Venous capacitance and venous return in young adults with typical vasovagal syncope: a cross-sectional study

Vasovagal syncope (VVS) has a high prevalence in the general population and is associated with potential complications. There is limited information on the possible association between venous capacitance (VC) and venous return (VR), important determinants of preload and VVS. Since the tilt test was reported to yield a high rate of false positive results, the aim of this study was to evaluate whether abnormal VC and VR at baseline could predispose individuals to VVS.To this end, 88 young, healthy volunteers were recruited and classified to 26 (29.5%) who experienced typical VVS and 62 (70.5%) who did not. VC and VR were evaluated with a commercial device and plethysmography applied to the elevated legs. Maximum venous outflow (MVO), segmental venous capacitance (SVC) and MVO/SVC ratio were calculated and averaged.No significant differences between MVO (5.0±0.5 vs 5.6±0.8, p>0.05), SVC (6.0±0.5 vs 6.3±0.8, p>0.05) or MVO/SVC ratio (0.83±0.02 vs 0.86±0.03, p>0.05) were observed for the non-VVS and VVS volunteers, respectively. There was a significant association between a higher MVO and SVC values and a larger decrease in diastolic blood pressure with standing, although correlations were weak (R2=0.0582 and 0.0681, respectively).In conclusion, at baseline, VC and VR are not impaired in healthy volunteers with a history of VVS. It remains unknown if similar results would be found in patients with cardiovascular comorbidities. Also, the sensitivity of VC and VR evaluations to identify a predisposition for VVS following physiological provocations merits further study.

Prayer-related Physical Activities for Cardiovascular Health

Introduction: Muslims are obligated to pray 5 times daily. Each prayer is a number of rakaa completed with a set of physical movements, preferably in the neighborhood masjid. The vascular effects of religious-related physical activities (RRPA) are not known, despite the well-known cardiovascular benefits of regular physical activity. Therefore, the current study examines the relationships of RRPA with vascular measures. Methodology: Arterial and venous indices at rest and after 5 of arterial occlusion were examined in 192 healthy participants (age: 19-85 years) using strain gauge plethysmography. The participants’ RRPA were collected in a 1-to-1 interview, including prayer (PN) and rakaa number (RN) performed, distance (DW) and time (TW) required to walk to the masjid, and the daily (DA) and weekly (WA) attendance to the masjid. Results: Resting blood flow correlated significantly with DW, TW, DA, and WA (r=0.2-0.4; p<0.01). Resting vascular resistance correlated with DW, TW, DA, and WA (r=-0.14-0.2; p<0.05). Resting venous capacitance correlated with DW, TW, DA, and WA (r=0.14-0.17; p<0.05). Resting outflow correlated with DW, TW, DA, and WA (r=0.15-0.2; p<0.05). Occlusion blood flow correlated with DW (r=0.17; p=0.02). Occlusion outflow correlated with DW and DA (r=0.16-0.17; p<0.05). Additionally, arterial and venous indices were greater (p<0.05) in the participants regularly prayed in the masjid. Discussion: The results confirm the importance of physical activities for the circulatory system. Uniquely, the data shows that RRPA might contribute to the maintenance of vascular function.

Conceptual Considerations for Device-Based Therapy in Acute Decompensated Heart Failure

Acute decompensated heart failure remains the most common cause of hospitalization in older adults, and studies of pharmacological therapies have yielded limited progress in improving outcomes for these patients. This has prompted the development of novel device–based interventions, classified mechanistically based on the way in which they intend to improve central hemodynamics, increase renal perfusion, remove salt and water from the body, and result in clinically meaningful degrees of decongestion. In this review, we provide an overview of the pathophysiology of acute decompensated heart failure, current management strategies, and failed pharmacological therapies. We provide an in depth description of seven investigational device classes designed to target one or more of the pathophysiologic derangements in acute decompensated heart failure, denoted by the acronym DRI 2 P 2 S. Dilators decrease central pressures by increasing venous capacitance through splanchnic nerve modulation. Removers remove excess fluid through peritoneal dialysis, aquaphoresis, or hemodialysis. Inotropes directly modulate the cardiac nerve plexus to enhance ventricular contractility. Interstitial devices enhance volume removal through lymphatic duct decompression. Pushers are novel descending aorta rotary pumps that directly increase renal artery pressure. Pullers reduce central venous pressures or renal venous pressures to increase renal perfusion. Selective intrarenal artery catheters facilitate direct delivery of short acting vasodilator therapy. We also discuss challenges posed in clinical trial design for these novel device–based strategies including optimal patient selection and appropriate end points to establish efficacy.

Cardiovascular System: Part II

This chapter gives an overview of blood circulation, then focuses on regional blood flow to a number of organs, and ends with a description of the microcirculation. It begins with venous return and blood volume. Most blood volume is contained within the venous system, and the chapter describes several mechanisms that allow for this volume of blood to be returned to the right heart. Next it describes the various means by which the blood circulation and volume are controlled. The chapter devotes considerable time describing the central, peripheral, and hormonal regulation of circulation and blood volume. Next, regional blood flow is described. Blood flow in different regions of the body is usually autoregulated, and variably controlled by the autonomic nervous system, and various humoral agents. The final section describes the mechanism by which blood flow in the microcirculation delivers nutrients, and removes wastes from the tissue by diffusion. Also described are the regulation of the microcirculation by pre and post capillary sphincters, and the effect of viscosity. This review contains 5 figures, and 40 references. Keywords: venous return, vascular compliance, venous capacitance, vasomotor center, hypothalamic-pituitary-adrenal axis (HPA), microcirculation, regional blood flow, mixed venous oxygen saturation

Blood reservoir function in patients with Fontan circulation and asplenia syndrome

Splanchnic circulation constitutes a major portion of the vasculature capacitance and plays an important role in maintaining blood perfusion. Because patients with asplenia syndrome lack this vascular bed as a blood reservoir, they may have a unique blood volume and distribution, which may be related to their vulnerability to the haemodynamic changes often observed in clinical practice. During cardiac catheterisation, the mean circulatory filling pressure was calculated with the Valsalva manoeuvre in 19 patients with Fontan circulation, including 5 patients with asplenia syndrome. We also measured the cardiac output index and circulatory blood volume by using a dye dilution technique. The blood volume and the mean circulatory filling pressure and the venous capacitance in patients with asplenia syndrome were similar to those in the remaining patients with Fontan circulation (85 ± 14 versus 77 ± 18 ml/kg, p = 0.43, 31 ± 8 versus 27 ± 5 mmHg, p = 0.19, 2.8 ± 0.6 versus 2.9 ± 0.9 ml/kg/mmHg, p = 0.86). Unexpectedly, our data indicated that patients with asplenia syndrome, who lack splanchnic capacitance circulation, have blood volume and venous capacitance comparable to those in patients with splanchnic circulation. These data suggest that (1) there is a blood reservoir other than the spleen even in patients with asplenia; (2) considering the large blood pool of the spleen, the presence of a symmetrical liver may represent the possible organ functioning as a blood reservoir in asplenia syndrome; and (3) if this is indeed the case, there may be a higher risk of hepatic congestion in patients with Fontan circulation with asplenia syndrome than in those without.

Hemodynamics for the Vascular Surgeon

Knowledge of the pathophysiology of peripheral vascular disorders is necessary for vascular surgeons to identify disease and develop appropriate treatment plans. Hemodynamics is the branch of physiology dealing with the forces involved in the circulation of the blood. Principles of hemodynamics and blood flow physiology are the basis for noninvasive vascular testing methods that are used for diagnosis and objective assessment of disease severity. Clinical decision making should incorporate anatomic, functional, and physiologic considerations. This review focuses on understanding clinical applications of fundamental hemodynamic principles as they apply in normal and pathologic states. Key concepts are presented in the context of common clinical scenarios. This review contains 18 figures, and 43 references. Key words: ambulatory venous hypertension; collateral development; fluid energy; Hagen-Poiseuille equation; laminar and nonlaminar (turbulent) flow; newtonian and nonnewtonian fluid characteristics; pressure and flow relationships; pressure, resistance, and regulation of perfusion; pulse wave propagation; venous capacitance; venous pump; wall tension, wall, shear, and the law of LaPlace

Vasodilators in critical illness

Vasodilators are commonly used in the intensive care unit (ICU) to control arterial blood pressure, unload the left or the right heart, control pulmonary artery pressure, and improve microcirculatory blood flow. Vasodilator refers to drugs acting directly on the smooth muscles of peripheral vessel walls and drugs are usually classified based on their mechanism (acting directly or indirectly) or site of action (arterial or venous vasodilator). Drugs that have a predominant effect on resistance vessels are arterial dilators and drugs that primarily affect venous capacitance vessels are venous dilators. Drugs that interfere with sympathetic nervous system, block renin-angiotensin system, phosphodiesterase inhibitors, and nitrates are some examples of drugs with indirect effect. Vasodilator drugs play a major therapeutic role in hypertensive emergencies, primary and secondary pulmonary hypertension, acute left heart, and circulatory shock. This review discusses the main types of vasodilators drugs commonly used in the ICU.