On the reliability of the Penaz cuff during systemic and local fingertip vasodilatation at rest and in exercise

A comparison of the time constant of the cerebral arterial bed using invasive and non-invasive arterial blood pressure measurements

OBJECTIVE

The time constant of the cerebral arterial bed (τ), which is an index of brain haemodynamics, can be estimated in patients using continuous monitoring of arterial blood pressure (ABP), transcranial Doppler cerebral blood flow velocity (CBFV) and intracranial pressure (ICP) if these measures are available. But, in some clinical scenarios invasive measurement of ABP is not feasible. Therefore, in this study we aimed to investigate whether invasive ABP can be replaced with non-invasive ABP, monitored using the Finapres photoplethysmograph (fABP).

APPROACH

Forty-six recordings of ICP, ABP, fABP, and CBFV in the right and left middle cerebral arteries were performed daily for approximately 30 min in 10 head injury patients. Two modelling approaches (constant flow forward [CFF, pulsatile blood inflow and steady blood outflow] and pulsatile flow forward [PFF, where both blood inflow and outflow are pulsatile]) were applied to estimate τ using either invasive ABP (τ_CFF, τ_PFF) or non-invasive ABP (fτ_CFF, fτ_PFF).

MAIN RESULTS

Bland-Altman analysis showed quite poor agreement between the fτ and τ methods of estimation. The fτ method produced significantly higher values than the τ method when calculated using both the CFF and PFF models (p < .001 for both). The correlation between fτ_CFF and τ_CFF was moderately high (r _s = 0.63; p < .001), whereas that between fτ_PFF and τ_PFF was weaker (r _s = 0.40; p = .009).

SIGNIFICANCE

Our results suggest that using non-invasive ABP for estimation of τ is inaccurate in head injury patients.

The Effect of Different Intensity Modalities of Resistance Training on Beat-to-Beat Blood Pressure in Cardiac Patients

Background

Resistance training has been introduced in cardiac rehabilitation to give more benefit than traditional training. Haemodynamic evaluation of cardiac patients to resistance training has generally consisted of continuous HR monitoring and discontinuous blood pressure measurements.

Design and Methods

Blood pressure (BP) and heart rate (HR) responses to resistance training were evaluated using continuous monitoring (Finapres) during low (four sets of 17 repetitions at 40% of the one-repetition maximum strength [1-RM]) and high intensity resistance training (four sets of 10 repetitions at 70% of 1-RM) on a leg extension machine in 14 patients who participated in a rehabilitation programme. Work volume was identical in the low- and high-level resistance training.

Results

The HR and systolic blood pressure (SBP) during low intensity resistance training were always larger than during high intensity (P<0.001). Peak SBP increased from set 1 to set 3 and 4 during both low and high intensity resistance training (P<0.05). Peak HR was larger in set 4 (95 ± 11 bpm) than in set 1 only during low intensity resistance training (91 ± 12 bpm) (P<0.05). One-minute recovery periods did not allow a return to baseline HR and SBP during both low and high intensity modalities.

Conclusions

The SBP and HR responses to resistance training are related to the duration of exercise. Sets with ≥ 10 repetitions of high intensity should be preferred to longer sets with low intensity. Pauses between exercise sets should exceed 1 min. Blood pressure should be measured during the last repetitions of the exercise set. Eur J Cardiovasc Prev Rehabil 12:12-17 © 2005 The European Society of Cardiology

Assessing the eligibility of a non-invasive continuous blood pressure measurement technique for application during total intravenous anaesthesia

OBJECTIVE

To assess the eligibility for replacement of invasive blood pressure as measured "within" the arterial vessel (IBP) with non-invasive continuous arterial blood pressure (cNIP) monitoring during total intravenous anaesthesia (TIVA), the ability of cNiP to track fast blood pressure changes needs to be quantified. A new method of statistical data analysis is developed for this purpose.

METHODS

In a pilot study on patients undergoing neurosurgical anaesthesia, mean arterial pressure MAPIBP measured with IBP was compared to MAPCNP measured by the CNAP Monitor 500 in ten patients (age: 63±13 a). Correlation analysis of changes of device differences ΔeMAP=ΔMAPCNP-ΔMAPIBP with changes of MAPIBP (ΔMAPIBP) during intervals of vasoactivity was conducted. An innovative technique, of linear trend analysis (LTA) applied to two signals, is described to perform this analysis without a priori knowledge of intervals of vasoactivity.

RESULTS

Analysis of ΔeMAP during vasoactivity revealed that ΔMAPCNP systematically underestimated ΔMAPIBP by 37%. This was confirmed in the complete data set using LTA technique showing a systematic, yet patient specific, underestimation in tracking ΔMAPIBP (16…120%).

CONCLUSION

The proposed LTA technique is able to detect systematic errors in tracking short-term blood pressure changes otherwise masked by established analysis. LTA may thus be a useful tool to assess the eligibility of cNIP to replace IBP during TIVA.

Relationship between ocular pulse amplitude and systemic blood pressure measurements

PURPOSE

This study aimed to determine whether ocular pulse amplitude (OPA) measured with dynamic contour tonometry (DCT) is related to systemic blood pressure (BP) parameters.

METHODS

Blood pressure was measured continuously and simultaneously with OPA in one randomly selected eye in 29 healthy subjects. Systemic parameters of interest were: systolic and diastolic BPs and their difference (BP amplitude), and left ventricle ejection time (LVET; defined as the time between the diastolic trough and the incisural notch in the BP curve). In addition, the axial length (AL) of the eye was measured. Associations between OPA, AL and systemic cardiovascular parameters were analysed in a multivariate regression model.

RESULTS

Measurements of OPA ranged from 1.0 mmHg to 4.9 mmHg (mean 2.3 +/- 0.9 mmHg, median 1.9 mmHg). In a univariate analysis with one predictor at a time, means of intraocular pressure (IOP) (p = 0.008), AL (p = 0.046) and LVET (p = 0.037) were significantly correlated with OPA, whereas systolic and diastolic BPs and their amplitude were not. A multiple linear regression analysis showed that mean IOP (p < 0.005), AL (p = 0.01) and LVET (p = 0.002) all independently contributed to OPA.

CONCLUSIONS

The OPA readings measured with DCT in healthy subjects were not related to BP levels and amplitude. It seems that the OPA strongly depends on the time-course of the cardiac contraction. Regulating mechanisms in the carotid system as well as scleral rigidity may be responsible for dampening the direct effect of BP variations.

Changes in finger-aorta pressure transfer function during and after exercise

Noninvasive finger blood pressure has become a surrogate for central blood pressure under widely varying circumstances. We tested the validity of finger-aorta transfer functions (TF) to reconstruct aortic pressure in seven cardiac patients before, during, and after incremental bicycle exercise. The autoregressive exogenous model method was used for calculating finger-aorta TFs. Finger pressure was measured noninvasively using Finapres and aortic pressure using a catheter-tip manometer. When applying the individual TFs found during rest for reconstruction of aortic pressure during all workloads, systolic pressure was increasingly underestimated, with large variation between subjects: +4.0 to −18.1 mmHg. In most subjects, diastolic pressure was overestimated: −3.9 to +5.5 mmHg. Pulse pressure estimation varied between +4.5 and −21.9 mmHg. In all cases, wave distortion was present. Postexercise, error in reconstructed aortic systolic pressure slowly declined, and diastolic pressure was overestimated. During rest, the TF gain had a minimum between 3.65 and 4.85 Hz (Fmin). During exercise, Fmin shifted to frequencies between 4.95 and 7.15 Hz at the maximum workload, with no change in gain. Postexercise, gain in most subjects shifted to values closer to unity, whereas Fmin did not return to resting values. Within each subject, aorta-Finapres travel time was linearly related to mean pressure. During exercise, Fmin was linearly related to both delay and heart rate. We conclude that, during increasing exercise, rest TFs give an increasingly unreliable reconstruction of aortic pressure, especially at higher heart rates.

Central and peripheral effects of angiotensin II on the cardiovascular response to exercise

The authors tested the hypothesis that angiotensin II modulates cardiovascular responses to dynamic exercise via peripheral and central effects on the autonomic nervous system. Ten subjects performed three identical exercise tests during treatment with placebo, valsartan (an angiotensin II type 1 receptor blocker), or enalapril (an angiotensin-converting enzyme inhibitor). With placebo, plasma concentrations of angiotensin II, norepinephrine, and epinephrine were elevated during cycling at 80% of heart rate reserve (HRR). Enalapril attenuated increases in heart rate, mean arterial pressure (MAP), and catecholamines during cycling, whereas valsartan only attenuated MAP and rate-pressure product above 60% HRR, and norepinephrine. The different responses provoked by the two drug treatments suggest that angiotensin-converting enzyme inhibition affects cardiovascular responses to exercise by mechanisms unrelated to production of angiotensin II. Indices of autonomic function during dynamic exercise were not changed by either drug. Attenuation of norepinephrine release during exercise by valsartan suggests that angiotensin II facilitates the release of norepinephrine from sympathetic postganglionic neurons. Angiotensin II, therefore, contributes to the pressor response to exercise by inducing peripheral vasoconstriction and facilitation of norepinephrine release from postganglionic sympathetic nerve endings that are unrelated to central activation of the autonomic nervous system.

Evaluation of digital blood pressure measured with the Omron F3 device as an index of brachial arterial pressure, under different thermal and hormonal conditions

BACKGROUND

Devices that record from the finger have potential practical advantages for home monitoring of blood pressure. However, digital arterial pressure may vary substantially from that in the brachial artery, due to the influence of peripheral wave reflection.

AIMS

(1) To compare digital arterial pressure, as measured with the Omron F3 device, with brachial arterial pressure and (2) to determine the effect on digital pressure of changing local vascular resistance.

METHOD

The subjects were normotensive young adult non-smokers (12 males, 14 females). Pressures were recorded simultaneously from arm (using an Omron HEM-705CP) and finger with subjects seated and both recording sites at the level of the xiphisternum. Measurements were made at ambient temperatures of 19 degrees C and 30 degrees C; at rest, during brief contralateral hand cooling and after hand rewarming.

RESULTS

In many cases, resting finger values differed substantially from arm values; sometimes by 20 mm Hg or more. The extent of individual variations was not correlated with gender or temperature. However, group pressure differences between the sites were greater in females at ovulation than at menstruation and greater at 30 degrees C than at 19 degrees C. For all groups, pressure differences between sites were attenuated during hand cooling and restored by rewarming.

CONCLUSIONS

Finger blood pressure, as measured with the Omron F3, misestimates brachial blood pressure in a high proportion of normal subjects. This error is increased under circumstances associated with cutaneous vasodilation. The Omron F3 does not appear to be suitable for unsupervised home monitoring of blood pressure.

Covariation and Temporal Stability of Peripheral and Brachial Blood Pressure Responses to Mental and Static Stress

Abstract Peripheral blood pressure measurement (Finapres technique) is a promising development in activation research. This paper tests and compares the temporal stability and covariation of peripheral and brachial blood pressure responses. Forty healthy subjects were tested four times at intervals of 1 day, 1 week, and 1 month. The tasks employed were two mental tasks (mental arithmetic and a Color Word Test) and a static (fingergrip) task. Recorded physiological parameters were peripheral and brachial systolic (SBP) and diastolic blood pressure (DBP). Mean peripheral SBP was about 20 mmHg higher than brachial SBP, but the difference between the DBP measures was negligible. Correlations between peripheral and corresponding brachial BP resting levels were low, with coefficients below 0.30. The correlations between peripheral and brachial SBP and DBP were higher for reactivity (change) scores (0.46-0.82) than for resting scores. Several types of inter- and intraindividual covariation were calculated to provide a deeper understanding of the relationship between the physiological parameters with respect to their dynamics. Temporal stability of peripheral BP level scores was lower (0.37-0.57) than for brachial BP (0.59-0.77), but the stability of the change scores was similar for both BP techniques. The results show that it is important to distinguish between several aspects of the mutual relationship between peripheral and brachial BP measures. Peripheral BP measurements are not suited to assess the BP level of a subject, but they are very useful to assess cardiovascular reactivity.

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--Beer's 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).

Effect of altering vasoactivity on the measurement of finger blood pressure

BACKGROUND

Finapres monitors and oscillometric sphygmomanometers are widely used in blood pressure measurements on the fingers. However, the reliability of finger blood pressure measurement devices still remains a matter of debate.

DESIGN

The volume clamp and modified oscillometric methods for non-invasive beat-to-beat finger mean arterial pressure monitoring are compared during intensive spontaneous changes in vascular tone. The degree of vasoconstriction is established by recording the thumb pulp skin blood flow with a laser Doppler instrument. The oscillometric mean arterial pressure (MAPo) and the Finapres mean arterial pressure (MAPf) are simultaneously recorded from adjacent fingers in eight healthy volunteers in a sitting position at room temperature 22-23 degrees C.

RESULTS

The changes in blood pressure were similarly tracked by the two blood pressure monitors, except the episodes with peripheral vasoconstriction. The difference (MAPo-MAPf) for all simultaneously recorded mean blood pressure values in episodes without vasoconstriction was (mean+/-SD) 0.7+/-1.8mmHg (P=0.33) and in episodes with vasoconstriction 10.6+/-5.6mmHg (P<0.01). A disagreement between the devices during vasoconstriction is assumed to be caused mainly by the tendency of the oscillometric method to overestimate the finger mean blood pressure, and by the tendency of the volume clamp method (Finapres) to underestimate the finger mean blood pressure in condition of peripheral vasoconstriction.

CONCLUSION

For both types of finger monitors (oscillometric blood pressure devices as well as Finapres or Portapres) it is recommended that intensive vasoconstriction in the subject be avoided during measurements. The presence of acute vasoconstrictions can be determined by simultaneous recording of finger skin blood flow.

Physiological influences on continuous finger and simultaneous intra-arterial blood pressure

Because of the clinical and experimental utility of continuous finger blood pressure measurements and the need for accuracy, we tested the performance of a new hydraulic device in 22 consecutive hypertensive subjects during physiological and pharmacological interventions. Ipsilateral brachial intra-arterial pressure was monitored during rest, Valsalva's maneuver, static handgrip, and mental arithmetic and after sublingual glyceryl trinitrate. In excess of 40,000 blood pressure values were analyzed. Average bias (intra-arterial minus finger blood pressure) was 8.2 +/- 17.0 mm Hg (mean +/- SD, P = NS) for systolic and 2.8 +/- 10.4 mm Hg (P = NS) for diastolic pressure. Two-way ANOVA of biases with subject and task factors showed a subject effect (P < .001). Intersubject and intrasubject standard deviations of bias were 13.8 and 9.8 mm Hg systolic and 8.7 and 5.7 diastolic, respectively. Linear drift (millimeters of mercury per minute) of finger pressure was greater (P < .001) for systolic than diastolic pressure during static exercise and math and after glyceryl trinitrate. Coefficients of determination for blood pressure ranged from 0.4 +/- 0.3 to 0.8 +/- 0.3 during the tasks. We conclude that (1) noninvasive finger blood pressure faithfully follows intra-arterial changes but with clinically relevant offsets, (2) this technique is best suited for assessing pressure changes, (3) physiological and pharmacological interventions do not consistently affect finger pressure accuracy, (4) many reports of finger blood pressure measuring devices are based on direct readings obtained with inadequate system response characteristics, and (5) the tested instrument falls short of the standard requirements (bias < or = 5 +/- 8 mm Hg) for devices that measure intermittently.

Noninvasive assessment of cardiac output from arterial pressure profiles during exercise

The stroke volume of the left ventricle (SV) was assessed in nine young men (mean age 22.2, ranging from 20 to 25 years) during cycle ergometer upright exercise at exercise intensities from 60 to 150 W (about 20% to 80% of individual maximal aerobic power). The SV was calculated from noninvasive tracings of the arterial blood pressure, determined from photoplethysmograph records and compared to the SV determined simultaneously by pulsed Doppler echocardiography (PDE). Given the relationship SV = As.Z-1 in which A(s) is the area underneath the systolic pressure profile (in millimetres of mercury and second), and Z (in millimetres of mercury and second per millilitre) is the apparent hydraulic impedance of the circulatory system, a prerequisite for the assessment of SV from the photoplethysmograph tracings is a knowledge of Z. The experimental value of Z (hereafter defined Z*) was calculated by dividing A(s) (from the finger photoplethysmograph) by SV as obtained by PDE. When the whole group of subjects was considered, Z* was not greatly affected by the exercise intensity: it amounted to 0.089 (SD 0.028; n = 36). The Z was also estimated independently of any parameter other than heart rate (HR), mean (MAP) and pulse (PP) arterial blood pressure obtained from the photoplethysmograph. A computerized statistical method allowed us to interpolate the experimental values of Z*, HR, PP and MAP by the equation Zm = a.(b + c.HR + d.PP + e.MAP)-1, thus obtaining the coefficients a to e. The mean percentage error between Zm (calculated from the coefficients obtained and Z* was 21.8 (SD 14.3)%. However, it was observed that, in a given subject, Z* was significantly affected by the exercise intensity. Therefore, to improve the estimate of Z a second algorithm was developed to update the experimental value of Z determined initially at rest (Zin). This updated value (Zcor) of Z was calculated as Zcor = Zin. [(f/(i + g.(HR/HRin) + h.(PP/PPin) + 1.(MAP/MAPin)], where HRin, PPin, MAPin, HR, PP, MAP are the above parameters at rest and during exercise, respectively. Also in this case, the coefficients f to 1 were determined by a computerized statistical method using Z* as the experimental reference. The values of Zcor so obtained allowed us to calculate SV from arterial pulse contour analysis as SVF = As.Z-1cor. The mean percentage error between the SVF obtained and the values simultaneously determined by PDE, was 10.0 (SD 8.7)%. It is concluded that the SV of the left ventricle, and hence cardiac output, can be determined during exercise from photoplethysmograph tracings with reasonable accuracy, provided that an initial estimate of SV at rest is made by means an independent high quality reference method.

Continuous non-invasive finger blood pressure monitoring in children

We evaluated the performance of continuous non-invasive finger arterial pressure measurement using the volume-clamp technique (Finapres). This study was designed to compare finger arterial pressure with brachial blood pressure estimated by the auscultatory method in 217 children (90 boys and 127 girls) aged 4-16 years and in 38 adults (aged 18-45 years). Finger and brachial artery pressure readings were obtained consecutively from the ipsilateral side in the supine position. Finger arterial pressure waveforms were recorded in all children except 4 with small and thin fingers. There was good agreement for systolic pressure with only a slight underestimation of 1.9 mmHg and 5.1 mmHg lower for diastolic pressure. This difference most probably reflects inaccuracy of the auscultatory cuff method rather than an error in the Finapres. There was large inter-individual variability in Finapres recordings which might be due to differences in vasomotor tone, as demonstrated by systolic amplification in 5 patients with anorexia. However, Finapres showed a small within-subject variability (3.8 mmHg for systolic and 4.1 mmHg for diastolic pressure) determined in 5 patients during phenylephrine infusion, and as good reproducibility as the auscultatory method. These results suggest that finger arterial pressure measurement in children older than 6 years of age has similar accuracy as that in adults, and that this method is useful for clinical applications in children, especially for the non-invasive evaluation of autonomic control and cardiovascular reflexes involving transient and rapid blood pressure changes.

Assessment of cardiac output from noninvasive determination of arterial pressure profile in subjects at rest

The stroke volume of the left ventricle (SV) was calculated from noninvasive recordings of the arterial pressure using a finger photoplethysmograph and compared to the values obtained by pulsed Doppler echocardiography (PDE). A group of 19 healthy men and 12 women [mean ages: 20.8 (SD 1.6) and 22.2 (SD 1.6) years respectively] were studied at rest in the supine position. The ratio of the area below the ejection phase of the arterial pressure wave (A(s)) to SV, as obtained by PDE, yielded a "calibration factor" dimensionally equal to the hydraulic impedance of the system (Zao = A(s).SV-1). The Zao amounted on average to 0.062 (SD 0.018) mmHg.s.cm-3 for the men and to 0.104 (SD 0.024) mmHg.s.cm-3 for the women. The Zao was also estimated from the equation: Zao = a.(d + b.HR + c.PP + e.MAP)-1, where HR was the heart rate, PP the pulse pressure, MAP the mean arterial pressure and the coefficients of the equation were obtained by an iterating statistical package. The value of Zao thus obtained allowed the calculation of SV from measurements derived from the photoplethysmograph only. The mean percentage error between the SV thus obtained and those experimentally determined by PDE amounted to 14.8 and 15.6 for the men and the women, respectively. The error of the estimate was reduced to 12.3 and to 11.1, respectively, if the factor Zao, experimentally obtained from a given heart beat, was subsequently applied to other beats to obtain SV from the A(s) measurement in the same subject.

Digital and brachial artery blood pressure measurements during peripheral, cold-induced vasoconstriction

Measurements of digital artery blood pressure made using an automated photoplethysmographic method (Finapres), in the middle finger of the left hands of nine male subjects, were compared with pressure measures in the right brachial artery using a method relying on the abolition of Karotkoff sounds during occlusion of the upper arm by a pressure cuff (Dinamap), during a 40-min immersion of the hand in cold (4 degrees C) and thermoneutral (32 degrees C) water. Blood flow in the left index finger was assessed and temperatures of the left and right ring fingers were also measured. Before immersion, systolic pressures in the digital artery were higher than systolic pressures in the brachial artery (P < 0.05), whereas the corresponding diastolic measurements were similar. However, both systolic (P < 0.01) and diastolic (P < 0.05) digital artery measurements increased with time. During cold immersion both systolic and diastolic pressures increased at both sites (P < 0.01), although the digital artery systolic readings rose sharply and then declined, whereas the brachial artery readings were stable. The cold-immersed digital artery diastolic measurements were greater than the brachial artery measurements (P < 0.01) and showed a continuation of the upward trend noted prior to immersion (P < 0.01). Thermoneutral diastolic digital artery measurements also showed this continued trend (P < 0.001). Some individual photoplethysmograph assessments of index finger blood flows showed intermittent vasodilatation, but cold immersion caused a decline in mean flow to 22% of pre-immersion value at 15 min, followed by an increase to 40%.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced slow caudad fluid shifts in orthostatic intolerance after 24-h bed-rest

To evaluate mechanisms of late orthostatic intolerance, slow fluid shifts along the body axis were studied during deconditioning by 24-h bed-rest and during 13-min upright tilts before and after this manoeuvre. In 11 healthy male subjects the fluid volumes of a thorax and a calf segment (impedance plethysmography) as well as tissue thickness at the forehead and the tibia (miniature ultrasonic plethysmograph) were recorded. Cardiovascular performance was monitored by recording heart rate (electrocardiogram), brachial and finger arterial pressure (by the Riva Rocci method and by the Finapres technique) as well as stroke volume (by impedance cardiography). Bed-rest led to a cephalad fluid shift with a mean interstitial leg dehydration of 2.2 ml.100 ml-1 with no changes in body mass and plasma volume. No syncope during the tilt occurred before bed-rest, while after bed-rest 8 subjects fainted between min 2.1 and 9.0 of the tilt. Bed-rest resulted in an augmented initial heart rate response to tilting which was similar in all subjects. In later orthostasis, bed-rest caused two- to threefold faster caudad fluid shifts with higher calf filtration rates in fainters (prior to hypotension) than in nonfainters. Through bed-rest the estimated extravasation within 10 min into general lower body tissue spaces increased by 192 ml in (late) fainters as opposed to only 23 ml in nonfainters. It was concluded that contributing factors to orthostatic intolerance may be slow transcapillary fluid shifts which are easily underestimated and whose quantity and time course call for further investigation after various deconditioning manoeuvres. In particular, the postflight fluid shifts in astronauts who will have markedly dehydrated legs, may impose a circulatory stress which needs to be evaluated. In general, the filtration rate in relevant areas appears to be an integrative and easily determined parameter, reflecting hormonal and neurogenic vascular as well as local interstitial control of the Starling forces.

Effect of temperature on finger artery pressure evaluated by volume clamp technique

We examined the effect of temperature on digital arterial blood pressure obtained by continuous beat-to-beat non-invasive monitoring with a volume-clamp technique (Finapres). In 10 normal volunteers and 13 patients with symptoms of vasospasm, digital pressure and brachial artery pressure (cuff method) was simultaneously recorded in control conditions at room temperature, during body cooling, finger heating, and truncal heating. In the control condition digital systolic blood pressure was significantly higher (16.1 +/- 14.2 mmHg) than brachial systolic pressure. The augmentation of digital systolic pressure correlated inversely with finger tip temperature. Diastolic and mean arterial pressure did not differ significantly between the two methods. Body cooling augmented the systolic finger-arm gradient while truncal heating and finger heating had the opposite effect. Finger heating reduced systolic augmentation without changing the mean and diastolic blood pressure. Similar changes were also observed in the patients with vasospasm except in one case with a pronounced Raynaud syndrome where digital blood pressure was lower than brachial artery pressure. We conclude that augmentation of finger systolic pressure seems to be dependent on local vasoconstriction of A/V shunts and that finger heating may be a useful procedure to improve the reliability of Finapres readings.

Cardiovascular limitations of active recovery from strenuous exercise

Recovery from muscle fatigue after exercise is known to have two beneficial effects: improved blood lactate elimination and a central nervous recuperation of the capacity for exercise. This study indicates circulatory mechanisms that might limit active recovery. Ten subjects were seated on a cycle ergometer and performed arm cranking exercise at an anaerobic intensity which was for each individual in three periods of 6 min, alternating with recovery intervals of 14 min. In two randomly assigned tests, recovery consisted either of passive sitting (control) or cycling at 80 W for 12 min. Both tests terminated with an identical final passive rest period of 25 min. In the cycling test arm cranking led to a heart rate increase which was further elevated with each repetition, while in the control test no differences were shown among the cranking periods. No corresponding difference was found for oxygen consumption. During the 25 min of final rest, the cycling test showed arterial hypotension and elevated heart rate both of which were absent in the control tests. Venous-occlusion-plethysmography revealed a postcranking forearm hyperaemia. In the cycling test hyperaemia was markedly reduced with the onset of cycling due to vasoconstriction; this effect was absent in the control test. A reduction in blood lactate occurred faster in the cycling test, mainly at the onset of cycling. Total plasma fluid loss combined with forearm fluid uptake was accentuated and prolonged by cycling recovery. Recovery exercise performed by muscles other than those that were fatigued could have led to arterial hypotension (shock-index about 1) through both plasma fluid loss and additional vasodilatation depending on the muscle mass involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood pressure and heart rate during rest-exercise and exercise-rest transitions

The transients of mean arterial blood pressure (BPa) and heart rate (fc) during rest-exercise and exercise-rest transitions have been studied in six healthy sport students. After 5 min of rest in an upright position on a cycle ergometer they exercised for 15 min and remained seated for a further 5 min. The subjects exercised at four different constant intensities (40 W, 80 W, 120 W, 160 W) in random order separated by at least 24 h. The BPa was determined by a noninvasive and continuous method. During the first minute of exercise, three phases of response could be distinguished, with the first two showing no clear relationship to intensity. Phase 1 consisted of simultaneous increases in both fc and BP during the first 6 s. In phase 2, BPa decreased while fc continued to increase. During phase 3, BPa and fc approximated constant values or a linear increase. Both parameters showed no comparable intensity-independent reactions during the off-transients. In conclusion, during the first 15 s of rest-exercise transitions there seems to be a fast and uniform cardiovascular drive which overrode other influences on fc.

The interstitial fluid content in working muscle modifies the cardiovascular response to exercise

The volume of interstitial fluid in the limbs varies considerably, due to hydrostatic effects. As signals from working muscle, responsible for much of the cardiovascular drive, are assumed to be transmitted in this compartment, blood pressure and heart rate could be affected by local or systemic variations in interstitial hydration. Using a special calf ergometer, eight male subjects performed rhythmic aerobic plantar flexions in a supine position with dependent calves for periods of 7 min. During exercise heart rate, blood pressure, oxygen uptake (VO2) and blood lactate concentrations were measured in two different tests, one before and after interstitial calf dehydration through limb elevation for 25 min, compared to the other, a control with unaltered fluid volume in a maintained working position. Impedance plethysmography showed calf volume to be stabilized in the control position. Leg elevation by passive hip flexion to 90 degrees resulted in a fast (vascular) volume decrease lasting less than 2 min, followed by a slow linear fluid loss from the interstitial compartment. Then, when returned to the control position, adjustment of vascular volume was completed within 2 min and exercise could be performed with dehydration remaining in the interstitium only. Cardiovascular response was identical at the start of both tests. However, exercising with dehydrated calves elicited a significantly larger increase in heart rate compared to the control, whereas VO2 was identical. The blood pressure response was shown to be only slightly enhanced. Structural interstitial features varying with hydration, most likely chemical or mechanical ones, may have been responsible for this amplification of signals.