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Biomedical subjects

R Peslin

Publications and source records attributed to R Peslin.

At least 109 records · Page 6Linked to original sources
PubMed1988

Thoracic gas volume measurements in chronic obstructive pulmonary disease by low frequency ambient pressure changes.

The validity of a new method for measuring thoracic gas volume (Vtg) was studied in 18 bronchitic patients with mild to severe airway obstruction. The method entailed submitting the subject to very slow sinusoidal variations of ambient pressure (delta Pam) and studying the relationship between delta Pam and the resulting gas displacement at the mouth (delta Vaw): Vtgapc = PB.delta Vaw/delta Pam.cos phi, where PB is barometric minus alveolar water vapor pressure, and phi is the phase angle between Pam and Vaw. delta Pam of 40 cm H2O at 0.05 Hz were achieved by placing the subject in a 410-I body chamber connected to a large stroke volume reciprocating pump. Pam and Vaw were processed digitally by Fourier transform to obtain their amplitude ratio and phase angle at the frequency of interest. Vtg was also measured by body plethysmography (Vtgplet) during slow panting maneuvers (0.79 +/- 0.19 Hz) and also in order to detect any artifactual frequency dependence at a higher panting frequency (1.71 +/- 0.27 Hz); the agreement between the 2 estimates in all subjects (r = 0.975) suggested that Vtgplet could be taken as a valid reference. Functional residual capacities derived from Vtgapc and Vtgplet were not significantly different (5.113 +/- 1.198 versus 5.260 +/- 1.328 L) and were highly correlated (r = 0.915). Intermethod differences averaged 1.7 +/- 10.5% and were not significantly correlated to functional indices. We conclude that the new method provides accurate Vtg values in patients with chronic airway obstruction.

Adult↗
PubMed1988

An incremental method to assess the linearity of gas flowmeters: application to Fleisch pneumotachographs.

A new method of studying the linearity of gas flowmeters was tested on different models of Fleisch pneumotachographs. The method applies a steady flow to the test flowmeter, which is increased in a stepwise manner by adding a constant flow-increment. This is achieved using two flow sources in parallel. The method does not require any reference flow channel and may be implemented with standard laboratory equipment. Using this method, the gain of Fleisch pneumotachographs, whatever their size, decreased by about 2-3% from low flows to about 40% of their nominal full scale (FS), and then increased almost linearly with increasing flow. The error was 8-13% at 200% FS. The following equation was devised to correct the data at high flow: Vc = Vt (1-K (Vt-S] where Vc and Vt are the corrected and measured flow respectively, K a gain correction factor and S a flow threshold below which no correction is needed. Applying this correction with suitable coefficients, the maximal error was below 3% from 0-200% FS.

Humans↗
PubMed1988

Density dependence of respiratory input impedance re-evaluated with a head generator minimizing upper airway shunt.

Total respiratory impedance was assessed from 4 to 30 Hz in ten normal subjects breathing air and a helium-oxygen gas mixture using two methods of applying pressure oscillations at the airway opening: 1) the conventional method where pressure is varied at the mouth: 2) the method recently developed by Peslin et al. (J Appl Physiol, 1985, 59, 1790-1795) in which pressure is varied both at the mouth and around the head to minimize transmural pressure across upper airway walls, and the corresponding artefact. When breathing air slightly lower resistances (p less than 0.05) and considerably higher inertances (p less than 0.001) were found using the head generator. Breathing helium-oxygen reduced respiratory resistance and its frequency dependence, as well as respiratory inertance very significantly (p less than 0.001), with minor differences between the changes seen with the two methods. In contrast, the changes in respiratory compliance were small, and not in the same direction, when pressure was varied at the mouth and around the head. It is concluded that the accuracy of the conventional method may be sufficient for diagnostic purposes in subjects without gross mechanical abnormalities, i.e. for early detection of mechanical abnormalities.

Airway Resistance↗
PubMed1988

Assessment of thoracic gas volume by low-frequency ambient pressure changes in children.

The validity of a new method for measuring thoracic gas volume (TGV) was studied in 69 children, 4-16 yrs old, including twelve normal children and 57 children with an obstructive (n = 38) or restrictive (n = 19) respiratory disease. The method consisted of applying very slow (0.05 Hz) sinusoidal variations of ambient pressure around the body (delta Pam = 40 cmH2O peak to peak) and studying the relationship between delta Pam and the resulting gas displacement at the mouth (Vaw): TGVapc = PB.delta Vaw/delta Pam.cos phi, where PB is barometric minus alveolar water vapour pressure and phi the phase angle between Pam and Vaw. Functional residual capacities derived from TGVapc (FRCapc) were compared to the values obtained by plethysmography (FRCplet) and by helium dilution (FRCdil). FRCapc did not differ significantly from FRCplet in either the entire group (1.75 +/- 0.62 l vs 1.79 +/- 0.45 l) or in the patient subgroups. However, with the new method a trend to slightly lower FRCs was seen in patients with the most obstruction (p less than 0.05). FRCdil was significantly lower than both FRCapc and FRCplet (p less than 0.001), particularly in children with obstruction. Significant correlations were found between the three methods (p less than 0.001). On the other hand, the method investigated requires that the subject breathe very regularly for a period of several minutes. This was rarely achieved, so that the reproducibility of the measurements was unacceptably low. At present, the method cannot be recommended for routine use in 4-16 yr old children.

Adolescent↗
PubMed1987

Measurement of thoracic gas volume by low-frequency ambient pressure changes.

When the whole body is exposed to sinusoidal variations of ambient pressure (delta Pam) at very low frequencies (f), the resulting compression and expansion of alveolar gas is almost entirely achieved by gas flow through the airways (Vaw). As a consequence thoracic gas volume (TGV) may be computed from the imaginary part (Im) of the delta Pam/Vaw relationship: TGV = PB/[2 pi f X Im(delta Pam/Vaw)], where PB is barometric minus alveolar water vapor pressure. The method was tested in 35 normal subjects and compared with body plethysmography. The subjects sat in a chamber connected to a large-stroke-volume reciprocating pump that brought about pressure swings of 40 cmH2O at 0.05 Hz. delta Pam and Vaw were digitally processed by fast Fourier transform to extract the low-frequency component from the much larger respiratory flow. Total lung capacities (TLC) obtained by ambient pressure changes and by plethylsmography were highly correlated (r = 0.959, p less than 0.001) and not significantly different (6.96 +/- 1.38 l vs. 6.99 +/- 1.38). TLC obtained by ambient pressure changes were not influenced by lowering the frequency to 0.03 Hz, adding an external resistance at the mouth, or increasing abdominal gas volume. We conclude that the method is practical and in agreement with body plethysmography in normal subjects.

Adolescent↗
PubMed1987

Relation of mouth flow to body surface flow during forced oscillation at the chest.

We have investigated the body surface flow/mouth flow transfer function (magnitude ratio and phase difference) in seven healthy male subjects driven at the chest from 4 to 30 Hz. The measurements were performed with a specially designed plethysmograph and analyzer. The subjects were driven with a mechanical oscillator placed on the sternum. After differences in gas temperature and humidity were taken into account, the data were in agreement up to 15 Hz with a simple second-order model including an airway compartment, with a resistance and an inertance, and a shunt compliance representing alveolar gas. At larger frequencies, closer inspection revealed that a third-order model was optimal. We interpret these results as indicating a compartmentalization of gas compliance within the thorax, communicating via a resistive element. Airway inertance did not seem to be distributed.

Humans↗
PubMed1986

Comparison between ventilatory and mouth occlusion pressure responses to hypoxia and hypercapnia in healthy sleeping man.

Ventilatory and mouth occlusion pressure (P0.1) responses to progressive isocapnic-hypoxia and hyperoxic-hypercapnia were compared in eleven healthy sleeping men during the same night. Hypoxic and hypercapnic responses were determined during wakefulness, non-rapid and rapid-eye-movement sleep. The following parameters were measured: minute ventilation (VE), tidal volume (VT), 'duty cycle' (TI/TT), mean inspiratory flow rate (VT/TI) and P0.1, an index of the neuromuscular inspiratory drive. To allow a direct comparison between the two types of chemostimuli, responses were characterized by the value of the different parameters at 'equivalent' levels of hypoxia and hypercapnia, i.e., at levels which produced the same P0.1 during wakefulness: an oxyhaemoglobin saturation (Sao2) of 94% during the isocapnic-hypoxic tests (PETCO2 = 42.5 +/- 1.2 mmHg) was found to be equivalent to a PETCO2 of 47.4 +/- 3.7 mmHg during hypoxic-hypercapnic tests. For both tests, the arousal levels of the stimulus and of P0.1 were similar in all sleep stages. Sleep did not significantly modify P0.1 or breathing pattern responses to hypoxia (Sao2 = 94%). In contrast, at the 'equivalent' level of hypercapnic stimulation, P0.1 (P less than 0.05) and VE (P less than 0.01) responses were significantly impaired, particularly in REM sleep, with a decrease in VT (P less than 0.01) and VT/TI (P less than 0.05) responses. The results suggest that CO2 intracranial receptor mechanisms are more affected by sleep than the O2 peripheral receptor activity.

Adult↗
PubMed1986

Respiratory transfer impedances with pressure input at the mouth and chest.

Two methods of measuring respiratory transfer impedance (Ztr) were compared in 14 normal subjects, from 4 to 30 Hz, 1) studying the relationship between transrespiratory pressure (Prs) and flow at the chest when varying pressure at the mouth (Ztrm) and 2) studying the relationship between Prs and flow at the mouth when varying pressure around the chest wall (Ztrw). The similarity of the two relationships was expected on the basis of a T-network model. Almost identical phase responses were obtained from the two methods. Pressure-flow ratios were slightly larger for Ztrw than for Ztrm, but differences did not exceed 2% on average in 11 of 14 subjects. When the data were analyzed with the six-coefficient model proposed by DuBois et al. (J. Appl. Physiol. 8: 587-594, 1956), similar values were found for tissue compliance and tissue inertance but slightly different values for gaseous inertance in the airways (1.97 +/- 0.35 X 10(-2) cmH2O X l-1 X s2 for Ztrw vs. 1.73 +/- 0.26 for Ztrm; P less than 0.01). Similar results were also found for total respiratory resistance but with a slightly larger contribution of airway resistance for Ztrw (64 +/- 14 vs. 57 +/- 10%; P less than 0.05). As a practical conclusion it is recommended to measure Ztrw, which is technically much easier.

Adult↗
PubMed1986

Pulmonary haemodynamic response to two-stage exercise in patients with chronic bronchitis.

The pressure/flow relationship in the pulmonary circulation has been studied in 43 patients with chronic bronchitis, at rest (R) and during exercise at two levels: 30 or 40 W (E1), and 60 or 80 W (E2), without interruption. For the entire group, pulmonary vascular resistance was 142 +/- 70 dyn X s X cm-5 at rest, 131 +/- 55 at the first exercise level and 118 +/- 60 at the second level. Individual changes were variable, however; a "linearity index" was computed as delta(PPA-PW)/delta Q from the first to the second exercise level divided by the same value from rest to the first exercise level. This index was below 0.75 in 27 patients (i.e. the pressure/flow slope was lower for the second exercise level and the pressure/flow curve was concave to the flow axis), it was above 1.25 in nine patients (i.e. the slope increased with exercise and the pressure/flow curve was convex to the flow axis), and the pressure/flow relationship was close to rectilinear in seven patients. Functional disturbances were mild in these subjects, and in the majority of them pulmonary vascular resistance did not increase with exercise.

Adult↗
PubMed1985

Evaluation of phase correction and low gas density to improve thoracic gas volume measurement.

We investigated two methods of decreasing the error on plethysmographic determinations of thoracic gas volume (TGV) related to cheeks movements during panting maneuvers: lowering gas density in the airways with an 80% He-20% O2 mixture and computing TGV from the in-phase component of the plethysmographic signal (TGVr). The methods were tested by measuring how TGV estimates varied when panting frequency was raised from 0.8 to 2.5 Hz during the same occlusion. The measurements were performed in 6 normal subjects and 12 patients with chronic bronchitis with and without cheeks support and when the airway was connected to an external device simulating an increased cheeks compliance. A small negative frequency dependence of TGV (delta TGV/delta f = -1.2 +/- 0.8%/Hz with cheeks support), most probably unrelated to upper airway walls, was found in normal subjects. Delta TGV/delta f was positive and algebraically larger in patients than in normals, reaching 2.2 +/- 3.4%/Hz without cheeks support and 11.8 +/- 8.0%/Hz with the additional cheeks. The latter value was only 20% smaller when computed on the basis of TGVr, demonstrating the limited usefulness of the phase-based correction. In contrast, breathing He-O2 decreased delta TGV/delta f to approximately 50% of its air value (P less than 0.01) and appears as an effective way to diminish the error in obstructive patients.

Adult↗
PubMed1985

Total respiratory input and transfer impedances in humans.

Total respiratory input (Zrs,in) and transfer (Zrs,tr) impedances were obtained from 4 to 30 Hz in 10 healthy males by simultaneously measuring mouth and chest flow while applying pseudo-random pressure variations at the mouth. Compared with Zrs,in, the real part of Zrs,tr was larger up to 10 Hz but exhibited a much stronger negative frequency dependence. The imaginary part was larger at all frequencies, with a resonant frequency (fn) at 6.0 +/- 0.8 Hz compared with 8.2 +/- 2.9 Hz for Zrs,in. The two impedances were analyzed with a model featuring airway resistance and inertance, alveolar gas compressibility, and tissue resistance, inertance, and compliance. A good fit was generally obtained but, in most cases, with a different partitioning of resistance between airway and tissue for Zrs,in and Zrs,tr. The data were also used to compute separately airway and tissue (Zt) impedances. In most subjects Zt could not be properly fitted with a simple resistance-inertance-compliance unit and was consistent with a slow (fn = 7.4 +/- 2.3 Hz) overdamped compartment in parallel with a fast (fn = 37.1 +/- 5.6 Hz) underdamped one.

Airway Resistance↗
PubMed1985

Respiratory impedance measured with head generator to minimize upper airway shunt.

A new method for measuring total respiratory input impedance (Zrs), which ensures minimal motion of extrathoracic airway walls, was tested over frequencies of 4-30 Hz in 14 normal subjects and 10 patients with airway obstruction. It consists of applying pressure variations around the head, rather than at the mouth, so that transmural pressure across upper airway walls is equal to the small pressure drop across the pneumotachograph. Compared with reference Zrs values obtained by directly measuring airway wall motion with a head plethysmograph and correcting the data for it, the investigated method provided similar values for respiratory resistance at all frequencies (30 Hz, 3.67 +/- 2.24 cmH2O X 1(-1) X s compared with 3.55 +/- 2.00) but slightly overestimated respiratory reactance at the largest frequencies (30 Hz, 2.82 +/- 1.28 cmH2O X 1(-1) X s compared with 2.52 +/- 1.22, P less than 0.01). In contrast, when the data were not corrected for airway wall motion, resistance was largely underestimated, especially in patients (-48% at 30 Hz, P less than 0.001), and the reactance-frequency curve was shifted to the right. The investigated method is almost as accurate as the reference method, provides equally reproducible data, and is much simpler.

Airway Resistance↗
PubMed1985

Upper airway artifact in respiratory impedance measurements.

When studying respiratory impedance by forced oscillations, part of the flow measured at the mouth is lost in upper airway wall motion and does not enter the trachea. The corresponding error was studied in 10 normal subjects and 8 patients with chronic obstructive pulmonary disease (COPD) by measuring respiratory impedance with the cheeks unsupported, with the cheeks supported, and when upper airway wall motion was simultaneously measured with a head plethysmograph, and corrected for. In normal subjects, wall motion had little influence on respiratory resistance but, whether the cheeks were supported or not, increased the resonant frequency (p less than 0.05) and respiratory compliance (p less than 0.001) and decreased respiratory inertance (p less than 0.001). In patients with COPD, average resistance from 4 to 30 Hz was significantly lower when the cheeks were not supported (3.32 +/- 0.57 cm/H2O X L-1 X s; m +/- SD) than when they were (4.59 +/- 0.73, p less than 0.01) and when the data were corrected (5.41 +/- 1.14, p less than 0.001). Moreover, resistance increased with increasing frequency when wall motion was corrected for and decreased when it was not. Upper airway wall motion also tended to increase resonant frequency and decrease inertance in patients. The data show that supporting the cheeks does not prevent large errors on respiratory impedance and derived parameters, especially in obstructive patients; accurate measurements require that airway wall motion be evaluated and corrected for.

Airway Resistance↗
PubMed1984

In-phase rejection requirements for measuring respiratory input impedance.

Respiratory flow is commonly obtained by measuring the pressure difference across a pneumotachograph. When respiratory input impedance is studied, that pressure difference may be very small with respect to the absolute pressure swings inside the pneumotachograph. Then the in-phase rejection of the differential pressure transducer is expected to markedly influence the accuracy of the data. The problem was investigated by computer simulation and by measurements on a mechanical analog of the respiratory system made of a resistance, an inertance, and a compliance arranged in series. Both studies demonstrated that comparatively small differences in the volumes of the chambers or in the lengths or diameters of the connecting tubes led to artifactual frequency dependence of resistance and serious misestimation of compliance and inertance. Errors were larger when the resistance of the pneumotachograph was smaller and the impedance of the subject larger. In practice, with usual pneumotachographs accurate impedance measurements require using the most symmetrical transducers presently available (common-mode rejection ratio of about 70 dB at 30 Hz).

Airway Resistance↗
PubMed1984

Upper airway walls impedance measured with head plethysmograph.

Respiratory input impedance (Zrs) measured by forced oscillations needs to be corrected for the motion of extrathoracic airway walls. Two methods of obtaining the impedance of this shunt pathway [upper airway impedance (Zuaw)] were compared in six normal subjects. In the first, flow was measured at the airway opening during Valsalva maneuvers, as described by Michaelson et al. (10). In the second, motions of upper airway walls were directly assessed during respiratory impedance measurements by use of a head plethysmograph. Larger upper airway impedance values were found during Valsalva maneuvers, corresponding to a larger upper airway resistance (Ruaw) (at 20 Hz, Ruaw = 9.1 +/- 4.7 compared with 7.0 +/- 2.1 cmH2O X 1-1 X s with the second method) and inertance (Iuaw) (Iuaw = 0.053 +/- 0.036 vs. 0.025 +/- 0.008 cmH2O X 1-1 X s2, P less than 0.05) and a lower upper airway compliance (Cuaw) (Cuaw = 0.78 +/- 0.33 vs. 1.15 +/- 0.15 ml X cmH2O-1, P less than 0.05). Active contraction of facial muscles during Valsalva maneuvers may be responsible for this finding. As a consequence, respiratory impedance values are undercorrected when using the Valsalva method, leading in normal subjects to an overestimation of respiratory compliance by 30% and an underestimation of inertance by 16% (P less than 0.05) and promoting positive frequency dependence of respiratory resistance. Substantial errors may be avoided by using a head plethysmograph, which permits measuring Zrs and Zuaw simultaneously.

Airway Resistance↗