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Cardiovascular responses to hypovolemic circulatory stress in women: With special reference to venous compliance and capacitance
Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Acute haemorrhage is a leading cause of death in trauma. Young women (YW) seem more susceptible to hypovolemic circulatory stress than young men (YM), but the underlying mechanisms are not clear. Elderly subjects are more vulnerable to haemorrhage, with a decreased defence of central blood volume in elderly men, but the defence has not been evaluated in elderly women  (EW). The aims were to assess differences in cardiovascular responses to hypovolemic circulatory stress, emphasizing compensatory mechanisms to maintain central blood volume in YW, EW and in women prone to vaso‐vagal reaction (VW).

Lower body negative pressure (LBNP) was used as a model for haemorrhage and to create acute hypovolemic stress. Volumetric techniques were used to assess venous compliance, capacitance and capillary fluid exchange both caused by LBNP in the calf and the response to maintain central blood volume.

LBNP induced a comparable hypovolemic stimulus in YW and YM, with lower calf venous compliance and capacitance but higher net capillary fluid filtration in YW. YW responded with smaller vasoconstriction without association between P‐NE and peripheral vascular resistance in contrast to YM. Venous capacitance response was decreased with time in YW. Further, net capillary fluid absorption from peripheral tissues to central circulation was decreased in YW in response to hypovolemic stress. All in all, this indicates less efficiency to defend central blood volume in young women.

Calf venous compliance and capacitance was maintained in EW compared to YW but capillary filtration was decreased, implying reduced capillary function with age. With increasing transmural pressures however, filtration and capillary filtration coefficient (CFC) increased indicating increased capillary susceptibility to transmural pressure load in dependent regions with age. Heart rate increase was attenuated in EW while peripheral vascular conductance was maintained suggesting reduced cardiovagal baroreceptor function in response to hypovolemia with age. Venous capacitance response and fluid absorption from peripheral tissues to central circulation were decreased with age, indicating less efficiency to defend central blood volume.

LBNP induced a slower hypovolemic stimulus in VW compared with nonvagal women. Further, the cardiopulmonary baroreflex was less efficient, and the venous capacitance response from peripheral tissues to central circulation was decreased, which may explain their susceptibility to orthostatic challenge.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2008. , 70 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1087
National Category
Cardiac and Cardiovascular Systems
Identifiers
URN: urn:nbn:se:liu:diva-15420ISBN: 978-91-7393-756-6 (print)OAI: oai:DiVA.org:liu-15420DiVA: diva2:114155
Public defence
2008-11-21, Elsa Brändström salen, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 09:15 (English)
Opponent
Supervisors
Available from: 2008-11-06 Created: 2008-11-06 Last updated: 2017-04-15Bibliographically approved
List of papers
1. Sex-related effects on venous compliance and capillary filtration in the lower limb
Open this publication in new window or tab >>Sex-related effects on venous compliance and capillary filtration in the lower limb
2007 (English)In: American Journal of Physiology. Regulatory Integrative and Comparative Physiology, ISSN 0363-6119, Vol. 292, R852-R859 p.Article in journal (Refereed) Published
Abstract [en]

Recent studies in humans have suggested sex differences in venous compliance of the lower limb, with lower compliance in women. Capillary fluid filtration could, however, be a confounder in the evaluation of venous compliance. The venous capacitance and capillary filtration response in the calves of 12 women (23.2 ± 0.5 years) and 16 men (22.9 ± 0.5 years) were studied during 8 min lower body negative pressure (LBNP) of 11, 22, and 44 mmHg. Calf venous compliance is dependent on pressure and was determined using the first derivative of a quadratic regression equation that described the capacitance-pressure relationship [compliance = 1 + (2·2· transmural pressure)]. We found a lower venous compliance in women at low transmural pressures, and the venous capacitance in men was increased (P < 0.05). However, the difference in compliance between sexes was reduced and not seen at higher transmural pressures. Net capillary fluid filtration and capillary filtration coefficient (CFC) were greater in women than in men during LBNP (P < 0.05). Furthermore, calf volume increase (capacitance response + total capillary filtration) during LBNP was equivalent in both sexes. When total capillary filtration was not subtracted from the calf capacitance response in the calculation of venous compliance, the sex differences disappeared, emphasizing that venous compliance measurement should be corrected for the contribution of CFC.

Keyword
Lower body negative pressure, capillary filtration coefficient, venous capacitance
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-15416 (URN)10.1152/ajpregu.00394.2006 (DOI)
Available from: 2008-11-06 Created: 2008-11-06 Last updated: 2017-03-27Bibliographically approved
2. Decreased capillary filtration but maintained venous compliance in the lower limb of aging women
Open this publication in new window or tab >>Decreased capillary filtration but maintained venous compliance in the lower limb of aging women
2007 (English)In: American Journal of Physiology. Heart and Circulatory Physiology, ISSN 0363-6135, Vol. 293, H3568-H3574 p.Article in journal (Refereed) Published
Abstract [en]

There are sex-related differences in venous compliance and capillary filtration in the lower limbs, which to some extent can explain the susceptibility to orthostatic intolerance in young women. With age, venous compliance and capacitance are reduced in men. This study was designed to evaluate age-related changes in venous compliance and capillary filtration in the lower limbs of healthy women. Included in this study were 22 young and 12 elderly women (23.1 ± 0.4 and 66.4 ± 1.4 yr). Lower body negative pressure (LBNP) of 11, 22, and 44 mmHg created defined transmural pressure gradients in the lower limbs. A plethysmographic technique was used on the calf to assess venous capacitance and net capillary filtration. Venous compliance was calculated with the aid of a quadratic regression equation. No age-related differences in venous compliance and capacitance were found. Net capillary filtration and capillary filtration coefficient (CFC) were lower in elderly women at a LBNP of 11 and 22 mmHg (0.0032 vs. 0.0044 and 0.0030 vs. 0.0041 ml·100 ml–1·min–1·mmHg–1, P < 0.001). At higher transmural pressure (LBNP, 44 mmHg), CFC increased by 1/3 (0.010 ml·100 ml–1·min–1·mmHg–1) in the elderly (P < 0.001) but remained unchanged in the young women. In conclusion, no age-related decrease in venous compliance and capacitance was seen in women. However, a decreased CFC was found with age, implying reduced capillary function. Increasing transmural pressure increased CFC in the elderly women, indicating an increased capillary susceptibility to transmural pressure load in dependent regions. These findings differ from earlier studies on age-related effects in men, indicating sex-specific vascular aging both in the venous section and microcirculation.

Keyword
Capillary filtration coefficient; lower body negative pressure; age
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-15417 (URN)10.1152/ajpheart.00725.2007 (DOI)
Available from: 2008-11-06 Created: 2008-11-06 Last updated: 2017-03-27Bibliographically approved
3. Lower capacitance response and capillary fluid absorption in women to defend central blood volume in response to acute hypovolemic circulatory stress
Open this publication in new window or tab >>Lower capacitance response and capillary fluid absorption in women to defend central blood volume in response to acute hypovolemic circulatory stress
2008 (English)In: American Journal of Physiology. Heart and Circulatory Physiology, ISSN 0363-6135, Vol. 295, H867-H873 p.Article in journal (Refereed) Published
Abstract [en]

Acute hemorrhage is a leading cause of death in trauma, and women are more susceptible to hypovolemic circulatory stress than men. The mechanisms underlying the susceptibility are not clear, however. The aim of the present study was to examine the compensatory mechanisms to defend central blood volume during experimental hypovolemia in women and men. Twenty-two women (23.1 ± 0.4 yr) and 16 men (23.2 ± 0.5 yr) were included. A lower body negative pressure (LBNP) of 11–44 mmHg induced experimental hypovolemic circulatory stress. The volumetric technique was used to assess the capacitance response (redistribution of peripheral venous blood to the central circulation) as well as to assess net capillary fluid transfer from tissue to blood in the arm. Plasma norepinephrine (NE) and forearm blood flow were measured before and during hypovolemia, and forearm vascular resistance (FVR) was calculated. LBNP created comparable hypovolemia in women and men. FVR increased less in women during hypovolemic stress, and no association between plasma NE and FVR was seen in women (R2 = 0.01, not significant), in contrast to men (R2 = 0.59, P < 0.05). Women demonstrated a good initial capacitance response, but this was not maintained with time, in contrast to men [e.g., decreased by 24 ± 4% (women) vs. 4 ± 5% (men), LBNP of 44 mmHg, P < 0.01], and net capillary fluid absorption from tissue to blood was lower in women (0.086 ± 0.007 vs. 0.115 ± 0.011 ml·100 ml–1·min–1, P < 0.05). In conclusion, women showed impaired vasoconstriction, reduced capacitance response with time, and reduced capillary fluid absorption during acute hypovolemic circulatory stress, indicating less efficiency to defend central blood volume than men.

Keyword
Gender, orthostatic tolerance, baroreceptor sensitivity
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-15418 (URN)10.1152/ajpheart.00332.2008 (DOI)
Available from: 2008-11-06 Created: 2008-11-06 Last updated: 2017-03-27Bibliographically approved
4. Reduced defense of central blood volume during acute hypovolemic circulatory stress in aging women
Open this publication in new window or tab >>Reduced defense of central blood volume during acute hypovolemic circulatory stress in aging women
2012 (English)In: Shock, ISSN 1073-2322, E-ISSN 1540-0514, Vol. 37, no 6, 579-585 p.Article in journal (Refereed) Published
Abstract [en]

Elderly men respond with decreased defense of central blood volume during hypovolemic stress, but this response has not been evaluated with age in women. The aim was to examine the compensatory mechanisms to defend central blood volume during experimental hypovolemia in elderly compared to young women. Cardiovascular responses in 34 women, 12 elderly (66.4±1.4 yr) and 22 young (23.1±0.4 yr) were studied during experimental hypovolemic circulatory stress induced by lower body negative pressure (LBNP) of 11-44 mmHg. Volumetric technique was used to assess the capacitance response (redistribution of peripheral venous blood to the central circulation) as well as to assess net capillary fluid transfer from tissue to blood in the arm. LBNP created comparable hypovolemia in elderly and young women. Heart rate increased less in elderly women (LBNP of 44 mmHg: 20±2 vs. 37±4 %, P < 0.01), but with similar decrease in forearm vascular conductance (FVC). Mobilization of capacitance blood from the peripheral circulation was both slower and decreased by ~60 % in elderly, and net capillary fluid absorption from surrounding tissues was reduced by ~40 % (LBNP of 44 mmHg). In conclusion, during acute hypovolemic circulatory stress elderly women responded with less increase in heart rate but with an equal change in FVC, implying decreased cardiovagal baroreceptor sensitivity. Furthermore, both capacitance response and net capillary fluid absorption were reduced, indicating less efficiency to defend central blood volume in elderly than in young women.

Place, publisher, year, edition, pages
Lippincott Williams & Wilkins, 2012
Keyword
Female, trauma, baroreceptor sensitivity, orthostatic tolerance, adrenergic receptor response
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-15419 (URN)10.1097/SHK.0b013e31824fbb3e (DOI)000304202200004 ()
Note

funding agencies|Medical Faculty, Linkoping University||Futurum-The Academy of Health Care, Jonkoping County Council||Medical Research Council| 12661 |Heart and Lung Foundation||

Available from: 2008-11-06 Created: 2008-11-06 Last updated: 2017-03-27Bibliographically approved

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