Quantification of microvascular resistance in patients with diabetes mellitus [abstract]

Near Infrared Photoplethysmography (NIRP) is a non-invasive technique that has the potential to be used to assess the state of the peripheral nerves and microcirculation. However, the parameters that reflect the state of the microvascular system have not been established. Therefore, we tested the hypothesis that the resistance of the blood vessels in the microcirculation can be determined by analyzing the temporal components of the photoplethysmographic trace. NIRP incorporates two light-emitting diodes and a photodetector. The emergent light enters the skin and penetrates to the level of the dermis, is backscattered, collected by the photodetector and converted to a recordable trace. This trace consists of a series of pulses synchronous with the heart period, Th. It is possible to divide each pulse into a rise time from baseline to peak, Tg, and fall time from peak to baseline, Ta. All NIRP recordings were taken from the right index finger with the person in the supine position. In a first study involving five healthy male volunteers, the subjects right arm was cuffed approximately three minutes during which he exercised the fingers to increase a buildup of tissue metabolites; this was done in order to decrease microvascular resistance. In a second study, the above parameters (Th, Tg and Ta) were measured in 31 patients with chronic diabetes mellitus (diabetic group, DG) and compared to those of 29 healthy normal persons (healthy group, HG). In the first study, the ratio of the rise time to the heart period (Tg/Th) or of the rise time of the fall time (Tg/Ta) was increased, whereas that to the fall time of the heart period (Ta/Th) was decreased. In the second study, the mean for the Tg/Th was 0.235 ñ 0.008 (mean ñ sem) for the HG and 0.292 ñ 0.007 for the DG; the increase was highly significant, p< 0.001 (one-tail unpaired t-test). The mean for the Tg/Ta was 0.312 ñ 0.013 for the HG and 0.413 ñ 0.012 for the DG; this increase was also highly significant, p< 0.001. The mean for the Ta/Th was 0.765 ñ 0.008 for the HG and 0.711 ñ 0.006 for the DG; the decrease was highly significant, p< 0.001. In conclusion, an increase in microvascular resistance was reflected in an increase in the rise time and a decrease in the fall time. Thus this system appears to be a useful one in quantifying the increase in microvascvular resistance in diabetics. (AU)

Children with lower birthweight have higher forearm vascular resistance - abstract

Undernutrition in utero is associated with the development of hypertension in rat models, as well as in man. The nature of this association remains unclear. The aim of the present study was to determine the effect of pregnancy programming on blood pressure and forearm blood flow in children. Subjects were randomly selected from the upper, middle and lowest quintiles of a distribution based on their birthweights. There were no significant differences in anthropometry and resting indices of cardiovascular response. Children were tested, using cold pressor test (CT) and mental arithmetic (M). Thus children in the lowest quintile of this population experienced greater change in FVR and FBF to the cold pressor test than their counterparts in the middle and upper quintiles. They also showed greater changes in SBP, HR, and RPP with mental arithmetic testing. Children in the middle and lower quintiles had higher SBP to the cold pressor test. The results demonstrate that children in the lowest quintile of this population have increased cardiovascular reactivity to standard laboratory stressors - table included (AU)

Daily variability in resting levels of cardiovascular variable in normal subjects and those with homozygous sickle cell disease

Measurements were made of cardiovascular variables and oral temperature in 16 male subjects with homozygous sickle cell disease (SS) and in 17 matched controls (AA) at 10.00 a.m, 1.00 p.m and 4.00 p.m. All subjects were in a rested state throughout. At 10.00 a.m. mean arterial pressure was lower, while heart rate, total forearm blood flow and cutaneous red cell flux in the forearm were higher in SS than AA. Vascular resistance in total forearm and forearm skin, calculated by dividing arterial pressure by blood flow or red cell flux, were lower in SS but hand cutaneous red cell flux and vascular resistance were not significantly different in SS and AA. In both SS and AA, there were parallel increase over the three sessions, in mean arterial pressure (by approximately 12 and 10 percent respectively) forearm vascular resistance (by approximately 17 and 27 percent) and hand cutaneous vascular resistance and hand cutaneous resistance (by approximately 2240 and 350 percent) whereas forearm blood flow and hand cutaneous red cell flux fell. By contrast, forearm cutaneous resistance showed no change during the day in SS, but increased progressively in AA (by approximately 75 percent). These results indicate that, during the day, there is progressive vasconstriction in forearm muscle and hand skin in SS and AA and also in forearm skin of AA that contributes to a progressive rise in the resting level of mean arterial pressure. We suggest this daily variability should be considered in studies of cardiovascular function: within a given study they should be performed at the same time of day.(AU)