Influence of unequal ventilation on the single breath K(CO) in COPD revealed by comparison with the rebreathing K(CO).

In 16 patients with chronic obstructive pulmonary disease (COPD) we investigated the relation between unequal ventilation and diffusion by means of lung volumes and Krogh factors (K(CO)) using the single breath (SB) and the rebreathing (RB) methods. We used both methods because the SB measurement is sensitive to unequal ventilation and diffusion whereas the RB measurement is not. Because K(CO) depends on inspired volume (VI), the SB and RB measurement have to be performed at the same VI. We therefore determined K(CO)SBm by making a SB measurement at VI equal to the mean inspired volume during the RB measurement and then calculated K(CO)RBm by dividing the RB transfer factor for CO by the mean RB lung volume. In 10 patients K(CO)SBm/K(CO)RBm, a parameter determined by the combined effect of unequal ventilation and diffusion, was almost equal to unequal ventilation, the quotient of the SB and mean RB lung volumes (VSBm/VRBm), just as in normal subjects (Jansons et al., Respiration 67 (2000) 383). This finding means that we can correct for the effects of unequal ventilation by dividing K(CO)SBm by VSBm/VRBm. We suggest that the SB measurement of K(CO) at vital capacity can be corrected in a similar way.

Rebreathing K(CO) and single breath K(CO) measured at the same mean alveolar volume reveal a physiological relationship between unequal diffusion and unequal ventilation in normal subjects.

BACKGROUND: The single breath (SB) method for determining the transfer factor for carbon monoxide is influenced by an unequal distribution of diffusion and ventilation. The rebreathing (RB) method is thought not to be influenced by these inequalities. Therefore, a comparison of the results of the two methods enables us to investigate unequal ventilation and diffusion. We have previously shown that even in normal subjects unequal ventilation influences the relation between the transfer factor as measured by the RB method and by the SB method. OBJECTIVES: To investigate to what extent unequal diffusion influences the relation between the RB and SB transfer factor in normal subjects. METHODS: Measurements were performed in 8 normal subjects. Differences in alveolar volume as measured by the RB and SB method were prevented from influencing the results by comparing the RB and SB transfer factor per liter of alveolar volume, i.e. the RB and SB Krogh factor, instead of the RB and SB transfer factor. The effect of the known dependence of the Krogh factor on inspired volume was prevented by measuring the SB Krogh factor at an inspired volume equal to the mean inspired volume of the RB measurement. This SB Krogh factor was compared with the RB Krogh factor calculated as the quotient of the RB transfer factor and the mean alveolar volume during the RB measurement. RESULTS: This RB Krogh factor was always larger than the corresponding SB Krogh factor. The difference was significant (p = 0.006). A high percentage (80%) of the variance in the quotient of the two Krogh factors, which can be considered as a parameter for unequal diffusion, was explained by the variance in the quotient of the mean RB volume and the corresponding SB volume. The latter quotient is a measure of unequal ventilation. CONCLUSIONS: The finding suggests a physiological relation between unequal diffusion and unequal ventilation. A plausible explanation was found in the decrease of the Krogh factor with an increasing ratio of inspired volume to residual volume for each part of the lung separately. The consequence is that in the absence of unequal ventilation the RB transfer factor is equal to the SB transfer factor measured at an inspired volume equal to the mean RB inspired volume.

Re-breathing vs single-breath TLCO in patients with unequal ventilation and diffusion.

The single-breath (SB) method for determining the transfer factor for carbon monoxide (TLCO) is of limited value for the detection of diffusion disorders on the alveolar level, because the results are influenced by unequal distribution of ventilation and diffusion. The rebreathing method (RB) is thought not to be influenced by these inequalities. To the authors' knowledge, no study has measured both TLCORB and TLCOSB systematically and compared them with regard to the influence of unequal ventilation and diffusion. Therefore, the present study measured total lung capacity (TLC) as well as TLCO, both with the RB vital capacity method and the SB method, using the same apparatus in 10 healthy subjects and in 35 patients with chronic obstructive pulmonary disease (COPD). These patients are known to have increased unequal ventilation and diffusion in comparison with healthy subjects. In the healthy subjects, a small difference was found between TLC measured with the RB method (TLCRB) divided by the predicted value (TLCRB/pred) and TLCSB/pred (mean difference 0.07; SE = 0.02); no significant difference was found between TLCORB divided by the predicted value of TLCOSB (TLCORB/pred) and TLCOSB/pred. In the COPD patients, however, TLCRB/pred was larger than TLCSB/pred (mean difference 0.17; SE = 0.02) and TLCORB/pred was larger than TLCOSB/pred (mean difference 0.23; SE = 0.05). Multiple regression analysis revealed that in the COPD patients, 54% of the variance of the difference between TLCRB/pred and TLCSB/pred, and 76% of the variance of the difference between TLCORB/pred and TLCOSB/pred, were explained by parameters related to unequal ventilation and diffusion. In 25 of the 35 COPD patients, TLCOSB/pred was less than 0.8, whereas in 11 of these 25 patients, TLCORB/pred was more than 0.8. This difference was significant (P = 0.0005). In these 11 patients, the SB measurement resulted in the incorrect diagnosis of a diffusion disorder on the alveolar level. The RB method, however, never resulted in the diagnosis of a diffusion disorder when TLCOSB/pred was larger than 0.8. It is concluded that in a significant number of COPD patients, TLCOSB is below the normal range, whereas TLCORB is not below the normal range. This difference between TLCORB and TLCOSB is related to the combined effect of unequal ventilation and diffusion, and is of clinical importance for the detection of a diffusion disorder on the alveolar level.

Electron and mechanical properties of bone during heating, evaluated by exoelectron emission and ultrasound.

Exoelectron spectroscopy and ultrasound velocity (USV) measurements have been applied to analyse both the electron and mechanical behaviour of compact bone tissue and its main components--collagen and hydroxyapatite (HAP)--in the temperature range 20-80 degrees C. The special exoelectron method with additional IR illumination has been pioneered for the above objective. Thermally induced variations of the electron structure of bone tissue and HAP were manifested at 55 degrees C, but in collagen they were near 75 degrees C. The greatest decrease in USV was at 35-65 degrees C in collagen and at 55-70 degrees C in bone. No changes of USV in HAP were revealed. The coincidence of temperatures of the exoemission maxima and of the USV most expressed gradient in fresh bone and collagen proves the correlation between electron and mechanical behaviour during heating, connected with the partial denaturation of collagen.

Rebreathing TLCO versus single breath TLCO at different degrees of unequal ventilation.

The influence of unequal ventilation on the differences between the rebreathing (RB) and the single breath (SB) measurement of the transfer factor of the lung for carbon monoxide (TLCO) was investigated. An apparatus was developed which measured both TLCORB and TLCOSB. Unequal ventilation increases with lung volume, caused by the combined effect of increasing ratio of total volume to RV from apex to basis, the fact that apex inspires before basis and asymmetric intra-acinar branching patterns. Therefore measurements were done at three different values of inspired volume (VI) in 10 normal subjects. To separate the effects of gas mixing and diffusion, residual volume (RV) was measured by He dilution in addition to TLCO. We found that RV and TLCO increase with increasing VI. The increase is larger with RB. We also found that RVRB is larger than RVSB at the three values of VI. TLCORB is smaller than TLCOSB except at vital capacity (VC). We concluded from the different behavior of RVRB and RVSB as a function of VI that the SB measurement increasingly underestimated RV with increasing unequal ventilation. This is also reflected in the measurement of TLCOSB. From the different behavior of TLCORB and TLCOSB as a function of VI we concluded that TLCORB was smaller than TLCOSB when unequal ventilation was minimal. This is caused by the smaller mean alveolar volume during RB. But increasing unequal ventilation causes an increasing underestimation with the SB method, resulting in TLCOSB being equal to TLCORB at VC.

Constructional peculiarities of the human tibia defined by reference to ultrasound measurement data.

The distribution of the acoustic properties of the human tibia was studied by the method of ultrasound probing. This enabled the determination of some constructional peculiarities of the tibia. A considerable non-uniformity of ultrasound propagation velocity has been revealed along the entire length of the bone. The uniform velocity fields were longitudinally orientated in the diaphysis whereas in the epiphyseal parts of the bone they had a cross-sectional orientation. Isorapid zones formed spiral structures positioned at an angle of 6.7 +/- 0.5 degrees to the bone axis. Moreover, right-wound spiral was characteristic of the left bone but left-wound spiral of the right. A new parameter--acoustic stiffness of the construction is suggested. In the proximal third of the bone its acoustic stiffness was more pronounced in the sagittal plane; in the middle part it was best defined in the direction of the angular zones of the bone, but in the distal part it had a clearly marked frontal orientation. A statistically valid distinction of ultrasound velocity in the cross-sectional and longitudinal zones of separate bones has been established in all the bones studied.

Artificial bioconstructions as behavioural systems.

Human organ replacement is studied from the biomechanical, ergonomic and biocybernetic viewpoint and a new concept of endoprosthetics based on these sciences is advanced. Criteria are formulated for the evaluation of complex living systems originating after biomaterials implantation. The ergonomic concept suggests that many clinical and technical problems of endoprosthetics can be solved by a systematic approach, by patient selection on psychological as well as engineering grounds and by effective guiding of the endoprosthetized outcome of the man-machine system, so that the aim of endoprosthetics is effective functioning of the established man-machine system. The need to provide communication between the endoprosthesis and the operator after complex bioconstructions have been implanted, as well as the importance of purposeful training to handle the new system, is emphasised. Tasks are set in the context of a behavioural system for physicians, design engineers and patients.