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The cardiac cycle related pulsatile behavior of the absorption and scattering coefficients of diffuse light and the corresponding alterations in hemoglobin concentrations in the human patella was studied. The pulsations in scattering is considerably smaller than absorption. The difference in amplitude of absorption coefficient pulsations for different wavelengths was translated to pulsations in oxygenated and deoxygenated hemoglobin, which leads to strong pulsations in the total hemoglobin concentration and oxygen saturation. The physiological origin of the observed signals was confirmed by applying a thigh-cuff. Moreover, we have investigated the optical and physiological properties of the patella bone and their changes in response to arterial cuff occlusion.

Human bone blood flow, mean blood speed and the number of moving red blood cells were assessed (in arbitrary units), as a function of time, during one cardiac cycle. The measurements were obtained non-invasively on five volunteers by laser-Doppler flowmetry at large interoptode spacing. The investigated bones included: patella, clavicle, tibial diaphysis and tibial malleolus. As hypothesized, we found that in all bones the number of moving cells remains constant during cardiac cycles. Therefore, we concluded that the pulsatile nature of blood flow must be completely determined by the mean blood speed and not by changes in blood volume (vessels dilation). Based on these results, it is finally demonstrated using a mathematical model (derived from the radiative transport theory) that photoplethysmographic (PPG) pulsations observed by others in the literature, cannot be generated by oscillations in blood oxygen saturation, which is physiologically linked to blood speed. In fact, possible oxygen saturation changes during pulsations decrease the amplitude of PPG pulsations due to specific features of the PPG light source. It is shown that a variation in blood oxygen saturation of 3% may induce a negative change of ∼1% in the PPG signal. It is concluded that PPG pulsations are determined by periodic 'positive' changes of the reduced scattering coefficient of the tissue and/or the absorption coefficient at constant blood volume. No explicit experimental PPG measurements have been performed. As a by-product of this study, an estimation of the arterial pulse wave velocity obtained from the analysis of the blood flow pulsations give a value of 7.8 m s(-1) (95% confidence interval of the sample mean distribution: [6.7, 9.5] m s(-1)), which is perfectly compatible with data in the literature. We hope that this note will contribute to a better understanding of PPG signals and to further develop the domain of the vascular physiology of human bone.

Using a small, but very instructive experiment, it is demonstrated that laser-Doppler flowmetry (LDF) at large interoptode spacing represents a unique tool for new investigations of thermoregulatory processes modulating the blood flow of small muscle masses in humans. It is shown on five healthy subjects that steady-state values of blood flow (perfusion) in the thenar eminence muscle group depend in a complex manner on both the local intramuscular temperature and local skin temperature, while the values of blood flow parameters measured during physiological transients, such as the post-ischaemic hyperhaemic response, depend only on the intramuscular temperature. In addition, it is shown that the so-called biological zero (i.e. remaining LDF signal during arterial occlusion) is influenced not only as expected by the intramuscular temperature, but also by the skin temperature. The proposed results reveal that the skeletal muscle has unique thermoregulatory characteristics compared, for example, to human skin. These and other observations represent new findings and we hope that they will serve as a stimulus for the creation of new experimental protocols leading to better understanding of blood flow regulation.

Laser-Doppler flowmetry (LDF) is an outstanding tool to monitor blood flow in a continuous and non-invasive way. In this work, we study LDF at large interoptode spacing applied to a human bone model (i.e. tibia diaphysis). To that aim, we first performed an extensive set of Monte Carlo (MC) simulations for 10 and 25 mm interoptode spacing. Second, we have assembled a dedicated LDF instrumentation based on an optimized industrial avalanche photo-detector. We performed LDF experimental measurements on human muscle using well-known physiological protocols, which confirmed the reliability of our instrumentation and the relevance of the LDF algorithms tested with the MC simulations. In a second set, we repeated the measurements on human tibia diaphysis. Again, the experiments corroborate the MC simulations and demonstrate the effectiveness of LDF to monitor blood perfusion in bone. The proposed technique has great potential for non-invasive neuro-vascular studies since it will certainly help to reveal the mechanisms underlying the interaction between bone/bone marrow, the circulatory system and the nervous system.

Near infrared spectroscopy (NIRS) can readily report on changes in blood volume and oxygenation. However, it has proved more problematic to measure real-time changes in blood flow and oxygen consumption. Here we report the development of a novel method using NIRS to measure local oxygen consumption in human muscle. The method utilizes the blood volume changes induced by the muscle pump during rhythmically contracting exercising skeletal muscle. We found that the saturation of the blood during the contraction phase was lower than that during the relaxation phase. The calculated oxygen drop was then divided by the contraction time to generate a value for the muscle oxygen consumption in the optical region of interest. As a test we measured the muscle oxygen consumption in the human vastus lateralis during exercise on a cycle ergometer by 11 trained male athletes (32 +/- 11 years old) at 40% and 110% peak aerobic power. We saw an increase from 13.78 micromol 100 g(-1) min(-1) to 19.72 micromol 100 g(-1) min(-1) with the increase in power. The measurements are theoretically exempt from usual NIRS confounders such as myoglobin and adipose tissue and could provide a useful tool for studying human physiology.