Red Blood Cell Transit Time Research Articles

Exercise-induced hypoxaemia in highly trained athletes.

Traditionally, the pulmonary system has not been considered the limiting factor in determining maximal oxygen uptake (VO2max) in healthy individuals since arterial oxygen-haemoglobin saturation is thought to remain high during intense exercise. However, there appears to be a major exception to this rule. Recent evidence suggests that arterial hypoxaemia results during heavy exercise in well trained individuals with a high VO2max. Further, the degree of arterial desaturation is inversely related to VO2max. This exercise-induced hypoxaemia does not appear to be due to hypoventilation although athletes who have limited hyperventilation seem to exhibit the lowest arterial oxygen-haemoglobin saturation. A significant venoarterial shunt has been ruled out as a primary cause of the hypoxaemia based on both experimental and theoretical considerations. Therefore, it appears that the exercise-induced hypoxaemia seen in highly trained athletes during heavy exercise is primarily due to diffusion limitations and ventillation-perfusion inequality. It is postulated that incomplete diffusion in the healthy lung may be due to a rapid red blood cell transit time through the pulmonary capillary. In summary, recent findings suggest that the limits of the human pulmonary system may be reached or even exceeded during intense exercise in some individuals. In light of these findings the role of the pulmonary system as a limiting factor during maximal exercise in the highly trained endurance athlete warrants further investigation.

Imaging of red blood cell and plasma dispersion in the brain cortex.

Most of the methods for measuring regional or local blood flow cannot specify the respective fractions of the measured flow attributable to red blood cell (RBC) flow and plasma flow within the measured volume. It is obviously important to know this because of the decisively different microhaemodynamic behaviour of these two components in the microcirculation and their specialized roles in gas and solute exchange in tissue metabolism. Beyond obtaining a separate measure of RBC and plasma flow for a given volume of tissue, a separate assessment of the complexity of RBC and plasma transit routes within that volume seems equally important. This parameter reveals the dissimilarity between seemingly identical conditions when total volume flows are equal but are realized via vascular transit routes of different geometrical complexity, which could indicate the presence in one, and the absence in the other, of certain conditions such as highly focal oedema, capillary obstruction, vasomotion, etc. It has been repeatedly demonstrated, that the television densitometric method of Eke (1982, 1983, 1984) can yield separate images of RBC and plasma flow at high topographical and temporal resolution by monitoring the transit of RBC and plasma indicator pulses through an array of tissue areas and by analysing these indicator-dilution arrays for arrays of RBC and plasma mean transit time (t) and flow. This method has been recently supplemented by a statistical procedure adopted from Knopp and Bassingthwaighte (1969) to analyse the arrays of RBC and plasma indicator-dilution curves for the scatter of the individual transit times over the mean transit time, t (Eke, 1986). This analysis yields a parameter assessing the spatial complexity of indicator transit pathways confined by the monitored tissue volume and is analogous to the approach reported by Tomita et al. (1983). Their concept is based on some a priori assumptions of the distribution of parenchymal transit times (gamma distribution) and the calculation of the ‘gamma index’ as the spatial parameter of the gamma density function applied in the procedure to obtain the transport function of the parenchymal region. The major differences between their approach and mine, beyond the mathematics, are attributable to the facts that their indicator-dilution technique does not allow for imaging, requires invasion of the tissue and derives the gamma index for a cerebrocortical tissue volume of around 1–2 cm3 in contrast to the reflectometric measuring volume of 0.01 mm3.KeywordsTransit TimeBrain CortexReactive HyperaemiaGeometrical ComplexitySpatial ComplexityThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Effects of pulmonary edema on regional blood volume and red blood cell transit time. Comparison of high pressure and oleic acid-induced edema.

The present study was designed to determine the effects of pulmonary vascular pressure, vascular injury, and pulmonary edema on regional blood volume (Vr) and regional red blood cell (RBC) transit time (Tr) in the lung. The experiments were carried out in 15 dogs. Six served as controls, six had oleic acid-induced pulmonary edema (OAPE), and three had high pressure pulmonary edema (HPPE). Regional blood flow (Qr) was measured with 99mTc macroaggregates, Vr with 51Cr homologous RBC, and regional transit time was calculated (Vr/Qr). The dogs were killed, and the lungs removed and sampled completely. Regional extravascular lung water (EVLW) was measured in grams per gram of dry lung and ranged from 3.7 +/- 1.1 in the control group to 6.0 +/- 1.3 in OAPE and 5.6 +/- 0.6 in HPPE. The data show that in normal lungs, increased Qr was associated with a recruitment of blood volume. In OAPE, data show that regional blood volume was decreased and that vascular injury and edema formation interfered with a further increase in Vr as Qr increased. In HPPE, Vr has already fully distended and it changed little with increased blood flow. We conclude that oleic acid-induced pulmonary injury and edema interfere with vascular recruitment and shorten regional RBC transit times. HPPE, on the other hand, is associated with normal regional RBC transit times because the vessels are fully recruited.