Do alterations in pulmonary vascular tone result in changes in central blood volumes? An experimental study

Background The effects of selective pulmonary vascular tone alterations on cardiac preload have not been previously examined. Therefore, we evaluated whether changing pulmonary vascular tone either by hypoxia or the inhalation of aerosolized prostacyclin (PGI2) altered intrathoracic or pulmonary blood volume (ITBV, PBV, respectively), both as surrogate for left ventricular preload. Additionally, the mean systemic filling pressure analogue (Pmsa) and pressure for venous return (Pvr) were calculated as surrogate of right ventricular preload. Methods In a randomized controlled animal study in 6 spontaneously breathing dogs, pulmonary vascular tone was increased by controlled moderate hypoxia (FiO2 about 0.10) and decreased by aerosolized PGI2. Also, inhalation of PGI2 was instituted to induce pulmonary vasodilation during normoxia and hypoxia. PBV, ITBV and circulating blood volume (Vdcirc) were measured using transpulmonary thermo-dye dilution. Pmsa and Pvr were calculated post hoc. Either the Wilcoxon-signed rank test or Friedman ANOVA test was performed. Results During hypoxia, mean pulmonary artery pressure (PAP) increased from median [IQR] 12 [8–15] to 19 [17–25] mmHg (p < 0.05). ITBV, PBV and their ratio with Vdcirc remained unaltered, which was also true for Pmsa, Pvr and cardiac output. PGI2 co-inhalation during hypoxia normalized mean PAP to 13 (12–16) mmHg (p < 0.05), but left cardiac preload surrogates unaltered. PGI2 inhalation during normoxia further decreased mean PAP to 10 (9–13) mmHg (p < 0.05) without changing any of the other investigated hemodynamic variables. Conclusions In spontaneously breathing dogs, changes in pulmonary vascular tone altered PAP but had no effect on cardiac output, central blood volumes or their relation to circulating blood volume, nor on Pmsa and Pvr. These observations suggest that cardiac preload is preserved despite substantial alterations in right ventricular afterload.

Associations between spleen volume and exercise capacity in advanced heart failure patients with left ventricular assist device

Background The spleen has been recognized as an important organ with several functions such as a reservoir of blood volume, and an involvement in iron metabolism by processing of aged red blood cells and recycling iron. During exercise, spleen contracts, and red blood cells pooled in the spleen are recruited into the systemic circulation. So far, we reported that spleen size changed in advanced heart failure (HF) with left ventricular assist device (LVAD). In addition, spleen volume was related to pulmonary capillary wedge pressure (PCWP) or right atrial pressure (RAP) as parameters of cardiac preload. However, it remains unclear about the relationship between spleen volume and exercise capacity in advanced HF with LVAD. Purpose The purpose of this study was to investigate the associations between spleen volume and exercise capacity in advanced HF patients with LVAD. Methods We enrolled 27 HF patients (21 males, 45±12 years) with LVAD (HeartMate II™; Abbott, Chicago, IL, USA) for use as a bridge to heart transplantation. All patients underwent blood test, echocardiography, right heart catheterization, computed tomography (CT) and cardiopulmonary exercise testing (CPET). Spleen size was measured by CT volumetry. We excluded patients with splenic infarction or aortic valve closure surgery. Results At baseline, body mass index, blood brain natriuretic peptide levels, hemoglobin levels, left ventricular ejection fraction were 21.4±3.1 kg/m2, 73.8 (51.9–165.8) pg/mL, 12.1 (10.6–13.4) g/dL, 24.8±14.7%, respectively. Total cardiac output (CO), the sum of pump flow and CO of native heart was 4.6±0.9 L/min, and spleen volume was 184.9±48.8 mL. As for parameters of CPET, peak heart rate (HR), peak VO2, and peak O2 pulse were 128±25 beats/min, 14.2±3.3 mL/kg/min, and 6.6±1.9 mL/beat. At rest, there were significant correlations between spleen volume and PCWP (r=0.382, p=0.049), RAP (r=0.406, p=0.035) or pulsatility index (r=0.384, p=0.047), despite no correlations with total CO or pump flow. During exercise, there were significant interrelations of spleen volume with peak VO2 (r=0.451, p=0.018) and peak O2 pulse (r=0.427, p=0.026). Furthermore, peak VO2 was interrelated with peak HR (r=0.481, p=0.011) or hemoglobin levels (r=0.649, p&lt;0.001). Remarkably, spleen volume was significantly correlated with hemoglobin levels (r=0.391, p=0.043) (Figure). Interpreting these results based on Fick's formula, the proportion of native CO to total CO is very small at rest, but increases during exercise. The spleen during exercise may contribute to increased native CO, especially stroke volume. Moreover, the spleen may be related to both cardiac preload and oxygen carrying capacity, resulting in a significant association between spleen volume and peak VO2. Conclusion Spleen volume could be a useful predictor of exercise capacity in advanced HF patients with LVAD, reflecting splenic function to modulate cardiac preload and blood hemoglobin levels. Spleen volume and exercise parameters Funding Acknowledgement Type of funding source: None

Diagnostic characteristics of 11 formulae for calculating corrected flow time as measured by a wearable Doppler patch

Background Change of the corrected flow time (Ftc) is a surrogate for tracking stroke volume (SV) in the intensive care unit. Multiple Ftc equations have been proposed; many have not had their diagnostic characteristics for detecting SV change reported. Further, little is known about the inherent Ftc variability induced by the respiratory cycle. Materials and methods Using a wearable Doppler ultrasound patch, we studied the clinical performance of 11 Ftc equations to detect a 10% change in SV measured by non-invasive pulse contour analysis; 26 healthy volunteers performed a standardized cardiac preload modifying maneuver. Results One hundred changes in cardiac preload and 3890 carotid beats were analyzed. Most of the 11 Ftc equations studied had similar diagnostic attributes. Wodeys’ and Chambers’ formulae had identical results; a 2% change in Ftc detected a 10% change in SV with a sensitivity and specificity of 96% and 93%, respectively. Similarly, a 3% change in Ftc calculated by Bazett’s formula displayed a sensitivity and specificity of 91% and 93%. FtcWodey had 100% concordance and an R2 of 0.75 with change in SV; these values were 99%, 0.76 and 98%, 0.71 for FtcChambers and FtcBazetts, respectively. As an exploratory analysis, we studied 3335 carotid beats for the dispersion of Ftc during quiet breathing using the equations of Wodey and Bazett. The coefficient of variation of Ftc during quiet breathing for these formulae were 0.06 and 0.07, respectively. Conclusions Most of the 11 different equations used to calculate carotid artery Ftc from a wearable Doppler ultrasound patch had similar thresholds and abilities to detect SV change in healthy volunteers. Variation in Ftc induced by the respiratory cycle is important; measuring a clinically significant change in Ftc with statistical confidence requires a large sample of beats.

A hydraulic model of cardiovascular physiology and pathophysiology embedded into a computer-based teaching system for student training in laboratory courses

Functional understanding of the different parts of the cardiovascular system is essential for an insight into pathomechanisms of numerous diseases. During training cardiovascular physiology, students and early-stage medical personnel should understand the role of different functional parameters for systolic and diastolic blood pressure, as well as for blood flow. The impact of isolated parameters can only be studied in models. Here physical hydraulic models are an advantage in which the students have a direct contact to the mechanical properties of the circulatory system. But these models are often difficult to handle. The aim of the present study was to develop a comprehensive model of the cardiovascular system, including a mechanical heart with valves, an elastic aorta, a more rigid peripheral artery system, a total peripheral resistance, and a venous reservoir representing the variable cardiac preload. This model allows one to vary systematically several functional parameters and to continuously record their impact on pressure and flow. This model is embedded into a computer-based teaching system (LabTutor) in which the students are guided through the handling of the model (as well as the systematic variation of parameters), and the measured data can be analyzed. This hybrid teaching system, which is routinely integrated in physiology laboratory courses of medical students, allows students to work with a complex hydraulic model of the cardiovascular system and to analyze systematically the impact of influencing variables (e.g., increased peripheral resistance or changed cardiac preload) as well as pathophysiological dysfunctions (e.g., reduced aortic compliance).

A novel technique of reimplantation of a radial artery that makes a hairpin turn to reduce the excessive vascular access flow in a dialysis patient

We report a new technique called “reimplantation of an artery with a hairpin turn (RAHT)” to reduce excessive vascular access flow. A 73-year-old woman on dialysis consulted us for vascular surgery because of an increased cardiac preload. Chest radiography and echocardiography revealed an excessive shunt flow in the brachial artery (flow rate, 2336 mL/min). Vascular echo-Doppler of the left upper limb showed that the radial artery made a hairpin turn at the arteriovenous fistula (diameter, 9 mm). Diameters of the radial artery proximal and distal to the arteriovenous fistula were 5.4 and 3.7 mm, respectively. We ligated and divided the juxta-anastomosis proximal radial artery and subsequently created an end-to-side anastomosis between the proximal radial artery and the distal radial artery. The anastomosis ostium in the distal radial artery (the recipient) was formed with a 4-mm longitudinal and gently curved incision. We performed RAHT so that the small anastomosis between both arteries and the small diameter of the distal radial artery juxta-anastomosis segment could reduce the vascular access flow. The flow rates in the brachial artery were 500 mL/min just after surgery and 560 mL/min at 2 months after surgery. Postoperative chest radiography and echocardiography confirmed a decrease in cardiac preload. We believe that this RAHT technique could be useful as one of the options to reduce the flow in patients who have excessive vascular access flow with a radial artery that makes a hairpin turn.