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Distensibility in Arteries, Arterioles and Veins in Humans: Adaptation to Intermittent or Prolonged Change in Regional Intravascular Pressure
KTH, School of Technology and Health (STH), Environmental Physiology.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present series of in vivo experiments in healthy subjects, were performed to investigate wall stiffness in peripheral vessels and how this modality adapts to iterative increments or sustained reductions in local intravascular pressures. Vascular stiffness was measured as changes in arterial and venous diameters, and in arterial flow, during graded increments in distending pressures in the vasculature of an arm or a lower leg. In addition, effects of intravascular pressure elevation on flow characteristics in veins, and on limb pain were elucidated. Arteries and veins were stiffer (i.e. pressure distension was less) in the lower leg than in the arm. The pressure-induced increase in arterial flow was substantially greater in the arm than in the lower leg, indicating a greater stiffness in the arterioles of the lower leg. Prolonged reduction of intravascular pressures in the lower body, induced by 5 wks of sustained horizontal bedrest (BR), decreased stiffness in the leg vasculature. BR increased pressure distension in the tibial artery threefold and in the tibial vein by 86 %. The pressure-induced increase in tibial artery flow was greater post bedrest, indicating reduced stiffness in the arterioles of the lower leg. Intermittent increases of intravascular pressures in one arm (pressure training; PT) during a 5-wk period decreased vascular stiffness. Pressure distension and pressure-induced flow in the brachial artery were reduced by about 50 % by PT. PT reduced pressure distension in arm veins by 30 to 50 %. High intravascular pressures changed venous flow to arterial-like pulsatile patterns, reflecting propagation of pulse waves from the arteries to the veins either via the capillary network or through arteriovenous anastomoses. High vascular pressures induced pain, which was aggravated by BR and attenuated by PT; the results suggest that the pain was predominantly caused by vascular overdistension. In conclusion, vascular wall stiffness constitutes a plastic modality that adapts to meet demands imposed by a change in the prevailing local intravascular pressure. That increased intravascular pressure leads to increased arteriolar wall stiffness supports the notion that local pressure load may serve as a “prime mover” in the development of vascular changes in hypertension.

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , 51 p.
Series
Trita-STH : report, ISSN 1653-3836 ; 2010:5
Keyword [en]
arterial stiffness, venous distensibility, venous flow characteristics, bedrest, pressure training
National Category
Physiology
Identifiers
URN: urn:nbn:se:kth:diva-25965ISBN: 978-91-7415-778-9 (print)OAI: oai:DiVA.org:kth-25965DiVA: diva2:361172
Public defence
2010-11-26, sal 3:221, Alfreds Nobels Alle 10, Flemingsberg, Huddinge, 09:00 (Swedish)
Opponent
Supervisors
Note
medicine doktorsexamen QC 20101109Available from: 2010-11-09 Created: 2010-11-08 Last updated: 2012-03-20Bibliographically approved
List of papers
1. Comparison of vascular distensibility in the upper and lower extremity
Open this publication in new window or tab >>Comparison of vascular distensibility in the upper and lower extremity
2004 (English)In: Acta Physiologica Scandinavica, ISSN 0001-6772, E-ISSN 1365-201X, Vol. 181, no 3, 281-287 p.Article in journal (Refereed) Published
Abstract [en]

Aim: Because of the great differences in hydrostatic pressure acting along the blood vessels in the erect posture, leg vessels are exposed to greater transmural pressures than arm vessels. The in vivo pressure-distension relationship of arteries, arterioles and veins in the arm were compared with those of the leg. Methods: Experiments were performed with the subject (n = 11) positioned in a pressure chamber with an arm or lower leg (test limb) extended at heart level through a hole in the chamber door. Intravascular pressure in the arm/lower leg was increased by stepwise increasing chamber pressure to +180 and +210 mmHg, respectively. Diameters of blood vessels and arterial flow were measured using ultrasonographic/Doppler techniques. Changes in forearm and lower leg volumes were assessed using an impedance technique. The subject rated perceived pain in the test limb. Results: The brachial and radial arteries were found to be more distensible than the posterior tibial artery (P < 0.001). Likewise, the distension was more pronounced in the cephalic than in the great saphenous vein (P < 0.001). In the brachial artery, but not in the posterior tibial artery, flow increased markedly at the highest levels of distending pressure (P < 0.001). At the highest intravascular pressures, the rate of change in tissue impedance was greater in the forearm than the lower leg (P < 0.01). At any given level of markedly increased pressure, pain was rated higher in the arm than in the leg (P < 0.001). Conclusion: It seems that the wall stiffness of arteries, pre-capillary resistance vessels and veins adapts to meet the long-term demands imposed by the hydrostatic pressure acting locally on the vessel walls.

Keyword
arterial pressure, body position, gravity, local vascular resistance, vascular compliance, venous return
Identifiers
urn:nbn:se:kth:diva-25947 (URN)10.1111/j.1365-201X.2004.01291.x (DOI)000222049400002 ()15196088 (PubMedID)
Note
QC 20101108Available from: 2010-11-08 Created: 2010-11-08 Last updated: 2017-12-12Bibliographically approved
2. Pressure-distension relationship in arteries and arterioles in response to 5 wk of horizontal bedrest
Open this publication in new window or tab >>Pressure-distension relationship in arteries and arterioles in response to 5 wk of horizontal bedrest
2008 (English)In: American Journal of Physiology. Heart and Circulatory Physiology, ISSN 0363-6135, E-ISSN 1522-1539, Vol. 295, no 3, H1296-H1302 p.Article in journal (Refereed) Published
Abstract [en]

We hypothesized that exposure to prolonged recumbency (bedrest), and thus reductions of intravascular pressure gradients, increases pressure distension in arteries/arterioles in the legs. Ten subjects underwent 5 wk of horizontal bedrest. Pressure distension was investigated in arteries and arterioles before and after the bedrest, with the subject seated or supine in a hyperbaric chamber with either one arm or a lower leg protruding through a hole in the chamber door. Increased pressure in the vessels of the arm/leg was accomplished by increasing chamber pressure. Vessel diameter and flow were measured in the brachial and posterior tibial arteries using Doppler ultrasonography. Electrical tissue impedance was measured in the test limb. Bedrest increased (P < 0.01) pressure distension threefold in the tibial artery (from 8 +/- 7% to 24 +/- 11%) and by a third (P < 0.05) in the brachial artery (from 15 +/- 9% to 20 +/- 10%). The pressure-induced increase in tibial artery flow was more pronounced (P < 0.01) after (50 +/- 39 ml/min) than before (13 +/- 23 ml/min) bedrest, whereas the brachial artery flow response was unaffected by bedrest. The pressure-induced decrease in tissue impedance in the leg was more pronounced (P < 0.01) after (16 +/- 7%) than before (10 +/- 6%) bedrest, whereas bedrest did not affect the impedance response in the arm. Thus, withdrawal of the hydrostatic pressure gradients that act along the blood vessels in erect posture markedly increases pressure distension in dependent arteries and arterioles.

Keyword
gravity, microgravity, vascular compliance, vascular deconditioning, vascular stiffness
Identifiers
urn:nbn:se:kth:diva-25950 (URN)10.1152/ajpheart.00576.2008 (DOI)000258949200049 ()18660441 (PubMedID)
Note
QC 20101108Available from: 2010-11-08 Created: 2010-11-08 Last updated: 2017-12-12Bibliographically approved
3. Increased distensibility in dependent veins following prolonged bedrest
Open this publication in new window or tab >>Increased distensibility in dependent veins following prolonged bedrest
2009 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 106, no 4, 547-554 p.Article in journal (Refereed) Published
Abstract [en]

Displacement of blood to the lower portion of the body that follows a postural transition from recumbent to erect is augmented by a prolonged period of recumbency (bedrest). Information is scarce as to what extent this augmented blood-volume shift to dependent veins is attributable to increased distensibility of the veins. Accordingly, we studied the effect of 5 weeks of horizontal bedrest on the pressure-distension relationship in limb veins. Elevation of venous distending pressure was induced by exposure of the body except the tested limb to supra-atmospheric pressure with the subject seated in a pressure chamber with one arm, or supine with a lower leg, protruding through a hole in the chamber door. Diameter changes in response to an increase of intravenous pressure (distensibility) from 60 to about 140 mmHg were measured in the brachial and posterior tibial veins using ultrasonographic techniques. Prior to bedrest, the distensibility was substantially less in the tibial than in the brachial vein. Bedrest increased (P < 0.01) pressure distension in the tibial vein by 86% from 7 +/- A 3% before to 13 +/- A 3% after bedrest. In the brachial vein, bedrest increased (P < 0.05) pressure distension by 36% from 14 +/- A 5% before to 19 +/- A 5% after bedrest. Thus, removal of the gravity-dependent pressure components that act along the blood vessels in erect posture increases the distensibility of dependent veins.

Keyword
Sustained bedrest, Venous compliance, Gravity, Blood-volume distribution, Vascular deconditioning
Identifiers
urn:nbn:se:kth:diva-25954 (URN)10.1007/s00421-009-1044-3 (DOI)000266814800008 ()19347352 (PubMedID)
Note
QC 20101108Available from: 2010-11-08 Created: 2010-11-08 Last updated: 2017-12-12Bibliographically approved
4. Repeated exposures to moderately increased intravascular pressure increases stiffness in human arteries and arterioles
Open this publication in new window or tab >>Repeated exposures to moderately increased intravascular pressure increases stiffness in human arteries and arterioles
2011 (English)In: Journal of Hypertension, ISSN 0263-6352, E-ISSN 1473-5598, Vol. 29, no 10, 1963-1971 p.Article in journal (Refereed) Published
Abstract [en]

The aim was to investigate whether repeated exposures to moderate pressure elevations in the blood vessels of the arms (pressure training; PT) affect pressure distension in arteries/arterioles of healthy subjects (n=11). PT and vascular pressure-distension determinations were conducted with the subject seated in a pressure chamber with one arm slipped through a hole in the chamber door. Increased intravascular pressure was accomplished by increasing chamber pressure. Before PT, one arm was investigated (control arm) during stepwise increases in chamber pressure to 180 mmHg. Artery diameter and flow were measured in the brachial artery using ultrasonography/Doppler techniques. Thereafter, the contralateral arm underwent a PT regimen consisting of three 40 min sessions/ week during 5 weeks. Chamber pressure was increased during PT from 65 mmHg during the first week to 105 mmHg during the last week. After PT, pressure-distension relationships were examined in both the trained arm and the control arm. Prior to and following PT, endothelium-dependent and endothelium-independent dilatations of the brachial artery were studied. PT reduced (p<0.01) arterial pressure distension by 46 ± 18%. Likewise, the pressure-induced increase in arterial flow was less pronounced after (350 ± 249%) compared with before (685 ± 216 %) PT. The PT-induced reductions in arterial/arteriolar pressure distension were reversed 5 weeks post-PT. Neither endothelium-dependent nor endothelium-independent arterial dilatation were affected by PT. It thus appears that the in vivo wall stiffness in arteries and arterioles increases markedly in response to intermittent, moderate increments of transmural pressure during 5 weeks. The increases in arterial/arteriolar stiffness are reversible and do not reflect a reduced capacity to dilate the vessels. The findings are compatible with the notion that local load serves as “ a prime mover” in the development of vascular changes in hypertension.

Keyword
hypertension, pressure habituation, vascular remodeling, wall tension
National Category
Cardiac and Cardiovascular Systems
Identifiers
urn:nbn:se:kth:diva-26004 (URN)10.1097/HJH.0b013e32834ae3ab (DOI)000294718500018 ()2-s2.0-84855998975 (Scopus ID)
Note
QC 20101109. Updated from manuscript to published.Available from: 2010-11-09 Created: 2010-11-09 Last updated: 2017-12-12Bibliographically approved
5. Distensibility in human veins as affected by 5 weeks of repeated elevations of local transmural pressure
Open this publication in new window or tab >>Distensibility in human veins as affected by 5 weeks of repeated elevations of local transmural pressure
2011 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 111, no 12, 3119-3125 p.Article in journal (Refereed) Published
Abstract [en]

The objectives were to investigate the effects of repeated increments in local intravascular pressure (pressure training; PT) on (1) distensibility in two arm veins, and (2) pain in the arm induced by markedly increased intravascular pressure. Elevation of venous distending pressure (DP) in an arm was induced by placing the subject (n = 8) in a pressure chamber with one arm protruding to the outside via a port in the chamber door, and increasing chamber pressure. During 5 weeks, venous DP in one arm was repeatedly (3 × 40 min/week) increased (65-105 mmHg). Pressure-distension relationships were determined in the brachial and cephalic veins by measuring diameter changes by ultrasonography during stepwise increments in DP to 180 mmHg. In the brachial vein, the diameter change in response to an increase in DP from 30 to 180 mmHg (distensibility) was reduced (P < 0.05) in the pressure-trained arm (11%) compared to that in the control arm before (23%) and after (21%) PT. The cephalic vein showed a similar response with a reduced (P < 0.05) distensibility in the pressure-trained arm (20%) compared to that in the control arm before (29%) and after (25%) PT. At any given DP, arm pain was less (P < 0.05) in the pressure-trained arm than in the control arm before and after PT, presumably reflecting the reduced venous distensibility in the pressure-trained arm. The results support the concept that the distensibility of venous walls adapts to meet the demands imposed by the prevailing local transmural pressures.

Keyword
Venous compliance, G-induced arm pain, Vascular remodeling, Vascular adaptation
National Category
Physiology
Identifiers
urn:nbn:se:kth:diva-44497 (URN)10.1007/s00421-011-1939-7 (DOI)000297174800024 ()21461927 (PubMedID)2-s2.0-84855641495 (Scopus ID)
Note
QC 20111104Available from: 2011-10-21 Created: 2011-10-21 Last updated: 2017-12-08Bibliographically approved
6. Antegrade pulsatile arterial-like flow in human limb veins at increased intravascular pressure
Open this publication in new window or tab >>Antegrade pulsatile arterial-like flow in human limb veins at increased intravascular pressure
2009 (English)In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 29, no 3, 209-215 p.Article in journal (Refereed) Published
Abstract [en]

The purpose was to study the effects of moderately to markedly increased local intravascular pressures on the flow characteristics in human limb veins. The subject was either seated inside a pressure chamber with one arm slipped through a hole in the chamber door (n = 7) or positioned supine with a lower leg extended to the outside (n = 15). By increasing chamber pressure, transmural pressure in the vessels of the test limb was increased up to +150 mmHg for the arm and +240 mmHg for the leg. Venous flow profiles and arterial flow and vessel diameters were measured with ultrasonographic/Doppler techniques. The arm vessels were studied before and during blocking of the blood flow (BBF) through the hand. Antegrade, pulsatile, arterial-like flow were observed at high distending pressures in the brachial and radial veins in all subjects and in similar to 50% of the subjects also in the cephalic vein and posterior tibial veins. In five of seven subjects, blood flow in the brachial vein remained pulsatile even during BBF. That pulsatile flow was observed in all veins may suggest that moderately to markedly elevated intravascular pressures induce propagation of pulse waves from the arteries via the capillaries to the veins, and/or induce considerable arteriovenous shunting, by forcing open arteriovenous anastomoses.

Keyword
arteriovenous anastomoses, A-V shunts, transmural pressure, venous flow, venous pulsations
Identifiers
urn:nbn:se:kth:diva-25960 (URN)10.1111/j.1475-097X.2009.00859.x (DOI)000264545000009 ()19236434 (PubMedID)
Note
QC 20101108Available from: 2010-11-08 Created: 2010-11-08 Last updated: 2017-12-12Bibliographically approved

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