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At least 973 records · Page 54Linked to original sources
PubMed1982

Reassessment of lung volume measurement by helium dilution and by body plethysmography in chronic air-flow obstruction.

We have previously shown that in some asthmatic patients, plethysmographic total lung capacity, measured from mouth pressure versus plethysmographic volume (Vbox) changes (TLCm), is overestimated, whereas TLCes, derived from esophageal pressure versus Vbox changes, is an accurate estimate of lung volume (VL). We studied 24 patients with chronic airflow obstruction (mean forced expiratory volume in one second, 1.23 L(SD:0.64 L) and mean specific airway conductance, SGaw, 0.052 +/- 0.016 cm H2O-1 X S-1) to reassess the relative merits of TLCm and the 7-min closed-circuit He dilution technique (TLCHe) in this condition. The TLCHe (6.54 +/- 1.09 L) was significantly less (p less than 0.001) than both TLCm (7.53 +/- 1.20 L) and TLCes (7.16 +/- 1.12 L), whereas TLCm was greater than TLCes (p less than 0.001). Differences between TLCes and TLCHe (ranging from -0.11 to 2.17 L) and between TLCm and TLCes (from -0.10 to 1.48 L) were correlated to the degree of airway obstruction as assessed by SGaw (p less than 0.001 and p less than 0.01, respectively). We conclude that VL is overestimated by TLCm and underestimated by TLCHe in moderate to severe chronic air-flow obstruction. The "trapped gas" volume (TLCm to TLCHe difference) is actually made up by these two additive errors.

Adult↗
PubMed1985

Calibration of computer-assisted (Respicomp) respiratory inductive plethysmography in newborns.

We investigated the accuracy of a computer-assisted, respiratory inductive plethysmograph (Respicomp) on 50 awake human newborns who were lying supine. Breaths were selected with different rib cage (RC) to pneumotach (PNT) and abdomen (AB) to pneumotach (PNT) values. The equation RC/PNT + AB/PNT = 1 was solved using the least squares method (LSQ) of calculation of calibration factors. Validation of the calibration factors was performed with a range of consecutive breaths between 6 and 22. Of the 1,128 validation or revalidation breaths, 628 (56%) were within 10% of the simultaneously measured PNT volume, 1,024 (91%) were within 20%, and 1,128 (100%) were within 30%. The RC or AB compartment contributions to ventilation changed spontaneously in the awake newborns. This change eliminated the need to wait for varying sleep states to obtain calibration factors and reduced total time required for calibration. (Some loss of accuracy is a compromise with this method; the calibration factors obtained do not remain accurate while the infant is asleep.) This method provided a reliable and rapid calibration and validation technique of the respiratory inductive plethysmograph (Respicomp) on awake newborns.

Abdomen↗
PubMed1977

Measurement of pulmonary capillary blood flow in infants by plethysmography.

An accurate method for measuring effective pulmonary capillary blood flow (Qc eff) in infants has been developed with an adaptation of the plethysmographic technique. Measurements were made on 19 preterm. 14 small-for-dates, and 7 fullterm normal infants with a constant volume whole body plethysmograph in which the infant rebreathed nitrous oxide. There was a highly significant correlation between Qc eff and body weight, and this relationship was unaffected by premature delivery or intrauterine growth retardation. Mean Qc eff in preterm, small-for dates, and fullterm infants was 203, 208 and 197 ml min-1 kg-1, respectively, with no significant differences between the groups. A significant negative correlation existed between Qc eff and haematocrit in the preterm infants. There was no relationship between weight standardized Qc eff and postnatal age in any of the groups. With this technique, it was possible to readily recognise the presence of rapid recirculation (indicative of shunting) in several of the infants, suggesting that rebreathing methods for the assessment of Qc eff should not be applied indiscriminately during the neonatal period. By taking care to overcome the potential sources of technical error, it was possible to obtain highly reproducible results of Qc eff in infants over a wider age range than has been previously reported.

Body Weight↗
PubMed1981

Comparative study of strain gauge plethysmography and Doppler ultrasound in patients with occlusive arterial disease of the lower extremities.

A series of 305 normal subjects and 77 patients with angiographically proven stenotic or occlusive arterial disease of the lower limbs was studied with Doppler ultrasound pressure measurements and strain gauge plethysmographic arterial flow measurements. The 2 techniques were compared singly and in combination at rest and after exercise or reactive hyperemia. Pressure-flow patterns were found to correlate well with the segment(s) and extent of involvement with arterial disease, especially in patients with superficial femoral artery disease. However, it was found that calf blood flow measurements were of little assistance in predicting the level and severity of involvement over and above the information obtained by pressure measurements alone.

Ankle↗
PubMed1985

Assessment of venous insufficiency using photoplethysmography: a comparison to strain gauge plethysmography.

Simultaneous photoplethysmographic (PPG) and strain gauge plethysmographic (SPG) recordings were obtained in normal subjects and patients with venous insufficiency. In PPG tracings, a so called "negative segment," which represented a further fall below the baseline after exercising, was often observed. This negative segment is produced by blood flow from the superficial to the deep veins during relaxation, which indicates that PPG can be used to assess the circulatory hemodynamics in the skin. PPG and SPG tracings from limbs with primary varicosis showed a shorter refilling time after exercise than those from normal limbs at the distal as well as the midcalf levels. The mean refilling time measured at the distal level by PPG was unaffected by tourniquets applied proximal to the transducer, indicating that the PPG tracings determined at the distal level were not always influenced by the reflux of blood through the incompetent saphenous system, but by altered cutaneous circulation. SPG was of greater diagnostic value for deep venous disease than PPG. From these results, it would be concluded that PPG in combination with SPG offers a rational approach to the assessment and the understanding of the pathophysiology of venous diseases.

Adult↗
PubMed1992

Digital blood flow in cooled and contralateral finger in patients with Raynaud's phenomenon. Comparative measurements between photoelectrical plethysmography and laser Doppler flowmetry.

The effects of cooling of a hand on lateral and contralateral digital skin blood flow were investigated in 18 patients with primary or secondary Raynaud's phenomenon. The aim of the study was to compare photoelectrical plethsmography (PhEP) and laser Doppler flowmetry (LDF). PhEP and LDF were used simultaneously for skin blood flow measurements of the third finger of both hands. One hand was cooled in water from 33 degrees to 3 degrees C in steps of 3 degrees C, each step lasting four minutes. It was followed by a recovery period of ten minutes in room air of 24 degrees C. During stepwise cooling from 33 degrees to 9 degrees C the relative PhEP and LDF values, measured on the cooled hand, decreased to 6.2% +/- 3.2% and 10% +/- 12% respectively. The correlation coefficients between LDF and PhEP varied between 0.79 and 0.99. In the contralateral hand the relative PhEP and LDF values decreased to 38% +/- 30.% and 64% +/- 7.9% respectively. The correlation coefficients between LDF and PhEP values were lower on the contralateral hand and ranged from 0.26 to 0.95. By calculating the LDF/PhEP ratios during cooling and recovery, more specific changes in red blood cell velocities during cooling were studied. Increasing LDF/PhEP ratios suggest increasing red blood cell velocities during cooling at 9 degrees C and a difference in the measuring methods. For testing the severity of Raynaud's phenomenon and the effect of treatment the results of both methods show consistent and quite comparable results when measured on the cooled hand. The effect of indirect cooling on the contralateral hand is, however, less consistent.

Adult↗