Flicker-induced changes in retinal blood flow assessed by Doppler optical coherence tomography

We used Doppler Fourier-domain optical coherence tomography (OCT) to investigate flicker-induced changes of total retinal blood flow. Total retinal blood flow was measured by summing flows in veins imaged in double-circular scans around the optic disc. In 3 healthy volunteers, total retinal blood flow was measured before and 10-15 seconds after 30 seconds of flicker stimulation. The average blood flow increased 22.2% (p = 0.002). The total venous and arterial vessel cross-sectional area increased 11.3% (p < 0.001) and +2.7% (p = 0.28) respectively. The average venous and arterial flow velocity were calculated indirectly by dividing total retinal blood flow by total venous and arterial cross-sectional areas. They also increased by 8.8% (p = 0.046) and 18.3% (p = 0.004), respectively. These results show that human retinal blood flow increases after visible flicker stimulation, and this could be measured with OCT.     

Mechanism of Effect of Thoracic Inferior Vena Cava Constriction on Renal Water Excretion

Persistent secretion of vasopressin and/ or diminished distal fluid delivery have been proposed to explain the impaired water excretion associated with low-output cardiac failure. In the present investigation cardiac output (CO) was diminished in anesthetized dogs undergoing a water diuresis by constriction of the thoracic inferior vena cava (TIVC). In intact animals (group I) acute TIVC constriction decreased CO from 3.5 to 2.2 liters/min (P < 0.005) as urinary osmolality (U(osm)) increased from 103 to 543 mosmols/ kg (P < 0.001) and free water clearance (C(H2o)) decreased from 2.1 to -0.6 ml/min (P < 0.001). This antidiuretic effect was disassociated from changes in renal arterial and venous pressures, glomerular filtration rate, solute excretion, and renal innervation. To examine the role of vasopressin in this antidiuresis, studies (group II) were performed in acutely hypophysectomized, steroid-replaced animals. In these animals TIVC constriction decreased CO to a similar degree from 3.4 to 2.1 liters/min (P < 0.001). However, the effects on U(osm) (87-104 mosmols/kg) and C(H2o) (2.1-1.6 ml/min) were significantly less than in intact dogs. In another group of hypophysectomized animals, (group III) renal arterial and venous pressures were not controlled, and the effect of TIVC constriction on U(osm) was not significant (65-79 mosmols/kg) although C(H2o) decreased from 3.3 to 1.9 ml/min (P < 0.001). In both the group II and III studies, there were linear correlations between the changes in C(H2o) and the urine flow. Studies were also performed in baroreceptor-denervated animals with intact hypothalamo-neurohypophyseal tracts, and acute TIVC constriction altered neither U(osm) nor C(H2o) when renal arterial pressure was controlled. These results therefore indicate that the effect of TIVC constriction on U(osm) is primarily vasopressin mediated while the effect on C(H2o) is mediated both by vasopressin release and diminished distal fluid delivery. A decrease in renal arterial pressure, or some consequence thereof, seems to be an important determinant of the latter effect.     

A Comparison of Ventricular Function During High Right Ventricular Septal and Apical Pacing after His-Bundle Ablation for Refractory Atrial Fibrillation

This study compares LV performance during high right ventricular septal (RVS) and apical (RVA) pacing in patients with LV dysfunction who underwent His-bundle ablation for chronic AF. We inserted a passive fixation pacing electrode into the RVA and an active fixation electrode in the RVS. A dual chamber, rate responsive pulse generator stimulated the RVA through the ventricular port and the RVS via the atrial port. Patients were randomized to initial RVA (VVIR) or RVS (AAIR) pacing for 2 months. The pacing site was reversed during the next 2 months. At the 2 and 4 month follow-up visit, each patient underwent a transthoracic echocardiographical study and a rest/exercise first pass radionuclide ventriculogram. We studied nine men and three women (mean age of 68 +/- 7 years) with congestive heart failure functional Class (NYHA Classification): I (3 patients), II (7 patients), and III (2 patients). The QRS duration was shorter during RVS stimulation (158 +/- 10 vs 170 +/- 11 ms, P < 0.001). Chronic capture threshold and lead impedance did not significantly differ. LV fractional shortening improved during RVS pacing (0.31 +/- 0.05 vs 0.26 +/- 0.07, P < 0.01). RVS activation increased the resting first pass LV ejection fraction (0.51 +/- 0.14 vs 0.43 +/- 0.10, P < 0.01). No significant difference was observed during RVS and RVA pacing in the exercise time (5.6 +/- 3.2 vs 5.4 +/- 3.1, P = 0.6) or the exercise first pass LV ejection fraction (0.58 +/- 0.15 vs 0.55 +/- 0.16, P = 0.2). The relative changes in QRS duration and LV ejection fraction at both pacing sites showed a significant correlation (P < 0.01). We conclude that RVS pacing produces shorter QRS duration and better chronic LV function than RVA pacing in patients with mild to moderate LV dysfunction and chronic AF after His-bundle ablation.     

Impact of Right Ventricular Pacing Sites on Exercise Capacity during Ventricular Rate Regularization in Patients with Permanent Atrial Fibrillation

Background: The deleterious effects of right ventricular apical (RVA) pacing may offset the potential benefit of ventricular rate (VR) regularization and rate adaptation during an exercise in patient's atrial fibrillation (AF). Methods: We studied 30 patients with permanent AF and symptomatic bradycardia who receive pacemaker implantation with RVA (n = 15) or right ventricular septal (RVS, n = 15) pacing. All the patients underwent an acute cardiopulmonary exercise testing using VVI‐mode (VVI‐OFF) and VVI‐mode with VR regularization (VRR) algorithm on (VVI‐ON). Results: There were no significant differences in the baseline characteristics between the two groups, except pacing QRS duration was significantly shorter during RVS pacing than RVA pacing (138.9 ± 5 vs 158.4 ± 6.1 ms, P = 0.035). Overall, VVI‐ON mode increased the peak exercise VR, exercise time, metabolic equivalents (METs), and peak oxygen consumption (VO₂max), and decreased the VR variability compared with VVI‐OFF mode during exercise (P < 0.05), suggesting that VRR pacing improved exercise capacity during exercise. However, further analysis on the impact of VRR pacing with different pacing sites revealed that only patients with RVS pacing but not patients with RVA pacing had significant increased exercise time, METs, and VO₂max during VVI‐ON compared with VVI‐OFF, despite similar changes in peaked exercise VR and VR variability. Conclusion: In patients with permanent AF, VRR pacing at RVS, but not at RVA, improved exercise capacity during exercise.     

Atrial natriuretic factor: comparability of venous and arterial plasma measurements in man at rest and during exercise

1. Simultaneously obtained arterial and venous plasma atrial natriuretic factor (ANF) concentrations were compared at supine rest and during graded dynamic leg exercise in 10 healthy male subjects (aged 33-51 years). 2. Arterial ANF concentrations ranged between 12 and 179 pg/ml and venous concentrations between 9 and 177 pg/ml. 3. A positive correlation between arterial and venous concentrations was found (r = 0.984). 4. Arterial ANF concentrations were higher than venous concentrations in all pairs of samples (n = 31), but the difference was small and changed little with exercise: the mean difference was 5 pg/ml at rest, 12 pg/ml during submaximal exercise and 6 pg/ml during maximal exercise. 5. The extraction ratios for ANF varied greatly, but were in general lower (P less than 0.05) during maximal exercise (median 0.07, range 0.01-0.32) than at rest (median 0.22, range 0.05-0.33). 6. It was concluded that the plasma ANF concentration in a peripheral arm vein is a good indicator of the systemic peptide concentration at rest as well as during dynamic leg exercise.     

Non-invasive assessment of endothelial function in normal pregnancy.

OBJECTIVE: To assess endothelial function in normal pregnancy by non-invasive methods. METHODS: Flow-mediated dilatation of the brachial artery was measured by ultrasonography in 157 women with normal singleton pregnancies between 10 and 40 weeks' gestation and 19 non-pregnant controls. RESULTS: Flow-mediated dilatation in the non-pregnant controls was 6.42 +/- 2.45%. In pregnant women, between 10 and 30 weeks, the mean flow-mediated dilatation (8.84 +/- 3.18%) was significantly higher than the non-pregnant controls (P = 0.002), but after 30 weeks of gestation there was a decrease to prepregnancy levels. Resting vessel diameter and blood flow were significantly increased in pregnancy, mainly after 30 weeks' gestation (P < 0.001, P < 0.001, respectively). Flow-mediated dilatation was significantly correlated to resting vessel diameter and reactive hyperemia. CONCLUSION: Normal pregnancy is associated with enhanced endothelial function which is apparent from at least 10 weeks' gestation.     

呼气末正压通气对伴有低血容量趋势行机械通气患者血流动力学的影响

目的探讨呼气末正压（PEEP）对低血容量趋势患者行机械通气时血流动力学的影响。 方法选择20例伴有低血容量趋势需行机械通气的患者作为研究对象。所有患者均在基础呼吸模式上分别加用PEEP 0、5、10、15 cmH₂O,每次持续约30 min。记录所有患者的心率、平均动脉压（MAP）、肺动脉嵌压（PAWP）、每搏指数（SVI）、心排血量（CO）、心指数及体循环血管阻力指数（SVRI）等血流动力学指标,中心静脉压（CVP）、髂总静脉压（CIVP）及ΔCVP等静脉回流梯度指标,吸气峰压（PIP）、气道阻力（RAW）、用吸气暂停键测出平台压（Pplat）、气道平均压力（Pmean）及肺循环血管阻力指数（PVRI）等呼吸力学指标。 结果随着PEEP水平的增加,患者心率、PAWP及SVRI均显著增加,而MAP、CO、心指数及SVI则逐渐下降（F = 20.311、15.100、32.915、15.100、198.635、435.100、17.000,P均< 0.001）,且CO于PEEP为5 cmH₂O时与PEEP为0 cmH₂O时比较,已经出现显著降低[（5.31 ± 0.11）L / min vs.（5.46 ± 0.24）L / min];患者的CVP、CIVP的水平逐渐升高,而ΔCVP逐渐下降（F = 47.879、27.578、21.393,P均< 0.001）;患者的PIP、Pplat、Pmean、PVRI水平均逐渐升高,且PEEP为15 cmH₂O时达最高（F = 67.152、74.025、818.208、31.141,P均< 0.001）,而RAW在不同PEEP间比较差异无统计学意义（F = 2.082,P = 0.131）。 结论对有低容量趋势行机械通气的患者,当PEEP ≥ 5 cmH₂O即出现CO明显下降,因此对于有低容量趋势患者尽量使用最小PEEP来达到治疗目的。     

Endothelial flow-mediated dilatation and exercise capacity in highly trained endurance athletes

Brachial artery ultrasound during reactive hyperemia is a noninvasive method of assessing peripheral endothelium-dependent vasodilatation. Aerobic exercise has the potential to improve local endothelial function. We sought to analyze the effects of regular aerobic training on brachial artery endothelial function in endurance athletes. We studied diameter and blood flow of the brachial artery in 32 endurance male athletes and 30 healthy male subjects. In the same subjects flow-mediated dilatation of the brachial artery was recorded by inducing an ischemia through a forearm arterial occluding cuff. Maximal oxygen consumption was significantly higher in the athletes group than in the controls (61.24 +/- 5.43 vs 44.49 +/- 2.68 ml/kg/min, p < 0.001). Flow-mediated dilatation of the brachial artery induced by forearm arterial occlusion in athletes was also higher than that of the control subjects (17.1 +/- 2.3 vs 11.2 +/- 1.7, p=0.002). Furthermore, there was an association between flow-mediated dilatation and VO2max (r=0.69, p < 0.001). Baseline measurements of the diameter and the blood flow volume of the brachial artery were similar in both groups. During reactive hyperemia period, the percent of the changes of endothelial diameters and flow were significantly higher in athletes than in controls. Higher flow-mediated dilatation levels in athletes reflect better vascular adaptation to habitual aerobic exercise.     

Arterial stiffness, endothelial function and microcirculatory reactivity in healthy young males

Large (C1) and small (C2) arterial stiffness has been suggested to parallel endothelial reactivity and has led researchers to suggest parameters of arterial stiffness may be alternative measures to brachial sonographic assessments of flow-mediated dilatation (FMD). However, past studies comparing these measures can be criticized. In addition to %FMD responses, we recorded concurrent hyperaemic responses of the microcirculation and both were compared with C1 and C2. Twenty-nine subjects 18-30 years of age were investigated. Radial blood pressure was recorded with a tonometer. Pulse waveform analysis was performed to calculate C1 and C2. These were compared with %FMD responses and responses of finger flux measured by laser Doppler fluxmetry (LDF); pulsatile finger volume measured by photoplethysmography (PPG); and palm skin temperature measured by infrared thermography (Tpalm) (i.e. microcirculatory responses). Responses were determined as % changes from control. We only found weak relationships between C1 and %FMD (r=0.4, P=0.04); C2 and %PPG (r=0.38, P=0.07); and C2 and %LDFdorsal (r=-0.38; P=0.04). Responses of %FMD weakly parallel those of C1. Neither C2 nor C1 are viable indicators of endothelial or microcirculatory reactivity (i.e. hyperaemic or venous constriction) in healthy, resting young males. These findings refute the claims that C1 and C2 are substitute measures to sonographic assessments of brachial FMD.     

The impact of arterial oxygen tension on venous oxygen saturation in circulatory failure

Central and mixed venous oxygen saturations have been used to guide resuscitation in circulatory failure, but the impact of arterial oxygen tension on venous oxygen saturation has not been thoroughly evaluated. This observational study investigated the impact of arterial oxygen tension on venous oxygen saturation in circulatory failure. Twenty critically ill patients with circulatory failure requiring mechanical ventilation and a pulmonary artery catheter in an intensive care unit in a tertiary hospital in Western Australia were recruited. Samples of arterial blood, central venous blood, and mixed venous blood were simultaneously and slowly drawn from the arterial, central venous, and pulmonary artery catheter, respectively, at baseline and after the patient was ventilated with 100% inspired oxygen for 5 min. The blood samples were redrawn after a significant change in cardiac index (>or =10%) from the baseline, occurring within 24 h of study enrollment while the patient was ventilated with the same baseline inspired oxygen concentration, was detected. An increase in inspired oxygen concentration significantly increased the arterial oxygen tension from 12.5 to 38.4 kPa (93.8-288 mmHg) (mean difference, 25.9 kPa; 95% confidence interval [CI], 7.5-31.9 kPa; P < 0.001) and the venous oxygen saturation from 69.9% to 76.5% (mean difference, 6.6%; 95% CI, 5.3% - 7.9%; P < 0.001). The effect of arterial oxygen tension on venous oxygen saturation was more significant than the effect associated with changes in cardiac index (mean difference, 2.8%; 95% CI, -0.2% to 5.8%; P = 0.063). In conclusion, arterial oxygen tension has a significant effect on venous oxygen saturation, and this effect is more significant and consistent than the effect associated with changes in cardiac index.     

Association between an increased surface area of peritoneal microvessels and a high peritoneal solute transport rate.

OBJECTIVE: The peritoneal solute transport rate (PSTR) often increases, especially for small solutes, during long-term peritoneal dialysis (PD) treatment. Although the mechanism by which PSTR increases in PD patients is not known, it is likely that an increased PSTR reflects an increased surface area of the peritoneal capillary and post-capillary venules (microvessels), but this has not previously been investigated. The aim of this study was to clarify the relationship between PSTR and peritoneal microvessel alterations in biopsy specimens of peritoneum obtained from PD patients after various times on PD, and the possible contribution of the duration of PD in relation to these alterations. DESIGN: Tissue from the parietal peritoneum was obtained from 22 PD patients (age 48.5 +/- 9.0 years, duration of PD 66.3 +/- 46.6 months, incidence of peritonitis 0.3/patient-year).The patients were subdivided into three groups according to duration of PD: zero months (group 0, n = 4), less than 60 months (group I, n = 7), and more than 60 months (group II; n = 11). METHODS: For each specimen, the relative microvessel area (RVA) calculated as total area of microvessels/total area of peritoneal field, and the relative microvessel number (RVN), calculated as number of microvessels/total area of peritoneal field, were determined. The ratio RVA/RVN was used to assess the average area of microvessels. The PSTR was evaluated for creatinine, glucose, beta2-microglobulin, and albumin using the peritoneal equilibration test. RESULTS: The dialysate-to-plasma concentration ratio (D/P) for creatinine showed a significant positive correlation with both RVA (rho = 0.77, p < 0.001) and RVA/RVN (rho = 0.51, p = 0.01), but not with RVN. The D/P for beta2-microglobulin correlated with RVA (rho = 0.51, p = 0.015) but not with RVN or RVA/RVN. No differences were found between the three groups in the values for RVN, whereas there was an apparent significant increase in RVA with time on PD (p < 0.001 for group 0 vs both groups I and II). Furthermore, in high transporters, RVA tended to be higher in group II than in group I. CONCLUSIONS: The present study demonstrates for the first time that an increased peritoneal solute transport rate (for both creatinine and beta2-microglobulin) is associated with an increased surface area of peritoneal microvessels, especially in patients on long-term PD treatment. This indicates that increased vascularization and/or dilatation of peritoneal microvessels may play a key role in the development of a high PSTR.     

Initial color Doppler findings in retinal vein occlusion

PURPOSE: We assessed early hemodynamic characteristics of various types of retinal vein occlusion using color Doppler imaging and spectral analysis. METHODS: We measured the maximum systolic and diastolic blood flow velocities and the resistance index (RI) in the central retinal artery and the maximum and minimum blood flow velocities in the central retinal vein of affected eyes and contralateral unaffected eyes in 102 adults (63 men and 39 women; mean age, 61 +/- 14.6 years) who presented with retinal vein occlusion. Sixty-three control subjects (27 men and 36 women; mean age, 50 +/- 22.1 years) were also investigated. RESULTS: No significant differences in hemodynamic characteristics were found between the control subjects' eyes and the patients' unaffected eyes. In the 18 cases of ischemic central retinal vein occlusion, the mean diastolic arterial flow velocity (p = 0.005) and venous flow velocity (p < 0.04) were lower and the mean RI was higher (p = 0. 0002) in the affected eyes than in the unaffected contralateral eyes. In the 51 cases of nonischemic central retinal vein occlusion, the mean diastolic arterial flow velocity (p < 0.0001) and venous flow velocity (p < 0.0001) also were lower and the mean RI (p < 0.0001) was higher in the affected eyes than in the unaffected contralateral eyes. These variables were different in the ischemic versus nonischemic types of central retinal vein occlusion. In the 33 cases of branch retinal vein occlusion, no significant differences were observed in arterial or venous blood flow velocities in the affected versus unaffected eyes. The mean RI in the affected eyes was significantly higher (p = 0.009) in patients with central versus branch retinal vein occlusion. CONCLUSIONS: These results suggest that previous arterial disorders were not involved in the pathogenesis of central retinal vein occlusion in these patients. The findings also support the value of Doppler imaging and spectral analysis in the diagnosis and evaluation of retinal vein occlusion and confirm the involvement of arterial flow in venous occlusion.     

Transvaginal color Doppler assessment of venous flow in adnexal masses.

OBJECTIVE: To analyze the usefulness of transvaginal color Doppler assessment of venous flow in the differential diagnosis of adnexal masses. MATERIAL AND METHODS: Ninety-one consecutive patients (mean age: 46.6 years, range: 16-81 years) diagnosed as having an adnexal mass were evaluated by transvaginal color Doppler sonography prior to surgery. Color Doppler was used to detect and analyze the flow velocity waveform from arterial and venous blood flow within the tumor. For arterial signals the resistance index and peak systolic velocity, and for veins the maximum venous flow velocity, were calculated. Receiver operator characteristic curves were plotted to determine the best venous flow velocity cut-off. According to our previous study using arterial Doppler, a tumor was considered as malignant when flow was detected and the lowest resistance index was < or = 0.45. Using venous Doppler a mass was considered as malignant when flow was detected and the venous flow velocity was > or = the best cut-off found on the receiver operator characteristic curve. Definitive histopathological diagnosis was obtained in all cases. Sensitivity, specificity, positive predictive value and negative predictive value for B-mode morphology (evaluation performed according to Sassone's scoring system), arterial Doppler, venous Doppler, and a combination of both arterial and venous Doppler were calculated. RESULTS: Twenty-five masses (27.5%) were malignant and 66 (72.5%) benign. Arterial and venous flow was found more frequently in malignant than in benign masses (92% vs. 41% (P < 0.001) and 72% vs. 21% (P < 0.001), respectively). The resistance index was significantly lower in malignant tumors (0.42 vs. 0.60, P = 0.0003). No differences were found in peak systolic velocity. Venous flow velocity was significantly higher in malignant masses (18.1 cm/s vs. 8.9 cm/s, P = 0.0006). The best cut-off of venous flow velocity was 10 cm/s. Sensitivity, specificity, positive predictive value and negative predictive value for morphology, arterial Doppler, venous Doppler, and the combination of both arterial and venous Doppler were 92%, 71%, 45%, 96%; 76%, 95%, 87%, 91%; 68%, 94%, 81%, 89%; and 88%, 91%, 79%, 95%, respectively. CONCLUSIONS: Our results indicate that preoperative evaluation by venous flow assessment of adnexal masses may be useful to discriminate between malignant and benign tumors.     

Left ventricular dyssynchrony resulting from right ventricular apical pacing: relevance of baseline assessment

Objectives: Evaluation of left ventricular (LV) dyssynchrony in patients undergoing short‐term right ventricular apical (RVA) pacing and correlation with baseline echocardiographic and clinical characteristics. Background: RVA pacing causes abnormal ventricular depolarization that may lead to mechanical LV dyssynchrony. The relationships between pacing‐induced LV dyssynchrony and baseline echocardiographic and clinical variables have not been fully clarified. Methods: Tissue Doppler echocardiography was performed in 153 patients before and after RVA pacing. LV dyssynchrony was measured by the time between the shortest and longest electromechanical delays in the five basal LV segments (intra‐LV). The prevalence and degree of LV dyssynchrony after RVA pacing was evaluated in three groups: baseline LV ejection fraction (LVEF) <35%, 35–55%, and ≥55%. The intrapatient effect of RVA pacing was determined as the percent increase in intra‐LV value (Δintra‐LV%). The pacing‐induced intra‐LV was correlated with baseline variables. Results: The prevalence and degree of LV dyssynchrony after RVA pacing was significantly higher in patients with lower LVEF (P < 0.001). ΔIntra‐LV% was inversely correlated with baseline intra‐LV and LVEF (B =?2.6, B =?4.2, P < 0.001). Baseline intra‐LV and LV end‐systolic volume correlated positively with intra‐LV after RVA pacing (B = 0.49, B = 0.6, P < 0.001), whereas LVEF showed an inverse correlation. Conclusions: The degree of LV dyssynchrony induced by RVA is variable. Patients with higher baseline LV dyssynchrony, more dilated LV, and more depressed LVEF showed a higher degree of LV dyssynchrony during pacing. These findings may assume importance in predicting the risk of heart failure in pacemaker patients.     

The effect of exercise on large artery haemodynamics in healthy young men

BACKGROUND: Brachial blood pressure predicts cardiovascular outcome at rest and during exercise. However, because of pulse pressure amplification, there is a marked difference between brachial pressure and central (aortic) pressure. Although central pressure is likely to have greater clinical importance, very little data exist regarding the central haemodynamic response to exercise. The aim of the present study was to determine the central and peripheral haemodynamic response to incremental aerobic exercise. MATERIALS AND METHODS: Twelve healthy men aged 31 +/- 1 years (mean +/- SEM) exercised at 50%, 60%, 70% and 80% of their maximal heart rate (HRmax) on a bicycle ergometer. Central blood pressure and estimated aortic pulse wave velocity, assessed by timing of the reflected wave (T(R)), were obtained noninvasively using pulse wave analysis. Pulse pressure amplification was defined as the ratio of peripheral to central pulse pressure and, to assess the influence of wave reflection on amplification, the ratio of peripheral pulse pressure to nonaugmented central pulse pressure (PPP : CDBP-P1) was also calculated. RESULTS: During exercise, there was a significant, intensity-related, increase in mean arterial pressure and heart rate (P < 0.001). There was also a significant increase in pulse pressure amplification and in PPP : CDBP-P(1) (P < 0.001), but both were independent of exercise intensity. Estimated aortic pulse wave velocity increased during exercise (P < 0.001), indicating increased aortic stiffness. There was also a positive association between aortic pulse wave velocity and mean arterial pressure (r = 0.54; P < 0.001). CONCLUSIONS: Exercise significantly increases pulse pressure amplification and estimated aortic stiffness.     

Differential reactivity in the pulmonary circulation

A new method for relating regional intravascular resistance to pulmonary arterial, capillary, and venous pressure and volume was used to evaluate local differences of reactivity in the pulmonary blood vessels in the isolated lung lobe of the dog.Intravascular infusion of isoproterenol caused active dilatation of pulmonary arteries and veins. Capillary conductance (1/resistance) and volume increased, possibly as a result of the opening of previously closed capillaries. Serotonin infusion caused active constriction of both the pulmonary arteries and veins. A low dose of serotonin (1.5 mug/min per kg) caused predominant constriction of whichever vessels were upstream (arteries during forward perfusion, veins during reverse perfusion). A high dose of serotonin (4.5-5.0 mug/min per kg) caused constriction of both upstream and downstream vessels. Metabolic inactivation of serotonin by the lung is suggested as an explanation for these observations. Histamine infusion caused predominant venous constriction whether veins were upstream or downstream. Capillary volume and conductance decreased during forward and reverse perfusion, perhaps as a result of pericapillary edema formation. Large arterial vessels constricted slightly, whereas small arterial vessels appeared to be passively dilated.     

The effect of exercise on adrenocortical responsiveness of patients with chronic low back pain, controlled for psychological strain

OBJECTIVE: To investigate the effects of high-intensity aerobic exercise on adrenocortical responsiveness and on standard outcome measures in patients with chronic low back pain. DESIGN: Controlled clinical trial. SETTING: Physical therapy department of a university general hospital. SUBJECTS: Sixty-four patients with chronic low back pain were randomly allocated into positive and negative suppression test groups and assigned to exercise protocol. INTERVENTIONS: Subjects in the positive and negative dexamethasone suppression test groups received a 12-week high-intensity aerobic exercise programme. MAIN OUTCOME MEASURES: Dexamethasone suppression test as an index of adrenocortical responsiveness, pain measured with the McGill Pain Questionnaire, functional status measured with the Roland Morris Disability Questionnaire, and psychological strain measured with the Hospital Anxiety and Depression Scale. RESULTS: Data analysis in the positive group identified a significant reduction of pain by 30% (t(30) = 11.2, P<0.001), a recovery of the lost functioning by 34% (t(30) = 19.7, P<0.001), a reduction of anxiety/depression by 25% (t(30) = 10.2, P<0.001), and a change in adrenocortical responsiveness by 40% (t(30) = 14.1, P<0.001). In the dexamethasone suppression test negative group, data analysis identified a significant reduction of pain by 8% (t(31) = 4.2, P<0.001), a recovery of lost functioning by 10% (t(31) = 4.8, P<0.001), a reduction of anxiety/depression by 11% (t(31) = 5.0, P<0.001), and no change in adrenocortical responsiveness (t(31) = 1.2, P=0.22). In univariate analysis between-subject differences were significant for dexamethasone suppression test (F(61) = 163, P<0.001), and for anxiety/depression (F(61) = 21.3, P<0.001). CONCLUSION: Exercise alleviated pain, functional disability and anxiety/depression, also improved adrenocortical responsiveness in patients with chronic low back pain with dexamethasone suppression test positive values.     

Effects of folate treatment and homocysteine lowering on resistance vessel reactivity in atherosclerotic subjects

Hyperhomocysteinemia is associated with arterial hypertension and endothelial dysfunction in healthy humans. Placebo-controlled vitamin intervention studies cannot distinguish intrinsic actions of homocysteine (tHcy) and folate concentrations on the endothelium. The present two-period crossover study investigates the effects of tHcy lowering through oral folic acid on antioxidant status and resistance vessel reactivity in patients with established coronary artery disease (CAD). We investigated 27 male patients with angiographically documented multivessel CAD aged 50 (range 46-56) years. Resistance vessel reactivity was assessed by measurement of postischemic reactive hyperemia (RH) in the forearm using venous occlusion plethysmography at baseline, after 6 weeks of treatment with 5 mg of oral folic acid, and after a washout period of another 6 weeks. Plasma folate increased 3.49-fold with a mean tHcy reduction of 21.3%. Peak reactivity of resistance vessels improved significantly (18.97-23.60 ml/min(-1) per 100 ml; P = 0.01) with unchanged total antioxidant status (TAS; 0.912-0.944 microM; P = 0.4). This effect was limited to subjects (n = 14) with a tHcy reduction >2 microM (median reduction, 14.4-9.6 microM, P < 0.001). In the 13 subjects with a below-median reduction, tHcy remained unaltered (9.7-9.6 microM, P = 0.88) and TAS increased significantly (0.923-1.055 microM, P = 0.006), whereas RH peak flow was not affected (20.22-22.99 ml/min(-1) per 100 ml, P = 0.28). Homocysteine lowering >2 microM through folic acid supplementation improves resistance vessel reactivity in patients with CAD. Our data support the hypothesis that homocysteine lowering may have intrinsic vasoprotective effects largely independent of folate.     

前列地尔对脓毒性休克患者复苏达标后血流动力学指标的疗效观察

目的观察前列地尔对脓毒性休克患者复苏达标后血流动力学指标及预后的影响。 方法选择2016年9月至2018年9月就诊于兰州大学第一医院东岗院区重症医学科的80例脓毒性休克患者，待患者按早期目标导向治疗（EGDT）复苏达标后，将80例患者分为治疗组和对照组，每组各40例。所有患者进行抗感染、机械通气、器官功能维护及营养代谢等一般治疗，治疗组在此基础上静脉滴注前列地尔脂微球注射液，对照组则静脉滴注等渗NaCl溶液，均连续应用14 d。记录两组患者的一般资料，治疗前及治疗1、2、7 d后的急性病生理学和长期健康评价（APACHE）Ⅱ评分、序贯器官衰竭估计（SOFA）评分、平均动脉压、心率、中心静脉压、血乳酸、pH值、中心静脉血氧饱和度（ScvO₂）等血流动力学指标以及住院病死率，28 d病死率，ICU住院时间及总住院时间。 结果治疗组与对照组患者治疗前及治疗1、2、7 d后APACHEⅡ评分、SOFA评分、平均动脉压、心率、中心静脉压、血乳酸、pH值及ScvO₂水平比较，差异均有统计学意义（F = 11.661、8.689、11.005、12.006、9.045、10.217、11.065、6.031，P = 0.026、0.043、0.009、0.023、0.037、0.045、0.041、0.044）。进一步两两比较发现，治疗组患者治疗2、7 d后APACHEⅡ评分、SOFA评分、心率、中心静脉压及血乳酸水平均较对照组同时间点显著降低（P均< 0.05），治疗1、2、7 d后平均动脉压及治疗2、7 d后pH值和ScvO₂水平均较对照组同时间点显著升高（P均< 0.05）。治疗组患者的住院病死率[20.0%（8/40）vs. 35.0%（14/40），χ² = 53.333，P<0.001]、28 d病死率[25.0%（10/40）vs. 40.0%（16/40），χ² = 48.000，P < 0.001]、ICU住院时间[（6.7 ± 2.2）d vs.（12.2 ± 2.5）d，t = 2.831，P = 0.047]及总住院时间[（14.4 ± 3.6）d vs.（25.2 ± 4.9）d，t = 3.007，P = 0.037]均较对照组显著降低。 结论前列地尔可有效改善脓毒性休克患者的血流动力学指标及预后。     

Endogenous vasopressin and copeptin response in multiple trauma patients

Endogenous arginine vasopressin (AVP) levels in multiple trauma patients are unknown. Arginine vasopressin is considered to play an important role in severe hemorrhage. In this prospective study, 87 multiple trauma patients (Injury Severity Score >15) and 50 healthy volunteers were enrolled. On admission to the emergency department (ED), demographic, clinical, and laboratory data were documented, and blood was sampled for determination of AVP (radioimmunosassay) and copeptin, a stable fragment of the AVP precursor (immunoluminometric assay). In patients requiring intensive care unit (ICU) therapy, blood and data sampling were repeated at 4, 6, and 24 h after ED admission. Linear logistic and mixed-effects regression analyses were used for statistical analysis. On ED admission, AVP plasma concentrations (43.2 +/- 84.9 pM) were significantly increased when compared with controls (0.92 +/- 0.44 pM, P < 0.001). Plethysmographic oxygen saturation was the only parameter independently associated with AVP (regression coefficient, -0.126; 95% confidence interval, -0.237 to -0.014; P = 0.03). No correlation was observed between AVP and survival (P = 0.62), hemodynamic variables (systolic arterial pressure, P = 0.24; MAP, P = 0.59; diastolic arterial pressure, P = 0.74; central venous pressure, P = 0.36), or brain trauma (P = 0.46). In ICU patients, AVP decreased during the first 24 h (P < 0.001) and was independently associated with heart rate (P = 0.02) and blood glucose (P = 0.009). Copeptin concentrations were correlated with AVP (r2 = 0.718, P < 0.001). In conclusion, AVP was significantly increased in multiple trauma patients and seems to be an integral part of the neuroendocrine response to severe injury. In ICU patients, AVP decreased to moderately elevated levels within 24 h after ED admission.