1
|
Næsheim T, How OJ, Myrmel T. Propulsion of blood through the right heart circulatory system. SCAND CARDIOVASC J 2017; 52:4-12. [PMID: 29189081 DOI: 10.1080/14017431.2017.1409909] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Venous return, the right heart function and the pulmonary circulation is an integrated functional unit. The right ventricle is particularly load sensitive, and will be influenced directly by the venous and pulmonary physiology. In this paper we present important physiological principles that govern the diagnosis and treatment of dysfunctions affecting the return of blood to the heart and the transfer of the cardiac output from the right to the left side. We do evaluate both basic science and the clinical literature pointing to practical aspects of physiological knowledge.
Collapse
Affiliation(s)
- Torvind Næsheim
- a Department of Anesthesiology , University Hospital North Norway , Tromsø , Norway.,b Institute of Clinical Medicine , University of Tromsø, The Arctic University of Norway , Tromsø , Norway
| | - Ole-Jakob How
- c Institute of Medical Biology , University of Tromsø, The Arctic University of Norway , Tromsø , Norway
| | - Truls Myrmel
- b Institute of Clinical Medicine , University of Tromsø, The Arctic University of Norway , Tromsø , Norway.,d The Heart and Lung Clinic , University Hospital North Norway , Tromsø , Norway
| |
Collapse
|
2
|
Tyberg JV, Bouwmeester JC, Burrowes LM, Parker KH, Shrive NG, Wang JJ. A new teaching model of the systemic circulation that incorporates reservoir characteristics. Artery Res 2015. [DOI: 10.1016/j.artres.2015.02.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
|
3
|
Krabbendam I, Jacobs LCA, Lotgering FK, Spaanderman MEA. Venous response to orthostatic stress. Am J Physiol Heart Circ Physiol 2008; 295:H1587-93. [PMID: 18708445 DOI: 10.1152/ajpheart.00571.2008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Head-up tilt (HUT) induces a reduction in preload, which is thought to be restored through sympathetic venoconstriction, reducing unstressed volume (V(u)) and venous compliance (VeC). In this study, we assessed venous inflow and outflow responses and their reproducibility and determined the relation with autonomic function during HUT. Eight healthy non-pregnant women were subjected to 20 degrees head-down tilt to 60 degrees HUT at 20 degrees intervals. At each rotational step, we randomly assessed forearm pressure-volume (P-V) curves (venous occlusion plethysmography) during inflow (VeC(IN)) and outflow [venous emptying rate (VER(OUT))]. VeC(IN) was defined as the ratio of the slope of the volume-time curve and pressure-time curve, with direct intravenous pressure measurement. VER(OUT) was determined using the derivate of a quadratic regression model using cuff pressure. We defined V(u) as the y-intercept of the P-V curve. We calculated, for both methods, the coefficients of reproducibility (CR) and variation (CV). Vascular sympathetic activity was determined by spectral analysis. VeC(IN) decreased at each rotational step compared with the supine position (P<0.05), whereas VER(OUT) increased. CR of VeC(IN) was higher in the supine position than VER(OUT) but lower during HUT. CV varied between 19% and 25% (VeC(IN)) and between 12% and 21% (VER(OUT)). HUT decreased V(u). The change in VeC(IN) and VER(OUT) correlated with the change in vascular sympathetic activity (r= -0.36, P<0.01, and r=0.48, P<0.01). This is the first study in which a reproducible reduction in VeC(IN) and V(u) and a rise in VER(OUT) during HUT are documented. The alterations in venous characteristics relate to changes in vascular sympathetic activity.
Collapse
Affiliation(s)
- Ineke Krabbendam
- Department of Obstetrics and Gynecology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
| | | | | | | |
Collapse
|
4
|
de Boer D, Ring C, Wood M, Ford C, Jessney N, McIntyre D, Carroll D. Time course and mechanisms of mental stress-induced changes and their recovery: hematocrit, colloid osmotic pressure, whole blood viscosity, coagulation times, and hemodynamic activity. Psychophysiology 2007; 44:639-49. [PMID: 17521375 DOI: 10.1111/j.1469-8986.2007.00536.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The mechanisms for stress-induced changes in hematocrit and blood viscosity are unclear. Twenty-two males completed experimental (30 min baseline, 10 min mental stress, 30 min recovery) and no-stress control conditions (70 min). Hemostatic and hemodynamic activity were measured throughout. Hematocrit, colloid osmotic pressure, and blood viscosity displayed parallel patterns: a progressive increase with stress, followed by a gradual recovery. Correlational and covariance analyses indicated that the increase in hematocrit may be mediated by arterial pressure whereas recovery may be mediated by colloid osmotic pressure. Analyses also indicated that acute changes in blood viscosity may depend on hematocrit. These data suggest that stress disturbs hematocrit, colloid osmotic pressure, and blood viscosity through arterial pressure. Poststress, elevated colloid osmotic pressure may drive its own recovery and that of hematocrit and blood viscosity.
Collapse
Affiliation(s)
- Dolf de Boer
- Behavioural Medicine Group, School of Sport and Exercise Sciences, University of Birmingham, Birmingham, UK.
| | | | | | | | | | | | | |
Collapse
|
5
|
Mitzner W, Tyberg JV, Stickland MK, Robinson VJB, Rowell LB, Sandblom E, Axelsson M, Farrell AP, Shoukas AA. The following letters are in response to the Point:Counterpoint series “Hypoxic pulmonary vasoconstriction is/is not mediated by increased production of reactive oxygen species” that appears in this issue. J Appl Physiol (1985) 2006; 101:1267-8. [PMID: 16973821 DOI: 10.1152/japplphysiol.00794.2006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
|
6
|
Reddi BAJ, Carpenter RHS. Venous excess: a new approach to cardiovascular control and its teaching. J Appl Physiol (1985) 2005; 98:356-64. [PMID: 15322065 DOI: 10.1152/japplphysiol.00535.2004] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The circulatory control system is driven partly by factors relating to the arterial side and partly by factors relating to the venous side. Students are generally provided with a conceptually clear account of the arterial side, based on sound homeostatic mechanisms of negative feedback from a well-defined error signal, arterial pressure. However, on the venous side, teaching is often based on the notion of venous return, a concept that, as normally presented, is imprecise and intangible, a frequent cause of confusion that may lead to errors of clinical practice. Although one can trace these misconceptions back to some of Guyton's publications, Guyton himself was well aware of the complexities of venous resistance and capacitance but has not always been well served by subsequent misinterpretation. The fundamental problem with venous return that makes it inappropriate for controlling the circulation is that it lacks the essential requirement of being an error signal. We propose instead a new variable, venous excess, which represents the accumulation of any mismatch between the rate of blood entering the great veins and the rate of leaving, the cardiac output. As well as being directly observable without intervention (in a patient's jugular vein), it meets all of the requirements of an error signal: via the Starling mechanism it stimulates cardiac output, regulates venous compliance, and in the longer term is an important determinant of fluid intake and excretion, and these effects act to reduce the original perturbation. Based on this concept, we suggest a simple and secure basis for teaching the control of the circulation that avoids undue reliance on entities that are difficult to specify or measure and emphasizes the role of feedback and the similarities between the arterial and venous mechanisms.
Collapse
Affiliation(s)
- B A J Reddi
- Physiological Laboratory, University of Cambridge, CB2 3EG Cambridge, UK
| | | |
Collapse
|
7
|
Tanaka G, Sawada Y. Examination of normalized pulse volume-blood volume relationship: toward a more valid estimation of the finger sympathetic tone. Int J Psychophysiol 2003; 48:293-306. [PMID: 12798989 DOI: 10.1016/s0167-8760(03)00056-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The pulsatile ac component (DeltaI) superimposed on the transmitted dc components (I: tissue plus blood) are obtained from a near-infrared finger photoplethysmogram using a wavelength of 810 nm. Only the dc component is given in an ischaemic circulatory state (I(t): tissue only). Based on Lambert-Beer's law, normalized pulse volume (NPV; =DeltaI/I) and blood volume [BV; =ln(I(t)/I)] have recently been advocated as quantitative measures. In this study, the NPV-BV relationship was examined using the finger occlusion method during rest and mental arithmetic in 16 female undergraduates. Finger vascular tone during stress was evaluated by the distance of the linear and parallel NPV-BV regression lines (D(NB)) between rest and stress conditions. A reference standard was provided by the linear regression lines of compliance index (CI=NPV/pulse pressure) and BV to the transmural pressure. The estimates at 40 mmHg of transmural pressure, as an arbitrarily chosen reference point, were calculated (CI40 and BV40). D(NB) correlated well with them (r=0.81 and 0.94, respectively). The multiple regression with mean blood pressure indicated that the combination of D(NB) and the reactivities in heart period could explain approximately 50% of valiance in pressor response. In conclusion, D(NB) is easily obtainable from the NPV-BV function and seems to be more specific and valid than NPV as an index of finger sympathetic tone, since it adjusts the mechanical effect of arterial distending pressure.
Collapse
Affiliation(s)
- Gohichi Tanaka
- Department of Psychology, School of Medicine, Sapporo Medical University, South 1 West 17, Chuo-ku, Sapporo 060-8556, Japan.
| | | |
Collapse
|
8
|
Dzeka TN, Arnold JMO. Prostaglandin modulation of venoconstriction to physiological stress in normals and heart failure patients. Am J Physiol Heart Circ Physiol 2003; 284:H790-7. [PMID: 12578811 DOI: 10.1152/ajpheart.00572.2001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Prostaglandins released from blood vessels modulate vascular tone, and inhibition of their production during exogenous infusions of catecholamines causes increased venoconstriction. To determine the influence of prostaglandin production on venoconstriction during physiological stimuli known to cause sympathetic activation, and to assess its importance in chronic heart failure (CHF), we studied 11 normal subjects (62 +/- 4 yr) and 14 patients with CHF (64 +/- 2 yr, left ventricular ejection fraction 23 +/- 1%, New York Heart Association classes II and III) (means +/- SE). Dorsal hand vein distension was measured during mental arithmetic (MA), cold pressor test (CPT), and lower body negative pressure (LBNP; -10 and -40 mmHg), with saline infusion in one hand and local indomethacin (cyclooxygenase inhibitor) infusion (3 microg/min) in the other. Acetylcholine (0.01-1 nmol/min) dilated veins preconstricted with PGF(2alpha) in normals but, consistent with endothelial dysfunction, barely did so in CHF patients (P = 0.001). Nonendothelial venodilation to sodium nitroprusside (0.3-10 nmol/min) was not different between normals and CHF patients. Resting venous norepinephrine levels were higher in CHF patients (2,812 +/- 420 pmol/l) than normals (1,418 +/- 145 pmol/l, P = 0.007). In normals, indomethacin caused increased venoconstriction to MA (from 4.9 +/- 1.5 to 19.2 +/- 4.5%, P = 0.022) and CPT (from 2.9 +/- 3.8 to 17.6 +/- 4.2%, P = 0.007). In CHF, indomethacin caused increased venoconstriction to MA (from 6.6 +/- 3.9% to 19.0 +/- 4.5%, P = 0.014), CPT (from 9.6 +/- 2.1% to 20.1 +/- 3.7%, P = 0.001), and -40 mmHg LBNP (from 10.7 +/- 3.0% to 23.2 +/- 3.8%, P = 0.041). Control responses for all tests were not different between normals and CHF patients. The effects of indomethacin on venoconstriction to MA and CPT were not different between normals and CHF patients, but venoconstriction to -40 mmHg LBNP was accentuated in CHF patients (P = 0.036). Inhibition of prostaglandins by indomethacin significantly enhances hand vein constriction to physiological stimuli in both normals and CHF patients, although a differential effect exists for LBNP.
Collapse
Affiliation(s)
- T Nancy Dzeka
- Department of Physiology, The University of Western Ontario, London, Ontario, Canada N6A 4G5
| | | |
Collapse
|
9
|
Schmitt M, Blackman DJ, Middleton GW, Cockcroft JR, Frenneaux MP. Assessment of venous capacitance. Radionuclide plethysmography: methodology and research applications. Br J Clin Pharmacol 2002; 54:565-76. [PMID: 12492602 PMCID: PMC1874491 DOI: 10.1046/j.1365-2125.2002.t01-7-01689.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
- Matthias Schmitt
- Department of Cardiology, Wales Heart Research Institute, University of Wales College of Medicine, Cardiff, UK.
| | | | | | | | | |
Collapse
|
10
|
Stewart JM, Lavin J, Weldon A. Orthostasis fails to produce active limb venoconstriction in adolescents. J Appl Physiol (1985) 2001; 91:1723-9. [PMID: 11568156 DOI: 10.1152/jappl.2001.91.4.1723] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Orthostasis is characterized by translocation of blood from the upper body and thorax into dependent venous structures. Although active splanchnic venoconstriction is known to occur, active limb venoconstriction remains controversial. Based on prior work, we initially hypothesized that active venoconstriction does occur in the extremities during orthostasis in response to baroreflex activation. We investigated this hypothesis in the arms and legs of 11 healthy volunteers, aged 13-19 yr, using venous occlusion strain gauge plethysmography to obtain the forearm and calf blood flows and to compute the capacitance vessel volume-pressure compliance relation. Subjects were studied supine and at -10, +20, and +35 degrees to load the baroreflexes. With +20 degrees of tilt, blood flow decreased and limb arterial resistance increased significantly (P < 0.05) compared with supine. With +35 degrees of tilt, blood flow decreased, limb arterial resistance increased, and heart rate increased, indicating parasympathetic withdrawal and sympathetic activation with arterial vasoconstriction. The volume-pressure relation was unchanged by orthostatic maneuvers. The results suggest that active venoconstriction in the limbs is not important to mild orthostatic response.
Collapse
Affiliation(s)
- J M Stewart
- Department of Pediatrics, The Center for Pediatric Hypotension, New York Medical College, Valhalla, NY 10595, USA.
| | | | | |
Collapse
|
11
|
Abstract
The venous system contains approximately 70% of the blood volume. The sympathetic nervous system is by far the most important vasopressor system in the control of venous capacitance. The baroreflex system responds to acute hypotension by concurrently increasing sympathetic tone to resistance, as well as capacitance vessels, to increase blood pressure and venous return, respectively. Studies in experimental animals have shown that interference of sympathetic activity by an alpha1- or alpha2-adrenoceptor antagonist or a ganglionic blocker reduces mean circulatory filling pressure and venous resistance and increases unstressed volume. An alpha1- or alpha2-adrenoceptor agonist, on the other hand, increases mean circulatory filling pressure and venous resistance and reduces unstressed volume. In humans, drugs that interfere with sympathetic tone can cause the pooling of blood in limb as well as splanchnic veins; the reduction of cardiac output; and orthostatic intolerance. Other perturbations that can cause postural hypotension include autonomic failure, as in dysautonomia, diabetes mellitus, and vasovagal syncope; increased venous compliance, as in hemodialysis; and reduced blood volume, as with space flight and prolonged bed rest. Several alpha-adrenoceptor agonists are used to increase venous return in orthostatic intolerance; however, there is insufficient data to show that these drugs are more efficacious than placebo. Clearly, more basic science and clinical studies are needed to increase our knowledge and understanding of the venous system.
Collapse
Affiliation(s)
- C C Pang
- Department of Pharmacology and Therapeutics, Faculty of Medicine, The University of British Columbia, 2176 Health Sciences Mall, Vancouver, B.C. V6T 1Z3, Canada.
| |
Collapse
|
12
|
Nightingale AK, Blackman DJ, Ellis GR, Schmitt M, Morris-Thurgood JA, Jones EA, Frenneaux MP. Preservation of venous endothelial function in the forearm venous capacitance bed of patients with chronic heart failure despite arterial endothelial dysfunction. J Am Coll Cardiol 2001; 37:1062-8. [PMID: 11263609 DOI: 10.1016/s0735-1097(01)01142-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
OBJECTIVES The goal of this study was to assess whether endothelial dysfunction occurs in the forearm venous capacitance bed of patients with chronic heart failure (CHF) and to determine the role of nitric oxide (NO) in modulating venous tone. BACKGROUND Control of venous tone is crucially important in CHF. More than 70% of blood volume lies in the venous capacitance beds. Therefore, small changes in venous tone may markedly affect cardiac filling pressures and cardiac output. METHODS Venous tone was measured using radionuclide forearm venous plethysmography in 24 patients with CHF and 16 age-matched controls. The effect of basal NO activity on venous tone was assessed by infusing N-monomethyl-L-arginine 12 mg/min and stimulated NO using carbachol 15 microg/min. Brachial artery flow-mediated dilation was assessed by ultrasonic wall-tracking. RESULTS Blockade of basal NO release caused a significant and similar venoconstriction in patients (9.6 +/- 1.8%, p < 0.01) and controls (6.6 +/- 1.7%, p < 0.01). Carbachol-induced venodilation was significant and similar in patients (36.8 +/- 3.9%, p < 0.001) and controls (40.7 +/- 3.9%, p < 0.001). Brachial artery flow-mediated dilation was impaired in patients compared with controls (2.0 +/- 0.6% vs. 7.5 +/- 2.5%, p < 0.01). CONCLUSIONS Our data indicate that, despite marked impairment of the function of the arterial endothelium, there is preservation of both basal and stimulated NO release in the forearm venous capacitance bed. This may provide important insights into mechanisms of endothelial dysfunction in CHF and the potential for novel therapy.
Collapse
Affiliation(s)
- A K Nightingale
- Department of Cardiology, University of Wales College of Medicine, Cardiff, United Kingdom
| | | | | | | | | | | | | |
Collapse
|
13
|
Abstract
The venous system contains about 70% of the blood volume, and approximately 75% of the venous volume is in the small veins and venules. Veins play an active role in the control of cardiac output (CO) and blood pressure. Drugs that interfere with venous tone have profound effects on CO and blood pressure due to the large venous capacity. Information on body venous tone cannot be obtained from studies using isolated venous preparations and perfused venous beds, which lack modulating cardiovascular reflex mechanisms. In vivo methods used for the assessment of venous function in experimental animals and humans are as follows: the mean circulatory filling pressure (MCFP) method for the determination of body venous tone, constant CO reservoir technique for measuring vascular compliance and unstressed volume, plethysmography or blood-pool scintigraphy along with venous occlusion for measuring the volume and compliance of an organ, linear variable differential transformer (LVDT) technique for estimating the diameter of a human dorsal hand vein, intravascular ultrasound (IVUS) imaging technique to monitor the cross-sectional area of a large vein, and ultrasonic crystals to estimate the dimension of an organ. These methods are described and critically evaluated to disclose their validity, merits and limitations.
Collapse
Affiliation(s)
- C C Pang
- Department of Pharmacology and Therapeutics, Faculty of Medicine, University of British Columbia, 2176 Health Sciences Mall, Vancouver, BC V6T 1Z3, Canada.
| |
Collapse
|
14
|
Manyari DE, Rose S, Tyberg JV, Sheldon RS. Abnormal reflex venous function in patients with neuromediated syncope. J Am Coll Cardiol 1996; 27:1730-5. [PMID: 8636561 DOI: 10.1016/0735-1097(96)00051-4] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
OBJECTIVES We sought to compare the forearm reflex venous response to mental arithmetic stress in patients with neuromediated syncope and in normal subjects. BACKGROUND Patients with neuromediated syncope have a paradoxic arterial vasodilation in response to stressors that usually provoke vasoconstriction. Given the postulated role of diminished preload in provoking the reflex responses resulting in syncope, we hypothesized that mental stress might provoke paradoxic reflex venodilation in patients with neuromediated syncope. METHODS Twelve normal subjects (mean age [+/-SD] 47 +/- 9 years) and 27 patients with neuromediated syncope (mean age 42 +/- 13 years) were studied before and during a mental arithmetic stress test. Forearm venous pressure-volume relations were determined by using radionuclide plethysmography. RESULTS During mental arithmetic stress, heart rate and systolic and diastolic blood pressure increased significantly and similarly both in normal subjects and in patients with neuromediated syncope. The heart rate and blood pressure changes were qualitatively similar in both groups. However, with mental arithmetic stress, forearm venoconstriction of 13 +/- 2% (mean +/- SEM) was noted in normal subjects (p < 0.001) but not in patients with neuromediated syncope (mean 2%, p = NS). This group response of patients with neuromediated syncope did not result from a lack of individual responses but occurred because these patients had a wide range of responses. The normal physiologic and methodologic variability of the method was +/- 4%. Thirteen of the 27 patients with neuromediated syncope had forearm venoconstriction of 14.5 +/- 6.8% during mental arithmetic stress, whereas 7 had paradoxic forearm venodilation of 14.6 +/- 8.8%, and 7 were considered nonresponders (-1.3 +/- 3.4%). Thus, 14 (52%) of the 27 patients with syncope did not have normal vasoconstriction in response to mental stress. CONCLUSIONS Patients with neuromediated syncope have an abnormal range of forearm venomotor responses to mental arithmetic stress. Reflex control of the veins may play an important role in the pathogenesis of neuromediated syncope.
Collapse
Affiliation(s)
- D E Manyari
- Cardiovascular Research Group, University of Calgary, Alberta, Canada
| | | | | | | |
Collapse
|
15
|
|
16
|
Baccelli G, Terrani S, Pacenti P, Omboni E, Bergonzi M, Reggiani P, Sardella F, Catalano M, Bianchi R. Simultaneous recording of blood volume shifts in different vascular beds in man by a versatile scintigraphic method. Angiology 1993; 44:615-21. [PMID: 8342877 DOI: 10.1177/000331979304400804] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
A device was developed to record the blood volume changes occurring in the lung and calf during postural changes, physical exercise, and the Valsalva maneuver in man. The changes in regional counting rates from the right middle lung and the calf mirrored the well-known changes in venous return that are expected to occur in response to the above-mentioned external stimuli. Thus a sustained decrease in lung blood volume was noted on assumption of the erect posture as well as during the forced expiration of the Valsalva maneuver. In addition a rapid increase and a sharp decrease in lung blood volume took place at the very onset and at the very end of walking, respectively. The calf blood volume declined immediately at the onset of walking, increased slightly in the ensuing two minutes, and returned to baseline quickly at the termination of walking. The authors' method enables real-time equilibrium blood pool scintigraphy to be recorded continuously and simultaneously from different districts over sustained periods of time irrespective of the posture and the physical activity performed by the patient. Their method might improve knowledge of the systemic circulatory responses to selective physiologic and therapeutic interventions in health and disease.
Collapse
Affiliation(s)
- G Baccelli
- Centro di Fisiologia Clinica e Ipertensione, Ospedale Maggiore, Milano, Italy
| | | | | | | | | | | | | | | | | |
Collapse
|
17
|
Abstract
The objective of this discussion has been to describe a simple conceptual model of the circulation that emphasizes the role of the venous capacitance vasculature and is based on simplified vascular pressure-volume relationships. First, it is hoped that this approach will avoid some of the misunderstandings and contradictions that have resulted from an approach to the veins that is based on pressure-flow relationships. As mentioned at the outset, the confusion between venous volume and flow has led to the anomalous but logical conclusion that decreased venous pooling corresponds to increased venous return (which must equal cardiac output in the steady state). Second, it is also hoped that the model will prove to be a useful starting point from which to better understand how the veins modulate cardiac output in the normal individual and how alterations in venous capacitance affect the hemodynamic profile of congestive heart failure.
Collapse
|