Yukihiro Sawada

Normalized pulse volume (NPV) derived photo-plethysmographically as a more valid measure of the finger vascular tone

Normalized pulse volume (NPV) was advocated as a more valid measure for the assessment of finger vascular tone. Based on the optical model in the finger tip expressed by Lambert--Beers law, NPV is expressed as Delta I(a)/I. Here, Delta I(a) is the intensity of pulsatile component superimposed on the transmitted light (I). Theoretically, NPV seems to be superior to the conventional pulse volume (PV; corresponding to Delta I(a)). Firstly, NPV is in direct proportion to Delta V(a), which is the pulsatile component of the arterial blood volume, in a more exact manner. Relatedly, NPV can be processed as if it is an absolute value. Secondly, the sensitivity of NPV during stressful stimulations is expected to be higher. These expectations were supported experimentally using 13 male students. Firstly, the correlation between cutaneous vascular resistance in the finger tip (CVR) and NPV was higher than that between CVR and PV among all the subjects, although there was not much difference between these correlations within each subject. Secondly, NPV decreased much more than PV during mental stress. Some limitations of the present study were addressed, including the point that certain factors can violate the direct proportional relationship of NPV and PV to Delta V(a).

Beat-by-beat double-normalized pulse volume derived photoplethysmographically as a new quantitative index of finger vascular tone in humans

Abstract Near-infrared finger photoplethysmograms were recorded and double-normalized pulse volumes (DNPV = ΔVb/Vb; Vb = total blood volume in the fingertip, ΔVb = pulsatile component of Vb) were calculated in ten subjects during, immersion of the contralateral hand in water at three different temperatures (44°C, 22°C, 11°C). The DNPV from the left finger was compared beat-by-beat with cutaneous vascular resistance (CVR) derived by dividing mean blood pressure of the left third finger by cutaneous blood flow of the left fourth finger. The correlations overall at the three temperatures between log DNPVLF and log CVRLF (LF, low frequency component of DNPV and CVR) ranged from −0.89 to −0.96 among the subjects. After adjusting for a maximal extension of the vascular wall (DNPVmax), the correlations became stronger. It was concluded that DNPV was a reliable and valid indicator of vascular tone in the finger.

A novel photoplethysmography technique to derive normalized arterial stiffness as a blood pressure independent measure in the finger vascular bed

Stiffening of the small artery may be the earliest sign of arteriosclerosis. However, there is no adequate method for directly assessing small arterial stiffness. In this study, the finger arterial elasticity index (FEI) was defined as the parameter n which denotes the curvilinearity of an exponential model of pressure (P)-volume (V(a)) relationship (V(a) = a - b exp (-nP)). For the original estimation, the FEI was calculated from a compliance index from the finger photoplethysmogram whilst occluding the finger. A simple estimation of the FEI was devised by utilizing normalized pulse volume instead of the compliance index. Both estimations yielded close agreement with the exponential model in healthy young participants (study 1: n = 19). Since the FEI was dependent on finger mean blood pressure, normalized finger arterial stiffness index (FSI) was defined as standardized residual from their relationship: mean and standard deviation (SD) of the FSI were 50 ± 10 (study 2: n = 174). The mean coefficient of variation of the FSI for four measurements was 5.72% (study 3: n = 6). The mean and SD of the FSI in seven arteriosclerotic patients were 100.0 ± 13.5. In conclusion, the FEI and FSI by simple estimation are valid and useful for arteriosclerosis research.

Mirror Tracing and the Provocation of Vascular-Dominant Reaction Pattern Through Heightened Attention

Abstract After a hint from Lang et al.s (1997) defence cascade, researchers considered cognitive process experienced when encountering mental stress to be composed of four elements: (serially) fir...

Examination of normalized pulse volume-blood volume relationship: toward a more valid estimation of the finger sympathetic tone.

The pulsatile ac component (DeltaI) superimposed on the transmitted dc components (I: tissue plus blood) are obtained from a near-infrared finger photoplethysmogram using a wavelength of 810 nm. Only the dc component is given in an ischaemic circulatory state (I(t): tissue only). Based on Lambert-Beers law, normalized pulse volume (NPV; =DeltaI/I) and blood volume [BV; =ln(I(t)/I)] have recently been advocated as quantitative measures. In this study, the NPV-BV relationship was examined using the finger occlusion method during rest and mental arithmetic in 16 female undergraduates. Finger vascular tone during stress was evaluated by the distance of the linear and parallel NPV-BV regression lines (D(NB)) between rest and stress conditions. A reference standard was provided by the linear regression lines of compliance index (CI=NPV/pulse pressure) and BV to the transmural pressure. The estimates at 40 mmHg of transmural pressure, as an arbitrarily chosen reference point, were calculated (CI40 and BV40). D(NB) correlated well with them (r=0.81 and 0.94, respectively). The multiple regression with mean blood pressure indicated that the combination of D(NB) and the reactivities in heart period could explain approximately 50% of valiance in pressor response. In conclusion, D(NB) is easily obtainable from the NPV-BV function and seems to be more specific and valid than NPV as an index of finger sympathetic tone, since it adjusts the mechanical effect of arterial distending pressure.

A preliminary study of the comfort of paced respiration

In order to obtain basal information about what type of externally paced respiration is comfortable, 25 male and 25 female undergraduate students were asked to practice self-paced respiration. After a 1-min rehearsal following instructions on comfortable self-paced respiration, subjects carried out 2 min of self-paced respiration and rated their level of comfort on a scale of 1–5. This was repeated (up to a maximum of seven times) until the subject recorded a high rating. Results indicated that self-paced respiration was most comfortable, irrespective of sex, when a respiratory pattern was attained of half the respiratory rate and nearly twice the tidal volume of the trainees resting condition. Although respiratory sinus arrhythmia and heart rate were indicative of a decrease in cardiac vagal activity and end-tidal PCO2 was suggestive of a reduction in anxiety, these effects were small. The results have implications for the utilization of externally paced respiration.

Intertask consistency of blood pressure responses to laboratory stressors may increase with prolonged exposure

In this study, one of the predictions of the reactivity hypothesis was investigated: the intertask consistency of blood pressure (BP) responses. Twelve young male subjects underwent cold-pressor (14°C) and digit-scan (counting even numbers) tests in randomized order. Cardiovascular parameters were recorded during a 2-min pretask baseline, a 10-min stressful exposure, and over a 5-min post-task baseline. The intertask correlations between the cold pressor and digit scan increased with prolonged exposure and were higher for almost all of the systolic BP measurements than for the diastolic measurements. After prolonged exposure, the hemodynamic mechanisms of BP elevations during the digit scan shifted from an increase in both cardiac output and peripheral vascular resistance to solely an increase in peripheral vascular resistance. Increased peripheral vascular resistance was the consistent cause of the BP elevations with the cold pressor. Accordingly, the hemodynamic shift on the part of the digit scan seemed to heighten the intertask BP correlations. Some other factors influencing the intertask BP correlations are also discussed.

How carryover has an effect on recovery measures related to the area under the curve: theoretical and experimental investigations using cardiovascular parameters

This study examines cardiovascular recovery from mental stress. Investigating the absence or presence of carryover effect, the effect of the final reactivity observed at the end of stressful task on the successive recovery, was the major objective. A recently advocated recovery measure related to the area under the curve, mean recovery rate (MRR), was investigated, comparing with the two relatives of this type, total carryover (TCO) and literally area under the curve (AUC). At the onset, a detailed theoretical formulation of each measure was carried out, starting from its original definition. It was predicted that MRR, but not TCO or AUC, could be free from the carryover effect. Next, 88 male students underwent a 5-min mental arithmetic during which blood pressure and heart rate were measured. Nearly all the theoretical predictions (i.e., 5/6 for the three recovery measures by two cardiovascular parameters) were supported by experimental data. There was only one exception: for heart rate, there was a proportional relationship even for MRR versus the final reactivity. Vagal rebound in the recovery period was conceived as the main contributor of this contradiction. The implications of these results for the understanding of future directions in recovery studies are discussed.

Stress Reduction Intervention: A Theoretical Reconsideration with an Emphasis on Breathing Training

In recent years, considerable attention has been focused on studies of stress reduction interventions. However, there have been controversies regarding their positive effects. The present paper is an attempt to initiate reconciliation of the discrepant findings. First, the term “stress” is redefined from a standpoint of cardiovascular hemodynamics. Then the attention-affect model is newly introduced in order to have a clearer understanding of the hemodynamic reaction patterns during stressful stimulation. Based on these reconsiderations, the stress reduction interventions are revaluated, with an emphasis on breathing training.

Application of the maximum‐entropy method to data on short‐term variability in inter‐beat interval and an interpretation of the calculated powers

Sixteen young males underwent resting and mental arithmetic and were injected with 100 μg phenylephrine during the interventions. Half of them further underwent trinitroglycerine injections. Power spectral density for inter-beat interval variability was calculated using the maximum-entropy method (MEM) with a very high lag, and its validity was checked by nonlinear least-squares method. It was found that the MEM could produce a very accurate power spectral density. Results on the low- and high-frequency (LF and HF) powers indicated that the phenylephrine injection increased both the LF and HF powers, that the trinitroglycerine injection increased the LF power to some degree, and that the mental arithmetic decreased both the LF and HF powers with both phenylephrine and trinitroglycerine. Therefore, the LF power could be interpreted as a marker of both the vagal and sympathetic activities, whereas the HF power seemed to be solely associated with vagal activity. The implications of the interpretation are discussed in terms of the controversy on the LF power (vagal plus sympathetic vs. sympathetic).