contour analysis and received paracetamol concurrently. ResultsMean arterial blood pressure decreased significantly by 4.7% from baseline (95% CI 1.75–8.07%) in 31 children following 148 doses of paracetamol. The nadir was 2-hour post-dose. The effect was pronounced in children with fever at baseline (6.4%, 95% CI 2.8–10%), although this was not statistically significant. There was no simple relationship between this effect and body surface area to weight ratio. The association between a change in blood pressure and changes in heart rate or measured stroke volume was poor; therefore it was likely that a change in the systemic vascular resistance contributes most to this effect. ConclusionThere is a significant but modest reduction in blood pressure post-paracetamol in critically-ill children. This is likely related to a change in systemic vascular resistance.

Impact of mild orthostatic stress on aortic-cerebral hemodynamic transmission: insight from the frequency domain.

High cerebral pressure and flow fluctuations could be a risk for future cerebrovascular disease. This study aims to determine whether acute systemic vasoconstriction affects the dynamic pulsatile hemodynamic transmission from the aorta to the brain. We applied a stepwise lower body negative pressure (LBNP) (-10, -20, and -30 mmHg) in 15 young men to induce systemic vasoconstriction. To elucidate the dynamic relationship between the changes in aortic pressure (AoP; estimated from the radial arterial pressure waveforms) and the cerebral blood flow velocity (CBFV) at the middle cerebral artery (via a transcranial Doppler), frequency-domain analysis characterized the beat-to-beat slow oscillation (0.02-0.30 Hz) and the intra-beat rapid change (0.78-9.69 Hz). The systemic vascular resistance gradually and significantly increased throughout the LBNP protocol. In the low-frequency range (LF: 0.07-0.20 Hz) of a slow oscillation, the normalized transfer function gain of the steady-state component (between mean AoP and mean CBFV) remained unchanged, whereas that of the pulsatile component (between pulsatile AoP and pulsatile CBFV) was significantly augmented during -20 and -30 mmHg of LBNP (+28.8% and +32.4% vs. baseline). Furthermore, the relative change in the normalized transfer function gain of the pulsatile component at the LF range correlated with the corresponding change in systemic vascular resistance (r = 0.41, P = 0.005). Regarding the intra-beat analysis, the normalized transfer function gain from AoP to CBFV was not significantly affected by the LBNP stimulation (P = 0.77). Our findings suggest that systemic vasoconstriction deteriorates the dampening effect on the pulsatile hemodynamics toward the brain, particularly in slow oscillations (e.g., 0.07-0.20 Hz).NEW & NOTEWORTHY We characterized the pulsatile hemodynamic transmission from the heart to the brain by frequency-domain analysis. The low-frequency transmission was augmented with a mild LBNP stimulation partly due to the elevated systemic vascular resistance. A systemic vasoconstriction deteriorates the dampening effect on slow oscillations of pulsatile hemodynamics toward the brain.

PS 08-15 ORAL DOSE OF CAPSAICIN INCREASES BLOOD PRESSURE IN HEALTHY SUBJECTS.

Objective: Capsaicin, the active pungent of spicy foods, is the endogenous ligand of the transient receptor potential cation channel vanilloid subfamily member 1 (TRPV1). Experimental data show that TRPV1 activation leads to vasodilation, water retention and natriuresis - effects that may reduce blood pressure (BP). Recent data found an association between spicy food consumption and improved outcomes, including cardiovascular disease. Capsaicin-induced BP lowering might explain this protective effect. We therefore investigated the BP effects of TRPV1 activation by capsaicin in healthy subjects. Design and Method: In this double blind, randomized, placebo-controlled, cross-over study, participants received either two doses of capsaicin (5.2–6.2 mg, 81.250–97.200 SHU) or matching placebo in random order on two different study days, separated by at least one week. In the 2-hour follow-up after the first dose, BP, heart rate (HR), cardiac output (CO) and systemic vascular resistance index (SVRI) using Omron and NexfinTM and both plasma and urine sodium were repeatedly measured. To challenge osmoregulation, we studied the same parameters for 4 hours after a water loading test (20 mL/kg in 20 minutes) combined with the second dose. Results: We included 12 healthy male subjects (mean age: 23 years). Relative to placebo, 30 min after first capsaicin dose systolic BP significantly increased (after 2 hours: +2.8 ± 1.1 mmHg; p=0.02), but not diastolic BP (Fig 1A). The second capsaicin dose plus water load increased placebo-subtracted diastolic, but not systolic, BP with 4.2 ± 3.6 mmHg after 30 min (p = 0.04). Compared to placebo, capsaicin did affect neither water balance nor natriuresis (Fig 1B,C). Effects on HR, CO and SVRI did not differ from placebo. Conclusions: In healthy subjects, capsaicin increased BP on the short term. We could not identify changes in systemic vascular resistance or water and sodium balance, which were thought to underlie the hypothesized BP effects. Whether long-term capsaicin has similar effects remains to be determined.

Impact of changes in systemic vascular resistance on a novel non-invasive continuous cardiac output measurement system based on pulse wave transit time: a report of two cases

The inaccuracy of arterial waveform analysis for measuring continuos cardiac output (CCO) associated with changes in systemic vascular resistance (SVR) has been well documented. A new non-invasive continuous cardiac output monitoring system (esCCO) mainly utilizing pulse wave transit time (PWTT) in place of arterial waveform analysis has been developed. However, the trending ability of esCCO to measure cardiac output during changes in SVR remains unclear. After a previous multicenter study on esCCO measurement, we retrospectively identified two cases in which apparent changes in SVR developed in a short period during data collection. In each case, the trending ability of esCCO to measure cardiac output and time component of PWTT were analyzed. Recorded data suggest that the time component of PWTT may have a significant impact on the accuracy of estimating stroke volume during changes in SVR. However, further prospective clinical studies are required to test this hypothesis.

The relationship between the area of peripherally-derived pressure volume loops and systemic vascular resistance

Arterial and photoplethysmographic (PPG) waveforms have been utilized to non-invasively estimate stroke volume from the pulse contour. The ability of these pulse contour devices to accurately predict stroke volume is degraded when afterload changes significantly. There is a need for a non-invasive device capable of identifying when vascular tone has changed. Shelley et al. previously described a qualitative relationship between peripheral pressure volume (PV) loops (in which pressure waveforms from an intra-arterial catheter are combined with volume waveforms from the PPG waveform) and changes in vascular tone. The purpose of this study was to quantitatively compare changes in the area of peripheral PV loops with changes in systemic vascular resistance (SVR) in a patient population undergoing major surgery. Physiologic data from ten patients undergoing liver transplantation was extracted from a hemodynamic database. A peak detection algorithm was applied to both the arterial and PPG waveforms, which were manually aligned so that the troughs occurred at identical time points. PV loop area (PVA) for each heartbeat was calculated and median PVA was recorded for each minute. PVA for each patient was indexed to the average value for the first 5min (because PPG amplitude has no standard and is not comparable between patients) and compared to indexed SVR at all points for which SVR was available. SVR and PVA were plotted as a function of time and outliers (3.1%) removed. The Pearson correlation coefficient describing the relationship between PVAi and SVRi was 0.67 (1,728min of data, p=0.0020, sign test over 10 patients) and between MAP and SVR was 0.71. There was no meaningful correlation between ΔSVR and either ΔPVA or ΔMAP (based on minute-to-minute changes). Indexed values of PVA are correlated with indexed values of SVR and may serve as a useful monitor for changes in afterload but in their present form do not offer added value above the measurement of MAP. Incorporation of different (e.g. finger, forehead) and redundant (e.g. bilateral) sites may significantly improve the accuracy of this technique.

Changes in Vascular Hemodynamics in Older Women Following 16 Weeks of Combined Aerobic and Resistance Training

The purpose of this study was to determine whether combined (aerobic and anaerobic) training decreases blood pressure (BP) and improves vascular properties. Seventy-nine postmenopausal women were randomly assigned to 3 groups that trained at different frequencies. Maximum oxygen uptake, body composition, BP, and arterial elasticity were evaluated prior to training and after 16 weeks of training. There was a significant time effect (decrease) for resting systolic BP (SBP) and rate pressure product. Exercise SBP, diastolic BP (DBP), heart rate, and RPP also decreased. Changes in total vascular impedance were related to SBP and changes in systemic vascular resistance were related to changes in DBP independent of body composition changes. Our findings suggest that combined training reduces SBP and improves vascular properties and that combined training 1 d/wk decreases BP similar to more frequent combined training. Training-induced changes in arterial resistance and impedance may be involved in inducing changes in BP.

Evaluation of Hemodynamic Autonomic Control in an Animal Model of Acute Heart Failure Induced by High Dose of Halothane

Acute animal models of cardiac failure are necessary to study new therapeutic options and should be thoroughly characterized from the hemodynamic point of view, including the response of the autonomic nervous system. Thus, the aim of this work was to characterize the pathophysiological adaptation of the autonomic nervous system to acute cardiac failure induced by high doses of halothane (4%). In six sheep, electrocardiogram, aortic pressure and flow were obtained and calculation of systemic vascular resistances was done. Variability analyses in the time and frequency domains were also performed. In the time domain, after heart failure induction using halothane 4%, a significant decrease of both aortic blood flow variability (from 0.13 ± 0.05 to 0.09 ± 0.02 L min−1, p < 0.05) and the broad band spectra (from 1.80 ± 0.66 to 1.25 ± 0.57 L2 min−2, p < 0.005) was observed. Both mean RR (472 ± 44 to 567 ± 68 ms, p < 0.01), and low frequency band of RR intervals (from 6.2 ± 0.9 to 7.7 ± 1.5 ms2, p < 0.05), showed a significant increase, and no change in systemic vascular resistance (from 54.9 ± 29.5 to 50.3 ± 38.4 mmHg min L−1), all of them after heart failure induction. We conclude that in this model of heart failure the autonomic nervous system activity is still functioning, the combination of increased mean and RR low frequency band, with no change in systemic vascular resistance suggest an increase in the sympathetic control (due to maintained SVR), in an attempt to compensate the depression in the cardiac activity and hemodynamic alterations after severe myocardial depression induced by halothane.

Multicenter Study Verifying a Method of Noninvasive Continuous Cardiac Output Measurement Using Pulse Wave Transit Time

Many technologies have been developed for minimally invasive monitoring of cardiac output. Estimated continuous cardiac output (esCCO) measurement using pulse wave transit time is one noninvasive method. Because it does not require any additional sensors other than those for conducting 3 basic forms of monitoring (electrocardiogram, pulse oximeter wave, and noninvasive (or invasive) arterial blood pressure measurement), esCCO measurement is potentially useful in routine clinical circulatory monitoring for any patient including low-risk patients. We evaluated the efficacy of noninvasive esCCO using pulse wave transit time in this multicenter study. We compared esCCO and intermittent bolus thermodilution cardiac output (TDCO) in 213 patients, 139 intensive care units (ICUs), and 74 operating rooms (ORs), at 7 participating institutions. We performed electrocardiogram, pulse oximetry, TDCO, and arterial blood pressure measurements in patients in ICUs and ORs; a single calibration was performed to measure esCCO continuously. TDCO measurement was performed once daily for ICU patients and every hour for OR patients, and just before the removal of the pulmonary arterial catheter from patients in both the ICU and OR. We evaluated esCCO against TDCO with correlation analysis and Bland and Altman analysis and also assessed the change of bias over time. Furthermore, we inspected the impact of change in systemic vascular resistance (SVR) on change in bias because abnormal SVR was assumed to be a factor contributing to the change of the bias. From among 588 esCCO and TDCO datasets (excluding calibration points), 587 datasets were analyzed for 213 patients. The analysis results show a correlation coefficient of 0.79 (P < 0.0001, 95% confidence limits of 0.756-0.819), a bias (mean difference between esCCO and TDCO) of 0.13 L/min (95% confidence interval of bias 0.04-0.22 L/min), and a precision (1 SD) of 1.15 L/min (95% prediction interval was -2.13 to 2.39 L/min). There were no significant differences among 3 defined time intervals over 48 hours after calibration (repeated-measures analysis of variance P = 0.781) in the ICU. The influence of SVR on esCCO analysis showed a correlation coefficient between SVR and an error of 0.37 (P < 0.0001, 95% confidence interval 0.298-0.438). The efficacy of noninvasive esCCO technology was compared with TDCO in 213 cases. Five hundred eighty-seven datasets comparing esCCO and TDCO showed close correlation and small bias and precision, which were comparable to current arterial waveform analysis technologies.

Hypotension from spinal anesthesia in patients aged greater than 80 years is due to a decrease in systemic vascular resistance

Study ObjectivesTo determine the exact mechanism underlying spinal anesthesia-induced hypotension in the elderly patient. DesignRetrospective case-control study. SettingOperating room (OR) in a general hospital. MeasurementsRecords from 60 consecutive patients over 80 years of age, who underwent hip fracture repair (intramedullary nail or compression hip screw) during spinal anesthesia were studied. After injection of isobaric 0.5% bupivacaine in the L3-L4 intervertebral space in the lateral decubitus position, patients were turned supine. Acetate Ringer’s solution (300 mL) was infused over 30 minutes after subarachnoid puncture. A decrease in systolic arterial pressure to less than 100 mmHg was treated with an intravenous injection of 5 mg ephedrine. The hypotension group (n=18) comprised patients who required ephedrine during the 30 minutes after the puncture, and the nonhypotension group (n=42) consisted of patients who maintained stable arterial pressure with crystalloid infusion only. MeasurementsCardiac output (CO) and stroke volume variation (SVV) every 20 seconds using the Vigileo-FloTrac system continuously from arrival in the operating room (OR) to 30 minutes after the subarachnoid puncture were recorded. Serial changes in systemic vascular resistance (SVR), CO, and SVV from baseline after puncture were compared between the two groups. Main ResultsThe decrease in SVR over 20 minutes after the puncture was significantly greater in the hypotension group than the nonhypotension group (P = 0.047). Cardiac output was stable in the two groups. Stroke volume variation in the first 10 minutes after the puncture increased to similar levels in the two groups, then decreased gradually to baseline. No significant differences were noted in circulatory parameters on arrival at the OR. ConclusionsA decrease in SVR, not CO, is the main mechanism of hypotension seen during spinal anesthesia in elderly patients.