On cardiovascular responses to hypovolemic circulatory stress. An experimental study in man.
Author
Summary, in English
Aged subjects have a decreased tolerance to hypovolemia, which could contribute to their increased cardiovascular morbidity. One possible etiological factor might be an age-related reduction in the efficiency of the baroreceptor reflex axis. In this study lower body negative pressure (LBNP) was used as a model for hypovolemic circulatory stress, and volumetric techniques applied for the study of peripheral vascular responses.
Venous capacitance in the legs is reduced by 25 % from 22 to 64 years of age due to decreased venous compliance. This leads to an age-related reduction of blood pooling in the lower body half during LBNP with less reduction in central blood volume and reduced response of the baroreceptor reflex axis. By adjusting the LBNP-stimulus, similar hypovolemic circulatory stress in both young and old may be achieved. The efficiency of the baroreceptor reflex axis is well compensated with age. Thus, the previous finding of a reduced baroreflex response to orthostasis with increasing age seems to be explained by a reduced hypovolemic stimulus. The capacitance response (mobilisation of peripheral blood to the central circulation) in tissue not exposed to an increased hydrostatic pressure load, i.e. the first line of defence during hypovolemic circulatory stress however, is reduced by 50 % in old subjects.
Diabetic patients also have a reduced tolerance to hypovolemia. The capacitance response in the legs during LBNP in type 1 diabetic patients without microvascular complications is unaffected. Transcapillary fluid absorption from tissue to blood during hypovolemia is, however, reduced indicating impaired plasma volume regulation. The explanation seems to be a reduction in capillary water permeability (CFC) in diabetic patients. The expected increase in CFC as well as the calculated driving force for transcapillary fluid absorption during hypovolemic circulatory stress seems, on the contrary, to be intact indicating preserved sympathetic microcirculatory regulation. Diabetic patients with microangiopathy (retinopathy) are further affected by a reduced capacitance function with a decreased mobilisation of peripheral venous blood to the central circulation during hypovolemic circulatory stress, which increases their susceptibility to hypovolemia even more. In experiments applying the clamp technique to healthy young individuals, hyperglycaemia, but not hyperinsulinemia is found to increase transcapillary fluid absorption during hypovolemic circulatory stress, probably due to its osmotic action.
Venous capacitance in the legs is reduced by 25 % from 22 to 64 years of age due to decreased venous compliance. This leads to an age-related reduction of blood pooling in the lower body half during LBNP with less reduction in central blood volume and reduced response of the baroreceptor reflex axis. By adjusting the LBNP-stimulus, similar hypovolemic circulatory stress in both young and old may be achieved. The efficiency of the baroreceptor reflex axis is well compensated with age. Thus, the previous finding of a reduced baroreflex response to orthostasis with increasing age seems to be explained by a reduced hypovolemic stimulus. The capacitance response (mobilisation of peripheral blood to the central circulation) in tissue not exposed to an increased hydrostatic pressure load, i.e. the first line of defence during hypovolemic circulatory stress however, is reduced by 50 % in old subjects.
Diabetic patients also have a reduced tolerance to hypovolemia. The capacitance response in the legs during LBNP in type 1 diabetic patients without microvascular complications is unaffected. Transcapillary fluid absorption from tissue to blood during hypovolemia is, however, reduced indicating impaired plasma volume regulation. The explanation seems to be a reduction in capillary water permeability (CFC) in diabetic patients. The expected increase in CFC as well as the calculated driving force for transcapillary fluid absorption during hypovolemic circulatory stress seems, on the contrary, to be intact indicating preserved sympathetic microcirculatory regulation. Diabetic patients with microangiopathy (retinopathy) are further affected by a reduced capacitance function with a decreased mobilisation of peripheral venous blood to the central circulation during hypovolemic circulatory stress, which increases their susceptibility to hypovolemia even more. In experiments applying the clamp technique to healthy young individuals, hyperglycaemia, but not hyperinsulinemia is found to increase transcapillary fluid absorption during hypovolemic circulatory stress, probably due to its osmotic action.
Department/s
Publishing year
2000
Language
English
Document type
Dissertation
Publisher
Department of Endocrinology, Wallenberg laboratory, Malmö University Hospital
Topic
- Endocrinology and Diabetes
Keywords
- diabetology
- secreting systems
- Endocrinology
- vein.
- type 1 diabetes
- skeletal muscle
- LBNP
- compliance
- CFC
- Ageing
- baroreceptor
- Endokrinologi
- sekretion
- diabetologi
- Cardiovascular system
- Kardiovaskulära systemet
Status
Published
Supervisor
- [unknown] [unknown]
ISBN/ISSN/Other
- ISRN: LUMEDW/MEEK-1010-SE
Defence date
11 February 2000
Defence time
13:00
Defence place
Medicinklinikens Aula Malmö University Hospital, Malmö
Opponent
- Bengt Fagrell (Professor)