Henrik Olsen

Reduced venous compliance in lower limbs of aging humans and its importance for capacitance function

Venous compliance in the calf of humans and its importance for capacitance function in relation to age were studied with the aid of 22, 44, and 59 mmHg lower body negative pressure (LBNP). Negative pressure transmission to the calf as well as changes in calf volume were studied, and venous compliance was calculated [change in volume with pressure change (dV/dP)]. The change in capacitance response of the calf with age (20-70 yr) was evaluated during LBNP 44 mmHg. Transmission of negative pressure to the subcutaneous tissue was almost full without any changes with age (92%). However, it was reduced to 80% in the underlying muscle tissue, irrespective of depth. Venous compliance in the young was 0.051 ml ⋅ 100 ml-1 ⋅ mmHg-1and was reduced by 45% to 0.029 ml ⋅ 100 ml-1 ⋅ mmHg-1in the old ( P < 0.05). Accordingly, the capacitance response was reduced by 0.015 ml ⋅ 100 ml-1 ⋅ yr-1( P < 0.005). Furthermore, the hemodynamic response to hypovolemic circulatory stress was attenuated with age. The reduced pressure transmission in muscle tissue is probably due to restriction of the muscle fascia envelope. The reduced venous compliance with age and the concomitant reduction in capacitance response during LBNP have implications for both the sympathetic reflex responses as well as the capacitance response during acute hypovolemic circulatory stress, which might be defected in aging humans.Venous compliance in the calf of humans and its importance for capacitance function in relation to age were studied with the aid of 22, 44, and 59 mmHg lower body negative pressure (LBNP). Negative pressure transmission to the calf as well as changes in calf volume were studied, and venous compliance was calculated [change in volume with pressure change (dV/dP)]. The change in capacitance response of the calf with age (20-70 yr) was evaluated during LBNP 44 mmHg. Transmission of negative pressure to the subcutaneous tissue was almost full without any changes with age (92%). However, it was reduced to 80% in the underlying muscle tissue, irrespective of depth. Venous compliance in the young was 0.051 ml . 100 ml-1 . mmHg-1 and was reduced by 45% to 0.029 ml . 100 ml-1 . mmHg-1 in the old (P < 0.05). Accordingly, the capacitance response was reduced by 0.015 ml . 100 ml-1 . yr-1 (P < 0.005). Furthermore, the hemodynamic response to hypovolemic circulatory stress was attenuated with age. The reduced pressure transmission in muscle tissue is probably due to restriction of the muscle fascia envelope. The reduced venous compliance with age and the concomitant reduction in capacitance response during LBNP have implications for both the sympathetic reflex responses as well as the capacitance response during acute hypovolemic circulatory stress, which might be defected in aging humans.

Lower capacitance response and capillary fluid absorption in women to defend central blood volume in response to acute hypovolemic circulatory stress

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 (R(2) = 0.01, not significant), in contrast to men (R(2) = 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.

Reduced capillary hydraulic conductivity in skeletal muscle and skin in Type I diabetes: a possible cause for reduced transcapillary fluid absorption during hypovolaemia.

Aims/hypothesis. Patients with Type I (insulin-dependent) diabetes mellitus have a reduced transcapillary fluid absorption from skeletal muscle and skin and thus defective plasma volume regulation during hypovolaemia. Our aim was to find whether a defective capillary filtration coefficient or impaired transcapillary driving force are aetiologic factors for this reduction. Methods. We investigated 11 diabetic patients (diabetes duration 6.9 ± 1.1 years, age 26 ± 1 years), without complications and 12 control subjects (26 ± 1 years). Their capillary filtration coefficient was measured in the upper arm using a volumetric technique at rest and during lower body negative pressure (LBNP). We calculated the driving force for transcapillary fluid transfer. Results. The increase in heart rate and the decrease in systolic blood pressure during lower body negative pressure were similar in diabetic and control subjects. The resting capillary filtration coefficient was decreased in the diabetic subjects, 0.033 ± 0.003 vs 0.051 ± 0.007 ml · 100 ml–1· min–1· mmHg–1 (p < 0.05). During lower body negative pressure, the capillary filtration coefficient increased 35 % in both groups compared with resting capillary filtration coefficient and was still decreased in diabetes; 0.046 ± 0.004 compared with 0.069 ± 0.006 ml · 100ml–1· min–1· mmHg–1 (p < 0.01). The established driving force during lower body negative pressure was 1.37 ± 0.11 vs 1.30 ± 0.15 mmHg (NS) in diabetic and control subjects, respectively. Conclusions/interpretation. Our study indicates that a reduced capillary filtration coefficient rather than defective regulation of transcapillary driving force, is the reason for the reduced transcapillary fluid absorption during hypovolaemic circulatory stress found in Type I diabetic patients. [Diabetologia (2000) 43: 1178–1184]

Impaired compensatory response to hypovolaemic circulatory stress in type 1 diabetes mellitus

Diabetes mellitus is associated with decreased haemodynamic stability and reduced tolerance to hypovolaemia. Compensatory haemodynamic responses during experimental hypovolaemia in type 1 diabetes patients with (DMR+) and without (DMR-) retinopathy as well as healthy controls (C) were studied. Lower body negative pressure created hypovolaemic circulatory stress. Volumetric techniques were used to assess the compensatory capacitance response (redistribution of peripheral venous blood to the central circulation) and to assess capillary fluid absorption from tissue to blood. The compensatory capacitance response was 1/3 lower in DMR+ compared with C (p = 0.002) and DMR- (p = 0.01). Net capillary fluid absorption was reduced by one-third in DMR- and DMR+ compared with C (each p < 0.05). Type 1 diabetes patients with retinopathy demonstrate reduced mobilisation of peripheral venous blood to the central circulation. Furthermore, type 1 diabetes patients present with impaired capillary fluid absorption, which in combination with potentially decreased sympathetic vasoconstriction impedes cardiovascular homeostasis during acute hypovolaemic stress.