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P Gizdulich

Publications and source records attributed to P Gizdulich.

16 recordsLinked to original sources
PubMed1999

Statistical characterization of piezoelectric coefficient d23 in cow bone.

In a newly developed, highly sensitive dilatometer we applied pulsatile electric fields to five dry bone samples cut from mid-tibial sections within a 90 degrees angle from the rear to front axis. Samples of five cows were studied. We measured the piezoelectric coefficient d23 establishing its mean and confidence interval for the first time. An analysis of variance detected a significant difference of the coefficient between animals (P < 0.01) but not between samples (P = 0.5). Between animals the coefficient ranged from 9.6 x 10(-14) to 27.1 x 10(-14) C/N. It can no longer be assumed that piezoelectricity is an inherent property of bone, constant between animals.

Analysis of Variance↗
PubMed1997

Models of brachial to finger pulse wave distortion and pressure decrement.

OBJECTIVE: To model the pulse wave distortion and pressure decrement occurring between brachial and finger arteries. Distortion reversion and decrement correction were also our aims. METHODS: Brachial artery pressure was recorded intra-arterially and finger pressure was recorded non-invasively by the Finapres technique in 53 adult human subjects. Mean pressure was subtracted from each pressure waveform and Fourier analysis applied to the pulsations. A distortion model was estimated for each subject and averaged over the group. The average inverse model was applied to the full finger pressure waveform. The pressure decrement was modelled by multiple regression on finger systolic and diastolic levels. RESULTS: Waveform distortion could be described by a general, frequency dependent model having a resonance at 7.3 Hz. The general inverse model has an anti-resonance at this frequency. It converts finger to brachial pulsations thereby reducing average waveform distortion from 9.7 (s.d. 3.2) mmHg per sample for the finger pulse to 3.7 (1.7) mmHg for the converted pulse. Systolic and diastolic level differences between finger and brachial arterial pressures changed from -4 (15) and -8 (11) to +8 (14) and +8 (12) mmHg, respectively, after inverse modelling, with pulse pressures correct on average. The pressure decrement model reduced both the mean and the standard deviation of systolic and diastolic level differences to 0 (13) and 0 (8) mmHg. Diastolic differences were thus reduced most. CONCLUSION: Brachial to finger pulse wave distortion due to wave reflection in arteries is almost identical in all subjects and can be modelled by a single resonance. The pressure decrement due to flow in arteries is greatest for high pulse pressures superimposed on low means.

Adult↗
PubMed1996

Converse piezoelectric effect detected in fresh cow femur bone.

A piezoelectric effect has been reported to exist in biological tissues, in particular in dry bone. Since the precision and resolution now obtainable are much greater, we decided to verify the presence of the converse effect (dimensional change under the application of an electric field) in fresh bone samples, by using a very high sensitivity instrument. We took, in varying orientations, five fresh femur cylindrical bone specimens from a cow leg and placed them as a single piece, or as a stack of 10 thin interlayered slices from one specimen to improve sensitivity, in a special microwave double cavity differential dilatometer. The thickness of the specimen was approximately 10mm. The applied field strength for the nonstacked specimen was near 10 kV m-1. Thickness variation was measured along and across the electric field lines. We applied the electric field as a switched polarity square wave. This allows the thermal dilution of specimen warming and possible electrostriction effects, which are insensitive to the direction of the applied field, to be separated from an electromechanical effect which is sensitive to direction. Using coherent signal averaging over approximately 600 cycles to combat instrumental noise we observed nonthermal, nonelectrostrictional thickness variations in all samples. The amplitudes we observed were near 3 pm for the 1 cm nonstacked specimen, and the bone's responses to electric fields ranged from 26 to 38 fm V-1. With response magnitudes approximating those predicted theoretically for the converse piezoelectric effect in bone we conclude that the piezoelectric theory could not be falsified with our experiments.

Animals↗
PubMed1996

Finapres tracking of systolic pressure and baroreflex sensitivity improved by waveform filtering.

OBJECTIVE: Arterial pressure waveforms distort between brachial and finger arteries, causing differences mainly in systolic pressure. Distortion, reportedly, can be removed by applying a waveform filter to the finger pressure. DESIGN: We analysed the data from two studies that detected discrepancies in systolic tracking between Finapres and brachial pressures. The first set comprised waveforms of seven volunteers during incremental bicycle exercise to exhaustion and the second set comprised waveforms of eight volunteers during increasing phenylephrine infusion. METHODS: We applied the filter and compared 1 min averaged unfiltered and waveform-filtered finger and brachial pressures. RESULTS: During exercise, finger systolic pressure overestimated brachial increasingly, from 7(SD 10) mmHg at rest to 27(17) mmHg at maximal exertion. Differences were reduced by waveform filtering from 3 (SD 9)mmHg at rest to 1 (SD 15)mmHg at maximal exertion. During phenylephrine infusion finger systolic pressure overestimated brachial pressure, but the magnitude of the overestimate decreased from 14 (SD 15)mmHg at baseline to -1(SD 16)mmHg at maximal rate. After waveform filtering overestimation was an almost constant 6(SD 11)mmHg. Median baroreflex sensitivities from brachial, unfiltered and waveform-filtered finger pressure were 5.8, 7.5 and 5.3 ms/mmHg and correlation increased after filtering. The results indicate improved systolic pressure tracking after waveform filtering. CONCLUSIONS: Finger pressure distortion follows a general pattern correctable by waveform filtering. Waveform filtering allows a 'brachial' view to be obtained from Finapres data.

Adolescent↗
PubMed1992

Approach to the estimation of alveolar pressure from noninvasive measurement of upper airway resistance.

An alternative to whole body plethysmography is proposed for estimating upper airway resistance. The feasibility study indicates that the method should be suitable for diagnostic and clinical purposes, following a proper survey and the testing of its reproducibility. 11 subjects are asked to breath normally through 12 small resistances while flow and pressure are monitored at the mouth. Chest movements are recorded by sampling a chest cross-section, and relative variations of the cross-section are compared to the expired and inspired volumes. No viscoelastic effects are significantly documented so that in a first approximation a model consisting only of resistors is applied to the airways. In each subject the patterns of the flow and mouth-pressure are heuristically estimated as a polynomial function of the added resistance. From the fit of the resistor model, the internal resistance of the airways is estimated as that value able to link the flow-resistance function to the pressure-resistance function, according to the classic Kirchhoff laws. We obtain resistances of (mean resistance +/- SD) 2.9 +/- 1.1, range 1.1 to 5.2, hPasdm-3 during expiration and 2.5 +/- 0.8, range 1.3 to 3.7, hPasdm-3 during inspiration.

Adolescent↗
PubMed1989

Anaerobic threshold: reproducibility out from ventilatory parameter estimation.

Anaerobic threshold (AT) during exercise is usually noninvasively determined by assuming a two-segment mathematical relationship between two ventilatory parameters. In the literature, all the possible pairs of segments are first considered, and the most appropriate pair is then selected according to at least-squares method. In such a model, the AT is considered to be related to the joining point of the two segments. In order to test the reliability of the model, we compare the results of the least-squares method to those based on maximum probability method in discriminating the two regression coefficients. In order to test the reproducibility of the two different criteria, comparisons have been repeated after data have been filtered. A paired t test was used to carry out comparisons. Ventilatory parameters were collected in 10 healthy subjects during the use of a bicycle ergometer. The required power was increased every 15 s by steps of 30 W, starting from 50 W. Ve, VO2 and VCO2 have been sampled every 15 s, then the three functions--Ve versus VO2, Ve versus VCO2 and VCO2 versus VO2--were considered. Each function was stylized with two linear segments. Each segment was estimated by using a second-kind linear fitting. We verified that: (i) the AT may be reliably appreciated depending on the pair of selected parameters; (ii) only when data are smoothed is no difference between the two criteria documented (Ve vs. VO2, p = 0.99; Ve vs. VCO2, p = 0.54); (iii) no significant difference, related to smoothing, is documented both in using the least-squares method (Ve vs. VO2, p = 0.61; Ve vs. VCO2, p = 0.15) and the maximum p level criterion (Ve vs. VO2, p = 0.59; Ve vs. VCO2, p = 0.19).

Adolescent↗
PubMed1988

Forearm arterial pressure-volume relationships in man.

Pressure-volume (p-V) relationships of a segment of the forearm circulation have been measured in nine male healthy subjects. Forearm volume was measured using electrical impedance plethysmography, arterial transmural pressure by subtracting mean arterial pressure measured contralaterally in a finger from the pressure in a cuff placed over the sensing electrodes of the plethysmograph. A special two-phase measurement waveform was designed with which cuff pressure was first increased step wise to a suprasystolic level and held at that level for 120 s, then ramped down to zero pressure in another 300 s. The step phase inflation allowed us to estimate the parameters of the interstitial liquids and total blood compartments. The total blood compartment amounted to 6.2 ml per 100 ml of tissue. The ramp phase deflation allowed us to discriminate between a first phase in which only the arteries refilled and a second phase in which the veins also distended. An arctangent function was fitted to the first phase arterial p-V relationship, describing it in model form. Total arterial volume per 100 ml of tissue amounted to 3.8 ml at physiological pressures, total arterial compliance of the forearm per centimetre length to 19.5 microliter kPa-1 cm-1 (2.6 microliter mmHg-1 cm-1) at physiological pressures, and to 340 microliter kPa-1 cm-1 (45 microliter mmHg-1 cm-1) maximum compliance at the lower, inflection point pressures. These values are in general agreement with the literature. Pulse wave velocity cannot be computed reliably from these data.

Adult↗
PubMed1986

Bronchoprovocation tests in bronchial asthma and other respiratory disorders: a short review and some personal contributions.

The purpose of this paper, after a brief review of the main features of bronchoprovocation challenges, was to determine whether the administration of an ultrasonic mist of distilled water can influence the bronchial tone of normal subjects and patients affected by various respiratory disorders, in order to assess the effectiveness of this bronchoprovocation test in discriminating between patients. Of the 129 subjects tested 13 were classified as normal, 60 as extrinsic asthmatics, 21 as intrinsic asthmatics, 25 as allergic rhinitics and 37 as chronic bronchitics. Ultrasonic mist, was administered for 5 min and the bronchial response was evaluated in terms of difference between that after the mist minus baseline values of specific airways conductance. The data suggest that the bronchial challenge with ultrasonic mist, a safe, non-pharmacological and simple test, allows a good discrimination between asthma patients and those affected by other respiratory disorders.

Adolescent↗
PubMed1982

STI usefulness during isometric exercise in labile hypertensive patients.

Measurement of the left ventricular systolic time intervals (STI) was considered a valid method in demonstrating the presence of a state of beta-drenergic hyperstimulation. The authors used this method during isometric exercise to differentiate between a group of 16 normal subjects (N) and 16 random labile hypertensives (LH), and between the N and 16 fixed hypertensives (FH). Exercise resulted in a general shortening (p less than 0.01) of the STI, an increase (p less than 0.01) in the systolic arterial pressure (SAP), and an increase (p less than 0.01) in the heart rate (HR) in all the groups studied. The study also demonstrated that the state of blood pressure (diagnosis) alone does not significantly influence the course of the exercise test, and that the interaction diagnosis-exercise gives quantitatively different results in the three groups, to the extent that it is possible to recognize a specific polygraphic pattern for the LH. In this group there is a greater shortening of the Q--S2 and the non-corrected LVET (p less than 0.01) than for the N. The behaviour for the FH falls between the other groups, but it is not possible to distinguish clearly between this group and its neighbour on either side. We conclude that the measurement of the STI during isometric exercise could be useful in determining a diagnostic pattern for subjects who show a lability in their blood pressure.

Adult↗
PubMed1980

Reproducibility of strain gauge venous occlusion plethysmography in long-run measurements in man.

In order to evaluate strain gauge venous occlusion plethysmography as a tool to test the effects of treatment on peripheral blood flow, some biasing effects due to this technique were studied in relation to a long-run session and to cuff and gauge displacement. Arm peripheral blood flow was estimated by a computerized procedure during three successive days in a young male subject. The measurements were arranged as follows: 1) 75 replications under constant conditions, lasting 1.6 hours; 2) 18 triplets with alternative cuff displacement between two forearm positions, lasting 1.5 hours; 3) 40 measurements taken alternatively with a fixed gauge and a displaced one from a proximal to a distal position and vice versa, lasting 2.1 hours. Statistical comparison revealed: 1) a good long-run reproducibility during the first session; 2) a significant difference between the first and third day sessions under the same conditions; 3) a significant difference between the distal and proximal cuff mean flows during the second day session; 4 significant differences among the third day means in dependence of gauge position; 5) no significant dependence on strain gauge tension during the third day session. It is thus concluded that strain gauge plethysmography may be a reliable technique mainly in a longitudinal experimental design when the acute effect of some drug administration is to be evaluated.

Adult↗
PubMedDate not supplied

Prazosin-induced haemodynamic modification in human hypertension. Evidence from strain-gauge plethysmography. Part II.

Three hypertensive in-patients responsive to a single oral administration of 1 mg prazosin were studied to compare the delays of drug effect on peripheral blood flow (PBF), heart rate (HR) and blood pressure (BP). Arm PBF was measured by venous occlusion strain-gauge plethysmography in a long run session (lasting at least 2 hours) every 5 - 10 minutes. HR and BP were measured accordingly, by conventional methods. The delays of the effect were compared by a cross correlation function of HR, systolic and diastolic BP versus PBF. The results show both advance and delay of HR increase as compared with PBF increase, suggesting some independent mode of action of prazosin at peripheral (vasodilation) and central (HR) level. BP decrease is instead always delayed with respect to PBF increase, by a variable amount (10 - 60 minutes) and with some difference in time response to systolic and diastolic BP, suggesting some independent feed-back loops controlling systolic and diastolic BP adjustment due to primary vasodilation effect.

Blood Pressure↗
PubMedDate not supplied

Prazosin-induced vasodilatation of muscle blood vessels in human hypertension. Evidence from strain-gauge plethysmography. Part I.

The fall of blood pressure provoked in hypertensive men by a single oral dose of 1 mg of prazosin is associated with an increase of forearm muscle blood flow. This phenomenon may be demonstrated by a sequence of strain-gauge plethysmographic measurements, taken at regular intervals (5-10 minutes), before and during the action of the drug, lasting more than 2 hours.

Blood Pressure↗