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At least 919 records · Page 51Linked to original sources
PubMed1993

A reassessment of mercury in silastic strain gauge plethysmography for microvascular permeability assessment in man.

1. We have used non-invasive mercury in a silastic strain gauge system to assess the effect of pressure step size, on the time course of the rapid volume response (RVR) to occlusion pressure. We also obtained values for hydraulic conductance (Kf), isovolumetric venous pressure (Pvi) and venous pressure (Pv) in thirty-five studies on the legs of twenty-three supine control subjects. 2. The initial rapid volume response to small (9.53 +/- 0.45 mmHg, mean +/- S.E.M.) stepped increases in venous pressure, the rapid volume response, could be described by a single exponential of time constant 15.54 +/- 1.14 s. 3. Increasing the size of the pressure step, to 49.8 +/- 1.1 mmHg, gave a larger value for the RVR time constant (mean 77.3 +/- 11.6 s). 4. We propose that the pressure-dependent difference in the duration of the rapid volume response, in these two situations, might be due to a vascular smooth muscle-based mechanism, e.g. the veni-arteriolar reflex. 5. The mean (+/- S.E.M.) values for Kf, Pvi and Pv were 4.27 +/- 0.18 (units, ml min-1 (100 g)-1 mmHg-1 x 10(-3), 21.50 +/- 0.81 (units, mmHg) and 9.11 +/- 0.94 (units, mmHg), respectively. 6. During simultaneous assessment of these parameters in arms and legs, it was found that they did not differ significantly from one another. 7. We propose that the mercury strain gauge system offers a useful, non-invasive means of studying the mechanisms governing fluid filtration in human limbs.

Arm↗
PubMed1997

The effect of passive tilting on microvascular parameters in the human calf: a strain gauge plethysmography study.

1. Cumulative small steps in venous congestion pressure were used to study the effect of passive tilt on vascular parameters in dependent tissues. Using this protocol we have non-invasively assessed venous pressure (Pv,est), isovolumetric cuff pressure (Pv,i), which is the congestion cuff pressure (Pcuff) that has to be exceeded to induce fluid filtration. We have also assessed microvascular filtration capacity (Kf), which is the linear relationship between filtration rate (Jv) and Pcuff, when Pcuff > Pv,i, and is the product of the available exchange vessel surface area and wall conductance. 2. Subjects were passively tilted to increase the venous pressure at the level of the calf by 47.4 +/- 2.4 mmHg (mean +/- S.E.M.). The value of Pv,i increased from 20.6 +/- 1.8 to 48.5 +/- 3.8 mmHg after the imposition of the tilt. This change may reflect the increased colloid osmotic pressure at the microvascular interface that is known to occur in response to this manoeuvre. 3. The pre-tilt value of Kf did not change after the imposition of the passive tilt, the values being 3.2 +/- 0.4 x 10(-3) and 3.6 +/- 0.4 x 10(-3) ml min-1 (100 ml-1) mmHg-1, respectively, (n = 13). 4. These results support the notion that passive postural change alters the pre-capillary resistance, thereby altering the pressure and flow characteristics within the exchange vessels, but does not alter the surface area available for fluid exchange in the calf, contrary to previous findings in the dependent human foot using a single-step venous occlusion protocol.

Adult↗
PubMedDate not supplied

Experimental study of the relationship between the base impedance and its time derivative in impedance plethysmography.

Transthoracic electrical impedance Z consists of a constant baseline component Z0 and the time variable component delta Z such that Z = Z0 + delta Z. The first time derivative of Z has a negative peak, the magnitude of which is (dZ/dt)min. Measurements of 170 volunteers show that (dZ/dt)min is a function of the constant baseline component Z0. This implies that at least a part of the difference of the magnitudes of (dZ/dt)min on Z0 must be taken into account in order to avoid erroneous conclusions or inaccurate calculations.

Adolescent↗
PubMed1990

Estimation of lung volume in infants by echo planar imaging and total body plethysmography.

Echo planar imaging (an extremely fast method of magnetic resonance imaging) was used to measure lung volume in a group of nine infants, all of whom had had respiratory problems. The mean echo planar imaging estimate of total lung volume was 44 +/- 9 ml/kg. In each case the right lung was larger than the left (ratio 52.8:47.2%). The mean thoracic gas volume was 36 +/- 8 ml/kg. The entire sequence of images of the thorax (about 400) takes five minutes to complete, infants require no sedation, and there are no side effects.

Female↗
PubMed1993

Lung function in white children aged 4 to 19 years: II--Single breath analysis and plethysmography.

OBJECTIVE: A study was performed to determine reference ranges for whole body plethysmographic gas volumes and single breath gas transfer in healthy prepubertal and pubertal schoolchildren. METHODS: The study was performed in 772 white London schoolchildren (455 male) who were clinically examined, assessed auxologically and, in 63% of cases, pubertally staged. Regression equations for the calculation of standard deviation scores were derived. RESULTS: Male lung function variables showed a discontinuous pattern of increase with standing height. Linear increases until puberty were followed by a sudden pubertal rise and a further increase with height which was more marked than before puberty. Correction for varying thoracic dimensions eliminated these changes. In females a smoother curvilinear relationship was observed with no correction possible for thoracic size. CONCLUSIONS: Male puberty leads to profound changes in pulmonary function mostly related to thoracic size, an effect not observed in females.

Adolescent↗
PubMedDate not supplied

Whole-body plethysmography, does it measure tidal volume of small animals?

A whole-body plethysmograph was used for mice. The increase in pressure caused by each inhalation was equivalent to the increase that could be calculated to result from heating and humidification of the inhaled air. However, comprehending that a drop in temperature and humidity would cause an abrupt pressure decline during exhalation was difficult. Pressure changes in the plethysmograph were also studied with an artificial chest, modeling the respiratory mechanics, but without the "inhaled" air being heated or humidified. The "chest" consisted of a metal bellows oscillated by a stepper motor 25 to 175 times per minute. Hereby air (0.05 to 0.20 mL) moved in and out of the bellows. The air passed through a polyethylene tube, the length of which was proportional to "airway resistance" and varied from 5 to 35 cm. It was found that the pressure oscillation was affected not only by "tidal volume" of the mechanical chest but also by "respiratory rate" and by "airway resistance." We concur with previous investigators that the plethysmograph pressure reflects alveolar pressure and that fluctuations cannot be explained by changes in temperature and humidity. Accordingly, tidal volume can only be qualitatively and not quantitatively assessed.

Animals↗
PubMed1976

Temperature measurements and photoelectric plethysmography in the evaulation of acute and long-term effects of acupuncture upon vasomotor activity of hand skin: a methodological study.

Skin temperature measurements and photoelectric plethysomgraphy were used evaluating the changes in vasomotor activity of hand skin induced by acupuncture in 8 normal subjects, 10 patients with a chronic pain syndrome and 3 patients with an acute pain syndrome of one upper extremity. In normal persons acupuncture induced short-term fall in the skin temperature and the amplitude of photoelectric plethysmogram. This was undoubtedly a normal physiological reaction to pain. In cold sick hands with a chronic pain syndrome acupuncture induced warming of the hand skin and prolongation of the propagation time in the photoelectric plethysmogram. In warm sick hands with an acute pain syndrome acupuncture induced equalization of the temperature difference and shortening of the propagation time. It seems possible to evaluate the effects of acupuncture upon vasomotor activity of hand skin with these methods.

Acupuncture Therapy↗
PubMed1988

Acute changes in forearm venous volume and tone using radionuclide plethysmography.

In this investigation blood pool scintigraphy was validated as a method to study acute changes in human forearm veins. Changes in regional forearm vascular volume (capacity) and the occluding pressure-volume (P-V) relationship induced by sublingual nifedipine (NIF) and nitroglycerin (GTN) were recorded in 16 patients with simultaneous data collection by the radionuclide and the mercury-in-rubber strain-gauge techniques. The standard error of estimate (Syx) between successive control measurements using the radionuclide method was 3.1% compared with 3.2% for the strain-gauge method. The venous P-V curves were highly reproducible using both techniques. Strain gauge and radionuclide measurements of acute changes in forearm venous volume correlated well (r = 0.86; Syx = 7%, n = 156). After 20 mg of NIF or 0.6 mg of GTN, mean heart rate increased from 71 +/- 10 to 77 +/- 9 and from 68 +/- 10 to 75 +/- 11 beats/min, respectively, and group systolic blood pressure decreased from 128 +/- 22 to 120 +/- 19 and from 136 +/- 18 to 126 +/- 23 mmHg, respectively (P less than 0.05). At venous occluding pressures of 0 and 30 mmHg, the forearm vascular volume did not change after NIF (2 +/- 4 and -1 +/- 4%; P greater than 0.05), whereas it increased after GTN (8 +/- 5 and 12 +/- 7%; P less than 0.001). The forearm venous P-V relationship did not change after NIF, whereas a significant rightward shift (venodilation, with an increase in unstressed volume) occurred after GTN.(ABSTRACT TRUNCATED AT 250 WORDS)

Forearm↗